Frequency Control and Unbalances Compensation in Autonomous Micro-Grids Supplied by RES

Abstract

This paper deals with the unbalances compensation in autonomous micro-grids, supplied by renewable energy sources (RES). The study focuses on generating units with rated powers around tens of kilowatts. In isolated low-power micro-grids, which feed three-phase and single-phase loads, unbalanced currents appear. These currents will produce unequal voltage drops on all three phases, and as a result, unbalanced voltages will appear. The analyzed micro-grid contains a synchronous generator (SG) and an induction one (IG). Constant speed hydraulic turbines drive both generators. The SG is Y connected, with neutral available, while the IG is Y connected. In a stand-alone micro-grid, the frequency control is a main concern. At any moment, the power balance in the system must be achieved, by continuously matching the power supplied by the generators with the consumed one. In order to solve the above-mentioned maters, a frequency regulator is used, based on a complex 3-phase dump load (DL). The goal of this paper is to use the same DL that controls the micro-grid frequency as compensator for unbalanced currents too. For the proposed configurations, simulations were performed using Matlab/Simulink environment; also, a test bench was developed in order to validate the simulation results.