This article reviews existing capacitive power transfer (CPT) systems and aims to provide a universal methodology to systematically construct CPT topologies with zero-phase angle (ZPA) and load-independent output property. There are three contributions. First, y, z, g, and h parameters of a two-port network are adopted to model the capacitive coupler for four basic CPT compensations, which facilitates the resonant circuit analysis by forming parallel or series LC resonance. Second, four basic CPT compensations, series&#x2013;series (SS), series&#x2013;parallel (SP), parallel&#x2013;series, and parallel&#x2013;parallel (PP), are developed and analyzed. ZPA frequencies are identified with a load-independent output, and a unified efficiency analysis is also provided. Third, by selectively deploying high-order T&#x002F;&#x03A0;-type LCL&#x002F;CLC networks and the SS mutual inductance with basic CPT compensations, a universal CPT design methodology is provided. In total, 144 feasible CPT topologies are derived with ZPA property and constant-current (CC) or constant-voltage output, which not only summaries existing ones but also predicts new topologies. Considerations are provided to guide the topology selection, from which ten typical CPT topologies are elaborated and recommended. A 500-W LCL&#x2013;PP&#x2013;LCL compensated CPT circuit is implemented. Experiments validate the proposed methodology by a ZPA property and a load-independent CC output, and a peak dc&#x2013;dc efficiency of 87.76&#x0025; is also achieved at 478&#x00A0;W.

Review, Analysis, and Design of Four Basic CPT Topologies and the Application of High-Order Compensation Networks

The single-switch topologies, e.g., the Class E topology, have the advantages of low component count, no shoot-through problem, simple driving circuit, which make it more suitable for high frequency low/medium-power wireless power transfer (WPT) applications. However, due to the high switch voltage stress, narrow soft switching range, bulky input choke, or ac inductor, its power delivery capability and applications are limited. In order to solve these problems, this article proposed a novel active clamp topology for high cost-performance medium-power WPT systems. The proposed topology offers low component count with no bulky inductor and low switch voltage stress, leading to high power-density, low cost, and compact size, i.e., high cost-performance for WPT applications. And the switch peak voltage can be adjusted and the soft switching operation can be achieved in a wide load range by designing the compensation capacitor and clamp capacitor. In this article, the detailed theoretical analysis and parameter design are discussed and the proposed topology is compared with the existing single-switch topology in terms of voltage stress, cost, and component count. A 120 W and 1 MHz active clamp WPT system is built and a 92.4% system efficiency is achieved with high cost-performance, which validate the feasibility of the proposed topology and the theoretical analysis. 

A Multi-MHz Active Clamp Topology for High Cost-Performance Wireless Power Transfer

The full-bridge can further improve the output power through parallel inverters. The inverter output voltage of single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC -resonant circuit is a combination of trapezoidal wave and half-sine wave; there is no relevant research on parallel connection of single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC -resonant circuit. Therefore, this article presents a novel input-parallel single-switch <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LC -resonant circuit; this topology adopts switchable secondary networks for constant-current (CC) and constant-voltage (CV) output, and prevents shoot-through of power switches. The decoupling between transmitters simplifies the analysis and calculation. The input-parallel structure avoids the unbalanced input voltage of each inverter and improves the stability of the wireless power transfer system. CC and CV output modes can be achieved by controlling one relay without adding dc–dc converters or changing the switching frequency. This article includes decoupling equivalent analysis of coils, topologies analysis of CC mode and CV mode, calculation of equivalent input ac voltage source, design of magnetic coupler, and circuit parameters. Finally, a 1-kW experimental prototype is built to verify the theoretical analysis; the maximum efficiency can reach up to 92.5%.

