Multi-cell Power Supply Switching Loss Reduction via SHE Control
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Solution Overview
Problem
High-frequency applications in multi-cell power supplies face increased switching losses and cost per kilowatt due to the need for IGBTs to operate below their nominal current rating, especially when the wanted frequency exceeds 60 hertz, making it difficult to maintain efficient power delivery.
Innovation Solution
The implementation of a selective harmonic elimination (SHE) control pattern that allows each switching device to turn ON and OFF only once per cycle, with a switching frequency equal to the wanted frequency, reducing switching losses and eliminating harmonics by adjusting the output voltage angles of power cells within a phase group.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If PWM control is used to achieve power quality with harmonic elimination, then the switching frequency must be four times the wanted frequency, but this causes increased switching losses and reduced efficiency
Solution Approach 1:
The patent changes the control parameter from PWM switching duty cycle to selective harmonic elimination switching angles. By eliminating specific harmonics through angle selection and allowing switching frequency to equal the wanted frequency (rather than 4x), the system achieves comparable power quality with reduced switching losses.
2Productivity
If IGBTs operate at high switching frequencies above 60 hertz, then power delivery efficiency decreases, but operating below nominal current rating increases cost per kilowatt
Solution Approach 1:
The patent changes the operating parameter from high-frequency PWM switching to fundamental-frequency switching with harmonic elimination. This allows IGBTs to operate at the wanted frequency (e.g., 60 Hz) rather than 4x frequency, maintaining efficiency while operating within nominal current ratings to reduce cost per kilowatt.
3Loss of energy
If switching frequency is reduced to lower switching losses, then harmonic elimination becomes more difficult, but the patent applies angle commands to multiple cells to maintain power quality
Solution Approach 1:
The patent segments the power delivery into multiple power cells (at least two cells) and applies different angle commands to each cell. This segmentation allows harmonic elimination through coordinated angle control while maintaining fundamental-frequency switching, achieving both low switching losses and high power quality.
Solution Approach 2:
The system uses feedback from the multi-cell configuration where angle commands are applied to individual cells based on their contribution to harmonic content. By monitoring and adjusting angles across multiple cells, the system eliminates harmonics while maintaining power quality at reduced switching frequency.
Data Source
AI summary
A method of reducing switching losses in a power supply includes the steps of advancing the output voltage of a first pole of a power cell by a first angle, retarding the output voltage of a second pole of the power cell by a second angle, and producing a combined output voltage of the power cell equal to a positive pulse of a duration angle equal to the sum of the first angle and the second angle for a first half of a switching cycle of the power cell, and equal to a negative pulse of a duration angle equal to the sum of the first angle and the second angle for a second half of the switching cycle of the power cell.