Series-connected Mixed-switching-frequency Power Cells Featuring an Islanded Microgrid with Enhanced Power Quality Control

In this paper, an islanded microgrid is developed using series-connected mixed switching frequency power cells. The system consists of a few low switching frequency (LSF) power cells in a simple fixed modulation index operation manner to reduce the switching loss and the computational load of the control system. The reference voltages of LSF power cells are obtained from a frequency inverse power factor droop controller to get proper power sharing between power cells without any communications. Meanwhile, a high switching frequency (HSF) power cell with a floating DC bus can effectively absorb the harmonics from these LSF power cells. The HSF power cell also behaves as an inherent harmonic virtual impedance to mitigate the islanded microgrid’s resonance and provide an accurate point of common coupling (PCC) voltage magnitude restoration. With the help of this HSF power cell, various types of power quality issues of the cascaded power cells based on the islanded microgrid can be solved without any interference with the power-sharing among LSF power cells.