Patent Publication Number: US-2022239140-A1

Title: Charging method and power conversion apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of International Application No. PCT/CN2021/074175, filed on Jan. 28, 2021, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     FIELD OF TECHNOLOGY 
     The present application relates to the field of power battery, and more specifically, relates to a charging method and a power conversion apparatus. 
     BACKGROUND 
     With the development of the society, an electrical vehicle, due to its advantages such as high environmental protection, low noise and low use cost, has a huge market prospect and can effectively promote emission reduction, be beneficial to social development and progress. 
     For the electric vehicle, a power battery technology is an important factor concerning its development. Due to the electrochemical characteristics of the power battery, in a low temperature environment, a direct current charging may have a big impact on the performance of the power battery, effecting the customer&#39;s car experience. 
     Therefore, how to ensure the battery performance of the power battery is a technical problem to be solved. 
     SUMMARY 
     Embodiments of the present application provide a charging method and a power conversion apparatus, which can ensure the battery performance of the power battery. 
     In a first aspect, a charging method is provided, which includes: acquiring a state parameter of a power battery by a power conversion apparatus, the state parameter including a battery temperature; setting a charging mode to a pulse charging mode by the power conversion apparatus when the battery temperature is lower than a first preset threshold; and converting charging power of a charging apparatus and then charging the power battery by the power conversion apparatus in the pulse charging mode, the pulse charging mode being a charging mode outputting a pulsed voltage or a pulsed current. 
     Through the technical solutions of the embodiment of the present application, the power conversion apparatus acquires the battery temperature of the power battery, when the battery temperature is low, for example lower than the first preset threshold, the charging mode is set to the pulse charging mode. In the pulse charging mode, the power conversion apparatus converts the charging power output by the charging apparatus, and outputs a pulse current to charge the power battery, to prevent impacting the performance of the power battery when the charging apparatus directly charges the power battery in low temperatures, thereby ensuring the performance of the power battery. In addition, with the technical solution of embodiments of the present application, there is no need to configure a thermal management system for the power battery. On the basis of reducing the overall cost of the power battery, the heating time for the power battery at low temperatures is saved, and the charging efficiency is improved. 
     In some possible implementations, the method further includes: switching the charging mode from the pulse charging mode to a direct current charging mode by the power conversion apparatus when the battery temperature is not lower than the first preset threshold; and transmitting the charging power of the charging apparatus to the power battery to charge the power battery by the power conversion apparatus in the direct current charging mode, where the direct current charging mode is a charging mode outputting constant voltage or constant current. 
     Through the technical solutions of the embodiment of the present application, the power conversion apparatus continually acquires the battery temperature of the power battery. When the battery temperature is high, for example not lower than a first preset threshold, the power conversion apparatus switches its charging mode from a pulse charging mode to a direct current charging mode. Further the power conversion apparatus directly transmits the charging power of the charging apparatus to the power battery to charge the power battery, thereby increasing the charging efficiency of the power battery at non-low temperature. Therefore, with the technical solutions of the embodiment of the present application, the power conversion apparatus can flexibly sets its charging mode on the basis of the battery temperature of the power battery, and improve the charging efficiency of whole charging process on the premise of ensuring the performance of the power battery. 
     In some possible implementations, the state parameter further includes: a battery voltage; and the setting the charging mode to a pulse charging mode by the power conversion apparatus when the battery temperature is lower than the first preset threshold, includes: setting the charging mode to the pulse charging mode by the power conversion apparatus when the battery temperature is lower than the first preset threshold and the battery voltage is lower than a second preset threshold. 
     Through the technical solutions of the embodiment of the present application, in addition to acquiring the battery temperature of the power battery, the power conversion apparatus also acquires the battery voltage of the power battery. The power conversion apparatus combines the information of both battery temperature and battery voltage to set its charging mode to a pulse charging mode, it can further determine whether the power battery is in a low voltage charging state under low temperature, which can further ensure charging safety. 
     In some possible implementations, the state parameter further includes: a battery voltage, and the switching the charging mode from the pulse charging mode to a direct current charging mode by the power conversion apparatus when the battery temperature is not lower than the first preset threshold, includes: switching the charging mode from the pulse charging mode to the direct current charging mode by the power conversion apparatus when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than a second preset threshold. 
     Through the technical solutions of the embodiment of the present application, the power conversion apparatus continually acquires the battery temperature of the power battery and battery voltage. The power conversion apparatus combines the information of both battery temperature and battery voltage to switch its charging mode from the pulse charging mode to a direct current charging mode. In the non-low temperature or non-low voltage state of the battery, the power conversion apparatus directly charges the rechargeable battery using a direct current, which can further improve the charging efficiency. 
     In some possible implementations, the state parameter further includes: a battery state of charge; and the setting a charging mode to a pulse charging mode by the power conversion apparatus, includes: sending first direct current charging information to the charging apparatus by the power conversion apparatus, the first direct current charging information being determined by the power conversion apparatus according to pulse charging information, where the pulse charging information includes at least one of the following information: pulse current information, pulse voltage information, pulse direction information, pulse frequency information and pulse time information, the pulse charging information is determined by the power conversion apparatus according to the battery temperature and the battery state of charge; the charging the power battery after converting charging power of a charging apparatus by the power conversion apparatus in the pulse charging mode, includes: outputting a pulse current to the power battery, where the pulse current is generated by converting a direct current based on the pulse charging information, the direct current is a direct current output to the power conversion apparatus by the charging apparatus according to the first direct current charging information. 
     Through the technical solutions of the embodiment of the present application, the power conversion apparatus can determine the corresponding pulse charging information according to the state parameter of the power battery it acquires. And the power conversion apparatus converts and acquires different pulse currents according to the pulse charging information, so as to adapt to the different charging requirements of the power battery in different situations, and has high flexibility and adaptability. 
     In some possible implementations, before setting a charging mode as a pulse charging mode by the power conversion apparatus, the method further includes: sending a charging prohibition message to the charging apparatus by the power conversion apparatus, the charging prohibition message being configured to indicate the charging apparatus to stop outputting a direct current to the power conversion apparatus. 
     In some possible implementations, after sending a charging prohibition message to the charging apparatus by the power conversion apparatus, the method further includes: conducting a pre-charging by the power conversion apparatus. 
     Through the technical solutions of the embodiment of the present application, after sending a charging prohibition message to the charging apparatus, the power conversion apparatus pre-charges a capacitor in the power conversion apparatus. In this way, during the subsequent charging process of the power battery, the capacitor may no longer cause a large pulse current, which can ensure normal charging process and charging safety. 
     In some possible implementations, the conducting a pre-charging by the power conversion apparatus, includes: acquiring a voltage difference between an input end and output end of the power conversion apparatus by the power conversion apparatus; conducting a pre-charging by the power conversion apparatus if the voltage difference is less than a third preset threshold. 
     Through the technical solutions of the embodiment of the present application, in order to protect the relay in the power conversion apparatus and to ensure the performance of the power conversion apparatus, before controlling the switch of the relay to pre-charge the power conversion apparatus, the power conversion apparatus may also acquire the voltage difference between its input end and output end, and judge whether the voltage difference is less than a third preset threshold, if the voltage difference is less than the third preset threshold, the power conversion apparatus conduct a pre-charging. 
     In some possible implementations, where the switching the charging mode from the pulse charging mode to a direct current charging mode by the power conversion apparatus, includes: stopping outputting a pulse current to the power battery by the power conversion apparatus; acquiring second direct current charging information of the power battery and sending the second direct current charging information to the charging apparatus by the power conversion apparatus; and the transmitting the charging power of the charging apparatus to the power battery to charge the power battery the power conversion apparatus, includes: outputting a direct current output by the charging apparatus according to second direct current charging information to the power battery to charge the power battery by the power conversion apparatus. 
     In some possible implementations, before stopping outputting a pulse current to the power battery by the power conversion apparatus, the method further includes: sending a charging prohibition message to the charging apparatus by the power conversion apparatus, the charging prohibition message being configured to indicate the charging apparatus to stop outputting a direct current to the power conversion apparatus. 
     In some possible implementations, the outputting a direct current output by the charging apparatus according to the second direct current charging information to the power battery to charge the power battery by the power conversion apparatus, includes: acquiring a voltage difference between an input end and an output end of the power conversion apparatus by the power conversion apparatus; outputting the direct current output by the charging apparatus according to second direct current charging information to the power battery to charge the power battery by the power conversion apparatus if the voltage difference is less than a fourth preset threshold. 
     Through the technical solutions of the embodiment of the present application, in order to protect the relay in the power conversion apparatus and ensure the performance of the power conversion apparatus, before controlling the switch of relay to output the direct current output by the charging apparatus to the power battery, the power conversion apparatus may also acquire the voltage difference between input end and output end thereof, and judge whether the voltage difference is less than a fourth preset threshold. If the voltage difference is less than the fourth preset threshold, the power conversion apparatus outputs a direct current output by the charging apparatus to the power battery to charge the power battery. 
     In some possible implementations, the acquiring a state parameter of a power battery by the power conversion apparatus includes: receiving the state parameter of the power battery sent by a battery management system of the power battery by the power conversion apparatus. 
     In a second aspect, a power conversion apparatus is provides, which includes: a control unit and a power unit; where the control unit is configured to acquire a state parameter of a power battery; the state parameter includes a battery temperature of the power battery; the control unit is configured to set a charging mode of the power unit as a pulse charging mode when the battery temperature is lower than a first preset threshold, the power unit is configured to convert charging power of a charging apparatus and then charge the power battery in the pulse charging mode, the pulse charging mode is a charging mode using pulsed voltage or pulsed current. 
     In some possible implementations, when the battery temperature is not lower than the first preset threshold, the control unit is further configured to: switch the charging mode of the power unit from the pulse charging mode to a direct current charging mode, and the power unit is configured to transmit the charging power of the charging apparatus to the power battery to charge the power battery in the direct current charging mode, where the direct current charging mode is a charging mode using a constant voltage or a constant current. 
     In some possible implementations, the state parameter further includes: a battery voltage, the control unit is configured to set the charging mode of the power unit to the pulse charging mode when the battery temperature is lower than the first preset threshold and the battery voltage is lower than a second preset threshold. 
     In some possible implementations, the state parameter further includes: a battery voltage, the control unit is configured to switch the charging mode of the power unit from the pulse charging mode to the direct current charging mode when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold. 
     In some possible implementations, the state parameter further includes: a battery state of charge; the control unit is configured to determine the pulse charging information according to the battery temperature and the battery state of charge, and send the pulse charging information to the power unit, the pulse charging information including at least one of following information: pulse current, pulse voltage, pulse direction, pulse frequency and pulse time; the power unit is configured to determine first direct current charging information corresponding to the pulse charging information according to the pulse charging information, and send the first direct current charging information to the control unit; and the control unit is configured to send the first direct current charging information to the charging apparatus, and control the power unit output a pulse current to the power battery, where the pulse current is generated by converting a direct current based on the pulse charging information, the direct current is a direct current output to the power unit by the charging apparatus according to the first direct current charging information. 
