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 inductive power transfer (IPT) systems, impedance matching is critical in obtaining high efficiency. However, since the load impedance is subject to variations in most applications, especially wireless charging, maintaining impedance matching is a challenge. One valid solution is to, by controlling a load-side power converter, maintain the equivalent load impedance at the optimal value against load variations. Nonetheless, the system overall cost, size, and complexity can be increased. In this paper, based on a proper selection between full-bridge and half-bridge modes of the inverter and rectifier, an operation mode selection method is proposed that can achieve semi-impedance-matching with large load variations. In general, with the proposed method, high overall efficiency can be obtained while neither additional power converters nor complicated control is required. A 1 kW prototype has been developed and the experimental results have verified the proposed method.

In this study, a novel modulation of an isolated three-phase bidirectional dc-dc converter is proposed for the high-voltage input power supply to low-voltage output energy storage systems. The wye-delta connection of the transformers is employed to reduce the voltage stress at the high side and the current stress at the low side of the transformers. Frequency control allows the output voltage regulation, and a phase-shift algorithm with a resonant tank is proposed following with the switching frequency to reduce the frequency range with the specific power. Furthermore, the zero-voltage-switching condition for all mosfets in the entire power range, which is the major restriction of a single-phase converter, is also discussed in this paper. The three-phase wye-delta converter significantly reduces the ripple of inductor current compared with that of a single-phase converter. A 2 kW prototype converter was built and successfully tested to verify the capability of such control modulation.

Circuit analysis and design criteria of a two-phase bidirectional converter with high voltage-gain are presented in this paper. The operating principle of the forward or reverse mode is similar to that of the conventional buck or boost converter. Compared with the conventional converter, the switch stresses can be reduced significantly depending on the operating region of the voltage ratio in the two-phase converter. The power losses can be also reduced due to the use of low-voltage rating switches. The derivate converters are discussed to demonstrate the advantages of the proposed topology. A 200 W/ 1 MHz two-phase prototype converter with Gallium Nitride (GaN) devices is built and tested to verify the feasibility.

This study presents a control method for isolated bidirectional dual‐active‐bridge converters to optimise the efficiency by achieving the zero‐voltage switching (ZVS) in high‐voltage applications, which the switching losses are the major issues. At light‐load condition, the duty control algorithm is proposed to achieve the ZVS for all switches while the triple phase shift with ZVS condition is realised at heavy load condition. The operating principles and the design considerations of the proposed control scheme are analysed in detail. A 2 kW prototype converter is built up and tested to verify the feasibility of the proposed control strategy.