Fault-Tolerant Control Strategy for Three-Level ANPC Inverter Based on Finite-Time Controller

An improved fault-tolerant control strategy is proposed for Active neutral point clamped (ANPC) multilevel inverter switches open-circuit faults. Unlike traditional fault-tolerant control methods, this method reconstructs switching sequence under different switches faults with high power quality and quickly balances the neutral point (NP) voltage using a finite-time controller (FTC). The finite-time NP potential controller is constructed to control the NP voltage by adjustment of the amplitude of the reference voltage in real time. Switching sequence is reconstructed by replacing redundant vector without increasing the number of switches and level-cross jump. Based on the finite time theory, the Lyapunov function is constructed and the finite time stability is proved, and it is concluded that the tracking error will converge to zero during a finite time. Compared with traditional PI control, the proposed control strategy can balance the NP much faster to achieve better performance, and there is no need to add any extra switches or hardware cost. Therefore, this scheme improves the reliability and robustness of the ANPC inverter. Simulation results confirm the feasibility and correctness of the proposed control scheme.

I. Introduction

With the rapid advancement of power electronics technology, different types of three-level converter topologies have been widely used in new energy systems. Among them, NPC converters are particularly suitable for high-voltage high-power applications such as flexible AC transmission system (FACTS), aerospace, photovoltaic power generation and energy storage industries [1]. Due to the low harmonic distortion and stable performance of the NPC inverter, it makes up for the shortcomings of the two-level inverter such as high harmonics and high switching stress. NPC inverters can be used to improve power quality in low-voltage drive applications [2]. However, uneven loss distribution is a key issue in NPC converters. Therefore, the ANPC converter with the addition of two extra switch formations solves this problem and significantly increases the output power and switching frequency of the converter. Fig. 1.

Topology of three-level ANPC inverter.