Angle stability enhancement of off-grid microgrids based on model predictive control

To compensate for the lack of inertia and damping, virtual synchronous generator (VSG) control which mimic the synchronous generator (SG) is applied to converters of distributed generation. The synchronous operation of SG and multi-VSG are more likely not be maintained after a large disturbance due to the difference of frequency regulation for the VSG and SG. The rotor motion equations of SG and VSG combination as well as multi-VSG combination are established based on the VSG common reference frame. On this basis, the angle stability of an off-grid microgrid is analyzed and the impact of the controlled current source model of energy storage system (ESS) on transient stability is investigated. A model predictive control (MPC) method using ESS is proposed to enhance the angle stability of the off-gird microgrid. By establishing the prediction model of angle difference, angular frequency difference, and ESS output power and designing the cost function to minimize angle and angular frequency difference and variations of reference power as control variables, the reference active and reactive power can be optimized and then transmit to ESS. The simulation results validate the effectiveness of the proposed MPC method using ESS to enhance the angle stability of off-grid microgrid after large disturbances in the system.