The double-sided LCC (DLCC) compensation has been widely used in inductive power transfer (IPT) systems because it has a load-independent current source output directly proportional to the coils’ coupling, which makes it inherently safe against misalignment. The input current of the DLCC typically has high harmonic distortion due to the low-pass filter characteristic of the input LC components. Consequently, predicting the inverter’s turn-off current through circuit modeling using the first-harmonic approximation (FHA) would result in a significant estimation error. However, an accurate computation is essential to determine whether the inverter’s zero-voltage switching (ZVS) turn-on is achieved. This paper defines an analytical model that effectively predicts the inverter turn-off current point for any operating condition, i.e., when the diode rectifier operates in continuous and discontinuous conduction modes. It has been found that the inverter turn-off current depends on the loading condition. Therefore, the proposed method is based on modeling the equivalent load as the rectifier together with the battery. Experimental verification has been conducted using two IPT systems with nominal power levels of 3.7 kW and 7.7 kW.

The compensation and high-efficiency operation of the multimodular inductive power transfer (IPT) systems has been a challenge because of the inter- and cross-coupling between modular charging pads. This article analyzes the series–series (S–S) compensation and the associated bifurcation problem in multimodular IPT systems based on closed-form analytical modeling of the coupled circuits. From the analytical results, an improved compensation tuning method for multimodular systems is demonstrated. This improved compensation addresses the intercoupling between coils on the same side, in addition to the self-inductance of the charging pad. As a result, the system’s efficiency improves while also saving an extra capacitor compared with other circuit-based decoupling methods. In addition, a design guideline based on the sum of the coupling coefficients including cross-coupling is derived to avoid bifurcation. The phase angle of the input impedance is studied under various scenarios, demonstrating the validity of the proposed design guideline. Experimental results on a downscaled prototype show that the improved compensation method enhances efficiency by more than 2% compared with scenarios where intercoupling is not compensated, and verification of the proposed bifurcation mitigation guideline.

This article presents an optimal multivariable control (OMC) strategy for the LCC-LCC compensated wireless power transfer systems. To mitigate reactive power and achieve higher efficiency, the proposed OMC method incorporates dual-side hybrid modulation and primary-side switch-controlled-capacitor (SCC) tuning into the triple-phase-shift (TPS) control. First, the impact of hybrid modulation and SCC tuning on the system characteristics is investigated. The inverter and rectifier zero-voltage-switching (ZVS) conditions are then analyzed to achieve dual-side ZVS with minimal reactive power. Furthermore, a multivariable optimization problem is established based on the power loss analysis. The solution to this problem provides optimal control variables that minimize the overall system loss. Through collaborative modulation and control of the inverter, rectifier, and SCC, the proposed method reduces the rms values of the currents and lowers the turn-off currents for the converters. As a result, this approach improves efficiency in both light- and heavy-load conditions, enabling wide output regulation and full-range efficiency optimization simultaneously. Finally, the proposed method is benchmarked with the existing TPS method. Experimental results demonstrate that the proposed method achieves higher dc-to-dc efficiency in the power range of 0.2-2.2 kW, with a maximum efficiency improvement of up to 6.3%.

Inductive power transfer systems can process higher power using multiple charging pad modules connected in parallel. However, the effects on the system operation of the inter-/cross coupling among the pads have to be studied. This paper analyses the power transfer efficiency and current distribution of a quadruple modular IPT system. Additionally, a sensitivity analysis of the power transfer efficiency is provided based on the tolerances of the secondary resonant capacitors. The analysis shows that the efficiency of a multi-modular IPT system will increase compared to a single module and that there would not be a negligible imbalance in the current due to the inter-/cross coupling. In the experiments, the results of the quadruple modular IPT system's estimated AC efficiency are lower than a single module. It also shows that the could be bifurcation when multiple modules are deployed. Both can be attributed to the mismatch in resonant frequency, self-inductance and main mutual inductance between the modules. Future work will focus on mitigating the circulating currents caused by the mismatch between modules.

