A Decentralized Secondary Frequency Control Method for Maintaining Regulation Margin in Islanded Microgrids

Existing decentralized secondary frequency control methods can be mainly classified into two categories from the perspective of the actual regulation effect of the droop curve: intercept adjustment methods and slope adjustment methods. As the name implies, the intercept adjustment method restores system frequency by adjusting the intercept of the droop curve, which reduces the regulation margin of the distributed generators' primary control in responding to subsequent load disturbances. On the other hand, the slope adjustment method restores system frequency by adjusting the slope of the droop curve. When the load power increases, the regulation margin of the primary control can be maintained unchanged by adopting this method. However, when the load power decreases, using this method will still reduce the regulation margin of the primary control. The decrease in regulation margin can adversely affect system stability and reliability. To address this issue, this paper proposes a novel decentralized secondary frequency control method. In the proposed approach, only the slope is adjusted when the load demand increases, while both the intercept and slope are adjusted when the load demand decreases. As a result, the regulation margin of primary control can be preserved under any load variation conditions. In addition, this paper establishes a synchronized adjustment mechanism and further investigates the case of consecutive application of the proposed method. The stability of the proposed method is analyzed, and its feasibility is verified through simulations and hardware experiments.