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The surge in electric vehicle technology has brought attention to the manufacturing and design of 22-kW on-board chargers using printed circuit boards (PCBs), owing to their manufacturability and compact nature. However, designing transformers for these applications is challenging due to the demands of higher power and a smaller profile. The challenges include achieving optimal current distribution in parallel windings and easier transformer structure with better thermal performance. In addition, the integration of resonant inductance is crucial for regulatory functions and higher power densities. The integration with parallel windings also impacts the overall transformer performance, which needs to be analyzed. This article presents a detailed analysis and design approach for a 22-kW PCB-based transformer with good current sharing, controllable leakage inductance, and a simplified core structure. The study also includes an in-depth analysis of the transformer's flux distribution to minimize core loss. A 22-kW CLLC resonant converter is developed to validate the proposed transformer using PCB-packaged devices. With its modified flux distribution and good current sharing, the integrated transformer enables the converter to achieve a power density of 11.6 kW/L and a peak efficiency of 98.5%.

This article proposed a printed-circuit-board (PCB) based integrated magnetics with a winding cancellation technique to reduce common-mode (CM) noise for an 11-kW single-phase CLLC (1PCLLC) resonant converter. Shielding design is effective in reducing CM noise; however, its benefits come along with increased cost with more layers of PCB and increased winding loss due to increased eddy effect in the shielding layers. More shielding layers are required for multiple-turn applications, which makes the idle shielding design unattractive. Implementing windings as active shielding for noise cancellation is a good solution. A symmetrical 1PCLLC converter with symmetrical resonant tanks and symmetrical integrated magnetics is required to achieve the winding cancellation technique. The proposed integrated magnetics consists of three elemental transformers (ETs) with two identical ETs with built-in leakage inductance and one pure transformer. The physical middle points in the primary and secondary windings of the pure transformer become the static-electrical-potential points that can adopted as the starting point to achieve winding cancellation with proper winding arrangements. The effectiveness of the proposed concept was demonstrated through a high-efficiency, high-power density 1PCLLC dc/dc converter for an 800-V 11-kW onboard charger. The designed converter can achieve a power density of 420 W/in3 and a peak efficiency of 98.5%. Compared with the existing solution, the proposed integrated transformer with winding cancellation techniques shows 17-dB CM noise reduction at switching frequency.

This article proposed a universal method of integrating magnetizing inductance with built-in leakage inductance based on multiple perfectly coupled transformers (PCTs). The integration of built-in leakage inductance can be achieved by connecting several PCTs using a standardized core type for cost considerations or can be further integrated into a customized core with interleaved magnetomotive force polarities across transformer legs to achieve better flux distribution and smaller core loss. The proposed concept can be applied to single-input single-output and multiple-input multiple-output integrated transformer applications. A 3 × 3 PCTs based integrated transformer built with printed circuit board windings was designed for a three-phase CLLC (3 PCLLC) resonant converter, which integrates three primary resonant inductors, three secondary resonant inductors, and three transformers into one magnetic core to simplify the complexity of the converter. The effectiveness of the proposed concept was demonstrated through a high-efficiency, high-power density 3 PCLLC dc/dc converter for an 800-V 16.5-kW on-board charger. The designed converter can achieve a power density of 500 W/in3 and a peak efficiency of 98.8%.

Transformer design is critical to high-power high-frequency dc/dc resonant converters. For the design of a high-current transformer with parallel windings, current sharing, resonant inductance integration, as well as performance optimization are still quite challenging. Therefore, a comprehensive analytical model of the current distribution between the parallel litz wire windings is developed in this article. Based on this model, a novel winding structure is proposed to eliminate the current discrepancy. Furthermore, the performances of two typical resonant inductance integration methods are compared when applied to parallel windings. With the selected transformer structure, loss and volume optimization is also conducted. It is worth mentioning that the proposed transformer structure and design principles have good scalability and can be extended to higher power ratings easily. Finally, the analysis and design are verified in two 100-kHz transformers for a 30-kW LLC resonant converter. The current difference between parallel windings does not exceed 3.6%. The efficiency and power density of the transformer at 30 kW is up to 99.6% and 22.4 kW/L, respectively.