This paper presents a control strategy for an islanded medium voltage microgrid to coordinate hybrid power source (HPS) units and to control interfaced multilevel inverters under unbalanced and nonlinear load conditions. The proposed HPS systems are connected to the loads through a cascaded H-bridge (CHB) multilevel inverter. The CHB multilevel inverters increase the output voltage level and enhance power quality. The HPS employs fuel cell (FC) and photovoltaic sources as the main and supercapacitors as the complementary power sources. Fast transient response, high performance, high power density, and low FC fuel consumption are the main advantages of the proposed HPS system. The proposed control strategy consists of a power management unit for the HPS system and a voltage controller for the CHB multilevel inverter. Each distributed generation unit employs a multiproportional resonant controller to regulate the buses voltages even when the loads are unbalanced and/or nonlinear. Digital time-domain simulation studies are carried out in the PSCAD/EMTDC environment to verify the performance of the overall proposed control system.
MICROGRIDS aim to provide a solution to reform the conventional power system toward a new concept for future energy distribution systems. A microgrid plays a key role for renewable energy integration and energy management capability improvement. The increasing use of medium voltage (MV) microgrid demands more reliable components and advanced control strategies –. A microgrid may inherently be subjected to significant degrees of unbalanced conditions due to the presence of singlephase loads and/or distributed generation (DG) units. Moreover, the inclusion of nonlinear loads in an islanded microgrid leads to various power quality problems, e.g., distortion of voltage and current. Nevertheless, a microgrid should be able to operate under unbalanced and nonlinear load conditions while complying with the existing standards, e.g., IEEE Std 141 and 519 .Based on the IEEE standards , , the voltage unbalance factor (VUF) and the voltage total harmonic distortion (THD) should be maintained within 2% and 5%, respectively, in a distribution