A hybrid converter for medium voltage using a low-voltage current source active filter connected via a series capacitor

This paper proposes a new three phase hybrid inverter topology suitable for medium to high voltage inverter applications. The topology shown in Fig. 1 consists of a 3-phase VSI rated at medium voltage acting as a main inverter bridge processing the bulk power whilst being connected in parallel to a CSI acting as an active filter to cancel out the switching current ripple produced by the VSI. The CSI is connected via a series capacitor which minimises the voltage stress to only a small fraction of the fundamental grid voltage via a control approach shown in the paper. Therefore, the added installed power of the CSI is less than 4% of the main inverter bridge which should account for a small added cost. As a result, the hybrid topology allows for optimal device utilization to achieve high output current quality with minimal device ratings and potentially improved efficiency. The control of the CSI is independent to the main inverter bridge which means that the auxiliary converter solution can be retrofitted to existing medium voltage installations for power quality improvement.