Power Electronic Converters in DC Microgrid

Abstract

There are not many sustainable sources of energy other than renewable energy sources (RES), which are called solar, wind, water and various forms of biomass. The most effective way to increase the use of renewable energy sources is to make use of renewable energy systems in villages, townships or small island-shaped districts where there are significant amounts of energy consumers. For this reason, the microgrid (MG) idea of small power system which is controllable, autonomous and balanced has been developed. Microgrids (MGs) playing a role of carrier for distributed generation resources (DGR), includes different distributed generation (DG) units, storage devices, energy converters, protection devices and load control devices. A MG generally includes renewable small power sources consisting of interconnected distributed energy sources with capacity of providing sufficient and sustained energy for a significant portion of the load. Different architecture types of MGs are presented in the literature. In recent years, the use of MGs being able to operate in two different modes depending on the island and grid-connected, has been expanded for DGR integration. Direct current (DC) microgrid has become an important subject of study in recent years as they have a more reliable and lower losses. A DC MG task distributes the DC power required by loads on a campus. Power generation in DC MG systems can be AC or DC; however, in most cases AC power supplies is converted to DC for distribution. The major advantage of DC microgrids when compared to AC systems is its property of unidirectional power flow. This allows power control to be easily controlled by the power flow direction. In DC MG, the loads must be controllable to keep all loads at the DC range of the voltage in the default range and to regulate the voltage regulation. Besides voltage level and voltage regulation, the voltage ripple ratio should be kept as low as possible in DC microgrids. Therefore, power electronic converters are the most important part of the DC MG systems. There are although many studies published on MGs that control strategy and power electronic circuits make their important portions. It is obvious that the development of power electronic circuits and control methods has further enhanced the applicability of microgrids. In this study, the types, circuit structures and functions of power electronic converters used in DC microgrid are discussed. Power electronics converters used in DC MGs are grouped and evaluated according to their targets. These power electronic converters have been detailed in terms of AC-DC rectifiers, inverters (for AC loads) and DC-DC converter circuit types. The simulation results of some topologies have been evaluated.