This paper presents a thermal management framework for 120 kV hybrid commutated converter (HCC) valves, addressing critical cooling challenges in multi‐hundred‐MW power conversion systems. Power loss calculations under rated (1.0 p.u.) and overload (1.2 p.u.) conditions demonstrate that HCC valves achieve comparable loss levels to line commutated converter counterparts while enabling active turn‐off control. Comparative analysis of radiator configurations identifies 2‐parallel branch connections as optimal. Integrated thermal‐fluid models combining 3D finite element analysis and computational fluid dynamics reveal significant temperature gradients and flow maldistribution in baseline designs. On this basis, this paper modifies the flow from equal flow resistance allocation to heat‐based allocation and it reduces maximum integrated gate‐commutated thyristor temperature rise by 7.3% at 1.2 p.u. with minimal pressure drop variation. Experimental validation confirms the proposed cooling strategy enhances valve safety margins through improved heat dissipation balance, providing a validated theoretical foundation for high‐power converter thermal design.

The power transformation process at the level of hundreds of MW generates significant loss, posing great challenges to the heat dissipation of the converter valve. This paper calculates the loss under overload conditions of a 120kV hybrid conversion converter (HCC) valve and proposes a design method for a thermal-balanced converter valve cooling structure. An improved model of the converter valve cooling structure is established, and flow distribution and thermal analyses are conducted. The results show that the improved cooling system can reduce the maximum surface temperature of the power device by 1.6°C, which decreases the temperature rise by 7.3%. The proposed thermal-balanced cooling method enhances the safety margin of the converter valve, and provides support for the thermal design of the converter valve.

The control strategy in current research of chopper controlled DC breaking resistor in offshore wind farm DC integrating systems shows many shortcomings, such as its large voltage fluctuating range, uncontrollable switching frequency, and significant difference in control performance under different operating conditions. To overcome these shortcomings, a control strategy of DC breaking resistor in offshore wind farm DC integrating system is proposed, in which the DC voltage is collected as the only input signal, and the surplus power is calculated based on the voltage change rate and the equivalent charging capacitance of DC system; duty cycle of the power electronic switches are roughly determined by the surplus power, and then further adjusted according to the error between DC voltage and its reference value, so as to stabilize the DC voltage. Simulation results show that this control strategy successfully realizes the function of automatically deblocking when a fault occurs at the receiving AC power grid, maintaining DC voltage stable during the fault, and automatically blocking after the fault is cleared. At the same time, the control strategy performs stable under different operating conditions, with the characteristics of fast adjustment speed, small adjustment oscillation, and low steady-state ripple.

Although the modular multilevel converters (MMCs) that contain submodules (SMs) with negative voltage capability have various advantages, they usually demand many more semiconductors than the conventional half-bridge SM-based MMC (HB-MMC). This study proposes a unidirectional-current clamp-double submodule (UC-CDSM) by combining two unidirectional-current full-bridge SMs (UC-FBSMs) using a shared switching device. The sharing design enables the UC-CDSM-based MMC (UC-CD-MMC) to have 25% fewer switching devices compared with the UC-FBSM-based MMC. The quantity of switching devices is rather similar to that in a conventional HB-MMC while the UC-CD-MMC still retains the advantages, such as low capacitor usage, dc fault clearing capability, and wide-range dc voltage adjustability. Moreover, a unidirectional-current hybrid MMC composed of UC-CDSMs and UC-FBSMs (UC-HYB-MMC) is presented to further enlarge the adjustable range of dc voltage. Detailed comparisons indicate that the UC-CD- and UC-HYB-MMCs can reduce the valve costs by 32% and 25%, respectively, and volumes by 39% and 34%, respectively, compared with HB-MMCs. Simulation and experimental results verify the steady-state and dc-fault clearance of the proposed topologies, and that the capacitor voltages in the UC-FBSMs and UC-CDSMs are well maintained and balanced in the UC-HYB-MMC.

Integrated Gate Commutated Thyristors (IGCT) has a natural advantage in high voltage and large capacity power electronic equipment due to its high current processing capability. However, due to the positive feedback in the IGCT turn on process, the turn-on clamp circuit must be added to limit the switching speed which reduces system efficiency. This paper firstly introduces the working principle of opening clamp circuit. Secondly, the bus current in Modular Multilevel Converter (MMC) and Double Active Bridge (DAB) are compared, and pointed that the backflow power of DAB will significantly increase the loss of clamped circuit. In order to reduce the loss if clamped circuit and further improve the efficiency of IGCT-DAB, reducing the inductance and buffer capacitor in parallel with the IGCT were proposed, and their feasibility was analyzed. Finally, a DAB prototype of 1.5kV/3MW was constructed in MATLAB/Simulink to verify the correctness of the theory.

An IGCT-Series-Based DC Transformer (IGCT-Series-DCT) and a quasi-zero switching loss modulation technique are proposed together to realize the direct access of single module DCT to medium voltage DC network in DC distribution network and DC pooling. Through IGCTs directly in series, IGCT-Series-DCT has a medium voltage port. In order to prevent surge current in buffer capacitors used for voltage balancing, soft commutation modulation (SCM) is used to ensure the zero voltage switching (ZVS) of ICGT under light and no load. Then, the ZVS conditions are analyzed in detail considering buffer capacitor and dead time. The relationship between the system power and the phase shift ratio at the minimum backflow power is derived. Through accurate system parameter design, the voltage balance of IGCT-Series-DCT series in the full power range is realized. Finally, a 10kV 3MW IGCT-series-DCT prototype was built to verify the feasibility of the system solution.

Application of power electronic and DC distribution are the development trend of medium voltage distribution network in the future. The compactness and miniaturization of power electronic equipment are the technical difficulties that must be overcome in the application process of medium voltage DC distribution. This paper analyzes the quantitative relationship between the number of MMC sub-modules, the capacitor voltage ripple, and the total capacitance consumption, purposing to reduce the capacitance consumption of the whole MMC to achieve a compact design. Meanwhile, in order to ensure the overall modulation performance of the MMC in which number of modules is reduced and the sub-module voltage ripple is increased, a carrier phase-shifting indirect modulation method based on the energy prediction of the bridge arm is proposed, this modulation method is effective to improve the utilization ratio of the sub-module capacitor voltage. Simulation results show that the MMC using the high-ripple compact design performs as well as the MMC using conventional design under various power levels, while the high-ripple compact design has a 30% reduction of total capacitance consumption.