Multiple Switch Node Power Converter Control Scheme Avoiding Sub-Harmonics
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Solution Overview
Problem
Multiple switch node power converters face inefficiencies due to transitional buck-boost modes caused by overlapping modulation ramps, leading to subharmonic switching and increased output voltage ripple, which complicates control and increases power loss.
Innovation Solution
A method that controls multiple switch node power converters by generating fixed-width or fixed-duty cycle reference pulses for nonmodulated switching pairs when their pulse widths approach limits, allowing pseudo-buck-boost mode operation without overlapping buck and boost modulation ramps, thus eliminating subharmonic switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If overlapping buck and boost modulation ramps are used to control multiple switch node power converters, then the converter can operate through transitional buck-boost modes, but this causes subharmonic switching and increased output voltage ripple
Solution Approach 1:
The patent segments the control of multiple switch node power converters by assigning separate modulation ramps (buck ramp and boost ramp) to different switching pairs. Each switching pair (S1-S2 for buck, S3-S4 for boost) is controlled independently with its own modulation ramp, preventing the overlapping that causes subharmonic switching. This segmentation allows mode transition capability while eliminating the harmful effects of ramp overlap.
2Adaptability or versatility
If conventional PWM control with overlapping modulation ramps is used, then mode transitions are enabled, but control complexity increases and power loss increases
Solution Approach 1:
The control system is segmented into independent buck and boost control channels, each with its own modulation ramp and switching pair. This eliminates the need for complex overlapping ramp management and reduces control complexity while maintaining buck-boost mode operation capability.
Solution Approach 2:
The patent introduces a control mechanism that selects which modulation ramp to use based on operating conditions. By using one ramp at a time as an intermediary control approach, the system avoids the complexity of managing overlapping ramps while still enabling smooth transitions between buck and boost modes.
3Adaptability or versatility
If duty cycles of all four switches are modulated simultaneously, then buck-boost mode operation is achieved, but switching losses increase
Solution Approach 1:
The patent implements periodic action by using fixed-frequency switching for each switching pair with their respective modulation ramps. The buck switching pair operates at one frequency and the boost switching pair operates at another frequency, both periodic but non-overlapping. This reduces simultaneous switching events and thereby reduces switching losses while maintaining buck-boost conversion capability.
Data Source
AI summary
A method of and system for modulating buck and boost modulation ramps of a multiple switch node power converter without overlap. As the pulse width or duty cycle of the signal to a modulated complementary switching pair approaches a pre-established reference pulse width or duty cycle, plural fixed-width or fixed duty cycle pulses are generated and introduced to a nonmodulated complementary switching pair. A controller detects proximity to the pulse width or duty cycle limit and, correspondingly, initiates prematurely a pseudo-buck-boost mode in the power converter by generating fixed-width or fixed duty cycle pulses to the nonmodulated complementary switching pair while the duty cycles or pulse widths to the modulated complementary switching pair are still controlled by the appropriate modulation ramp. The net effect is that the power converter reaches its optimal operating point without overlap and eliminates any sub-harmonic switching.