Search

DC fault protection is the bottleneck that restricts the development of modular multilevel converter based high voltage direct current (MMC-HVDC) system. Superconducting fault current limiters (SFCL) is an ideal protection device that can significantly limit short circuit current and enhance the fault tolerance ability of MMC-HVDC system. At present, several topologies of SFCLs have been proposed, but there is no systematical study of their current-limiting characteristics in MMC-HVDC. This paper studies the development process of DC short-circuit faults in MMC-HVDC system, and analyzes its demand for fault current limiting. Then, resistive type, saturated iron core type and hybrid type SFCL are modeled and their limiting effect of critical fault current under DC pole-to-pole fault is tested. By comparison, the current-limiting characteristics of three types of SFCL are concluded. Results show that resistive SFCL has best performance in steady state, while saturated iron core SFCL has best performance in transient state. The current-limiting characteristic of hybrid type SFCL is between the other two types. [ABSTRACT FROM AUTHOR]

Currently, HVDC is in the spotlight for long-distance transmission and power connection between countries. Among them, MMC-HVDC is a new conversion technology that can solve the problems of switching loss and harmonics. MMC consists of many submodules connected in series. And the one submodule is composed of IGBTs, Diode, and Capacitor. At the transient state, the charged capacitor is discharged and added to the fault current. It will generate tens of times the surge current during the delays all IGBTs turn-off. This causes semiconductor device destruction. To solve this problem, we applied SFCL with fast response characteristics to the MMC. The response speed of the resistive SFCL is faster than that of the MMC system protection device, which can effectively limit the capacitor discharge current before the protection device operates. In this paper, AC grid, MMC-HVDC, DC cable and SFCL were modeled using PSCAD/EMTDC. After that, we confirmed the capacitor discharge current, current limiting rate, and interruption characteristics through DC line short circuit failure simulation. As a result, SFCL effectively limits the capacitor discharge current and continuously lowers the level of the fault current. [ABSTRACT FROM AUTHOR]

The medium voltage direct current (MVDC) is a promising direction of future shipboard power system (SPS). However, one of the main limitations encountered in its development is the fault isolation of DC side. This paper reveals the evolution process of short-circuit fault in typical MVDC SPS through equivalent circuit and transient simulation. Based on the analysis of protection needs, a superconducting current-limiting switch (SCLS) topology is proposed, which includes one superconducting coupled coil and two DC circuit breakers (DCCBs). The models of SCLS is built on MATLAB/Simulink and the current limiting principle and current sharing principle of SCLS are verified. The results show that the SCLS has effective current limiting performance and fault clearing effect. [ABSTRACT FROM AUTHOR]

DC fault is one of the most important and critical challenges for stable operation of DC microgrids. Resistive type superconducting fault current limiter (R-SFCL) is an ideal protective solution to limit DC fault current. However, the effect of only using SFCL may further deteriorate the DC bus voltage stability. This paper first analyzes the effect of R-SFCL on DC microgrid under different operation modes and different fault locations, and then presents a coordinated control method of SMES-battery hybrid energy storage system (HESS) and SFCL in ground fault. This method can not only reduce the fault current level but also regulate the DC bus voltage. Finally, the comparative study is conducted in PSCAD/EMTDC, the feasibility and superiority of the proposed method is verified. [ABSTRACT FROM AUTHOR]