This work develops an isolated bidirectional CLLC converter that achieves a wide output-voltage range for residential energy storage systems (ESS), while maintaining high efficiency and achieving high power density. The circuit is a two-stage architecture, where the first stage is an isolated CLLC converter with open-loop fixed-frequency control and the second stage is a buck converter used for output voltage regulation. The influence of the bus voltage on the efficiency of the system in both forward and reverse operation modes is analyzed. Then, an asymmetric resonant tank design is developed such that different voltage gains are achieved in each mode with high switching frequency operation at the resonance point to optimize efficiency. For high power density, an improved integrated transformer structure with controllable leakage is designed for the high step-down ratio specification of the ESS application. The core design is optimized based on core loss, copper loss, and core volume. A 1-kW experimental prototype using GaN switches was implemented with an input voltage of 380 V, output voltage of 35–50 V, highest efficiency of 94.55%, and power density of 5.56 W/cm3. The front-end stage CLLC converter operates at 700 kHz with a maximum efficiency of 97.02%.

This article proposes a high-performance, high-switching-frequency triangular-conduction-mode (TCM) bidirectional-interleaved buck converter for battery charging using digital control. Accurate conditions for achieving zero-voltage switching (ZVS) without zero-crossing detection (ZCD) are derived while considering the nonlinear parasitic capacitance of the switch components. This article also optimizes the method of calculating the switching frequency to reduce the delay time of pulsewidth modulation, thereby enhancing system stability. The conventional control method has inadequate resolution in the phase shift register of the digital controller under high switching frequency, hindering perfect interleaving of the two phases at 180°, which affects the characteristics of current ripple offset. The proposed control method effectively reduces the phase error between the two phases in an interleaving structure under high-frequency operation. In this way, full-range ZVS can be achieved when the circuit operates at the correct switching frequency. ANSYS Q3D Extractor software is employed to simulate the impedances of the power loops and investigate parasitic parameters, enabling optimization of the layout and modification of the switching frequency. An experimental prototype of a bidirectional buck converter using GaN switches was implemented with an output power of 1 kW, an input voltage of 66 V, an output voltage of 35-50 V, a switching frequency of 350 kHz-1 MHz, a highest efficiency of 97.52%, and a power density of 10 W/cm ³ .

In this study, a light emitting diode (LED) driver containing an integrated transformer with adjustable leakage inductance in a high-frequency isolated LLC resonant converter was proposed as an LED lighting power converter. The primary- and secondary-side topological structures were analyzed from the perspectives of component loss and component stress, and a full-bridge structure was selected for both the primary- and secondary-side circuit architecture of the LLC resonant converter. Additionally, to achieve high power density and high efficiency, adjustable leakage inductance was achieved through an additional reluctance length, and the added resonant inductor was replaced with the transformer leakage inductance without increasing the amount of loss caused by the proximity effect. To optimize the transformer, the number of primary- and secondary-side windings that resulted in the lowest core loss and copper loss was selected, and the feasibility of the new core design was verified using ANSYS Maxwell software. Finally, this paper proposes an integrated transformer without any additional resonant inductor in the LLC resonant converter. Transformer loss is optimized by adjusting parameters of the core structure and the winding arrangement. An LLC resonant converter with a 400 V input voltage, 300 V output voltage, 1 kW output power, and 500 kHz switching frequency was created, and a maximum efficiency of 97.03% was achieved. The component with the highest temperature was the transformer winding, which reached 78.6 °C at full load.

A three-phase interleaved boost converter stage of an ac-dc PFC converter that uses GaN switches is developed that utilizes a feed-forward band-stop filter control method to suppress low-frequency output voltage ripple. To increase power density, the converter switches at 500 kHz, operates in triangular current mode (TCM) to achieve zero voltage switching (ZVS), and uses GaN switching devices. A 1-kW laboratory prototype was designed and tested to verify feasibility. With the proposed controller, output ripple was reduced by 70%. Overall efficiency is greater than 96.5% and power density is 65.028 W/in ³ .