ULSR Three-Phase Rectifier for High Power Factor Conversion
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Solution Overview
Problem
Current AC/DC converters face challenges in achieving high power quality with low harmonic distortions and efficient power factor correction, particularly in applications like the More Electric Aircraft, where stringent requirements for power factor and harmonic limits are necessary, while also considering constraints on weight, size, cost, complexity, and electromagnetic compatibility.
Innovation Solution
The Ultra Linear Switching Rectifier (ULSR) is a unidirectional three-phase three-switch pulse-width modulation rectifier with integrated buck-boost converter capabilities, offering high power factor (>99.9%) and low total harmonic distortion (≤0.5%) across a wide range of line frequencies and output powers, featuring a simple and robust analog fixed-frequency PWM controller for regulated output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If passive AC/DC conversion with diode pairs is used, then the conversion is simple and reliable, but current harmonics are substantial and power quality deteriorates
Solution Approach 1:
The patent divides the three-phase AC input into multiple rectifier bridges (e.g., three single-phase bridges) that process each phase separately. Each bridge generates a pulse train that is then combined through a capacitor network to produce a synthesized DC voltage with reduced harmonics. This segmentation allows each component to operate independently while achieving overall low harmonic distortion.
Solution Approach 2:
The patent transitions from time-domain rectification to frequency-domain synthesis by using pulse train generation and capacitive combination. Instead of directly rectifying and filtering in the traditional time domain, the system generates high-frequency pulse trains from each phase and combines them in a different dimensional space (frequency domain), achieving superior harmonic performance.
2Object-generated harmful factors
If multi-phase transformers are used to reduce current harmonics, then harmonic distortion decreases, but device complexity and weight increase
Solution Approach 1:
The patent extracts the harmonic reduction function from the transformer and relocates it to the rectifier bridge output stage. Instead of using complex multi-phase transformers to achieve harmonic cancellation at the input, the system uses simple single-phase bridges with pulse train generation and capacitive combination at the output, separating the power transformation function from the harmonic filtering function.
Solution Approach 2:
The patent introduces capacitors as intermediary elements between the rectifier bridges and the DC output. These capacitors serve as mediators that combine the pulse trains from multiple phases while blocking harmonic currents, achieving harmonic reduction without requiring complex transformer connections.
3Object-generated harmful factors
If active power factor correction topologies are used, then power factor improves and harmonic limits are met, but weight and cost increase
Solution Approach 1:
The patent merges the power factor correction and harmonic filtering functions into the basic rectifier structure itself. By using pulse train generation from each phase and capacitive combination, the system achieves active PFC performance without requiring separate active PFC circuits, energy storage devices, or complex control systems that would add weight.
Solution Approach 2:
The rectifier bridges automatically generate the required pulse trains and the capacitor network automatically synthesizes the low-harmonic DC voltage without requiring external active PFC components or complex control systems. The system serves its own power factor correction needs through its inherent structure.
4Stability of the object's composition
If regulated AC/DC conversion is implemented, then output voltage stability improves, but device complexity increases
Solution Approach 1:
The patent implements a feedback control system that monitors the synthesized DC voltage and adjusts the pulse train generation accordingly. The controller receives feedback about the output voltage level and modulates the rectifier bridge operation to maintain stable DC output, ensuring voltage regulation without requiring complex multi-stage conversion.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
ULSR provides efficient 3-phase AC-to-DC conversion with high power factor and low harmonic distortions, supporting various voltage conversion ratios and line frequencies, while maintaining low complexity and weight, and is compatible with 'wild' line frequencies, ensuring reliable operation under unbalanced mains conditions.
Implementation Method 1
unidirectional three-phase three-switch pulse-width modulation rectifier
Data Source
AI summary
The present invention relates to methods and corresponding apparatus for efficient 3-phase AC to DC conversion with high power quality, for example, high power factor and low harmonic distortions. The invention further relates to methods and corresponding apparatus for regulation and control of said AC to DC conversion.