Multi-Modular Capacitive Wireless Power Transfer Circuit
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Solution Overview
Problem
Designing high-power, high-efficiency capacitive wireless power transfer systems for electric vehicle charging is challenging due to large air-gaps and limited coupling capacitance, which results in high fringing electric fields that must be kept within safety limits.
Innovation Solution
A multi-modular capacitive wireless power transfer system using near-field phased-array field-focusing techniques, where adjacent modules are out-phased to reduce fringing electric fields, and inter-module interactions are modeled and decoupled using L-section matching networks to absorb parasitic capacitances within individual modules.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If capacitive WPT systems operate at high power with large air-gaps, then power transfer capability is improved, but fringing electric fields exceed safety limits
Solution Approach 1:
The system divides the single large air-gap WPT system into multiple modular units, each operating at a lower power level. By segmenting the total power transfer into N modules, the fringing field from each individual module remains below safety thresholds while the cumulative power transfer achieves the desired high-power capability. The patent specifically implements this with multi-modular configurations where each module contributes to the total power while maintaining field safety.
Solution Approach 2:
Multiple modular WPT units are combined in a phased-array configuration to achieve high power transfer. The modules are strategically positioned and phase-controlled to merge their electromagnetic fields constructively in the target region (vehicle chassis) while maintaining individual module fringing fields below safety limits. This merging approach allows the system to achieve kilowatt-scale power transfer without any single module exceeding field safety thresholds.
2Adaptability or versatility
If the air-gap distance is increased, then system flexibility and vehicle compatibility are improved, but coupling capacitance decreases resulting in lower power transfer efficiency
Solution Approach 1:
The system employs dynamic phase control and impedance matching that adapt to varying air-gap distances. By dynamically adjusting the operating frequency and phase relationships among modules, the system maintains optimal power transfer efficiency across different gap distances. This dynamic adaptation allows the system to accommodate various vehicle types and positions while sustaining high power transfer levels.
Solution Approach 2:
The system changes key operating parameters including frequency, phase angle, and impedance matching conditions to optimize performance at different air-gap distances. By adjusting these parameters in response to detected gap variations, the system maintains efficient power transfer whether the vehicle is positioned close to or far from the charging surface, thereby achieving both versatility and efficiency.
3Power
If multiple modules are used to achieve high power transfer, then power capability is improved, but inter-module interactions and parasitic capacitances increase
Solution Approach 1:
The patent introduces decoupling networks as intermediary elements between adjacent modules to eliminate parasitic capacitance interactions. These networks act as mediators that block unwanted capacitive coupling paths while allowing the modules to operate independently. By inserting these intermediary decoupling structures, the system achieves high power transfer through multiple modules without suffering from efficiency-degrading inter-module interactions.
Solution Approach 2:
The patent extracts and eliminates the harmful parasitic capacitances between modules by designing decoupling networks that specifically target and remove these unwanted interactions. By taking out the problematic capacitive coupling effects and replacing them with controlled impedance paths, the system maintains module independence while achieving the desired high power transfer capability through modular aggregation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves a 50% reduction in fringing electric fields and a peak efficiency of 89.8% with a power transfer density of 21.2 kW/m2, meeting safety limits and surpassing state-of-the-art capacitive WPT systems.
Implementation Method 1
capacitive WPT systems do not require ferrites and can operate at high frequencies
Implementation Method 2
using electric fields between capacitively coupled plates
Implementation Method 3
The fringing fields are reduced using near-field phased-array field-focusing techniques, wherein the adjacent modules of the multi-modular system are out-phased with respect to one another
Data Source
AI summary
A high performance kilowatt-scale large air-gap multi-modular capacitive wireless power transfer (WPT) system is provided for electric vehicle (EV) charging. In one particular implementation, the multi-modular system achieves high power transfer while maintaining fringing electric fields within prescribed safety limits. The fringing fields are reduced using near-field phased-array field-focusing techniques, wherein the adjacent modules of the multi-modular system are out-phased with respect to one another. The inter-module interactions in this multi-modular system can be modeled, and an approach to eliminate these interactions in a practical EV charging environment is provided. To illustrate one example implementation, a prototype 1.2-kW 6.78-MHz 12-cm air-gap multi-modular capacitive WPT system comprising two 600-W modules is provided. This prototype system achieves 21.2 kW/m2 power transfer density and a peak efficiency of 89.8%. This multi-modular system also achieves a fringing field reduction of 50% compared to its individual modules.