混合级联十一电平逆变器功率与开关损耗双均衡倍频调制方法

Frequency-doubling Modulation Method for Hybrid Cascaded Eleven-level Inverter Power Equalization

混合级联多电平逆变器可以利用较少的开关器件实现较高电平输出,进而得到了广泛应用;但实现高低压单元间功率均衡难度更大。直流侧采用电池组模块进行供电时,功率达不到均衡会使得各H桥单元对应的电池组模块处于不同的放电特性,增大了故障概率和维修难度且增加了后期的维修成本。针对此问题,提出2种1:1:1:2混合级联十一电平逆变器功率和开关损耗双均衡倍频调制方法。首先,2种方法分别对3个低压单元采用三角载波、重构载波进行移相,从而实现在全调制度范围内将逆变器的等效开关频率由fc提高至6fc/12fc;使得低压单元各开关器件开关次数均围绕在60次/174次左右上下浮动,实现了低压单元内开关损耗均衡;使得调制度M=0.9/0.6/0.3时低压单元输出功率均围绕在657.5 W/293.5 W/73.5 W上下浮动,实现低压单元间的功率均衡,其次对高压单元采用阶梯波低频调制,随调制度的变化对导通角进行动态调整,使得高压单元各开关器件开关次数均为1次,实现了高低压单元内开关损耗均衡;使得调制度M=0.9/0.6/0.3时高压单元与低压单元输出功率均围绕在1317 W/657.5 W、586 W/293.5 W、146.5 W/73.5 W上下浮动,实现了高低压单元间功率均衡,之后对比分析2种方法各自的优缺点及其适用场合。最后,通过实验验证该方法的正确性和可行性,并给出了直流电压比为1:1:1:...:x的混合级联H桥逆变器双均衡的普适方法。

Hybrid cascaded multilevel inverters can achieve higher level output with fewer switching devices and have been widely used,but they cannot achieve power balance between high-and low-voltage units.When the battery pack module is used for power supply on the DC side,if the power is not balanced,the battery pack module corresponding to each H-bridge unit will be in different discharge characteristics,which increases the failure proba-bility and maintenance difficulty and increases the maintenance cost in the later period.To solve this problem,two power equalization methods based on frequency doubling modulation are proposed.Firstly,the two methods use triangular carrier and reconstructed carrier to perform phase shift for the three low-voltage units,respectively,so as to increase the equivalent switching frequency of the inverter from fc to 6fc/12fc within the full modulation range.The switching times of each switching device in the low-voltage unit is around 60 times/174 times,and the switching loss balance in the low-voltage unit is realized.When the modulation degree M=0.9/0.6/0.3,the output power of the low-voltage unit fluctuates around 657.5 W/293.5 W/73.5 W,and the power balance between the low-voltage units is realized.Secondly,the step wave low-frequency modulation is adopted for the high voltage unit,and the conduction angle is dynamically adjusted with the change of modulation degree,so that the switching times of each switching device in the high voltage unit is 1,and the switching loss balance in the high-and low-voltage units is realized.When the modulation degree M=0.9/0.6/0.3,the output power of the high-voltage unit and the low-voltage unit fluctuates around 1317 W/657.5 W,586 W/293.5 W,and 146.5 W/73.5 W,and the power balance between the high-and low-voltage units is realized.Then,the advantages and disadvantages of the two methods and their application occasions are compared.Finally,the correctness and feasibility of the method are verified by experiments,and a general method for double equalization of cascaded H-bridge inverters with a DC voltage ratio of 1:1:1:…:x is given.