Resonant circuits are commonly used in inductive power transfer (IPT) systems for the charging of electric vehicles because of the high power efficiency. Transient behaviors of the resonant circuits, which play a significant role in the design and analysis of IPT systems, are cumbersome to model analytically because of the high-order. This article develops a reduced-order continuous dynamic model based on the energy interactions among the resonant tanks. By applying the proposed energy balancing method (EBM), the order of the dynamic model is reduced to half of the number of the passive components in the resonant circuits. To show the accuracy of the EBM, the dynamics of a series-series (SS) compensated IPT system are modeled using Laplace phasor transformation (LPT) and EBM separately and the results are compared. The order of the EBM is found to be one-fourth of that of the LPT method. The sensitivity of the EBM to the switching frequency is discussed when the zero voltage switching turn-on operation is attained. Besides, to prove the advantage of reducing the order of the dynamic model, model predictive controls (MPCs) based on EBM and LPT are developed. The transient performances of the MPC controllers are simulated and the control inputs are applied to an experimental setup. Finally, experiments are conducted to verify the accuracy of the proposed EBM under zero and nonzero conditions and the effectiveness of the developed MPC controller.

Due to the urgent desire for a fast, convenient, and efficient battery charging technology for electric vehicle (EV) users, extensive research has been conducted into the design of high-power inductive power transfer (IPT) systems. However, there are few studies that formulate the design as a multiobjective optimization (MOO) research question considering both the aligned and misaligned performances and validate the optimal results in a full-scale prototype. This article presents a comprehensive MOO design guideline for highly efficient IPT systems and demonstrates it by a highly efficient 20-kW IPT system with the dc-dc efficiency of 97.2% at the aligned condition and 94.1% at 150-mm lateral misalignment. This achievement is a leading power conversion efficiency metric compared to IPT EV charging systems disseminated in today's literature. Herein, a general analytical method is proposed to compare the performances of different compensation circuits in terms of the maximum efficiency, voltage/current stresses, and misalignment tolerance. An MOO method is proposed to find the optimal design of the charging pads, taking the aligned/misaligned efficiency and area/gravimetric power density as the objectives. Finally, a prototype is built according to the MOO results. The charging pad dimension and total weight, including the housing material, are 516∗552∗60 mm3/25 kg for the transmitter and 514∗562∗60 mm3/21 kg for the receiver. Correspondingly, the gravimetric, volumetric, and area power density are 0.435 kW/kg, 581 kW/m3, and 69.1 kW/m2, respectively. The measured efficiency agrees with the anticipated value derived from the given analytical models.

The increase in popularity of electric vehicles (EVs) and the pursuit of user convenience makes wireless power transfer (WPT) an attractive technology for the charging of batteries. The usage of WPT in e-transportation is not straightforward because the current standardization limits the allowed operating frequency range and magnitude of the irradiated magnetic field. Although, to safeguard the zero voltage switching (ZVS) of the intrinsic inverter switches, their operating frequency needs to be slightly adapted at all time such that the circuit functions in the equivalent inductive region of the passive network. Besides the semiconductors’ soft switching, another control objective is limiting the inverter current to restrain the irradiated magnetic field. The start-up of the WPT system can be particularly challenging because uncertainties on the loading condition and coils’ misalignment can complicate these control objectives. This paper benchmarks three start-up modulation strategies for the H-bridge inverter which aim to reduce the amplitude of the transient currents and to ensure ZVS operation for the S-S compensation and double-sided LCC compensation. In addition two soft shut-down strategies are compared for the S-S compensation. The results show that the symmetrical phase-shift (SPS) control with self-oscillating feedback control, also known as Dual Control gives the best performance for S-S compensation at start-up and shut-down. The combination of frequency and SPS control starting below resonance gives the best results for the soft start-up of the double-sided LCC compensation.