Improving the grid power quality using virtual synchronous machines

This paper presents the improvement of power quality and grid stability for distributed generation using the virtual synchronous machine (VISMA) which embodies a hysteresis controlled three phase inverter with a synchronous machine model on an embedded control computer to calculate the reference currents. Currently the conventional grid-connected inverters are predominantly designed to transmit electrical energy to the grid discounting the maintenance of frequency and voltage and also its transient stability. However, the VISMA is able to regulate both the active and reactive power separately and bidirectionally by setting the virtual torque and virtual excitation to meet the power system requirements. Furthermore, a virtual rotating mass is implemented in the VISMA in order to increase the inertia in the grid and improve the transient frequency stability in analogy to the conventional synchronous generator. Additionally, the virtual damping of the VISMA can reduce the frequency and power oscillation in the grid. All these properties mentioned above have been verified in simulations and measurements in an experimental micro grid.