Multiphase PFC Phase-Enable Timing to Prevent Current Oscillation
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Solution Overview
Problem
Existing totem pole interleaved PFC topologies face challenges in dynamically enabling additional phases without introducing sub-harmonic current oscillations, leading to inefficiencies and increased power switching losses, especially at light load conditions.
Innovation Solution
A digital circuitry-based controller calculates a delay value based on positive and negative current slopes for the first phase, enabling a second phase out of phase with the first phase at the beginning of the boost charging portion of the switching cycle, optimizing phase interleaving and reducing THD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a second phase is dynamically enabled to improve efficiency at light load conditions, then power efficiency is improved, but sub-harmonic current oscillation occurs due to improper phase positioning
Solution Approach 1:
The controller calculates the delay value in advance based on current slopes before enabling the second phase. This preliminary calculation ensures that when the second phase is enabled, it is properly positioned out of phase with the first phase, preventing sub-harmonic current oscillation while achieving efficient light load operation.
2Ease of operation
If a new phase is enabled at AC zero crossing to simplify control, then control simplicity is improved, but power switching losses increase
Solution Approach 1:
Instead of enabling the new phase at the fixed AC zero crossing point, the controller calculates an optimal delay value based on the actual current slopes (positive and negative) of the first phase. This dynamic parameter adjustment optimizes the phase insertion timing to occur during low-stress periods, minimizing switching power losses while maintaining control effectiveness.
3Loss of energy
If switching frequency is reduced and inductors increased to enable new phase, then switching losses are reduced, but power density decreases and board space increases
Solution Approach 1:
The system dynamically enables or disables the second phase based on real-time load conditions rather than operating continuously. The controller monitors the average current reference and adjusts the number of active phases accordingly, allowing the system to maintain high power density at full load by using only one phase while achieving efficient operation at light load by enabling the second phase, all without changing the physical inductor sizes or switching frequency.
Data Source
AI summary
A multi-phase PFC (power factor correction) system, controller for the multi-phase PFC system and method of controlling the multi-phase PFC system are described. The controller includes a digital circuitry configured to calculate a delay value based on a positive current slope and a negative current slope for a first phase of the plurality of phases which is enabled for all load current conditions. In response to an increase in an average current reference, the digital circuitry is configured to enable a second phase of the plurality of phases such that a current output by the second phase is out of phase with a current output by the first phase by an amount corresponding to the delay value as referenced to a beginning of a boost charging portion of a switching cycle for the first phase.