Research On An Improved Power Decoupling Control Strategy Based On Virtual Impedance

Because of the issues of resources and the environment, renewable energy power generation, such as photovoltaic, wind power and etc., has attracted increasing attention. And the microgrid is an independent and controllable system formed by energy storage devices, loads and renewable energy sources with interfacing inverters to the microgrid, which plays an important role in power transformation. The droop control is widely employed when multiple inverters operate in parallel. However, due to inconsistent line impedance and the local load, there exists power circulation when the droop control is adopted, thereby reducing the efficiency of the system. In addition, there is a coupling between the active power and reactive power with the conventional droop control, which affects the stability of the system. Though the traditional power decoupling control is able to realize power decoupling, the actual real power and reactive power can not be shared equally.To deal with the power sharing and power coupling problem, this paper explicitly analyzes the causes of the power sharing error and power coupling with the traditional droop control respectively, quantizes the power sharing error and the extent of power coupling, and also gives the basic solution to reducing the power sharing error and solving the problem of power coupling. Besides, three basic principles to reduce the power sharing error and their relationships are derived. To solve the inaccurate power sharing problem of the traditional power decoupling control, this paper presents an improved power decoupling control strategy with five impedance angles based on the virtual impedance. The five methods proposed in this paper are compared based on system frequency and PCC voltage. By adding the virtual impedance, these schemes can not only decouple the active and reactive power, but also achieve accurate power sharing. Small signal analysis proves the stability of the proposed power decoupling control strategy.Finally, the proposed method is verified by simulation, and also validated on the experimental platform of two paralleling inverters. The simulation and experiment results verify the accuracy and effectiveness of the proposed power control scheme.