Minimum-Voltage Vector Injection Method for Sensorless Control of PMSM for Low-Speed Operations

In this paper, a simple signal injection method is proposed for sensorless control of permanent-magnet synchronous machine (PMSM) at a low speed, which ideally requires one voltage vector only for position estimation. The proposed method is easy to implement, resulting in low computation burden. No filters are needed for extracting the high-frequency current signals for position estimation. The use of low-pass filters (LPFs) in the current control loop to obtain the fundamental current component is not necessary. Therefore, the control bandwidth of the inner current control loop may not need to be sacrificed. The proposed method may also be further developed to inject two opposite voltage vectors to reduce the effects of inverter voltage error on the position estimation accuracy. The effectiveness of the proposed method is demonstrated by comparing with other sensorless control method. Theoretical analysis and experimental results are given for validating the proposed new sensorless control method.