Abstract:
A system for controlling a motor of a hybrid vehicle that secures robustness and stability of control by selecting an optimal approximation model according to a driving condition of the motor and determines current order for controlling the motor by using the selected optimal approximation model is disclosed. In particular, a current order generator utilizes a reference current determination module to determine reference currents of the first and second axes, a compensation value determination module to determine compensation values of the reference currents of the first and second axes, and a current determination module to determine the currents of the first and second axes from the reference currents of the first and second axes and the compensation values of the reference currents of the first and second axes in order to control the motor more efficiently.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to and the benefit of Korean Patent Application No. 10-2010-0123712 filed in the Korean Intellectual Property Office on Dec. 6, 2010, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     (a) Field of the Invention 
     The present invention relates to a system for controlling a motor of a hybrid vehicle. More particularly, the present invention relates to a system for controlling a motor of a hybrid vehicle that can secure robustness and stability of control by selecting an optimal approximation model according to a driving condition of the motor and determining current order for controlling the motor by using the selected optimal approximation model. 
     (b) Description of the Related Art 
     Recently, environmentally-friendly vehicles such as hybrid vehicles and electric vehicles have attracted increasing attention due to energy depletion and environmental pollution. These environmentally-friendly vehicles typically include a motor generating driving torque by using electrical current from a battery. According to a conventional method for controlling the motor, a demand torque according to the current driving conditions of the vehicle is calculated and an operating current for generating and producing the demand torque is calculated so that the operating current can be applied to the motor. 
     However, operation of the motor is greatly affected by the motor temperature and an inverter voltage (i.e., input voltage). Therefore, the operating current is generally corrected according to the motor temperature and the inverter voltage. That is, the operating current is primarily corrected by the motor temperature and is secondarily corrected by the inverter voltage. 
     According to a conventional method that corrects the operating current according to the motor temperature, a map according to the driving condition of the vehicle is set at every reference temperature of the motor, and a compensation value of the operating current is calculated by substituting the driving condition of the vehicle into the map that corresponds to a respective reference temperature. If the motor temperature is not a predetermined reference temperature, the first and second reference temperatures closest to the motor temperature are selected, compensation values of the first and second operating currents are calculated from the maps according to the first and second reference temperatures, and the compensation value of the operating current is calculated from the compensation values of the first and second operating currents by interpolation. 
     Since one map is required at each reference temperature according to a conventional method that primarily corrects the operating current using the motor temperature, a plurality of maps are created so as to secure control reliability. Therefore, since a great many experiments are performed and a significant amount of time is required to create these maps, development costs are higher than most manufactures would like. 
     Even further, according to a conventional method that secondarily corrects the operating current by the inverter voltage, a motor speed is normalized according to the inverter input voltage and the compensation value of the current is calculated according to the normalized motor speed. Since voltage usage efficiency of the motor, however, is changed according to a load condition of the vehicle, control reliability may be deteriorated. In order to secure control reliability, weight value according to the load condition of the vehicle should be calculated as well. 
     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in an effort to provide a system for controlling a motor of a hybrid vehicle having advantages of reducing development cost and securing reliability and stability of control by selecting one optimal approximation model according to a driving condition of a motor and determining a current order for controlling the motor by using the selected optimal approximation model. 
     A system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention may include: a current order generator determining currents of a first and second axes according to a driving condition; a current controller generating voltages of the first and second axes by using the currents of the first and second axes determined by the current order generator and feedback currents of the first and second axes; a coordinate transformer converting the voltages of the first and second axes into 3-phase voltage, and converting 3-phase feedback current into the feedback currents of the first and second axes and transmitting the feedback currents of the first and second axes to the current controller; a signal generator receiving the 3-phase voltage from the coordinate transformer and generating 3-phase signal corresponding thereto; a pulse-width modulation (PWM) inverter generating 3-phase current based on the 3-phase signal, and transmitting the 3-phase current to the coordinate transformer as the 3-phase feedback current; a motor driven by receiving the 3-phase current from the PWM inverter; and a resolver detecting a phase of the motor and transmitting detected the phase of the motor to the current order generator and the coordinate transformer. More specifically, the current order generator has a reference current determination module that is configured to determine reference currents of the first and second axes, a compensation value determination module that is configured to determine compensation values of the reference currents of the first and second axes, and a current determination module that is configured to determine the currents of the first and second axes from the reference currents of the first and second axes and the compensation values of the reference currents of the first and second axes. 
     In some embodiments of the present invention, the reference current determination module may determine the reference currents of the first and second axes from a demand torque at a current driving condition and a current speed of the motor. The compensation value determination module may determine the compensation values of the reference currents of the first and second axes from the demand torque associated with the current driving condition, the current speed of the motor, an input voltage, and a current temperature of the motor. The compensation value determination module may also determine the compensation values of the reference currents of the first and second axes based on an optimal approximation model. The optimal approximation model may be selected by design of experiment. 
