Secondary Control Scheme for Voltage Unbalance Compensation in an Islanded Droop-Controlled Microgrid

TLDR: The results show the effectiveness of the proposed control structure in compensating the voltage unbalance in an islanded microgrid.

Abstract: The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme 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, voltage and current controllers, and virtual impedance control loop. The central secondary controller is designed to manage the compensation of voltage unbalance at the point of common coupling (PCC) in an islanded microgrid. Unbalance compensation is achieved by sending proper control signals to the DGs local controllers. The design procedure of the control system is discussed in detail and the simulation results are presented. The results show the effectiveness of the proposed control structure in compensating the voltage unbalance.

Figures

Fig. 11. Bode diagrams of oZ − (red dashed line), 1Z (black dashed line) and 2Z (solid line).

Fig. 1. Power stage and hierarchical control scheme.

TABLE II CONTROL SYSTEM PARAMETERS

TABLE I POWER STAGE PARAMETERS

Fig. 10. Equivalent circuit for calculation of negative sequence current. (a) Basic circuit according to symmetrical component theory (b) Equivalent circuit for α-component in a two-DG microgrid

Fig. 3. Schematic diagram of DG local controller.

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The concept of microgrid hierarchical control is presented recently. In this paper, a hierarchical scheme is proposed which includes primary and secondary control levels.