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A high-power inductive power transfer system with overlapped transmitters driven by a multi-inverter topology is proposed in this article. Each inverter drives an independent primary coil to transfer energy to the common secondary coil. A phase-shifted control strategy at inverter-level is proposed to regulate the output of the system. A dynamic model based on virtual resonant loop is proposed to describe the system with the phase-shift angle and the output voltage as the input and output variables, respectively. With the introduction of virtual resonant loop, n practical resonant loops at the primary side can be expressed by two equations, which greatly reduce the scale and order of the model. A PI controller is developed to evaluate the system regulating performance. A laboratory prototype driven by three inverters connected in parallel was built to verify the theoretical analysis. Experiments have shown that the setting times were within 13 ms under load resistance and reference disturbances, which verified the validity of the model and the controller.

This article is to present the design, analysis, and verification of a new hybrid wireless power transfer (HWPT) system, which has a space-saving coupler structure. The key of the design is to simplify the two coupling capacitor plates into one single frame-shaped plate at each side. Then, the coupling coil for inductive power transfer (IPT) is embedded into the metal frame to form a compact hybrid coupler. Meanwhile, the coupling polarity between the coils is specified to realize the superposition of the inductive and capacitive coupling. As a result, the proposed HWPT system can offer a good comprise of efficiency promotion and a space-saving coupler structure simultaneously. To illustrate the system working principles, the equivalent circuit model is first derived. Then, a detailed analysis is conducted in terms of the reflected impedance. Consequently, the mechanism of the efficiency promotion can be clearly explained. Finally, a prototype is constructed with several experiments, which validate the effectiveness of the proposed HWPT system. Results show that an efficiency increase of 14% over the pure IPT is obtained at 35-cm distance. Moreover, the effects of varying the resonant frequency are also carried out to instruct the practical system design.

This article presents an input-series output-equivalent-parallel (ISOEP) multi-inverter system for high-power wireless power transfer (WPT), where preisolation dc/dc converter is concealed to achieve higher efficiency, and the number of inverter modules is allowed to be flexibly adjusted to satisfy different voltage and power requirements. The main contribution of this article is to analyze the possible factors that may lead to voltage unbalance in the series inverters of the proposed ISOEP multi-inverter topology. At the same time, the dividing capacitor suppression and duty cycle adjustment are adopted to achieve input voltage sharing. To confirm and validate the effectiveness and merit of the proposed WPT system, a prototype consisting of three inverters connected in series was designed, built, and tested. Experiments show that the proposed topology achieved both high-power output and effective input voltage sharing. The maximum output power is 38.37 kW with an efficiency of 89.31%.

In order to provide high and extendable power levels for inductive power transfer (IPT) system, a parallel multi-inverter system based on modular inverter is presented. Various power requirements can be implemented by an adjustment of the number of paralleled inverters, which provides a high modularity. A master−slave scheme is employed for the switching-driver signals of parallel inverters, where one acts as a leader while others act as followers. Despite the master−slave scheme, the proposed circuit topology has natural robustness because of the equality in terms of the hardware configuration of each modular inverter. For proper parameters, the output phase (current lagging corresponding voltage) of an inverter is lower than the average of output phase of all inverters, when its output voltage lags behind others, and vice versa . Based on this approach, PI controllers are designed to implement phase synchronization for output voltages of all inverters. An IPT prototype supplied by the proposed parallel multi-inverter with three inverters was designed, built, and tested. Experiments show that the proposed parallel multi-inverter system has not only good circulating current suppression capacity but also excellent performance of phase synchronization. The maximum dc−dc efficiency was 94% at a 35.1 kW receiving power. This paper is accompanied by a Matlab/Simulink file demonstrating phase synchronization control.

A multiphase inverter with phase-shifted control is proposed for the inductive power transfer (IPT) of electric vehicles where the charging voltage can be regulated by adjusting the angle among the inverter phases. An equivalent circuit model is developed and linearized to analyze the system dynamic characteristics at its operating point. In terms of the high-order model, a balanced model reduction method is used to remove the fast modes that are outside the desired system bandwidth and insignificant to controller design. In addition, the model is discretized and the communication delay of the feedback loop is considered in the discretized model. Based on this model, the parameters of a PI controller are designed to achieve the expected performance indexes. A 6.5 kW S-S compensation IPT system prototype with constant voltage control is built and tested to verify the control performance. The experimental results show that the charging voltage can be maintained constant within 6 ms and has no overshoot under disturbances, which verifies that the closed-loop system with PI controller operates properly and efficiently for IPT. Besides, the measured transmission efficiency of the system at a receiving power of 6.5 kW is 95.1%.

A coil with a high quality factor $Q$ is desired to obtain a high efficiency for inductive power transfer (IPT). $Q$ is proportional to the coil inductance and operating frequency, while it is inversely proportional to the coil resistance, which increases with frequency. An optimized frequency exists to achieve the maximum efficiency. Eddy currents and resulting ac resistance in Litz-wire coils are attributed to magnetic field. Especially, the induction component of the ac resistance is approximately proportional to the squared magnetic field to which the coil is exposed to. FEA simulations are conducted and surface integral method is employed to determine the squared field. Additionally, the volume integral method is proposed to evaluate the overall effect of the field on the induction resistance. The optimized frequency for the maximum efficiency is obtained, using the squared field calculation and resulting ac resistance evaluation. Sample prototype coils are manufactured to verify the resistance analysis methods. An IPT system is built employing these coils. Experiments show that the IPT system achieves the highest efficiency at frequencies closed to the predicted optimized ones.