Sector Reconfiguration Virtual Space Vector Pulse Width Modulation and Neutral Point Balance Strategy of NPC Inverter in Medium and High Modulation Depth
Hu Hanlin, Zhao Mi, Huang Yi, Yan Haichao, Lu Min
School of Mechanical and Electrical Engineering Shihezi University Shihezi 832003 China
Abstract：As a typical multilevel inverter, a neutral point clamped (NPC) three-level inverter is suitable for large-capacity and high-voltage converters, which can effectively reduce current harmonic content. However, the NPC three-level inverter has the problem of neutral point voltage imbalance due to the structural characteristics of capacitive voltage division. The traditional virtual space-vector pulse width modulation (VSVPWM) has limited ability to suppress neutral point voltage fluctuation. Correcting its offset is challenging, especially in the medium and high modulation depths. Therefore, this paper proposes a sector reconfiguration VSVPWM. By introducing equivalent medium vectors and reconstructing sectors in medium and high modulation depths, small and medium vectors can fully participate in neutral point balance adjustment while retaining fixed sector division. This method can effectively suppress the neutral point voltage fluctuation and accelerate the recovery of the neutral point offset. There is only one balance coefficient for each fixed sector, which is easy to implement. Firstly, the equivalent relationship between a large vector and a medium vector is analyzed. An equivalent medium vector with constant amplitude is then constructed. The equivalent medium vector can participate in the neutral point balance by adjusting the proportion of medium and large vectors. After that, a virtual vector group, including equivalent medium vectors, is constructed. Furthermore, an equivalent medium vector VSVPWM (EMV-VSVPWM) is proposed, which improves the neutral point adjustment ability in the sector with a medium vector. Secondly, the level of modulation depth is divided based on the operational sector position, and the neutral point margin of the EMV-VSVPWM strategy depths is analyzed in one modulation period. It is found that the regions with weaker capacity of neutral point balance exist in high modulation depth. Therefore, a sector reconstruction VSVPWM (SR-VSVPWM) is then designed. The sector boundary and vector selection boundary in the medium and high modulation depths are separated to increase the proportion of small and medium vectors in such regions, which can enhance the neutral point adjustment margin. Furthermore, the neutral point balance coefficient of small and medium vectors is unified to reduce the computational complexity. Meanwhile, the vector sequence is optimized according to the principle of constant switching state, and the switching loss is reduced. The initial neutral point voltage offset and modulation depth experiments are carried out on a hardware experimental platform in the loop. The results indicate that the SR-VSVPWM strategy can achieve the fast balance of the middle point in pure resistor load and resistor-inductance load conditions. Compared with the traditional VSVPWM single small vector adjustment, the neutral point voltage offset is eliminated, and the balance time in the high modulation depth is reduced by about 46%. In addition, the current harmonics are also reduced. When the experiment on variable modulation depth is considered, SR-VSVPWM still exhibits strong suppression of neutral point fluctuations and good current quality in high modulation depth. After the switching frequency is reduced to 5 kHz, the neutral point fluctuation level of SR-VSVPWM is 79.1% of the traditional VSVPWM.
胡瀚林, 赵咪, 黄毅, 闫海超, 鲁敏. 中高调制度下NPC逆变器扇区重构型虚拟空间矢量脉宽调制及中点平衡策略[J]. 电工技术学报, 2025, 40(8): 2573-2586.
Hu Hanlin, Zhao Mi, Huang Yi, Yan Haichao, Lu Min. Sector Reconfiguration Virtual Space Vector Pulse Width Modulation and Neutral Point Balance Strategy of NPC Inverter in Medium and High Modulation Depth. Transactions of China Electrotechnical Society, 2025, 40(8): 2573-2586.