     In some possible implementations, before the control unit is configured to set the charging mode of the power unit to the pulse charging mode, the control unit is further configured to: send a charging prohibition message to the charging apparatus, where the charging prohibition message is configured to indicate the charging apparatus to stop outputting a direct current to the power unit. 
     In some possible implementations, after the control unit is configured to send a charging prohibition message to the charging apparatus, the control unit is further configured to: send a precharge instruction to the power unit; and the power unit is configured to conduct a pre-charging according to the precharge instruction. 
     In some possible implementations, the control unit is configured to acquire a voltage difference between an input end and an output end of the power unit; and if the voltage difference is less than a third preset threshold, the control unit is configured to send the precharge instruction to the power unit. 
     In some possible implementations, the control unit is further configured to acquire second direct current charging information of the power battery; the control unit is configured to control the power unit to stop outputting a pulse current; and the control unit is configured to control the power unit to output a direct current output by the charging apparatus according to the second direct current charging information to the power battery. 
     In some possible implementations, before the control unit is configured to control the power unit to stop outputting a pulse current, the control unit is further configured to: send a charging prohibition message to the charging apparatus, the charging prohibition message is configured to indicate the charging apparatus to stop outputting the direct current to the power unit. 
     In some possible implementations, the control unit is configured to acquire a voltage difference between an input end and an output end of the power unit; and if the voltage difference is less than a fourth preset threshold, the control unit is configured to control the power unit to output the direct current output by the charging apparatus according to the second direct current charging information to the power battery. 
     In some possible implementations, the control unit is configured to receive the state parameter of the power battery sent by a battery management system of the power battery. 
     In a third aspect, a power conversion apparatus is provided, which includes: a processor and a memory, the memory is configured to store a computer program, the processor is configured to call the computer program, and execute the method in any possible implementation of the first aspect and the first aspect described above. 
     In a fourth aspect, a computer readable storage media is provided, which is configured to store a computer program, the computer program is configured to execute the method in any possible implementation of the first aspect and the first aspect described above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order to more clearly illustrate the technical solution of embodiments of the present application, the accompanying drawings required in the embodiments of the present application will be introduced briefly, obviously, the accompanying drawings described below are merely some embodiments of the present application, those of ordinary skill in the art can also acquire other accompanying drawings according to the accompanying drawings without paying a creative work. 
         FIG. 1  is a schematic diagram of a charging system disclosed in one embodiment of the present application; 
         FIG. 2  is a schematic diagram of an application architecture of the charging system disclosed in one embodiment of the present application; 
         FIG. 3  is a schematic flow diagram of a method disclosed in one embodiment of the present application; 
         FIG. 4  is a schematic flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 5  is a schematic flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 6  is a schematic flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 7  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 8  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 9  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 10  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 11  is a schematic flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 12  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 13  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 14  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 15  is a schematic interaction flow diagram of the charging method disclosed in another embodiment of the present application; 
         FIG. 16  is a schematic block diagram of a power conversion apparatus disclosed in one embodiment of the present application; 
         FIG. 17  is a schematic block diagram of the power conversion apparatus disclosed in another embodiment of the present application; 
         FIG. 18  is a schematic block diagram of the power conversion apparatus closed in another embodiment of the present application. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Implementations of the present application are described in further detail below in conjunction with the accompanying drawings and embodiments. The following detailed description of the embodiments and the accompanying drawings are used to illustrate the principles of the present application, but are not intended to limit the scope of the present application, i.e., the present application is not limited to the described embodiments. 
     In description of the present application, it should be noted that, unless otherwise noted, all technical and scientific terms used in the present application have the same meaning as usually understood by those skilled in the field to which the present application belongs to; the terms used in the specification of the present application are only for the purpose of describing the specific embodiments, and are not intended to limit the present application; the terms “include” and “have” and any variant thereof in the specification and claims of the present application and the above-mentioned accompanying drawings are intended to cover the non-exclusive inclusion. The terms “first”, “second” etc. in specification and claims or the above-mentioned accompanying drawings of the present application are used to distinguish different objects, and not used to describe a particular order or a primary and secondary relation. 
     “Embodiment” mentioned in the present application means that, a specific feature, structure or characteristic described in conjunction with an embodiment can be included in at least one embodiment of the present application. The phrase presented at various locations of the specification does not necessarily refer to the same embodiment, and not the independent or alternative embodiment being mutually exclusive with other embodiments. Those skilled in the art can explicitly and implicitly understood that, the embodiments described in the present application can be combined with other embodiments. 
     In the description of the present application, it should also be noted that unless expressly specified and defined otherwise, the terms “mounted”, “linked”, “connected” and “attached” are understood in a broad sense, for example, it can be a fixed connection or a detachable connection, or being integrally connected; it can be being directly connected or connected through an intermediate medium. The specific meanings of the above terms in the present application will be understood by those of ordinary skill in the art depending on specific circumstances. 
     In the field of new energy, as the main power source of electrical devices, such as electrical vehicles, ships or spacecraft, the importance of power batteries is self-evident. Where the temperature of power battery has great influence on its performance, life, and safety. At present, most of the power batteries in the market are rechargeable batteries, and the common ones are lithium-ion batteries or lithium-ion polymer batteries. At low temperatures, lithium-ion batteries will experience increased internal resistance and reduced capacity, and extreme conditions will lead to electrolyte freezing and battery failure to discharge, which will greatly affect the low-temperature performance of the battery system, resulting in reduced power output and range of electric vehicles. Furthermore, direct current charging of lithium-ion batteries at low temperatures will cause phenomenon of lithium deposition. Lithium deposition not only degrades the performance of lithium batteries, greatly shortens the cycle life, but also limits the fast charging capacity of batteries, and may cause disastrous consequences such as combustion and explosion. 
     In order to solve the problem of charging electric vehicles in low temperature environment, most of the power batteries of electric vehicles in the market are equipped with a thermal management system. When the temperature of the power battery is too low, the thermal management system can convert a part of electric energy into heat energy, thereby heating the whole battery pack. This preheating method can make the power battery at a more suitable temperature, based on this, the power battery is charged. However, this preheating method is to charge the power battery after the temperature of the power battery is increased. The space for increasing the heating efficiency of the power battery is limited, and the heating time cannot be saved, which makes it impossible to fundamentally solve the problem that the charging time of electric vehicles is too long in a low-temperature environment. In addition, the configuration of thermal management system in the power battery will not only increase the weight of the power battery, but also increase the cost of the power battery. 
     In view of this, compared with the prior art, the present application provides a new charging system and a charging method thereof, which can solve the above charging problem of the electric vehicle in the low-temperature environment without using a thermal management system to preheat the power battery. 
       FIG. 1  illustrates a charging system to which embodiments of the present application apply. The charging system can be applied to various types of electrical devices including but not limited to electric vehicles and the like. 
       FIG. 1  shows a schematic diagram of a charging system  10  according to the present application. 
     As shown in  FIG. 1 , the charging system  10  may include: a power conversion apparatus  110 , a charging apparatus  120  and an electric vehicle  130 . 
     Specifically, the charging apparatus  120  is a device for supplementing electric energy for the electric vehicle  130  (including a pure electric vehicle and a pluggable hybrid electric vehicle), which can be divided into two categories: an alternative current charging apparatus and a direct current charging apparatus. Where the direct current charging apparatus directly charges the power battery of the electric vehicle by outputting adjustable direct current power, and the output voltage and current adjustment range are large, which can meet the demand of rapid charging. The alternative current charging apparatus only provides power output, but has no charging function. The subsequent rectification and direct current-direct current (DC-DC) conversion are completed by an on-board charger, and the charging apparatus serves as a power controller. In the embodiment of the present application below, the charging method of the present application is explained by using the charging apparatus as the direct current charging apparatus as an example, and the relevant charging method of the on-board charger can refer to the relevant description of the embodiments below. 
     Specifically, electric vehicle  130  may include battery system. At least one battery pack may be provided in the battery system to provide energy and power for the electric vehicle, and the at least one battery pack may be collectively referred to as a power battery. In terms of the type of battery, the power battery may be a lithium-ion battery, a lithium-metal battery, a lead-acid battery, a nickel-cadmium battery, a nickel-hydrogen battery, a lithium-sulfur battery, a lithium-air battery, a sodium-ion battery, and the like, which are not specifically limited in the embodiment of the present application. In terms of battery scale, the power battery in the embodiment of the present application may be a cell/battery cell, may also be a battery module or a battery pack, which is not specifically limited in the embodiment of the present application. 
     In addition, in order to intelligently manage and maintain the power battery, prevent over-charging and over-discharging of the battery, and prolong the service life of the battery, the battery system is generally provided with a battery management system (BMS)  122  for monitoring the state of the power battery. Optionally, the BMS may be integrated with the power battery in the same device/apparatus, or the BMS may be disposed outside the power battery as an independent device/apparatus. 
     Compared with the prior art, the charging system  10  is additionally provided with a power conversion apparatus  110 . Specifically, the power conversion apparatus  110  may be electrically connected to the charging apparatus  120 , and electrically connected to the battery system of the electric vehicle  130 . The power conversion apparatus  110  can be used as a power transfer apparatus between the charging apparatus  120  and the battery system of the electric vehicle  130 . Specifically, the power conversion apparatus  110  can be used as a power transfer apparatus between the charging apparatus  120  and the power battery of the electric vehicle  130 . 
     Specifically, in the present application, the power conversion apparatus  110  is configured to receive first electric energy of a first power type transmitted by the charging apparatus  120 , and convert it into second electric energy of a second power type different from the first power type, and then send the second electric energy to the power battery of the electric vehicle  130 , to realize power conversion. As an example, the first electric energy of the first power type transmitted by the charging apparatus  120  is the direct current, the direct current can be a constant voltage direct current or a constant current direct current, and the power conversion apparatus  110  can convert the direct current into a second electric energy of other power types such as voltage change, current change, power state change, current, voltage, power timing change, etc., and then send the second electric energy to the power battery of the electric vehicle  130 , to charge the power battery. 
     Optionally, as shown in  FIG. 1 , the power conversion apparatus  110  is used as an independent power transfer apparatus and is set outside the charging apparatus  120  and the electric vehicle  130 . As an optional electrical connection manner, the charging apparatus  120  is provided with a first charging gun head, and the power conversion apparatus  110  is provided with a first charging socket corresponding to the first charging gun head to receive the electric energy transmitted from the charging apparatus  120 . In addition, the power conversion apparatus  110  is also provided with a second charging gun head, the second charging gun head is configured to be electrically connected with a second charging socket on the electric vehicle  110 , to realize power conversion apparatus  110  to transmit electric energy to the electric vehicle. 
