Abstract:
A power maintaining method of electric vehicle includes the following step. In step  01,  an energy power is provided by a main battery pack to drive a first electric vehicle (EV) moving to a first power supply station. In step  02,  a first swap battery pack is installed on the first EV at the first power supply station, and the first swap battery pack is electrically connected to the main battery pack of the first EV so that the main battery pack is charged by the first swap battery pack. In step  03,  the first EV is driven to a second power supply station from the first power supply station. In step  04,  the first swap battery pack is uninstalled from the first EV at the second power supply station. In addition, an electric vehicle and a power supply station is disclosed in the present application.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The disclosure relates to an electric vehicle, a power supply station, and a power maintaining method for providing power to the electric vehicle. 
         [0003]    2. Description of Related Art 
         [0004]    With gradual rising of environmental protection and energy saving awareness, in the technology field of transport vehicles, the reduction of energy consumption and pollution exhaust emission has always been one of the objectives of endeavor for each vehicle factory; therefore, relevant studies on Hybrid Electric Vehicle (HEV) and Electric Vehicle (EV) with energy saving and carbon reduction efficiency have never stopped. According to the survey of Japan Automobile Research Institute, JARI,FC.EV Center, the energy consumption in the driving of general gasoline engine vehicle is 3 times of electric vehicle, besides, the carbon emission in gasoline engine vehicle (vehicle driving for every kilometer) is 4 times of the electric vehicle (conversion of electrical energy). Therefore, each automobile manufacturer such as Nissan, BMW, Tesla etc. has been producing electric vehicles successively and sell them in the market, despite they have not been popularized, they have been attracting attention from the market gradually. 
         [0005]    In the aspect of technology, the biggest challenges faced by electric vehicle are to improve the battery&#39;s energy storage capacity and shorten the battery&#39;s charging time. In order to facilitate the energy needed by electric vehicle motor, the battery itself must possess the capability to be able to provide the output of large current for a long time, and able to provide instant output of high current. Therefore, the batter capacity must be of a certain level, however, how to charge the electric energy of the battery with such large capacity to be full quickly is the great challenge faced by electric vehicle. 
         [0006]    When the battery power is running out, electric vehicle must stop at the place with charging unit (such as at home or charging station) to charge the battery. However, take the electric vehicle currently on sale in the market and that can travel about 150 km when the battery is in full electric energy as the example, currently it takes at least 1.5 hours to charge its battery to be full, even charging the battery up to 80% through quick charge technology still takes about 30 minutes. Also due to the inconvenience in supplementing electric energy, hence certain efforts still need to be made in the aspect of battery for the popularization of electric vehicle. 
         [0007]    Therefore, how to prolong the service time of battery used in electric vehicle to maintain the power source of electric vehicle and how to achieve the convenience of use with easy charging are indeed one of the important issues currently, which are also the objectives of the industry to be achieved with efforts. 
       SUMMARY OF THE INVENTION 
       [0008]    In view of the foregoing, the invention is to provide an electric vehicle, a power supply station and a power maintaining method, which can easily maintain the power source of the electric vehicle. 
         [0009]    To achieve the above purpose, a power maintaining method of an electric vehicle includes the following steps. Step  01  is providing an energy power by a main battery pack to drive a first electric vehicle moving to a first power supply station. Step  02  is installing a first swap battery pack with appearance different from the main battery pack to the first electric vehicle at the first power supply station, and making electrical connection between the first swap battery pack and the main battery pack of the first electric vehicle so as to charge the main battery pack by the first swap battery pack. Step  03  is electrically connecting a first DC charging device to the main battery pack to charge the main battery pack at the same time when installing the first swap battery pack. 
         [0010]    In one embodiment of the invention, the power maintaining method further includes the following steps. Step  04  is driving the first electric vehicle moving to a second power supply station. Step  05  is uninstalling the first swap battery pack from the swap battery holding space of the first electric vehicle at the second power supply station. Step  06  is installing a second swap battery pack to the swap battery holding space of the first electric vehicle. Step  07  is electrically connecting a second DC charging device to the main battery pack to charge the main battery pack at the same time when uninstalling the first swap battery pack. 
