Flying Capacitor PFC Converter With Active Voltage Balancing

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Solution Overview

Problem

Existing flying capacitor multi-level power factor correction (PFC) converters face challenges in dynamically balancing the voltage of multiple capacitors, leading to inefficiencies and increased costs due to passive balancing methods or slow natural charge balance.

Innovation Solution

Implementing active balancing of flying capacitor voltages through a controller that adjusts the duty cycle of switches based on error voltages, using proportional and integral control to maintain balanced voltages across capacitors.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If passive balancing methods or natural charge balance are used, then device complexity is reduced, but voltage balancing speed and dynamic response deteriorate

Engineering Contradiction:

Improvebalancing control complexityVSAvoidvoltage balancing speed

Core Design Contradiction:

Device complexityVSSpeed

Solution Approach 1:

The controller continuously monitors the voltages across multiple flying capacitors and adjusts the duty cycle of switches based on voltage differences. This closed-loop feedback mechanism enables rapid dynamic balancing of capacitor voltages during transient conditions, resolving the contradiction by providing fast response without requiring complex additional hardware.

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically adjusts switch duty cycles in real-time based on instantaneous capacitor voltage states. This dynamic control approach allows the converter to adapt to changing load conditions and maintain voltage balance across flying capacitors, achieving fast balancing speed while keeping the control structure relatively simple.

Inventive Principle:

Principle #15Dynamics

2Reliability

If higher voltage rated switches are used, then reliability is improved, but switching losses increase

Engineering Contradiction:

Improveswitch voltage handling capabilityVSAvoidswitching losses

Core Design Contradiction:

ReliabilityVSLoss of energy

Solution Approach 1:

The voltage stress across switches is segmented and distributed through the multi-level topology with flying capacitors. Each switch only needs to block a portion of the total output voltage rather than the full voltage, allowing the use of lower voltage rated switches with lower on-resistance, thereby reducing switching and conduction losses while maintaining reliable voltage handling through the series arrangement of multiple switches.

Inventive Principle:

Principle #1Segmentation

Data Source

PatentUS20250350195A1Flying capacitor multi-level power factor correction converter of power supply with active balancing of voltage of flying capacitors

Publication Date: 2025.11.13 DELTA ELECTRONICS INC(CN)

AI summary

A power factor correction (PFC) converter includes an inductor to electrically connect to an alternating current (AC) source, a first set of switches to be electrically connected to a terminal of the inductor at one end and to a negative output terminal at an opposite end, and a second set of switches to be electrically connected to the terminal of the inductor at one end and to a positive output terminal at an opposite end. An output voltage of the PFC converter is between the positive output terminal and the negative output terminal. Two or more flying capacitors are connected between different pairs of adjacent ones of the first set of switches and corresponding adjacent ones of the second set of switches. A controller controls duty cycle of the first set of switches and the second set of switches based on balancing voltages of the two or more flying capacitors.