A Broad Frequency Range Harmonic Reduction for Cascaded-Power-Cell-Based Islanded Microgrid With Lumped PCC Filter

Series connection of low-voltage power cells has been considered as an alternative microgrid configuration to supply rated voltage power to point of common coupling (PCC) loads. However, in the previous studies, the major focus was on the power regulation of system. Similar to the conventional shunt-distributed generation (DG)-unit-based islanded microgrid, the PCC voltage harmonic problem can be serious without any active control. In order to provide enhanced power quality in this system, a flexible PCC harmonic voltage compensation approach is developed via the hierarchical control of series-connected power cells. First, the selected low-order PCC harmonic voltage components are mitigated by using the closed-loop equivalent impedance shaping method, via cooperation among the PCC central and power cell local controllers. Second, the medium-range lumped output
LC
filter resonance is suppressed with the help of internal virtual impedance, which is implemented only at the power cell local controllers. Finally, the high-frequency switching ripples of PCC voltage are mitigated by phase-shifting pulsewidth modulation in distributed power cells, through exploring the output current signal of power cells as an inherent synchronizer for carrier shifting control. It has been experimentally validated that with the proposed approaches, the PCC voltage quality can be significantly improved in broad frequency range without any interferences.