[1] 董志强, 王琛琛, 周明磊, 等. 基于SHEPWM的三电平三相逆变器中点电位主动平衡控制策略[J]. 电工技术学报, 2024, 39(4): 1147-1158. Dong Zhiqiang, Wang Chenchen, Zhou Minglei, et al.Active neutral-point voltage balance control strategy for three-level three-phase inverter under SHEPWM[J]. Transactions of China Electrotechnical Society, 2024, 39(4): 1147-1158. [2] 陈兮, 黄声华, 李炳璋, 等. 一种零序注入的三电平中点钳位型变换器中点电位平衡控制策略[J]. 电工技术学报, 2019, 34(2): 337-348. Chen Xi, Huang Shenghua, Li Bingzhang, et al.A novel zero sequence injection scheme for three-level NPC converters considering neutral-point potential balance[J]. Transactions of China Electrotechnical Society, 2019, 34(2): 337-348. [3] 张志, 陈浩辉, 陈思哲, 等. 一种基于ghγ 坐标系的三电平四桥臂逆变器简化空间矢量脉宽调制方法[J]. 电工技术学报, 2023, 38(16): 4324-4338. Zhang Zhi, Chen Haohui, Chen Sizhe, et al.A simplified space vector pulse width modulation method based on ghγ coordinates system for the three-level four-leg inverter[J]. Transactions of China Electrotechnical Society, 2023, 38(16): 4324-4338. [4] 夏帅, 郑京港, 陈瑞成, 等. 低共模电压双三电平变换器中点电位主动控制调制策略[J]. 电工技术学报, 2022, 37(24): 6388-6398. Xia Shuai, Zheng Jinggang, Chen Ruicheng, et al.Low common mode voltage strategy with active neutral point voltage control of dual three level converters[J]. Transactions of China Electrotechnical Society, 2022, 37(24): 6388-6398. [5] 高瞻, 李耀华, 葛琼璇, 等. 适用于大功率三电平中点钳位整流器的SVPWM和DPWM策略研究[J]. 电工技术学报, 2020, 35(23): 4864-4876. Gao Zhan, Li Yaohua, Ge Qiongxuan, et al.Research on SVPWM and DPWM strategies suitable for high power three-level neutral point clamped rectifier[J]. Transactions of China Electrotechnical Society, 2020, 35(23): 4864-4876. [6] 王金平, 翟飞, 姜卫东, 等. 一种全范围内中点电压平衡的中点钳位型三电平变换器的扩展非连续脉宽调制策略[J]. 中国电机工程学报, 2019, 39(6): 1770-1782, 1873. Wang Jinping, Zhai Fei, Jiang Weidong, et al.An extended DPWM for neutral point clamped three-level converter with a full range of neutral point voltage balance[J]. Proceedings of the CSEE, 2019, 39(6): 1770-1782, 1873. [7] 孙青松, 吴学智, 唐芬. 考虑中点电位平衡的三电平逆变器断续脉宽调制策略研究[J]. 中国电机工程学报, 2017, 37(增刊1): 177-185. Sun Qingsong, Wu Xuezhi, Tang Fen.Three-level inverter discontinuous pulse-width modulation strategy considering neutral point potential balance[J]. Proceedings of the CSEE, 2017, 37(S1): 177-185. [8] 陈仲, 许亚明, 那显龙. 基于中点电流的三电平NPC逆变器电容电压均衡控制分析[J]. 中国电机工程学报, 2016, 36(19): 5308-5317, 5413. Chen Zhong, Xu Yaming, Na Xianlong.Analysis of a new voltage balance method for three-level NPC inverters based on neutral-point current[J]. Pro-ceedings of the CSEE, 2016, 36(19): 5308-5317, 5413. [9] 李宁, 王跃, 蒋应伟, 等. 三电平NPC变流器虚拟空间矢量调制策略与载波调制策略的内在关系研究[J]. 电网技术, 2014, 38(1): 166-174. Li Ning, Wang Yue, Jiang Yingwei, et al.Research on internal relation between virtual space vector pulse width modulation strategy and carrier sinusoidal pulse width modulation strategy for three-level neutral point clamped converter[J]. Power System Tech-nology, 2014, 38(1): 166-174. [10] He Yingjie, Lei Chao, Liu Yunfeng, et al.Research on the equivalent virtual space vector modulation output of diode clamped N-level converter under multi-modulation carrier modulation[J]. Energies, 2020, 13(15): 1-18. [11] 王金平, 刘斌, 董浩, 等. 中点钳位型三电平逆变器基于调制波分解的调制策略[J]. 电工技术学报, 2023, 38(12): 3221-3233. Wang Jinping, Liu Bin, Dong Hao, et al.A modulation strategy based on modulation wave decomposition for neutral point clamped three-level inverter[J]. Transactions of China Electrotechnical Society, 2023, 38(12): 3221-3233. [12] Guo Feng, Yang Tao, Bozhko S, et al.3L-NPC AC-DC power converter using virtual space vector PWM with optimal switching sequence based on g-h coordinate[C]//2018 IEEE International Conference on Electrical Systems for Aircraft, Railway, Ship Propulsion and Road Vehicles & International Trans-portation Electrification Conference (ESARS-ITEC), Nottingham, UK, 2018: 1-7. [13] Wu Xiang, Tan Guojun, Ye Zongbin, et al.Virtual-space-vector PWM for a three-level neutral-point-clamped inverter with unbalanced DC-links[J]. IEEE Transactions on Power Electronics, 2018, 33(3): 2630-2642. [14] Jiang Weidong, Wang Peidong, Ma Mingna, et al.A novel virtual space vector modulation with reduced common-mode voltage and eliminated neutral point voltage oscillation for neutral point clamped three-level inverter[J]. IEEE Transactions on Industrial Electronics, 2020, 67(2): 884-894. [15] Ma Zhixun, Niu Haichuan, Wu Xiang, et al.An improved overmodulation strategy for a three-level NPC inverter considering neutral-point voltage balance and common-mode voltage suppression[J]. Sustainability, 2022, 14(19): 1-16. [16] Dong Lei, Zang Zetian, Ming Yuanshan, et al.Research on the coordination suppression strategy of neutral point potential and common mode voltage for NPC three-level inverter[J]. Symmetry, 2022, 15(1): 35. [17] Fan Bo, Fu Zhumu, Fu Jiangtao, et al.Midpoint potential compensation balance control method based on virtual space vector pulse-width modulation for NPC three-level inverter[J]. International Transa-ctions on Electrical Energy Systems, 2019, 29(9): 1-17. [18] Guo Feng, Yang Tao, Li Chen, et al.Active modulation strategy for capacitor voltage balancing of three-level neutral-point-clamped converters in high-speed drives[J]. IEEE Transactions on Industrial Electronics, 2022, 69(3): 2276-2287. [19] 向超群, 陈春阳, 韩丁, 等. 中点电位不平衡度反馈的三电平虚拟空间矢量调制方法[J]. 电机与控制学报, 2018, 22(3): 50-58. Xiang Chaoqun, Chen Chunyang, Han Ding, et al.VSVPWM for NPC three-level inverter with neutral point potential unbalance degree feedback[J]. Electric Machines and Control, 2018, 22(3): 50-58. [20] Fan Bo, Cao Zhe, Wang Chunguang, et al.A novel neutral-point potential balance control method based on voltage feedback for neutral-point clamped three-level inverter[J]. International Journal of Electrical Power & Energy Systems, 2023, 145: 108583. [21] Xiang Chaoqun, Shu Cheng, Han Ding, et al.Improved virtual space vector modulation for three-level neutral-point-clamped converter with feedback of neutral-point voltage[J]. IEEE Transactions on Power Electronics, 2018, 33(6): 5452-5464. [22] 桂石翁, 吴芳, 万山明, 等. 变虚拟空间矢量的三电平NPC变换器中点电位平衡控制策略[J]. 中国电机工程学报, 2015, 35(19): 5013-5021. Gui Shiweng, Wu Fang, Wan Shanming, et al.A strategy for considering neutral-point potential balance for three-level NPC inverters with the varied virtual space vector[J]. Proceedings of the CSEE, 2015, 35(19): 5013-5021. [23] Yuan Qingqing, Li An, Qian Jinyue, et al.DC-link capacitor voltage control for the NPC three-level inverter with a newly MPC-based virtual vector modulation[J]. IET Power Electronics, 2020, 13(5): 1093-1102. [24] 周冠卿, 张国荣, 解润生, 等. 改进的三电平逆变器变虚拟空间矢量调制策略[J]. 电力系统自动化, 2023, 47(1): 172-182. Zhou Guanqing, Zhang Guorong, Xie Runsheng, et al.Improved variable virtual-space-vector modulation strategy for three-level inverter[J]. Automation of Electric Power Systems, 2023, 47(1): 172-182. [25] 杨清, 黄景涛, 关海平, 等. 高调制深度下三电平NPC逆变器中点电位快速均衡控制[J/OL]. 电源学报, 2023, https://kns.cnki.net/kcms2/detail/12.1420.TM.20230524.1732.004.html. Yang Qing, Huang Jingtao, Guan Haiping, et al. Fast neutral point potential balancing of three-level NPC inverter under high modulation depth[J/OL]. Journal of Power Supply, 2023, https://kns.cnki.net/kcms2detail/12.1420.TM.20230524.1732.004.html. [26] Xia Shuai, Wu Xiaojie, Zheng Jinggang, et al.A virtual space vector PWM with active neutral point voltage control and common mode voltage suppression for three-level NPC converters[J]. IEEE Transactions on Industrial Electronics, 2021, 68(12): 11761-11771.
2025, Vol. 40 
