Hardware-in-the-Loop Methods for Stability Analysis of Multiple Parallel Inverters in Three-Phase AC Systems

Abstract

Modern electric distribution systems typically contain several feedback-controlled parallel inverters that together form a complex power distribution system. Consequently, a number of issues related to stability arise due to interactions among multiple inverter subsystems. Recent studies have presented methods where the stability and other dynamic characteristics of a paralleled inverter system can be effectively analyzed using impedance measurements. This paper presents implementation techniques for a comprehensive online stability analysis of grid-connected paralleled inverters using power hardware-in-the-loop measurements based on an OPAL-RT real-time simulator. The analysis is based on simultaneous online measurements of current control loop gains of the inverters and the grid impedance, and aggregated terminal admittance measurements of the inverters. The analysis includes the measurement of the inverters’ aggregated output impedance, inverters’ loop gains, global minor loop gain, and grid impedance. The presented methods make it possible to rapidly evaluate the system on both global and local level in real time, thereby providing means for online stability monitoring or adaptive control of such systems. Experimental measurements are shown from a high-power energy distribution system recently developed at DNV GL, Arnhem, Netherlands.