Decentralized control approach for voltage unbalance compensation in islanded microgrid

Microgrid as an effective complement to large power grid and also as an important achievement of construct smart grid has been widely developed. It is important to enhance the power quality in the island Microgrids (MGs). The voltage and frequency of the microgrid are determined by the Voltage Source Inverters (VSIs); therefore the power quality can be deteriorated under unbalanced and non-linear loads. In this paper, a decentralized control approach for voltage unbalance compensation is proposed, which includes primary and secondary control levels. The primary level comprises distributed generators (DGs) local controllers. The local controllers mainly consist of power droop control loop, voltage and current control loop, and virtual impedance control loop. Also in the secondary control level, the decentralized secondary controller is designed to remove the deviations of voltage unbalance compensation at the Point of Common Coupling (PCC). Each unit is independently controlled and the entire system of controllers is connected by communication network. So the secondary controller to exchange information each other through the network, which sending appropriate control signals to local controller, which avoids the use of a single centralized controller for the secondary level. Comparing to the centralized control system, the proposed method reduces the requirements of communication links bandwidth and be easy to expand. The control system design is discussed in detail. The simulation results show that the PCC voltage unbalance is compensated to the desired value, while active and reactive powers are shared properly.