         [0011]    In one embodiment of the invention, the power maintaining method further includes the following step after step  505 . Step  08  is electrically connecting a second DC charging device to the main battery pack to charge the main battery pack at the same time when uninstalling the first swap battery pack. 
         [0012]    In one embodiment of the invention, the power maintaining method further includes the following steps. Step  09  is charging the first swap battery uninstalled from the first electric vehicle at the second power supply station. Step  10  is installing the first swap battery already charged to a second electric vehicle, wherein the appearance of the first swap battery is different from the appearance of the main battery pack of the second electric vehicle. 
         [0013]    In one embodiment of the invention, wherein the first swap battery pack has a power conversion unit, and the first swap battery charges the main battery pack of the first electric vehicle through the power conversion unit. 
         [0014]    In one embodiment of the invention, wherein the electric current of the first DC charging device for charging the main battery pack is 3 times greater than the nominal capacity of the main battery pack. 
         [0015]    In one embodiment of the invention, wherein the first swap battery pack and the second swap battery pack have the same appearance and the different capacity. 
         [0016]    In one embodiment of the invention, wherein the first swap battery pack has a DC power conversion unit and a plurality of batteries, which are electrically connected to each other, a DC charging device of the second power supply station is electrically connected to the DC power conversion unit to charge the batteries through the DC power conversion unit. 
         [0017]    In one embodiment of the invention, wherein the first swap battery pack has a DC power conversion unit and a plurality of batteries, which are electrically connected to each other, a DC charging device of the second power supply station is electrically connected to the batteries to directly charge the batteries. 
         [0018]    Besides, to achieve the above purpose, the invention is to provide an electric vehicle, which has a main electrical connector, a main battery pack, a direct-current (DC) recharge socket, a swap battery pack holding space, and a first swap battery pack. The main battery pack is electrically connected to the main electrical connector. The DC recharge socket is electrically connected to the main battery pack, and transmits a first DC power to the main battery pack after receiving it. A first electrical connector is disposed in the swap battery pack holding space. The first electrical connector is used for electrical connection to the main electrical connector. The first swap battery pack is placed at the swap battery pack holding space, and electrically connected to the first electrical connector. The first swap battery pack provides a second DC power to the main battery pack through the first electrical connector. 
         [0019]    In one embodiment of the invention, wherein the first swap battery pack includes a first housing, a plurality of batteries, a power conversion unit, a first electrical connecting unit. The batteries are contained in the first housing and electrically connected to each other. The power conversion unit is electrically connected to the batteries. The first electrical connecting unit includes a first body and a first terminal. The first body is connected to the first housing. The first terminal is electrically connected to the power conversion unit and partially covered by the first housing. At least two of the first housing, the first body and the first terminal can be relatively moved. 
         [0020]    In one embodiment of the invention, wherein the first swap battery pack includes a second electrical connecting unit, which is electrically connected to the first housing and a second swap battery pack. 
         [0021]    Furthermore, to achieve the above purpose, the invention is to provide a power supply station used for electric vehicle. The power supply station is used for providing an electric vehicle to carry out power maintenance operation. The power supply station at least includes a first swap battery pack, a swap battery pack installing and uninstalling device, a DC/AC power conversion device, an AC/DC power conversion device and a DC charging device. The swap battery pack installing and uninstalling device is used for installing the first swap battery pack to an electric vehicle, or uninstalling it from the electric vehicle. The AC/DC power conversion device is electrically connected to the first swap battery pack, and output a first DC power according to a first AC power, so as to provide charging to the first swap battery pack. The DC/AC power conversion device is electrically connected to the first swap battery pack and an electric power grid respectively, and converts a second DC power output from the first swap battery pack into a second AC power to output to such electric power grid. The DC charging device outputs a third DC power to provide charging to a main battery pack of the electric vehicle. 
         [0022]    In one embodiment of the invention, wherein the DC charging device is electrically connected to the AC/DC power conversion device, and outputs the third DC power according to the first DC power. 
