Two-Transformer Resonant Converter for Wide Bidirectional Voltage Gain
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Solution Overview
Problem
Existing bidirectional resonant converters, such as LLC, CLLC, and L3C, face limitations in high voltage conversion ratios due to design constraints on resonant parameters, leading to inefficiencies and impractical component values.
Innovation Solution
A symmetric bidirectional resonant converter topology with two transformers (2T-LLC) is introduced, allowing for adjustable resonant parameters through additional transformer turn ratios, enabling wide voltage conversion ranges and suitable for both DC-to-DC and AC-to-AC conversions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If traditional LLC resonant converter topology is used, then the converter achieves good efficiency and wide voltage gain range, but the normalized backward gain range is always less than unity, limiting bidirectional applications
Solution Approach 1:
The patent divides the single transformer in traditional LLC converter into two separate transformers (first transformer with primary and secondary windings, second transformer with primary and secondary windings). This segmentation allows independent optimization of forward and backward conversion paths, enabling symmetric bidirectional voltage gain while maintaining manageable complexity through modular structure
Solution Approach 2:
The patent introduces asymmetric control by applying different phase shift angles to the primary side switches and secondary side switches of the two transformers. The first phase shift angle controls forward power flow while the second phase shift angle controls backward power flow, creating asymmetric control capability that achieves symmetric bidirectional voltage conversion characteristics
2Adaptability or versatility
If CLLC resonant converter with second resonant tank is used, then proper voltage gain range is achieved in both forward and backward modes, but the extra resonant tank increases cost and volume, and voltage gain is reduced compared with traditional LLC converter
Solution Approach 1:
The patent extracts the second resonant tank (second resonant capacitor and second resonant inductor) from the CLLC topology and replaces it with a second transformer. This extraction removes the volume-increasing components while preserving the bidirectional voltage gain capability through the transformer's galvanic isolation and turns ratio, achieving the same function with reduced volume
Solution Approach 2:
The patent introduces a second transformer as an intermediary component between the resonant circuit and the load. This intermediary provides galvanic isolation and enables bidirectional power flow control through phase shift modulation, replacing the need for a second resonant tank and achieving volume reduction while maintaining functionality
3Ease of manufacture
If CLLC converter resonant parameters are determined by rated power and voltage, then design is simplified, but extreme resonant parameters that cannot be practically achieved are required for high voltage conversion ratios
Solution Approach 1:
The patent introduces dynamic control through phase shift modulation of the two transformers. By dynamically adjusting the phase shift angles, the converter can adapt to different voltage conversion ratios without requiring fixed extreme resonant parameters. This dynamic control mechanism provides flexibility to handle high voltage conversion ratios with practical, achievable component values
Solution Approach 2:
The patent changes the control parameters from fixed resonant parameter design to variable phase shift angle control. By varying the phase shift angles between primary and secondary side switches, the converter can achieve different voltage conversion ratios dynamically, eliminating the need for extreme fixed resonant parameters and enabling practical implementation for high voltage conversion ratio applications
4Device complexity
If DAB converter is used, then simple structure and wide-range soft-switching capability are achieved, but high reverse energy and high turn-off power loss deteriorate overall efficiency
Solution Approach 1:
The patent employs resonant oscillation in the LLC circuit formed by the resonant capacitor, resonant inductor, and transformer leakage inductance. This resonant vibration enables soft switching by ensuring that switches turn on and off at optimal points in the resonant cycle, minimizing turn-off power loss while maintaining the simple DAB-like structure with dual transformers and phase shift control
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 2T-LLC converter achieves low power loss, high efficiency, and wide voltage conversion symmetry, particularly in high voltage conversion scenarios, overcoming limitations of traditional topologies.
Implementation Method 1
the resonant inductor Lr, the magnetizing inductor Lm2 of the second transformer and the resonant capacitor Cr form an LLC resonant circuit
Implementation Method 2
a first transformer having a first winding connected to the first switch network; a second transformer having a first winding connected to the second switch network
Data Source
AI summary
When existing power converters are used bidirectionally, they may be limited by efficiency or restricted conversion ranges. Disclosed herein is a symmetric bidirectional resonant converter. The converter is suitable for both DC-to-DC, AC-to-DC and AC-to-AC conversion. The converter includes a first switch network, a first transformer, a resonant tank, a second transformer, and a second switch network. The converter has a symmetrical structure, providing more degrees of freedom for the design of resonant component parameters while achieving bidirectional power transmission, and can achieve high bidirectional voltage-conversion ratios. The converter's semiconductor and resonant components provide both output voltage regulation and soft switching in both power conversion directions, which enhances power conversion efficiency.