A Self-Regulated Virtual Impedance control of VSG in a microgrid

In this paper, a self-regulated virtual impedance (SRVI) control of virtual synchronous generator (VSG) is proposed. In the modern power system, large penetration of inverter-interfaced distributed generator (DG) decreases the equivalent inertia of the grid. The system, therefore, becomes more prone to frequency instability, and the fault current limits are reduced due to inverter power ratings. The VSG control of the inverter is used to maintain and enhance the transient stability of the system by introducing virtual inertia in it. In the proposed control, the SRVI control block is added in VSG control to further improve the damping and to limit the fault current during overloads and/or faults. The virtual impedance in the SRVI block is regulated as a function of the rate of change of root mean square (RMS) value of DG current during the transient case. The design of virtual impedance for the proposed control is also discussed in this paper. To see the effectiveness of the proposed technique, electromagnetic transient (EMT) simulation is performed using a real-time digital simulator (RTDS) for disturbances that result in large frequency deviations. The simulation results show that the proposed scheme outperforms the conventional VSG control.