Sinusoidal PWM Inverter Control for Wireless Charging Emission Reduction
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Solution Overview
Problem
Wireless charging systems face challenges with high harmonic distortion and radiated spurious emissions due to the use of conventional rectangular clock signals in inverter control, leading to increased magnetic cross-coupling and leakage between coils, which complicates meeting regulatory requirements.
Innovation Solution
Implementing a sinusoidal pulse-width modulation (PWM) control signal with varying pulse widths, generated by a comparator using a sinusoidal waveform and a higher frequency reference signal, to reduce harmonic distortion and filter out undesired high-frequency components, thereby decreasing radiated spurious emissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional rectangular clock signals are used to control the inverter, then the control circuit is simple, but harmonic distortion and radiated spurious emissions increase
Solution Approach 1:
The patent applies parameter changes by transforming the control signal waveform from rectangular to sinusoidal and implementing pulse-width modulation. The sinusoidal PWM control signal varies the pulse width according to the sinusoidal reference signal, which fundamentally changes the spectral characteristics of the control signal. This parameter transformation reduces harmonic distortion by eliminating the abrupt transitions inherent in rectangular waves, thereby decreasing radiated spurious emissions while maintaining acceptable control circuit complexity through standard PWM generation techniques.
Solution Approach 2:
The patent employs periodic action through the use of sinusoidal pulse-width modulation, where the control signal consists of periodic pulses whose widths are modulated according to a sinusoidal reference signal. This periodic sinusoidal modulation creates a control signal that maintains the fundamental frequency needed for inverter operation while distributing energy across harmonics in a controlled manner, reducing peak harmonic distortion compared to conventional rectangular wave control.
2Object-generated harmful factors
If sinusoidal PWM control signal is used, then harmonic distortion and radiated spurious emissions are reduced, but the control circuit complexity increases
Solution Approach 1:
The patent uses an intermediary approach by introducing a sinusoidal reference signal as a mediator between the control system and the inverter switching. The PWM generator compares this sinusoidal reference with a triangular carrier signal to produce the sinusoidal PWM control output. This intermediary sinusoidal modulation stage acts as a buffer that transforms simple switching control into harmonically reduced control signals, achieving emission reduction without requiring complex custom control circuits.
Solution Approach 2:
The patent applies dynamics by implementing variable pulse width control where the pulse width dynamically adjusts according to the instantaneous amplitude of the sinusoidal reference signal. This dynamic modulation allows the control circuit to maintain optimal switching patterns that reduce harmonic distortion across different operating conditions, adapting the control signal characteristics to minimize radiated emissions while preserving the essential inverter functionality.
3Device complexity
If rectangular clock signals are used for inverter control, then the control signal generation is simple, but magnetic cross-coupling and leakage between coils increase
Solution Approach 1:
The patent changes the temporal parameters of the control signal by transitioning from rectangular waves with abrupt edges to sinusoidal PWM signals with smooth transitions. This parameter change in waveform shape reduces the high-frequency spectral content that drives magnetic cross-coupling between coils. The sinusoidal modulation preserves the fundamental switching frequency needed for power transfer while eliminating the sharp edges that generate harmful radiated emissions and magnetic leakage.
Solution Approach 2:
The patent converts the potential harm of complex PWM generation into benefit by using standard sinusoidal PWM techniques that are well-established in power electronics. The complexity of generating sinusoidal PWM is offset by the significant reduction in magnetic cross-coupling and radiated emissions, transforming what could be seen as a disadvantage (increased control complexity) into a benefit (compliance with electromagnetic emission standards and improved system performance).
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 use of sinusoidal PWM control signals significantly reduces harmonic distortion and radiated spurious emissions, improving compliance with regulatory standards by minimizing harmonic content and re-radiation among coils.
Implementation Method 1
a resonant circuit, an inverter for driving the resonant circuit... The resonant circuit may include a wireless power transmitting coil and a capacitor coupled to the wireless power transmitting coil
Implementation Method 2
an inverter for driving the resonant circuit... The inverter may include a first switch, a second switch coupled in series with the first switch
Implementation Method 3
a capacitor that is coupled in parallel with the first switch and that is configured to filter out undesired high-frequency components
Implementation Method 4
The portable electronic device has a coil and rectifier circuitry. The coil in the portable electronic device receives alternating-current wireless power signals... The rectifier circuitry converts the received signals into direct-current power
Data Source
AI summary
A wireless power system has a wireless power transmitting device and a wireless power receiving device. The wireless power transmitting device may include an inverter configured to drive a resonant circuit and may further include a sinusoidal pulse-width modulation (PWM) signal generator configured to generate a corresponding sinusoidal PWM control signal. The inverter may have an input that receives the sinusoidal PWM control signal. The sinusoidal PWM control signal may exhibit a plurality of different pulse widths summing to the target duty cycle of the sinusoidal PWM control signal. Operated in this way, the wireless power transmitting device exhibits reduced harmonic distortions, which mitigates undesired radiated spurious emissions.