A High and Low Frequency Hybrid Modular Multilevel Converter for Output Performance Optimization and Its Control Strategy
Hou Yuchao1, Guo Qi1, Tu Chunming1, Wang Xin1, Wang Ying2
1. National Electric Power Conversion and Control Engineering Technology Research Center Hunan University Changsha 410082 China; 2. College of Electrical Engineering Sichuan University Chengdu 610065 China
Abstract The traditional modular multilevel converter (MMC) generally adopts a single type of device. The typical Si-based MMC (Si-MMC) has low cost, while SiC-based MMC (SiC-MMC) has high efficiency. In addition, under the same specifications, the price of SiC MOSFET devices is usually 5~8 times that of Si IGBT devices. It is difficult to effectively balance the output performance, cost, and efficiency of the medium voltage MMC. This paper proposes a new MMC (NMMC) topology. Each arm of the proposed NMMC contains a high-frequency sub-module featuring a heterogeneous cross-connect module (HCCM) and a low-frequency sub-module composed of N-1 half-bridge converters. The high-frequency bridge arm of HCCM adopts SiC MOSFET devices, while the commutation bridge arm and low-frequency sub-module adopt Si IGBT devices. Firstly, the NMMC topology employs a high-low frequency hybrid modulation strategy, providing low switching loss of SiC MOSFET devices and low on-state loss of Si IGBT devices. Secondly, the energy fluctuation mechanism and working state of the high-frequency sub-module in different modes are analyzed. A specific capacitor voltage balancing strategy is proposed for the high-frequency sub-module, and a detailed voltage balancing control flow chart is given. Simulation and experiments are carried out to verify the proposed topology, modulation strategy, and voltage balancing strategy. The proposed structure achieves 2N+1 levels. Its high-frequency switching action is mainly concentrated in SiC MOSFET devices, while Si IGBT devices work in the low-frequency state. The total loss at different equivalent switching frequencies and output power is analyzed on the Matlab/Simulink and PLECS joint simulation platform. Taking the rated load power of 1.5 MW and the equivalent switching frequency of feq= 20 kHz as an example, the total loss of the proposed NMMC is 37.5%, lower than that of Si-MMC and close to that of SiC-MMC. The proposed topology is 80% lower cost than the Si-MMC and 51.8% lower than the SiC-MMC. The following conclusions can be drawn: (1) The NMMC topology outputs 2N+1 levels with only one high-frequency sub-module per arm, reducing the number of SiC MOSFET devices and overall device cost. (2) The high-frequency action primarily involves SiC MOSFET devices, while the low-frequency action of Si IGBT devices is adopted. Under high equivalent switching frequency and output power, the operation efficiency of the proposed scheme is significantly enhanced. (3) The energy fluctuation mechanism of the high-frequency sub-module DC capacitor is analyzed, and a specific voltage balance strategy is proposed, which can effectively maintain the stability of the high and low-frequency sub-module capacitor voltage.
Hou Yuchao,Guo Qi,Tu Chunming等. A High and Low Frequency Hybrid Modular Multilevel Converter for Output Performance Optimization and Its Control Strategy[J]. Transactions of China Electrotechnical Society, 2024, 39(14): 4467-4479.
[1] 束洪春, 邵宗学, 江耀曦, 等. 具备闭锁和非闭锁模式抑制直流故障电流的新型模块化多电平变换器拓扑[J]. 电工技术学报, 2022, 37(21): 5526-5540. Shu Hongchun, Shao Zongxue, Jiang Yaoxi, et al.A new modular multilevel converter topology with capability of DC faults clearing under blocking and non-blocking mode[J]. Transactions of China Elec-trotechnical Society, 2022, 37(21): 5526-5540. [2] 任鹏, 涂春鸣, 侯玉超, 等. 基于Si和SiC器件的混合型级联多电平变换器及其调控优化方法[J]. 电工技术学报, 2023, 38(18): 5017-5028. Ren Peng, Tu Chunming, Hou Yuchao, et al.Research on a hybrid cascaded multilevel converter based on Si and SiC device and its control optimization method[J]. Transactions of China Electrotechnical Society, 2023, 38(18): 5017-5028. [3] 刘计龙, 陈鹏, 肖飞, 等. 面向舰船综合电力系统的10 kV/2 MW模块化多电平双向直流变换器控制策略[J]. 电工技术学报, 2023, 38(4): 983-997. Liu Jilong, Chen Peng, Xiao Fei, et al.Control strategy of 10 kV/2 MW modular multilevel bidi-rectional DC-DC converter for vessel integrated power system[J]. Transactions of China Electrotech-nical Society, 2023, 38(4): 983-997. [4] 江畅, 程启明, 马信乔, 等. 不平衡电网电压下基于模块化多电平变流器的统一电能质量调节器的微分平坦控制[J]. 