Research on Input-Parallel Single-Switch Wireless Power Transfer System With Constant-Current and Constant-Voltage Output

The single-switch topologies, e.g., the Class E topology, have the advantages of low component count, no shoot-through problem, simple driving circuit, which make it more suitable for high frequency low/medium-power wireless power transfer (WPT) applications. However, due to the high switch voltage stress, narrow soft switching range, bulky input choke, or ac inductor, its power delivery capability and applications are limited. In order to solve these problems, this article proposed a novel active clamp topology for high cost-performance medium-power WPT systems. The proposed topology offers low component count with no bulky inductor and low switch voltage stress, leading to high power-density, low cost, and compact size, i.e., high cost-performance for WPT applications. And the switch peak voltage can be adjusted and the soft switching operation can be achieved in a wide load range by designing the compensation capacitor and clamp capacitor. In this article, the detailed theoretical analysis and parameter design are discussed and the proposed topology is compared with the existing single-switch topology in terms of voltage stress, cost, and component count. A 120 W and 1 MHz active clamp WPT system is built and a 92.4% system efficiency is achieved with high cost-performance, which validate the feasibility of the proposed topology and the theoretical analysis.

In a single-phase charging system of electric vehicles, the current control performance of the single-phase ac–dc factor correction (PFC) converter with a deadbeat predictive current control (DPCC) method is affected by the distorted grid voltage, parameter dependence, and control delay. To tackle these problems, a modified DPCC method is proposed in this article. By introducing a phase adjustment parameter θc, which can be directly calculated according to the required power factor, into the grid voltage feedforward of the current loop, an improved input current control performance with lower harmonic components and higher power factor can be achieved when the converter operates at unity power factor. At the same time, compared with the traditional method, a reactive power compensation function is added in the modified DPCC and a deadtime compensation method is adopted in the modulation. Finally, a 7.8-kW single-phase PFC converter prototype is built to verify the feasibility and effectiveness of the proposed control method.

Modified Deadbeat Predictive Current Control Method for Single-Phase AC–DC PFC Converter in EV Charging System

Traditional Class-E circuit features fewer components, high reliability, and soft switching. However, due to the unidirectional excitation, the application of such a topology circuit is limited, i.e., usually used in low-power applications. To relieve this issue, this article proposes a switched-capacitor-based Class-E circuit, to extend the operating power range of the Class-E circuit. With the proposed new circuit, both constant current (CC) and constant voltage (CV) output modes can be achieved by switching the branch once without changing the switching frequency or compensation network. Compared with the existing CC and CV charging strategies, the proposed circuit has the advantages of fewer components, simpler implementation, and higher reliability. Moreover, the studied compensation network can also be extended to other inverter topologies. The working principle of the proposed circuit is described in detail, and the variable zero-voltage switching (ZVS) margin is introduced to make an accurate design of parameters. Subsequently, the influence of high-order harmonic components on the circuit and the sensitivity of parameters are analyzed. Finally, the proposed circuit is simulated and experimented on a 180–450-W prototype with CC and CV characteristics to verify the feasibility of the circuit and the accuracy of theoretical analysis.

A Hybrid Class-E Topology With Constant Current and Constant Voltage Output for Light EVs Wireless Charging Application

Class E circuit has the advantages of less components, high reliability and soft switching, but the traditional Class E circuit can only be used in low power condition because of the unidirectional excitation. In order to extend the power range, this paper proposes a novel hybrid Class E circuit, which can be operated at high power. Moreover, the proposed topology can achieve constant current (CC) and constant voltage (CV) output by switching the branch once without changing the switching frequency or compensation network. Compared with the existing CC and CV scheme, it has the advantages of less components, simple control and high stability. In this paper, the working principle of the circuit is analyzed, and the variable zero-voltage switching (ZVS) margin is introduced to make the calculation of parameters design method more accurate. Subsequently, the influence of higher order harmonics on the circuit and the sensitivity of parameters is analyzed. Finally, an 180W experimental platform with CC and CV characteristics is built to verify the feasibility of the circuit and the accuracy of theoretical analysis.

Houji Li

Papers

A Hybrid Class-E Topology With Constant Current and Constant Voltage Output for Light EVs Wireless Charging Application

A Novel Hybrid Class E Topology with load-independent Output for WPT