When integrating multi-grid renewable energy systems, modular multi-level converters (MMCs) are promising for high-voltage DC (HVDC) transmission. Because of the characteristics of the system, however, it is more difficult to prevent a fault at the DC terminal than at the AC terminal of the MMC. Accordingly, a fault ride-through (FRT) strategy for the operation of the MMC in the DC terminal is required for stable system operation. In this paper, a solution for closed-circuit overcurrent caused by a permanent line-to-line DC fault is proposed. This method is able to reduce the fault current through the adjustment of the slope of the total voltage in the system by operating a sub-module having lower switching losses and fewer passive devices compared with existing topologies. Additionally, through the equivalent circuit of the proposed scheme in a sub-module in case of a fault, the FRT mechanism for the fault current is explained. The feasibility of this proposed technique was verified through time-domain simulations implemented by Powersim, Inc.
Power semiconductors based on wide bandgap (WBG) devices are capable of fast switching and have low on-resistance. Accordingly, a fast sensor with a higher bandwidth is required for circuit inspection based on switch current measurements. Thus, it is necessary to have a current sensor in the printed circuit board (PCB) circuit for diagnosis and protection of the surface mount device (SMD) type circuit system. Accordingly, a pickup coil with the advantages of a high degree of sensor configuration freedom, wide bandwidth, and low cost can be a good alternative. This study analyzes the influence of coil shape and parameters on sensor design as a guideline for embedding a pickup coil in an SMD-type PCB circuit of a WBG power semiconductor-based, half-bridge structure. The mutual inductance and self-inductance values of the coil are considered large variables in the design of a sensor coil for simultaneously maintaining high bandwidth and sensor sensitivity. Therefore, magnetic and frequency response analyses were conducted to verify the correlation with inductance, the influence of coupling capacitance, and the influence of the magnetic field formation via the current flowing through the external trace inside the PCB. The coil model is verified and discussed through simulation and double pulse tests.
Recently, as the perception of eco-friendliness has changed, the demand for energy storage devices has been rapidly increasing due to the growth of the electric vehicle industry and smart grid facilities, which are emerging as an alternative to next-generation electricity supply and demand. Therefore, the importance of battery management technology is growing, and various voltage balancing techniques between battery cells are being studied in order to maintain high efficiency and continuous performance of batteries. This paper proposes a voltage balancing topology using a single input-multiple output (SIMO) two-switch flyback converter in a series battery configuration to resolve voltage imbalance between batteries. The characteristic of the proposed topology is that each cell on the secondary side of the two-switch flyback converter is connected to one high-frequency transformer to share the magnetic flux, and voltage balancing is performed according to the switch operation of the converter. At this time, the accumulated excess energy of the converter is refluxed to the power supply side through the freewheeling diode and converted into reactive power. The verification of the usefulness of the theoretical analysis in this paper was based on the analysis of the dynamic characteristics and steady state of the circuit through PSIM and experiments, and was conducted for one module composed of four cells.
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