Capacitive Wireless Power Transfer Circuit Using Parasitic Capacitance
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Solution Overview
Problem
Challenges in designing high-power, high-efficiency capacitive wireless power transfer (WPT) systems for electric vehicle charging due to large air-gaps and limited coupling capacitance, along with the risk of arcing and the need for expensive ferrites in inductive systems, which are mitigated by capacitive WPT systems but require innovative solutions to enhance power transfer density and safety.
Innovation Solution
A high-power-transfer-density capacitive WPT system is achieved through a combination of techniques including a four-capacitance or three-capacitance equivalent model, split-inductor matching networks, and the use of parasitic capacitances to eliminate discrete capacitors, along with circular or elliptical coupling plates coated with high dielectric breakdown materials like PTFE to prevent arcing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If inductive WPT systems use ferrites for magnetic flux guidance, then magnetic coupling is achieved, but the system becomes expensive, heavy, and requires large size with low operating frequency
Solution Approach 1:
The patent replaces the inductive WPT system with ferrites (mechanical/magnetic system) with a capacitive WPT system using electric fields between capacitively coupled plates. This substitution eliminates the need for heavy ferrite materials while achieving wireless power transfer through capacitive coupling, directly resolving the contradiction between reliable magnetic coupling and system weight.
2Productivity
If capacitive WPT systems use large air-gap coupling plates, then wireless power transfer is achieved, but the coupling capacitance becomes very small due to limited area under vehicle chassis
Solution Approach 1:
The patent changes the operating parameters by using high-frequency operation and optimized plate geometries (circular, elliptical, or square configurations) to maximize coupling capacitance within the limited space under the vehicle chassis. This allows achieving high power transfer capability despite the small available area, resolving the contradiction between productivity and quantity of coupling capacitance.
3Power
If power transfer density is increased in capacitive WPT systems, then more power is transferred, but the risk of arcing increases
Solution Approach 1:
The patent addresses the arcing risk by carefully controlling the electric field distribution and using appropriate spacing and grounding strategies. The system converts the potential harmful effect of high electric fields into beneficial high power transfer density by maintaining fields below safety limits while optimizing the capacitive coupling configuration to achieve 51.6 kW/m² power transfer density without arcing.
4Power
If discrete capacitors are used in matching networks, then power transfer is achieved, but system cost, complexity, and failure rate increase
Solution Approach 1:
The patent extracts and eliminates the need for discrete capacitors in the matching networks by utilizing the inherent parasitic capacitances of the system components and structure. This simplification reduces system complexity, component count, and potential failure points while maintaining effective power transfer capability, directly resolving the contradiction between power transfer and device complexity.
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 power transfer density of 51.6 kW/m² with a 74.7% efficiency, exceeding previous reports by a factor of two, while eliminating the risk of arcing and reducing system complexity and cost.
Implementation Method 1
using electric fields between capacitively coupled plates
Implementation Method 2
using electric fields between capacitively coupled plates
Implementation Method 3
covering, or coating, the coupling plates with materials having high dielectric breakdown strength
Data Source
AI summary
Capacitive wireless power transfer systems are provided. In one embodiment, for example, the system comprises two pair of coupled conducting plates; a first matching network coupled to the first pair of conducting plates; and a second matching network coupled to the second pair of conducting plates. At least one of the first and second matching networks comprises an inductor having inductance value selected based on at least one parasitic capacitance value of the capacitive wireless power transfer system. In another embodiment, a method of designing a capacitive wireless power transfer system is provided comprising determining a parasitic capacitance value of a capacitive wireless power transfer system and determining an inductance value of an inductor of at least one of the first and second matching network having a value selected based on at least one parasitic capacitance value of the capacitive wireless power transfer system.