Reverse recovery characteristics of high power thyristors in HVDC converter valve

The reverse recovery characteristics of high power thyristor are important device physical properties influencing the reliable operation of HVDC thyristor valve. In this paper, the reverse recovery characteristics of high power thyristor are investigated from the aspects of both external circuit and internal device physics. By analyzing the depletion of carrier during the reverse recovery of thyristors, a determination method of minority carrier lifetime is proposed to construct a connection between the macroscopic reverse recovery characteristics and the microscopic device physical parameter such as minority carrier lifetime. Meanwhile, the influence of the current with a power frequency on the characteristics of reverse recovery especially on the reverse recovery time is investigated experimentally, and the relationship between external circuit and internal physical property is discussed. The results show that thyristor reverse recovery storage time is independent of sinusoidal currents under power frequency, which is approximately equal to its minority carrier lifetime in the base region of high power thyristors; Finally, the influences of reverse recovery characteristics on the protection strategy of thyristor unit are analyzed, and the related methods of thyristor unit routine test are also discussed. This work will be beneficial to the operational maintenance of thyristor valve in power system.