Wireless Charging Transmitter Q-Factor Sensing Without PI-Filter Distortion
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Solution Overview
Problem
Wireless charging systems face inefficiencies and safety compromises due to the presence of foreign objects, which affect resonance and charging performance, especially when using PI-filters that introduce distortion and make it difficult to measure resonance signals effectively without lossy measurement circuits.
Innovation Solution
A controller for a wireless charging transmitter circuit that includes a full-bridge inverter and a resonant circuit with a PI-filter, allowing for the measurement of the Q-factor by disconnecting the PI-filter inductors and measuring the voltage decay across the transmitter inductor, enabling 'clean' resonance and power-loss determination without distortion, and using differential voltage measurements for demodulation and system protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Difficulty of detecting and measuring
If a PI-filter is included in the wireless charging transmitter circuit, then filtering performance is improved, but resonance measurement accuracy deteriorates due to distortion
Solution Approach 1:
The measurement process is segmented into distinct phases: excitation phase where the PI-filter is connected, and measurement phase where the PI-filter is disconnected. This allows the filter to perform its filtering function during normal operation while enabling accurate resonance measurement during the measurement phase without filter interference.
Solution Approach 2:
The system performs preliminary excitation of the resonant circuit before measurement by connecting the input voltage supply through the full-bridge inverter to charge the resonant circuit, then disconnects the supply and the PI-filter before initiating the actual resonance measurement. This preliminary action ensures the resonant circuit is energized and ready for accurate measurement without the distorting influence of the PI-filter.
2Difficulty of detecting and measuring
If lossy measurement circuits are used to measure resonance with PI-filter, then resonance measurement becomes possible, but energy loss increases
Solution Approach 1:
The harmful element (PI-filter) is temporarily extracted from the circuit during the measurement phase. By disconnecting the PI-filter inductors from the resonant circuit during Q-factor measurement, the system enables accurate resonance detection without requiring lossy measurement circuits, as the measurement is performed on the clean resonant oscillation free from filter distortion and losses.
3Reliability
If foreign objects are present in the wireless charging system, then charging performance is affected, but detection capability is improved by resonance methods
Solution Approach 1:
The system uses feedback from Q-factor measurements to detect foreign objects. By measuring the Q-factor of the resonant circuit and comparing it against reference values, the system can identify changes in resonant characteristics caused by foreign objects. This feedback mechanism enables real-time detection and allows the system to adjust or terminate charging operations to maintain reliability and safety.
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 allows for accurate Q-factor measurement and power-loss determination, enhancing the efficiency and safety of wireless charging by avoiding distortion and enabling effective identification of foreign objects, thus improving charging performance and system protection.
Implementation Method 1
a first resonant circuit including the transmitter inductor and the series capacitor, and a second resonant circuit including the receiver inductor and the second capacitor
Implementation Method 2
the resonance of the transmitter is typically affected by any foreign object which would also affect the charging performance (for instance by changing the resonant frequency)
Implementation Method 3
measuring a decay of the voltage across the transmitter inductor
Data Source
AI summary
A wireless charging transmitter, controller and system are disclosed. The transmitter has a full-bridge inverter having two full-bridge output nodes, a resonant circuit comprising a series arrangement of a transmitter inductor and a first capacitor, and a second capacitor in parallel with the series arrangement, a PI-filter coupled between the second capacitor and the full-bridge inverter; wherein the controller is configured to measure a Q-factor of the resonant circuit by: controlling the full-bridge inverter to connect an input voltage supply to the PI-filter to supply an excitation pulse to the resonant circuit; controlling the full-bridge inverter to disconnect the input voltage supply and initiate a resonance in the resonant circuit; controlling a switch in the full-bridge inverter to provide an reference ground to a first terminal of the transmitter inductor; and measuring a decay of the voltage at a second terminal of the transmitter inductor.