Adaptive Second-Order Active-Flux Observer for Sensorless Control of PMSMs With MRAS-Based VSI Nonlinearity Compensation

This article proposes an adaptive second-order active-flux observer (ASO-AFO) for sensorless control of permanent magnet synchronous machines (PMSMs) with online voltage-source inverter (VSI) nonlinearity compensation, which is based on the model reference adaptive system (MRAS). First, an ASO-AFO is introduced to observe the active flux. The parameters of the observer are speed-adaptive, thus reducing the observation error in different speed ranges. Then, a method based on MRAS is proposed to compensate for the VSI nonlinearity. The VSI nonlinearity makes the actual voltage different from the ideal output voltage, resulting in a specific harmonic current vector in addition to the fundamental current vector. The fundamental current vector and the current vector composed of the fundamental and harmonic current vectors are selected as the output of the reference model and the adaptive model. The cross-product of their output reflects the severity of the VSI nonlinearity. The root mean square (rms) value of the cross-product is selected as the objective function. The nonlinearity is compensated by minimizing the objective function, which is realized by the gradient descent method. Finally, the effectiveness of the proposed ASO-AFO with MRAS-based VSI nonlinearity compensation is verified by comprehensive experiments.