Abstract
The Large-scale Superconductor Test Facility (LSTF) is an important part of comprehensive research facilities in support of China Fusion Engineering Test Reactor (CFETR). In order to protect the superconducting magnets from being damaged in quench accident, the Quench Protection System (QPS) should be designed to commutate the energy stored in the coils. The snubber circuit is used to reduce the reverse recovery current and voltage of thyristor in QPS, and it can impact the reliability and stability of the QPS. In general, the studies of snubber circuit are focused on the DC turn-off process of thyristor used in HVDC, which has small turn-off current. However, the turn-off current can reach to 100 kA in the QPS of LSTF. In this paper, a thyristor reverse recovery model is described, and the key parameters of reverse recovery current are obtained from the testing experiment. Based on the transient analysis of snubber circuit, a systematic approach is used to minimizing the resistance and capacitance of snubber circuit of QPS working condition is proposed. By the MATLAB simulation and comparison, minimum parameters of snubber circuit were obtained, and proved that the approach can improve the reliability and stability of system, while reduce the cost of QPS.
Highlights
The huge superconducting magnets are chosen for the higher current densities and the lower energy consumption of fusion reactor [1]
In order to verify the advantage of the optimum parameters, the thyristor valve characteristics have been compared by applying the different snubber circuits, which integrated the optimum parameters and the experimental parameters
PARAMETER OPTIMIZATION FOR THE SNUBBER CIRCUIT The parameters of the RC snubber circuit of Quench Protection System (QPS) depends on the operating conditions and the performance of thyristor itself
Summary
The huge superconducting magnets are chosen for the higher current densities and the lower energy consumption of fusion reactor [1]. The thyristor reverse recovery model based on the pulsed turn-off current condition is built. The transient analysis of the snubber circuit during the reverse recovery process is carried out. A systematic approach to minimizing the resistance and capacitance of snubber circuit in QPS is proposed and a set of optimum and minimum parameters can be obtained by this approach. The mathematical analysis of the reverse recovery process should take the time constant τ into consideration There is another analytical model based on the physical model of thyristor. Using exponential function to simulate the reverse recovery current can effectively overcome the shortcomings of the first mentioned model It is suitable for most soft-recovery thyristors and can obtain more accurate results by this analytical model. Two time constants τc and τh need to be derived, which it is not suitable for general engineering applications [13]
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