Stacked Switched Capacitor Energy Buffer for Low-Loss DC-AC Buffering
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Solution Overview
Problem
Conventional power conversion systems for DC-AC interfaces face limitations in miniaturization due to high energy buffering requirements, and electrolytic capacitors used for energy storage suffer from reliability and efficiency issues at twice-line-frequency operations.
Innovation Solution
The stacked switched capacitor (SSC) energy buffer circuit employs a switching network operating at low frequencies, utilizing film and ceramic capacitors with optimized capacitance ratios to achieve high efficiency and energy density without the need for electrolytic capacitors, allowing for smaller and more reliable grid interface systems.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If electrolytic capacitors are used for energy storage in DC-AC power conversion systems, then high energy density is achieved, but reliability and efficiency deteriorate at twice-line-frequency operations
Solution Approach 1:
The patent changes the operating parameters by switching from high-frequency switching (conventional) to low-frequency switching at twice line frequency (120 Hz). This parameter change allows film capacitors to operate within their optimal range, achieving both high reliability and acceptable energy density when combined with the stacked configuration
Solution Approach 2:
The patent uses a composite approach by stacking multiple film capacitors in series to create an energy buffer system that achieves high voltage operation and high energy density equivalent to electrolytic capacitors, while maintaining the reliability advantages of film capacitors
2Quantity of substance
If electrolytic capacitors are used for energy storage, then high energy density is achieved, but efficiency deteriorates due to thermal and RMS current limits
Solution Approach 1:
The patent changes the frequency parameter from high-frequency switching to low-frequency operation at 120 Hz, which dramatically reduces RMS current and thermal losses in film capacitors, thereby achieving high efficiency while maintaining energy density through the stacked configuration
3Productivity
If switching frequency is increased to reduce energy buffer size, then productivity is improved, but energy buffering requirements cannot be reduced due to proportionality with system average power and line period
Solution Approach 1:
The patent transitions from a single-capacitor approach to a stacked multi-capacitor configuration, adding a spatial dimension to the energy storage system. This allows the energy buffer to achieve high voltage operation and high energy density equivalent to much larger single capacitors, enabling miniaturization without increasing buffering capacity
4Reliability
If film and ceramic capacitors are used instead of electrolytic capacitors, then reliability is improved, but energy density deteriorates
Solution Approach 1:
The patent uses a composite approach by stacking multiple film capacitors in series to create an energy buffer system that achieves high voltage operation and high energy density equivalent to electrolytic capacitors, while maintaining the reliability advantages of film capacitors
Solution Approach 2:
The patent segments the energy storage function across multiple capacitor units stacked in series, allowing each capacitor to operate at lower voltage stress while collectively achieving high voltage and high energy density, thereby resolving the contradiction between reliability and energy density
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 SSC energy buffer circuit achieves high efficiency and energy density comparable to electrolytic capacitor systems while reducing the size and increasing reliability, with optimized capacitance ratios enhancing energy buffering ratios and minimizing passive volume.
Implementation Method 1
a plurality of energy storage capacitors coupled to a DC bus and interconnected through the switching network
Data Source
AI summary
SSC energy buffer circuit includes a switching network and a plurality of energy storage capacitors. The switching network may operate at a relatively low switching frequency and can take advantage of soft charging of the energy storage capacitors to reduce loss. Efficiency of the SSC energy buffer circuit can be extremely high compared with the efficiency of other energy buffer circuits. The SSC energy buffer architecture exhibits losses that scale with the amount of energy buffered, such that a relatively high efficiency can be achieved across a desired operating range. Improvements in SSC energy buffer circuits include, in various implementations, the use of ground reference gate drive, the elimination of a separate precharge circuit through control of at least a portion of the switches of the SSC energy buffer circuit, and/or optimized ratio of capacitance values of two or more capacitors in an SSC energy buffer circuit.