     In order to adapt to the electrical connection between the existing charging apparatus  120  and the battery system of the electric vehicle  130 , optionally, the specific type and structure of the second charging gun head on the power conversion apparatus  110  may be the same as the specific type and structure of the first charging gun head on the charging apparatus  120 . Correspondingly, the specific type and structure of the first charging socket on the power conversion apparatus  110  may be the same as the specific type and structure of the second charging socket on the electric vehicle. Of course, the second charging gun head and the first charging socket on the power conversion apparatus  110  can also be different from the first charging gun head on the charging apparatus  120  and the second charging socket on the electric vehicle, the embodiment of the present application does not specifically limit this, and it is intended to realize the electrical connection between the charging gun head and the corresponding charging socket. 
     Optionally, in addition to being designed as an independent power conversion apparatus, the power conversion apparatus  110  can also be integrated in the charging apparatus  120  or integrated in the electric vehicle  130 . Or part of the functional modules in the power conversion apparatus  110  is provided in the charging apparatus  120 , and another part of the functional modules is provided in the electric vehicle  130 . The embodiment of the present application also does not specifically limit the specific setting manner of the power conversion apparatus  110 , and it is intended to be electrically connected between the charging apparatus  120  and the battery system of the electric vehicle  130  to achieve the function of power conversion. 
       FIG. 2  is a schematic diagram of an application architecture of the above charging system  10  according to an embodiment of the present application. 
     As shown in  FIG. 2 , the battery system may be the battery system in the electric vehicle  130  in the above charging system  10 , and the battery system includes a power battery  131  and a battery management system (BMS)  132 . 
     Optionally, the power conversion apparatus  110  may include a power unit  111  and a control unit  112 . The power unit  111  is configured to convert the power type output by the charging apparatus  120  into the power type required by the power battery  131 . As an example, the power unit  111  may include a power conversion module, the power conversion module may include a pulse generating circuit used for generating a pulse current to provide the power battery  131 . In addition, the power conversion module may also include other functional circuits such as a drive circuit, a communication circuit, a processing circuit and the like. The control unit  112  may include a controller and/or a processor, which are responsible for detecting the states of the charging apparatus  120  and the BMS  130  during the charging process, and controlling operations of other electrical components in the power unit  111  and the power conversion apparatus. 
     Specifically, the power unit  111  is separately connected with the charging apparatus  120  and the power battery  131  via a high voltage line  150 , to convert the charging power output by the charging apparatus  120  through the high-voltage line  150  and output converted charging power to the power battery  131  to charge the power battery  131 . As an example, as shown in  FIG. 2 , the power conversion module in the power unit  111  is separately connected with a positive electrode output port (for example: direct current positive electrode output port DC+) and a negative electrode output port (for example: direct current negative electrode output port DC−) of the charging apparatus through the high voltage line  150 , and connected to the positive electrode output port and the negative electrode output port of the power battery. 
     Optionally, in addition to the power conversion module, the power unit  111  also includes at least one relay. For example, as shown in  FIG. 2 , the power unit  111  includes a first relay K 1 , a second relay K 2  and a third relay K 3 . The power conversion module is respectively connected to the charging apparatus  120  and the power battery  131  through the second relay K 2  and the third relay K 3 . It is possible to control whether the power conversion module is connected to the charging apparatus  120  and the power battery  131  by controlling the second relay K 2  and the third relay K 3 . 
     In addition, the charging apparatus  120  and the power battery  131  are connected with each other through the first relay K 1 . In other words, if the second relay K 2  and the third relay K 3  are both disconnected, the first relay K 1  is closed, the charging power output by the charging apparatus  120  may directly be transmitted to the power battery  131  at this time, without being converted by the power conversion module. 
     It should be noted that, the first relay K 1 , the second relay K 2  and the third relay K 3  in  FIG. 2  are only schematic illustrative circuit structure, which can also be realized by replacement with other functional circuits. It is designed to realize the selective connection of the power conversion module between the charging apparatus  120  and the power battery  131 . 
     It can be understood that, the first relay K 1 , the second relay K 2  and the third relay K 3  can be controlled by the control unit  112  in the power conversion apparatus  110 . 
     It can also be understood that, the power unit  111  may not include the first relay K 1 , the second relay K 2 , and the third relay K 3 . Directly controlling the operating state of the power conversion module through software can also realize the selective connection of the power conversion module between the charging apparatus  120  and the power battery  131 , so that the power conversion apparatus  110  is in different charging modes. 
     Further referring to  FIG. 2 , the charging apparatus  120  and the BMS  132  can also be separately connected to the power conversion apparatus  110  through a communication line  140 , to realize an information interaction among the charging apparatus  120 , the BMS  132  and the power conversion apparatus  110 . Specifically, the control unit  112  is separately connected to the charging apparatus  120  and the BMS  130  through the communication line  140 , to realize information interaction with the charging post  120  and the BMS  130  respectively. In addition, the control unit  112  is also connected to the power unit  111  through the communication line  140 , to realize information interaction with the power unit  111 , and control the power unit  111  to conduct a power conversion. 
     As an example, the communication line  140  includes but not limited to a control area network (CAN) communication bus or a daisy chain communication bus. Optionally, the charging apparatus  120 , the BMS  132 , the power conversion apparatus  110  may communicate based on the related protocol of physical layer, data link layer and application layer of CAN communication protocol or daisy chain communication protocol. 
     Specifically, in a conventional charging system on the market, an information interaction is directly conducted between the charging apparatus  120  and the BMS  132  via a communication protocol. In the embodiment of the present application, the power conversion apparatus  110  can receive and send notices and a message between the charging apparatus  120  and the BMS  132 , in case of being compatible with present communication protocol between the charging apparatus  120  and BMS  132 , the power conversion between the charging apparatus  120  and the BMS  132  is realized. 
       FIG. 3  a shows a schematic flow diagram of a charging method  200  provided by an embodiment of the present application. The method  200  is applied to a power conversion apparatus. For example, the power conversion apparatus can be a power conversion apparatus  110  in above  FIG. 1  and  FIG. 2 . 
     As shown in  FIG. 3 , the charging method  200  may include the following steps. 
     Step  210 : a power conversion apparatus acquires a state parameter of a power battery, where the state parameter includes a battery temperature. 
     Optionally, in this step, the power battery may be the power battery  131  shown in  FIG. 2  above. The power battery generally includes at least one battery pack, every battery pack may include multiple battery cells connected in series or parallel. The battery temperature of the power battery includes but not limited to the temperature of every battery cell. In the related technologies, the battery cell may be also referred to as a battery core. 
     Optionally, in some implementations, the BMS of the power battery, such as BMS  132  shown in  FIG. 2 , is configured to detect the state parameter of the power battery, such as the battery temperature of the power battery, and transmit it to the power conversion apparatus, such that the power conversion apparatus acquires the state parameter of the power battery. As an example, a communication may be realized between the BMS and the power conversion apparatus based on CAN. In this example, the battery temperature of the power battery may be the minimum power storage battery temperature in the battery state message (BSM) sent by the BMS. In some other examples, the BMS can also communicate with the power conversion apparatus based on other communication protocols, the embodiment of the present application do not specifically limit this. 
     Of course, in some other implementations, the power conversion apparatus may also acquire the state parameter of the power battery by other manners. As an example, other control unit in an electric vehicle besides BMS is configured to acquire the state parameter of the power battery, then the state parameter of the power battery is transmitted to the power conversion apparatus by the control unit; or, as another example, BMS or other control unit in the electric vehicle stores the state parameter of the power battery into a storage unit or a cloud, the power conversion apparatus acquires the battery state parameter from the storage unit or the cloud, the embodiment of the present application do not specifically limit specific manner in which the power conversion apparatus acquires the state parameter of the power battery. 
     Step  220 : the power conversion apparatus sets a charging mode to a pulse charging mode when the battery temperature is lower than a first preset threshold. 
     Specifically, in this step, the pulse charging mode is a charging mode using a pulsed voltage or a pulsed current, in other words, in the pulse charging mode, the power conversion apparatus may generate the pulsed voltage or the pulsed current. 
     Optionally, the operation state of each functional module in the power conversion apparatus may be controlled by controlling software programs and/or hardware circuits in the power conversion apparatus, such that the power conversion apparatus can convert the direct current electricity received from the charging apparatus to a pulse current electricity. 
     As an example, in the power conversion apparatus  110  shown in  FIG. 2 , the second relay K 2  and the third relay K 3  can be controlled to be closed, so that the power conversion module is connected between the charging apparatus  120  and power battery  131 , such that the power conversion apparatus  110  can convert the direct current electricity received from charging apparatus  120  to a pulse current electricity. 
     Optionally, the above first preset threshold may be a preset arbitrary value, which intends to indicate that the power battery is in a low-temperature state. The first preset threshold can be correspondingly set according to the geographical position of the power battery, the battery type, attribute parameters, the system architecture of the power battery and other related factors, and the embodiments of the present application do not limit the specific value thereof. As an example, the first preset threshold may be any value below  10  degree centigrade (° C.), for example, the first preset threshold may be 5° C. 
     Step  230 : the power conversion apparatus converts the charging power of the charging apparatus and then charges the power battery in the pulse charging mode. 
     Specifically, in this step, the power conversion apparatus is configured to realize a conversion of the charging power of the charging apparatus, and output the converted charging power to the power battery, so as to charge the power battery. Where, in the pulse charging mode, the charging power converted by the power conversion apparatus is a pulsed charging voltage or a pulsed charging current. 
     To sum up, through the technical solutions of the embodiment of the present application, the power conversion apparatus acquires a battery temperature of the power battery, when the battery temperature is low, for example, when it is lower than a first preset threshold, the charging mode of the power conversion apparatus is set to the pulse charging mode. In the pulse charging mode, the power conversion apparatus converts the charging power output by the charging apparatus and outputs pulsed electricity to charge the power battery, so as to prevent performance of the power battery from being affected by directly charging the power battery at a low temperature, thereby ensuring the performance of the power battery. In addition, through the technical solution of the embodiment of the application, the power battery does not need to be configured with a thermal management system, and on the basis of reducing the overall cost of the power battery, the heating time of the power battery at a low temperature is saved, and the charging efficiency is improved. 
       FIG. 4  shows a schematic flow diagram of another charging method  300  provided by an embodiment of the present application. 
     As shown in  FIG. 4 , the charging method  300  may include the following steps. 
     Step  310 : the power conversion apparatus acquires the battery state parameter of the power battery, where the state parameter includes the battery temperature and the battery voltage. 
     Step  320 : the power conversion apparatus sets the charging mode to the pulse charging mode when the battery temperature is lower than the first preset threshold and the battery voltage is lower than a second preset threshold. 
     Step  330 : the power conversion apparatus converts the charging power of the charging apparatus and then charges the power battery in the pulse charging mode. 
     In the embodiment of the present application, compared with step  210  above, in step  310 , the power conversion apparatus acquires the battery voltage of the power battery in addition to the battery temperature of the power battery. 
     Specifically, in the charging and discharging process of the power battery, besides the battery temperature has a great influence on it, detecting its voltage at the same time can better reflect the current charging and discharging state of the power battery, and prevent it from over-charging or over-discharging and causing permanent damage to the power battery. 
