Dual Active Bridge Converter Switching for Low Reactive Current
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Solution Overview
Problem
Commonly used DAB converters experience reactive current production and hard switching issues, especially during light load conditions and bidirectional power transfer, due to the charging of reactors from both DC power sources.
Innovation Solution
A bidirectional insulated DC-DC converter design featuring a first and second bridge circuit connected in parallel, with an insulated transformer and a control circuit that fixes phase differences and controls simultaneous off periods of switching elements to prevent reactive current and hard switching, enabling efficient power transfer by stepping up or stepping down voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a commonly-used DAB converter charges the reactor from both DC power sources, then bidirectional power transfer capability is achieved, but reactive current is produced and hard switching occurs
Solution Approach 1:
The patent applies dynamics by making the switching patterns adaptive rather than fixed. The control circuit dynamically selects different switching patterns based on power flow direction and load conditions. Specifically, when power flows from primary to secondary, a first switching pattern is used, and when power flows from secondary to primary, a second switching pattern is used. This dynamic adaptation eliminates reactive current production while maintaining bidirectional capability.
Solution Approach 2:
The patent changes the switching parameter (phase difference and switching timing) based on operating conditions. By adjusting the switching patterns of the bridge circuits according to power flow direction, the system optimizes energy transfer efficiency. The control circuit modifies switching parameters to prevent hard switching and reactive current under different load conditions.
2Productivity
If the converter operates with light load, then power conversion is maintained, but hard switching occurs increasing losses
Solution Approach 1:
The patent uses partial action by selectively applying different switching patterns based on load conditions. Instead of using a fixed switching pattern for all load levels, the control circuit applies appropriate switching patterns only when needed. For light load conditions, specific switching patterns are used to prevent hard switching, while full power transfer patterns are used when higher loads are present.
3Power
If phase difference control is used for power transfer, then voltage conversion is achieved, but reactive power and conduction losses increase
Solution Approach 1:
The patent applies preliminary action by pre-configuring optimal switching patterns for different power flow directions. The control circuit has predetermined switching sequences that are activated based on the detected power flow direction. This preliminary preparation allows the system to immediately use the most efficient switching pattern without transitioning through intermediate states that would produce reactive power or increase conduction losses.
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 realizes a highly efficient, insulated DC-DC converter that reduces reactive power and conduction losses, preventing hard switching and improving conversion efficiency across a wide voltage range.
Implementation Method 1
an insulated transformer connected between the first bridge circuit and the second bridge circuit
Data Source
Figure 1
Figure 2A~2F
Figure 3A~3B
AI summary
For power transfer from a first DC part to a second DC part in a dual active bridge (DAB) converter by stepping up a voltage, the second bridge circuit 12 includes a period in which a secondary winding n2 of an insulated transformer TR1 and the second DC part conduct and a period in which ends of the secondary winding n2 of the insulated transformer TR1 are short-circuited in the second bridge circuit 12. A control circuit 13 fixes a phase difference between a first leg a the second leg, variably controls a simultaneous off period of a fifth switching element S5 and a sixth switching element S6, and variably controls a simultaneous off period of a seventh switching element S7 and an eighth switching element S8.