A modular approach for integrating harmonic cancellation in a multi-cell based UPQC

This paper presents a three-phase unified power quality conditioner (UPQC) based on two types of power cells. Differently to topologies based on symmetrical units, the proposed topology is assembled using one type of single-phase power cells for compensating disturbances at the fundamental frequency and another type for compensating harmonic currents. This feature allows the implementation of the power cells with different types of semiconductors, so the cells that compensate at the fundamental frequency can use slower semiconductors but with higher voltage/current ratings and the power cells that compensate harmonics can use faster semiconductors but with lower voltage/current ratings. In addition, as the control objectives of the two types of cells are different, two control schemes are designed to operate independently. Particularly, power cells for harmonic compensation can dynamically adjust its own DC voltage to follow the load conditions in order to operate with maximum efficiency. Simulated preliminary results confirm the theoretical considerations.