Active DC Voltage Balancing PWM Technique for High-Power Cascaded Multilevel Converters
Multilevel power electronic converter has wide range of applications. In multilevel power electronic converters the output can be synthesized by combining several DC voltage sources. Cascade H-Bridge multilevel inverter generally requires more number of DC sources. An alternative option is to replace all the DC sources feeding H-Bridge cells with capacitors, leaving only one H-Bridge cell with a real DC sources.This Project presents a dedicated PWM technique specifically designed for single-phase and four wire three-phase multilevel Cascaded H-Bridge Converters is presented. The aim of the proposed technique is to minimize the DC-Link voltage unbalance, independently from the amplitude of the DC-Link voltage reference, and compensate the switching device voltage drops and on-state resistances. Such compensation can be used to achieve an increase in the waveform quality of the converter. This is particularly useful in high-power, low supply voltage applications where a low switching frequency is used. The DC-Link voltage balancing capability of the method removes the requirement for additional control loops to actively balance the DC-Link voltage on each H-Bridge, simplifying the control structure.