Harmonic Virtual Impedance Design for Optimal Management of Power Quality in Microgrids

Power quality is an important concern for practical microgrid (MG) applications due to the widespread use of nonlinear loads, and it is characterized by the implicit trade-off between voltage quality in the MG nodes and harmonic current sharing between distributed generators (DGs). Active and passive filters can be used to address this problem. Nevertheless, modification of the control system of the DGs represents a cheaper and more practical solution. To this end, virtual impedances (VIs) can be included in the controller. However, the power quality trade-off is difficult to adjust, especially in the presence of electrical distribution lines. In this article, an optimization algorithm for setting the harmonic VIs of the DGs in a multibus MG is presented. This optimization algorithm can be easily configured for any degree of harmonic current sharing between the DGs, while improving the voltage quality is set as the main objective. Compared to other works presented in the literature, power quality can be managed without relying on time-critical communications since only the values of the harmonic VIs are modified in the optimization problem. The optimization is executed periodically so that the VIs are adapted to changes in the grid. Theoretical developments were validated by simulation in a benchmark model, and in a laboratory environment.