The Compensation Techniques Of Torque Pulsations In Permanent Magnet Synchronous Motor Drives

Permanent Magnet Synchronous Motors (PMSMs) are appealing candidates for many high performance motion control applications. Their popularity is justified by several advantages over commonly used motors in these applications, such as highly efficient, high power density and rapid dynamic response. Besides these, the absence of the external rotor excitation slip rings on the rotor and brushes obsolete, eliminates the commutation spark, makes the PMSMs more suitable for these applications with very strict conditions, Such as weapon systems, vehicle drives, aeroplanes and spacecrafts.The main disadvantage of PMSMs is its pulsating torque. Torque smoothness is an essential requirement in a wide range of high-performance motion control applications. So the compensation of pulsating torque is very importance for the application of PMSMs.This paper addresses on the problem of the compensating techniques of pulsating torque in PMSMs. The techniques of pulsating torque minimization based on the improvement of control schemes are focused on. Several control algorithms are proposed in this paper. The main contribution of this dissertation is summarized as following:1. A standard model of PMSM deduced from the stator flux linkage equations isstudied. The models of PMSM in the αβ (stator two phases )frame and dq (synchronous rotating )frame are proposed by transformation.2. The structure of id =0 vector control is introduced. The analysis model of thetotal control system is described.3. With Fourier decomposition, the main component of pulsating torque, torque ripple is studied. It can be determined that torque ripple is caused by harmonic order 6n under the usual common conditions. This is confirmed by simulation.4. The pulsating torque components caused by stator current divergence from ideal conditions are studied. Three conclusions are educed from different situations. These are justified by simulation.5. The principle of compensating pulsating torque is proposed. A pulsating torque component can be compensated by inject a selected harmonic component to the phase current. Selected Harmonic Injection Techniques is described.6. A model of PMSM that includes torque ripple effect is developed and tested. An adaptive control algorithm is described. The rotor flux is estimated by adaptivecontrol system in the dq frame. As a feedback the estimated flux are used toactively changing the excitation current waveforms to generate smooth output torque. The stability of the control system is studied. The performance of the system is simulated using Matlab/Simulink toolbox.7. A scheme for compensating torque ripple in vector control system is presented.The stator flux linkage are identified in αβ frame by a Kalman filter and used tocompensate torque current to eliminate the torque ripple. This technique does not need the pro-knowledge of the motor flux. Parameter deviations do not affect system performance substantially.8. A pulsating torque minimization approach based on disturbance observer is proposed. The new disturbance observer is designed to observe the unknown torque disturbance caused by the torque ripple, the varying of the motor parameters, the changing of load torque and the not ideal performance of the inverter. The observed disturbance is used to compensate the torque pulsations.9. A fuzzy reasoning controller is designed to improve the performance of the mentioned disturbance observer. As the motor speed and load torque varying, the parameter of the disturbance observer can be changed by the fuzzy controller based on experiences. The pulsating torque can be compensated more strictly in a extended range.