Flying-Capacitor PFC Rectifier Phase Shifting for Ripple Reduction
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Solution Overview
Problem
Three-phase power factor correction (PFC) rectifiers with flying capacitors face challenges in achieving center alignment of midpoint voltages across totem-pole legs, which affects the ripple frequency of PFC inductor currents and subsequently the power density and efficiency of the rectifiers.
Innovation Solution
The method involves determining specific segments of a line cycle and voltage levels where an additional phase shift is applied to the gate pulses of totem-pole switches, ensuring that the midpoint voltages of all three totem-pole legs are center aligned, thereby doubling the ripple frequency of the PFC inductor currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If phase-shifted PWM is applied to three-phase multi-level boost PFC rectifier with flying capacitors, then the ripple frequency of PFC inductor current is increased, but the midpoint voltages of totem-pole legs are not center aligned in some segments of line cycle
Solution Approach 1:
The patent applies dynamic phase shifting to the PWM signals of different totem-pole legs. By dynamically adjusting the phase shift angles based on the operating quadrant and voltage levels, the system achieves center alignment of midpoint voltages while maintaining high ripple frequency. The phase shift is not fixed but adapts to different line cycle segments, resolving the contradiction between frequency increase and voltage alignment.
Solution Approach 2:
The patent changes the phase shift parameter dynamically throughout the line cycle. Different phase shift values are applied in different quadrants and voltage level combinations to ensure that midpoint voltages remain center aligned. This parameter adjustment allows the system to maintain both high ripple frequency and proper voltage alignment simultaneously.
2Stress or pressure
If 2-level totem-pole legs are replaced with N-level totem-pole legs with flying capacitors, then voltage stress of switches is reduced, but the midpoint voltages are not center aligned
Solution Approach 1:
The patent implements dynamic phase shifting specifically tailored for N-level totem-pole legs with flying capacitors. The phase shift angles are adjusted based on the current voltage level and operating quadrant, ensuring that despite the reduced voltage stress from using lower-rated switches, the midpoint voltages remain center aligned through adaptive control.
Solution Approach 2:
The patent adjusts PWM phase shift parameters as a function of voltage levels and line cycle position. This allows N-level switches with reduced voltage ratings to operate correctly while maintaining proper center alignment of midpoint voltages through continuous parameter adaptation.
3Object-generated harmful factors
If additional phase shift is applied to center align midpoint voltages, then inductor current ripple is reduced, but the control complexity increases
Solution Approach 1:
The patent divides the line cycle into distinct quadrants and further segments based on voltage level combinations. For each segment, a specific phase shift value is applied. This segmentation approach reduces control complexity by providing a lookup-table-based solution rather than requiring continuous complex calculations, while still achieving effective ripple reduction through proper center alignment.
Solution Approach 2:
The patent introduces phase shift angles as intermediary control parameters that mediate between the PWM switching signals and the midpoint voltage alignment requirement. By using these intermediate phase shift variables, the system achieves ripple reduction without directly complex control of switch timings, simplifying the overall control architecture.
Data Source
AI summary
In one embodiment, a method to reduce inductor current ripple in a three-phase, flying capacitor multi-level boost power factor correction rectifier circuit having three totem-pole legs, the method including: determining, for the three-phase, flying capacitor multi-level boost power factor correction rectifier circuit, for which of at least one of a segment in a line cycle or a voltage level of a phase-to-neutral voltage, and for which totem-pole leg selected from any one of the three totem-pole legs, to apply an additional phase shift at one or more instances of time in the line cycle; and applying the additional phase shift in such a way as to center align midpoint voltages of the three totem-pole legs.