Dual Active Bridge Converter On-Time Control for Step-Down Current
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Solution Overview
Problem
In dual active bridge (DAB) converters, the output current increases over time in step-down mode due to lower output voltage, making it difficult to adjust the output current sufficiently, limiting the range of adjustment.
Innovation Solution
A power conversion device with a first and second bridge circuit connected by an insulated transformer, where the control circuit adjusts the phase difference and on-time of switching elements to reduce output power, switching to on-time control when the phase difference reaches a predefined lower limit in step-down mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If phase difference control is used to reduce output power in step-down mode, then output power is reduced, but output current cannot be reduced sufficiently due to lower output voltage
Solution Approach 1:
The patent changes the control parameter from phase difference to on-time of switching elements. By controlling the on-time (duty cycle) of the switching elements in the bridge circuits, the output current can be directly regulated regardless of the output voltage level, overcoming the limitation of phase difference control in step-down mode where output current cannot be reduced sufficiently.
2Power
If phase difference is controlled to be sufficiently small to reduce output power, then output power decreases, but output current increases with time due to step-down voltage ratio
Solution Approach 1:
The patent implements feedback control by monitoring the output current and adjusting the on-time of switching elements accordingly. This feedback mechanism maintains output current stability over time by compensating for the inherent current increase tendency in step-down mode, ensuring the output current remains within the desired range throughout operation.
3Measurement precision
If phase difference control range is limited by lower limit value, then control precision is maintained, but range of adjustment of output current is insufficient
Solution Approach 1:
The patent transitions from static phase difference control to dynamic on-time control. By making the switching on-time a variable parameter that can be dynamically adjusted, the system achieves both precise control (maintaining the benefit of controlled phase difference) and extended adjustment range (improving adaptability for different output current requirements in step-down mode).
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
Improves the range of adjustment for output current in step-down mode by controlling the on-time of switching elements, stabilizing power conversion and preventing inefficient hard switching.
Implementation Method 1
an insulated transformer connected between the first bridge circuit and the second bridge circuit
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
A control circuit 15 converts power by controlling a phase difference between a switching phase of a plurality of switching elements of a first bridge circuit 11 and a switching phase of a plurality of switching elements of a second bridge circuit 12 such that the control circuit controls the phase difference to be smaller to reduce the output power. When the phase difference reaches a predefined lower limit value in a step-down mode of stepping down the input power, the control circuit controls an on-time of the plurality of switching elements of the second bridge circuit 12 to be shorter while the phase difference is fixed at the lower limit value.