Abstract：In view of the oscillated bus voltage and imbalanced current distribution caused by imbalanced load condition at vehicle to home (V2H) mode, this paper proposed a 3-phase 4-wire on-board bidirectional charger operating at V2H mode. Split DC-link capacitor is utilized with a neutral leg which provides a path for the zero-sequence current. Switches of the neutral leg are controlled to solve the problem of DC-link voltage oscillation. Firstly, the fundamental reason of the DC-link voltage oscillation under imbalance load is analyzed, and the selection guidance of DC-link capacitance for different imbalance loads is provided. A simulation model is introduced to verify the theoretical analysis. Based on the neutral leg and equivalent model of topology, a control method that is decoupled from others three phases is proposed to ensure the stability of output voltage and suppress voltage oscillation of DC-link capacitor. Meanwhile, this paper indicates the risks of system starting under V2H mode and introduces soft starting method by adjusting PWM dead time to enhance reliability of the system. Finally, the dual active bridge (DAB) is connected with 3-phase 4-wire inverter to deliver a 10kW V2H prototype. Imbalanced loads are simulated by switching resistance loads. The experimental results match the simulation results, which verifies the effectiveness of the proposed scheme.
付永升, 李静, 胡文婷, 雷鸣. 不平衡负载下车载三相四线双向充电器中线桥臂控制与软启动设计[J]. 电工技术学报, 2019, 34(24): 5176-5188.
Fu Yongsheng, Li Jing, Hu Wenting, Lei Ming. Neutral Leg Control and Soft-Start Design of 3-Phase 4-Wire on-Board Bidirectional Charger under Imbalance Load Condition. Transactions of China Electrotechnical Society, 2019, 34(24): 5176-5188.
 Wanlu Li.Electric vehicles V2H energy management and optimization system[J]. Heilongjiang Electronics Power, 2012, 34(1): 78-80.  刘文霞, 徐慧婷. 考虑电压控制成本的分布式电源优化配置[J]. 电网技术, 2016, 40(10): 2998-3005. Liu Wenxia, Xu Huiting.Optimal distributed generator allocation method considering voltage control cost[J]. Power System Technology, 2016, 40(10): 2998-3005.  Green Car Congress.Nissan to launch the “LEAF to home V2H power supply system with nichicon EV power station in June”[Online]. Available: http:// www.greencarcongress.com/2012/05/leafvsh-20120530.html.  Zhou Xiaohu.Multi-function bi-directional battery charger for plug-in hybrid electric vehicle appli- cation[C]//Energy Conversion Congress and Expo- sition (ECCE), San Jose, CA, 2009: 3930-3936.  Pinto J G, Monteiro Vitor, Goncalves Henrique.Bidirectional battery charger with grid-to-vehicle, vehicle-to-grid and vehicle-to-home technologies[C]// IEEE Industrial Electronics Society (IECON), Vienna, Austria, 2013: 5934-5939.  Guo Xiaoqiang, Li Jian, Wang Xiaoyu.Impact of grid and load disturbances on electric vehicle battery in G2V/V2G and V2H mode[C]//Energy Conversion Congress and Exposition (ECCE), Montreal, QC, Canada, 2015: 5406-5410.  张佳佳, 石东源. 分布式电源用四桥臂变换器中点电压漂移控制[J]. 电工技术学报, 2013, 28(2): 225-232. Zhang Jiajia, Shi Dongyuan.Control of neutral point voltage shift for four-leg converter in distributed generation[J]. Transactions of China Electrotechnical Society, 2013, 28(2): 225-232.  Wang Chenchen, Yi Li.Analysis and calculation of zero-sequence voltage considering neutral-point potential balancing in three-level NPC converters[J]. IEEE Transcaction Industrial Electronic, 2010, 57(7): 2262-2271  周啸, 金新民, 唐芬. 微电网孤岛工况下基于四桥臂变流器的不平衡负载分配策略[J]. 电工技术学报, 2015, 30(12): 76-86. Zhou Xiao, Jin Xinmin, Tang Fen, et al.Four-leg converter based unbalanced load sharing method in islanding microgrid[J]. Transactions of China Elec- trotechnical Society, 2015, 30(12): 76-86.  Zhang R, Boroyevich D, Prasad V H, et al.A three- phase inverter with a neutral leg with space vector modulation[C]//Applied Power Electronics Conference and Exposition (APEC), Atlanta, GA, USA, 1997: 857-863.  