Study On Z-Source Inverter Applied To Electric Vehicle

The motor drive system is an important component of electric vehicle, which is afront research field in borne and abroad. The traditional motor drive system generallyadopts the voltage source inverter which supplies power by power batteries directly。when the motor runs above the base speed, the power battery voltage will limit theinverter’s output voltage, the limited stator voltage can not measure up to therequirement of rotor electromotive force to rise motor speed, and restrict the motortorque output when it runs at high speed. The discharge of large current may lead to theDC bus voltage sag, thus affect the dynamic performance of electric vehicle. Z-sourceinverter is an inverter which can boost/buck voltage, and it can adapt to a large range ofinput voltage variation, it has the characteristics of high reliability, so the study that theZ-source inverter is applied to electric vehicle’s motor drive system has positivesignificance which can improve reliability of the motor drive system and improvedynamic performance of the motor.On the basis of analyzing the control of shoot-through zero vector SVPWM, thepaper puts forward the shoot through segment SVPWM control. The shoot through vectoris divided into six points without changing the reference voltage vector (On the premiseof effective time). The shoot through SVPWM control is realized by changing theconduction time of switch tube， and inserting through electric current between theupper and lower bridge arm. The SVPWM control is simulated by MATLAB, and it isrealized by TMS320F2808and used in motor control, and the experiment proves thatcontrol method is feasible.The paper researches on a closed-loop control strategy for Z-source inverter, thestrategy uses the method which detects the capacitor voltage and the input voltage to getthe closed-loop control of DC bus voltage, and realizes the dynamic regulation of DCbus voltage. Under the simulated environment of Simulink, a model of Z-sourceinverter closed loop control is established, and the verifiable system is built. It has wellanti-interference capability to battery voltage sags and load current changes.In the paper, the shoot segment control for SVPWM and the closed-loop controlstrategy are introduced to the motor control, so that can realize the vector control forZ-source inverter and V/F control. In the motor control, when the output voltage of theinverter gets the maximum point, to enhance the maximum output voltage in order to measure up to the requirement of rotor electromotive force to rise motor speed, andimprove the motor torque output when it runs at high speed. At the same time, it canenhance the motor torque output by enhancing the DC bus voltage. A simulated modelbased on Z-source inverter motor vector control and V/F control is built by MATLAB,and the Simulation results show its effectiveness.The paper studies the oscillation problems which caused by the DC bus voltagewhen the Z-source inverter converts the straight-through state into a straight-throughstate. Based on analyzing the main loop stray parameters, an equivalent model of strayparameter on Z-source inverter is built, and the paper analyzes the influence of the strayparameter on DS bus voltage. On this basis, the paper puts forward to use a proper lowinductance bus-bur and a proper low equivalent series inductance (ESL) capacitive tosuppress the voltage oscillation, the experiment proves that model is feasible. Finally, a3KW Z-Source inverter applied to electric vehicle is implemented.