Totem Pole PFC Converter Voltage Stress Reduction
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Solution Overview
Problem
Conventional totem pole PFC converters face challenges in reducing the working voltage between primary and secondary grounds, leading to increased volume and cost of optoelectronic isolators due to higher voltage requirements.
Innovation Solution
A PFC converter with a control method that adjusts the high level duration ratio on the middle node of the line frequency bridge to be smaller than a threshold value, reducing the working voltage between primary and secondary grounds, thereby minimizing the distance and volume of optoelectronic isolators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If totem pole PFC converter is used to eliminate rectification bridge, then efficiency is improved, but working voltage between primary and secondary grounds increases
Solution Approach 1:
The patent applies dynamic control by adjusting the duty cycle of the high-frequency switch based on the detected working voltage between primary and secondary grounds. The control unit dynamically modifies the switching ratio to regulate the output voltage, thereby reducing the working voltage to a predetermined safe level while preserving the efficiency benefits of the totem pole configuration.
Solution Approach 2:
The patent changes the operating parameters of the high-frequency switch, specifically the duty cycle ratio, to control the voltage transformation ratio. By adjusting this parameter, the working voltage between primary and secondary grounds is reduced to an acceptable level, resolving the contradiction between maintaining high efficiency and reducing voltage stress.
2Power
If working voltage between primary and secondary grounds is higher, then power density increases, but distance between primary and secondary grounds increases
Solution Approach 1:
The control unit dynamically adjusts the duty cycle of the high-frequency switch to regulate the working voltage between primary and secondary grounds. By maintaining this voltage at a predetermined level, the patent enables compact optoelectronic isolator design with reduced creepage and clearance distances, thus achieving high power density without increasing the physical distance between grounds.
3Power
If working voltage between primary and secondary grounds is higher, then power transmission capability improves, but volume of optoelectronic isolator increases
Solution Approach 1:
The patent employs dynamic duty cycle control to maintain the working voltage between primary and secondary grounds at a predetermined level. This voltage regulation enables the use of compact optoelectronic isolators with smaller creepage and clearance distances, thereby reducing the isolator volume while preserving adequate power transmission capability through controlled voltage levels.
Data Source
AI summary
A PFC converter and a control method thereof are provided. The PFC converter includes a first bridge, an inductor, a second bridge and a control unit. The first bridge includes a first switch and a second switch connected in series. There is a first node between the first and second switches. Two terminals of the inductor are coupled to the first node and a first terminal of an AC power source respectively. The second bridge includes a third switch and a fourth switch connected in series. There is a second node between the third and fourth switches, and the second node is coupled to a second terminal of the AC power source. The control unit controls a ratio of a high level duration on the second node in every line frequency cycle to be smaller than (250/Vbus)2, where Vbus is an output voltage of the PFC converter.