Improved position signal demodulation method for sensorless control based on HF sinusoidal pulsating voltage injection

Abstract

High frequency (HF) sinusoidal pulsating voltage injection is a reliable method for position sensorless control in low speed range. For HF voltage injection based methods, position signal demodulation plays a key role. However, the conventional sinusoidal demodulation suffers from long settling time and limited bandwidth because of requirement of a low-pass filter (LPF) to suppress HF harmonics in the estimated position. Additionally, the overall performance is deteriorated due to the characteristic of linear demodulation. To address these issues, the cube of q-axis HF current instead of itself is used as the carrier of position estimation error. In this way, the input variable for phase-locked loop (PLL) is the cube function with respect to the position deviation. During steady state, the equivalent gain in PLL is very small and thus the estimated position is nonsensitive against high-frequency harmonics, thereby the LPF is no longer required in the proposed method. While during dynamic process, the equivalent gain is increased leading to a fast converging rate when compared with the conventional method. The stability and dynamic performance are theoretically analysed by the magnitude-frequency diagram. The superiority of the proposed method was experimentally justified and the obtained results show that both steady-state and dynamic performance are improved when compared with the prior art.