Torque Ripple Minimization Of PMSM Using PI Type Iterative Learning Control

The permanent magnet synchronous motor(PMSM) has many excellent performances such as high power density , simple drive system and structure, which make PMSM receive widespread application in industrial servo control system. However, the periodic torque ripple in PMSM due to non-sinusoidal flux density distribution around the air-gap, cogging torque and current measurement error is not acceptable in high performance application such as direct drive system such as elevator cabin control system and electric vehicle motor system. Electromagnetic torque of AC motor is described in mathematical details in this paper based on the principles of electromechanically energy conversion, and the relations among ripple torque, stator current and non-sinusoidal flux density distribution are also proposed. The mathematic model of electromagnetic torque is established in dq-axis coordinate based on the analysis of ripple torque and cogging torque, which provide fundamentals to torque ripple reduced.A PI type iterative learning controller is designed as a speed loop controller in this thesis to take place of the structure that P type iterative learning controller in paprallel with PI speed controller to reduce periodic torque ripple in PMSM. Compare with conventional P type ILC controller, it is not necessary for the newer to estimate or detect electromagnetic torque signal, which can increase the bandwidth of the speed controller and make the structure of the controller simpler. The method proposed modulates the next period control signals by the experiences stored in the memory to generate a proper q-axis reference current to reduce torque ripple.The simulation results of P type ILC and PI type ILC are compared in this thesis, and rejection of repeatable perturbation is also proved for the two iterative learning control. Stability and convergence of PI type ILC are all discussed, based on which the parameter of the controller is designed. In addition, the performance of the controller affected by the parameter is provided.A PMSM drive system originated from vector control system is designed to verify the method presented using PI type ILC. Thus q-axis current reflects electromagnetic as d-axis current is controlled to be zero. Therefore, q-axis current of PMSM under PI control and PI type ILC in different conditions are proposed as an experimental verification, meanwhile, performance of PI type ILC is analyzed as different parameter of the controller are adopted, which can validate the method proposed in this thesis.