Power Sharing in Hybrid Microgrids Using a Harmonic-Based Multidimensional Droop

Droop-based control strategies are generally used in hybrid microgrids (HMGs) for voltage and frequency regulation in the dc and ac microgrids (MGs). The control of interlinking converters (ICs) that connect ac and dc MGs plays a vital role in the stability and efficiency of HMGs. However, conventional P-V droops for the dc side may not be effective due to line resistances and local nature of voltage. Also, conventional Q-V droops for the ac side may result in circulating power and current among parallel ICs diminishing their performance. In this paper, dc voltage harmonic frequencies are employed to create a global variable in the dc side of HMGs and to introduce an efficient droop control strategy for the dc MG without deteriorating power quality. Accordingly, accurate active power sharing is achieved and circulating power is eliminated. In addition, a three-dimensional (3-D) droop is suggested for voltage control at the ac MG using virtual impedances. Thus, proper reactive power sharing is accomplished among parallel ICs, while circulating currents are suppressed as well. The optimal gains of the 3-D droop are determined via an optimization problem. The efficacy of the proposed method is evaluated by examining it on a typical HMG in different situations.