Interleaved Parallel Power Converter Threads for High Power Machines
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Solution Overview
Problem
High power converters face thermal limitations that restrict switching frequencies, leading to high harmonic content and filtering requirements, which increase costs and reduce efficiency, especially in applications like motor drives where torque ripple and grid noise further degrade power quality.
Innovation Solution
A power converter system comprising multiple grid side transformer and switchgear units, converter units with inverters, and a master controller that interleaves carrier waveform signals between threads, achieving high power quality by optimizing switching patterns and reducing harmonic content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If semiconductor switches are operated at high frequency, then power quality improves and filtering requirements reduce, but thermal limitations prevent high power switches from being switched at high frequency
Solution Approach 1:
The system divides a single high-power converter into multiple parallel converter threads (e.g., 4 threads), each handling a portion of the total power. This segmentation allows each thread to operate at lower individual power levels while collectively achieving high power conversion, enabling higher effective switching frequencies without exceeding thermal limits of individual switches.
Solution Approach 2:
The patent implements interleaved periodic switching across multiple converter threads, where each thread switches at a phase-shifted frequency (e.g., 500 Hz base frequency with 125 Hz interleaving). This periodic action with phase shifting effectively multiplies the overall switching frequency (achieving 2000 Hz effective frequency), improving power quality while keeping individual switch frequencies within thermal limits.
2Power
If multiple converter modules are connected in series to increase voltage level, then voltage capability improves, but harmonic content is passed through series from module to module requiring significant filtering
Solution Approach 1:
Instead of series connection, the patent uses parallel connection of multiple converter threads, each with its own inverter bridge. This segmentation approach allows independent control of each thread's output waveform, enabling harmonic cancellation through phase shifting while maintaining high voltage capability through proper transformer and reactor configuration.
Solution Approach 2:
The patent converts the potentially harmful harmonic content into a beneficial effect by using phase-shifted interleaved switching. The harmonic frequencies from each thread, when properly phase-shifted, cancel each other out, transforming what would be harmful harmonics into a clean sinusoidal output waveform with significantly reduced total harmonic distortion.
3Manufacturing precision
If switching frequency is increased to reduce harmonic content, then power quality improves, but switching losses increase and stress on components increases
Solution Approach 1:
The total switching burden is segmented across multiple parallel threads, where each thread operates at a moderate switching frequency (e.g., 500 Hz). This segmentation reduces the switching losses per thread compared to a single high-frequency switch, while the combined effect of interleaved threads achieves the equivalent of high-frequency operation for power quality.
Solution Approach 2:
By using periodic interleaved switching with phase shifting between threads, the system achieves effective high-frequency operation (e.g., 2000 Hz) without requiring any single switch to operate at that frequency. This periodic action distributes the switching stress and losses across multiple devices operating at lower individual frequencies.
4Device complexity
If single-phase converter modules are used to simplify design, then design complexity reduces, but voltage level and power quality are limited
Solution Approach 1:
The system segments the power conversion function into multiple identical or near-identical converter threads that can be based on standardized single-phase or three-phase modules. This segmentation allows using simpler modular building blocks while achieving high power and voltage levels through parallel operation and proper transformer/reactor configuration.
Solution Approach 2:
Multiple converter threads are merged in parallel operation with interleaved switching control. The combining of multiple threads' outputs through differential mode reactors and common mode reactors achieves high voltage capability and improved power quality, while maintaining the simplicity of individual thread designs.
Data Source
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AI summary
Methods and apparatus for converting power from a power source are described. In one example embodiment, the method includes controlling multiple transformer and switchgear units (12) coupled to a power source, and controlling multiple converter units (22, 24, 26, 28) connected in parallel. Each converter unit is coupled to a respective one of the transformer and switchgear units to form an individual thread (14, 16, 18, 20). The transformer and switchgear unit and power converters are controlled so that the carrier waveforms for each individual thread are interleaved between each other over a carrier cycle.