RESEARCH
Flying Capacitor Voltage Balancing Method by Sensing Inductor Current
Year: 2009
Fig. 1. Three Level Buck Converter Schematic and control timing diagrams.
- Inductor size reduced significantly by reducing volt-second balance and doubling the effective frequency across the inductor
- Higher efficiency obtained with lower voltage rated devices. Devices see half the input voltage when flying capacitor balanced to 0.5Vin
All previous balancing methods have measured the capacitor voltage directly and balanced the capacitor voltage at the expense of performance by altering one duty cycle (T1,B1) to maintain output voltage and the other (T2,B2) to maintain capacitor balance. This adds complexity, degrades performance, and adds an additional control loop.
The method proposed in by CPES is to regulate the flying capacitor without a separate capacitor balancing loop is by using leading edge modulation current mode control. Current mode control is widely used in fast transient applications because of its ability to have good line regulation and to ease current sharing for multiple phases. Leading edge modulation can be adapted and naturally balance the capacitor in the three level converter by balancing the inductor current. This is possible because the inductor current contains the capacitor voltage information and is balanced when the inductor current is balanced.
