Distribution level SiC FACTS devices with reduced DC bus capacitance for improved load capability and solar integration

FACTS devices, such as STATCOMs and UPFCs can be directly applied in the low voltage distribution system to regulate the sequence voltages within a network while simultaneously cancelling zero and negative sequence currents that are introduced by load unbalance or by high levels of distributed photovoltaic generation. Instantaneous reactive power theory shows that for FACTS devices the DC-bus capacitor power will fluctuate at twice mains frequency during unbalanced operation. High rating non-polarized bus capacitors can be applied if the double frequency fluctuations are restricted. In combination with silicon carbide devices it becomes possible to produce compact pole mounted systems. This paper proposes control methods that allow distribution level or dFACTS compensators with finite rating to best allocate its capacity to voltage, current balancing and reactive power compensation.