Frequency to On-Time Converter for Power Factor Correction
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Solution Overview
Problem
Switched mode power converters often result in low Power Factor and excessive harmonic content, leading to underutilization of power infrastructure and other issues like radiation and excess neutral current, necessitating regulatory limits on these parameters.
Innovation Solution
A power converter control scheme that uses frequency to on-time conversion, where the duration of the power switch on-time is determined by its switching frequency, allowing for variable on-time and frequency control to reduce output voltage ripple and improve Power Factor Correction (PFC) without significantly affecting it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional switched mode power converter control is used, then high efficiency and small size are achieved, but low Power Factor and excessive harmonic content result
Solution Approach 1:
The patent applies dynamics by making the on-time of the power switch variable rather than fixed. The on-time is dynamically adjusted based on the instantaneous switching frequency to achieve unity power factor. This is accomplished through a frequency-to-on-time converter that translates frequency information into corresponding on-time durations, allowing the system to adapt its switching characteristics in real-time to match the line frequency and reduce harmonic content.
Solution Approach 2:
The patent changes the parameter of on-time from a fixed value to a variable parameter that depends on switching frequency. By establishing a relationship where on-time is determined by frequency through the frequency-to-on-time converter, the system can modify its switching behavior to achieve unity power factor correction while maintaining high efficiency operation.
2Device complexity
If fixed frequency and on-time control is used, then simple control is achieved, but output voltage ripple increases
Solution Approach 1:
The patent introduces dynamic control where the on-time varies with frequency rather than remaining fixed. The frequency-to-on-time converter enables the system to adjust on-time based on instantaneous frequency conditions, which reduces output voltage ripple by optimizing the switching waveform to better match the line frequency and reduce harmonic content.
3Object-generated harmful factors
If variable on-time and frequency control is implemented, then output voltage ripple and Power Factor are improved, but control complexity increases
Solution Approach 1:
The patent introduces a frequency-to-on-time converter as an intermediary component that automatically translates frequency information into corresponding on-time durations. This intermediary device simplifies the control architecture by handling the complex relationship between frequency and on-time automatically, eliminating the need for complex control algorithms while achieving unity power factor correction.
Solution Approach 2:
The frequency-to-on-time converter enables the system to self-adjust its on-time based on instantaneous frequency conditions without requiring external complex control intervention. The converter internally maintains the relationship between frequency and on-time, allowing the system to automatically achieve unity power factor correction through self-service operation.
Data Source
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Figure 2
AI summary
A controller for use in a power converter includes a secondary controller coupled to receive a feedback signal representative of an output of the power converter to generate d a request signal. A primary controller is coupled to receive the request signal to generate a primary drive signal. The primary drive signal is coupled to control switching of a power switch to control a transfer of energy from the input to the output of the power converter. A frequency to on-time converter included in the primary controller is coupled to receive the request signal. The frequency to on-time converter is coupled to control the duration of on-time pulses included in the primary drive signal in response to a period of the request signal.