Decoupled frequency and voltage control for stand-alone microgrid with high renewable penetration

In South Korea, the stand-alone microgrid on an island has synchronous diesel generators and multiple distributed generations (DG) based on renewable energy, and energy storage systems (ESS). According to the active policy of government to develop eco-friendly microgrids with zero carbon emission, many diesel generators in stand-alone microgrids are being replaced by the DGs. It brings challenges on the operation and control of multiple DGs because this causes the lack of inertia, which is originally provided from the diesel generators. This paper proposes a new decoupled frequency and voltage controller for DGs, which is able to keep the grid frequency and voltage magnitude constant. For frequency control, a frequency recovery control loop is newly added to conventional droop and inertia control loops for both effective power sharing and stabilization of frequency response after a disturbance. For voltage control, the proposed controller regulates the grid voltage in an inertia-free mode, in which all diesel generators are disconnected, while providing the conventional reactive power-voltage droop control under a normal condition. Moreover, the adaptive power sharing strategy is newly proposed to avoid the overcharge/discharge conditions of ESSs. As the result, the proposed controller can enhance the resilience and increase the penetration of renewable energies to the stand-alone microgrid. To verify the effectiveness of proposed controller, several case studies are being carried out by using the practical data of a real stand-alone microgrid in South Korea.