     Therefore, in the embodiments of the present application, the power conversion apparatus acquires the battery voltage of the power battery in addition to the battery temperature of the power battery, and judges the charging mode of the power battery by synthesizing various information, which improves the charging safety performance Specifically, the battery voltage of the power battery includes, but is not limited to, the voltage of each battery cell in the power battery and/or the total voltage of the entire power battery. 
     Similar to the power conversion apparatus to acquire the battery temperature of the power battery in the above step  210 , in some implementations, the BMS of the power battery is configured to detect the battery voltage of the power battery, and transmit it to the power conversion apparatus, such that the power conversion apparatus acquires the battery voltage of the power battery. In the implementation, the battery voltage of the power battery may be transmitted to the power conversion apparatus via a battery charge state (BCS) message. 
     In step  320 , when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the power conversion apparatus sets the charging mode as the pulse charging mode. Optionally, the second preset threshold value may be a preset arbitrary value, which intends to indicate that the power battery is in a low-voltage state to be charged. The second preset threshold may be set to different values according to different power battery types and structures, which is not specifically limited in the embodiment of the present application. 
     Specifically, the related technical solutions of step  330  in the embodiment of the present application can refer to the related description of above step  230 , it will not be repeated here. 
     In the technical solution of the embodiment of the present application, in addition to acquiring the battery temperature of the power battery, the power conversion apparatus also acquires the battery voltage of the power battery. Combining information on the two aspects of battery temperature and battery voltage, the charging mode is set to the pulse charging mode, and it is further judged whether the power battery is in a low-voltage state to be charged at low temperature, which can further ensure the charging safety. 
     It should be noted that, in the embodiment of the present application, in addition to acquiring the battery temperature of the power battery and the battery voltage, the power conversion apparatus can also acquire other state parameters of the power battery, and further sets its charging mode as the pulse charging mode according to other state parameters. Specifically, other state parameters of the power battery include but not limited to related parameters such as: battery current, battery state of charge (SOC), and estimated remaining charging time, etc. Where the SOC can be regarded as a thermodynamic quantity, which can be used to evaluate the potential electric energy of the battery 
     In the charging methods of above  FIG. 3  and FIG. 4 , the power conversion apparatus sets its charging mode to the pulse charging mode, and converts the output power of the charging apparatus and outputs it to the power battery. Further, on the basis of that, the power conversion apparatus may also switch its charging mode into the direct current charging mode, and directly transmit the charging power of the charging apparatus to the power battery. 
       FIG. 5  shows a schematic flow diagram of another charging method  200  provided by an embodiment of the present application. 
     As shown in  FIG. 5 , the above charging method  200  may also include the following steps. 
     Step  240 : the power conversion apparatus switches the charging mode from the pulse charging mode to the direct current charging mode when the battery temperature is not lower than the first preset threshold. 
     Step  250 : the power conversion apparatus transmits the charging power of the charging apparatus to the power battery in the direct current charging mode. 
     Specifically, in the embodiment of the present application, the above steps  240  and  250  are conducted after step  230  in  FIG. 3 . If the battery temperature acquired by the power conversion apparatus in the current state is not lower than the first preset threshold, it means that the current power battery is in a non-low temperature state, and the charging mode of the power conversion apparatus can be switched from pulse charging mode to direct current charging mode. In the direct current charging mode, the power conversion apparatus directly transmits the charging power output by the charging apparatus to the power battery, to charge the power battery, where, the direct current charging mode is a charging mode which outputs a constant voltage or a constant current, in other words, the charging power of the charging apparatus is a constant voltage or a constant current. 
     As an example, the software programs and/or hardware circuits in the power conversion apparatus can be controlled to control the operating status of each functional module in the power conversion apparatus, so that the power conversion apparatus can directly output the direct current received from the charging apparatus to the power battery. 
     For example, in the power conversion apparatus  110  shown in  FIG. 2 , by controlling the second relay K 2  and the third relay K 3  to be disconnected, and controlling the first relay K 1  to be closed, to achieve a direct electrical connection between the charging apparatus  120  and the power battery  131 , so that the power conversion apparatus  110  can directly output the direct current received from the charging apparatus  120  to the power battery  131 . 
     Furthermore, in the power conversion apparatus  110  shown in  FIG. 2 , the power conversion module can also be controlled to stop running to further enhance the reliability and flexibility in the charging mode switching process. 
     Through the technical solution of the embodiment of the present application, the power conversion apparatus can continuously acquire the battery temperature of the power battery, when the battery temperature is higher, for example, when the battery temperature is not lower than the first preset threshold, the power conversion apparatus switches its charging mode from pulse charging mode to direct current charging mode. Further, the power conversion apparatus directly transmits the charging power of the charging apparatus to the power battery to charge the power battery, and the charging efficiency of the power battery in the non-low temperature is improved. Therefore, through the technical solution of the embodiment of the present application, the power conversion apparatus can flexibly set its charging mode, and the charging efficiency of the whole charging process is improved on the premise of ensuring the performance of the power battery. 
     Similarly,  FIG. 6  shows a schematic flow diagram of another charging method  300  provided by an embodiment of the present application. 
     As shown in  FIG. 6 , the above charging method  300  may also include the following steps. 
     Step  340 : the power conversion apparatus switches the charging mode from the pulse charging mode to the direct current charging mode when the battery temperature is not lower than the first preset threshold, or the battery voltage is not lower than the second preset threshold. 
     Step  350 : the power conversion apparatus transmits the charging power of the charging apparatus to the power battery in the direct current charging mode. 
     In the embodiment of the present application, the steps  340  and  350  are conducted after the above step  330  in  FIG. 4 . If the battery temperature acquired by the power conversion apparatus in the current state is not lower than the first preset threshold, it means that the current power battery is in a non-low temperature state, or if the battery voltage acquired by the power conversion apparatus in the current state is not lower than the second preset threshold, it means that the current power battery is not in the state to be charged, or is in the state to be charged with a higher voltage. The charging mode of the power conversion apparatus can be switched from pulse charging mode to direct current charging mode, and In the direct current charging mode, the charging apparatus charges the power battery through the power conversion apparatus. 
     Through the technical solutions of the embodiments of the present application, the power conversion apparatus continuously obtains the battery temperature and battery voltage of the power battery, and combines the information on the two aspects of the battery temperature and battery voltage to switch its charging mode from the pulse charging mode to the direct current charging mode. In the non-low temperature or non-low voltage state, direct current is configured to charge the rechargeable battery, which can further improve the charging efficiency. 
     It should be noted that, in the above application embodiments, in case that the power conversion apparatus is in the pulse charging mode, if the detected battery temperature is not lower than the first preset threshold, or the battery voltage is not lower than the second preset threshold, the power conversion apparatus need to switch its charging mode from the pulse charging mode to the direct current charging mode. In other application embodiments, in an initial state of the power conversion apparatus, namely, when the charging mode of the power conversion apparatus is not set, if the battery temperature of the power battery acquired by the power conversion apparatus is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold at this time, the power conversion apparatus can directly set its charging mode to the direct current charging mode. 
     In addition, it should also be noted that, in the above step  220  and step  320 , in some cases, if the power conversion apparatus is in initial state, when the battery temperature is lower than the first preset threshold, or the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the power conversion apparatus directly set its charging mode to the pulse charging mode. In other cases, if the power conversion apparatus is in a direct current charging mode, when the battery temperature is lower than the first preset threshold, or the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the power conversion apparatus may switch its charging mode from the direct current charging mode into the pulse charging mode. 
     In conclusion, through the technical solutions of the embodiment of the present application, the power conversion apparatus can adjust its charging mode at any time according to the state parameter of the power battery during the entire charging process. Specifically, it is possible to realize pulse charging of the power battery at a low temperature, and direct current charging of the power battery at a non-low temperature, flexibly adapting to different charging environments, and improving charging efficiency. 
     FIG. 7  shows a schematic flow diagram of a charging method  400  of another embodiment provided by the present application. 
     As shown in  FIG. 7 , the charging method  400  may include the following steps. 
     Step  410 : the battery management system (BMS) sends the battery state parameter of the power battery to the power conversion apparatus, where the state parameter includes battery temperature and battery state of charge. 
     Specifically, in this step, in addition to sending the battery temperature of the power battery to the power conversion apparatus, the battery management system (BMS) also sends battery state of charge (SOC) of the power battery. The SOC can accurately reflect the remaining electric quantity in the power battery. Optionally, the battery management system (BMS) can also send other parameters such as battery voltage of the power battery to the power conversion apparatus. 
     Optionally, in an embodiment of the present application, the battery temperature of the power battery may be sent to the power conversion apparatus via power storage battery state information message (BSM), and parameters such as battery state of charge (SOC), battery voltage of the power battery may be sent to the power conversion apparatus via battery charge state message (BCS). 
     Step  421 : the power conversion apparatus determines pulse charging information according to the state parameter when the battery temperature is lower than the first preset threshold. 
     Specifically, in the step, when the battery temperature is lower than the first preset threshold, the pulse charging information jointly determined according to the battery temperature and the SOC by the power conversion apparatus can be adapted to both the current temperature of the power battery and the SOC of the power battery. 
     Or, in another implementation of the step, when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the power conversion apparatus determines the pulse charging information according to the battery temperature and SOC jointly. 
     Optionally, determining pulse charging information according to the battery temperature and the SOC can be achieved in a variety of ways. As an example, the mapping relationship of the battery temperature, the SOC and the pulse charging information may be determined, and the specific pulse charging information is determined according to the mapping relationship. Where the mapping relationship can be a mapping relationship acquired by fitting a large number of experimental data, and the mapping relationship has a high reliability and accuracy. The mapping relationship may be specifically a mapping table, a mapping diagram or a mapping formula, and the like. In addition, in other examples, a special neural network model can be trained according to a large number of experimental data, and the neural network model can output pulse charging information according to the input battery temperature and SOC. 
     In some implementations, the above pulse charging information includes but not limited to: effective value of pulse current, peak value of pulse current, pulse voltage, pulse direction, pulse frequency, pulse interval and pulse duration. 
     Step  422 : the power conversion apparatus determines first direct current charging information according to the pulse charging information. 
     Specifically, the power conversion apparatus can calculate the first direct current charging information corresponding to the pulse charging information according to the pulse charging information. The first direct current charging information may include at least one of the following information: charging demand voltage, charging demand current and charging demand mode. Where the charging demand mod can be a constant current mode or a constant voltage mode. 
     Step  423 : the power conversion apparatus sends the first direct current charging information to the charging apparatus. 
     Optionally, in some implementations, the first direct current charging information can be sent to the charging apparatus as the charging demand of BMS. Optionally, the power conversion apparatus may send the first direct current charging information via a battery charging demand (BCL) message. Or, in other implementations, the first direct current charging information can also be sent to the charging apparatus via other messages, the embodiment of present application does not specifically limit the message type and the sending method. 
     Optionally, the above steps  421  to  423  may be the implementation manners included in step  220  in  FIG. 3  above. 
     Step  431 : the charging apparatus outputs a direct current to the power conversion apparatus. 
