Inter-turn insulation made of polyimide (PI) is considered to be the weakest part of the solid-state transformers (SST) composites insulation system due to the existence of an interface between the cast epoxy resin (EP) and itself. Ion-exchange strategy can be used to regulate the dielectric and electrical properties of PI insulating dielectric to ensure the stability of the composite insulation system. Therefore, this paper intends to investigate the effects of the ion-exchange strategy on the space charge accumulation and interface insulation performance between PI and EP composites insulation. Our experimental results demonstrate that the wide-bandgap alumina (Al ₂ O ₃ ) nanoparticles can effectively improve the dielectric compatibility of PI and EP and significantly suppress the space charge accumulation on the PI/EP interface. The novel PI/EP composite structures insulation with breakdown strength about 39.5% higher than that of traditional PI/EP is obtained. The improvement mechanism is that the Al ₂ O ₃ layer introduces a large number of deep traps on the surface of the PI film as well as reduces its dielectric compatibility with the EP, suppresses charge accumulation at the PI/EP composites insulation interface, and thus enhances the high-frequency insulation performance. In this paper, the proposed surface engineering strategy is convenient and scalable, providing new insights into the regulation of composite insulation interfacial compatibility in high-voltage power equipment.

This study targets insulation challenges in high-frequency power transformers (HFPTs), which are an integral part of the high-voltage, high-capacity isolated DC/DC converter under development for offshore renewable energy systems. We propose a nano-silicon carbide (SiC)-doped polyimide (PI) winding insulation strategy to enhance discharge resistance and thermal stability under high-frequency electric stress. Experimental results show that 10 wt% SiC doping significantly improves insulation performance, extending failure time from 17 to 50 min and reducing maximum discharge amplitude by 76%, owing to enhanced charge trapping and interfacial polarization suppression. Surface and volume resistivity measurements further confirmed the improvement; at 120 °C, the 10 wt% SiC composite maintained high surface resistivity 3.30 × 10¹⁴ Ω and volume resistivity 1.41 × 10¹⁵ Ω·cm, significantly outperforming pure PI. In contrast, 20 wt% SiC, though still resistive, showed reduced stability due to agglomeration and interfacial defects, with a surface resistivity of 2.07 × 10¹⁴ Ω and degraded dielectric performance. Dielectric analysis revealed that 10 wt% SiC suppressed dielectric constant and loss across the frequency range, while 20 wt% SiC exhibited increased values at high frequency. These results highlight 10 wt% SiC as an optimal formulation for HFPT winding insulation.

This paper focuses on the Input-Independent Output-Series (IIOS) DC converters within fully DC aggregation systems, which enable independent submodule control and high voltage gain. DC aggregation systems experience output voltage imbalance among submodules due to offshore wind power fluctuations. The proposed isolated DC/DC converter topology incorporates power-balancing capacitors, leveraging intrinsic characteristics to achieve self-power balancing within the system. In addition, this paper proposes an innovative PFMT-PSMN hybrid control strategy that is well-suited for the proposed topology. Firstly, this study performs a time-domain analysis of the intrinsically power-balanced DC series-connected aggregation topology and elucidates the corresponding power-balancing principle. Secondly, based on soft-switching boundary conditions, a hybrid control strategy, PFMT-PSMN, adjusts phase-shift duty cycles to maintain soft-switching conditions while minimizing the system operating frequency. Finally, MATLAB/Simulink simulations validate the power-balancing capability of the intrinsically balanced DC series-connected aggregation system and the effectiveness of the proposed PFMT-PSMN control strategy.

As the core component of offshore wind power converter, the encapsulated silicone gel insulation material of insulated gate bipolar transistor (IGBT) module is prone to deterioration under the long-term action of ocean salt fog operation environment. In order to study the surface discharge of silicone gel in salt fog environment, this article designs a discharge experimental platform and measurement samples. Based on the partial discharge measurement results along the sample surface under square wave voltages, it is found that the number and phase of surface discharge of silicone gel under the salt fog environment are positively correlated with the voltage frequency. Meanwhile, the amplitude and the phase of discharge under the ocean standard condition show an increase of 54.4% and 32.8% compared with those under the condition without salt fog. Furthermore, the measurement finds that there is a special frequency-induced inflection point phenomenon of surface breakdown voltage at 15 kHz under the salt fog environment. Therefore, a mathematical model of the inflection point is established by further combining the influencing mechanism of salt fog ions and voltage frequency on the discharge, and the calculated inflection frequency of 16.99 kHz is close to the measurement result. The results of this article can provide theoretical support for the characteristics and mechanism of surface discharge of IGBT silicone gel insulation under salt fog environment.