电工技术学报, 2021, 36(16): 3410-3421. Jiang Chang, Cheng Qiming, Ma Xinqiao, et al.Differential flat control for unified power quality controller based on modular multilevel converter under unbalanced grid voltage[J]. Transactions of China Electrotechnical Society, 2021, 36(16): 3410-3421. [5] 武鸿, 王跃, 薛英林, 等. 适用多功率的最近电平调制下MMC子模块开路故障诊断策略[J]. 电工技术学报, 2024, 39(1): 233-245, 302. Wu Hong, Wang Yue, Xue Yinglin, et al.A diagnosis strategy for open-circuit submodule faults in MMCs under nearst level modulation suitable for different powers[J]. Transactions of China Electrotechnical Society, 2024, 39(1): 233-245, 302. [6] 公铮, 张海军, 戴鹏, 等. 新型并联交错型多电平变换器的桥臂统一脉宽调制策略[J]. 中国电机工程学报, 2018, 38(23): 7026-7034, 7136. Gong Zheng, Zhang Haijun, Dai Peng, et al.Leg-unified pulse width modulation strategy for novel parallel interleaved multilevel converters[J]. Pro-ceedings of the CSEE, 2018, 38(23): 7026-7034, 7136. [7] 刘浩然, 陈武, 舒良才, 等. 一种新型串联单链式模块化多电平变换器[J]. 中国电机工程学报, 2023, 43(21): 8444-8456. Liu Haoran, Chen Wu, Shu Liangcai, et al.A novel series single chain-link modular multilevel con-verter[J]. Proceedings of the CSEE, 2023, 43(21): 8444-8456. [8] 杜舒, 赵成勇, 冯谟可, 等. 用于全直流海上风电系统的单相混合型MMC直流变压器及其控制策略[J]. 高电压技术, 2023, 49(1): 51-60. Du Shu, Zhao Chengyong, Feng Moke, et al.Single-phase hybrid MMC DC transformer and its control strategy for all-DC offshore wind power system[J]. High Voltage Engineering, 2023, 49(1): 51-60. [9] 张国荣, 颜丽花. 单极倍频CPS-SPWM传输带宽的研究[J]. 电力系统保护与控制, 2018, 46(12): 1-8. Zhang Guorong, Yan Lihua.Study on the trans-mission bandwidth of unipolar frequency doubled CPS-SPWM[J]. Power System Protection and Control, 2018, 46(12): 1-8. [10] Li Zixin, Wang Ping, Zhu Haibin, et al.An improved pulse width modulation method for chopper-cell-based modular multilevel converters[J]. IEEE Transa-ctions on Power Electronics, 2012, 27(8): 3472-3481. [11] 魏承志, 练睿, 杨桦, 等. 一种混合型模块化多电平换流器的改进载波移相调制方法[J]. 电力系统自动化, 2016, 40(7): 68-73, 106. Wei Chengzhi, Lian Rui, Yang Hua, et al.An improved phase shifted carrier modulating method for hybrid modular multilevel converter[J]. Automation of Electric Power Systems, 2016, 40(7): 68-73, 106. [12] Hu Pengfei, Jiang Daozhuo.A level-increased nearest level modulation method for modular multilevel converters[J]. IEEE Transactions on Power Elec-tronics, 2015, 30(4): 1836-1842. [13] Wu Deliang, Peng Li.Characteristics of nearest level modulation method with circulating current control for modular multilevel converter[J]. IET Power Electronics, 2016, 9(2): 155-164. [14] 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. [15] Wang Zhen, Peng Li, Zhang Jiawei.Decomposed nearest level PWM method with reduced switching frequency for MMC[J]. IEEE Transactions on Power Electronics, 2023, 38(3): 3340-3351. [16] 任鹏, 涂春鸣, 侯玉超, 等. 考虑异质器件混用与输出电平倍增的混合型MMC及其调控方法[J]. 电力系统自动化, 2024, 48(5): 128-136. Ren Peng, Tu Chunming, Hou Yuchao, et al.Hybrid modular multilevel converter considering hetero-neous device mixing and output level doubling and its regulation method[J]. Automation of Electric Power Systems, 2024, 48(5): 128-136. [17] 缪惠宇, 梅军, 张宸宇, 等. 一种新型的n+1混合式模块化多电平换流器拓扑结构及其控制策略[J]. 电力自动化设备, 2018, 38(3): 88-95. Miao Huiyu, Mei Jun, Zhang Chenyu, et al.A novel topology of n+1 hybrid modular multilevel converter and its control strategy[J]. Electric Power Automation Equipment, 2018, 38(3): 88-95. [18] Shahane R, Belkhode S, Shukla A, et al.A highly efficient hybrid devices-based MMC with a novel modulation scheme using hardware-in-loop system[C]// 022 IEEE Applied Power Electronics Conference and Exposition (APEC), Houston, TX, USA, 2022: 675-680. [19] Li Chushan, Lu Rui, Li Chengmin, et al.Space vector modulation for SiC and Si hybrid ANPC converter in medium-voltage high-speed drive system[J]. IEEE Transactions on Power Electronics, 2020, 35(4): 3390-3401. [20] Liu Chuang, Zhuang Kehao, Pei Zhongchen, et al.Hybrid SiC-Si DC-AC topology: SHEPWM Si-IGBT master unit handling high power integrated with partial-power SiC-MOSFET slave unit improving performance[J]. IEEE Transactions on Power Elec-tronics, 2022, 37(3): 3085-3098. [21] Zhang Chao, Wang Jun, Qu Kun, et al.WBG and Si hybrid half-bridge power processing toward optimal efficiency, power quality, and cost tradeoff[J]. IEEE Transactions on Power Electronics, 2022, 37(6): 6844-6856 [22] Yin Tianxiang, Lin Lei, Xu Chen, et al.A hybrid modular multilevel converter comprising SiC MOSFET and Si IGBT with its specialized modulation and voltage balancing scheme[J]. IEEE Transactions on Industrial Electronics, 2022, 69(11): 11272-11282.
2024, Vol. 39 
