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ORIGINAL ARTICLE

Fix‑frequency robust power model predictive control method for three‑phase PWM rectifiers under unbalanced grid conditions Xin Guo1   · Min Xiao1 · Yu‑er Gao1 · Qingyu Wang1 · Yihao Wan1 Received: 10 November 2019 / Revised: 18 June 2020 / Accepted: 20 June 2020 © The Korean Institute of Power Electronics 2020

Abstract Under unbalanced grid conditions, the controller design of a three-phase pulse width modulation (PWM) rectifier is based on an instantaneous power model. By calculating the current references of the converter according to the instantaneous power model, traditional voltage-oriented control (VOC) methods realize the positive-sequence and negative-sequence active and reactive current control of the converter separately using the proportional-integral (PI) controller. However, due to the inner current loop control structure of the traditional VOC method, it is impossible to realize the regulation of all six power components in a common instantaneous power model under an unbalanced grid. Meanwhile, the control performance of the traditional VOC method with a PI controller is degraded under the circuit parameters uncertainty condition. In this paper, a fixed switching frequency robust power model predictive control method (FRP-MPC) is proposed for three-phase PWM rectifiers under the unbalanced grid condition. The proposed control strategy has a number of advantages. An improved instantaneous power model is used for the fixed switching frequency model predictive controller design under the unbalanced grid condition, which has less power variables than the common instantaneous power model. The robustness of the MPC controller is improved by adding a robust item into the predictive model under circuit parameters uncertainty. Simulation and experiment results verify the effectiveness of the proposed control method. Keywords  Three-phase PWM · Model predictive control · Unbalanced grid · Circuit parameters uncertainty · Robustness

1 Introduction Three-phase pulse width modulation (PWM) rectifiers have been wildly used in many fields including industrial power supply, electro mobile, motor drive systems, distributed generation [1–3], etc. Some of the widely used control strategies for the threephase PWM rectifiers include the voltage oriented control (VOC) method [4], the direct power control (DPC) method [5], the model predictive control (MPC) method [6], etc. Most research achievements in terms of the above control strategies focus on the balanced grid condition [4–9]. However, the grid unbalance is one of the most common problems in power systems, which can be caused by highpower single-phase load access, grid impedance unbalances, short-circuit faults and so on [10]. Under the unbalanced * Xin Guo [email protected] 1



Department of Information and Control Engineering, Xi’an University of Technology, Xi’an, China

grid condition, the three-phase input voltage amplitude values of a three-phase PWM rectifier are not the same and the phase differences between the three-phase voltages are