Abstract：Strong electrical and control coupling exists between the sending and receiving ends of a high voltage direct current (HVDC) transmission system. Therefore, disturbances on the sending end can affect the operation state of the receiving end system through changes in control logic, electrical, or control quantities, increasing the risk of commutation failure (CF) on the receiving end. The phenomenon and mechanism of CF at the receiving end caused by large disturbances at the sending end have been studied in existing literature. This paper identifies the existence of inherent oscillation modes with frequencies situated in the low-frequency range in the system. When oscillations of similar frequencies manifest in the sending AC system, resonance in the DC system becomes alikely outcome, causing CF in the receiving end. Without timely control of this resonance, it triggers switching of constant current control and constant extinction angle control at the inverter side. An uncontrolled extinction angle during control switching will likely cause subsequent CFs, even DC blocking. Therefore, discovering the mechanism of such CF is important to contribute to the operational safety and stability of HVDC transmission systems. Firstly, the whole process of the CF caused by the sending end oscillation is analyzed using simulation curves from the CIGRE benchmark HVDC system. According to the simulation results, four different stages have been identified after the first detection of the sending end oscillation. Secondly, the eigen values of the CIGRE benchmark HVDC system are calculated using a small-signal stability model, and the inherent oscillation modes of the system are determined. A special mode, in which the sending end current controller plays a pivotal role, is identified based on participation factor values. The frequency of the special mode of the CIGRE benchmark system is 1.2 Hz, located in the low-frequency range. When the sending system encounters oscillations of nearby frequencies, resonance is easily induced, causing corruption in the sending end controller. The quasi-steady-state equations are used to derive the DC current equation to analyze the rise of DC current after resonance, resulting in a fall in the extinction angle and triggering the first CF. Then, the control equations are used to analyze the switching process of the system controller and elucidate the mechanism through which control switching leads to subsequent CFs. Finally, the theoretical analysis is validated by simulations in PSCAD/EMTDC. A series of oscillations with different frequencies are tested, i.e., 0.1 Hz, 0.6 Hz, 0.8 Hz, 1.2 Hz, 2.5 Hz, 7.6 Hz, and 66 Hz. The results show that oscillations in the low-frequency band of 0.1~2.5 Hz can trigger resonance in the system, leading to CF at the receiving end. Moreover, the first CF is observed around 0.5 s after injecting the 1.2 Hz oscillation into the sending end system, faster than other oscillations from 0.1 Hz to 2.5 Hz, given that 1.2 Hz is the inherent oscillation frequency. Additionally, oscillations of 7.6 Hz and 66 Hz donot cause CFs, although they are also inherent oscillation frequencies. Their participation factors indicate that these two inherent oscillations are unrelated to the system controller. The following conclusions can be drawn from the paper: (1) Four stages exist after the sending end oscillation occurs, and CFs will happen if the frequency is in a specific range. (2) The root cause of CFs arising from sending end oscillations is the resonance between these oscillations and the inherent oscillation modes of the HVDC system, inducing fluctuations in electrical and control quantities. The rise of DC current induces the first CF, and the control switching leads to subsequent CFs. (3) The key to preventing CFs caused by sending end oscillations is to tune the system parameters so that the inherent oscillation mode has a strong damping ratio in the common frequency band.
郑乐, 吴晶, 徐衍会, 孙英云, 刘崇茹. HVDC送端系统振荡引发受端换相失败的机理分析[J]. 电工技术学报, 2024, 39(9): 2743-2754.
Zheng Le, Wu Jing, Xu Yanhui, Sun Yingyun, Liu Chongru. Mechanism Analysis of Receiving End Commutation Failure Caused by Sending End Oscillation in HVDC Transmission System. Transactions of China Electrotechnical Society, 2024, 39(9): 2743-2754.
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