Introduction  The system commission of HVDC is used to verify the overall performance of the project. It is necessary to analyze the recorded data of the electric values collected during commissioning in order to obtain the conclusion.

  Method  Some recorded figure were not easy to understand. The converter circuit needed to be analyzed to understand the mechanism. This type of analysis method was demonstrated by analyzing typical electric quantity recorded figure.The voltage and current values change greatly when the recorded wave was triggered, which was related to the complex change of the trigger angle caused by the control. During this period, the single valve intermittent conduction, the two valve intermittent conduction, and the valve commutation conduction generated continuous current.Using circuit theory and power electronics technology to analyze the state of the inverter, it was found that inverter was an AC-DC hybrid circuit during the single-valve intermittent conduction, regardless of leakage current of the shut-off valve, the DC voltage was constant.

  Result  Based on the theoretical results, analyze the inverter side electric quantity recording wave when a low-voltage valve group of a UHV project is blocked, can be concluded that if the applied DC voltage is greater than the average DC voltage of the inverter, under the supplemental pulse mechanism a continuous current occur.

  Conclusion  The process of voltage and current in the recording wave is well explained, and the necessity and correctness of the control behavior are verified. It can be used as reference for HVDC project commission analysis and provide support for commission conclusions.