Secondary Voltage Control in a Hybrid Microgrid

Compared to individual DC or AC microgrids, the Hybrid microgrids (HMGs) are more efficient and inexpensive due to eliminating of multiple DC-AC-DC conversions. In HMGs, where AC loads are supplied by DC link, load demand disturbance has direct negative effects on the DC link voltage. In this study, primary and secondary controllers are applied to realize suitable operation conditions and control the microgrid converters. Each converter has primary controller to compensate the demand power fluctuations. The secondary controller is also designed for extra demand varieties and sends the proper control signals for primary controllers. The expressed capability of primary controllers can be obtained by designing a simple and robust secondary controller. Hence, the effects of demand fluctuations are eliminated and the system is stabilized. The overall state space model of system is conducted for stability analysis. To demonstrate the proposed controller efficiency, a prototype HMG is modeled and simulated. The stability analysis reveals that the system is stable when the secondary controller tracks the error signal of DC link. Simulation results show that the proposed method could efficiently manage the AC side voltage under load fluctuations.