中压模块化多电平换流器降低开关频率的锯齿载波最近电平-脉宽调制方法  

A Reduced-Switching Frequency NL-PWM Method Based on Sawtooth Carrier for Medium Voltage Modular Multilevel Converter

作　　者：张雪垠 徐永海 李卫国 肖湘宁 Zhang Xueyin;Xu Yonghai;Li Weiguo;Xiao Xiangning(State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University,Beijing 102206 China;State Key Laboratory of Advanced Power Transmission Technology Global Energy Interconnection Research Institute Beijing,102211 China)

机构地区：[1]新能源电力系统国家重点实验室(华北电力大学),北京102206 [2]先进输电技术国家重点实验室(全球能源互联网研究院),北京102211

出　　处：《电工技术学报》2020年第8期1716-1727,共12页Transactions of China Electrotechnical Society

基　　金：北京市自然科学基金项目(3172036);新能源电力系统国家重点实验室(华北电力大学)自主研究课题(LAPS2019-20)资助。

摘　　要：最近电平-脉宽调制(NL-PWM)适用于中压模块化多电平换流器(MMC),较最近电平调制(NLM)可大幅减少谐波电流。NL-PWM通过电压排序实现桥臂子模块均压,均压切换设置在阶梯波跳变点,可减少额外的开关切换,但也限制了均压频率,影响了均压效果。PWM开关频率较高,在其开关点进行均压切换可大幅提高均压频率。现有NL-PWM方法基于三角载波,其开关点随参考电压变化,不便于均压控制的实施。该文提出非倍频和倍频的基于锯齿载波的NL-PWM方法,锯齿载波具有固定的跳变点便于均压控制。分析了所提调制的谐波特性,研究表明,采用倍频锯齿载波NL-PWM方法可在降低开关频率的同时保证良好的均压效果与输出电能质量。此外,所提调制亦可避免功率开关的窄脉冲。仿真与实验研究验证了理论分析的正确性。The nearest level pulse width modulation(NL-PWM)is suitable for the medium voltage modular multilevel converters(MMCs),which can greatly reduce the current distortion compared with the nearest level modulation(NLM).The NL-PWM achieves bridge-arm sub-module voltage balancing by the sorting algorithm.The implementation of the voltage-balancing rotating at each edge of the stair wave can reduce extra switching,but it also limits the balancing frequency and consequently affects the balancing effect.Since the switching frequency of PWM is relatively high,conducting the voltage-balancing rotating at the edges of PWM wave can greatly increase the balancing frequency.The state-of-the-art NL-PWM is based on triangle carrier,and its switching point varies with the reference voltage,which is not convenient for the implementation of the voltage-balancing control.In this paper,a non-frequency-doubling and a frequency-doubling NL-PWM methods based on sawtooth-carrier are proposed.The sawtooth wave has fixed edges to facilitate the voltage-balancing control.The hormonic characteristics of the proposed modulations are analyzed.It is shown that the frequency-doubling sawtooth-carrier based NL-PWM method can ensure both good voltage-balancing effect and output power quality while reducing the switching frequency.Besides,the proposed modulation can also avoid narrow pulse of power switches.Simulation and experiments verify the correctness of the theoretical analysis.

关 键 词：中压模块化多电平换流器 最近电平-脉宽调制 锯齿载波 开关频率 窄脉冲 

分 类 号：TM46[电气工程—电器]