An SVPWM Modulation Algorithm For Voltage Equalization In Cascaded NPC H-Bridge Single-Phase Converter

Cascaded multilevel converter has been used to all kinds of high voltage power converters, due to its advantages of being easy to expand and simple control. The balance and stability of dc-side voltages are the important conditions for its regular work, whitch can be achieved by the modulation algorithm and hardware equalizing circuits. Compred to Single-phase SPWM modulation algorithm, the SVPWM modulation algorithm possess stronger ability to balance the dc-side voltage. For the more, it has the advantages of lower costs and less power loss in contrast with hardware equalizing circuits.Firstly, structure and operation principle of single-phase cascaded NPC H-bridge inverter is analyzed. For the dc-side voltage imbalance causes and types, appropriate voltage balancing strategy is adopted. The traditional space vector modulation algorithm is introduced in this article and excellent simulation and experimental results are obtained.Secondly, an SVPWM modulation is proposed to solve the problem of DC voltage imbalance in the single-phase cascaded neutral-point-clamped H-bridge inverter. To avoid the harm of module port voltage level-skip, the transition states are introduced in the redundant vector selection process, which makes current vector gradually switching to the vector with the strongest voltage balance ability, and reduce the switching frequency of the converter.The selection method of the optimal transition is present. The simulation and experimental results are given in the fourth chapter.Finally, all control algorithms are designed by the Verilog hardware description language and realized on FPGA, including the SVPWM algorithm and the transient current control. Experiments for one module to three module of Cascaded NPC H-bridge single-phase converter are completed and good experimental effects are achieved.