Harmonic Mitigation in Grid Connected and Islanded Microgrid Via Adaptive Virtual Impedance

In an effort to overcome the economic and ecological challenges posed by conventional sources of energy, renewable energy based sources have come a long way. However, reliable and efficient commissioning of renewable energy sources in microgrids still have issues to be addressed. Power quality, power sharing and stability are the key issues in microgrids due to presence of power converters and non-linear loads. To improve power quality, harmonic compensation techniques have been used in past, but these are single objective control techniques and make the system complex and inefficient. zDroop control based control techniques have been adapted to improve power sharing, but again it is dependent on line impedance and seamless power sharing is not achieved due to mismatch. In this paper, a novel method of mitigating harmonics and improving power sharing has been implemented which also takes care of load dynamics. Capacitive virtual impedance has been implemented which improves harmonic current sharing, and offers decoupled control of active and reactive power. The capacitive virtual resistance have been implemented in the form of proportional resonant (PR) controllers which have added advantages over PI controller. Further, the resistance part in the capacitive virtual impedance has been made adaptive in nature, taking load dynamics into consideration. Simulation results have been provided to validate the proposed concept in both grid connected and islanded mode.