Abstract The control system of the DC solid-state transformer with the input-series-output-parallel dual active bridge converters typically consists of output voltage control and input voltage sharing control. In the conventional control strategy, the loop gain characteristics of each control loop change considerably with the load and other working conditions, and the dynamic performance is ignored in the controller parameter design. This paper proposes a novel linearization control strategy to achieve the linearization of the loop models of both the output voltage control and input voltage sharing control, thereby simplifying the design of controller parameters and enhancing the adaptability of the converter. Firstly, the control command output by the PI controller of the output voltage control loop is changed from the phase shift command to a current command. A secondary-side current command is generated after the control command is superimposed with the output current. Then, the control command output by the PI controller of the input voltage sharing control loop is changed from the phase shift increment to the primary-side current increment. The method for superimposing the control commands of the two loops is changed from the phase-shift superposition to the primary-side current superposition. Finally, the phase shift ratio of each DAB is calculated based on the input current command generated by the control system, which is no longer directly output by the PI controller. In simulations, frequency sweep analyses are conducted on the output voltage control loop and input voltage sharing control loop. With the conventional control strategy, the closed-loop gain exhibits a high resonance peak with light loads. This peak disappears with heavier loads, but the bandwidth is low. In contrast, the frequency characteristics of the control loops change little with the load using the proposed linearization control strategy. An experimental prototype of a DC solid-state transformer composed of three DAB units is built. Experimental results show that under full-load conditions, the output voltage’s response speed is slow using the conventional control strategy. When the load is reduced to 10%, the overshoot significantly increases, indicating a noticeable decrease in stability. In contrast, with the proposed linearization control strategy, the output voltage’s step response waveforms under various load conditions roughly overlap, demonstrating high stability and fast response. Moreover, when switching from half-load to full-load, the voltage drop and recovery time are significantly lower than those using the conventional control strategy. The conclusions are as follows. (1) Using the conventional control strategy, the closed-loop gain's resonance frequency-domain indicators (peak, frequency bandwidth) and time-domain indicators (overshoot, rise time, and adjustment time) vary significantly with operating conditions. These dynamic performance indicators show slight variation using the proposed control strategy, facilitating the comprehensive optimization of dynamic performance. (2) The proposed control strategy enhances the suppression capability of the DC solid-state transformer against load disturbances using output current information for load compensation during the linearization process.
[1] Shao Shuai, Chen Linglin, Shan Zhenyu, et al.Modeling and advanced control of dual-active-bridge DC-DC converters: a review[J]. IEEE Transactions on Power Electronics, 2022, 37(2): 1524-1547. [2] Segaran D, Holmes D G, McGrath B P. Enhanced load step response for a bidirectional DC-DC con- verter[J]. IEEE Transactions on Power Electronics, 2013, 28(1): 371-379. [3] 侯聂, 宋文胜, 武明义. 全桥隔离DC/DC变换器的直接功率控制方法[J]. 电力系统自动化, 2016, 40(17): 204-209. Hou Nie, Song Wensheng, Wu Mingyi.Direct power control scheme of full-bridge isolated DC/DC con- verters[J]. Automation of Electric Power Systems, 2016, 40(17): 204-209. [4] 刘子薇, 孙兆龙, 刘宝龙, 等. 基于直接功率控制的双有源桥暂态直流偏置抑制策略[J]. 电工技术学报, 2023, 38(12): 3234-3247. Liu Ziwei, Sun Zhaolong, Liu Baolong, et al.Transient DC bias suppression strategy of dual active bridge based on direct power control[J]. Transactions of China Electrotechnical Society, 2023, 38(12): 3234-3247. [5] Song Wensheng, Hou Nie, Wu Mingyi.Virtual direct power control scheme of dual active bridge DC-DC converters for fast dynamic response[J]. IEEE Transa- ctions on Power Electronics, 2018, 33(2): 1750-1759. [6] Shan Zhenyu, Jatskevich J, Iu H H C, et al. Simplified load-feedforward control design for dual-active- bridge converters with current-mode modulation[J]. IEEE Journal of Emerging and Selected Topics in Power Electronics, 2018, 6(4): 2073-2085. [7] Dutta S, Hazra S, Bhattacharya S.A digital predictive current-mode controller for a single-phase high- frequency transformer-isolated dual-active bridge DC-to-DC converter[J]. IEEE Transactions on Indu- strial Electronics, 2016, 63(9): 5943-5952. [8] Ali M, Yaqoob M, Cao Lingling, et al.Disturbance- observer-based DC-bus voltage control for ripple mitigation and improved dynamic response in two- stage single-phase inverter system[J]. IEEE Transa- ctions on Industrial Electronics, 2019, 66(9): 6836-6845. [9] Wu Yuheng, Mahmud M H, Zhao Yue, et al.Uncertainty and disturbance estimator-based robust tracking control for dual-active- bridge converters[J]. IEEE Transactions on Transportation Electrification, 2020, 6(4): 1791-1800. [10] Li Kerui, Yang Yun, Tan S C, et al.Sliding- mode-based direct power control of dual-active- bridge DC-DC converters[C]//2019 IEEE Applied Power Electronics Conference and Exposition (APEC), Anaheim, CA, USA, 2019: 188-192. [11] 安峰, 宋文胜, 杨柯欣. 