A Reduced-Switching Frequency NL-PWM Method Based on Sawtooth Carrier for Medium Voltage Modular Multilevel Converter
Zhang Xueyin1, Xu Yonghai1, Li Weiguo2, Xiao Xiangning1
1. State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China; 2. State Key Laboratory of Advanced Power Transmission Technology Global Energy Interconnection Research Institute Beijing 102211 China
Abstract：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.
张雪垠, 徐永海, 李卫国, 肖湘宁. 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[J]. 电工技术学报, 2020, 35(8): 1716-1727.
Zhang Xueyin, Xu Yonghai, Li Weiguo, Xiao Xiangning. A Reduced-Switching Frequency NL-PWM Method Based on Sawtooth Carrier for Medium Voltage Modular Multilevel Converter. Transactions of China Electrotechnical Society, 2020, 35(8): 1716-1727.
[1] Lesnicar A, Marquardt R.An innovative modular multilevel converter topology suitable for a wide power range[C]//IEEE Power Technology Conference, Bologna, Italy, 2003: 1-6. [2] 尹太元, 王跃, 段国朝, 等. 基于零直流电压控制的混合型MMC-HVDC直流短路故障穿越策略[J]. 电工技术学报, 2019, 34(增刊1): 343-351. Yin Taiyuan, Wang Yue, Duan Guochao, et al.Zero DC voltage control based DC fault ride-through strategy for hybrid modular multilevel converter in HVDC[J]. Transactions of China Electrotechnical Society, 2019, 34(S1): 343-351. [3] 王一凡, 赵成勇, 郭春义. 双馈风电场孤岛经模块化多电平换流器直流输电并网系统小信号稳定性分析与振荡抑制方法[J]. 电工技术学报, 2019, 34(10): 2116-2129. Wang Yifan, Zhao Chengyong, Guo Chunyi.Small signal stability and oscillation suppression method for islanded double fed induction generator-based wind farm integrated by modular multilevel converter based HVDC system[J]. Transactions of China Electrotechnical Society, 2019, 34(10): 2116-2129. [4] 李子欣, 王平, 楚遵方, 等. 面向中高压智能配电网的电力电子变压器研究[J]. 电网技术, 2013, 37(9): 2592-2601. Li Zixin, Wang Ping, Chu Zunfang, et al.Research on medium- and high-voltage smart distribution grid oriented power electronic transformer[J]. Power System Technology, 2013, 37(9): 2592-2601. [5] Briz F, López M, Rodríguez A, et al.MMC based SST[C]//IEEE 13th International Conference on Industrial Informatics (INDIN), Cambridge, 2015: 1591-1598. [6] Pacheco J, Honório D, Oliveira D.An AC-DC isolated MMC-based structure suitable for MV SST traction applications[J]. IEEE Access, 2019, 7: 106395-106406. [7] Jing L, Xu Cai, Molinas M.Optimal design of controller parameters for improving the stability of MMC-HVDC for wind farm integration[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2018, 6(1): 40-53. [8] 赵争鸣, 冯高辉, 袁立强, 等. 电能路由器的发展及其关键技术[J]. 中国电机工程学报, 2017, 37(13): 3823-3834. Zhao Zhengming, Feng Gaohui, Yuan Liqiang, et al.The development and key technologies of electric energy router[J]. Proceedings of the CSEE, 2017, 37(13): 3823-3834. [9] Hu Pengfei, Jiang Daozhuo.A level-increased nearest level modulation method for modular multilevel converters[J]. IEEE Transactions on Power Electro- nics, 2015, 30(4): 1836-1842. [10] Wang Kun, Deng Yan, Peng Hao, et al.An improved CPS-PWM scheme-based voltage balancing strategy for MMC with fundamental frequency sorting algorithm[J]. IEEE Transactions on Industrial Elec- tronics, 2019, 66(3): 2387-2397. [11] 白志红, 周玉虎. 模块化多电平换流器的载波层叠脉宽调制策略分析与改进[J]. 电力系统自动化, 2018, 42(21): 139-144. Bai Zhihong, Zhou Yuhu.Analysis and improvement on carrier level-shifted pulse width modulation strategy for modular multilevel converter[J]. Auto- mation of Electric Power Systems, 2018, 42(21): 139-144. [12] Deng Yi, Wang Yebin, Teo K H, et al.Optimized control of the modular multilevel converter based on space vector modulation[J]. IEEE Transactions on Power Electronics, 2018, 33(7): 5697-5711. [13] Wang Yi, Hu Can, Ding Ruoyu, et al.A nearest level PWM method for the MMC in DC distribution grids[J]. IEEE Transactions on Power Electronics, 2018, 33(11): 9209-9218. [14] Choi J, Han B, Kim H.New scheme of phase-shifted carrier PWM for modular multilevel converter with redundancy submodules[J]. IEEE Transactions on Power Delivery, 2016, 31(1): 407-409. [15] Tariq M, Meraj M, Azeem A, et al.Evaluation of level-shifted and phase-shifted PWM schemes for seven level single-phase packed U cell inverter[J]. CPSS Transactions on Power Electronics and Applications, 2018, 3(3): 232-242. [16] Deng Yi, Harley R G.Space-vector versus nearest- level pulse width modulation for multilevel con- verters[J]. IEEE Transactions on Power Electronics, 2015, 30(6): 2962-2974. [17] Lin Lei, Lin Yizhe, He Zhen, et al.Improved nearest-level modulation for a modular multilevel converter with a lower submodule number[J]. IEEE Transactions on Power Electronics, 2016, 31(8): 5369-5377. [18] 苟锐锋, 赵方舟, 肖国春, 等. 基于修正优化归并排序的MMC电容均压策略[J]. 中国电机工程学报, 2017, 37(1): 251-261. Gou Ruifeng, Zhao Fangzhou, Xiao Guochun, et al.A capacitor voltage balancing strategy for MMC based on optimized merge sort[J]. Proceedings of the CSEE, 2017, 37(1): 251-261. [19] Li Yufei, Wang Yue, Li Q Ben.Generalized theory of phase-shifted carrier PWM for cascaded H-bridge converters and modular multilevel converters[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2016, 4(2): 589-605. [20] Hagiwara M, Maeda R, Akagi H.Control and analysis of the modular multilevel cascade converter based on double-star chopper-cells (MMCC-DSCC)[J]. IEEE Transactions on Power Electronics, 2011, 26(6): 1649-1658. [21] 李敏裕, 马晓军, 魏曙光, 等. 三电平虚拟空间矢量脉宽调制算法窄脉冲抑制研究[J]. 电工技术学报, 2018, 33(14): 3264-3273. Li Minyu, Ma Xiaojun, Wei Shuguang, et al.Research on narrow pulse suppression of three-level virtual space vector pulse width modulation algorithm[J]. Transactions of China Electrotechnical Society, 2018, 33(14): 3264-3273.
2020, Vol. 35 
