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This letter proposes a novel voltage-gain design method for domino wireless power transfer (WPT) systems that can achieve load-independent zero-phase-angle and constant voltage conditions simultaneously. In the proposed method, only three compensation capacitors are tuned to achieve the design goals without changing the structures of identical domino coils, which increases the interface flexibility and stabilities of domino WPT systems to match the voltage difference between the power source and the load in various applications. A new character that the compensation capacitors in certain coil loops have monotonic influences on the input and output is revealed. Based on the transfer coefficient model, this character is modeled and explained in detail, resulting in an explicit capacitor design flowchart. The validity and accuracy of the proposed method are demonstrated using a five-coil experimental prototype to achieve three different voltage gains.

Maximum efficiency point tracking (MEPT) is a key concept to improve the ac-ac efficiency of the wireless power transfer (WPT) systems by controlling the equivalent load impedance with a dc-dc converter or an active rectifier. The on-off keying (OOK) modulation can reduce the switching losses of the converters to achieve MEPT but generates relatively large dc voltage ripples. In order to solve this problem, this article proposes an enhanced on-off keying (EOOK) modulation method by adding a half-bridge mode based on OOK modulation for WPT systems. By combining the three operation modes, both the inverter and the active rectifier can operate in full-bridge-half-bridge mode or half-bridge-zero mode to adapt to different power levels and achieve MEPT simultaneously. Meanwhile, the ZVS condition and the low voltage ripple are achieved as well. The circuit model of the proposed method is analyzed to derive the equivalent load resistance, the output voltage gain, and the output power with respect to the modulation of EOOK. The reason for output voltage ripples and the power losses on both the transmitting and receiving sides are also revealed. An experimental prototype is built to verify the effectiveness of the proposed method. The experimental results show that the proposed method can maintain constant voltage output and achieve MEPT as well as ZVS operation, with high efficiency of up to 94.761% over a wide range of load conditions.

Wide output voltage range applications are challenging for wireless power transfer systems. Under conventional single-mode control [i.e., single full-bridge (FB) or single half-bridge (HB)] based on phase-shift modulation, the system efficiency would be degraded when satisfying wide voltage gain requirement, especially in low gain. The main reason is that wide output voltage regulation requires the conducting angle varying in large operating ranges. When pulsewidths of the square voltage are adjusted to narrow, the switching loss increases and the system efficiency decreases significantly. Therefore, to address the abovementioned issue, in this work, a multimode control is proposed for wide output voltage range applications. Using the multimode control, the inverter can operate in HB mode, HB–HB mode, and FB–HB mode. Compared with an FB inverter, the conducting angle can be effectively maintained larger, and all the switches can realize zero-voltage-switching in a wide range. Thus, the system efficiency can be improved significantly. Furthermore, the online mutual inductance detection unit is not necessary. A 1.7 kW experimental prototype is built to verify the feasibility and effectiveness of the proposed method. The results show that the proposed system can achieve high efficiency from 91.5% to 97.1% under a wide output voltage range.