Bidirectional Power Converter Switching Sequence for Return Current Reduction
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Solution Overview
Problem
Bidirectional power converters with sub-circuits connected in parallel face issues with return currents causing losses, as existing designs do not effectively restrict reverse recovery currents and return currents between sub-circuits, especially when switching elements are turned on and off in the same order.
Innovation Solution
The bidirectional power converter incorporates sub-circuits with upper and lower switching elements, diodes, and sub-reactors connected in a specific configuration, where the controller alternates the switching order of the elements based on current direction to minimize return currents, and uses sub-reactors with different magnetic saturation current values to manage inductance effectively, reducing losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If switching elements are turned on and off sequentially in the same order, then control is simplified, but return current is generated between sub-circuits causing loss
Solution Approach 1:
The patent applies dynamics by making the switching order adaptive rather than fixed. The control unit changes the switching sequence of the second switching element based on the current flow direction detected in the sub-circuit. When current flows in the forward direction, one switching sequence is used; when current flows in reverse, a different sequence is applied. This dynamic adjustment eliminates return current between sub-circuits while maintaining simple control logic.
2Power
If sub-circuits are connected in parallel, then power conversion capacity is increased, but return current flows between sub-circuits
Solution Approach 1:
The patent applies local quality by introducing individual control mechanisms for each sub-circuit rather than uniform control. Each sub-circuit is equipped with detection means to sense current direction and control means to adjust switching sequences locally. This localized control ensures that each sub-circuit operates independently without generating return current to other sub-circuits, thereby maintaining high power conversion capacity while eliminating losses.
3Loss of energy
If sub-reactors are added to reduce reverse recovery current loss, then diode reverse recovery loss is reduced, but device complexity increases
Solution Approach 1:
The patent applies the taking out principle by extracting the reverse recovery current suppression function from the diode and relocating it to the switching element control. Instead of adding sub-reactors to physically suppress reverse recovery current, the invention uses control means to manage the switching timing of the second switching element, which indirectly suppresses reverse recovery effects. This approach achieves the same loss reduction without adding physical components, thereby avoiding increased device complexity.
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
This configuration effectively restricts return currents and reduces losses in bidirectional power conversion, maintaining efficient power conversion while minimizing the impact on main current flow.
Implementation Method 1
One end of each sub-reactor is connected to a midpoint of the series connection of the two switching elements... The sub-reactors reduce loss caused by reverse recovery current of the diodes
Implementation Method 2
A first end of the main reactor is connected to the first terminal... enables bidirectional power conversion between a first device and a second device
Data Source
AI summary
A bidirectional power converter includes a first terminal, a second terminal, a main reactor, a plurality of sub-circuits and a controller. The sub-circuits each include an upper switching element, a lower switching element, two diodes, and a sub-reactor. The controller sequentially controls the sub-circuits such that: the lower switching element is turned on and turned off and then the upper switching element is turned on and turned off in each of the sub-circuits, while a current is flowing from the first terminal toward the second terminal; and the upper switching element is turned on and turned off and then, the lower switching element is turned on and turned off in each of the sub-circuits, while the current is flowing from the second terminal toward the first terminal.