EV Wireless AC Power Transfer Without Bulky DC Link Capacitors
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Solution Overview
Problem
Conventional wireless energy transfer systems for electric vehicles (EVs) are inefficient due to reliance on DC link platforms and bulky capacitors, and existing AC-to-AC converter topologies suffer from high voltage and current stresses, leading to poor power quality and increased costs.
Innovation Solution
A method and system for wirelessly providing AC power to EVs using a modulated high-frequency voltage signal with an AC-to-AC bidirectional converter, which includes half-bridges and coupling capacitors to transmit power efficiently, reducing the need for bulky capacitors and improving power factor and total harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional DC link platform with bulky capacitor is used for wireless power transfer, then power factor correction and DC voltage stabilization are achieved, but system weight and volume increase significantly
Solution Approach 1:
The patent extracts and eliminates the bulky DC link capacitor from the conventional wireless power transfer system by transitioning to an AC-to-AC converter architecture. The capacitor is completely removed while its essential functions of power factor correction and voltage stabilization are achieved through the resonant AC-to-AC conversion process, thereby reducing system weight and volume.
Solution Approach 2:
The patent changes the operating parameters from DC voltage stabilization to AC voltage resonance at high frequency. By operating the AC-to-AC converter at resonant frequency, the system achieves voltage stabilization without requiring large energy storage capacitors, thus reducing the capacitor size and overall system volume while maintaining power factor correction capabilities.
2Loss of energy
If conventional AC-to-AC converter with direct energy injection is used, then switching losses are reduced, but input current total harmonic distortion becomes too high
Solution Approach 1:
The patent employs periodic switching action at resonant frequency in the AC-to-AC converter. The switches operate periodically at the resonant frequency of the coupled inductors, enabling efficient energy transfer while maintaining sinusoidal current waveforms. This periodic operation at resonance reduces switching losses while the resonant nature of the circuit inherently filters harmonics, keeping input current total harmonic distortion low.
Solution Approach 2:
The patent utilizes resonant phase relationships between voltage and current in the coupled inductor system. By operating at resonant frequency, the system achieves unity power factor and sinusoidal current draw from the source. The resonant phase alignment ensures that energy transfer occurs efficiently during appropriate phases of the AC cycle, minimizing switching losses while maintaining clean current waveforms without excessive harmonics.
3Ease of manufacture
If conventional single stage AC-to-DC and DC-to-AC conversion is used, then system cost is reduced, but voltage and current stresses increase requiring additional commutation circuits
Solution Approach 1:
The patent segments the power conversion function into two distinct stages: AC-to-DC conversion for battery charging and DC-to-AC conversion for wireless power transmission. This segmentation allows each stage to be optimized independently, with the AC-to-DC stage handling power factor correction and the DC-to-AC stage handling resonant wireless transfer, thereby reducing voltage and current stresses without requiring additional commutation circuits.
Solution Approach 2:
The patent introduces a DC link as an intermediary between the AC-to-DC converter and the DC-to-AC wireless power transmitter. This DC intermediary decouples the two conversion stages, allowing independent optimization of each stage. The DC link buffers voltage and current stresses, enabling the AC-to-DC stage to operate at unity power factor while the DC-to-AC stage operates at resonant frequency, reducing the need for complex commutation circuits.
4Stability of the object's composition
If bulky capacitor is used in on-board charger system, then DC voltage stabilization is maintained, but system volume and weight increase
Solution Approach 1:
The patent extracts and removes the bulky DC link capacitor from the on-board charger system by implementing AC-to-AC resonant conversion. The capacitor is completely eliminated while voltage stabilization is achieved through the resonant AC-to-AC converter, which maintains stable AC voltage output without requiring large energy storage elements, thereby significantly reducing system volume.
Solution Approach 2:
The patent changes the voltage stabilization mechanism from DC capacitor-based stabilization to AC resonant frequency-based stabilization. By operating the AC-to-AC converter at the resonant frequency of the coupled inductors, the system inherently maintains stable voltage output through the resonant relationship, eliminating the need for bulky capacitors and reducing on-board charger volume.
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 solution enables efficient wireless AC power transfer to EVs, reducing infrastructure costs and complexity, while eliminating the need for bulky capacitors, thereby enhancing power quality and reducing system weight and volume.
Implementation Method 1
wireless power transfer (WPT) system is often integrated to the DC charging platform that requires three power converter stages: AC-to-DC and DC-to-AC stages outside of the vehicle, and an AC-to-DC stage in the vehicle. High frequency sinusoidal current is generated by the DC-to-AC stage in a resonant manner in a primary coil and transmitted to a magnetically coupled pick-up coil.
Implementation Method 2
High frequency sinusoidal current is generated by the DC-to-AC stage in a resonant manner in a primary coil and transmitted to a magnetically coupled pick-up coil. High frequency AC current in the pick-up coil is converted to DC through the AC-to-DC stage
Data Source
AI summary
A method for wirelessly or conductively (non-wireless) providing AC or DC power in AC or DC load applications and bidirectional applications.