Research On The Motor Controller Of Electric Vehicles Based On Silicon Carbide

With the development of power electronics technology,the third-generation semiconductor material technologies and processes represented by silicon carbide(SiC)tend to mature.Compared with traditional silicon(Si)materials power devices such as IGBT and MOSFET,SiC power devices have the advantages of high withstand voltage,low loss,high thermal conductivity,and high switching frequency.At present,Si modules are mainly used in the motor control unit(MCU)of electric vehicles as the power device of the inverter circuit.Due to the limitation of the characteristics of the Si material itself,the efficiency improvement of the motor controller encounters a bottleneck.Therefore,in electric vehicles,it is urgent to use SiC power devices to replace Si power devices in MCU,and the resulting increase in driving range can reduce battery consumption;At the same time,increasing the high switching frequency of SiC power devices can effectively reduce the high-order harmonic content of motor current,thereby reduce motor torque ripple and improve noise,vibration,harshness(NVH)characteristics of electric vehicles;in the application of electric vehicle’s MCU,thereby improving the economy and drivability of electric vehicles.In this paper,the loss composition of power devices is firstly studied,and the loss difference between SiC and Si due to different device characteristics is compared.The simulation model of loss calculation is built through Matlab.At the same time,the factors affecting the loss of power devices are analyzed,and the influence of the value of the drive resistor in the drive circuit on the loss of the power device is mainly explored,which provides a theoretical basis for the design of the drive circuit of MCU.Then,according to the high efficiency,high reliability and high integration requirements of MCU in the electric vehicle,the parameter indicators of MCU are formulated,and the overall system scheme and key device selection of MCU are planned.For the design of driving circuit,the selection of driving resistance is determined through the switching waveform test of SiC device,and the active shortcircuit protection function is added to the drive circuit,and the "sandwich" structure is used in the structural design to realize the integrated water channel of the co-shell,and a 150 k W motor controller prototype suitable for electric vehicle industry applications is developed.Thirdly,it’s necessary to set a dead zone when applying power devices,torque fluctuations and thus noise are generated when controlling permanent magnet synchronous motors(PMSM).In order to improve the NVH characteristics of the automotive electric drive system,the harmonic current compensation algorithm is introduced to reduce the torque fluctuation on the basis of the vector control principle of the permanent magnet synchronous motor;since the SiC has the characteristics of fast switching,the switching frequency is increased by applying the SiC power device,which further improves the suppression effect of the harmonic current compensation algorithm on the torque wave;and the proposed harmonic current compensation algorithm is verified by Matlab/Simulink simulation.The magnitude of the torque ripple amplitude of the switching frequency at 8k Hz and 20 k Hz is compared and analyzed,and it is verified that the MCU can more effectively suppress the torque fluctuation by increasing the carrier frequency by applying SiC power devices.Finally,MCU is tested and verified by double pulse test,bench and vehicle test.Through the double pulse test,the turn-on and turn-off times of the power device are within 150 ns,and the voltage spike at the switching moment is within the design range,which verifies the rationality of the drive circuit design.Through the efficiency map test,the maximum efficiency of the SiC motor controller is 99.4%.Compared with the Si IGBT motor controller,the maximum efficiency is increased by more than 1%,and the efficiency in the low-speed and low-torque region is increased by up to 5.1%.The effect is obvious.Through the test results of the whole vehicle,the harmonic compensation has a significant improvement effect on the NVH of the whole vehicle.When the motor is lower than 4000 rpm,the harmonic compensation function can reduce the near-field noise by 18-25 dB.