Two-Stage Bidirectional DC/DC Converter with Constant Duty Ratio LLC
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Solution Overview
Problem
Conventional bidirectional DC/DC power converters face inefficiencies due to high costs of control ICs and voltage/current stress on MOSFETs, leading to decreased efficiency, especially as converter capacity increases.
Innovation Solution
A two-stage bidirectional DC/DC power converter using a controlled bidirectional converter with a switching device instead of a diode and an unregulated LLC resonant converter, operating at a constant duty ratio to perform booster and buck functions, reducing stress and costs while maintaining efficient energy transfer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional full-bridge converter topology is used, then bidirectional power conversion is achieved, but the control IC cost increases and switching device stress increases leading to decreased efficiency
Solution Approach 1:
The patent divides the bidirectional DC-DC converter into two separate unregulated converters: a boost converter for forward direction and a buck converter for reverse direction. Each converter operates independently with its own switching devices, eliminating the need for a complex full-bridge topology. This segmentation reduces switching loss and improves efficiency while maintaining bidirectional power conversion capability.
Solution Approach 2:
The patent extracts the regulation function from the power conversion stage by using unregulated converters. The boost converter and buck converter are designed to operate without active regulation, simplifying the control IC requirements and reducing cost. The converters rely on inherent voltage transformation ratios and passive components to achieve the desired power conversion.
2Reliability
If a conventional full-bridge converter topology is used, then bidirectional power conversion is achieved, but the control IC cost increases
Solution Approach 1:
The patent segments the bidirectional converter into two independent unregulated converters, each with simpler control requirements. The boost converter uses basic PWM control for forward power flow, while the buck converter uses similar simple control for reverse power flow. This eliminates the need for expensive multi-phase or high-complexity control ICs required by full-bridge topologies.
Solution Approach 2:
The patent extracts the active regulation function from the power conversion stage, using unregulated converters instead. This removes the need for complex feedback control loops and advanced control algorithms, significantly reducing control IC complexity and cost while maintaining adequate performance for the application.
3Power
If converter capacity is increased, then power output is improved, but switching loss increases leading to decreased efficiency
Solution Approach 1:
The patent divides the high-power bidirectional converter into two separate unregulated converters operating in parallel or sequence. Each converter handles a portion of the total power, reducing the switching frequency and voltage-stress requirements for individual switching devices. This segmentation allows higher overall power output while maintaining lower switching loss per device.
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 solution achieves higher efficiency and reduced costs for control ICs and switching devices, enabling stable energy transfer across a wide range of loads and operations, improving upon the inefficiencies of conventional converters.
Implementation Method 1
an unregulated LLC resonant converter, which only provides a fixed booster ratio function (fixed buck ratio function when operated in the reverse direction) according to the insulation between input and output as well as the turn ratio of the transformer
Data Source
AI summary
A two-stage insulated bidirectional DC/DC power converter is disclosed. A two-stage insulated bidirectional DC/DC power converter according to an embodiment of the invention has the characteristic of including: an LLC resonant converter operating at a constant duty ratio; a bidirectional converter joined to a front part of the LLC resonant converter and configured to perform a booster converter function of outputting the input voltage at a consistent input voltage for the LLC resonant converter, and a buck converter function of reducing the voltage by way of the LLC resonant converter and then outputting a consistent voltage; and a bidirectional converter control unit configured to control changes in an input voltage of the bidirectional converter and regulate an output voltage of the LLC resonant converter to thereby maintain a consistent input voltage of the LLC resonant converter, such that the LLC resonant converter operates at a constant duty ratio.