A Novel Method for Operation Monitoring of Thyristor Converter Based on Real-Time Virtual Measurement of Valve Current in LCC-HVDC

The thyristor converter is a core equipment for AC/DC hybrid power grids of high-voltage direct current (HVDC) where overheating does harm to its reliability. In reality, overheating is closely related to the broken three-phase symmetry when the AC side is disturbed. Particularly, when commutation failures occur, the valve forced to reconduct will suffer from severe short-circuit current for a long period, risking the overheating damage. Therefore, the accurate measurement of valve current is fundamental to acquire valve temperature. This paper adopts a real-time virtual measurement scheme, which is based on temporal features of the converter terminal current, to calculate valve current fundamental for the calculation of valve loss under the transient state. Then, an equivalent circuit model is built based on the actual heat-flow path of the converter valve, considering the high thermal sensitivity of the heat source material layer. Next, a monitoring system for transient valve temperature is established. Finally, the proposed method is tested in CIGRE HVDC benchmark model. The simulation results indicate that the proposed method can reflect the actual valve state, and model the actual heat transfer process more accurately compared to the Foster network, which can support the basic configuration of the overheat protection. (c) 2024 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.