Power Converter Zero-Crossing Control for Unity Power Factor
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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 system for power converters that updates control signals only at zero-crossings of the input signal, using a controller with a compensator and on-time generator to regulate output voltage, allowing for high gain and frequency without loop instability, and incorporating multiple operation levels for dynamic load responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous-time, linear time-invariant control is used to regulate output voltage, then voltage regulation is achieved, but bandwidth and gain are limited causing power factor degradation
Solution Approach 1:
The patent transitions from static linear time-invariant control to dynamic nonlinear control by implementing discrete-time control that adapts to instantaneous operating conditions. The controller dynamically adjusts control parameters based on real-time voltage and current measurements, enabling high gain and bandwidth while maintaining stability and unity power factor.
Solution Approach 2:
The patent replaces the continuous-time analog control mechanism with a discrete-time digital control system. This substitution allows for more flexible control algorithms that can achieve higher gain and bandwidth without the limitations of analog circuitry, thereby improving power factor performance while maintaining voltage regulation.
2Productivity
If control bandwidth is increased to improve power factor, then power factor performance improves, but loop instability occurs
Solution Approach 1:
The discrete-time nonlinear control system dynamically adapts control parameters based on instantaneous operating conditions, allowing the system to maintain stability while achieving high gain and bandwidth. The control algorithm adjusts its behavior in real-time to prevent oscillations and instability that would occur with fixed high-gain continuous-time control.
Solution Approach 2:
The patent implements a closed-loop feedback control system that continuously monitors output voltage and input current, and adjusts control parameters accordingly. This feedback mechanism ensures stability by detecting and correcting deviations from desired operating conditions, enabling high power factor correction without loop instability.
3Reliability
If conventional control attempts to regulate input power, then voltage regulation is achieved, but power factor is compromised by ripple on bulk capacitor
Solution Approach 1:
The patent extracts the problematic continuous regulation attempt from the control system and replaces it with discrete-time control that operates at specific sampling instants. By removing the continuous feedback loop that tries to eliminate capacitor ripple, the system achieves unity power factor while maintaining adequate voltage regulation through strategically timed control updates.
Solution Approach 2:
The patent implements periodic control updates synchronized with the AC line frequency, sampling and adjusting control parameters at specific intervals rather than continuously. This periodic action allows the system to maintain unity power factor by updating control signals only when necessary, avoiding the degradation caused by continuous regulation attempts.
Data Source
AI summary
An apparatus for controlling a power converter includes a controller configured to detect an error in an output voltage of the power converter at a zero-crossing of a cyclically varying input signal and a compensator coupled to the controller and the power converter and configured to regulate the output voltage of the power converter in response to the error.