An Improved Minor Loop Gain Criterion and Stability Estimation for Multi-Inverters Paralleled System

Abstract

With the increasing popularity of new energy integration, the parallel operation of multiple inverters in power systems has become commonplace. Traditional theories and methods for analyzing power system stability face challenges in high-proportion new energy systems. Additionally, existing inverter analysis methods are inadequate for directly addressing multi-inverters paralleled system, resulting in unclear instability mechanisms and uncertain operational stability. To tackle these issues, this paper focuses on systems with multiple parallel LCL-type inverters and proposes an improved minor loop gain criterion (IMLG). Unlike traditional impedance ratio criteria, this improved criterion fully integrates considerations such as inverter capacity, short-circuit ratio, and other pertinent factors affecting system stability. Furthermore, treating each inverter as a subsystem by equivalent the grid conductance to the inverter side, this criterion accurately identifies the primary inverter responsible for system instability. Finally, case and experimental studies are employed to verify the correctness of the theoretical analysis and demonstrate the effectiveness of the improved stability criterion.