Bidirectional DC/DC Converter Control for Accurate Power Flow Direction
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Solution Overview
Problem
Existing DC/DC converters of the open-loop LLC type face challenges in accurately determining the power flow direction, particularly when no external power setpoint is available, leading to potential misdirection and increased switching losses, especially when using bipolar devices like IGBT, GTO, IGCT.
Innovation Solution
A DC/DC converter with a control unit that switches operation modes based on power transfer measurements through an AC coupling circuit, using current sensors to determine when to activate or deactivate converter stages as active inverters or passive rectifiers, ensuring correct power direction by threshold-based switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If voltage gain observation method is used to determine power flow direction, then the converter can operate bidirectionally, but the determination may be wrong at low power transfers due to flat voltage ratio characteristics
Solution Approach 1:
The patent implements a feedback mechanism where the control unit continuously monitors the actual power flow direction and compares it with the determined direction. When a mismatch is detected, the control unit corrects the operation mode of converter stages. This feedback loop ensures accurate power flow direction determination even when voltage gain observation alone would be insufficient at low power transfers.
Solution Approach 2:
The system uses its own operational parameters (actual power flow direction) to self-correct and verify the determined power flow direction. The converter stages automatically adjust their operation modes based on the detected mismatch, enabling the system to self-validate and self-correct without external intervention.
2Productivity
If converter stages are switched based on incorrect power flow direction determination, then switching losses increase, but the system continues to operate
Solution Approach 1:
The control unit employs feedback by monitoring the actual power flow direction and comparing it with the determined direction. When they mismatch, the control unit immediately switches the operation modes of converter stages to correct the error. This feedback mechanism minimizes the duration of incorrect operation, thereby reducing switching losses while maintaining continuous operation capability.
3Productivity
If high voltage gain mismatch occurs due to wrong power flow direction, then inrush current increases which can be destructive, but the converter continues operating
Solution Approach 1:
The control unit takes preliminary anti-action by detecting the power flow direction determination in advance and comparing it with the actual direction before high voltage gain mismatch can occur. When a mismatch is detected, the control unit proactively switches the converter stages to correct operation modes, preventing the development of destructive inrush currents before they can damage the system.
Solution Approach 2:
The feedback mechanism continuously monitors the actual power flow direction and immediately triggers correction when a mismatch is detected. This rapid feedback response prevents high voltage gain mismatch from developing into destructive inrush current conditions, while allowing the converter to maintain operational continuity.
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
Ensures accurate power flow direction determination and reduces switching losses by alternating converter stage operation, minimizing inrush currents and network disturbances.
Implementation Method 1
LLC resonant converter has a resonant tank consisting at least of two inductors (that might be integrated in a transformer) and one capacitor and is switched with a constant 50% duty cycle with a switching frequency near or at a resonant frequency of the resonant tank
Data Source
AI summary
The present invention relates to a DC/DC converter (1) for transferring an active power between two DC subsystems (5, 6) comprising: —a first converter stage (3) and a second converter stage (4) both configured to be selectively operated as an active inverter or as a passive rectifier; —an AC coupling circuit (2) for coupling the first and the second converter stage (3, 4) by means of an AC power transfer; and —a control unit (10) configured to switch the operation mode of the first and second converter stages (3, 4) depending on a measurement of an amount of power transfer through the AC coupling circuit (2).