The proposed research is to accomplish a converter for driving DC load or AC load with wireless power transfer (WPT) technique. In this novel scheme, a full-bridge LLC resonant converter is adopted to deliver the energy from the primary to the secondary side. Besides, the LLC converter has soft-switching characteristic of the switches at the primary to improve the efficiency of the converter if the switching frequency is selected appropriately. In order to achieve the feature of wireless power transfer, the WPT (transmitting/receiving) coils are utilized to replace the transformer. The leakage inductor can be treated as a resonant inductor integrated in the transmitting coil. In the output side, a sinusoidal pulse width modulation (SPWM) technique is added to generate AC voltage for specific load. In other words, the proposed converter can output DC or AC voltage by user's demand. In the end of this research, a LLC converter with WPT technique for 1kW is implemented. The experimental results and the related waveforms are also shown in the content. In this topology, the highest efficiency of DC output is 89.2%, and the highest efficiency of AC output is 82.6% respectively.

This paper proposes a new control technology that enables a synchronous rectifier (SR) buck converter to realize zero voltage switching (ZVS) in light load condition. The SR control technique is applicable to dc low voltage output because the replacement of output rectifier diode by MOSFET can minimize conduction losses and increase the efficiency of the whole circuit. However, the technique cannot achieve good efficiency in light load condition. The control technique introduced in this paper enables an SR buck converter to carry out ZVS in light load condition to increase efficiency. No extra auxiliary switches or RLC passive components are required; thus, it is low cost and easy to control. The output of buck converter with 5 V/25 W featured by SR is developed in this paper; the availability of the technique introduced, herein, is also proven. The experimental results are satisfactory.

A non-contact isolated bidirectional symmetrical resonant converter with dual active bridge as the main structure is proposed in this study. This scheme is combined with the symmetrical resonant network and integrated into an isolated bidirectional symmetrical resonant conversion circuit. The symmetrical resonance technique is used in this work to realize the voltage regulation of a wide range of output and the function of soft switching under the appropriate operating frequency; reduce the electromagnetic noise and power loss caused by hard switching of power switches in the circuit; and improve the overall converter efficiency, voltage regulation, and hard switching from conventional bidirectional converters. In addition, a pair of non-contact loosely coupled inductors (wireless coils) is used to replace the conventional transformer to transfer the bidirectional energy wirelessly. The digital signal processor TMS320F28335 is the control core of the system in this study. The proposed converter with DC grid input voltage is set to 400 V, and the EV battery side is set to 670–800 V. The rated power capacity of the bidirectional wireless charger is 2 kW. Finally, the maximum efficiency of forward charging mode (grid to vehicle [G2V; 400 V charge to 800 V]) can reach 90.2% while that of reverse discharging mode (vehicle to grid [V2G; 800V discharge to 400V]) can reach 91.4%.

In this paper, a bidirectional full-bridge phase-shift converter with high transformation ratio scheme is proposed. The main architecture of this converter is dual active full-bridge circuit. By using phase-shift modulation, the energy can be transmitted between high-voltage-side and low-voltage-side, and also can make the power switches have the function of soft-switching. This converter is designed with the transmission power of 1kW and the digital signal processor TMS320F28335 is utilized as the main system controller core. Finally, it realizes the bidirectional power conversion mechanism between battery 50 Vdc and DC grid 400 Vdc. The experimental results show that the maximum conversion efficiency of this converter when operating in the forward charging mode (G2V mode) is up to 92.25 %, and in the reverse discharging mode (V2G mode), the maximum conversion efficiency is up to 93.02 %. In comparison with the related studies for dual active full-bridge converters, the conventional transformation ratio is lower or equal to 4. This study with high transformation ratio can reach 8 for practical high-low voltage bidirectional applications. After the validation for both modes, the proposed concept is practical in the high transformation scenarios.

In this paper, a fast charging balancing circuit for LiFePO₄ battery is proposed to address the voltage imbalanced problem of a lithium battery string. During the lithium battery string charging process, the occurrence of voltage imbalance will activate the fast balancing mechanism. The proposed balancing circuit is composed of a bi-directional converter and the switch network. The purpose of bi-directional is that the energy can be delivered to the lowest voltage cell for charging mode. On the other hand, the energy stored in the magnetizing inductors of the transformer can be charged back to the higher voltage cell in recycling mode. This novel scheme includes the following features: (1) The odd-numbered and even-numbered cells in the string with the maximum differential voltage will be chosen for balancing process directly. In this topology, there is no need to store and deliver the energy through any intermediate or the extra storing components. That is, the energy loss can be saved to improve the efficiency, and the fast balancing technique can be achieved. (2) There is only one converter to complete the energy transfer for voltage balancing process. The concept makes the circuit structure much simpler. (3) The structure has bi-directional power flow and good electrical isolation features. (4) A single chip controller is applied to measure the voltage of each cell to achieve the fast balancing process effectively. At the end of the paper, the practical test of the proposed balancing method on LiFePO₄ battery pack (28.8 V/2.5 Ah) is verified and implemented by the experimental results.

In this study, a new control strategy was proposed to improve transient response and the input current harmonic distortion of power factor correction (PFC) regulators operating in an average current mode. The proposed technique required only two additional gain selectors and a peak detector circuit on the feedforward voltage loop and output voltage feedback loops. It provided a direct reading for the average voltage value of feedback control loops and the peak voltage of feedforward control loops, producing PFC boost regulators with fast dynamic responses and low-input current harmonic distortion. The use of digital potentiometers for directly changing the gain of control loops did not require any divider or squarer to reduce the complexity of control circuits. The operating principles and control strategies of 300 W boost PFC with the new control strategy are presented with detailed analysis and discussion. The experimental results were satisfactory.