     A system for controlling a motor of a hybrid vehicle according to another exemplary embodiment of the present invention may determine a current of a first axis and a current of a second axis according to a driving condition, may convert the currents of the first and second axes into a 3-phase AC current, and may drive the motor by applying the 3-phase AC current to the motor. The system may include: a reference current determination module that is configured to determine the reference currents of the first and second axes from a demand torque at a current driving condition and a current speed of the motor; a compensation value determination module that is configured to determine compensation values of the reference currents of the first and second axes based on an optimal approximation model; and a current determination module that is configured to determine the currents of the first and second axes from the reference currents of the first and second axes and the compensation values of the reference currents of the first and second axes. 
     The compensation value determination module may determine the compensation values of the reference currents of the first and second axes by substituting the demand torque at the current driving condition, the current speed of the motor, an input voltage, and a current temperature of the motor into the optimal approximation model. Again, the optimal approximation model may be selected by design of experiment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic diagram of a motor system in a hybrid vehicle according to an exemplary embodiment of the present invention. 
         FIG. 2  is a schematic diagram of a system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention. 
         FIG. 3  is a schematic diagram of a current order generator in a system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention. 
         FIG. 4  is a flowchart illustrating processes for selecting an optimal approximation model according to an exemplary embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     It is understood that the term “vehicle” or “vehicular” or other similar term as used herein is inclusive of motor vehicles in general such as passenger automobiles including sports utility vehicles (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft, and the like, and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles and other alternative fuel vehicles (e.g., fuels derived from resources other than petroleum). As referred to herein, a hybrid vehicle is a vehicle that has two or more sources of power, for example both gasoline-powered and electric-powered vehicles. 
     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings. 
       FIG. 1  is a schematic diagram of a motor system in a hybrid vehicle according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 1 , a motor system of a hybrid vehicle according to an exemplary embodiment of the present invention includes an inverter module and a motor  50 . 
     The inverter module receives a DC voltage V dc  of a battery, determines a current according to a driving condition of a vehicle, and applies the determined current to the motor  50 . For these purposes, the inverter module includes a capacitor  10 , a power module  20 , a CPU  40 , and an RDC circuit  70 . 
     The capacitor  10  is connected to both ends of the battery and protects the power module  20  by preventing the voltage of the battery from being directly applied to the power module  20 . A voltmeter  12  detects the DC voltage V dc  of the battery applied to the capacitor  10  and delivers a signal corresponding thereto to the CPU  40 . 
     The power module  20  includes a plurality of switching elements  22 . The power module  20  converts the DC voltage of the battery into a 3-phase AC current by operations of the switching elements  22 , and applies the 3-phase AC current to the motor  50 . An ammeter  30  detects the converted 3-phase AC current and delivers a signal corresponding thereto to the CPU  40 . 
     The CPU  40  generates a pulse width modulation (PWM) signal for controlling the switching elements  22  according to the driving condition of the vehicle and applies the PWM signal to the power module  20 . The driving condition of vehicle includes but is not limited to a demand torque, the DC voltage of the battery, a speed of the motor  50 , and a temperature of the motor  50 . 
     The RDC circuit  70  calculates the speed of the motor  50  by receiving a signal corresponding to a phase of the motor  50  and delivers a signal corresponding to the calculated speed of the motor  50  to the CPU  40 . The motor  50  receives the 3-phase AC current from the power module  20 , and thereby operates. A resolver  60  is mounted at the motor  50 . The resolver  60  detects the phase (rotating angle) of the motor  50 , and delivers the detected phase of the motor  50  to the RDC circuit  70 . 
       FIG. 2  is a schematic diagram of a system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 2 , a system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention includes a current order generator  100 , a current controller  110 , a coordinate transformer  120 , a signal generator  130 , a PWM inverter  140 , the motor  50 , and the resolver  60 . 
     The current order generator  100  determines a d-axis current and a q-axis current according to the driving condition of the vehicle. For this purpose, the current order generator  100  has a d-axis current map and a q-axis current map. Therefore, if a torque T* demanded by a current driving condition and a current speed ω of the motor  50  are input into the current order generator  100 , the current order generator  100  calculates the d-axis current i d * and the q-axis current i q * corresponding to the torque and the speed of the motor. 
     The current controller  110  calculates a d-axis voltage V d * and a q-axis voltage V q * by using the d-axis current i d * and the q-axis current i q * delivered from the current order generator  100  and a d-axis feedback current i d  and a q-axis feedback current i q . The coordinate transformer  120  receives the d-axis voltage V d * and the q-axis voltage V q * from the current controller  110  and converts the d-axis voltage V d * and the q-axis voltage V q * into 3-phase AC voltages V a *, V b *, and V c *. In addition, the coordinate transformer  120  receives 3-phase AC currents i a , i b , and i c  applied to the motor  50  as the feedback currents and converts the 3-phase AC currents i a , i b , and i c  into the d-axis feedback current i d  and the q-axis feedback current i q . 
