Flying Capacitor DC-DC Converter Peak Current Control
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Solution Overview
Problem
Existing DC-DC converters face challenges in miniaturization and cost reduction due to the need for large switching elements with high current capacity, especially at heavy loads, which limits the miniaturization of reactors in power conditioners for devices like solar power generation systems.
Innovation Solution
A flying capacitor type DC-DC converter with a control circuit that manages the on/off timing of switching elements to keep the reactor current's peak value below a predetermined level, allowing for the use of switching elements with smaller current capacity, and incorporating a flying capacitor to achieve multilevel control and reduce peak current values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a general boosting chopper is used to boost DC voltage, then the voltage boosting function is achieved, but the reactor size and device cost increase due to high peak current requirements
Solution Approach 1:
The patent divides the single-stage boosting process into multiple stages by introducing a flying capacitor and four switching elements arranged in series. The reactor current is segmented into multiple smaller current paths through the switching elements, reducing the peak current that the reactor must handle. This allows for a smaller reactor volume while maintaining the voltage boosting function.
Solution Approach 2:
The patent introduces a new dimension to the circuit by adding the flying capacitor connected between intermediate nodes of the series switching elements. This creates additional current paths and voltage levels, transforming the single-level boosting circuit into a multilevel circuit that reduces peak current stress on the reactor.
2Power
If switching elements with large current capacity are used to handle heavy load peak current, then the voltage boosting function is maintained, but device cost and size increase
Solution Approach 1:
The patent segments the current handling responsibility among four switching elements connected in series. Each switching element only needs to handle a fraction of the total peak current compared to a single switching element in a conventional circuit. This reduces the current capacity requirement and cost of each individual switching element while maintaining overall heavy load handling capability.
Solution Approach 2:
The flying capacitor acts as an intermediary energy storage element that smooths current fluctuations and reduces peak current demands on the switching elements. By storing and releasing energy at appropriate times, it mediates the current stress on the switching elements, allowing the use of lower current capacity components.
3Volume of stationary object
If the reactor is miniaturized to reduce device size, then cost is reduced, but the ability to handle peak current at heavy load is compromised
Solution Approach 1:
The patent segments the peak current into multiple smaller current paths through the series arrangement of four switching elements. This segmentation allows a miniaturized reactor to handle the same effective power load because the peak current stress on any single path is reduced, maintaining reliability while enabling reactor miniaturization.
Solution Approach 2:
The patent changes the circuit topology parameters by introducing multilevel switching and a flying capacitor. This transforms the current waveform characteristics, reducing the peak current magnitude that the reactor must handle. The parameter change in circuit configuration allows reactor miniaturization without compromising peak current handling capability.
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 approach enables the use of smaller current capacity switching elements and reactors, reducing the size and cost of the device while maintaining efficiency, particularly at heavy loads, by suppressing the peak value of the reactor current through multilevel control.
Implementation Method 1
Magnetic energy is stored in a reactor 52, and the magnetic energy is converted into electric energy again and emitted, thereby boosting the input voltage
Data Source
AI summary
A switching element with a small current capacity is provided to be able to be used in a DC-DC converter. The DC-DC converter includes a switching circuit in which a first switching element, a second switching element, a third switching element, and a fourth switching element are connected in series, a flying capacitor that is connected between a connection portion between the first switching element and the second switching element and a connection portion between the third switching element and the fourth switching element, a reactor that is connected between a connection portion between the second switching element and the third switching element and a positive electrode of an input unit, and a control circuit that turns on/off the switching element, in which the control circuit turns on/off the switching elements so that a peak value in a reactor current becomes equal to or smaller than a predetermined value.