Variable-Gain Soft-Switching Converter for Wide EV Charging Voltage
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Solution Overview
Problem
Conventional LLC resonant converters face challenges in achieving high power density and efficiency while providing a wide range of DC output voltages for electric vehicle charging, often requiring oversized components and compromising on cost or efficiency due to limitations in switching frequency and transformer design.
Innovation Solution
A variable gain soft switching power converter with a second stage capable of selectively converting high frequency AC voltage into DC voltage of varying amplitudes, using a high frequency transformer with a turns ratio that allows for adjustable gain and symmetrical secondary current, and a control unit to manage power conversion switches for optimal voltage regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional LLC resonant converters are used for wide voltage range EV charging, then the converter can provide high power density, but the transformer and other components become oversized and cost increases
Solution Approach 1:
The patent divides the power conversion process into two distinct stages: a first stage (LLC resonant converter) that operates at high frequency for efficient power conversion, and a second stage (isolated DC-DC converter) that handles the voltage range extension. This segmentation allows each stage to be optimized independently, preventing the need for an oversized transformer in a single-stage design while maintaining high power density.
2Power
If switching frequency is increased to reduce component size, then power density improves, but switching losses increase and efficiency decreases
Solution Approach 1:
The first stage operates at high switching frequency to achieve high power density with reduced component size, while the second stage operates at lower frequency to minimize switching losses. This segmentation of switching frequencies across stages resolves the contradiction between power density and efficiency.
Solution Approach 2:
The patent employs soft switching techniques including zero-voltage switching (ZVS) in the first stage and zero-current switching (ZCS) in the second stage. These phase transition techniques enable lossless or low-loss switching even at high frequencies, allowing high power density without proportionally increased switching losses.
3Device complexity
If single-stage converter design is used for wide voltage range, then device complexity is reduced, but component sizing becomes problematic and efficiency compromises
Solution Approach 1:
The two-stage architecture segments the power conversion function into specialized stages: the first stage handles high-frequency resonant conversion with optimized components, while the second stage handles isolated DC-DC conversion for voltage range extension. This segmentation improves overall efficiency and reliability despite increased structural complexity, as each stage can be independently optimized.
4Adaptability or versatility
If transformer turns ratio is optimized for high voltage output, then voltage range is extended, but the transformer becomes oversized for low voltage operation
Solution Approach 1:
The patent segments the voltage transformation function: the first stage transformer handles high-frequency isolation and moderate voltage transformation, while the second stage extends the voltage range through isolated DC-DC conversion. This allows the first stage transformer to be sized appropriately without being oversized for extreme voltage ranges, as the second stage provides the additional voltage extension capability.
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 provides a wide range of selectable DC output voltages with high power density without increasing component size or cost, ensuring symmetrical transformer currents and improved efficiency across the output voltage range.
Implementation Method 1
a resonant tank including a resonant inductor, a resonant capacitor and a magnetizing inductor
Implementation Method 2
an intermediary stage electrically coupling the first stage and the resonant tank to the second stage
Data Source
AI summary
A power converter, a control unit, a charging device and a method for transferring power to an EV from a power grid are provided. The power converter includes an isolated DC-DC converter having a first stage converting a DC voltage into a high frequency AC voltage having an amplitude V1, an intermediary stage having a high frequency transformer, a resonant tank which outputs a resonant sinusoidal current scaled by the high frequency transformer, and a second stage, connected to a secondary winding of the high frequency transformer, including a power conversion switch, three diodes, and two or more capacitors, that selectively converts the high frequency AC voltage of amplitude V2 into a DC voltage of amplitude ranging from V2 to 2V2.