混合级联H桥低压单元功率均衡策略

Low Voltage Cell Power Equalization Strategy of Hybrid Cascaded H-bridge

目的三单元直流侧电压比为1∶1∶2型的混合级联H桥逆变器,在采用传统调制策略下,虽能够输出较好的电能质量,但逆变器低压单元在全调制度下会存在输出功率不均衡的问题,基于此,提出一种新型调制策略。方法基于传统的混合频率调制策略,首先对低压单元第二层载波进行重构,并利用重构后的载波特性为低压单元提供逻辑信号;其次通过对两个低压单元的脉冲信号进行逻辑运算控制,以获得低压单元功率开关器件的实际驱动信号,实现对低压单元脉冲信号的重新分配;为减少逆变器高压模块的开关损耗,对高压单元采用阶梯波调制方法。结果仿真结果表明:新型混合调制策略可以解决逆变器在全调制度下低压单元输出功率不均衡的问题,并且通过实验验证了新型调制策略可使低压单元输出功率达到近似1∶1的效果;仿真分析表明:采用新型调制策略的逆变器总谐波畸变率(Total Harmonic Distortion,THD)值有所降低。结论新型调制策略能够减少载波数目,均衡开关损耗,并且在保留传统混合频率调制优势的基础上,降低逆变器的THD含量,提高逆变器的电能输出质量,同时在两个载波周期内解决了低压单元全调制下输出功率不均衡的问题。

Objective For the hybrid cascaded H-bridge inverter with a voltage ratio of 1∶1∶2 on the DC side of the three-unit,the inverter can output better power quality under the traditional modulation strategy.However,the low-voltage unit of the inverter will have the problem of unbalanced output power under the full degree of modulation.Based on this,a new hybrid modulation strategy was proposed.Methods Firstly,based on the traditional hybrid frequency modulation strategy,the second layer carrier of the low-voltage unit was reconstructed and the reconstructed carrier characteristics were used to provide the logic signal for the low-voltage unit.Secondly,by logically operating and controlling the pulse signals of the two low-voltage units,the actual driving signal of the low-voltage unit power switching device was obtained,and the pulse signal of the low-voltage unit was redistributed.In order to reduce the switching losses in the high voltage module of the inverter,the step wave modulation method was used for the high voltage unit.Results The simulation results show that the new hybrid modulation strategy can solve the problem of unbalanced output power of the low-voltage unit of the inverter under the full degree of modulation system.It was verified that the new modulation strategy can achieve an approximate 1∶1 output power of the low-voltage unit through experiments.The simulation analysis showed that the value of total harmonic distortion(THD)of inverters using the new modulation strategy was reduced.Conclusion The new modulation strategy can reduce the number of carriers and balance the switching losses.In addition,while retaining the advantages of traditional mixed frequency modulation,it reduces the THD content of the inverter and improves the power output quality of the inverter.At the same time,the problem of unbalanced output power under a full degree of modulation of the low-voltage unit is solved in two carrier cycles.