Research On Common Mode Voltage Suppression Strategy Of Dual Three-Level Inverter Based On An Open-end Winding Induction Motor

The multi-level inverter topology of double inverter cascade can greatly improve the speed regulation performance of medium and high voltage variable frequency speed regulation system,improve the power density of the system,reduce energy loss,reduce carbon emissions,and also help the development of China’s inverter industry to the direction of high voltage and high power.In this thesis,the open winding permanent magnet synchronous motor(OW-PMSM)is taken as the control object,and the zero sequence voltage elimination,common mode voltage suppression and neutral point potential balance of the common bus dual-T three-level inverter system are studied.According to the mathematical model of PMSM and the topology structure of common bus dual three-level inverter,the open end winding motor is modeled.On this basis,the switching state of each phase of the common bus dual T-type three-level inverter connecting the two ends of the motor winding is analyzed,and the switching model of the topology is established.Based on this,the zero sequence voltage and common mode voltage of the system are defined,and the zero sequence voltage of the system is analyzed.According to the switching function of the dual T-type inverter,the space voltage vector diagram of the topology is given,which is the basis of the followup research on the control algorithm of the dual three-level inverter.In order to eliminate the zero sequence circulating current in the zero sequence path of a common bus dual-T three-level inverter system,a 180° decoupling modulation method of reference voltage vector is studied in this thesis,which can eliminate the average zero sequence voltage in a switching cycle of the system,and then eliminate the zero sequence circulating current.However,there are still high frequency components in the zero sequence voltage of this method.Therefore,an improved reference vector 120° decoupling modulation method is studied in this thesis,which eliminates the instantaneous zero sequence voltage of the system and solves the problem of high frequency zero sequence voltage component in 180° decoupled reference voltage vector method;aiming at the problem of neutral point potential offset caused by zero sequence voltage elimination of vector decoupled modulation strategy,this thesis designs a neutral point potential control algorithm to suppress the fluctuation of neutral point potential.In order to suppress the common mode voltage in the 120° decoupling method of space voltage vector,this thesis improves a reference voltage decoupling modulation strategy based on virtual space vector,and simplifies the algorithm through 60°coordinate system.This method can eliminate the instantaneous zero sequence voltage,reduce the common mode voltage amplitude by 50%,and reduce the harm of common mode voltage.In this thesis,a novel zero common mode voltage vector modulation strategy is proposed,which can eliminate the instantaneous common mode voltage of the system,realize the neutral point potential balance,and reduce the complexity of the modulation algorithm through the 60 ° coordinate system.In this thesis,a common bus dual-T three-level inverter open winding permanent magnet synchronous motor speed control system is built on the software and hardware platform.Simulation and experiments show that the proposed modulation strategy is effective and correct.