Patent Publication Number: US-2017353139-A1

Title: Control method and system for converter of vehicle

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority to Korean Patent Application No. 10-2016-0070033 filed on Jun. 7, 2016, the entire content of which is incorporated herein for all purposes by this reference. 
     TECHNICAL FIELD 
     The present disclosure relates to a control method and system for a converter of a vehicle capable of controlling a converter as a power system constituting a vehicle in the light of an overall energy efficiency of a vehicle. 
     BACKGROUND 
     A hybrid vehicle efficiently combines with different two or more power source. In most cases, the hybrid vehicle is driven by an engine obtaining a rotational power by combusting a fuel (fossil fuel such as gasoline) and a motor obtaining a rotational power through a battery power. 
     The hybrid vehicle can travel with drive modes such as an electric (EV) mode as a pure electric vehicle mode using only the power of an electric motor, a hybrid electric vehicle (HEV) mode using a rotational power of an engine as primary power while using a rotational power of a drive motor as assist power, and a regenerative braking mode recovering a driving brake energy by braking or inertia of a vehicle and an inertial energy through generation of a drive motor and charging it to a battery. 
     As the hybrid vehicle uses with mechanical energy of an engine and electrical energy of a battery, uses Optimum operating region of the engine and drive motor and recovers energy to a drive motor when braking, it is able to improve fuel efficiency and efficiently use energy. 
     Typically, the hybrid vehicle typically using two or more power sources can configure a variety of power transmission structure through an engine and a drive motor as a power source. Most current hybrid vehicles have adopted one of the power train structures of parallel or serial type. 
     The serial type is the type that the engine and the motor is directly connected with each other, and has the merits of simple structure and simple control logic compared to the parallel type. However, the serial type is disadvantageous to the energy conversion since it stores the mechanical energy from the engine to the battery and then drives the hybrid vehicle using the motor again. 
     On the other hand, the parallel type has been widely adapted to a car, and so on, since it is possible the efficient use of energy because of simultaneously using the mechanical energy of the engine and the electric energy of the battery while it has demerits of relatively complex control logic compared to the serial type. Therefore, the study about the vehicle electric power conversion system capable of improving the energy efficiency of a hybrid vehicle by using the electrical energy of the battery properly in such the parallel type has been made actively. 
     The foregoing is intended merely to aid in the understanding of the background of the present disclosure, and is not intended to mean that the present disclosure falls within the purview of the related art that is already known to those skilled in the art. 
     SUMMARY 
     The present disclosure has been made keeping in mind the above problems occurring in the related art, and the present disclosure is intended to propose a control method and system for a converter of a vehicle capable of improving the energy efficiency of the overall vehicle power conversion system by deciding converter voltage command considering energy loss of a converter due to boosting as well as energy gain of a drive motor due to boosting of the converter in the vehicle power conversion system. 
     According to an exemplary embodiment of the present disclosure, a control method of a converter of a vehicle for achieving the above object may include: deriving, by controller, an energy gain of a drive motor and an energy loss of a converter when the converter is operating in a boosting mode; comparing, by the controller, the energy gain of the drive motor with the energy loss of the converter; and adjusting, by the controller, a voltage command of the converter depending on a comparison result in the controller. 
     The energy gain of the drive motor may be an energy gain of an inverter which is generated by boosting of the inverter connected between the drive motor and the converter as the converter is operated in the boosting mode. 
     The energy loss of the converter may be derived by the controller using a request output of the drive motor, a switching frequency of the converter, a battery voltage and a boosted output voltage of the converter. 
     The step of adjusting the voltage command of the converter may be that the controller adjusts the voltage command of the converter to the battery voltage when the energy gain of the drive motor is equal to or less than the energy loss of the converter. 
     The step of adjusting the voltage command of the converter may be that the controller operates the converter with the boosting mode and adjusts the voltage command of the converter to a final voltage command derived by using magnetic flux and a rotational speed of the drive motor and the battery voltage when the energy gain of the drive motor is greater than the energy loss of the converter. 
     According to another exemplary embodiment of the present disclosure, a converter system of a vehicle according to the present disclosure may include: a drive motor supplying a rotational power to a drive shaft of a vehicle; a chargeable and dischargeable battery; a converter connected between the drive motor and the battery and converting an output voltage of the battery into an operating voltage for operating the drive motor; and a controller deriving an energy gain of the drive motor and an energy loss of the converter when the converter is operating in a boosting mode, comparing the energy gain of the drive motor with the energy loss of the converter, and adjusting a voltage command of the converter depending on the comparison result. 
