Flying-Capacitor Totem-Pole PFC Switching Around Line Zero Crossings
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Solution Overview
Problem
Existing multi-level bridgeless totem-pole boost PFC devices suffer from zero-crossing distortions in the line current, particularly at light loads, due to duty cycle limitations.
Innovation Solution
The implementation of a control circuit that drives the switches in a flying capacitor, totem-pole configuration to reduce line current distortions by disabling the conduction of totem-pole synchronous rectifiers and unfolder synchronous rectifiers around zero-crossings, and employing feedforward duty cycle control with mixed conduction modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If duty cycle limitation is applied in multi-level bridgeless totem-pole boost PFC devices, then switching losses are reduced, but zero-crossing distortions in line current increase
Solution Approach 1:
The control circuit detects zero-crossing points of the line voltage in advance and proactively adjusts the duty cycle of the totem-pole switches around these points. By preparing the duty cycle adjustment before the zero-crossing occurs, the circuit prevents current spikes and distortions while maintaining efficient switching operation throughout the AC cycle
Solution Approach 2:
The duty cycle is made dynamic and adaptive rather than fixed. The control circuit continuously monitors the line voltage and adjusts the duty cycle in real-time based on the operating phase, particularly modifying it around zero-crossing points to eliminate distortions while maintaining optimal switching performance during other phases
2Loss of energy
If switching frequency is kept low to reduce switching losses, then efficiency is improved, but the volume of PFC choke and EMI filter increases
Solution Approach 1:
The invention changes the operating parameters by implementing mixed conduction modes (CCM and DCM) with dynamic duty cycle adjustment. This allows the circuit to achieve better current waveform control and higher effective switching utilization, improving power factor and reducing the need for large choke volumes even at moderate switching frequencies
3Ease of operation
If totem-pole switches are hard switched in CCM, then control is simplified, but switching losses increase and efficiency decreases
Solution Approach 1:
The control scheme dynamically adjusts the duty cycle of hard-switched totem-pole switches based on real-time line voltage conditions, particularly around zero-crossing points. This dynamic control maintains simplicity of hard switching while optimizing efficiency by preventing lossy operations during critical transition phases
Solution Approach 2:
The control circuit uses feedback from line voltage and current measurements to continuously adjust the duty cycle of the totem-pole switches. This feedback mechanism enables the system to maintain optimal efficiency by adapting the switching duty cycle to actual operating conditions while keeping the control logic relatively simple
Data Source
AI summary
In one embodiment, a multi-level, bridgeless boost power factor correction (PFC) device, comprising: a circuit comprising an inductor, and at least a first pair and a second pair of switches and a capacitor arranged in a flying capacitor, totem-pole configuration; and a control circuit configured to drive the at least first and second pairs of switches in such a way as to reduce distortion in a line current, wherein for the first and second pairs of switches, the control circuit is configured to: for a first half line cycle, drive a first switch of each pair during an entire interval of the first half-line cycle and a second switch of each pair for less than the entire interval; and for a second half-line cycle, drive the first switch of each pair for less than an entire interval of the second half-line cycle and the second switch of each pair during an entire interval of the second half-line cycle.