Study Of Dynamic Voltage Restorer Based On Hybrid Cascaded Multilevel Inverter

Low voltage switching devices can be applied in high voltage and high capacity system by using cascade multilevel technology. When this technology is used in Dynamic Voltage Restorer (DVR), the voltage level, capacity and output voltage harmonic characteristics of the DVR can be improved.Based on the method of generating multilevel topology and analysis of the traditional H-bridge cascaded topology, a new hybrid cascaded multilevel inverter topology called2H-2H+is proposed. The new topology needs fewer switching devices and no clamping diodes or clamping capacitors, which simplifies the complex circuit structure of the conventional multilevel inverter. The structure and work principle of the topology are analyzed in details. Analysis of a hybrid modulation technique for the topology is illustrated. According to the control technique, the switching losses can be reduced effectively, and the output voltage spectrum of the inverter is improved. Based on the analysis of the transformerless DVR structure, the new topology is used as the inverter circuits of a single phase transformerless DVR. The effect of voltage sag compensation is verified by Matlab/Simulink in different conditions. Analysis and simulation show that the topology improves the DVR’s capacity, reduces the switching loss and improves the output voltage harmonic characteristics.Based on the analysis and simulation, a single phase hybrid cascade multilevel DVR prototype is built up, which includes software and hardware. The hardware includes control board based on ARM and FPGA, modulation circuit, drive circuit and inverter circuit. The voltage sag compensation experiment results are given under different work conditions, which prove that, the DVR prototype has a good load adaptability, the voltage of the load can keep stability, and the output voltage harmonic characteristics has been improved.