Uncertainty and Disturbance Estimator-Based Control for Voltage Robust Controller in DC Distribution Network
Lin Li1, Fan Mi1, Lin Yulu1, Luo Hao1,2, Wang Jingzhi1, Tan Huidan1
1. Xuefeng Mountain Energy Equipment Safety National Observation and Research Station Chongqing University Chongqing 400044 China;
2. State Grid Sichuan Economic Research Institute Chengdu 610041 China
The power system's power supply capacity, quality, and reliability can all be improved with the help of a DC distribution network, which also offers a practical and effective access interface for distributed energy. Therefore, the DC distribution network has become a development direction of power supply in the future. However, the DC distribution network is susceptible to system uncertainties and interference since it is a small inertial system, which leads to large fluctuations and even instability of the DC bus voltage. To address these issues, this paper proposes a voltage robust control strategy based on the uncertainty and disturbance estimator (UDE) control method, which is applied to the converter station level and converter valve level control of the DC distribution network, respectively.
At the converter station level, firstly, the capacity ratio of each converter station is introduced into the droop control, and the setting method of load current reference value is proposed to solve the influence of line impedance on load current distribution in the traditional droop control. Then, according to the UDE control theory, the uncertain dynamic model of the load current of each source converter branch is constructed. Finally, taking the load current output from each source converter can gradually track the reference value of the load current as the control objective, and the converter station level UDE robust droop control method is designed. At the converter valve level, firstly, the system state space model is constructed with the dq-axis current in the voltage source converter (VSC) inner loop as the state variable. Secondly, the dq-axis current reference vector is established according to the UDE standard model. Finally, to make the state vector of the dq-axis current tend to the reference vector, the control input vector is determined.
The simulation results of the three source DC distribution network system in PSCAD/EMTDC software show that, firstly, for the converter station level, under various disturbances, the minimum steady-state voltage of the disturbed DC bus is 740.6 V under the traditional droop control, which is a large deviation compared with the rated voltage of 780 V. When VSC2 suddenly exits, for VSC1 and VSC3 with the same capacity, their respective load currents are stable at 0.124 6 kA and 0.169 3 kA respectively, and current sharing is not achieved according to capacity. The lowest DC bus voltage under UDE robust droop control is 778.50 V, which is sTab.at the rated voltage of 780V. When VSC2 suddenly exits, the load current of VSC1 and VSC3 is finally adjusted to 0.194 kA, realizing current sharing. Then, at the converter valve level, when the AC system fails, compared with the traditional PI dual loop control and UDE robust current control, the corresponding DC bus voltage is 821.6 V and 814.5 V respectively. When the fault disappears, and the time for the system to recover to stability is 0.050 s and 0.041 s respectively. At the time of fault occurrence and disappearance, the peak value of q-axis current of traditional PI dual loop control is 0.0148 kA and -0.013 kA respectively, while that of UDE robust current control is 0.013 kA and -0.002 kA respectively, and the fluctuation range of q-axis current is smaller than the former.
The following findings can be drawn by the simulation analysis: (1) At the converter station level, the UDE robust droop control approach outperforms the conventional droop control method in terms of load current distribution and has a greater robust control impact on the DC bus voltage. (2) At the converter valve level, UDE robust current control has stronger anti-interference and better dynamic performance in voltage control in addition to good current tracking performance in the process of disturbance.
林莉, 范米, 林雨露, 罗皓, 王静芝, 谭惠丹. 基于不确定与扰动估计器的直流配电网电压鲁棒控制[J]. 电工技术学报, 2023, 38(17): 4657-4671.
Lin Li, Fan Mi, Lin Yulu, Luo Hao, Wang Jingzhi, Tan Huidan. Uncertainty and Disturbance Estimator-Based Control for Voltage Robust Controller in DC Distribution Network. Transactions of China Electrotechnical Society, 2023, 38(17): 4657-4671.
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2023, Vol. 38 
