A current DC-bias and BEMF observation strategy for PMSM using one sliding mode observer with a new PLL and phase angle compensation method

The conventional sliding mode observer (SMO)-based back electromotive force (BEMF) observation method for permanent magnet synchronous motor (PMSM) is sensitive to current DC-bias, resulting in worse sensorless control performance. To solve this problem, this paper proposed a new current DC-bias and BEMF observation strategy for PMSM using only one SMO. Since the current DC-bias can be observed and compensated using the proposed method, the observed BEMF is not sensitive to DC-bias anymore, achieving better sensorless control performance. In this paper, the design method of the new SMO is explained firstly. Next, the stability of the new SMO is verified. Then, the principles of the proposed current DC-bias observation strategy are analyzed in detail. After that, the insensitivity of the proposed BEMF observation method to current DC-bias is also revealed, and the parameter sensitivities of the proposed current DC-bias observation strategy are analyzed in the following. Additionally, to reduce the phase angle error during acceleration and deceleration caused by the conventional phase-locked loop (PLL) and compensate the phase error generated by the low-pass filter, a high-order PLL with a new phase angle compensation method is further proposed. Finally, experimental studies are carried out, which verify the effectiveness of the proposed method.