Flying-Capacitor Buck-Boost Converter for Switch Voltage Stress
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Solution Overview
Problem
Conventional buck-boost converters face issues with high voltage stress on switches, increased component costs, and complexity due to the need for high-voltage-rated switches and additional components for reverse current protection, which can lead to damage and increased costs.
Innovation Solution
A DC/DC flying capacitor power converter with an auxiliary switch and series-connected switches in pull-up and pull-down paths, controlled by a microcontroller unit to manage voltage stress and prevent overcharging, eliminating the need for high-voltage-rated switches and reducing complexity and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If conventional buck-boost converters use high-voltage-rated switches to handle 1500V DC voltage, then voltage stress on switches is reduced and system voltage is increased, but component costs increase and device complexity increases
Solution Approach 1:
The patent divides the high-voltage switch into multiple low-voltage switches (typically three switches rated at Vdc/2 or Vdc/3) connected in series. Each switch handles only a portion of the total voltage, allowing the use of cheaper, lower-voltage-rated components while maintaining the ability to handle the full 1500V DC system voltage.
Solution Approach 2:
The patent introduces flying capacitors as intermediary energy storage elements between the switches. These capacitors are charged and discharged in controlled sequences to transfer energy while limiting the voltage stress on each individual switch to a safe level, enabling the use of low-voltage-rated switches in a high-voltage application.
2Reliability
If conventional buck-boost converters use additional components for reverse current protection, then reliability is improved, but device complexity and costs increase
Solution Approach 1:
The patent designs the switching network and flying capacitors to serve multiple functions simultaneously. The same components that enable voltage division and energy transfer also inherently provide reverse current blocking capability through their controlled switching sequences, eliminating the need for separate protection components.
Solution Approach 2:
The controlled switching of the low-voltage-rated switches and flying capacitors creates inherent directional current flow paths. The circuit topology and switching control automatically prevent reverse current flow without requiring external protection devices, making the system self-protecting against reverse current conditions.
3Stress or pressure
If multilevel buck-boost converter is used to step up or step down voltage, then voltage stress on switches is reduced, but device complexity increases due to multiple switches and capacitors
Solution Approach 1:
The patent segments the voltage handling function across multiple switches and flying capacitors, where each component handles only a fraction of the total voltage. This segmentation reduces individual component stress while the coordinated operation of these segmented components achieves the overall voltage conversion function.
Solution Approach 2:
The patent employs dynamic switching control of the multiple switches and flying capacitors to achieve different voltage conversion modes (buck, boost, and bidirectional operation). The switching sequences are dynamically adjusted based on operating conditions, allowing the same circuit topology to provide multiple functions without requiring separate circuits for each mode.
Data Source
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AI summary
A DC/DC power converter (200) operable in a buck and/or a boost mode, a control unit (201), and a method of controlling the power converter (200) are provided. The power converter (200) includes a pull-up path having at least two series connected switches (S1-S2) and/or a pull-down path having at least two series connected switches (S3-S4), a first capacitor (C1) connected across the series connected switches (S1-S4) and between a first terminal (J1) and a second terminal (J2) of the power converter (200), a flying capacitor (Cfy) connected to a connecting node of the pull-up path and a connecting node of the pull-down path, an LC circuit, and an auxiliary switch (T) connected between the first terminal (J1) and a common node formed between a first terminal of the first capacitor (C1) and one of the at least two series connected switches (S1) of the pull-up path.