Current Control for Synchronous Motor Drives: Direct Discrete-Time Pole-Placement Design

Abstract

This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically salient rotor structure, such as interior permanent-magnet synchronous motors and synchronous reluctance motors (SyRMs). The dynamic performance of current controllers based on the continuous-time motor model is limited, particularly if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discretetime pole-placement design method for two-degrees-of-freedom proportional–integral current control is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (R_s,L_d,L_q) are required. The robustness of the proposed current control design against parameter errors is analyzed. Thecontroller is experimentally verified usinga 6.7-kW SyRM drive.Peer reviewe