Mutual Inductance Cancellation Circuit for Multi-Coil Wireless Power
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Solution Overview
Problem
Wireless charging systems with multiple transmit coils experience undesirable interaction due to transmitter-to-transmitter coupling, leading to inefficiencies and non-uniform magnetic fields, particularly when coils are closely spaced or overlapping.
Innovation Solution
The implementation of a circuit that cancels mutual inductance between multiple driver coils by sharing a common ground and using a cancellation circuit to adjust the mutual inductance, allowing for independent operation and efficient power transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If multiple transmit coils are used to provide wireless energy over a larger area, then the charging area and power distribution are improved, but mutual inductance between coils causes undesirable interaction and reduces efficiency
Solution Approach 1:
The system divides the charging area into multiple independent coil segments, each capable of operating autonomously. This segmentation allows the charging surface to be divided into multiple zones that can be independently controlled, reducing mutual interference while maintaining large-area coverage capability
Solution Approach 2:
A cancellation coil is introduced as an intermediary element between the primary transmit coils. This cancellation coil generates counteracting magnetic fields that neutralize the mutual inductance effects between adjacent transmit coils, allowing them to operate simultaneously without significant energy loss
2Stability of the object's composition
If multiple transmit coils are closely spaced to improve power distribution, then the uniformity of magnetic field is improved, but transmitter-to-transmitter coupling increases causing interference
Solution Approach 1:
Different regions of the charging surface are assigned different coil configurations and operating parameters. Coils in high-interference zones use different phasing or amplitude settings compared to coils in low-interference zones, optimizing the magnetic field uniformity while managing local interference conditions
Solution Approach 2:
Cancellation coils positioned between closely spaced transmit coils act as mediators that reduce the direct coupling between transmitters. These intermediary coils create opposing magnetic fields that cancel out the harmful interactions, enabling closer coil spacing while maintaining field uniformity
3Adaptability or versatility
If separate power amplifiers are used for each transmit coil to enable independent operation, then the versatility and charging capacity are improved, but the complexity of the system increases
Solution Approach 1:
The power amplifier system is designed with universal control capabilities that can manage multiple coils through a standardized interface. The control circuitry can dynamically allocate power to different coil combinations based on device presence and charging requirements, providing versatile charging capacity without proportionally increasing control complexity
Solution Approach 2:
Multiple power amplifiers are controlled through a unified control system that merges their operation under centralized management. The control circuitry coordinates the amplifiers to work together as an integrated system, reducing the operational complexity that would otherwise result from managing multiple independent amplifier systems
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
This solution enhances power and impedance measurements, reduces mutual inductance between transmit coils, and improves the uniformity and efficiency of wireless power transfer, enabling simultaneous charging of multiple devices over a larger area.
Implementation Method 1
generating a first wireless field via a first driver coil, generating a second wireless field via a second driver coil, generating a third wireless field via a third driver coil
Implementation Method 2
at least partially cancelling mutual inductance between the first driver coil, the second driver coil, and the third driver coil
Data Source
AI summary
This invention describes a method and apparatus to cancel the mutual inductance between mutually coupled transmit coils, each of the transmit coils fed by individual power amplifiers, and the transmit coils all sharing a common ground with the power amplifiers. The methods and systems disclosed consist of coupling the return legs of each transmit coil to a mutual inductance cancellation circuit near a common ground return connection. The cancellation circuit uses a combination of inductors and capacitors to bridge various combinations of the transmit coils without physically connecting the “bridged” transmit coils. Transmit coils “bridged” using inductors have positive mutual inductance added to them, while transmit coils “bridged” using capacitors have negative mutual inductance added to them. Additionally, manipulation of the transmit coil overlap of overlapping transmit coils and/or manipulation of the location of the cancellation circuit can be used finely tune the mutual inductance between the transmit coils.