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The high-voltage direct current (HVDC) power transmission short-circuit fault protection is a big challenge, and it is the main obstacle to promote the HVDC multi-terminal networks. A natural commutation current topology (NCCT) of hybrid HVDC circuit breaker (DCCB) integrated with limiting fault current is proposed in this paper, which shares several obvious merits, such as lower peak fault current, shorter fault isolation time and low turn-off loss. The main contributions in this paper are made as follows. (1). A second-order RLC circuit in novel NCCT circuit breaker is utilized as the current limiting circuit to dramatically reduce the fault current rising slope and its peak value. (2) A asynchronous NCCT circuit breaker has been investigated to broaden the proposed NCCT circuit breaker's optimal working area. (3) By taking China Zhangbei 500 kV four-terminal DC grid as an example, an optimization design technique of the asynchronous NCCT-DCCB is developed to demonstrate the process of the theoretical analysis and parameter design. The correctness of the proposed NCCT-DCCB and the feasibility of the optimization design technique are confirmed by EMT simulation on PSCAD/EMTDC and hardware-in-loop experiment on PLECS-RtBox.

Due to the low impedance of DC (Direct Current) power transmission line, short‐circuit current has a very high increment speed, which causes problems as difficulty in current limitation method. This paper proposes a new method to realize the current‐limiting control of short‐circuit current by using active control of power electronic transformer. The method improves the topology of dual active bridge modules that contribute the DC transformer, and installs an IGBT (Insulated Gate Bipolar Transistor) switch in reverse direction on supporting capacitor branch of each module to control the capacitor on or off, which can guarantee the storage energy within the capacitor will not release in initial stage in case of DC short circuit fault happen. Therefore, there is no large inrush current flow out. Furthermore, combined with the requirements of current tracking control during low‐voltage ride‐through, the transformer output current under short‐circuit condition is actively controlled in order to meet the needs of renewable energy power generation equipment. Finally, the simulation and hardware‐in‐the‐loop experiments verify the correctness of this method.

A physics‐based turn off model and its output characteristic analysing expressions have been investigated for the high voltage soft‐punch through IGBTs under extreme SOA (safe operating area) conditions to depict the excellent soft turn‐off behaviour in this paper. The main contributions have been made as the followings: (1) Based on the interior structure and features, one virtual capacitor and two Zener diodes are respectively employed to model its dynamic avalanche characteristic and switching self‐clamping mode. (2) By using the user datasheet and typical experimental waveforms, a parameter estimation approach is developed. (3) To simulate extreme SOA turn‐off waveforms of the IGBT by using MATLAB and MATHCAD program, the piece‐wise analysing expressions have been given out to simulate the output voltage and current characteristics. The new model and its analysing expressions have been validated with experiments. The simulation results show a good agreement with its experimental waveforms.

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