Research On Control Strategy Of PMSM Under Square Wave Operation

In recent years,the application of permanent magnet synchronous motor(PMSM)has received increasing attention in the field of rail transit.The traction drive system in the field of rail transit has the characteristics of high voltage,large current and wide operating range.In high-speed range,PMSM usually runs in square wave condition.The quality of motor control under square wave condition will directly affect the torque performance and safe and stable operation of the rail transit system.This paper focus on the control strategy and parameter compensation strategy of PMSM under square wave condition.The main research contents are as follows:In view of the reduced degree of voltage control freedom under square wave condition,single current loop control is adopted as the basic control strategy.By deducing the relationship among different variables under square wave condition,it is proved that there is a monotonic relationship between motor torque and voltage phase angle,d-axis and q-axis voltage.Combined with single d-axis current loop and single q-axis current loop,six different single current loop control strategies can be obtained under square wave condition where the double current loop control cannot be used.A systematic summary based on single current loop control method is realized.The control performance of different single current loop control strategies is comparative studied in theory.By means of pole-zero analysis,bode diagram and step response analysis,a comparative research of different single current loop strategies is carried out in terms of motoring/generating consistency,stability and dynamic response speed.The research result shows that there are three single current loop control strategies don’t need to adjust the controller;the single q-axis current loop adjust q-axis voltage method has the fastest dynamic response speed because it has no right half plane zero point.This method has global stability,but the controller needs to be switched when the motor motoring / generating state changes.In order to improve the torque control accuracy,a multi-parameter online compensation strategy under square wave condition is proposed based on the method of single q-axis current loop adjust q-axis voltage.By analyzing the influence of different motor parameter errors on torque control performance,it is proposed that d-axis flux linkage can be compensated by d-axis current loop and q-axis inductance can be compensated by d-axis voltage loop.This method can improve torque accuracy through double error loops and doesn’t need to change control structure.The theoretical analysis results of different single current loop control strategies and parameter compensation strategy are simulated and experimentally verified through MATLAB / Simulink,a real time simulation platform based on d Space and a 7.5k W PMSM experiment platform at laboratory.Simulation and experimental results confirm the correctness and effectiveness of above square wave control strategy and parameter compensation method.