Operation of islanded microgrid at constant frequency with distributed grid-supporting generators

Abstract

This paper presents a new method for operating microgrid. Basic control methodology is to de-couple PQ control for grid-forming distributed generator (DG) whose new extra role is to act as reactive power sensor besides generating real power into the microgrid. Reactive power from the grid-forming DG is transferred to and from the instantaneous var compensator when there is a switch-in or switch-off of inductive load. By doing so, accurate control of real power becomes feasible so long its reactive power output is kept at low value. Generations of real power reference of both grid-forming and grid-supporting DGs are based on voltage variation at their terminals, so they don't need instruction from energy management center and are de-centralized. A multiplying factor is introduced to expedite such real-time real power reference generation to cope with fast switch-in and switch-off of large loads. Each of grid-forming and grid-feeding DGs performs within their respective generation capability. The system steady-state voltages can be maintained almost at rated value. The system operates at constant 50Hz. The proposed method is validated using real-time modeling in SIMULINK.