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.

Automated summary

The lack of inertia and damping in converters of distributed generation can be compensated by the virtual synchronous generator (VSG) control, which mimics the synchronous generator (SG). However, the frequency regulation differences between VSG and SG may cause the synchronous operation of SG and multi-VSG to be disrupted after a large disturbance. This study establishes the rotor motion equations for the combinations of SG and VSG, as well as multi-VSG, based on the VSG common reference frame. The angle stability of an off-grid microgrid is analyzed, and the influence of the controlled current source model of the 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-grid microgrid, and simulation results confirm its effectiveness.