A modified control strategy for seamless switching of virtual synchronous generator-based inverter using frequency, phase, and voltage regulation

The growing integration of renewable energy sources and distributed generators (DGs) significantly reduces the system inertia and damping for microgrid operation and control, thereby affecting grid stability. A virtual synchronous generator (VSG) offers a promising solution to enhance power system stability by emulating the behavior of synchronous generators (SGs). A new modified control strategy for seamless switching is introduced in this study for the VSG inverter during the transition from off-grid to on-grid mode. The operation of the VSG inverter has been proposed for both islanding and grid-connected modes. To reduce the impact of inrush current during synchronization, a new modified pre-synchronization process based on voltage and frequency compensating signals has been proposed. A detailed stability analysis is also conducted for the VSG controller to verify the effectiveness of the proposed approach. A model with particular consideration of seamless switching is developed and analyzed in islanding and grid-connected modes with and without the pre-synchronization process. The proposed modified control strategy has been simulated in MATLAB and the results demonstrate an improved frequency transient response against the grid frequency perturbations along with fast presynchronization-based switching from islanding to grid-connected modes. The proposed approach efficiently addresses instantaneous inrush current during synchronization, successfully reducing it from 120A to its nominal value. Furthermore, the proposed pre-synchronization technique has been compared with other traditional methods, highlighting its superiority in terms of active power, reactive power, and frequency stability. This research indicates the efficacy of the control approach in enabling seamless and smooth switching of the VSG inverter from off-grid to on-grid modes.