PFC Converter Control Reducing THD and Switching Losses
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Solution Overview
Problem
Conventional AC to DC converters with power factor correction (PFC) face challenges in minimizing total harmonic distortion (THD) due to short off-times and high-frequency switching losses, which are exacerbated by variations in on- and off-times.
Innovation Solution
A control apparatus and method for a PFC power converter that includes a primary winding, an auxiliary winding, and a power switch, utilizing a reference signal generator, detection circuit, and driving circuit to adjust the slew rate of the reference signal and extend the off-time when the input voltage approaches zero, ensuring complete energy release and adaptive minimum off-time based on load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the off-time is shortened to increase switching frequency, then the response speed improves, but high-frequency switching losses increase
Solution Approach 1:
The patent applies dynamics by making the off-time variable rather than fixed. The control apparatus dynamically adjusts the off-time based on the detected input voltage level, extending it during zero-crossing periods and maintaining it at normal levels otherwise. This dynamic adjustment allows the system to optimize between response speed and switching losses adaptively to operating conditions.
Solution Approach 2:
The patent changes the time parameter (off-time duration) based on operating conditions. By detecting when the input voltage approaches zero and相应ly extending the off-time during these periods, the system modifies the switching characteristics to reduce high-frequency switching losses while maintaining adequate response speed during normal operation.
2Manufacturing precision
If the on-time is extended to reduce cross-over distortion, then the THD decreases, but the off-time becomes shorter causing higher switching losses
Solution Approach 1:
The patent applies preliminary action by detecting when the input voltage is approaching zero before the actual switching event occurs. By anticipating the zero-crossing condition and proactively extending the off-time in advance, the system prevents the trade-off between on-time extension and excessive off-time shortening, thereby reducing both cross-over distortion and switching losses.
Solution Approach 2:
The patent uses feedback by continuously detecting the input voltage level and using this information to control the off-time duration. The detection circuit monitors the input voltage and provides feedback to the control apparatus, which adjusts the off-time accordingly - extending it during zero-crossing periods and maintaining normal duration otherwise, thus optimizing both THD and switching losses.
3Loss of energy
If the off-time is extended to reduce switching losses, then the energy efficiency improves, but the response speed decreases
Solution Approach 1:
The patent changes the off-time parameter dynamically based on operating conditions rather than maintaining a fixed value. By extending off-time only during zero-crossing periods when switching losses are problematic and maintaining normal off-time duration during other periods, the system achieves energy efficiency improvements without sacrificing overall response speed.
Solution Approach 2:
The system dynamically adjusts the off-time duration based on real-time detection of input voltage conditions. This dynamic approach allows the system to optimize for energy efficiency when needed (during zero-crossing) while maintaining adequate response speed during normal operating conditions, resolving the contradiction between these two parameters.
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 approach reduces cross-over distortion and THD, decreases unnecessary high-frequency switching losses, and adapts to varying load conditions, improving the operational efficiency of the PFC converter.
Implementation Method 1
a primary winding, an auxiliary winding and a power switch. The primary winding is coupled to receive an input voltage and controlled by the power switch to increase or release the stored energy
Implementation Method 2
Secondary winding 39 corresponding to booster inductor 34 detects the zero-crossing of the current flowing through booster inductor 34, which is accomplished via a zero current detection (ZCD) terminal of IC 32
Data Source
AI summary
A control apparatus and a control method for a power factor correction power converter are provided. The control apparatus is configured to reduce the variation rate of a reference signal with a rising portion and a falling portion. When the primary winding almost completely releases the stored energy, and the falling portion of the reference signal reaches a determined condition, the control apparatus turns on a switch for increasing the stored energy of the primary winding.