Research And Design Of PMSM Drive Control System Based On Three-level Inverter

In PMSM drive systems,Neutral-point clamped（NPC）three-level inverters are widely used in medium and high voltage applications because of their significant advantages such as low withstand voltage of power components and low output harmonic content.However,due to load variations and space voltage vectoring,the neutral point voltage of this inverter can be shifted.If no balancing measures are taken,it will lead to the increase of PMSM current harmonics and speed fluctuation,which will affect the system speed regulation performance.When the offset is serious,the power switching tubes and support capacitors will be damaged and the PMSM stops operating,further affecting the normal operation of the system.Therefore,this paper investigates the NPC three-level inverter neutral point voltage balancing control method and PMSM speed control method,which are as follows.Firstly,the operating state of NPC three-level inverter is analyzed.The basic structure of PMSM is introduced and the mathematical model of PMSM is established.On the basis of the mathematical model,the PMSM vector control system driven by NPC three-level inverter is constructed,which lays the foundation for the following neutral point voltage balance control method and speed control method.Secondly,a neutral point voltage balancing control method based on improved space vector pulse width modulation is proposed for the neutral point voltage offset problem of NPC three-level inverter in PMSM drive system.By analyzing in detail the actual current loop corresponding to the twenty-seven space voltage vectors,a proportional-integral controller is designed using the fact that the positive and negative redundant small vectors have opposite relationships on the neutral point voltage.The upper and lower capacitor voltage deviations are introduced into this controller,and the neutral point voltage balance control is achieved by fine-tuning the positive and negative small vector action times.The neutral point voltage balancing control method is verified in Simulink.Simulation results show that the balancing control method has good ability to cope with load variations and improves the reliability of the PMSM drive system.Then,a fuzzy proportional-integral-based speed control method is proposed for the problems of large overshoot and slow response when traditional proportional-integral control is used for the speed loop in the PMSM vector control system driven by NPC three-level inverters.The fuzzy proportional-integral controller is used in the speed loop instead of the traditional proportional-integral controller.During the operation of the system,the fuzzy control is used to adjust the proportional-integral parameters in real time.The above neutral point voltage balance control method is combined with this speed control method.This speed control method is verified in Simulink.The simulation results show that the method has faster speed response,smaller overshoot and higher control accuracy than the traditional proportional-integral speed control.Finally,the experimental platform of the PMSM drive control system of the three-level inverter is built.The TMS320F28377 is used as the core chip to design the main circuit,drive circuit and detection circuit of the NPC three-level inverter.The neutral point voltage balance control algorithm and fuzzy proportional-integral control algorithm proposed in this paper are verified on the experimental platform.The experimental results show that the proposed control algorithm is feasible and effective.