     The converter system of a vehicle may further include an inverter being connected between the converter and the drive motor and converting a DC voltage converted by the converter into an AC voltage to supply it to the drive motor. 
     The energy gain of the drive motor may be an energy gain of the inverter which is generated by boosting of the inverter as the converter is operated in the boosting mode. 
     The controller may derive the energy loss of the converter by using a request output of the drive motor, a switching frequency of the converter, a voltage of the battery and a boosted output voltage of the converter. 
     The controller may adjust the voltage command of the converter to the voltage of the battery when the energy gain of the drive motor is equal to or less than the energy loss of the converter. 
     The controller may operate the converter with the boosting mode and adjust the voltage command of the converter to a final voltage command derived by using magnetic flux and a rotational speed of the drive motor and the voltage of the battery when the energy gain of the drive motor is greater than the energy loss of the converter. 
     Utilizing the control method and system for a converter of a vehicle according to the present disclosure, it is able to reduce the loss of the overall vehicle power conversion system, thereby reducing the heating of the power conversion system, and improve a fuel efficiency of a vehicle by energy efficiency rising. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, features and advantages of the present disclosure will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a flow chart of a control method of a converter of a vehicle according to an exemplary embodiment of the present disclosure; and 
         FIG. 2  is a block diagram of a converter system of a vehicle according to an exemplary embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, a control method and system of a converter of a vehicle according to a preferred exemplary embodiment of the present disclosure will be described with reference to the accompanying drawings. 
     A power conversion system including a battery  20 , a converter  30 , an inverter  50  and a drive motor  10 , and so on, may be installed in an eco-friendly vehicle including a hybrid vehicle. The drive motor  10  is connected to a drive shaft to supply a rotational power to the drive shaft such that the vehicle can be moved. The power should be supplied to the drive motor  10  in order to supply a rotational power to the drive shaft  10 . The battery  20  is a device for supplying the power to the drive motor  10 . The converter  30  and the inverter  50  is the device for appropriately converting the power of the battery  20  into the power of the drive motor  10 . 
     Therefore, a controller  40  controls the power supplied to the drive motor  10  according to the request output of a vehicle by appropriately controlling the converter  30  and the inverter  50 . In the present disclosure, it is proposed, as the control method of controlling the converter  30 , the step S 10  of deriving an energy gain of the drive motor  10  and an energy loss of the converter  30  in the controller  40  in case that the converter  30  constituting a power conversion system of a vehicle is operating in a boosting mode as shown in  FIG. 1 . In an exemplary embodiment of the present disclosure, the controller  40  may be an electronic control unit (ECU). 
     The converter  30  used in a vehicle is able to be operated as the boosting mode, as needed, which pertains to the case of not supplying sufficient voltage to the drive motor  10  with only the voltage of the battery  10  because the request output of a vehicle is very large. However, the energy loss is increased in the converter  30  as the converter  30  is operated in the boosting mode, apart from that the voltage supplied to the drive motor  10  increases so that a rotational speed, and so on, of the drive motor  10  increases to raise the energy gain of the drive motor  10 . 
     Therefore, as it is not necessary to increase the energy gain of the drive motor  10  by increasing a supply voltage supplied to the drive motor  10  in case that it is able to satisfy the request output of a vehicle with the voltage of the present drive motor  10 , at this case, the boosting mode of the converter  30  may not be used in terms of the overall efficiency of the power conversion system. Therefore, the present disclosure performs the step S 10  of deriving the energy gain of the drive motor  10  and the energy loss of the converter  30  as a prerequisite step for comparing the energy gain of the drive motor  10  with the energy loss of the converter  30  generated as the converter  30  is operated in the boosting mode. 
     The energy gain of the drive motor  10  can be derived through various methods such as the method of using a rotational speed or torque of the drive motor  10 , and so on. However, the energy gain of the drive motor  10  in the sense of the present disclosure can be considered as the energy gain depending on the boosting of the converter  30  rather than the energy gain generated by the actual increasing of the rotational speed of the drive motor  10 . Therefore, the method of obtaining the energy gain of the drive motor  10  by the actual operation of the drive motor  10  may cause an inaccurate value by a friction force loss depending on the operation of the drive motor  10  or the loss in the process of being passed from the converter  30  to the drive motor  10 , and so on. 
