Flying Capacitor Ripple Control for Compact Power Converters
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Solution Overview
Problem
Existing power converters, particularly those used in photovoltaic power generation, face challenges in reducing size and increasing lifespan due to the need for high-capacitance smoothing capacitors, which are bulky and have limited lifespan.
Innovation Solution
The implementation of a power converter design that includes a flying capacitor system, where the flying capacitor is controlled to maximize and minimize voltage at specific phase angles, allowing it to accommodate ripple components and reduce the capacitance required for smoothing, enabling the use of film capacitors with higher breakdown voltages and longer lifespans.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-capacitance smoothing capacitor is used to accommodate ripple components, then the power converter can handle ripple voltages effectively, but the device size increases and lifespan decreases
Solution Approach 1:
The patent divides the ripple accommodation function between two components: the flying capacitor (already present in the multi-level inverter circuit) and a new smoothing capacitor. The flying capacitor handles a portion of the ripple components through phase-shifted control, while the smoothing capacitor handles the remaining ripple. This segmentation allows using a smaller smoothing capacitor, reducing overall device size while maintaining reliability.
Solution Approach 2:
The flying capacitor serves dual functions: (1) its original function in the multi-level inverter topology for voltage division and switching, and (2) an additional function of accommodating ripple components through controlled phase shifting. This multi-functionality reduces the burden on the smoothing capacitor, allowing for a smaller, more reliable design.
2Volume of moving object
If the capacitance of the smoothing capacitor is reduced to decrease device size, then the power converter becomes more compact, but the ability to accommodate ripple components deteriorates
Solution Approach 1:
The ripple accommodation task is segmented between the flying capacitor and the smoothing capacitor. By controlling the phase difference between their respective ripple components, the patent ensures that when one capacitor's ripple is at peak, the other's is at trough, enabling effective cancellation and allowing reduced smoothing capacitor capacitance.
Solution Approach 2:
The patent utilizes periodic phase-shifted control where the flying capacitor's ripple component is deliberately phase-shifted relative to the smoothing capacitor's ripple. This periodic action creates destructive interference of ripple components, effectively reducing total ripple while allowing smaller capacitor sizes.
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 design reduces the size of power converters and allows for the replacement of aluminum electrolytic capacitors with film capacitors, enhancing the converters' efficiency and longevity by effectively managing ripple voltages and reducing the capacitance needed.
Implementation Method 1
The capacitor is provided between the first voltage converter and the second voltage converter, and receives the second direct-current voltage between its terminals
Data Source
AI summary
A Vfc balance controller includes a coefficient multiplying circuit that calculates a value of one half of a voltage, a subtractor, an adder, and a corrector. The adder adds a correction term Vα·sin to the output from the coefficient multiplying circuit. The subtractor calculates the difference between voltage Vfc1 of a flying capacitor and the output from the adder. The corrector outputs a correction time of a pulse width so that the output from the subtractor converges to zero. The voltage of the flying capacitor is varied in this manner to reduce ripples on a DC line.