         [0023]    In one embodiment of the invention, the power supply station further includes a DC/DC power conversion device, which s electrically connected to a second swap battery pack and the DC charging device, and outputs the third DC power according to a fourth DC power output from the second swap battery pack. 
         [0024]    As mentioned above, an electric vehicle, a power supply station and a power maintaining method of the electric vehicle according to the invention are to set a holding space at the electric vehicle to hold the swap battery pack, and the swap battery pack charges the main battery pack to ensure that the capacity of main battery pack is within a safety scope, so as to prolong its service time. Electric vehicle can travel to the power supply station to replace the swap battery pack, at the same time of replacement, the power supply station can carry out basic charging to the main battery pack. Through this, electric vehicle is able to efficiently prolong the power service time, and is easy to maintain its power source. 
         [0025]    The detailed technology and preferred embodiments implemented for the subject invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The parts in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of at least one embodiment. In the drawings, like reference numerals designate corresponding parts throughout the various diagrams, and all the diagrams are schematic. 
           [0027]      FIG. 1  is schematic diagram showing a part of an electric vehicle according to an embodiment of the invention. 
           [0028]      FIG. 2  is a schematic diagram showing a power system of an electric vehicle according to the embodiment of the invention. 
           [0029]      FIG. 3  is a schematic diagram showing a first swap battery pack according to the embodiment of the invention. 
           [0030]      FIG. 4  is a schematic diagram showing a first electrical connection unit and a first electrical connector according to the embodiment of the invention. 
           [0031]      FIG. 5  is a schematic diagram showing an appearance of the first swap battery pack according to another embodiment of the invention. 
           [0032]      FIG. 6  is a structure schematic diagram showing a power supply station according to an embodiment of the invention. 
           [0033]      FIG. 6A  is the structure schematic diagram showing of a part of the power supply station according to the another embodiment of the invention. 
           [0034]      FIG. 7  is a flow chart showing a power maintaining method of an electric vehicle according to an embodiment of the invention. 
           [0035]      FIG. 8  is a flow chart showing another power maintaining method of an electric vehicle according to the embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0036]    The parts in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of at least one embodiment. In the drawings, like reference numerals designate corresponding parts throughout the various diagrams, and all the diagrams are schematic. 
         [0037]    In order to make the charging of electric vehicle more convenient, the invention provides an electric vehicle capable of replacing the swap battery pack, among them, the electric vehicle may include the electric scooter and the electric automobile, here we take the electric automobile as the example for description. Please refer to  FIG. 1 , an electric vehicle according to the embodiment of the invention includes a main electrical connector  10 , a main battery pack  11 , a DC recharge socket  12 , a swap battery pack holding space  13  and a first swap battery pack  14 . 
         [0038]    Please also refer to  FIG. 2  and  FIG. 3  at the same time, the main battery pack  11  at least includes a main housing  111  and a plurality of main batteries  113 , which are electrical connected to each other. The main batteries  113  are placed and fixed in the main housing  111 . In the embodiment, the main battery pack  11  is disposed in the underbody space among the four wheels of the electric vehicle  1 , and is solidly combined with the body structure of the electric vehicle  1  (not shown in the figure). However, the collocating position of main battery pack  11  can be changed according to the design of each vehicle type. 
         [0039]    The main electrical connector  10  is electrically connected to the main battery pack  11 , so as to provide the power generated from the main battery  113  of the main battery pack  11  to each electrical unit needed of the electric vehicle  1 , and further drive it. The DC recharge socket  12  is also electrically connected to the main battery pack  11 . The DC recharge socket  12  receives a first DC power DC 01  transmitted from external, and transmits the first DC power DC 01  to the main battery  113  to charge it. In other words, the main electrical connector  10  includes receiving circuit and output circuit. 
