Voltage and frequency control of an islanded electronically-coupled distributed generation unit

In this paper, a Linear Parameter Varying (LPV) controller is proposed for the control of an islanded Distributed Generation (DG) system. The DG unit supplies a balanced three-phase passive load through a voltage-sourced converter (VSC). The dynamic model of the islanded DG system is represented by a set of nonlinear equations. Since the objective is to regulate voltage and frequency, the system is linearized about the operating point for a wide range of load changes. It is determined that load resistance changes have the greatest innuence on system dynamics. Thus the load resistance changes are taken into consideration in the design of the LPV controller, whilst changes in inductance are considered as disturbances. For each linearized model, a simply structured multivariable control system is designed based on the Nyquist Array method. The controllers are then combined into a single LPV controller which is self-scheduled against the changing load resistance. The load resistance is estimated online using robust Least Absolute Value (LAV) regression techniques. Simulation results show that the proposed controller is robust against dynamic load changes and disturbances inferred from an active load (in a multi-DG microgrid).