A new control strategy and overload protection based on model predictive control for islanded micro-grids under unbalanced and nonlinear load conditions

In this paper, a control scheme based on model predictive control (MPC) is proposed for parallel operation of distributed generations (DGs) in an islanded Micro-Grid (MG). DGs must provide powers of their local loads and contribute to sharing the common loads. To share powers of the common loads between DGs, conventional droop controller is used. DGs' controllers operate in two control modes: V/F and P/Q control mode. In V/F mode, the proposed scheme controls voltage and frequency of DGs to track references provided by the power sharing mechanism. To enhance the transient performance of the DGs for a wide range of load conditions, output currents at the point of connection (PC) of the DGs are considered as disturbances and used as feed-forward signals. If the output power of a DG exceeds its nominal capacity, V/F mode will be changed into P/Q mode, and the proposed scheme controls injected active and reactive powers of the DG so that the output power is limited to the nominal capacity thereby protecting the DG against overloading condition. The effectiveness of the proposed scheme is demonstrated by comparison with other schemes and time-domain simulations using PSCAD/EMTDC for various load types (e.g. balanced/unbalanced, nonlinear and dynamic loads) and overload conditions.

کلیدواژه ها:

Islanded micro-grid ، model predictive control ، voltage/frequency control ، overload protection ، unbalanced and nonlinear load