Bi-Directional DC Fast Charger Converter for Wide Battery Voltages
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Solution Overview
Problem
Existing DC fast chargers for electric vehicles require high-rated silicon carbide MOSFET switches due to varying battery voltages, leading to increased switch requirements and current demands, which are not efficiently met by current technology.
Innovation Solution
A bi-directional power converter with an isolated DC-DC converter featuring a first stage that converts DC to high-frequency AC and vice versa, and a second stage that generates DC voltage ranging from V2 to 2V2, utilizing a high-frequency transformer and asymmetrically arranged power conversion switches to optimize switch usage and voltage range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high-rated silicon carbide MOSFET switches are used to handle varying battery voltages, then the charger can support a wide voltage range, but the switch requirements and current demands increase significantly
Solution Approach 1:
The power converter is divided into two independent stages: a first stage converting DC to high-frequency AC, and a second stage converting high-frequency AC to DC. This segmentation allows each stage to operate at optimal voltage levels, with the first stage handling high voltage and the second stage handling lower voltage, thereby reducing the power and current demands on individual switches while maintaining wide voltage range support.
Solution Approach 2:
A high-frequency AC intermediary stage is introduced between the DC input and DC output. This intermediary converts the DC voltage to high-frequency AC, transforms it through a transformer with appropriate turns ratio, and then rectifies it back to DC. This intermediary approach enables voltage transformation without requiring high-voltage high-current switches, thus reducing switch current demands while supporting wide voltage ranges.
2Device complexity
If a conventional single-stage DC-DC converter is used, then the circuit is simpler, but it cannot efficiently handle the wide voltage range from 150V to 1500V
Solution Approach 1:
The converter is segmented into two functional stages with distinct roles. The first stage (DC to high-frequency AC conversion) handles the wide input voltage range, while the second stage (high-frequency AC to DC conversion) provides the output voltage. This segmentation enables each stage to be optimized for its specific function, allowing efficient handling of the wide voltage range despite increased structural complexity.
Solution Approach 2:
The converter employs dynamic high-frequency switching in both stages to adapt to varying input and output voltage conditions. The first stage switches at high frequency to accommodate the wide DC voltage range, and the second stage switches at high frequency to regulate the output DC voltage. This dynamic operation enables wide voltage range coverage while maintaining efficient power conversion.
3Reliability
If multiple high-voltage switches are connected in series to achieve required voltage rating, then the voltage handling capability increases, but the device complexity and switch quantity increase
Solution Approach 1:
The high-frequency AC intermediary stage with transformer enables voltage transformation without requiring series connection of multiple high-voltage switches. The transformer's turns ratio provides the necessary voltage step-down from the first stage to the second stage, eliminating the need for multiple series-connected switches and reducing both device complexity and switch quantity while maintaining voltage handling 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 bi-directional power converter efficiently handles a wide range of DC voltages, optimizing switch requirements and current demands, supporting charging of various electric vehicles from light to heavy-duty models, and enabling bi-directional power transfer between vehicles and the grid.
Implementation Method 1
The intermediary stage 203 includes a high frequency transformer connected between the first stage 201 and the second stage 202
Data Source
AI summary
A bi-directional power converter, a control unit, a charging device and a method for transferring power between an EV and a power grid are provided. The bi-directional power converter includes an isolated DC-DC converter having a first stage converting a DC voltage into a high frequency AC voltage, a second stage capable of converting a high frequency AC voltage having an amplitude V2 into the DC voltage having an amplitude of V2 or 2V2, and converting the DC voltage into a multi-level high frequency AC voltage, and an intermediary stage electrically coupled to the first and the second stages, having a high frequency transformer of a turns ratio V1:V2.