Hybrid Symmetric Asymmetric Control for Soft Switching in Wireless Power Transfer
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Solution Overview
Problem
Inductive power transfer (IPT) systems face inefficiencies due to hard switching, which leads to excessive power dissipation and potential failure of driver switches, as they struggle to maintain unity power factor due to varying inductance with the receiver, making symmetric duty cycle control insufficient.
Innovation Solution
Implementing a hybrid symmetric and asymmetric control method for soft switching, where a first voltage waveform is used for low power transfer and a second, asymmetric waveform is employed for higher power transfer, with durations of positive and negative portions adjusted to prevent hard switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If symmetric duty cycle control is used, then the system is simple to operate, but hard switching occurs causing excessive power dissipation and potential switch failure
Solution Approach 1:
The patent applies asymmetry by transitioning from symmetric duty cycle control to asymmetric duty cycle control when operating above a threshold power level. The controller adjusts the duty cycle of the switching waveform asymmetrically to achieve soft switching conditions, preventing hard switching and reducing power dissipation in the driver switches, thereby improving reliability while maintaining operational simplicity through automated control.
Solution Approach 2:
The patent implements dynamic control by automatically adjusting the duty cycle based on real-time operating conditions and power levels. The controller dynamically switches between symmetric and asymmetric duty cycle modes, and further adjusts the asymmetric duty cycle to maintain soft switching as inductance varies with receiver coupling, ensuring reliable operation across different operating conditions.
2Device complexity
If symmetric duty cycle control is used, then the control method is simple, but unity power factor cannot be achieved due to varying inductance
Solution Approach 1:
The patent uses asymmetric duty cycle control to achieve unity power factor when operating above the threshold power level. By adjusting the positive and negative voltage phase durations differently, the system compensates for varying inductance caused by changing receiver coupling, enabling the driving current to reach zero crossing points during voltage phase transitions and achieving soft switching with improved power factor efficiency.
Solution Approach 2:
The patent changes the duty cycle parameter dynamically based on operating power level and inductance variations. The controller adjusts the duty cycle from symmetric to asymmetric and further modifies the asymmetric duty cycle to maintain optimal power factor, allowing the system to adapt to varying inductance conditions and achieve unity power factor across different operating points.
3Power
If hard switching occurs, then the system can operate at high power levels, but excessive power dissipation and switch failure result
Solution Approach 1:
The patent applies preliminary action by ensuring the driving current reaches near-zero values before voltage phase transitions occur. The controller adjusts the duty cycle to position current zero crossings at the moments of voltage switching, enabling soft switching even at high power levels. This preliminary alignment of current and voltage waveforms prevents hard switching and the associated power dissipation and switch failure.
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 enhances efficiency by reducing power dissipation and preventing switch failure, achieving soft switching even at higher power levels, thereby improving the reliability and performance of IPT systems.
Implementation Method 1
An alternating current passing through a primary coupler produces an alternating magnetic field. When a secondary coupler is placed in proximity to the primary coupler, the alternating magnetic field induces an electromotive force (EMF) in the secondary coupler according to Faraday's law, thereby wirelessly transferring power to the receiver.
Data Source
AI summary
Systems, methods and apparatuses implementing hybrid symmetric and asymmetric control for soft switching in wireless power transfer applications are provided. An apparatus for wirelessly transferring charging power is provided. The apparatus comprises a wireless power coupler. The apparatus comprises driver circuit. The apparatus comprises a control unit configured to instruct a driver circuit to drive the wireless power coupler with a first voltage waveform when transferring wireless charging power less than a first amount. The first voltage waveform includes a positive portion having a first duration and a negative portion having the first. The control unit is further configured to selectively instruct the driver circuit to drive the wireless power coupler with a second voltage waveform when transferring wireless charging power greater than the first amount, the second voltage waveform including a positive portion having a second duration and a negative portion having a third duration that is not equal to the second duration.