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A flexible dc grid is important for supporting large-scale new energy integrations. To ensure the stable operation of the dc grid, a dc circuit breaker (DCCB) is needed for fault isolation. At present, the cost of DCCBs is high, and the breaking capacity is limited. This limitation can be effectively solved through the coordination of fault current limiters (FCLs) and DCCBs. In this article, a coordinated interruption topology of an magnetic coupling FCL (MCFCL) and hybrid DCCB is proposed. A coordinated interruption strategy based on magnetic coupling current-limiting and energy dissipation is proposed to improve the dynamic performance of the FCL and reduce the energy dissipation and breaking time of the DCCB. A two-stage mathematical model of coordinated interruption is established, and its control principle is analyzed. Furthermore, the influence of the inductance and resistance of the MCFCL secondary side, coupling coefficient and rated voltage of the arrester on the coordinated interrupting process is researched. On this basis, parameter optimization and economic analysis are carried out. Finally, a scaled test for the coordinated interruption of the DCCB and MCFCL was carried out, which verifies the feasibility of the coordinated interruption strategy based on magnetic coupling current-limiting and energy dissipation. [ABSTRACT FROM AUTHOR]

In this paper, elliptically contoured (EC) distributions are used to model outlier-contaminated measurement noises. Exploiting a heuristic approach to introduce an unknown parameter, we present an analytical update form of the joint posterior probability density function of the state vector and auxiliary random variable, from which a novel robust EC distributions-based Kalman filtering framework is first derived. To illustrate the effectiveness of the proposed framework, the convergence, robustness, optimality and computational complexity analyses of the proposed method are then given. In addition, to cope with complex noise environments, the interaction multiple model is employed to achieve the adaptive selection of EC distributions such that well-behaved estimation performance can be obtained for different noise cases. Simulation results demonstrate the validity and superiority of the proposed algorithm. [ABSTRACT FROM AUTHOR]

In a voltage-source converter dc grid, a dc fault current limiter (FCL) is a key apparatus. When faults occur, it is supposed to effectively and immediately suppress transient short-circuit current to protect other equipment, e.g., converters. Additionally, it is required to bring as little negative effect as possible under normal operation. Although the respective advantages are highlighted in different FCLs, one or two key disadvantages can significantly decrease the overall performance. In this article, a novel magnetic coupling FCL (MCFCL) is proposed and achieves a good balance among its advantages and disadvantages. An MCFCL consists of a mutual inductor and some power electronic switch modules. The mutual inductor metallic primary winding is connected in series to the transmission line and magnetically coupled with the secondary winding. The secondary side impedance is controlled by the power electronic switch modules. The novel 4-segment model is proposed to demonstrate the current-limiting physics, formulate the current-limiting effect, and support the design. One medium voltage (10 kV) case study is carried out based on the numerical simulation. The MCFCL shows a better current-suppressing effect and a lower impedance under normal operation than the benchmark Reactor FCL. Finally, this article is validated on a scaled-down experimental facility. [ABSTRACT FROM AUTHOR]

Hybrid dc circuit breakers (HCBs) usually require a large number of insulated-gate bipolar transistors (IGBTs) with high turn-off capability for series and parallel connections. This requirement entails excessive cost. Compared with IGBTs, integrated gate-commutated thyristors (IGCTs) are another kind of fully controlled power device with high surge current and voltage capability but are low cost. However, the weak turn-off capability of IGCTs hinders their application to high-powered HCBs. On the basis of the complementary advantages of IGBTs and IGCTs, this paper proposes a mixture solid-state switch (MSS) for HCBs that uses the switching action of several IGBTs to create a low-current condition that favors the turning off of large-scale series-connected IGCTs. The MSS topology can significantly reduce cost while maintaining the excellent performance of traditional solid-state switches. This study also introduces two different turn-off modes for MSS, namely, single oscillation and multiple oscillations. Finally, 25 kV/20 kA prototypes in both modes are developed to verify the effectiveness of the MSS topology. [ABSTRACT FROM AUTHOR]

The no-load curve of the dielectric recovery strength of the ultra-fast mechanical vacuum switch (MVS) changing with time is the theoretical foundation to optimize the turn-off strategy of the hybrid direct current circuit breaker with load commutation switch. To avoid the shortcomings of the classic synthetic circuit, a novel test circuit is proposed to measure the no-load dielectric recovery curve of the MVS in this paper. In the test circuit, a succession of pulse voltages is automatically applied on the MVS, and multiple breakdowns of the MVS occur in one test. Therefore, the dielectric strength of the MVS at multiple time points is obtained, and the envelope of the applied voltage on the MVS during one test can describe the dielectric recovery curve of the MVS; as a result, the test workload could be reduced dramatically and the measurement is more authentic. By changing test conditions, including the rate of rise of the test voltage and the operating speed of the MVS, no-load dielectric recovery characteristics are studied. The research has shown that the dielectric recovery speed of the MVS is irrelative with the rate of rise of the test voltage and it is directly proportional to the opening speed of the MVS. [ABSTRACT FROM AUTHOR]

