Q-Factor Detection in Wireless Power Transmitters
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Solution Overview
Problem
Existing wireless power systems face challenges in accurately determining the Quality Factor (Q-Factor) of resonant circuits, particularly in the presence of foreign objects, due to difficulties in maintaining low bridge input voltage, controlling equivalent series resistance, and efficiently sweeping frequencies to determine resonant frequency and Q-Factor.
Innovation Solution
A method involving charging a capacitor in an LC tank circuit to a voltage, then coupling it to ground to form a free-oscillating circuit, allowing for direct measurement of voltage over time to determine resonant frequency and Q-Factor without frequency sweeping, using a control circuit to analyze the oscillating waveform and calculate Q-Factor based on exponential decay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If frequency sweeping is used to determine resonant frequency and Q-Factor, then measurement completeness is improved, but measurement time increases
Solution Approach 1:
The system performs preliminary action by charging the capacitor to a known voltage before the measurement, establishing initial conditions that enable direct Q-Factor calculation without frequency sweeping. This preliminary charging step allows the system to determine Q-Factor from the decay characteristics alone, significantly reducing measurement time while maintaining accuracy.
Solution Approach 2:
The invention extracts the essential measurement information (Q-Factor and resonant frequency) from a single oscillation cycle by analyzing the voltage decay characteristics. Instead of requiring multiple frequency sweeps, the system extracts all necessary parameters from one charged-discharged cycle, dramatically reducing the time required while preserving measurement completeness.
2Reliability
If bridge input voltage is reduced to avoid receiver activation, then system safety is improved, but signal-to-noise ratio deteriorates
Solution Approach 1:
The system applies preliminary action by charging the capacitor to a sufficiently high voltage before measurement begins. This pre-charging ensures that even though the bridge input voltage remains low during measurement (preventing receiver activation), the initial energy stored in the capacitor provides a strong enough signal for accurate Q-Factor determination through decay analysis.
Solution Approach 2:
The invention transitions from measuring steady-state voltage at different frequencies to measuring the time-domain decay characteristics. By changing from frequency-domain measurement to time-domain analysis, the system can use higher initial voltages for better signal-to-noise ratio while keeping the operating bridge voltage low, thus resolving the contradiction between measurement accuracy and receiver activation prevention.
3Measurement precision
If equivalent series resistance is controlled for accurate Q-Factor measurement, then measurement precision is improved, but circuit complexity increases
Solution Approach 1:
The system applies self-service by using the inherent equivalent series resistance of the resonant circuit as part of the measurement mechanism. Rather than requiring external control or adjustment of the ESR, the invention utilizes the natural decay characteristics determined by the circuit's own resistance, allowing accurate Q-Factor measurement without adding complex control circuitry.
Solution Approach 2:
The invention replaces complex active control mechanisms with a passive measurement approach. Instead of actively controlling or adjusting the equivalent series resistance through complex circuitry, the system substitutes a simple voltage decay measurement that naturally reflects the ESR's effect on Q-Factor, thereby maintaining measurement precision while minimizing circuit 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
This approach provides a faster and more accurate determination of Q-Factor and resonant frequency, eliminating the need for frequency sweeps and reducing measurement time, while ensuring the system does not activate receivers during Q-Factor detection.
Implementation Method 1
a capacitor coupled in series with the transmit coil to form a resonant circuit
Implementation Method 2
a transmit coil; a capacitor coupled in series with the transmit coil to form a resonant circuit
Implementation Method 3
starting a Q-factor determining by coupling the LC tank circuit to ground to form a free-oscillating circuit
Implementation Method 4
monitoring the voltage across the capacitor as a function of time as the LC tank circuit oscillates
Data Source
AI summary
A method of measuring a Q-factor in a wireless power transmitter includes charging a capacitor in a LC tank circuit that includes a transmission coil to a voltage; starting a Q-factor determining by coupling the LC tank circuit to ground to form a free-oscillating circuit; monitoring the voltage across the capacitor as a function of time as the LC tank circuit oscillates; and determining the resonant frequency and the Q-factor from monitoring the voltage.