直流电压不均衡的级联H桥多电平变频器载波移相PWM调制策略的设计

Design for Phase-shifted Carrier Pulse Width Modulation of Cascaded H-bridge Multi-level Inverters with Non-equal DC Voltages

对于级联H桥多电平变频器,单元独立直流电源的参数差异及故障等多种因素均会导致各单元的直流电压不均衡。单元直流电压不均衡时,传统载波移相(PSC)PWM调制策略无法消除电压的低频边带谐波,导致变频器输出的电能质量明显降低。对单元载波相位、直流电压与变频器输出电压谐波的关系进行了研究,提出了按照单元直流电压调整单元载波相位的策略。该调制策略能够消除变频器输出电压的低频边带谐波,提高电能质量,增强变频器的容错能力。仿真与样机实验结果验证了所提出的调制策略的效果。

In practice, many factors result in non-equal cell DC voltages of the cascaded H-bridge multilevel（ CHBML） inverter,such as the differences amongthe DC sources of the H-bridge cells and the faults of the DC sources. The classical phase-shifted carrier（ PSC） pulse width modulation（ PWM） is unable to eliminate the low-frequency sideband-harmonics when the DC voltages of the cells are not equal. The quality of the output voltage degrades. In this paper,the relationship among the cell carrier-phases,the DC voltages,and the harmonics of the output voltage are analyzed. And then,a novel PSCPWM method,in which the carrier phases are regulated according to the different DC voltages,is proposed. This method improves the quality of the output power by eliminating the low-frequency sideband harmonics,and also enhances the fault-tolerance capability of the inverters. The simulation and experimental results obtained from the prototype of the CHBML inverter verify the suggested regulation strategy.