Auto-synchronization of LC filter based front-end converter with parallel inverters based weak distorted island grid using voltage injection

Front-end inverters are predominantly used as an interface in distributed generation. This paper addresses the synchronization aspect while connecting an incoming front-end inverter to parallel inverters based weak island grid. Difference between grid voltage and incoming inverter output voltage is injected to the voltage reference to minimize the voltage difference between grid and incoming inverter during hot-swap. It is shown that with the proposed voltage injection scheme, it is possible to tailor the output impedance of inverter to increase the stability of high penetration distributed generation systems. The emulated impedance also reduces the inrush currents. The effect of proposed voltage injection loop on hot-swap performance and system stability is analyzed along with the evaluation of current sharing performance among paralleled inverters. The design and realizability of the auto-synchronization scheme is validated with comprehensive experimental results of hot-swap event with nonlinear load condition, using two 110 Vac/2.5 kVA three phase inverters, paralleled to form a standalone grid.