Seamless Mode Transition Technique for Virtual Synchronous Generators and Method Thereof

This article deals with a method for seamless transition of three-phase virtual synchronous generator, switched between off-grid and grid-interfaced modes and vice-versa. The proposed control strategy achieves two-fold advantages. First, it eliminates the need for synchronizing tools such as phase-locked-loops, and separate islanding detection techniques during unintentional islanding events; the controller is so formulated to adapt automatically during mode transitions, by inheriting synchronization and islanding detection tasks within itself. As a result, the controller does not require any control reconfiguration during mode transitions, unlike the conventional control methods. Second, it eliminates multiple feedback loops and the need for rigorous tuning of proportional-integral regulators in practical systems. In this method, only the inverter current and voltage sensors are used, and the control over grid-side static transfer switch is not mandatory. The mathematical formulation of the controller is depicted and the closed-loop stability of the system is analyzed using Eigen value stability analysis. The effectiveness of the control strategy is demonstrated through simulations and comparative analysis with the state-of-art control methods. Experimental results validate the performance of the system under different operating conditions.