Novel detection scheme for commutation failure based on virtual blocking state

Commutation failure (CF) is the most common and adverse event for the HVDC systems, and CF will seriously affect the normal operation of converter and threaten the stable operation of power grid. Rapidly and accurately detecting CF is extremely important to control and protection. The study found when CF happens the valve is supposed to conduct will continue to turn off, so the valve blocking interval (BI) will be lengthened. With the BI difference of the valve, a novel detection method for CF is proposed. Based on the ratio of relative relationship of three-phase AC currents, the valve virtual blocking state (VBS) is constructed. With the temporal features of time accumulation of the valve VBS in one cycle, detection of the valve abnormal state is constructed. Utilizing the mutual restraint relationship between abnormal state of valves, criterion of CF is constructed. Based on the proposed detection method, through simulations and field record data shows the validity and reliability are verified, and the simulation results of different fault conditions verify the good robustness than ADCC. Moreover, the valve of CF can be accurately tracked based on VBS, which helps to locate the faulty valve and improve the accuracy of subsequent control.