Switched Mode Power Converter Controller for High Power Factor
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Solution Overview
Problem
Switched mode power converters typically have a low power factor, especially when operating in low-power modes, leading to mains supply distortion and inefficiency, and existing solutions for maintaining high power factor are either inefficient or require increased component costs.
Innovation Solution
A controller for AC-DC switched mode power converters that adjusts the switching frequency proportionally to the square of the sine of the phase relative to the zero-crossing of the alternating current supply, using a phase locked loop and comparator to ensure high power factor operation with minimal additional components, and optionally functioning as a digital signal processor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If switched mode power converters operate in low-power mode, then power consumption is reduced, but power factor falls below acceptable standards
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The switching frequency is dynamically adjusted according to the instantaneous phase of the AC supply voltage, following the relationship fs(Φ) = Fmax·sin²(Φ). This dynamic adaptation allows the converter to maintain high power factor across varying operating conditions including low-power modes, while still achieving energy efficiency through reduced power consumption.
2Object-generated harmful factors
If conventional AC-DC converters operate in boundary conduction mode with Ton control, then power factor is improved, but efficiency is not optimal
Solution Approach 1:
The patent applies parameter changes by modifying the switching frequency parameter based on the AC supply phase. Instead of using fixed Ton control or operating in boundary conduction mode, the invention varies the switching frequency fs according to the phase Φ of the AC voltage, using the relationship fs(Φ) = Fmax·sin²(Φ). This parameter adaptation enables the converter to achieve both high power factor and optimal efficiency across different operating conditions by optimally adjusting the switching frequency rather than relying on boundary conduction mode limitations.
3Adaptability or versatility
If digital control is implemented for sophisticated control, then control capability is enhanced, but component cost increases
Solution Approach 1:
The patent applies universality by designing a control system where the phase-locked loop and comparator serve multiple functions. These components not only determine the phase Φ of the AC supply for frequency modulation but also function as the analog-to-digital converter required for digital control. This multi-functional approach enables sophisticated digital control capability while minimizing additional component overhead, as the same hardware infrastructure serves both phase detection and ADC purposes.
Data Source
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AI summary
A method of controlling a switched mode converter is disclosed in which the switching frequency varies in proportion to the square of the sine of the phase of the input AC supply. Thus the switching frequency is a maximum, and the respective on period of the switch is a minimum, when the mains voltage is a maximum. Conversely, the switching frequency is reduced, and the respective on time of the switch is increased, when the mains voltage is reduced. Such a switching method provides for a high power factor. Implementation by means of a phase locked loop and a comparator may prevent the need for complex circuitry, and may provide for direct use of a digital controller or digital signal processing through a counter output in the phase locked loop. A controller configured to operate such a method, together with an AC/DC converter embodying such a controller are also disclosed,