Fractional Coil Current Sensing for Wireless Power Transfer
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Solution Overview
Problem
Current measurement in high-power wireless power transfer systems is challenging due to excessive heating and phase shift issues caused by sense resistors, and existing indirect measurement techniques are problematic with high currents and low impedance loads.
Innovation Solution
A method involving a current sensing resistor with low Ohmic value and parasitic inductance, placed in a fractional path within the coil windings, measures the current through a subset of conductors, allowing for accurate phase and current measurement without significant heating or phase shift, using a combination of filter capacitors and amplifiers to process the signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense resistor is used for current measurement in high-power wireless power transfer systems, then current measurement is achieved, but excessive heating and phase shift occur
Solution Approach 1:
The patent segments the coil windings into multiple parallel conductors and measures current through only a subset of them (e.g., one out of N conductors). This fractional current measurement approach divides the total current measurement task into smaller portions, allowing the use of lower-power sensing circuits that generate minimal heat while still providing accurate representation of the total current through scaling calculations.
Solution Approach 2:
The patent introduces filter capacitors and amplifiers as intermediary components between the fractional current measurement point and the control system. These intermediaries process the small measured current signal through filtering to remove noise and amplification to restore it to full-scale representation, eliminating the need for high-power direct measurement that would cause heating.
2Measurement precision
If a sense resistor is used for current measurement, then current measurement is achieved, but phase shift occurs affecting measurement accuracy
Solution Approach 1:
By segmenting the measurement to fractional current through selected conductors only, the patent reduces the burden on the sensing circuit. The reduced current level minimizes parasitic inductance effects and phase shift, simplifying the measurement system while maintaining accuracy through mathematical scaling of the fractional measurement to represent total current.
Solution Approach 2:
The patent replaces direct electrical measurement through high-power sense resistors with an indirect measurement approach using fractional current sampling, filtering, and digital processing. This substitution eliminates the need for high-power hardware components that introduce phase shift, replacing them with low-power electronic processing that preserves phase accuracy.
3Measurement precision
If indirect measurement techniques are used for high currents, then measurement is achieved, but the techniques are problematic with low impedance loads
Solution Approach 1:
The patent applies segmentation by measuring current through a fraction of the total conductors rather than attempting to measure all current through indirect techniques. This direct fractional measurement approach bypasses the limitations of indirect measurement methods when dealing with low impedance loads, providing reliable measurements even in high-current scenarios that would challenge traditional indirect techniques.
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 approach enables precise current measurement with reduced heating and phase shift, maintaining system efficiency and accuracy, even at high currents, by exploiting the multi-conductor construction of the coil windings and using bandpass filtering and amplification to digitize the voltage for control systems.
Implementation Method 1
measuring a voltage drop across the current sensing resistor
Implementation Method 2
The AC sense circuit includes a first path including at least one filter capacitor and the current sensing resistor and a second path in parallel with the first path. The second path includes a smoothing capacitor
Implementation Method 3
bandpass filtering and amplifying a voltage produced by the ripple current over the current sensing resistor by a low noise amplifier
Implementation Method 4
bandpass filtering and amplifying a voltage produced by the ripple current
Data Source
AI summary
A current sensing method measures a fractional current through a coil having a plurality of coil windings by using a current sensing resistor to measure a current through a subset of the plurality of coil windings and using a voltage sensor to measure a voltage drop across the current sensing resistor. The measured current and voltage values are provided to a processor to determine the fractional current and phase of the coil. For example, the fractional current and phase of the coil may be determined by calculating a total current of the coil as I=n(V/Rx), where n is the number of coil windings of the coil, V is the measured voltage, and Rx is the impedance of the current sensing resistor. The coil may be a secondary winding used in a wireless power transfer system.