Improved Integral Sliding Mode Control Scheme for Inverter-Based Four-Wire Autonomous Power Supply Units

Abstract

Connecting renewable energy-based distributed generations (DGs) through a DC-Link can create autonomous power supply units (APSUs). Three phase four-leg inverter is a beneficial solution to supply unbalanced loads which is inevitable in a typical APSU. The four-leg inverter can provide sinusoidal-shaped voltages but a high performance control method should be used. Sliding mode control (SMC) is a well-known non-linear control method with high robustness, high stability in a wide range of operation and fast dynamic response. However, it mainly suffers from high chattering problem, variable switching frequency and steady-state error which deteriorate all the previous advantages. In this paper, first, detailed model of the four-leg inverter in the abc reference frame considering the inductor series resistance is derived. Second, a high performance SMC method with zero steady-state error, fixed switching frequency and considerably reduced chattering voltage is proposed to control the output voltage of the four-leg inverter. The proposed method guarantees fast dynamic response and high robustness against model parameter mismatches and load variations. Finally, an improved SMC is also proposed to attenuate the chattering problem more effectively. Several experimental results on a 3-kW test bench are presented to verify the superior performance of the proposed methods.