         [0040]    The appearance of the first swap battery pack  14  is different from the appearance of the main battery pack  11 , and it is disposed in the swap battery pack holding space  13 . It is to be noted, the so-called different appearance is meaning that the first swap battery and the second swap battery cannot be placed into the same swap battery holding space, or meaning the connecting terminal of the first swap battery is incompatible with the connecting terminal of the second swap battery, wherein the connecting terminal is used for communicating to external device. In other words, the connecting terminal of the first swap battery and the connecting terminal of the second swap battery have the pins with the different amount or the different configuration. 
         [0041]    The swap battery pack holding space  13  may be located at any open space in the body of the electric vehicle  1 , or at the semi-closed space or closed space (not shown in the figure) of a swap battery cabin exclusively designed for it. The first swap battery pack  14  is electrically connected to a first electrical connector  15 , and the first electrical connector  15  is electrically connected to the main electrical connector  10 , with such configuration, a second DC power DC 02  output from the first swap battery pack is transmitted to the main battery pack  11  through the first electrical connector  15  and the main electrical connector  10 , and charge the main battery  113  of the main battery pack  11 . It is to be noted, the first swap battery pack charges the main battery pack in anytime such as when the electric vehicle is traveling, stopping or even without startup. Furthermore, the design of the first swap battery pack  14  quantity can be changed according to actual demand, in the embodiment, it takes the electric vehicle  1  can be equipped with two first swap battery pack  14  as the example for description, in other words, the electric vehicle  1  has two swap battery pack holding spaces. 
         [0042]    The first swap battery pack  14  has a first housing  141 , a plurality of batteries  142 , a power conversion unit  143  and a first electrical connection unit  144 . The batteries  142  and the power conversion unit  143  are electrically connected mutually and placed in the first housing  141 . The first electrical connection unit  144  is connected to the first housing  141  and goes through the first housing  141  to electrically connect to the power conversion unit  143 . Please refer to  FIG. 4 , the first electrical connection unit  144  has a first body  1441  and a first terminal  1442 . The first body  1441  is connected to the first housing  141 , and to cover at least part of the first terminal  1442 . Specifically speaking, an end of the first terminal  1442  is electrically connected to the power conversion unit  143  by passing the first body  1441  goes through the first housing  141 . The other end of the first terminal  1442  is exposed at the first housing  141  and the first body  1441 , so as to be electrically connected to the first electrical connector  15 . 
         [0043]    As shown in  FIG. 1 , in the embodiment, the electric vehicle  1  also includes a driving module  16 , which is electrically connected to the main battery pack  11 . The driving module  16  receives the power provided by the main battery pack  11  to drive the electric vehicle  1 . The driving module  16  at least includes a DC/AC power conversion unit (Inverter)  161  and an AC motor  162 . The DC/AC power conversion unit  161  receives the power provided by the main battery pack  11 , and converts it into an AC driving power AC 01  to provide to the AC motor  162 . The AC motor is driven by the AC driving power AC 01 , which driving the wheels to make the electric vehicle  1  travel. 
         [0044]    It is to be noted, the first swap battery pack  14  has certain weight (approximately from 50 kg to 150 kg), during the first swap battery pack  14  is placed into the swap battery pack holding space  13  and it intends to be electrically connected to the first electrical connection unit  144  and the first electrical connector  15 , it needs assistance from certain mechanisms to be mutually connected in a safer and more convenient way. 
         [0045]    Please refer to  FIG. 4 , the connection mode between the first body  1441  of the first electrical connection unit  144  and the first housing  141  is of floating type, in other words, the first body  1441  and the first terminal  1442  can slightly move from up and down and left and right relative to the first housing  141 . Besides, the first electrical connection unit  144  also has two lead terminals  1443 , which are disposed at two sides of the first body  1441  respectively. The front end of the lead terminal  1443  is of conform or globular shape, and the first electrical connector  15  also has a hole  151  relative to the lead terminal  1443 . When the first swap battery pack  14  is placed into the swap battery pack holding space  13 , the first electrical connection unit  144  is moved towards the first electrical connector  15 , after the lead terminal  1443  has entered into the hole  151  through such movement, the first body  1441  and the first terminal  1442  are combined with the first electrical connector  15 . Besides, what also needs to be described is that, when the first swap battery pack  14  is slightly deviated in the swap battery pack holding space  13 , its position can be adjusted through the lead terminal  1443  and the floating structure. 