     Step  432 : the power conversion apparatus converts the direct current into a pulse current. 
     Step  433 : the power conversion apparatus outputs the pulse current to the power battery. 
     Optionally, the above steps  431  to  433  may be the implementation manners included in step  230  of above  FIG. 3 . 
     Specifically, during above steps, the charging apparatus outputs a direct current to power conversion apparatus, the power conversion apparatus is configured to convert the direct current into a pulse current, and output the pulse current to the power battery, so as to realize a pulse charging to the power battery. Where the pulse current is a pulse current generated by converting a direct current based on the above pulse charging information. The direct current is a direct current output by the charging apparatus to the power conversion apparatus based on the first direct current charging information above. 
     Through the technical solution of the embodiment of the present application, the power conversion apparatus may determine the corresponding pulse charging information according to the state parameter of the power battery acquired by it. And the power conversion apparatus converts different pulse currents according to the pulse charging information to adapt to the different charging requirements of the power battery in different situations, and has high flexibility and adaptability. 
     In can be understood that, the charging method  400  described in  FIG. 7  above may be a schematic flowchart of a method for setting the charging mode of the power conversion apparatus to the pulse charging mode in the initial stage, that is, when the charging mode is not set. 
     In case that the power conversion apparatus switches its charging mode from the direct current charging mode to the pulse charging mode, or switches from other charging mode to the pulse charging mode,  FIG. 8  shows a schematic flow diagram of a charging method  500  according to another embodiment of the present application. 
     As shown in  FIG. 8 , the charging method  500  may include the following steps. 
     Step  510 : the battery management system (BMS) sends the battery state parameter of the power battery to the power conversion apparatus, where the state parameter includes battery temperature and battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as battery voltage of the power battery to the power conversion apparatus. 
     Optionally, the related technical solution of step  510  may refer to the related description for step  410  in above  FIG. 7 , it will not be repeated here. 
     Step  521 : the power conversion apparatus sends a charging prohibition message to the charging apparatus when the battery temperature is lower than the first preset threshold. 
     Specifically, in the step, the charging prohibition message is configured to indicate the charging apparatus to stop outputting the direct current to the power conversion apparatus. 
     Optionally, in another implementation of this step, when the battery temperature is lower than the first preset threshold and the battery voltage is lower than a second preset threshold, the power conversion apparatus sends a charging prohibition message to the charging apparatus. 
     Optionally, before step  521 , the power conversion apparatus may send a battery charging lab (BCL) message to the charging apparatus. Specifically, in the demand message, the demand voltage may be a total voltage of the power battery, the demand current is set as the minimum current of the charging apparatus that can be output, for example, a current value of  10 A. 
     Through the technical solution of the embodiment of the present application, before sending a charging prohibition message to charging apparatus, the power conversion apparatus first sends one small demand current to charging apparatus, then prohibits the output of the charging apparatus. Therefore, it is possible to prevent the charging prohibition message from being sent directly to the charging apparatus, which can quickly prohibit the charging apparatus from outputting current, and has less impact on the entire charging system. 
     Step  522 : the power conversion apparatus acquires the voltage difference between its input end and output end, and judges whether the voltage difference is less than a third preset threshold. 
     Optionally, in this step, in the process of switching the charging mode of the power conversion apparatus from the direct current charging mode to the pulse charging mode, the switch control of the relay is involved. When the voltage difference between the input end and the output end of the power conversion apparatus is too large, it is easy to cause damage to the relay and affect the normal operation of the power conversion apparatus. Therefore, in order to protect the relay and to ensure the performance of the power conversion apparatus, before controlling the relay switch, the power conversion apparatus may also acquire voltage difference between its input end and output end, and judge whether the voltage difference is less than the third preset threshold. If the voltage difference is less than the third preset threshold, the power conversion apparatus execute the subsequent action. If the voltage difference is not less than the third preset threshold, the power conversion apparatus stops outputting, or, it can also wait for a period of time until the voltage difference is less than the third preset threshold. 
     As an example, the third preset threshold includes but not limited to 10V. 
     Optionally, in some implementations, the power conversion apparatus may directly detect the voltage difference between its input end and output end, or, in some other implementations, the power conversion apparatus may receive a voltage value sent by the power battery and a voltage value sent by the charging apparatus, and the power conversion apparatus uses the voltage value sent by the power battery as the voltage of its output end, and the voltage value sent by the charging apparatus as the voltage of its input end. 
     Specifically, if the charging mode of the power conversion apparatus is switched from the direct current charging mode to the pulse charging mode, when the voltage difference between input end and output end of the power conversion apparatus is less than the third preset threshold, the relay state in the power conversion apparatus changes. For example, the second relay K 2  and the third relay K 3  in  FIG. 2  are closed, then the following pre-charging step is executed. 
     Step  523 : the power conversion apparatus conducts the pre-charging. 
     Specifically, in the power conversion module of the power conversion apparatus, there are capacitors with large-capacity in the charging high voltage circuit of the input end and the output end. At the moment when the power conversion module is connected to the high voltage circuit, the high voltage in the charging high-voltage circuit will charge the large-capacity capacitor and generate a pulsed large current. The pulsed large current may damage the device, such as a high voltage contactor in the power conversion apparatus or power battery. 
     Therefore, in the process of switching the power conversion apparatus from the direct current charging mode to the pulse charging mode, after the power conversion apparatus sends a charging prohibition message to the charging apparatus, the capacitor in the power conversion apparatus needs to be pre-charged first. Optionally, the capacitor can be pre-charged using the battery voltage of the power battery, so that in the subsequent charging process of the power battery, the capacitor will not cause a large pulse current. Thus, the normal progress of the charging process and the safety of charging can be ensured. 
     Further, if the pre-charging succeeds, a first relay K 1  in  FIG. 2  is disconnected, to disconnect the direct current connection between the charging apparatus and the power battery. 
     Step  524 : the power conversion apparatus determines the pulse charging information according to the state parameter. 
     Step  525 : the power conversion apparatus determines the first direct current charging information according to the pulse charging information. 
     Step  526 : the power conversion apparatus sends the first direct current charging information and a charging permission message to the charging apparatus. 
     Specifically, in this step  526 , in addition to sending the first direct current charging information to the charging apparatus, the power conversion apparatus also sends a charging permission message to the charging apparatus, the charging permission message is configured to indicate the charging apparatus can output a direct current. 
     Optionally, other related solutions of the above steps  524  to  526  may refer to related description of steps  421  to  423  in above  FIG. 7 , it will not be repeated here. 
     Step  531 : the charging apparatus outputs a direct current to the power conversion apparatus. 
     Step  532 : the power conversion apparatus converts the direct current into a pulse charging current. 
     Step  533 : the power conversion apparatus outputs the pulse charging current to the power battery. 
     Optionally, the above steps  531  to  533  may refer to the related description on steps  431  to  433  in above  FIG. 7 , it will not be repeated here. 
     The above description in conjunction with  FIG. 8  illustrates the related technical solution that the power conversion apparatus switches its charging mode from the direct current charging mode to the pulse charging mode in the embodiment of the present application. In the following, in conjunction with  FIG. 9 , a related technical solution for the power conversion apparatus to switch its charging mode from the pulse charging mode to the direct current charging mode in an embodiment of the present application will be described. 
       FIG. 9  shows a schematic flow diagram of a charging method  600  of another embodiment of the present application. 
     As shown in  FIG. 9 , the charging method  600  may include the following steps. 
     Step  611 : the battery management system (BMS) sends second direct current charging information of the power battery to the power conversion apparatus. 
     Optionally, in some implementations, the battery management system (BMS) may send the second direct current charging information of the power battery to the power conversion apparatus via the battery charging demand (BCL) message. The second direct current charging information is a charging information determined by the battery management system (BMS) according to the present state parameter of the power battery, and the second direct current charging information can include at least one of the following information: charging demand voltage, charging demand current and charging demand mode. Where the charging demand mod can be a constant current mode or a constant voltage mode. 
     Or, in some other implementations, the first direct current charging information can also be sent to the power conversion apparatus via other messages, the embodiment of the present application does not specifically limit the message type and sending method. 
     Step  612 : the battery management system (BMS) sends the battery state parameter of the power battery to the power conversion apparatus, where the state parameter includes the battery temperature and the battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as the battery voltage of the power battery to the power conversion apparatus. 
     Optionally, the related technical solution of step  612  may refer to the related description for step  410  in above  FIG. 7 , it will not be repeated here. 
     Step  621 : the power conversion apparatus stops outputting pulse current to the power battery when the battery temperature is not lower than first preset threshold. 
     Specifically, in the step, when the battery temperature is not lower than the first preset threshold, it indicates that the present state of the power battery can receive the direct current, and the direct current charge may have no impact on the power battery. At this moment, the power conversion apparatus stops outputting the pulse electricity to the power battery, and realizes output of direct current to the power battery in the subsequent steps. Therefore when the battery temperature is not lower than the first preset threshold, the charging speed and charging efficiency of the power battery are improved. 
     Optionally, in another implementation of this step, when the battery temperature is not lower than the first preset threshold, or the battery voltage is not lower than the second preset threshold, the power conversion apparatus stops outputting the pulse current to the power battery. 
     It can be understood that, in this step, the operation state of the functional module in the power conversion apparatus can be controlled through communication signaling and software programs to realize that the power conversion apparatus stops outputting pulse current to the power battery. 
     It also can be understood that, in this step, the relay in the power conversion apparatus can also be controlled to realize that the power conversion apparatus stops outputting pulse current to the power battery. As an example, the third relay K 3  in  FIG. 2  can be controlled to be disconnected to realize that the power conversion apparatus stops outputting the pulse current to the power battery. Further, the second relay K 2  and third relay K 3  in  FIG. 2  can be controlled to be disconnected to realize that the power conversion apparatus stops outputting the pulse current to the power battery. 
     Step  622 : the power conversion apparatus sends the second direct current charging information to the charging apparatus. 
     Specifically, in this step, the power conversion apparatus directly retransmits the second direct current charging information sent by the above battery management system (BMS) to the charging apparatus. For example, the power conversion apparatus retransmits the above battery charging demand (BCL) message to the charging apparatus. 
     Optionally, the above step  612  and step  622  may be an implementation included in step  240  in above  FIG. 5 . 
     Step  631 : the charging apparatus outputs a direct current to the power battery through the power conversion apparatus. 
     Specifically, in this step, by closing the first relay K 1 , and the second relay K 2  and third relay K 3  are disconnected, and a direct electrical connection between the charging apparatus and the power battery is realized, so that the charging apparatus outputs direct current to the power battery through power conversion apparatus, in other words, it can also be understood that the power conversion apparatus directly transmits the direct current of the charging apparatus to the power battery. 
     Specifically, in this step, the direct current output by the charging apparatus is a direct current output by the charging apparatus according to the above second charging information, which can meet the charging demand of the power battery. 
     Optionally, the above step  631  may be an implementation of step  250  included in above  FIG. 5 . 
       FIG. 10  shows a schematic flow diagram of a charging method  700  of another embodiment of the present application. 
