In order to solve the problem of three-phase voltage unbalance at the point of common coupling on the power system side caused by the negative sequence of tree bilateral interconnected power supply system, this paper proposes a negative sequence compensation scheme for power transfer by installing a compensation device composed of the step-down transformer, the power flow controller (PFC) and the controller in the tree bilateral interconnected power supply system. On the basis of establishing the topology and mathematical model of the interconnected traction power supply system using PFC, reasonable constraint parameters and control strategies are designed to control the compensation device to change the power distribution on the power system side to achieve negative sequence compensation. The MATLAB/Simulink simulation test platform is used to analyze the variation law of the required capacity of the compensation device with the degree of the negative sequence compensation, and the minimum negative sequence compensation capacity is calculated to verify the compensation scheme. The results show that the negative sequence compensation scheme based on power transfer can flexibly adjust the negative sequence power and reactive power content at the point of common coupling. The maximum value of three-phase voltage unbalance at the point of common coupling can be reduced to 4%, and 95% statistical value can be reduced to 2%, which meets the national standard and verifies the effectiveness of the negative sequence compensation scheme based on power transfer.
为实现牵引网全贯通供电,彻底消除电分相对电气化铁路的影响,有学者提出了基于树形供电结构的树形双边贯通供电系统[12]。树形双边贯通供电系统可消除电分相对电气化铁路产生的不良影响且无均衡电流问题,然而该系统中多个牵引变电所连接在同一母线的供电结构会导致电力系统侧公共连接点(Point of Common Coupling,PCC)处的负序超出国家负序考核标准[13],亟待解决。
采用PFC的树形双边贯通供电系统拓扑结构如图1所示。图中:为220 kV母线w(w=A,B,C)相电压;SS r 为第r(r=1,2,…,m)个牵引变电所;为SS r 一次侧w相馈线电流,其正方向为图1中标注方向;VSC k (k=1,2,3)为第k个电压源变流器(Voltage Source Converter,VSC);T k 为第k个降压变压器。
图1中,VSC k 直流侧背靠背连接组成PFC;T k,PFC和控制器组成补偿装置。其中,控制器的输入端用于接收和,输出端与PFC的控制端连接,并为其提供控制信号。
SHIJing, YANGZhipeng, ZHANGWenxuan, et al. Pantograph-Catenary Dynamic Characteristics of Articulated Phase Insulator [J]. China Railway Science, 2014, 35 (2): 46-51. in Chinese
LIUZhigang, MENGXiangyu, ZHANGQiao, et al. Issues, Challenges and Countermeasures in Traction Power Supply System of High-Altitude Mountain Railway [J]. Power System Technology, 2023, 47 (5): 2039-2053. in Chinese
LUOPei, YANGWeimin, ZHANGMin. Optimization of Negative Sequence Current in Public Power Grid under Regenerative Braking Condition of High Speed Railway [J]. China Railway Science, 2018, 39 (6): 126-132. in Chinese
CHENYinyu, CHENMinwu, LIDongyang, et al. Stochastic Optimal Operation Strategy of Co-Phase Power Supply System Considering Uncertainty of Traction Load [J]. China Railway Science, 2023, 44 (5): 191-200. in Chinese
CHENMinwu, CHENTianshu, DAIXianfeng, et al. Modeling and Control Strategy of Energy Storage Co-Phase Power Supply System Based on MMC [J]. China Railway Science, 2022, 43 (3): 132-143. in Chinese
WANGHui, LIQunzhan, LIUWei, et al. Scheme of Long Distance Power Supply for Electrified Railway Traction Network Based on Traction Cable [J]. China Railway Science, 2021, 42 (1): 137-146. in Chinese
[17]
LAOK W, WONGM C, DAIN Y, et al. Analysis of the Effects of Operation Voltage Range in Flexible DC Control on Railway HPQC Compensation Capability in High-Speed Co-Phase Railway Power [J]. IEEE Transactions on Power Electronics, 2018, 33 (2): 1760-1774.
WANGHui, LIQunzhan, XIEShaofeng, et al. Comprehensive Compensation Scheme of Cophase Power Supply for Electrified Railway with Dd Transformer and Static Var Generator [J]. China Railway Science, 2020, 41 (4): 116-126. in Chinese
CHENMinwu, ZHOUYingdong, HANXudong, et al. Scheme Optimization for Cophase Continuous Traction Power Supply Based on LCC in Area with Weak External Power Source [J]. China Railway Science, 2019, 40 (3): 103-111. in Chinese
ZHOUZhicheng. Cophase Connected Power Supply Scheme of Heavy Haul Railway Based on Tree Bilateral Power Supply [J]. Journal of Railway Science and Engineering, 2020, 17 (3): 722-731. in Chinese
Systems Aspects for Electrical Energy Supply. GB/T 15543—2008 Power Quality—Three-Phase Voltage Unbalance [S]. Beijing: Standards Press of China, 2009. in Chinese )
JIAOYingzong, QUANYue, LIBinbin, et al. Interline DC Power Flow Controller Based on Submodule-Bridge Energy Balancing [J]. Automation of Electric Power Systems, 2023, 47 (14): 114-123. in Chinese
ZHANGLiyan, HANDushuo, WANGHui, et al. Negative Sequence Compensation Model and Control Strategy for Interconnected Power Supply System of Traction Substation Group [J]. Automation of Electric Power Systems, 2021, 45 (22): 146-156. in Chinese