         [0046]    Furthermore, in order to further ensure the position of the first swap battery pack  14 , the track (not shown in the figure) may also be disposed in the swap battery pack holding space, so that the first swap battery pack can move along the track and cannot be deviated easily. Besides, the swap battery pack holding space  13  may have a fixed structure (not shown in the figure) to make the first swap battery pack be solidly placed in the swap battery pack holding space  13 , such as the lockup type or clamping type. 
         [0047]    In the embodiment, it takes the electric vehicle  1  with two swap battery pack holding spaces  13  respectively accommodated in the first swap battery pack  14  as the example, the first swap battery pack  14  is placed along with the tracks at two sides of vehicle body and then fixed with the clamping mechanism. However, in other embodiments, the swap battery pack may be set in other spaces according to the different designs of vehicle body. 
         [0048]    Besides, please refer to  FIG. 5 , the first swap battery pack  14  may also have a second electrical connection unit  145 . The second electrical connection unit  145  can be set at the other side relative to the first housing  141  and the first electrical connection unit  144 . The second electrical connection unit  145  has the same structure as the first electrical connector  15 , it can be used for connecting to a first electrical connection unit of a second swap battery pack, so as to make the first swap battery pack  14  and the second swap battery pack to form an electrical series structure. 
         [0049]    It is to be noted, under general condition, the capacity of main battery pack is greater than the capacity of swap battery pack (the maximum power capacity of battery charge and discharge), so that the main battery pack is able to handle the demand of providing instant high power, such as climbing acceleration or jack-rabbit start that needs greater torsion. Also for this reason, the preceding electric vehicle  1  is mainly provided of power by the main battery pack  11 , and the first swap battery pack  14  will cooperate with the main battery pack  11  to provide power to drive electric vehicle  1  to travel when the electric vehicle  1  is overloaded. When the installing of electric vehicle  1  is small, the first swap battery pack  14  will charge the main battery pack  11  to maintain the power of main battery pack  11 . However, when the first swap battery pack  14  is also running out of power, it must be replaced, at this moment, the electric vehicle  1  may travel to the nearby power supply station to replace the swap battery pack. 
         [0050]    Then, please refer to the above statements and  FIG. 6 , it is a structure schematic diagram of power supply station  2  according to the embodiment of the invention. The power supply station  2  can be provided to the electric vehicle  1  mentioned above to carry out power maintenance operation. The so-called power maintenance operation means maintaining the power of the main battery pack  11 , hence it can directly charge the main battery pack  11  through the DC recharge socket  12 , and replace the swap battery pack running out of power with the one full of power, and then charge the main battery pack  11 . 
         [0051]    The power supply station  2  stores a plurality of swap battery packs, and at least includes a swap battery pack installing and uninstalling device  21 , an AC/DC power conversion device  22 , a DC/AC power conversion device  23  and a DC charging device  24 . 
         [0052]    The swap battery pack installing and uninstalling device  21  is used for uninstalling the first swap battery pack  14  from the electric vehicle  1 , and then among such swap battery packs stored, installing a second swap battery pack to the electric vehicle  1  through the swap battery pack installing and uninstalling device  21 . In the embodiment, the swap battery pack installing and uninstalling device  21  includes a clamping bearing mechanism  211  and a mobile mechanism  212 . The calming bearing mechanism  211  can fix the swap battery pack, and extract it from the electric vehicle  1  or install it to the electric vehicle  1 . The mobile mechanism  212  can drive the swap battery pack installing and uninstalling device  21  to move between the storage location of the swap battery pack and the electric vehicle  1 . Besides, since the weight of the swap battery pack is approximately between 50 kg to 150 kg, comparing with the weight of main battery pack mostly between 250 kg to 600 kg, upon replacement operation, it can input part manpower to supersede the full automatic replacement equipment, in this way it can also reduce the cost expenditure of full automatic equipment. 