The direct-current (dc) fault-clearance capability of the modular multilevel converter (MMC) is a key issue for overhead line applications of voltage source converter-based high-voltage dc (VSC-HVDC) transmission systems. An MMC integrated with a dc circuit breaker (IDCB-MMC) is proposed to provide a cost-effective DC fault clearance and isolation solution. A mechanical switch (MS) and a load commutation switch are connected in series as the main branch of the dc circuit breaker. DC fault currents can be forced to transfer to converter- and line-side energy absorbing branches when submodule bypass protection and dc circuit breaker interrupting operations are coordinated. Therefore, the bulky and costly solid-state branch that uses numerous semiconductor devices and surge arresters can be eliminated. The dc fault clearance and isolation capability of the IDCB-MMC were verified through the simulation results for one pole of a 1000 MW/±320 kV VSC-HVDC system. Compared with an MMC that uses half-bridge SMs, the IDCB-MMC only requires few additional capacitors and switching devices and a simple MS, thereby resulting in several advantages, such as low cost, footprint requirements, and additional conduction losses. [ABSTRACT FROM AUTHOR]

Current commutation from the load current path to the commutation path is the precondition to interrupt current successfully for hybrid direct current circuit breakers (DCCB). With remarkable current commutation performance, current commutation drive circuit (CCDC), mainly consisting of air-core transformer, fast-closing switch (FCS), and precharged capacitor, is proposed by us. In this paper, to eliminate the operating losses of CCDC and to avoid unrecoverable damage of FCS, CCDC used in hybrid DCCB for current commutation has been improved. Different submodules (SM) of commutation path in hybrid DCCB are analyzed, and experiments have been carried out on a hybrid DCCB prototype. Theoretical analysis and experiment results have shown that no matter which kind of SM is used, improved CCDC can ensure reliable current commutation in hybrid DCCB. In the end, by taking total cost of CCDC into consideration, a novel optimization method is proposed to design the parameters of CCDC. With this optimization method, CCDC for hybrid DCCBs with different rated voltage and current can be designed individually and its cost could be reduced significantly. [ABSTRACT FROM AUTHOR]

As power semiconductor devices are the key components of hybrid DC circuit breakers (HCBs), how to select suitable devices is critical for the whole HCB design. First, this paper compared the general characteristics of press pack insulated gate bipolar transistor (IGBT), injection-enhanced gate transistor (IEGT), and integrated gate commutated thyristor (IGCT). Then working conditions of devices were analyzed from the perspective of HCBs. According to these, vital features of devices including maximum turn-off current, on-state voltage, conduction ability, and robustness of power semiconductor devices were carefully analyzed and compared. Related experiments were implemented to compare maximum turn-off capability, and the 4.5 kV/3 kA IGBT/IEGT was able to turn off 19 and 22 kA respectively after 5-ms current conduction. Analysis and experiments indicated that IGCT was suitable for natural commutation low-voltage and low-current hybrid circuit breakers, due to its low on-state voltage and huge surge current conduction ability. Comparatively, IGBT and IEGT were more suitable for very high current interruption, and IEGT was the superior selection among available commercial devices. However, the interference should be considered in applications. [ABSTRACT FROM AUTHOR]

The hybrid direct-current circuit breaker (DCCB) consists of a mechanical switch (MS) branch and a static DCCB branch. Once a short-circuit fault is detected, the current should commutate from the MS branch to the static DCCB branch first. In this paper, two current commutation measures have been investigated. A hybrid DCCB prototype with current commutated by the arc voltage of the SF${}_{6}$ switch is developed. Based on the prototype, current commutation and interruption tests have been carried out. The results show the current of 3.4 kA can be commutated within 2.4 ms, and be interrupted within 6 ms. Then, a current commutation drive circuit (CCDC) is proposed as the other current commutation measure. Equivalent current commutation tests have been carried out. The results show with the CCDC, both positive current and negative current can be commutated within tens of microseconds. Using a CCDC in series with a mechanical vacuum switch as the MS branch, a 44 kV/3.4 kA hybrid DCCB prototype is developed. Based on the prototype, current commutation and interruption tests are carried out. According to the results, the current of 3.4 kA can be commutated within 100 $\mu $s, and be interrupted within 2 ms. [ABSTRACT FROM PUBLISHER]