Stability Analysis for Grid-Connected Single Phase Asymmetrical Cascaded Multilevel Inverter with SRF Fuzzy Control with Improved Power Quality Features

Abstract

This project analyzes the influence of phase-locked loop (PLL) on the stability of LCL-type single-phase grid-connected asymmetrical cascaded H-bridge multilevel inverter (ACHMI) with synchronous reference frame fuzzy (SRF-Fuzzy) grid current control under weak grid scenarios. The ACHMI system composed of power stage circuit and control system, where the control system contains the dual loop current control strategy established in the hybrid reference frame (HRF), the synchronous reference frame PLL(SRF-PLL) and the hybrid modulation method employed to synthesize the multilevel output voltage. The small signal model of the whole ACHMI system is first established by using a simple step-by-step derivation method, and then, the small signal analysis method is adopted to linearize the ACHMI, which is then utilize to derive the impedance stability criterion is derived which is then to analyze the system stability. By using this criterion, the stability of the ACHMI can be evaluated with the variation of the bandwidth of PLL, the output power factor angle of the ACHMI and the amplitude of the grid current reference signal under weak grid conditions. in this paper, a systematic design procedure for the optimal selection of the proportional- integral (PI) and fuzzy controller the PLL is presented, which guarantees the steady-state performance and dynamic response of the ACHMI system. With this design method, the dual-loop current control and PLL can be taken into account simultaneously when analyzing the stability margin of the ACHMI. By using matlab software with simulink and simpower system toolbox design and analysis of an grid connected single phase asymmetrical multilevel inverter with improved power quality features.