     As shown in  FIG. 10 , the charging method  700  may include the following steps. 
     Step  711 : the battery management system (BMS) sends the second direct current charging information of the power battery to the power conversion apparatus. 
     Step  712 : the battery management system (BMS) sends the battery state parameter of the power battery to the power conversion apparatus, where the state parameter includes the battery temperature and the battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as the battery voltage of the power battery to the power conversion apparatus. 
     Step  721 : the power conversion apparatus sends charging prohibition message to the charging apparatus when the battery temperature is not lower than the first preset threshold. 
     Specifically, in the step, the charging prohibition message is configured to indicate the charging apparatus to stop outputting the direct current to the power conversion apparatus. 
     Optionally, in another implementation of this step, when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold, the power conversion apparatus sends a charging prohibition message to the charging apparatus. 
     Optionally, before step  721 , the power conversion apparatus may send a battery charging demand (BCL) message to the charging apparatus. Specifically, in the demand message, the demand voltage may be a total voltage of the power battery, the demand current is set as the minimum current of the charging apparatus that can be output, for example, a current value of 10 A. 
     Through the technical solution according to the embodiment of the present application, before stopping outputting the pulse current to the power battery, the power conversion apparatus first sends one small demand current to the charging apparatus, then prohibits the output of the charging apparatus. Therefore, it is possible to prevent the charging prohibition message from being sent directly to the charging apparatus, which can quickly prohibit the charging apparatus from outputting current, and has less impact on the entire charging system. 
     Step  722 : the power conversion apparatus stops outputting the pulse current to the power battery. 
     Specifically, in the step, the functional module in the power conversion apparatus stopping work can be controlled to stop, such that the power conversion apparatus stops outputting the pulse current to the power battery. 
     Step  723 : the power conversion apparatus acquires a voltage difference between its input end and output end, and judges the voltage difference whether is less than a fourth preset threshold. 
     Optionally, in this step, in the process of switching the charging mode of the power conversion apparatus from the pulse charging mode to the direct current charging mode, the switch control of the relay is involved. When the voltage difference between the input end and the output end of the power conversion apparatus is too large, it is easy to cause damage to the relay and affect the normal operation of the power conversion apparatus. Therefore, in order to protect the relay and ensure the performance of the power conversion apparatus, before controlling the relay switch, the power conversion apparatus may also acquire voltage difference between its input end and output end, and judge whether the voltage difference is less than the fourth preset threshold. If the voltage difference is less than the fourth preset threshold, the power conversion apparatus executes the subsequent action. If the voltage difference is not less than the fourth preset threshold, the power conversion apparatus stops output, or, can also wait for a period of time until the voltage difference is less than the fourth preset threshold. As an example, the fourth preset threshold includes but not limited to 10V. 
     Specifically, if the charging mode of the power conversion apparatus is switched from the pulse charging mode to the direct current charging mode, when the voltage difference between the input end and the output end of the power conversion apparatus is less than the fourth preset threshold, the relay state in the power conversion apparatus changes. For example, in  FIG. 2 , the first relay K 1  is closed, and the second relay K 2  and third relay K 3  are disconnected. 
     Further, when the voltage difference between the input end and the output end of the power conversion apparatus is less than the fourth preset threshold, and the first relay K 1  is closed, the following step  724  and step  731  are executed. 
     Step  724 : the power conversion apparatus sends the second direct current charging information and a charging permission message to the charging apparatus. 
     Specifically, in this step, in addition to sending the second direct current charging information to the charging apparatus, the power conversion apparatus also sends the charging permission message to the charging apparatus, where the charging permission message is use to indicate that the charging apparatus can output the direct current. 
     Step  731 : the charging apparatus outputs a direct current to the power battery through the power conversion apparatus. 
     Specifically, in this step, when the voltage difference between the input end and the output end of the power conversion apparatus is less than the fourth preset threshold, the power conversion apparatus outputs the direct current output by the charging apparatus according to the above second direct current charging information to the power battery to charge the power battery, which can meet the charging demand of the power battery. 
     Optionally, related solutions of the embodiment of the present application may refer to the related description in above  FIG. 9 , it will not be repeated here. 
     In the foregoing, the power conversion apparatus is used as the execution subject to describe various embodiments of the charging method provided in the present application. The following describes the charging process of the power conversion apparatus by taking the power conversion apparatus including the control unit and the power unit as an example. For example, the power conversion apparatus may be power conversion apparatus  110  in  FIG. 2 , and includes a control unit  112  and a power unit  111 . 
       FIG. 11  shows a schematic flow diagram of charging method of the power conversion apparatus according to another embodiment of the present application. The power conversion apparatus is used for power conversion between the charging apparatus and the power battery, and the power conversion apparatus includes a control unit and a power unit. 
     Referring back to the charging method  200  shown in  FIG. 3  above,  FIG. 11  shows another schematic flowchart diagram of the charging method  200  provided by an embodiment of the present application. 
     As shown in  FIG. 11 , the above step  210  may include step  211 : the control unit acquires the battery state parameter of the power battery, where the state parameter includes a battery temperature. 
     The above step  220  may include step  221 : the control unit sets the charging mode of the power unit as the pulse charging mode when the battery temperature is lower than the first preset threshold. 
     Specifically, in this step, in the pulse charging mode, control unit controls the operation of the power unit, such that power unit may generate a pulsed voltage or pulsed current. 
     Optionally, the control unit controls the software program and/or hardware circuit in the power unit to control the operating state of the power unit so that the power unit can convert the direct current electricity received from the charging apparatus into pulsed electricity. 
     As an example, in the power conversion apparatus  110  shown in  FIG. 2 , the control unit controls the second relay K 2  and the third relay K 3  to close, and control the first relay K 1  to be disconnected, to realize that the power conversion module is connected between the charging apparatus  120  and the power battery  131 , the power conversion module is operated, and the direct current electricity received from the charging apparatus is converted into pulse current electricity. 
     The above step  230  may include step  231 : the power unit converts the charging power of the charging apparatus and then charges the power battery in the pulse charging mode. 
     Specifically, in this step, the power unit in the power conversion apparatus is configured to convert the charging power of the charging apparatus and output the converted charging power to the power battery to charge the power battery. Where, in the pulse charging mode, the charging power converted by the power conversion apparatus is a pulsed charging voltage or a pulsed charging current. 
     Specifically, in the embodiment of the present application, the power conversion apparatus uses the pulse charging mode to charge the power battery through the cooperation of the control unit and the power unit. For the specific solution, please refer to the related description in  FIG. 3  above, which will not be described in detail here. 
     Similarly, with respect to the method  200  shown in  FIG. 5  above, the above step  240  may include: when the battery temperature is not lower than the first preset threshold, the control unit switches the charging mode of the power unit from the pulse charging mode to the direct current charging mode. 
     Specifically, in this step, in the direct current charging mode, the control unit controls the operation of the power unit, such that the power unit can output a constant voltage or a constant current. 
     As an example, the control unit can control the operating state of each functional module in the power unit by controlling the software program and/or hardware circuit in the power unit, so that the power unit can directly output the direct current received from the charging apparatus to the power battery. 
     For example, in the power conversion apparatus  110  shown in  FIG. 2 , the control unit can control the second relay K 2  and the third relay K 3  to be disconnected, and control the first relay K 1  to be closed, so as to realize a direct electrical connection between a charging apparatus  120  and a power battery  131 , such that the power unit  111  can directly output direct current received from the charging apparatus  120  to the power battery  131 . 
     Furthermore, in the power conversion apparatus  110  shown in  FIG. 2 , the control unit can also control the power conversion module to stop operation, to further enhance the reliability and the flexibility in the charging mode switching process. 
     The above step  250  may include step  251 : the power unit transmits charging power of the charging apparatus to the power battery in the direct current charging mode. 
     Similarly, with respect to the method  300  shown in above  FIG. 4  and  FIG. 6 , the above step  310  may include step  311 : the control unit acquires the battery state parameter of the power battery, where the state parameter includes battery temperature and battery voltage. 
     The above step  320  may include step  321 : the control unit sets the charging mode of the power unit as pulse charging mode when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold. 
     The above step  330  may include step  331 : the power unit converts the charging power of the charging apparatus and then charges the power battery in the pulse charging mode. 
     The above step  340  may include step  341 : the control unit switches charging mode of the power unit from the pulse charging mode into the direct current charging mode when battery temperature is not lower than first preset threshold, or the battery voltage is not lower than the second preset threshold. 
     The above step  350  may include step  351 : the power unit transmits charging power of the charging apparatus to the power battery in the direct current charging mode. 
     Specifically, in the embodiment of the present application, the power conversion apparatus realizes that the pulse charging mode is switched to the direct current charging mode to charge the power battery through the cooperation of the control unit and the power unit. For specific solutions, please refer to the related descriptions in  FIGS. 4 to 6  above, which will not be described in detail here. 
     Referring back to the charging method  400  shown in  FIG. 7 ,  FIG. 12  shows another schematic flow diagram of the charging method  400  provided by an embodiment of the present application. 
     As shown in  FIG. 12 , the above step  410  may include step  4101 : the battery management system (BMS) sends a battery state parameter of the power battery to the control unit, where the state parameter includes a battery temperature and a battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as a battery voltage of the power battery to the control unit. 
     Optionally, in the embodiment of the present application, the battery temperature of the power battery may be sent to the control unit via power storage battery state information message (BSM), and parameters such as the battery state of charge (SOC), the battery voltage of the power battery may be sent to the control unit via the battery charge state message (BCS). 
     The above step  421  may include step  4211 : the control unit determines the pulse charging information according to the state parameter when the battery temperature is lower than the first preset threshold. 
     Specifically, in this step, when the battery temperature is lower than the first preset threshold, the pulse charging information jointly determined according to the battery temperature and the SOC by the control unit can be adapted to both the current temperature of the power battery and the SOC of the power battery. 
     Or, in another implementation of the step, when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the control unit determines the pulse charging information according to the battery temperature and SOC jointly. 
     The above step  422  may include step  4221 : the control unit sends pulse charging information to the power unit. 
     Optionally, there are many ways to realize that the control unit determines the pulse charging information according to the battery temperature and SOC. As an example, the mapping relationship of the battery temperature, the SOC and the pulse charging information may be determined, and the specific pulse charging information is determined according to the mapping relationship. Where the mapping relationship can be a mapping relationship acquired by fitting a large number of experimental data, and the mapping relationship has a high reliability and accuracy. In addition, in other examples, a special neural network model can be trained according to a large number of experimental data, and the neural network model can output pulse charging information according to the input battery temperature and SOC. 
     Step  4222 : the power unit determines the first direct current charging information according to the pulse charging information. 
     Specifically, the power unit can determine the first direct current charging information corresponding to the pulse charging information according to the pulse charging information. The first direct current charging information may include at least one of the following information: charging demand voltage, charging demand current and charging demand mode. Where the charging demand mod can be a constant current mode or a constant voltage mode. 
     Step  4223 : the power unit sends the first direct current charging information to the control unit. 
