Elimination Strategy of Position Error for High Power Permanent Magnet Motor Drive

Permanent magnet synchronous machine (PMSM) becomes more and more popular in railway traction systems. Due to non-ideal factors of position sensor, obtained rotor position exists nonlinear error, which makes a bad influence to control performance of PMSM. In this paper, the effect of position error on current harmonics from the perspective of pulse width modulation is studied by detailed mathematical derivations. Severe dc offset and current harmonics problems caused by position error brings torque ripples and extra switching losses, which is unacceptable in railway traction systems. To solve the problem, an algorithm of reconstructing rotor position considering the characteristics of high power motor is proposed, which is consisted of low-pass filter (LPF) and phase-locked loop (PLL). The reconstruction is implemented on DSP chip, which is simple and reliable. The current harmonics problem can be well improved using the proposed scheme. Simulations have been carried out to verify the effectiveness of proposed rotor position reconstruction strategy.

I. Introduction

Recent years, the application of permanent magnet synchronous machine in railway traction systems has increased due to the advantages of high power density and high efficiency [1] - [3]. The field-oriented control (FOC) method is applied widely for the control of PMSM because of excellent performance. Different from induction motor, there is no concept of slip for PMSM. So the accuracy of rotor position play an important role in the performance of FOC. Rotor position can be obtained by position sensors or sensorless position estimation methods. Sensorless position estimation methods mainly contain voltage injection in low speed and model-based methods in high speed. However, extra voltage injection will bring out torque ripples and model-based methods are sensitive to motor parameters which frequently vary in high power motor. Hence, mechanical sensors are still the mainstream for obtaining rotor position. Position sensors include hall sensors, encoders and resolvers mostly. In order to satisfy the demand of robustness and reliability in complex electromagnetic environment of railway traction systems, resolvers are inclined to be applied to provide position information.