LCL-Transformer Dual Active Bridge for Wide-Load ZVS DC-DC Conversion
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Solution Overview
Problem
Resonant power converters face challenges in achieving zero voltage switching (ZVS) in current fed inverter stages, particularly in low-current high-voltage systems, limiting switching frequency and requiring higher-rated switches, which makes them impractical for certain applications like underwater ocean observatory systems.
Innovation Solution
A power converter design incorporating a primary H-bridge and secondary H-bridge with an LCL-T resonant network, utilizing a transformer and output capacitor to regulate constant DC output voltage, and employing symmetrical phase shift modulation to achieve ZVS and efficient power conversion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current fed inverter stage is used in resonant converters, then zero current switching can be achieved, but achieving zero voltage switching becomes challenging which limits switching frequency
Solution Approach 1:
The patent introduces an LCL-T resonant network as an intermediary between the current fed inverter and the load. This resonant network transforms the current waveform into a voltage waveform, enabling the subsequent voltage fed inverter stage to achieve zero voltage switching. The resonant network acts as a mediator that converts the operating mode from current-based to voltage-based while maintaining soft switching benefits.
Solution Approach 2:
The patent changes the operating parameters by transitioning from direct current fed inverter operation to a resonant voltage fed inverter operation. By adjusting the resonant frequency and impedance parameters of the LCL-T network, the system achieves both zero current switching in the first stage and zero voltage switching in the second stage, thereby increasing switching frequency capability.
2Reliability
If switches are rated for higher than average DC input voltage to achieve ZVS, then zero voltage switching can be achieved, but the CFI stage becomes impractical for low-current high-voltage systems
Solution Approach 1:
The LCL-T resonant network serves as an intermediary that transforms the high-voltage current-fed operation into a lower-voltage equivalent operation on the secondary side. This allows the use of appropriately rated switches without requiring excessively high voltage ratings, making the system practical for low-current high-voltage applications.
Solution Approach 2:
The patent segments the inverter stage into two separate H-bridge stages: a primary current-fed inverter and a secondary voltage-fed inverter. This segmentation allows each stage to use switches rated appropriately for its specific operating conditions, rather than requiring all switches to be rated for the maximum DC input voltage, thereby improving practicality for low-current high-voltage systems.
3Adaptability or versatility
If a voltage fed inverter stage is used at the front end, then the system can operate with varying DC input voltage, but achieving ZVS becomes challenging and switching frequency is limited
Solution Approach 1:
The patent divides the voltage fed inverter into two stages: a primary H-bridge that handles variable DC input voltage and operates at zero current switching, and a secondary H-bridge that operates at zero voltage switching with a more stable voltage input from the LCL-T resonant network. This segmentation allows variable input voltage operation while maintaining high switching frequency capability in the secondary stage.
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 design enables efficient power conversion with ZVS across a wide range of loads, maintaining constant output voltage and reducing switch stress, thus enhancing the practicality for high-power and high-frequency applications like underwater DC distribution networks.
Implementation Method 1
LCL-T resonant DC-DC converter
Implementation Method 2
a transformer with a primary side connected between a second end of the second inductor Lg and the second terminal B of the primary H-bridge, a secondary H-bridge that includes semi-conductor switches with an input connected to a secondary side of the transformer
Data Source
AI summary
A power converter includes a primary H-bridge with switches and an LCL-Transformer section with a first inductor with a first end connected to a first terminal of the primary H-bridge, a capacitor connected between a second end of the first inductor and a second terminal of the primary H-bridge, and a second inductor with a first end connected to the second end of the first inductor. The converter includes a transformer with a primary connected between a second end of the second inductor and the second terminal of the primary H-bridge, a secondary H-bridge with switches with an input connected to a secondary side of the transformer, and an output capacitor connected across output terminals of the secondary H-bridge. The primary H-bridge is fed by a DC constant current source and the output terminals of the secondary H-bridge have a regulated DC output voltage are connected to a load.