Design and analysis of robust backstepping controller for DC suppression of parallel UPS inverter system

Abstract

Here, an improved control strategy is proposed, which adopts a non‐linear robust backstepping controller to eliminate DC circulating current in a parallel uninterruptible power supply (UPS) system. The traditional active and reactive power sharing control can ideally suppress the AC circulating current, but cannot effectively restrict the DC circulating current. Based on the traditional active power and reactive power sharing control (TAPRPSC) of the parallel UPS system, the proposed control strategy is used in each parallel inverter module to suppress the DC component disturbance in the inverter output voltage, which varies within a certain range. Hence the desirable steady‐state and dynamic performance of the system can be obtained. Moreover, the Lyapunov method is utilized to ensure the stability and robustness of the system. A parallel system of two UPS inverters with the proposed control strategy is built by Matlab/Simulink, and further experiments are carried out on the semi‐physical simulation platform of the Modelling Tech. Both the simulation and experimental results verify the effectiveness of the proposed control strategy for DC circulating current suppression and ideal output voltage tracking.