PFC Converter Zero-Crossing Mode Switching for Stable High Gain
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Solution Overview
Problem
Conventional power factor correction systems face limitations in bandwidth and gain due to continuous-time, linear time-invariant control, which compromises power factor performance by attempting to regulate input power instead of resistive power, especially at AC zero crossings.
Innovation Solution
A nonlinear, discrete-time control method for power converters that updates control values only at zero-crossings of the input signal, using a controller and compensator to regulate output voltage by selecting between linear and nonlinear operation levels, adjusting on-time pulses, and sampling output voltage to maintain optimal power factor correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous-time, linear time-invariant control is used to regulate output voltage, then the control loop is stable, but the bandwidth and gain are limited which compromises power factor performance
Solution Approach 1:
The patent transitions from static linear time-invariant control to dynamic nonlinear control by implementing discrete-time updates at zero-crossings. The controller adapts its operation mode (linear vs. nonlinear) based on real-time conditions, allowing the system to achieve high gain and frequency response while maintaining stability through selective mode switching.
Solution Approach 2:
The patent changes the fundamental control parameters by switching from continuous-time to discrete-time control, and from linear to nonlinear operation. The controller selects between linear operation mode and nonlinear operation mode based on system state, fundamentally altering the control characteristics to achieve both stability and high performance.
2Reliability
If the control loop attempts to regulate input power, then the output voltage is stabilized, but the power factor deteriorates due to mismatch between input current and input voltage
Solution Approach 1:
The patent implements periodic control updates synchronized with the AC input waveform by updating control values only at zero-crossings. This periodic action ensures that the input current waveform naturally aligns with the input voltage waveform, achieving high power factor while maintaining output voltage stabilization through the compensator.
3Productivity
If high gain and frequency response are achieved through nonlinear control, then power factor performance improves, but loop instability may occur
Solution Approach 1:
The patent uses dynamic mode switching between linear and nonlinear operation based on real-time system conditions. The controller selects linear operation mode when stability is prioritized and nonlinear operation mode when high performance is needed, achieving both high gain/frequency response and loop stability through adaptive control.
Solution Approach 2:
The patent implements feedback mechanisms where the controller continuously monitors system state and selects the appropriate operation mode accordingly. The compensator provides feedback to ensure output voltage stabilization while the controller adjusts between linear and nonlinear modes based on feedback about system performance and stability margins.
Data Source
AI summary
An apparatus for controlling a power converter operable to receive a cyclically varying input signal includes a discrete-time, on-time generator coupled to the power converter and configured to regulate an output voltage of the power converter and a controller configured to compare the output voltage of the power converter against a first predetermined range to: obtain a comparison result at a zero-crossing of the cyclically varying input signal and select one of a plurality of operation levels of the discrete-time, on-time generator in response to the comparison result. The plurality of operation levels includes a linear, discrete-time operation level and a nonlinear, discrete-time operation level.