     The signal generator  130  receives the 3-phase AC voltages V a *, V b *, and V c * from the coordinate transformer  120  and converts the 3-phase AC voltages V a *, V b *, and V c * into 3-phase switching signals S a , S b , and S c . The PWM inverter  140  includes a plurality of switching elements. The PWM inverter  140  receives the 3-phase switching signal S a , S b , and S c  from the signal generator  130  and converts the 3-phase switching signal S a , S b , and S c  into the 3-phase AC current i a , i b , and i c . Accordingly, the motor  50  is driven by receiving the 3-phase AC current i a , i b , and i c  from the PWM inverter  140 . The resolver  60  is mounted at the motor  50 . The resolver  60  detects the phase of the motor  50 , and delivers a signal corresponding thereto to the coordinate transformer  120  and the current order generator  100 . 
       FIG. 3  is a schematic diagram of a current order generator in a system for controlling a motor of a hybrid vehicle according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 3 , the current order generator  100  includes a reference current determination module  102 , a compensation value determination module  104 , and a current determination module  106 . 
     The reference current determination module  102  determines a d-axis reference current i d,tref  and a q-axis reference current i q,tref  from the demand torque T* at the current driving condition and the current speed ω of the motor  50 . For this purpose, the reference current determination module  102  includes a map in which the d-axis reference current i d,tref  and the q-axis reference current i q,tref  according to the demand torque T* for the current driving condition and the current speed ω of the motor  50  are stored. 
     The compensation value determination module  104  determines the compensation value of the reference current of the d-axis Δi* d,t  and the compensation value of the reference current of the q-axis Δi* q,t  from the demand torque at the current driving condition T*, the current speed of the motor  50  ω, the input voltage (the DC voltage V dc  of the battery), and the current temperature t of the motor  50 . For this purpose, an optimal approximation model is stored in the compensation value determination module  104 . Referring to  FIG. 4 , processes for selecting the optimal approximation model will be described in detail. 
       FIG. 4  is a flowchart illustrating processes for selecting an optimal approximation model according to an exemplary embodiment of the present invention. 
     As shown in  FIG. 4 , a system or designer disposes design variables and design spaces at a step S 200 . The design variables includes the demand torque at a current driving condition T*, the current speed of the motor  50  ω, the input voltage (the DC voltage V dc  of the battery), and the current temperature t of the motor  50 , the design spaces represents driving regions of the vehicle. After that, the designer applies design of experiment by using the design variables and the design spaces at a step S 210 . Herein, a central composite design is used as the design of experiment. The design of experiment and the central composite design are well-known to a person of an ordinary skill in the art, and thus detailed description thereof will be omitted in this specification. 
     If data is obtained by performing experiments according to the central composite design, the system or the designer generates an approximated model corresponding to the data at a step S 220 . After that, the experiments are done again so as to obtain new data, and the data is substituted into the approximated model by the system so as to verify suitability of the approximated model at a step S 230 . Subsequently, the system/designer determines whether the approximated model is the optimal approximation model at a step S 240 . 
     If the approximated model is not the optimal approximation model, the system/designer returns to the S 220  and generates another approximated model. If the approximated model is the optimal approximation model, the designer stores the optimal approximation model in the compensation value determination module  104  at a step S 250 . 
     The current determination module  106  determines the d-axis current id* and the q-axis current iq* from the d-axis reference current i d,tref  and the q-axis reference current i q,tref  determined by the reference current determination module  102  and the compensation value of the reference current of the d-axis Δi* d,t  and the compensation value of the reference current of the q-axis Δi* q,t  determined by the compensation value determination module  104 . The d-axis current id* and the q-axis current iq* are delivered to the current controller  110 . 
     Furthermore, the present invention may be embodied as computer readable media on a computer readable medium containing executable program instructions executed by a processor. Examples of the computer readable mediums include, but are not limited to, ROM, RAM, compact disc (CD)-ROMs, magnetic tapes, floppy disks, and optical data storage devices. The computer readable recording medium can also be distributed in network coupled computer systems so that the computer readable media is stored and executed in a distributed fashion. 
     As described above, an optimal driving of the hybrid vehicle may be provide by calculating a current order for operating a motor considering of all the factors that can affect an operation of the motor according to an exemplary embodiment of the present invention. Accordingly, fuel economy of the vehicle may improve and reliability and stability of control may also improve. Since one optimal approximation model is produced by design of experiment, particularly by central composite design instead of producing a plurality of maps, developing time may be shortened and developing cost may be reduced. 
     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.