Power Factor Correcting Converter Zero-Cross Loss
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Solution Overview
Problem
Power-factor correcting converters experience increased conduction loss due to reverse flow of inductor current near the zero cross point of input AC voltage, which degrades efficiency and prevents size reduction.
Innovation Solution
A power-factor correcting converter with four switch circuits, including a bridge circuit with two series circuits and an output capacitor, where the control circuit manages the switch operations to prevent reverse flow by turning off slave switch circuits near the zero cross point, reducing the effective value of inductor current and conduction loss.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If bridge diodes are used in the power-factor correcting converter, then the circuit structure is simple, but conduction loss increases and efficiency degrades
Solution Approach 1:
The patent removes the bridge diodes from the conventional PFC circuit structure, extracting the problematic component that causes high conduction loss. By eliminating the bridge diodes and replacing them with a four-switch bridge circuit, the invention extracts the harmful element while maintaining the PFC functionality through alternative switching mechanisms.
Solution Approach 2:
The patent changes the operating parameters of the circuit by transitioning from diode-based rectification to switch-based rectification. The four switch circuits operate with specific on/off timing controlled by the control circuit, changing the conduction characteristics from passive diode behavior to actively controlled switching behavior, thereby reducing conduction loss.
2Reliability
If the four switch circuits operate continuously including near zero cross point, then power factor correction is maintained, but reverse flow of inductor current increases conduction loss
Solution Approach 1:
The patent implements periodic action by having the control circuit selectively turn off the slave switch circuits during specific periods when the absolute value of input AC voltage is small (near zero cross points). This periodic interruption of slave switch operation prevents reverse current flow during problematic voltage intervals while maintaining PFC functionality during normal operating intervals.
Solution Approach 2:
The patent applies dynamics by making the slave switch circuits dynamically controllable - they can be turned on or off based on real-time voltage conditions. The control circuit monitors input AC voltage and dynamically adjusts slave switch operation, transitioning from static continuous operation to dynamic conditional operation to eliminate reverse flow losses.
3Loss of energy
If slave switch circuits are turned off near zero cross point, then reverse flow is prevented, but control complexity increases
Solution Approach 1:
The patent implements feedback by having the control circuit monitor the absolute value of input AC voltage and use this feedback information to determine when to turn off the slave switch circuits. The control circuit continuously compares the measured voltage against predetermined thresholds and adjusts slave switch operation accordingly, creating a closed-loop control system that automatically prevents reverse flow.
Data Source
AI summary
A power-factor correcting converter includes: a series circuit including a first higher-potential switch and a first lower-potential switch connected in series to each other; and another series circuit including a second higher-potential switch and a second lower-potential switch connected in series to each other. In a positive phase period of the input AC voltage, a control circuit turns off the second higher-potential switch, turns on the second lower-potential switch, and alternately turns on and off the first lower-potential switch as a master switch and the first higher-potential switch as a slave switch. In a negative phase period of the input AC voltage, the control circuit reverses the on/off operation and the master/slave relationship, and turns on and off only the master switch and turns off the slave switch when the absolute value of the input AC voltage is smaller than or equal to a predetermined value.