Research On Torque Ripple Suppression Strategy Of Permanent Magnet Synchronous Motor Based On Harmonic Current Injection

Permanent magnet synchronous motor(PMSM)are widely used in robotics,machine tools,electric vehicles and other high performance industrial servo applications,because of its high efficiency,high power density and compact size.However,the main disadvantage of PMSM is the parasitic torque pulsations.There are various sources of torque pulsations in a PMSM such as the cogging torque,flux linkage harmonics,errors in current measurements,and dead zone effect of Voltage Source Inverter(VSI).Presence of these torque pulsations results in instantaneous torque that pulsates periodically with rotor position.These pulsations are reflected as periodic oscillations in the motor speed,especially for low-speed operation.At higher operating speeds,these torque pulsations are naturally filtered off by the rotor and load inertias and therefore,are not reflected back in the motor speed.Torque ripple suppression is a research topic worth studying.In this thesis,torque ripple suppression control strategy is further studied for PMSM running at low speed.First of all,this thesis analyzes the cause of torque ripple by modeling PMSM speed-current dual closed-loop control system.Based on Fourier decomposition method,the torque harmonics of PMSM in dq coordinate system is modeled,the coupling relationship between torque harmonics and current harmonics is analyzed,and the torque ripple suppression control strategy based on current harmonic injection method is studied.Aiming at torque ripple minimization,this strategy gets the torque ripple amplitude from the speed measurement,and uese Gradient Descent Optimization(GDO)algorithm to calculate the amplitude and phase of the injected harmonic current reference.It is simple to implement the strategy proposed in the hardware and software,because it does not require complex calculations.What is more,Adjustment effect of the Proportional Integral controller(PI)on the optimized harmonic current is analyzed.A discrete design method of tuning parameters of current loop PI controllers in the w’ domain is employed.The phase lag caused by the sampling time and the zero order holder(ZOH)are directly reflected in the design process.A simple and accurate tuning method for digital PI controllers of PMSM current loop is proposed.The method propsed can improve the dynamic and steady-state performance of PMSM control system based on harmonic current injection torque ripple suppression strategy.Next,comparing with the traditional PI control strategy,this thesis analyzes smooth speed control for PMSM using Proportional-Integral-Resonant(PI)controllers.Stability analysis is carried out,considering the delays caused by current loop and speed measurement as they may make the whole system unstable under the PIR control strategy,and the optimal phase adjustment parameters for resonant item to keep the system stable are then obtained through theoretical analysis and numerical simulations.Finally,the proposed torque ripple suppresion control approachs are investigated by simulation based on MATLAB/Simulink model and then,the experiments are carried out on the PMSM hardware platform based on dSPACE1103 rapid prototype development platform.Both experimental and simulation results can verify the effectiveness of the torque ripple suppresion methods proposed in this thesis.