Wireless Power System Harmonic Cancellation via Compensation Signal
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Solution Overview
Problem
Wireless power transfer systems face issues with unwanted harmonic interference due to the primary inductor acting as an efficient antenna, radiating spurious signals into the atmosphere, despite resonance-based band-pass filtering, and nonlinear rectifiers generating harmonics that couple back into the primary coil.
Innovation Solution
Incorporating a compensation signal generator to cancel undesired frequencies, which adapts the amplitude and phase of the compensation signal to minimize power at frequencies other than the fundamental, using a combination of inverter, power detector, and transformers to inject and adapt the compensation signal into the primary coil.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If resonance is used on the primary and/or secondary side to make the system easier to drive, then the system becomes easier to drive and power transfer is improved, but unwanted harmonic components are still radiated into the atmosphere causing interference
Solution Approach 1:
The patent uses the resonant frequency of the primary circuit to generate compensation signals at harmonic frequencies. These compensation signals are intentionally injected to cancel the harmful harmonic radiations. The resonance that causes the problem is transformed into a resource for generating the solution, as the same resonant characteristics are used to create canceling signals at frequencies 2f, 3f, 4f, etc.
Solution Approach 2:
The patent generates compensation signals at harmonic frequencies before the harmful radiations occur. By injecting these compensation signals into the primary circuit in advance, the system proactively cancels the harmonic components that would otherwise be radiated. This preliminary anti-action prevents the interference problem before it manifests.
2Ease of manufacture
If a rectifier is used in the portable device to convert AC to DC, then power conversion is enabled, but the nonlinear rectifier generates harmonics that couple back into the primary coil and are radiated
Solution Approach 1:
The patent implements a feedback mechanism where the harmonic content in the primary circuit is detected and used to generate compensation signals. The system continuously monitors the electrical characteristics of the primary circuit, identifies harmonic components generated by the rectifier, and adjusts the compensation signals accordingly to cancel these harmonics in real-time.
Solution Approach 2:
The patent introduces asymmetry by injecting compensation signals with specific amplitudes and phases that are tailored to counteract the asymmetric harmonic distortion caused by the nonlinear rectifier. The compensation signals are designed to be asymmetric in nature, matching the asymmetric distortion pattern of the rectifier output.
3Power
If the fundamental frequency is increased to supply sufficient power to the portable device, then adequate power transfer is achieved, but the primary inductor becomes an even more efficient antenna at higher harmonics, increasing radiation
Solution Approach 1:
The patent changes the parameter of harmonic content by injecting compensation signals with carefully controlled amplitudes and phases. By adjusting these parameters, the system reduces the amplitude of harmonic components at frequencies 2f, 3f, 4f, etc., while maintaining the fundamental frequency power level needed for adequate power transfer.
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 effectively reduces distortion in the alternating current signal, minimizing spurious signal radiation and interference, allowing for efficient power transfer with reduced harmonic interference.
Implementation Method 1
Within the portable device 14 there is a secondary coil 22 which is electromagnetically coupled to the primary coil 20 when the device is appropriately positioned on the charger 12. An alternating voltage is induced within the secondary coil 22.
Implementation Method 2
Capacitors 26 and/or 28 may therefore be positioned on the primary and secondary side respectively, such that both the primary side and secondary side are resonant at the frequency of the inverter 18. An additional feature of this resonance is that it acts as a band-pass filter, thereby attenuating the unwanted harmonic components present in the rectangular signal.
Data Source
AI summary
The specification discloses a wireless power charging system in which undesired frequencies in the primary coil are cancelled. Exemplary undesired frequencies are the harmonics of the primary coil drive signal. The system includes a sense transformer/coil, an injection transformer/coil, and a compensation signal generator. The sense transformer/coil senses the signal in the primary coil. The compensation signal generator receives the sensed signal and generates an injection signal whose constituent parts are equal in amplitude to, but pi phase different from, each undesired frequency. The combined signal is injected into the primary through the injection transformer/coil so that the injection signal cancels the undesired frequencies in the primary coil.