     The above step  423  may include step  4231 : the control unit sends the first direct current charging information to the charging apparatus. 
     Specifically, the control unit retransmits the first direct current charging information received from the power unit to the charging apparatus. 
     Optionally, in some implementations, the first direct current charging information can be sent to the charging apparatus as the charging demand of BMS. Optionally, the control unit may send the first direct current charging information via the battery charging demand (BCL) message. Or, in other implementations, the first direct current charging information can also be sent to the charging apparatus via other messages, the embodiment of present application does not specifically limit the message type and the sending method. 
     The above step  431  may include step  4311 : the charging apparatus outputs a direct current to the power unit. 
     The above step  432  may include step  4321 : the control unit sends a start output message to the power unit. 
     Specifically, the start output message is configured to indicate the power unit to start operation, so as to realize subsequent step  4322 . 
     Step  4322 : the power unit converts the direct current into a pulse current. 
     The above step  433  may include step  4331 : the power unit outputs the pulse current to the power battery. 
     Specifically, specific embodiments of the present application can be found in the description of the charging method  400  shown in  FIG. 7  above, and for the sake of brevity, no more specific details will be given here. 
     Referring back to the charging method  500  shown in  FIG. 8 ,  FIG. 13  shows another schematic flowchart diagram of the charging method  500  provided by an embodiment of the present application. 
     As shown in  FIG. 13 , the above step  510  may include step  5101 : the battery management system (BMS) sends the battery state parameter of the power battery to the control unit, where the state parameter includes the battery temperature and the battery state of charge. 
     The above step  521  may include step  5211 : the control unit sends the charging prohibition message to the charging apparatus when the battery temperature is lower than the first preset threshold. 
     Optionally, in another embodiment of this step, when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the control unit sends the charging prohibition message to the charging apparatus. 
     Optionally, before step  5211 , the control unit may send a battery charging demand (BCL) message to the charging apparatus. Specifically, in the demand message, the demand voltage may be a total voltage of the power battery, the demand current is set as minimum current of the charging apparatus that can be output, for example, a current value of  10 A. 
     The above step  522  may include step  5221 : the control unit acquires the voltage difference between input end and output end, and judge whether the voltage difference is less than the third preset threshold. 
     Optionally, in this step, in the process that the control unit switch the charging mode of the power unit from the direct current charging mode to the pulse charging mode, the switch control of the relay is involved. When the voltage difference between the input end and the output end of the power unit is too large, it is easy to cause damage to the relay and affect the normal operation of the power conversion apparatus. Therefore, in order to protect the relay and ensure the performance of the power conversion apparatus, before controlling the relay switch, the control unit may also acquire the voltage difference between the input end and the output end of the power unit, and judge whether the voltage difference is less than the third preset threshold. If the voltage difference is less than the third preset threshold, the control unit executes the subsequent action, If the voltage difference is not less than the third preset threshold, the control unit controls the power unit to stop outputting, or, it can also wait for a period of time until the voltage difference is less than the third preset threshold. 
     Optionally, in some implementations, the control unit may directly detect the voltage difference between the input end and the output end of the power unit, or, in some other implementations, the control unit may receive the voltage value sent by the power battery and the voltage value sent by the charging apparatus, and the control unit uses the voltage value sent by the power battery as the voltage of the output end of the power unit, and the voltage value sent by the charging apparatus as the voltage of the input end of the power unit. 
     Specifically, if the charging mode of the power unit is switched from the direct current charging mode to the pulse charging mode, when the voltage difference between the input end and the output end of the power unit is less than the third preset threshold, the relay state in the power conversion apparatus changes. For example, the second relay K 2  and the third relay K 3  in  FIG. 2  are closed, and the power unit is electrically connected with the charging apparatus and the power battery. 
     The above step  523  may include the following steps. 
     Step  5231 : the control unit sends a precharge instruction to the power unit. 
     Step  5232 : the power unit conducts a pre-charging. 
     Step  5233 : the power unit sends its pre-charging state to the control unit. 
     Step  5234 : the control unit judges whether the power unit is pre-charged successfully. 
     After the charging apparatus stops outputting direct current and the second relay K 2  and the third relay K 3  are closed, the control unit sends a pre-charge instruction to the power unit. The power unit starts the pre-charging according to the precharge instruction, and the pre-charging includes: charging the capacitor in the power unit. 
     During the pre-charging process of the power unit, the power unit sends its pre-charging state to the control unit in real time, and the control unit judges whether the pre-charging of the power unit is successful according to the pre-charging state. If it is successful, the control unit performs subsequent operations, and if it is unsuccessful, the control unit controls the power unit to stop outputting. 
     Further, if the pre-charging is successful, the control unit controls the first relay K 1  in  FIG. 2  to be disconnected, so as to disconnect the direct current connection between the charging apparatus and the power battery. 
     The above step  524  may include step  5241 : the control unit determines the pulse charging information according to the state parameter. 
     The above step  525  may include the following steps. 
     Step  5251 : the control unit sends the pulse charging information to the power unit. 
     Step  5252 : the power unit determines the first direct current charging information according to the pulse charging information. 
     Step  5253 : the power unit sends the first direct current charging information to the control unit. 
     The above step  526  may include step  5261 : the control unit sends the first direct current charging information to the charging apparatus. 
     The above step  531  may include step  5311 : the charging apparatus outputs a direct current to the power unit. 
     The above step  532  may include step  5321 : the control unit sends a start output message to the power unit; step  5322 : the power unit converts the direct current into a pulse current. 
     The above step  533  may include step  5331 : the power unit outputs the pulse current to the power battery. 
     Specifically, specific embodiments of the present application can be found in the description of the charging method  500  shown in  FIG. 8  above, and for the sake of brevity, no more specific details will be given here. 
     Referring back to the charging method  600  shown in  FIG. 9 ,  FIG. 14  shows another schematic flowchart diagram of the charging method  600  provided by an embodiment of the present application. 
     As shown in  FIG. 14 , the above step  611  may include step  6111 : the battery management system (BMS) sends the second direct current charging information of the power battery to the control unit. 
     Optionally, in some implementations, the battery management system (BMS) may send the second direct current charging information of the power battery to the control unit via the battery charging demand (BCL) message. 
     Or, in some other implementations, the first direct current charging information can also be sent to the control unit via other messages, the embodiment of the present application does not specifically limit the message type and sending method. 
     The above step  612  may include step  6121 : the battery management system (BMS) sends the battery state parameter of the power battery to the control unit, where the state parameter includes the battery temperature and the battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as the battery voltage of the power battery to the control unit. 
     The above step  621  may include step  6211 : the control unit sends a prohibit output message to the power unit when the battery temperature is not lower than the first preset threshold. 
     Specifically, in this step, when the battery temperature is not lower than the first preset threshold, the control unit sends a prohibit output message to the power unit to control the power unit to stop outputting the pulse current. 
     Optionally, in another implementation of this step, when the battery temperature is not lower than the first preset threshold, or the battery voltage is not lower than the second preset threshold, the control unit sends an prohibit output message to the power unit to control the power unit to stop outputting the pulse current to the power battery. 
     Optionally, the prohibit output message may include multiple types. For example, it may include a pause output message and a stop output message, where, the pause output message is configured to indicate the power unit to stop outputting the pulse current temporarily, and in this the state, if the power unit receives a start output message, it may restore outputting the pulse current. But the stop output message is configured to indicate the capacitor in the power unit to execute the power-off and discharge process, and the power unit enters a sleep state. 
     Optionally, the prohibit output message and the start output message sent to the power unit by the control unit is carried via the message of the same type. As an example, in the message, the start output message is represented as “1”, in the prohibit output message, the pause output message is represented as “2”, the stop output message is represented as “3”. 
     The above step  622  may include step  6221 : the control unit sends the second direct current charging information to the charging apparatus. 
     The above step  631  may include step  6311 : the charging apparatus outputs a direct current to the power battery through the power unit. 
     Specifically, in this step, by closing the first relay K 1  in the power unit, the second relay K 2  and the third relay K 3  are disconnected, and a direct electrical connection between the charging apparatus and the power battery is realized, so that the charging apparatus outputs a direct current to the power battery through the power unit. 
     Referring back to the charging method  600  shown in  FIG. 10 ,  FIG. 15  shows another schematic flowchart diagram of the charging method  700  provided by an embodiment of the present application. 
     As shown in  15 , the above step  711  may include step  7111 : the battery management system (BMS) sends the second direct current charging information of the power battery to the power conversion apparatus. 
     The above step  712  may include step  7121 : the battery management system (BMS) sends the battery state parameter of the power battery to the control unit, where the state parameter includes the battery temperature and the battery state of charge. 
     Optionally, the battery management system (BMS) can also send other parameters such as the battery voltage of the power battery to the control unit. 
     The above step  721  may include step  7211 : the control unit sends the charging prohibition message to the charging apparatus when the battery temperature is not lower than the first preset threshold. 
     Optionally, in another implementation of this step, when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold, the control unit sends the charging prohibition message to charging apparatus. 
     Optionally, before step  7211 , the control unit may send a battery charging demand (BCL) message to the charging apparatus. Specifically, in the demand message, the demand voltage may be a total voltage of the power battery, the demand current is set as the minimum current of the charging apparatus that can be output, for example, a current value of  10 A. 
     The above step  722  may include step  7221 : the control unit sends the prohibit output message to the power unit. 
     Specifically, the control unit sends the prohibit output message to the power unit, so as to control the power unit to stop outputting the pulse current. 
     Optionally, the related technical solution of this step can refer to the related description of step  6211  in above  FIG. 14 , and it will not be repeated here. 
     The above step  723  may include step  7231 : the control unit acquires the voltage difference between the input end and the output end of the power unit, and judges whether the voltage difference is less than the fourth preset threshold. 
     If the voltage difference is less than the fourth preset threshold, the control unit continues to execute the subsequent action. If the voltage difference is not less than the fourth preset threshold, the control unit may continue to wait until the voltage difference is less than the fourth preset threshold. In this case, if the wait time of the control unit is larger than a certain threshold, the control unit may send a charging stop message to the power unit so that the capacitor in the power unit performs power-off and discharge. 
     Specifically, when the voltage difference between the input end and the output end of the power unit is less than the fourth preset threshold, the relay state in the power conversion apparatus changes. For example, the first relay K 1  in  FIG. 2  is closed, the second relay K 2  and the third relay K 3  are disconnected, so as to disconnect the electrical connection of the power unit with the charging apparatus, and the electrical connection of the power unit with the power battery. The charging apparatus and the power battery are directly electrically connected. 
     Further, when the voltage difference between the input end and the output end of the power unit is less than the fourth preset threshold, and the first relay K 1  is closed, the following step  7241  is executed. 
     The above step  724  may include step  7241 : the control unit sends the second direct current charging information and a charging permission message to the charging apparatus. 
     The above step  731  may include step  7311 : the charging apparatus outputs a direct current to the power battery through the power unit. 
