A Comprehensive Strategy for Power Quality Improvement of Multi-Inverter-Based Microgrid With Mixed Loads

In order to solve the influence of nonlinear and unbalanced mixed loads on output voltage of microsource inverters in microgrid, this paper proposes a comprehensive strategy which can be used to accurate power distribution, harmonic suppression, negative-sequence voltage component suppression, and stability improvement. On one hand, a fundamental control strategy is proposed upon the conventional droop control; the problem of accurate reactive power distribution is solved by introducing virtual impedance to inverters, while considering the aggravating problem of stability because of introducing virtual impedance, a secondary power balance controller is added to improve the stability of voltage and frequency. On the other hand, the fractional frequency harmonic control strategy and negative-sequence voltage control strategy are proposed to solve the influence of mixed loads, which focus on eliminating specific harmonics caused by the nonlinear loads and the negative sequence component of the voltage. The power quality of microgrid can be improved effectively. Finally, small signal analysis is used to analyze the stability of the multiconverter parallel system after introducing the whole control strategy. The simulation results show that the strategy proposed in this paper has a great performance on distributing reactive power, regulating and eliminating harmonic components, eliminating negative-sequence components and stabilizing output voltage of inverters and frequency, and improving the power quality of multiinverter-based microgrid.