Voltage source converter-based high voltage direct current (VSC-HVDC) transmission is a key enabler for the large-scale integration of renewable energy into modern power systems. This paper proposes a novel step-wave AC collection system designed to enhance the efficiency of VSC-HVDC transmission by reducing both switching and conduction losses. In the proposed system, the sending-end converter operates directly at the line frequency (50 or 60 Hz), which significantly lowers switching losses. Moreover, the step-wave scheme improves DC voltage utilization by 15.5% compared to conventional sinusoidal collection systems, resulting in an estimated 25% reduction in conduction-related losses. The feasibility and performance of the proposed system are validated through detailed simulations and hardware experiments. A 3 kW laboratory prototype demonstrates a 6.1% improvement in transmission efficiency, highlighting the practical advantages of step-wave AC collection in high-efficiency VSC-HVDC applications.

This study proposes a novel active gate driver (AGD) to mitigate voltage and current overshoot issues for silicon carbide (SiC) MOSFETs. The AGD integrates the advantages of existing architectures with a closed-loop dv/dt and di/dt hybrid control mechanism, ensuring adaptability to varying load conditions. The circuit design employs simple BJT followers and passive resistor-capacitor networks, offering real-time feedback, rapid transient response and straightforward implementation. Experimental and simulation results demonstrate that the proposed AGD effectively suppresses voltage and current overshoot, while reducing switching losses by 23-35% compared to conventional gate drivers during hard-switching operations. The AGD’s simplicity, cost-effectiveness, and versatility validate its practicality for high-performance SiC MOSFET systems, proving its potential in modern power electronics applications.

Impedance-based methods are widely used and recognized for small-signal stability analysis of power-electronics-based power systems. However, the existing stability criteria for complex systems always aggregate all equipment/subsystem impedances. As a result, it is difficult to determine the impedance specification that each equipment/subsystem should meet to ensure system stability and a certain stability margin. In this paper, the stability analysis method for grid-connected dc distribution power systems is first proposed. Then, the port impedance specification of each converter is proposed for the system stability design. As long as all converters meet the proposed impedance specifications, the whole system must be stable and has sufficient stability margin. Finally, the case studies and experiments validate the proposed impedance specifications.

The existing power electronic transformer (PET) topologies are governed by the low power density, high cost and large size. Therefore, a multiport PET topology based on modular multilevel converter with the shared medium-frequency transformer (MFT) is proposed in this paper, where the proposed PET can provide four voltage interfaces, including medium-voltage AC and DC ports, low-voltage AC and DC ports. With the multi-frequency modulation and voltage decoupling circuit design, the circuit structure of PET is compact. And because of the shared MFT, the size of PET can be optimized. In addition, the simulation results verify that the proposed PET is feasible.

A novel dc-dc converter with symmetrical bipolar low-voltage dc (LVDC) outputs is proposed, which is based on dual-active-bridge converter with one active-neutral-point-clamped (ANPC) arm. With the ANPC arm, bipolar dc bus voltages can be balanced. The proposed dc-dc converter can be employed as the submodule of DCT and constitute the bipolar LVDC distribution grid. Comparing to the schemes which adopts two DCTs or voltage balancer, the scheme based on proposed converter can obtain lower volume and higher power density. Additionally, all switches in proposed converter can achieve ZVS turn-on, which help improves the conversion efficiency. In this paper, the operation principle of proposed converter is analyzed in detail, on the basis of which steady-state control strategy are derived. Also, considering the possible faults of dc bus, control strategy for fault situation is discussed. Finally, simulation with PLECS verifies the feasibility of proposed converter.

Constructing multi-terminal high voltage dc (HVDC) systems can effectively make it possible for the large-scale new energy to be integrated into the grid and make up the defects of the existing ac power system. When constructing the multi-terminal dc system, one cannot avoid the problem that how to control the dc power flow effectively. When nodes are increased and structure of dc grids becomes more complex, power flow of dc grids cannot be controlled effectively and distributed optimized. Inserting power flow controllers into dc grids can effectively control power flow. This paper firstly summarizes the existing dc power flow control technologies and points out the advantages, disadvantages and application occasions of the whole dc power flow controllers and proposes a new dc power flow controller. Different kinds of dc power flow controllers are chosen and simulated in a five-terminal HVDC system with PLECS.