Class EF Inverter Resonant Network for Wireless Power Transfer
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Solution Overview
Problem
Existing inductive power transfer systems face efficiency issues due to load-dependent magnetic field variations, which can exceed safety limits and reduce power throughput, especially when multiple devices are present, leading to increased power losses and inefficiencies.
Innovation Solution
A Class EF inverter with a resonant network tuned to a non-integer multiple of the switching frequency maintains constant current through the load resistance, independent of load variations, ensuring efficient operation and compliance with electromagnetic field safety limits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a large magnetic field is used to achieve efficient operation and maximum power throughput, then power transfer efficiency is improved, but electromagnetic field exposure limits may be exceeded
Solution Approach 1:
The patent changes the operating parameters of the inverter by implementing Class-EF operation with specific switching frequency relationships (resonant frequency as non-integer multiple of switching frequency). This parameter change enables the system to maintain high efficiency while controlling magnetic field strength to comply with ICNIRP limits, resolving the contradiction between efficiency and safety exposure
2Power
If the transmitter coil current is increased to maintain power throughput when load changes, then power delivery is improved, but power losses increase and efficiency decreases
Solution Approach 1:
The patent implements a control mechanism that monitors load changes and adjusts the inverter operating parameters accordingly. When receiver load changes occur, the system feedback controls the switching frequency and resonant network to maintain optimal Class-EF operation, preventing excessive current increases and associated power losses while maintaining power throughput
3Adaptability or versatility
If multiple receiver devices are present in the system, then system versatility is improved, but magnetic field distribution becomes unpredictable and may exceed safety limits
Solution Approach 1:
The patent employs Class-EF inverter operation with resonant frequency tuned to a non-integer multiple of switching frequency. This parameter configuration creates a more stable magnetic field distribution that can accommodate multiple receiver devices without unpredictable field variations, allowing system versatility to increase while maintaining safety compliance
Solution Approach 2:
The system monitors the presence and load of multiple receiver devices and provides feedback control to the inverter. This enables dynamic adjustment of operating parameters to maintain safe magnetic field distribution across the transmitter surface even when multiple devices are simultaneously present with varying positions and power requirements
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 maintains high efficiency and constant output current across varying loads, reducing switching losses and ensuring the magnetic field remains within safety limits, thus enhancing the power transfer efficiency and range of inductive power transfer systems.
Implementation Method 1
The power inverter comprises a switching device arranged between a power source and ground and arranged to switch at a switching frequency, and a resonant network arranged in parallel with the switching device between the power source and ground. The resonant network has a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.
Implementation Method 2
In a typical inductive power transfer system, an alternating current passes through a transmitter coil. This causes the transmitter coil to produce a time-varying magnetic field. When a receiver coil is placed in the time-varying magnetic field, the magnetic field induces an alternating current in the receiver coil, which can then be used to drive a load.
Data Source
Figure 1
Figure 2(a)~2(c)
Figure 3(a)~3(c)
AI summary
A power inverter is disclosed herein. The power inverter is suitable for driving a transmitter coil in an inductive power transfer system, wherein the inverter is suitable for class 'EF' operation. The inverter is arranged to drive a load resistance, and comprises a switching device arranged between a power source and ground and arranged to switch at a switching frequency. The inverter also comprises a resonant network arranged in parallel with the switching device between the power source and ground, the resonant network having a resonant frequency which is a non-integer multiple of the switching frequency, such that, in operation, a substantially constant current passes through the load resistance.