电力电子变压器的双有源全桥DC-DC变换器模型预测控制及其功率均衡方法[J]. 中国电机工程学报, 2018, 38(13): 3921-3929, 4034. An Feng, Song Wensheng, Yang Kexin.Model predictive control and power balance scheme of dual-active-bridge DC-DC converters in power electronic transformer[J]. Proceedings of the CSEE, 2018, 38(13): 3921-3929, 4034. [12] 汤旭东, 王学梅. 双有源桥变换器动态响应影响因素及改善对策[J]. 电气自动化, 2021, 43(4): 1-6. Tang Xudong, Wang Xuemei.Influencing factors and improving countermeasures of dynamic response of dual active bridge converter[J]. Electrical Automation, 2021, 43(4): 1-6. [13] Zumel P, Ortega L, Lazaro A, et al.Control strategy for modular dual active bridge input series output parallel[C]//2013 IEEE 14th Workshop on Control and Modeling for Power Electronics (COMPEL), Salt Lake City, UT, USA, 2013: 1-7. [14] 孙志峰, 肖岚, 王勤. 输出并联型双有源全桥变换器控制技术研究综述[J]. 中国电机工程学报, 2021, 41(5): 1811-1831. Sun Zhifeng, Xiao Lan, Wang Qin.Review research on control technology of output parallel dual-active- bridge-converters[J]. Proceedings of the CSEE, 2021, 41(5): 1811-1831. [15] Zhao Tiefu, Wang Gangyao, Bhattacharya S, et al.Voltage and power balance control for a cascaded H-bridge converter-based solid-state transformer[J]. IEEE Transactions on Power Electronics, 2013, 28(4): 1523-1532. [16] 武明义, 侯聂, 宋文胜, 等. 独立输入并联输出全桥隔离DC-DC变换器直接功率平衡控制[J]. 中国电机工程学报, 2018, 38(5): 1329-1337. Wu Mingyi, Hou Nie, Song Wensheng, et al.Direct power balance control scheme of the Input- independent-output-parallel operated full-bridge isolated DC-DC converters[J]. Proceedings of the CSEE, 2018, 38(5): 1329-1337. [17] 安峰, 宋文胜, 杨柯欣, 等. 输出并联双有源全桥DC-DC变换器虚拟功率均衡控制方法[J]. 电力系统自动化, 2018, 42(12): 106-112. An Feng, Song Wensheng, Yang Kexin, et al.Virtual power balance control scheme of dual active bridge DC-DC converters with output-parallel structure[J]. Automation of Electric Power Systems, 2018, 42(12): 106-112. [18] 曾进辉, 孙志峰, 雷敏, 等. 独立输入并联输出双有源全桥DC-DC变换器无电流传感器均流控制[J]. 中国电机工程学报, 2019, 39(7): 2144-2155. Zeng Jinhui, Sun Zhifeng, Lei Min, et al.Sensorless current sharing control strategy of independent-input- parallel-output dual-active-bridge converters[J]. Pro- ceedings of the CSEE, 2019, 39(7): 2144-2155. [19] 李国文, 杭丽君, 钱语安, 等. 考虑损耗的DAB变换器简化模型及线性化控制方法[J]. 高电压技术, 2019, 45(7): 2074-2081. Li Guowen, Hang Lijun, Qian Yu’an, et al.Simplified equivalent circuit model of DAB converter and the linearized control method with considering losses[J]. High Voltage Engineering, 2019, 45(7): 2074-2081. [20] Segaran D, McGrath B P, Holmes D G. Adaptive dynamic control of a bi-directional DC-DC con- verter[C]//2010 IEEE Energy Conversion Congress and Exposition, Atlanta, GA, USA, 2010: 1442-1449. [21] Rodríguez Alonso A R, Sebastian J, Lamar D G, et al. An overall study of a dual active bridge for bidirectional DC/DC conversion[C]//2010 IEEE Energy Conversion Congress and Exposition, Atlanta, GA, USA, 2010: 1129-1135. [22] Qin Hengsi, Kimball J W.Generalized average modeling of dual active bridge DC-DC converter[J]. IEEE Transactions on Power Electronics, 2012, 27(4): 2078-2084. [23] Zhao Chuanhong, Round S D, Kolar J W.Full-order averaging modelling of zero-voltage-switching phase- shift bidirectional DC-DC converters[J]. IET Power Electronics, 2010, 3(3): 400-410. [24] 涂春鸣, 管亮, 肖凡, 等. 基于扩展移相控制下双有源桥移相角优化选取与分析[J]. 电工技术学报, 2020, 35(4): 850-861. Tu Chunming, Guan Liang, Xiao Fan, et al.Parameter optimization selection and analysis of dual active bridge based on extended phase shift control[J]. Transactions of China Electrotechnical Society, 2020, 35(4): 850-861. [25] 王仁龙, 杨庆新, 操孙鹏, 等. 一种优化电流应力的双有源桥式DC-DC变换器双重移相调制策略[J]. 电工技术学报, 2021, 36(增刊1): 274-282. Wang Renlong, Yang Qingxin, Cao Sunpeng, et al.An optimized dual phase shift modulation strategy for dual active bridge DC-DC converter[J]. Transactions of China Electrotechnical Society, 2021, 36(S1): 274-282. [26] 王攀攀, 徐泽涵, 王莉, 等. 基于三重移相的双有源桥DC-DC变换器效率与动态性能混合优化控制策略[J]. 电工技术学报, 2022, 37(18): 4720-4731. Wang Panpan, Xu Zehan, Wang Li, et al.A hybrid optimization control strategy of efficiency and dynamic performance of dual-active-bridge DC-DC converter based on triple-phase-shift[J]. Transactions of China Electrotechnical Society, 2022, 37(18): 4720-4731. [27] Lu Minghui, Wang Xiongfei, Loh P C, et al.Graphical evaluation of time-delay compensation techniques for digitally controlled converters[J]. IEEE Transactions on Power Electronics, 2018, 33(3): 2601-2614. [28] 沈传文. 自动控制理论[M]. 西安: 西安交通大学出版社, 2007. [29] 陈伯时. 电力拖动自动控制系统——运动控制系统[M]. 3版. 北京: 机械工业出版社, 2018.
2024, Vol. 39 
