AC-DC Converter Circuit With Dual DC-Links for Fixed-Frequency Charging
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Solution Overview
Problem
Existing AC/DC converters for automotive on-board chargers face inefficiencies due to wide frequency modulation, leading to larger magnetic core sizes and higher weight, and require complex control systems for galvanic isolation.
Innovation Solution
A quasi 5-level PFC rectifier with two distinct DC-links and a fixed frequency DC/DC resonant converter, combined with a series resonant converter, allowing open-loop operation and optimized transformer design, reducing reactive power circulation and eliminating the need for additional power conversion stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If frequency modulation is used to achieve wide gain range in CLLC resonant converter, then the output voltage can be regulated across wide battery voltage range, but system efficiency drops due to higher reactive power and larger magnetic core size
Solution Approach 1:
The patent changes the operating parameter from frequency modulation to voltage level selection. By providing multiple DC-link voltages and selecting the appropriate one based on battery voltage, the system maintains operation near resonant frequency (where efficiency is high) while achieving wide adaptability across different battery voltage ranges.
Solution Approach 2:
The patent segments the voltage conversion function into two parts: the PFC rectifier provides multiple discrete DC-link voltage levels, and the DC/DC resonant converter selects and utilizes the most appropriate voltage level. This segmentation allows each component to operate in its optimal range, with the DC/DC converter operating near unity gain for high efficiency.
2Adaptability or versatility
If frequency modulation is used to achieve wide gain range, then output voltage regulation is possible across wide battery voltage range, but magnetic core size and weight increase
Solution Approach 1:
The patent changes the control parameter from frequency to voltage level selection, allowing the DC/DC converter to operate near resonant frequency with unity gain. This eliminates the need for oversized magnetic cores designed to handle wide frequency ranges, significantly reducing weight while maintaining wide adaptability through multiple DC-link voltage levels.
Solution Approach 2:
The system dynamically selects the most appropriate DC-link voltage level based on real-time battery voltage conditions. This dynamic voltage selection enables the DC/DC converter to operate in its optimal efficiency range across all battery voltage conditions, eliminating the need for static, oversized magnetic components.
3Reliability
If two-stage system with isolated DC/DC converter is used for galvanic isolation, then safety requirements are met, but device complexity increases
Solution Approach 1:
The resonant tank components (inductors and capacitor) naturally provide galvanic isolation between the PFC rectifier and DC/DC converter stages. This self-service approach to isolation eliminates the need for complex isolated DC/DC converter control systems, significantly reducing device complexity while maintaining safety requirements.
Solution Approach 2:
The resonant tank acts as an intermediary between the PFC rectifier and DC/DC converter, providing natural galvanic isolation through its inductive and capacitive elements. This intermediary approach simplifies the overall system by eliminating the need for complex isolated conversion control while maintaining safety.
4Ease of operation
If DC-link voltage is kept constant at around 400 V, then PFC stage regulation is simplified, but DC/DC converter requires wide frequency modulation leading to reduced efficiency
Solution Approach 1:
The patent segments the voltage regulation function: the PFC rectifier maintains a constant DC-link voltage for simplified operation, while a second DC-link provides variable voltage levels. The DC/DC converter then selects the optimal voltage level, operating near unity gain to minimize reactive power and maximize efficiency.
Solution Approach 2:
The patent adds another voltage dimension by providing multiple DC-link voltages instead of relying solely on frequency modulation. This dimensional change allows the system to maintain constant PFC operation while achieving efficient voltage conversion through selective voltage level matching.
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 configuration achieves high efficiency and compact size, minimizing transformer weight and reducing losses, while maintaining galvanic isolation without complex control, suitable for wide battery voltage ranges.
Implementation Method 1
a first DC voltage Vdc between a first DC terminal 102 and a third DC terminal 104 and a second DC voltage Vc2 between a second DC terminal 103 and the third DC terminal 104
Implementation Method 2
fixed frequency DC/DC resonant converter, combined with a series resonant converter
Data Source
Figure 1a
Figure 1b
Figure 2
AI summary
The disclosure relates to an AC-DC conversion device (150) for converting an alternating current, AC, voltage (101a) into a direct current, DC, voltage, the AC-DC conversion device (150) comprising: an AC input terminal (151) for receiving an AC voltage (101a); an AC-DC conversion stage (110) being configured to: convert the AC voltage (101a) into a first DC voltage (106a); convert the AC voltage (101a) into a second DC voltage (106b); and output the second DC voltage (106b) at an output (152) of the AC-DC conversion device (150); and a partial power DC-DC converter (130) configured to regulate the second DC voltage (106b) based on a required voltage across the output (152) of the AC-DC conversion device (150). The disclosure further relates to a voltage converter circuit comprising such an AC-DC conversion device (150) and an output (105) for providing an isolated output voltage (105a).