Multilevel Switched-Capacitor Rectifier for Wireless Charging
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Solution Overview
Problem
Existing wireless power transfer systems face challenges in achieving high efficiency and low harmonic content at high power levels, such as 20 W fast charging, due to conduction losses and harmonic generation in miniaturized AC-DC rectifiers and coils, which lead to overheating and electromagnetic interference issues.
Innovation Solution
A multilevel switched-capacitor (MSC) rectifier with output regulation is introduced, which monitors output voltage/current and adjusts electronic circuit behavior using a closed-loop control system to generate a multilevel output waveform, reducing conduction losses and harmonic content through intelligent control of switches and capacitors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a diode rectifier and receiver coil are used for 20 W fast charging, then power delivery capability is improved, but conduction losses increase resulting in overheating issues
Solution Approach 1:
The patent transforms the rectifier input from a conventional two-level square wave to a multilevel stepped waveform. This parameter change in voltage waveform reduces the current stress on the receiver coil and diodes, thereby decreasing conduction losses while maintaining 20 W power delivery capability
Solution Approach 2:
The rectifier voltage output is segmented into multiple levels (three-level or five-level) instead of a single square wave level. This segmentation creates a stepped waveform that approximates a sinusoid, reducing harmonic content and improving power transfer efficiency by minimizing resistive losses in the coil and rectifier components
2Volume of moving object
If miniaturized magnetics and WPT coils are used to meet space constraints, then device profile is reduced, but losses increase due to prohibitive conduction losses
Solution Approach 1:
By changing the voltage waveform parameter from square wave to multilevel stepped waveform, the patent reduces the RMS current required for the same power transfer. This allows miniaturized coils with higher resistance to operate at acceptable efficiency levels, enabling compact device profiles without excessive losses
3Device complexity
If a diode rectifier with square waveform input is used, then simple circuit structure is achieved, but harmonic content increases causing EMI issues
Solution Approach 1:
The rectifier voltage is segmented into multiple stepped levels that follow a sinusoidal envelope, replacing the harsh square wave. This segmentation reduces the spectral content of harmonics, particularly the 3rd and 5th order harmonics, thereby reducing EMI while maintaining relatively simple circuit topology using only capacitors and switches
Solution Approach 2:
The patent converts the inherently discontinuous switching nature of rectifiers, which generates harmonics, into a beneficial multilevel stepped waveform that naturally suppresses harmonics. The switching action still occurs but produces a waveform that is harmonically richer in fundamental frequency and poorer in harmonic content
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 MSC rectifier system achieves substantial reduction in conduction losses and harmonic content, enabling efficient high-power wireless charging with reduced size and heat dissipation, while maintaining compliance with electromagnetic compatibility standards.
Implementation Method 1
A multilevel switched-capacitor (MSC) rectifier with output regulation is introduced
Implementation Method 2
a transmitter converts a Direct Current (DC) voltage to an Alternating Current (AC) waveform, feeding a pair of magnetically coupled coils
Data Source
AI summary
Described herein is a wireless charging system including switched capacitor (SC) rectifiers with output regulation. The load for the receiver on mobile devices using wireless charging is a battery. Regulation is needed for battery charging applications, e.g. constant voltage charging, constant current charging, and pulsed charging. For this purpose, the wireless power transfer (WPT) receiver can possess some “intelligence” to monitor the output voltage/current, adjust the behavior of the electronic circuitries and achieve a closed-loop control. Because a multilevel switched-capacitor (MSC) rectifier has output control ability, this can allow the MSC rectifier to directly charge the battery without an additional DC/DC charger on-board the device.