         [0053]    The AC/DC power conversion device  22  outputs a first DC power DC 11  according to a first AC power AC 11  to provide to the first swap battery pack  14  running out of power to carry out the charging procedure. The first AC power AC 11  is the commercial power obtained from the electric power grid  25 . 
         [0054]    Many swap battery packs will be stored in the power supply station  2 , and during the peak time of power consumption, the power supply station  2  can be utilized according to the swap battery pack already charged. In the embodiment, after the first swap battery pack  14  is charged, it can be electrically connected to the DC/AC power conversion device  23 , and the DC/AC power conversion device  23  is further electrically connected to the electric power grid  25 . The DC/AC power conversion device  23  converts a second DC power DC 12  output from the first swap battery pack into a second AC power AC 12  to output to the electric power grid  25 . In other words, the power supply station  2  can feed back the power generated from the DC/AC power conversion device  23  to the electric power grid, which is equivalent to selling the power to electric power company. Besides, the swap battery pack already declined can be used for generating the second AC power AC 12  to output to the electric power grid. In respect of decline, if the swap battery pack fully charged only reaches to below 80% of the rated capacity, it is no longer suitable for installing to the electric vehicle, but it can be reutilized. 
         [0055]    The DC charging device  24  is used for electrical connection for the DC recharge socket  12  of the electric vehicle  1 , and outputs a third DC power DC 13  to provide to the main battery pack  11  of the electric vehicle  1  for quick charging. The DC charging device  24  is conforming to including but not limited to at least one of the specifications of CHAdeMO, GB/T 20234, SAE J1772 Combo and IEC 62196 Combo. 
         [0056]    In the embodiment, the power source of the DC charging device  24  can be the first DC power DC 11  output from the AC/DC power conversion device  22 . In other embodiments, as shown in  FIG. 6A , the power source of the DC charging device  24  can be a DC/DC power conversion device  26 . The DC/DC power conversion device  26  can be electrically connected to the first swap battery pack  14  already charged and the DC charging device  24  respectively, and convert the second DC power DC 12  output from the first swap battery pack into the first DC power DC 11  needed by the DC charging device  24 . Finally, the DC charging device  24  will generate the third DC power DC 13  according to the first DC power DC 11  and output it to the electric vehicle  1 . 
         [0057]    Then, as shown in  FIG. 7 , it describes, from the perspective of electric vehicle, the power maintaining method of an electric vehicle according to the embodiment of the invention. As shown in  FIG. 7 , the power maintaining method of the electric vehicle includes the following steps. 
         [0058]    Step S 11 : a main battery pack provides the energy to drive a first electric vehicle to a first power supply station. The energy provided by the main battery pack drives the electric vehicle through a voltage output bus bar. 
         [0059]    Step S 12 : at the first power supply station, install a first swap battery pack to a swap battery holding space of the first electric vehicle, and make electrical connection between the first swap battery pack and the main battery pack, so as to charge the main battery pack of the first electric vehicle. 
         [0060]    Step S 13 : at the same time when installing the first swap battery pack, at the first power supply station, electrically connect a DC charging device to the main battery pack to charge the main battery pack. The charging of main battery pack by the DC charging device is conforming to including but not limited to at least one of the specifications of CHAdeMO, GB/T 20234, SAE J1772 Combo and IEC 62196 Combo. The electric current of the DC charging device for charging the main battery pack is 3 times greater than the nominal capacity of main battery pack. 
         [0061]    Step S 14 : after the first swap battery pack has been installed to the first electric vehicle, the main battery pack provides the power to drive the first electric vehicle to a second power supply station. 
         [0062]    Step S 15 : at the second power supply station, uninstall the first swap battery pack from the first electric vehicle. 
         [0063]    Step S 16 : at the second power supply station, install a second swap battery pack to the first electric vehicle, and make electrical connection between the second swap battery pack and the main battery pack, so as to charge the main battery pack of the first electric vehicle. The first swap battery pack and the second swap battery pack have the same appearance, but the capacity can be different. It is to be noted, the so-called same appearance is meaning that the first swap battery and the second swap battery can be placed into the same swap battery holding space, or meaning the connecting terminal of the first swap battery is compatible with the connecting terminal of the second swap battery, wherein the connecting terminal is used for communicating to external device. In other words, the connecting terminal of the first swap battery and the connecting terminal of the second swap battery have the pins with the same amount or the same configuration. 
