Using Smart Impedance to Transform High Impedance Microgrid in a Quasi-Infinite Busbar

Isolated microgrids, due to the high values of the output converter impedances, suffer power quality problems, such as harmonic distortion and resonances. These impedances are normally the LCL output filter needed to suppress the switching ripple of the converters. As complex impedances, they are dependent on the frequency, therefore very sensitive to harmonic content of load current. This leads to a significant microgrid voltage distortion which results in undesirable power quality levels. Hybrid active power filters are a reasonable choice for harmonic compensation allowing good filtering performance at reduced cost. This paper describes the use of Smart Impedance, which is a new application of a hybrid active power filter, to change the microgrid bus impedance forcing it to behave as a quasi-infinite bus, without increasing active power capacity of the microgrid. The implementation can improve microgrid power quality by mitigating harmonic currents and harmonic voltage resonance. It allows connecting more nonlinear load in the bus keeping the microgrid voltage quality. Experimental results are presented to demonstrate the effectiveness of the proposed approach.