Predictive Current Control And Current Error Elimination For Permanent Magnet Ac Servo System

In permanent magnet AC(PM-AC) servo systems, cascaded control structure isoften applied in the form of position loop, speed loop and current loop. The innerloop, current loop decides the transient and steady-state performance of PM-ACsystem and is the key factor to improve it. Predictive current control(PCC), whichapplies the model of motor and inverter to predict the current response in the nextcontrol interval, and can broden the bandwidth of current loop and improve itstransient response, is being widely researched. According to the way voltage vectoris applied, PCC can be categorized into different groups, and is suitable fordifferernt applications. Besides, as PCC relies on the accuracy of model, themismatch of model parameter will lead to oscillation and error in current control,which may lead to system instability, reduction of efficiency, being unable to outputnominal torque or to work in torque servo mode, and so on. These will causedifficulties in the use of PCC in industrial applications.This paper introduced the priciple of direct predictive control(DPC) and PWMpredictive control(PPC), and conducted simulation in Simulink. The influence ofcontrol frequency on switching frequency and performance for DPC and thedifference between DPC and PPC under the same switching frequency are studied,which show their respective advantage and suitable applications. Apart from that,the current response of two predictive control method with controller parametermismatch is studied, reaching a conclusion that PPC is sensitive to parametermismatch and a current error elimination algorithm is required.On the basis of simulation, this paper analyzed the stability condition andparameter sensitivity of PPC numerically, and analyzed the effects of robust factorhave on system stability, transient response and current error. Based on robust factor,this paper proposed a current error elimination algorithm. By introducing errorintegration in d-axis control and adjusting flux parameter in controller dynamicallyaccording to q-axis current error, the algorithm can eliminate the current errorcaused by controller model parameter mismatch without weakening dynamicresponse.Finally, this paper realized and compared DPC and PPC on a3.3kW PMSMservo platform. Then, the current error elimination algorithm was tested. The resultsshow that the algorithm can eliminate d-q axis current error effectively.