Simultaneous Sensorless Rotor Position and Torque Estimation for IPMSM at Standstill and Low Speed Based on High-Frequency Square Wave Voltage Injection

In this article, a method of simultaneous sensorless rotor position and torque estimation is proposed for interior permanent magnet synchronous machines at standstill and low speed. The proposed method estimates the torque using high-frequency inductances identified from the current variations due to high-frequency square wave voltage injections in the estimated dq-axes, which are simultaneously used for sensorless rotor position estimation. The proposed method is not dependent on the fundamental model and has taken the cross-coupling effect into consideration, allowing for low cost and fast torque estimation at standstill and low speed. Both simulations and experiments are carried out to verify the effectiveness of the proposed method.

I. Introduction

Permanent magnet synchronous machines (PMSMs) have been widely used in domestic and industrial applications due to their having both high torque density and efficiency [1]. Precise torque control of PMSM is required in many applications, such as robotics, elevators, and electric vehicles [2]. Accurate torque feedback of the machine is essential for both control and monitoring purposes. Hardware transducers such as strain gauges [3] and torsional displacement [4] can be used to measure the machine torque. However, they are usually very expensive and require extra installation space and cables. Therefore, torque estimation without a sensor is a preferable solution.