A Virtual Impedance Optimization Method for Reactive Power Sharing in Networked Microgrid

Unlike the typical microgrid with a common ac bus, networked microgrid always suffers more serious reactive power sharing issues due to its complex inner structure. In such case, the system reactive power sharing error cannot be easily evaluated and eliminated. So, this paper proposes a wireless control strategy that employs optimized virtual impedance controllers and local load measurements for the reactive power sharing in networked microgrid. First, from the modeling of microgrid network, an estimation method for network reactive power sharing error is derived. Through the estimation method-based network feature analyses, corresponding design for virtual impedance controller is presented. Then, by introducing genetic algorithm, virtual impedance controller parameters of each distributed generation unit are optimized, which aims to minimize the microgrid global reactive power sharing error. The parameter optimization process is performed offline in microgrid configuration stage. By using these optimized virtual impedance controllers, the reactive power sharing performance of a networked microgird can be greatly improved. Finally, the accuracy of the estimation method is validated by MATLAB simulation results, and the feasibility of the proposed virtual impedance optimization method is verified through real power experiments.

I. Introduction

With the increased concerns on environment and clean energy, more and more renewable energy sources such as photovoltaic cells, wind turbines, and microturbines are integrated into the power grid in the form of distributed generation (DG) units. These DG units are normally interfaced to the grid through power electronic converters. To effectively manage these DG units, the microgrid concept is proposed, which is considered to pave the way to the future smart grid [1]–[3]. Microgrid usually connects to the power grid through the point of common coupling (PCC); it can operate in either islanded mode or grid-connected mode. Microgrid can not only solve the problem of large scale DG coupling but also play full advantages of DG units, improve power supply reliability and bring more benefits to its users. However, microgrid also faces some challenging problems, such as control stability and power sharing issues.