Discrete-Time Position Sensorless Current Control for Interior Permanent Magnet Synchronous Motors Based on Modified Back-Electromotive Force

A discrete-time sensorless current control method is proposed for the interior permanent magnet synchronous motor (IPMSM) in this paper. Due to the inconsistent dq -axis inductance of IPMSMs, the design of the discrete-time current control method and sensorless control method is complicated. The control methods are therefore widely designed in the continuous-time domain, while the performance of these continuous-time methods is poor. In the proposed scheme, the current regulator is designed in the discrete-frequency domain based on an entirely discretized state-space model, which improves the dynamic and steady-state performance of the current control system. In terms of the electrical angle estimation method, the continuous-time model-based method leads to a significant estimation error. To improve the accuracy of the estimated back-EMF, a state-space model with a modified back-EMF (MBEMF) model is derived in the discrete-time domain. Then the observer of MBEMF and a phase-locked loop (PLL) with phase compensation are proposed based on the discrete-time state-space model. The proposal improves the accuracy of the estimated electrical angle. The proposal is designed directly in the discrete-time domain, which avoids significant performance deterioration in digital implementations. Finally, the proposed method is implemented on an IPMSM drive test rig to verify its improvement.