Analysis of Fault Current Characteristics in AC Transmission Lines for Wind Power Integration through VSC-HVDC System Controlled by Virtual Synchronous Generator
Huang Xinran1, Wang Zengping1, Wang Tong1, Niu Aoxiang1, Song Liangliang2
1. State Key Laboratory for Alternate Electrical Power System with Renewable Energy Sources North China Electric Power University Beijing 102206 China; 2. State Grid Jiangsu Electric Power Company Electric Power Research Institute Nanjing 211103 China
Abstract：The active support-type VSC-HVDC converter based on virtual synchronous machine control exhibits excellent voltage-source characteristics, effectively suppressing oscillations caused by low system inertia. However, after an AC line fault, the weak feedback characteristics of the currents on both sides are affected by different low-voltage ride-through (LVRT) controls, resulting in significant differences compared to synchronous machine systems. Therefore, this paper proposes an analytical method for the steady-state fault currents of double-ended power-electronics equipment. This method does not rely on refined system models for multiple iterative calculations. It can obtain steady-state current values output from the VSC-HVDC converter under various fault scenarios, enabling accurate calculation of the AC grid fault response at the new energy generation end. In the typical offshore wind power island transmission scenario, the grid-side converter of the wind turbine and the sending-end converter of the VSC-HVDC system use grid-following control and VSG grid-forming control, respectively. This paper first constructs an equivalent system model based on the LVRT control strategies. Secondly, from the perspective of positive- and negative-sequence separation control, the symmetrical component method is applicable to decouple AC systems with a high proportion of power-electronic equipment. Then, combining the symmetrical component method and Kirchhoff's law, the equivalent sequence network diagram is solved for different fault scenarios, and the analytical expression of the current sequence component on the VSC-HVDC side is derived. The influencing factors of the current sequence component under symmetrical and asymmetrical fault scenarios are revealed, and differences in fault-current characteristics between active-support VSC-HVDC converters and synchronous machine systems are highlighted. Finally, an electromagnetic transient simulation model of the wind power transmission system via VSC-HVDC is built in PSCAD/EMTDC. The simulation results show that the proposed method's calculation error is less than 3%. The following conclusions can be drawn from the simulation analysis. (1) After an AC line fault, the current loop of the wind turbine grid-side converter with dual-loop control saturates is equivalent to a controlled current source. The power reference value switching of the VSC-HVDC sending-end converter based on VSG control is equivalent to a controlled voltage source with internal impedance. (2) On the power frequency protection time scale, the fault current on the wind turbine side consists of positive-sequence and zero-sequence components. As transition resistance increases, the zero-sequence component decreases, and the three-phase waveform becomes more symmetrical. The VSC-HVDC side provides a negative-sequence loop, and the fault current consists of positive-sequence, negative-sequence, and zero-sequence components. Affected by control parameters and the magnitude of transition resistance, the variations in sequence components differ significantly from those of synchronous machine systems, which may affect the adaptability of traditional power-frequency protection. (3) The proposed fault current analysis method has a calculation error of less than 3% in various fault scenarios, meeting the requirements for protection adaptability analysis and setting.
黄欣然, 王增平, 王彤, 牛翱翔, 宋亮亮. 风电经基于虚拟同步机控制的柔直系统送出交流线路故障电流特性分析[J]. 电工技术学报, 2026, 41(14): 4902-4918.
Huang Xinran, Wang Zengping, Wang Tong, Niu Aoxiang, Song Liangliang. Analysis of Fault Current Characteristics in AC Transmission Lines for Wind Power Integration through VSC-HVDC System Controlled by Virtual Synchronous Generator. Transactions of China Electrotechnical Society, 2026, 41(14): 4902-4918.
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