     Therefore, in the present disclosure, the method for deriving the gain of the drive motor  10  exactly without loss generated by the boosting of the converter  30  uses the energy gain of the inverter  50  connected between the drive motor  10  and the converter  30 . The inverter  50  is a device for converting the boosted voltage of the converter  30  into AC voltage. If the voltage of the converter  30  is boosted, the voltage applied to the inverter  50  is boosted as much again, and thus, deriving the energy gain of the inverter  50  can be considered to be the same as the energy gain according to the boosting of the converter  30 . 
     That is, in the present disclosure, by comparing the energy gain of the inverter  50  before the converter  30  operates into the boosting mode with the energy gain of the inverter  50  after the converter  30  operates into the boosting mode and obtaining the difference value, the energy gain of the drive motor  10  described above can be derived. 
     On the other hand, the energy loss of the converter  30  can be derived by using a request output of the drive motor  10 , a switching frequency of the converter  30 , a voltage of the battery  20  and a boosted output voltage of the converter  30 . Concretely, the larger the difference between the request output of the drive motor  10 , the switching frequency of the converter  30 , the voltage of the battery  20  and the boosted output voltage of the converter  30  become, the larger the energy loss of the converter  30  will become. The energy loss of the converter  30  can be derived by using map data inputting the request output of the drive motor  10 , the switching frequency and the output voltage of the converter  30 . 
     In this way, if the energy gain of the drive motor  10  and the energy loss of the converter  30  are derived, the controller  40  may change a voltage command of the converter  30  according to whether the energy gain of the drive motor  10  is equal to or less than the energy loss of the converter  30  or not, through a step S 20  of comparing the energy gain with the energy loss as shown in  FIG. 1 . 
     Concretely, in case that the energy gain of the drive motor  10  is equal to or less than the energy loss of the converter  30 , the controller  40  performs a step S 30  of adjusting the voltage command of the converter  30  to the voltage of the battery  20 . As described above, in case that the energy gain of the drive motor  10  is equal to or less than the energy loss of the converter  30 , it is not necessary to boost the voltage of the battery  20  by using the converter  30 . Furthermore, even in case that the energy gain of the drive motor  10  is equal to the energy loss of the converter  30  in accordance with the conditions, the controller  40  adjusts the voltage command of the converter  30  to the voltage of the battery  20 . This is because the efficiency of the converter  30  lowers by resonant phenomenon as well as the temperature of the converter  30  rises as an inductor or a capacity in the converter  30  should operate in case of operating the converter  30  into the boosting mode. Therefore, even in case that it is determined that the energy gain of the drive motor  10  is equal to the energy loss of the converter  30 , the controller  40  adjusts the voltage command of the converter  30  to the voltage of the battery  20  without the need to operate the converter  30  into the boosting mode. 
     On the contrary to this, in case that the energy gain of the drive motor  10  is more than the energy loss of the converter  30 , the converter  30  may be operated into the boosting mode. Therefore, in this case, the controller  40  performs a step S 40  of operating the converter  30  into the boosting mode and a step S 50  of adjusting the voltage command of the converter  30  to a final voltage command derived by using the magnetic flux and a rotational speed of the drive motor  10  and the voltage of the battery  20 . 
     In this regard, the final voltage command means an output voltage which the converter  30  aims, and can be derived by a map data inputting the magnetic flux and a rotational speed of the drive motor  10  and the voltage of the battery  20  and outputting the final voltage command. Furthermore, the magnetic flux of the drive motor  10  can be derived by using driving conditions of a vehicle and the temperature of the drive motor  10 . Therefore, the final voltage command corresponds to the voltage command of the converter  30  in case that the converter  30  operates into the boosting mode such that it will have the value larger than the voltage of the battery  20  and will be appropriately decided through the controller  40  within the scope of satisfying the request output of a vehicle. 
     Furthermore, the converter system of a vehicle according to the present disclosure, as shown in  FIG. 2 , may include the drive motor  10  supplying a rotational power to a drive shaft of a vehicle; a chargeable and dischargeable battery  20 ; the converter  30  being connected between the drive motor  10  and the battery  20  and converting an output voltage of the battery  20  into an operating voltage for operating the drive motor  10 ; the controller  40  deriving an energy gain of the drive motor  10  and an energy loss of the converter  30  in the case that the converter  30  is operating into the boosting mode, comparing the energy gain of the drive motor  10  with the energy loss of the converter  30 , and adjusting a voltage command of the converter  30  depending on the comparison result; and the inverter  50  being connected between the converter  30  and the drive motor  10  and converting a DC voltage converted by the converter  30  into an AC voltage to supply it to the drive motor  10 . 
     Although the exemplary embodiments of the present disclosure have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.