Pre-distortion of Sensed Current in Power Factor Correction
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Solution Overview
Problem
Conventional switched mode power supplies face challenges in achieving high power factor and low total harmonic distortion at low loads due to non-sinusoidal and out-of-phase current waveforms, which lead to increased losses and regulatory compliance issues.
Innovation Solution
A power factor enhancer is integrated into the controller of a PFC converter to apply controlled pre-distortion on the sensed current, compensating for waveform distortions by adjusting the multiplication factor based on load levels and input voltage, ensuring the current waveform is sinusoidal and in phase with the voltage waveform.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional switching control is used in PFC circuits, then the circuit structure remains simple, but power factor and total harmonic distortion performance deteriorate at low loads and high line voltages
Solution Approach 1:
The patent applies preliminary action by pre-distorting the current reference waveform before it is used for PWM generation. The controller pre-calculates and applies the necessary distortion compensation to the reference current, so that when the switching occurs, the actual current waveform is already corrected for the expected non-ideal behavior at low loads and high line voltages. This ensures sinusoidal current draw and high power factor without requiring complex real-time correction circuits.
2Device complexity
If the multiplication factor is kept constant in the current loop, then the control is simple, but the current waveform becomes non-sinusoidal and out of phase at varying load conditions
Solution Approach 1:
The patent implements dynamics by making the multiplication factor variable rather than constant. The controller dynamically adjusts the multiplication factor based on instantaneous operating conditions including load level and input voltage. This dynamic adjustment allows the current loop to maintain optimal performance across varying conditions, producing sinusoidal waveforms that remain in phase with the voltage regardless of load changes.
Solution Approach 2:
The patent applies parameter changes by modifying the multiplication factor parameter in response to changing operating conditions. The controller monitors load level and input voltage, then adjusts the multiplication factor parameter accordingly. This parameter adaptation enables the system to maintain high power factor and low THD across the full operating range without requiring a completely different control strategy for each condition.
3Device complexity
If no pre-distortion is applied to the sensed current, then the control algorithm is simple, but losses increase due to non-sinusoidal current at low loads
Solution Approach 1:
The patent applies preliminary action by pre-distorting the current reference waveform before switching control is applied. The controller pre-calculates the necessary waveform correction based on expected operating conditions, embedding the distortion compensation directly into the reference signal. This preliminary correction ensures that the actual current drawn from the source is sinusoidal, minimizing harmonic losses and improving efficiency at low loads without requiring complex post-processing or additional correction circuits.
Data Source
AI summary
A controller for use in a power factor correction converter includes a power factor enhancer that includes a zero-crossing detector coupled to receive an ac line input voltage signal and is coupled to output a zero-crossing signal. A peak detector is coupled to receive the ac line input voltage signal and the zero-crossing signal and is coupled to output a peak signal. A peak modulator is coupled to receive the zero-crossing signal and is coupled to generate a peak modulation function. A line feed forward function generator is coupled to generate a line feed forward function. A multiplier is coupled to receive the peak modulation function and the line feed forward function, and is coupled to output a pre-distortion signal each half line cycle.