Li Xiangfeng, Qiu Dongyuan, Zhang Bo.Three-mode pulse-width modulation of a three-phase four-wire inverter[J]. IET Power Electronics, 2015, 8(8): 1483-1489.  Mohamed Aissani, Kamel Aliouane.Three-dimensional space vector modulation for four-leg voltages-source converters used as an active compensator[C]//Power Electronics, Electrical Drives, Automation and Motion, Pias, Italy, 2010: 1416-1421.  Lohia P, Mishra M, Karthikeyan K, et al.A minimally switched control algorithm for three-phase four-leg VSI topology to compensate unbalanced and nonlinear load[J]. IEEE Transaction Power Elec- tronics, 2015, 23(4): 1935-1944.  Wu T F, Lin L C, Chang C H, et al.Iterative learning control with filter-capacitor current compensation for a three-phase four-wire inverter[C]//Applied Power Electronics Conference and Exposition (APEC), Long, Beach, CA, 2013: 2288-2294.  Wu T F, Chou T C, Chen K H, et al.Capacitor- current compensation with fast voltage loop for D-Σ digital control based three-phase four-wire inverter[C]// In Future Energy Electronics Conference (IFEEC), Taipei, China, 2015: 1-6.  罗锐, 何英杰, 陈晖, 等. 三电平变流器中点电位平衡机低开关损耗SVPWM策略[J]. 电工技术学报, 2018, 33(14): 3245-3254. Luo Rui, He Yingjie, Chen Hui, et al.SVPWM scheme for three-level converters with neutral-point potential balancing and switching loss reduction[J]. Transactions of China Electrotechnical Society, 2018, 33(14): 3245-3254.  Zheng Liping, Dong Le.Control of a three-phase four-wire inverter[C]//IECON 2012-38th Annual Conference on IEEE Industrial Electronics Society, Montreal, QC, Canada, 2012: 316-320.  Naderipour A, Mohd Zin A A, Habibuddin M H, et al. A control scheme to improve the power quality with the absence of dedicated compensation devices in microgrid[C]//IEEE Student Conference on Research and Development (SCOReD), Kuala Lumpur, 2015: 239-244.  陈杰, 赵冰, 陈新, 等. 不平衡负载条件下三相四线制并联逆变器的下垂控制[J]. 电工技术学报, 2018, 33(20): 4790-4801. Chen Jie, Zhao Bing, Chen Xin, et al.Droop control of three-phase four-wire parallel inverters under unbalanced load condition[J]. Transactions of China Electrotechnical Society, 2018, 30(20): 4790-4801.  殷晓东, 罗登, 李祖勇, 等. 一种双向隔离DC-DC变换器二次纹波电压抑制方法[J]. 电工技术学报, 2018, 33(6): 1356-1363. Yin Xiaodong, Luo Deng, Li Zuyong, et al.A second-order ripple voltage suppression algorithm of bidirectional isolation DC-DC converter[J]. Transa- ctions of China Electrotechnical Society, 2018, 33(6): 1356-1363.  孙孝峰, 吴晓颖, 申彦峰, 等.一种全功率范围零电压开通的电流型双向隔离DC-DC变换器[J]. 电工技术学报, 2018, 33(10): 2282-2292. Sun Xiaofeng, Wu Xiaoying, Shen Yanfeng, et al.A novel current-fed bidirectional isolated DC-DC converter with full-pperating-range ZVS[J]. Transa- ctions of China Electrotechnical Society, 2018, 33(10): 2282-2292.  Zhao Wenxin, Ruan Xinbo, Yang Dongsheng, et al.Neutral point voltage ripple suppression for a three-phase four-wire inverter with an independently controlled neutral module[J]. IEEE Transaction Industrial Electronics, 2017, 64(4): 2608-2619.  陈轶涵, 郭鸿浩, 陈洁, 等. 中频三相四桥臂逆变器控制策略不平衡负载状态向量模型分析[J]. 电工技术学报, 2019, 34(9): 1912-1923. Chen Yihan, Guo Honghao, Chen Jie, et al.Analysis on control strategies for unsymmetrical state of medium frequency three phase four leg inverter based on vector model[J]. Transactions of China Electro- technical Society, 2019, 34(9): 1912-1923.  林燎源, 林钊, 刘伟, 等. 基于阻性下垂的逆变器无线并联均流控制[J]. 电工技术学报, 2016, 31(8): 43-50. Lin Liaoyuan, Lin Zhao, Liu Wei, et al.Wireless current sharing scheme for parallel operation of inverters using resistive output impedance[J]. Transactions of China Electrotechnical Society, 2016, 31(8): 43-50.  顾和荣, 王德玉, 沈虹. 三相四桥臂逆变器控制技术研究[J]. 电力系统保护与控制, 2011, 39(24): 41-46. Gu Herong, Wang Deyu, Sheng Hong.Research on control scheme of three-phase four-leg inverter[J]. Power System Protection and Control, 2011, 39(24): 41-46.  Nicolas-Apruzzese Joan, Enrique Maset, Sergio Busquets-Monge, et al.Efficiency comparison between SiC-and Si-based active neutral-point clamped converters[C]//IEEE International Conference on Industrial Technology (ICIT), Seville, Spain, 2015: 3058-3063.