Modeling a Switching-Regulated Capacitively Coupled Power Supply for Medium-Voltage AC

The use of capacitive coupling has the potential of reducing the size and cost in the implementation of auxiliary power supplies. This is particularly advantageous in applications with medium-voltage (MV) ac feeders, where this arrangement can avert the use of a high-voltage transformer. The current standard for voltage control in this type of power supply is shunt regulation. This scheme maintains a low dc bus voltage, which increases the current demand through the input capacitors and, hence, decreases the power factor (PF). Switching regulation allows operation at a relatively high intermediate dc bus voltage that can improve the PF, in addition to providing galvanic isolation and achieving higher efficiencies. However, this type of regulation has not been thoroughly explored in the literature of capacitively coupled power supplies. This article presents a novel mathematical model to describe high-frequency switching dc-to-dc regulation in a power supply capacitively coupled to an MV input. The model is used in a case study for the design of a 50-W/12-V (dc) supply fed from a 1-kV (rms)/50-Hz ac input. The results of the design validate the model and demonstrate the advantages of the novel concept.