         [0064]    Step S 17 : at the same time when uninstalling the first swap battery pack and installing the second swap battery pack, at the second power supply station, electrically connect a DC charging device to the main battery pack to charge the main battery pack. The same as the statement above, the charging of main battery pack by DC charging device is conforming to including but not limited to at least one of the specifications of CHAdeMO, GB/T 20234, SAE J1772 Combo and IEC 62196 Combo. The electric current of the DC charging device for charging the main battery pack is 3 times greater than the nominal capacity of the main battery pack. 
         [0065]    Step S 18 : after the second swap battery pack has been installed, the main battery pack provides the energy to drive the first electric vehicle away from the second power supply station. In the embodiment, the first power supply station and the second power supply station can be the same power supply station or different power supply stations, it is not limited in the embodiment. 
         [0066]    As mentioned above, the electric vehicle is mainly provided of energy from main battery pack to drive the electric vehicle, the swap battery pack mainly charges the main battery pack, when the power of the main battery pack and the swap battery pack is consumed to a certain low level, the electric vehicle can go to the nearby power supply station to replace the swap battery pack, so as to maintain the power level of the main battery pack. Besides, when replacing the swap battery pack of the electric vehicle, the power supply station can utilize the DC charging device to charge the main battery pack at the same time. Through this, it can avoid circumstance that the main battery pack is still at low power status and cannot provide instant high power when the electric vehicle needs instant high power after replacing the swap battery pack. 
         [0067]    Please refer to  FIG. 8  for the following contents, it will continue the steps mentioned above to further describe the power maintaining method of the electric vehicle from the perspective of power supply station. As shown in  FIG. 8 , the power maintaining method also includes the following steps. 
         [0068]    Step S 19 : at the second power supply station, charge the first swap battery pack uninstalled from the first electric vehicle. In the embodiment, the first swap battery pack has a DC power conversion unit (Converter) and a plurality of batteries, which are electrically connected to each other. A DC charging device of the second power supply station is electrically connected to the DC conversion unit, and charges such battery through DC power conversion unit. In another embodiment, the DC charging device of the second power supply station is electrically connected to such battery directly, and charges such battery directly. In other words, for the charging operation of charging unit to the swap battery pack, apart from charging such battery through DC power conversion unit, it can also charge such battery directly without going through DC power conversion unit. 
         [0069]    Step S 20 : at the second power supply station, install the charged first swap battery pack to a second electric vehicle. And make electrical connection between the first swap battery pack and the main battery pack of the second electric vehicle, so as to charge the main battery pack of the second electric vehicle. 
         [0070]    In summary, as far as electric vehicle is concerned, the electric vehicle can accept the swap battery pack of different capacity to charge its main battery pack, and after charging the used swap battery pack, it can also be provided to different electric vehicles, which may have the different main battery pack for use. The so-called different main battery pack is meaning that at least one of the appearance, capacity and rated power of the main battery pack is different. The charging of main battery pack through the swap battery pack will be able to prolong the traveling distance and service time of the electric vehicle. And as far as power supply station is concerned, the power supply station can provide the electric vehicle an operation space for replacing the swap battery pack, and at the same time of replacing the swap battery pack, the power supply station can utilize the DC charging device to carry out basic charging to the main battery pack, so that the main battery pack is able to maintain a certain degree of energy, so as to prolong the life of the main battery pack. Besides, apart from providing power to the electric vehicle, the power supply station can also carry out power exchange through the stored swap battery pack, so as to convert DC power to AC power, and transmit it to electric power grid to sell it to the electric power company. 
         [0071]    Even though numerous characteristics and advantages of certain inventive embodiments have been set out in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only. Changes may be made in detail, especially in matters of arrangement of parts, within the principles of the present disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.