Adaptive Pulse Frequency Modulation for AC-DC Power Factor Correction
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Solution Overview
Problem
Conventional pulse frequency modulation in single-stage AC-DC power converters experiences reduced power factor during low-load conditions due to increased peak current near zero-crossing times, leading to output voltage regulation issues and audible noise from switching frequencies.
Innovation Solution
Adaptive pulse frequency modulation is implemented, where the switching frequency decreases from the beginning to the midpoint of the rectified input voltage cycle and increases towards the end, with the idle delay period calculated based on on-time, reset time, and proportionality constant, resulting in a higher number of small pulses that maintain output voltage regulation and improve power factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional pulse frequency modulation is used during low-load conditions, then the switching frequency drops to reduce power loss, but the power factor deteriorates due to increased peak current near zero-crossing times
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The controller dynamically adjusts the switching frequency within each rectified input voltage cycle - decreasing it during high-voltage periods and increasing it during low-voltage periods near zero-crossings. This dynamic adjustment allows the system to maintain low power loss during most of the cycle while improving power factor during critical zero-crossing regions.
Solution Approach 2:
The patent changes the switching frequency parameter as a function of the rectified input voltage level. By establishing a relationship where switching frequency increases as rectified input voltage decreases (and vice versa), the system optimizes both power loss and power factor. This parameter change is implemented through a controller that modulates the idle delay period based on detected rectified input voltage levels.
2Loss of energy
If the switching frequency is decreased during low-load operation, then power loss is reduced, but audible noise increases due to switching frequency entering the audible range
Solution Approach 1:
The switching frequency is made dynamic within each rectified input voltage cycle rather than maintaining a constant low frequency. By increasing the switching frequency during low-voltage periods near zero-crossings, the patent pushes switching events out of the audible range during these critical moments, reducing audible noise while still maintaining low power loss during high-voltage periods.
Solution Approach 2:
The patent implements periodic modulation of the switching frequency that correlates with the rectified input voltage cycle. This periodic action ensures that switching events are distributed in a pattern that avoids concentrated audible noise while maintaining efficient power conversion throughout the cycle.
3Stability of the object's composition
If the peak current is increased near zero-crossing times to maintain output voltage regulation, then output voltage stability is improved, but the power factor deteriorates due to current being out of phase with voltage
Solution Approach 1:
The patent changes the switching frequency parameter in response to rectified input voltage levels. When rectified input voltage is low (near zero-crossings), the switching frequency increases, which generates more current pulses in these regions. This approach maintains output voltage regulation by increasing current delivery when needed while keeping individual pulse amplitudes small, thus maintaining power factor.
Solution Approach 2:
The patent creates a relationship where the switching frequency profile copies or mirrors the inverse of the rectified input voltage profile. By detecting the rectified input voltage level and adjusting switching frequency accordingly, the system ensures that more switching events occur when voltage is low and fewer occur when voltage is high, achieving both voltage regulation and power factor correction.
Data Source
AI summary
An adaptive pulse frequency modulation for a switching power converter is provided that varies the switching frequency across a cycle of a rectified input voltage for the switching power converter From a beginning of the cycle of the rectified input voltage, the switching frequency decreases from a maximum value to a minimum value at a mid-point of the cycle and then increases from the mid-point back to the maximum value at an end of the cycle.