Bi-Directional Power Converter for Wide EV Battery Voltages
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Solution Overview
Problem
Existing DC fast chargers for electric vehicles require high-rated silicon carbide MOSFET switches and face challenges with current rating requirements due to varying battery voltages, necessitating multiple switches for wide voltage ranges, which is inefficient and costly.
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 multi-level AC or DC voltages, optimizing switch usage and accommodating a wide range of vehicle battery voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If high-rated silicon carbide MOSFET switches are used to handle wide voltage ranges, then the power converter can accommodate varying battery voltages, but the cost and device complexity increase due to requiring multiple high-voltage switches
Solution Approach 1:
The power converter circuit is divided into two functional stages: a first stage that converts DC voltage to high-frequency AC voltage, and a second stage that converts high-frequency AC voltage back to DC voltage. This segmentation allows each stage to operate with lower-voltage switches, eliminating the need for multiple high-voltage MOSFETs while still handling wide voltage ranges through the intermediary AC stage.
Solution Approach 2:
High-frequency AC voltage serves as an intermediary between the DC input and DC output stages. The first stage generates high-frequency AC from the DC input, and the second stage rectifies this AC to produce the DC output. This intermediary AC stage enables voltage transformation without requiring high-voltage switches, as the AC stage operates at lower voltages that can be handled by standard switches.
2Adaptability or versatility
If multiple high-voltage switches are used to cover wide voltage ranges, then the charger can support different EV battery voltages, but the current rating requirements and cost increase
Solution Approach 1:
The power conversion function is segmented into two stages with an intermediary AC stage. The first stage uses switches rated for the input DC voltage to generate high-frequency AC, and the second stage uses switches rated for the output DC voltage to rectify the AC. This segmentation allows each switch to be rated for lower voltages than the full range, reducing the total number of high-voltage switches needed.
Solution Approach 2:
The invention changes the voltage parameter dynamically through high-frequency switching. By converting DC to high-frequency AC and back to DC, the system can transform between different voltage levels (e.g., 400V to 800V) without requiring switches rated for the maximum voltage throughout the entire circuit. The switches only need to handle the voltage present in their respective stages.
3Device complexity
If a conventional single-stage DC-DC converter is used, then the circuit is simpler, but it cannot efficiently handle wide voltage ranges without high-rated switches
Solution Approach 1:
The converter is segmented into two stages: a first stage that converts DC to high-frequency AC, and a second stage that converts high-frequency AC back to DC. This segmentation enables wide voltage range handling because each stage can be designed with switches rated for its specific voltage level, rather than requiring all switches to handle the maximum voltage in a single-stage design.
Solution Approach 2:
The invention introduces dynamic high-frequency switching to enable voltage transformation. By switching at high frequency and using the intermediary AC stage, the system can dynamically adapt to different input and output voltage requirements, providing versatility that static single-stage converters cannot achieve without high-voltage components.
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 without overloading switches, supporting both grid-to-vehicle and vehicle-to-grid charging, and optimizing switch requirements.
Implementation Method 1
a first stage (201) converting a DC voltage V1 into a high frequency AC voltage V1ac
Implementation Method 2
a second stage (202) converting a high frequency AC voltage V2ac into a DC voltage Vdc
Implementation Method 3
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.