Inductive power transfer (IPT) converters are resonant converters that attain optimal energy efficiencies for a certain load range. To achieve maximum efficiency, it is common to cascade the IPT converter with front-side and load-side dc/dc converters. The two dc/dc converters are normally controlled cooperatively for the requirements of output regulation and maximum efficiency tracking using a control technique based on perturbation and observation, which is inevitably slow in response. In this paper, a decoupled control technique is developed. The load-side dc/dc converter is solely responsible for output regulation, while the front-side converter is responsible for impedance-matching of the IPT converter by controlling its input-to-output voltage ratio. The controls are linear and therefore fast. DC and small-signal transfer functions are derived for designing the control parameters. The performances of fast regulation and high efficiency of the IPT converter system are verified using a prototype system.

This paper studies wireless charging of lithium-ion batteries for electric vehicles. The charging profile mandates a constant-current (CC) charging for a discharged battery until the battery voltage reaches the cutoff voltage at rated power. The charging continues at the cutoff voltage with a constant-voltage (CV) charging at a power level down to 3% of the rated power in order to fully charge the battery. An inductive-power-transfer (IPT) converter should be designed with minimal number of stages to achieve high efficiency. However, high efficiency for such a wide load range is difficult to achieve. Moreover, the efficiency-to-load relationship is distinctly different for CC and CV charging operations, posing difficulties for the single-stage design. This paper describes the design of a single-stage IPT converter that complies with the battery charging profile and, at the same time, achieves optimal efficiency. Design optimization includes soft switching for the entire battery load range, efficiency optimization for CC and CV modes of operation, and system efficiency optimization for the whole battery charging profile. Measured results of two experimental IPT battery chargers are presented for illustration and verification.

This article proposes a single-stage inductive-power-transfer (IPT) converter operating as a wireless constant-power (CP) and maximum-efficiency battery charger. By maintaining a constant output power rather than providing a constant output current throughout the dominant stage of battery charging, the IPT converter can make the utmost of its power capability, thus having a faster charging rate. The proposed single-stage IPT converter adopts series-series compensation and includes a switch-controlled capacitor (SCC) and a semiactive rectifier (SAR) in the secondary side. Manipulating the SCC and the SAR to emulate the optimum impedance of the resonator and the load, we propose a novel operation approach combining the merits of load-independent transfer characteristic and load impedance matching, to achieve a simple solution to CP charging and maximum efficiency throughout the charging process. Since the control scheme is based on fixed operating frequency and secondary-side real-time regulation, wireless feedback communication is not required. Moreover, soft switching and low voltage stress can be easily achieved in this IPT converter.

A constant current (CC) output followed by a constant voltage (CV) threshold is usually needed for an inductive power transfer (IPT) charger to comply with the battery charging profile. This letter proposes a novel clamp coil assisted IPT battery charger that features inherent, passive, automatic, and smooth CC-to-CV transition. Since the CC-to-CV transition eliminates the necessity of state-of-charge detection, wireless feedback communication, and active control, the proposed IPT charger is rugged and reliable. The inherent CC-to-CV transition capability also tackles the open-circuit risk during a CC charging process. As minimalist design is achieved in the secondary, the proposed IPT charger is suitable for wireless onboard charging applications. Near-unity power factor design is also considered to minimize the voltage-ampere rating and permits soft switching. Experiment results validate the inherent CC-to-CV transition capability.

Inductive-power-transfer (IPT) converters should desirably achieve nearly zero reactive circulating power, soft switching of power devices and load-independent constant output voltage or current with optimized transfer efficiency and lowest component ratings. However, the load-independent output characteristic is dependent on IPT transformer parameters and their compensation. The space-constrained IPT transformer restricts the design of the low-order resonant circuit compensated IPT converter, making the IPT converter hard to optimize. This paper will analyze conditions under which any extra design freedom can be allowed for a double-sided LC compensation circuit in order to achieve load-independent output and zero reactive power input. A detailed analysis is given for the double-sided LC compensation achieving zero reactive power input and constant current output, without being constrained by the transformer parameters. Design conditions of the compensation circuit parameters for achieving these two properties are derived. A complementary LC-CC compensated IPT converter is further proposed to extend the output current amplitude limitation of the double-sided LC compensated IPT converter. Finally, prototypes of the IPT converters are constructed to verify the design flexibility of the proposed double-sided LC compensation circuit for achieving the multiple objectives.