     It should be noted that in this application, in addition to providing a charging method with a power conversion apparatus as the execution body, a charging method with a charging apparatus and a BMS as the execution body is also provided. Specifically, the charging method with the charging apparatus and the BMS as the execution body may correspond to the relevant descriptions of the above method embodiments, which will not be described in detail herein. 
     Specific embodiments of the charging method provided by the present application have been described above with reference to  FIGS. 3 to 15 , and the specific embodiments of the charging apparatus provided by the present application will be described below with reference to  FIGS. 16 to 18 . It is understood that the related description in the following embodiments can refer to the foregoing embodiments and will not be repeated here for the sake of brevity. 
       FIG. 16  shows a schematic structure diagram of power conversion apparatus  800  of an embodiment of the present application. As shown in  FIG. 16 , the power conversion apparatus  800  includes: a receiving module  810 , a sending module  820  and a processing module  830 . 
     In one embodiment of the present application, the receiving module  810  is configured to receive the state parameter of the power battery, the state parameter includes the battery temperature; the processing module  830  is configured to set the charging mode to the pulse charging mode when the battery temperature is lower than the first preset threshold; the processing module  830  is configured to convert the charging power of the charging apparatus and then charge the power battery in the pulse charging mode, the pulse charging mode is a charging mode which output pulsed voltage or pulsed current. 
     Optionally, the processing module  830  is also configured to: switch the charging mode from pulse charging mode to direct current charging mode when the battery temperature is not lower than the first preset threshold; the processing module  830  transmits the charging power of the charging apparatus to the power battery to charge the power battery in the direct current charging mode, where the direct current charging mode is a charging mode which outputs a constant voltage or a constant current. 
     Optionally, the state parameter also includes a battery voltage; the processing module  830  is configured to set the charging mode to the pulse charging mode when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold. 
     Optionally, the state parameter also includes a battery voltage, the processing module  830  is configured to switch the charging mode from the pulse charging mode to the direct current charging mode when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold. 
     In the processing that the processing module  830  is configured to set the charging mode to the pulse charging mode, optionally, the state parameter also includes a battery state of charge; the sending module  820  is configured to send first direct current charging information to the charging apparatus, the first direct current charging information is determined by the processing module  830  according to the pulse charging information, where the pulse charging information include at least one of the following information: pulse current information, pulse voltage information, pulse direction information, pulse frequency information and pulse time information. The pulse charging information is determined by the processing module  830  according to the battery temperature and battery state of charge. In the pulse charging mode, the processing module  830  is configured to output the pulse current to the power battery, where the pulse current is generated by converting a direct current based on the pulse charging information, the direct current is a direct current output to t the processing module  830  by the charging apparatus according to the first direct current charging information. 
     Optionally, before the processing module  830  sets the charging mode to the pulse charging mode, the sending module  820  is also configured to send a charging prohibition message to the charging apparatus, where the charging prohibition message is configured to indicate the charging apparatus to stop outputting direct current to processing module  830 . 
     Optionally, after the sending module  820  is configured to send the charging prohibition message to the charging apparatus, the processing module  830  is also configured to conduct a pre-charging. 
     Optionally, the processing module  830  is configured to acquire a voltage difference between its input end and output end; if the voltage difference is less than the third preset threshold, the processing module  830  conducts the pre-charging. 
     In the processing that the processing module  830  is configured to switch the charging mode from the pulse charging mode to the direct current charging mode. Optionally, the processing module  830  is configured to stop outputting a pulse current to the power battery. The receiving module  810  is also configured to receive second direct current charging information of the power battery, the sending module  820  is also configured to send the second direct current charging information to the charging apparatus; the processing module  830  is configured to output the direct current output by the charging apparatus according to the second direct current charging information to the power battery, to charge the power battery. 
     Optionally, before the processing module  830  is configured to stop outputting the pulse current to the power battery, the sending module  820  is also configured to send a charging prohibition message to the charging apparatus, the charging prohibition message is configured to indicate the charging apparatus to stop outputting the direct current to the power conversion apparatus. 
     Optionally, the processing module  830  is configured to acquire a voltage difference between its input end and output end; if the voltage difference is less than the fourth preset threshold, the processing module  830  is configured to output the direct current output by the charging apparatus according to the second direct current charging information to the power battery, to charge the power battery. 
     Optionally, the above state parameter of the power battery is a parameter acquired by the battery management system of the power battery. 
       FIG. 17  shows a schematic diagram of a power conversion apparatus  900  according to another embodiment of the present application. As shown in  FIG. 8 , the power conversion apparatus  900  includes a control unit  910  and a power unit  920 . Optionally, the control unit  910  may be the control unit  112  shown in  FIG. 2 , the power unit  920  may be the power unit  111  shown in  FIG. 2 , it may include the power conversion module, a first relay K 1 , a second relay K 2  and a third relay K 3  shown in  FIG. 2 . 
     Optionally, the power battery, the battery management system (BMS), and the charging apparatus in the following may correspond to the power battery  131 , the BMS  132 , and the charging apparatus  120  shown in  FIG. 2 . 
     Specifically, in the power conversion apparatus  900  provided by embodiments of the present application, the control unit  910  is configured to acquire the state parameter of the power battery, the state parameter includes the battery temperature of the power battery. The control unit  910  is configured to set the charging mode of the power unit  920  as the pulse charging mode when the battery temperature is lower than the first preset threshold. The power unit  920  is configured to convert charging power of the charging apparatus and then charge the power battery in the pulse charging mode, where the pulse charging mode is a charging mode using pulsed voltage or pulsed current. 
     Optionally, when the battery temperature is not lower than the first preset threshold, the control unit  910  is also configured to switch the charging mode of the power unit  920  from the pulse charging modes to the direct current charging mode. In the direct current charging mode, the power unit  920  is configured to transmit the charging power of the charging apparatus to the power battery to charge the power battery, where the direct current charging mode is a charging mode using a constant voltage or a constant current. 
     Optionally, the state parameter of the power battery acquired by the control unit  910  also includes the battery voltage, when the battery temperature is lower than the first preset threshold and the battery voltage is lower than the second preset threshold, the control unit  910  is configured to set the charging mode of the power unit  920  to the pulse charging mode. 
     Optionally, the state parameter of power battery acquired by the control unit  910  also includes the battery voltage, when the battery temperature is not lower than the first preset threshold or the battery voltage is not lower than the second preset threshold, the control unit  910  is configured to switch the charging mode of the power unit  920  from the pulse charging mode to the direct current charging mode. 
     In the process that the control unit  910  is configured to set the charging mode of the power unit  920  to the pulse charging mode, optionally, the state parameter also includes the battery state of charge; the control unit  910  is configured to determine the pulse charging information according to the battery temperature and the battery state of charge, and send the pulse charging information to the power unit  920 . The pulse charging information includes at least one of the following information: pulse current, pulse voltage, pulse direction, pulse frequency and pulse time. The power unit  920  is configured to determine first direct current charging information corresponding to the pulse charging information according to the pulse charging information, and send the first direct current charging information to the control unit  910 . The control unit  910  is configured to send the first direct current charging information to the charging apparatus, and control the power unit  920  to output pulse current to the power battery, where the pulse current is generated by converting a direct current based on the pulse charging information, and the direct current is a direct current output to the power unit  920  by the charging apparatus according to the first direct current charging information. 
     Optionally, before the control unit  910  is configured to set the charging mode of the power unit  920  to the pulse charging mode, the control unit  910  is also configured to send a charging prohibition message to the charging apparatus, where the charging prohibition message is configured to indicate the charging apparatus to stop outputting direct current to the power unit  920 . 
     Optionally, after the control unit  910  is configured to send the charging prohibition message to the charging apparatus, the control unit  910  is also configured to send a precharge instruction to the power unit  920 , and the power unit  920  is configured to conduct a pre-charging according to the precharge instruction. 
     Optionally, the power unit  920  is configured to acquire the voltage of its input end and the output end, and send the voltage of the input end and the output end to the control unit  910 . If the voltage difference between the input end and the output end is less than the third preset threshold, the control unit  910  is configured to send the precharge instruction to the power unit  920 . 
     In the process that the control unit  910  is configured to switch the charging mode of the power unit  920  from the pulse charging mode into the direct current charging mode, optionally, the control unit  910  is also configured to acquire second direct current charging information of the power battery. The second direct current charging information is a direct current charging information determined according to the state parameter of the power battery. 
     The control unit  910  is configured to control the power unit  920  to stop outputting the pulse current. The control unit  910  is configured to control the power unit  920  to output the direct current output by the charging apparatus according to the second direct current charging information to the power battery. 
     Optionally, before the control unit  910  is configured to control the power unit  920  to stop outputting the pulse current, the control unit  910  is also configured to send charging prohibition message to the charging apparatus, the charging prohibition message is configured to indicate the charging apparatus to stop outputting a direct current to the power unit  920 . 
     Optionally, the control unit  910  is configured to acquire a voltage difference between input end and output end of the power unit  920 ; if the voltage difference is less than the fourth preset threshold, the control unit  910  is configured to control the power unit  920  to output the direct current output by the charging apparatus according to the second direct current charging information to the power battery. 
     Optionally, the above state parameter of the power battery is a parameter acquired by battery management system of the power battery. 
       FIG. 18  shows a schematic diagram of an electronic device  1000  according to another embodiment of the present application. As shown in  FIG. 18 , the electronic device  1000  includes a memory  1010  and a processor  1020 , where the memory  1010  is configured to store a computer program, the processor  1020  is configured to read the computer program and execute the aforementioned method according to various embodiments of the present application based on the computer program. 
     Optionally, the electronic device  1000  may be used for any one or more of the apparatus, the BMS and the power conversion apparatus. In the embodiment of the present application, except that the processor in the power conversion apparatus reads the corresponding computer program and executes the charging method corresponding to the power conversion apparatus in the foregoing various embodiments based on the computer program, the processor in the charging apparatus or the BMS can also read the corresponding computer program and execute the charging method corresponding to the charging apparatus or the BMS in the foregoing various embodiments based on the computer program. 
     In addition, the present application embodiments also provide a readable storage media configured to store a computer program, the computer program is configured to execute the method of aforementioned various embodiments of the present application. Optionally, the computer program may be a computer program in one or more apparatuses of the above-mentioned power conversion apparatus, the charging apparatus and the BMS. 
     It should be understood that the specific examples herein are only intended to assist those skilled in the art to better understand the embodiments of the present application and are not intended to limit the scope of the embodiments of the present application. 
     It should also be understood that in various embodiments of the present application, the serial number of each process does not mean the sequence of execution, and the execution sequence of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application. 
     It should also be understood that the various embodiments described in this specification may be implemented individually or in combination, and the embodiments of this application are not limited thereto. 
     Although the present application has been described with reference to preferred embodiments various modifications may be made thereto and components therein may be replaced with equivalents without departing from the scope of the present application. In particular, the various technical features mentioned in the various embodiments may be combined in any manner so long as there is no structural conflict. The present application is not limited to the specific embodiments disclosed herein but includes all technical solutions falling within the scope of the claims.