Operational principle and control of the nine-switch converter for unified power quality conditioner

For dealing with the shortcomings of the unified power quality conditioner including considerable amount of power electronic devices and its complex structure, the paper proposes to replace the back-to-back double PWM converter with the nine-switch converter as the main circuit topology. Nine-switch converter has some advantages such as less switching devices, lower cost, smaller volume and etc. Firstly, the paper introduces the principle and modulation strategy of the nine-switch converter. Secondly, it analyzes steady-state circuit in the case of the voltage sag compensation and reveals the relationship between terminal voltage of the voltage and current compensation ports. According to the above analysis results, the occupancy ratio of the DC voltage can be dynamically allocated between the two output ports to effectively reduce the DC voltage requirement of the system. Then it gives a brief description of the control algorithms of the proposed topology. Finally, the paper verifies the feasibility of the proposed alternatives through simulation and experiment.