Phase Compensation for Power Factor Correction Circuits
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Solution Overview
Problem
Conventional power factor correction circuits suffer from zero-crossing distortion and increased total harmonic distortion due to the forward voltage drop of bridge rectifier diodes and the placement of high-frequency filtering capacitors, leading to reduced power factor and efficiency.
Innovation Solution
A phase compensation method for power factor correction circuits using a switching circuit and control unit with a low-pass filter, differential controller, and cosine multiplier to generate a pulse width modulation signal, which adjusts the phase of the input current to match the input voltage, thereby suppressing zero-crossing distortion and reducing total harmonic distortion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a bridge rectifier diode and high frequency filtering capacitor are used in the power factor correction circuit, then the circuit can perform basic power factor correction, but zero-crossing distortion occurs and total harmonic distortion increases
Solution Approach 1:
The patent applies preliminary action by predicting the present waveform of the input current based on the previous waveform before the actual current measurement is available. This prediction allows the system to pre-adjust the switching control to compensate for expected zero-crossing distortion, preventing the distortion from occurring in the first place rather than correcting it afterward.
Solution Approach 2:
The patent implements feedback by continuously comparing the predicted current waveform with the actual sampled current value and using this comparison to adjust the switching control signal. The control unit uses the difference between predicted and actual values to generate corrective adjustments, creating a closed-loop system that actively suppresses zero-crossing distortion and reduces total harmonic distortion.
2Reliability
If feedforward control is used to adjust output current according to AC input voltage, then power factor is increased, but zero-crossing distortion occurs due to diode voltage drop and capacitor placement
Solution Approach 1:
The patent introduces an intermediary prediction mechanism that acts as a mediator between the feedforward control signal and the actual switching control. Instead of directly applying feedforward control based on voltage sampling, the system uses waveform prediction as an intermediary step to generate a predicted current waveform, which then serves as the basis for generating the switching control signal. This intermediary prediction layer compensates for the harmful effects of diode voltage drop and capacitor placement.
3Device complexity
If conventional power factor correction circuit components are used, then the circuit structure is simple, but total harmonic distortion increases and power factor decreases
Solution Approach 1:
The patent replaces the conventional mechanical/component-based power factor correction approach with a signal-processing-based control system. Instead of relying solely on passive components like inductors and capacitors to correct power factor, the system uses digital signal processing techniques including waveform prediction, sampling, and controlled switching to achieve superior power factor correction while reducing total harmonic distortion.
Data Source
AI summary
A method for phase compensating a power factor correction circuit is provided. Firstly, a present current value of an input current is sampled, and the sampled signal is filtered. Then, a present waveform of the input current corresponding to the present current value of the filtered sampled signal and a previous waveform of the input current corresponding to a previous current value of the filtered sampled signal are predicted, and a current error signal is generated according to a difference between the present waveform and the previous waveform. Then, the current error signal is adjusted, and an adjusted signal is generated. Then, a feedforward signal is added to the adjusted signal, and a phase compensation signal. Then, a current control signal is added to the phase compensation signal, and a pulse width modulation signal is generated to control a switching circuit.