Decoupled Coil Wireless Power Transfer EMI Mitigation
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Solution Overview
Problem
Wireless power and data transfer systems face challenges in meeting electromagnetic compatibility (EMC) regulations due to electromagnetic interference (EMI) caused by capacitive coupling of the electric field to conductive objects, leading to unwanted emissions back through mains cables.
Innovation Solution
A primary unit with a coil configuration where both ends are decoupled from the driving means, allowing voltage fluctuations at one end to compensate for those at the other end, reducing induced charges and thus minimizing electromagnetic interference. This is achieved through capacitive decoupling and magnetic coupling between coil portions, ensuring balanced operation and reduced noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the coil is driven by conventional means with direct connection to driving circuit, then power transfer efficiency is maintained, but electromagnetic interference is generated through capacitive coupling to conductive objects
Solution Approach 1:
The coil is divided into two separate coils (first coil and second coil) with opposite polarities. Each coil is independently decoupled from the driving means, creating segmented electromagnetic fields that cancel each other's capacitive coupling effects on conductive objects.
Solution Approach 2:
The second coil is positioned and oriented to generate an electric field that acts as a counterbalance to the first coil's field. The opposite polarity configuration creates equal and opposite charge inductions on conductive objects, effectively canceling the net electromagnetic interference.
2Object-affected harmful factors
If both ends of the coil are decoupled from driving means, then electromagnetic interference is reduced, but the driving circuit complexity increases
Solution Approach 1:
Capacitive decoupling elements are introduced as intermediary components between the coil ends and the driving means. These capacitors block direct DC connection while allowing AC signal transmission, thereby reducing unwanted emissions without completely isolating the coil from the driving circuit.
Solution Approach 2:
The impedance characteristics of the coupling paths are modified by introducing capacitive elements. This changes the frequency-dependent behavior of the coil-drying circuit interface, allowing the system to maintain power transfer efficiency while reducing broadband electromagnetic interference.
3Reliability
If voltage fluctuations at coil ends are used for compensation, then electromagnetic compatibility is improved, but control precision requirements increase
Solution Approach 1:
The system intentionally creates asymmetric voltage fluctuations at the two coil ends relative to ground potential. Each end experiences equal magnitude but opposite phase voltage variations, which are asymmetric with respect to ground but symmetric in their cancellation effect on electromagnetic interference.
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 effectively cancels out positive and negative charges induced in conductive objects, reducing electromagnetic interference and meeting EMC regulations while maintaining efficient power and data transfer.
Implementation Method 1
use electromagnetic induction to transfer power wirelessly from the charger (primary unit or transmitter) to the portable device (secondary unit or receiver). These systems have a coil in the charger, through which an alternating current is passed to generate an alternating magnetic field in the vicinity of the coil.
Implementation Method 2
A second coil within the portable device is placed in close proximity, so that it couples with the magnetic field resulting in an alternating voltage (and thus, current) being generated in the second coil.
Implementation Method 3
a charger 2 comprises a primary coil Lp 4 which is series resonant with a capacitor Cp 6. This combination is driven by an inverter 8
Implementation Method 4
The field generated has to extend out from the charger in order to couple to the portable device. Consequently, it is not possible to completely shield the coil within the charger. One mechanism which is particularly troublesome is where the electric field generated capacitively couples to other conductors.
Data Source
AI summary
A primary unit for transmitting power and/or data wirelessly by electromagnetic induction to a secondary unit separable from the primary unit, the primary unit comprising: a coil (L1, L2); and driving means (30) operable to drive a fluctuating current through the coil, wherein both ends of the coil are decoupled from the driving means so that in use a voltage level at each end of the coil fluctuates with time.