Converter Pulse Pattern Control for DC-Link Ripple Constraints
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Solution Overview
Problem
Conventional energy conversion systems, particularly wind energy conversion systems, face issues with low frequency oscillations in DC-link voltages leading to excessive semiconductor stress and interharmonics due to low generator fundamental frequencies, violating stringent grid standards and necessitating large, costly DC-link capacitance solutions.
Innovation Solution
Implementing optimized pulse patterns for machine-side and grid-side converters to constrain DC-link voltage peaks and neutral point potential harmonics, using a PWM method that optimally distributes harmonic energy across the frequency spectrum, reducing converter size, weight, and cost while adhering to grid standards.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If DC-link capacitance is increased to reduce DC-link voltage ripple, then voltage ripple is reduced, but converter size and cost increase
Solution Approach 1:
The patent applies parameter changes by optimizing the pulse patterns (switching sequences and timing) of the converter to fundamentally alter how voltage ripple is generated and distributed. Instead of passively compensating with larger capacitance, the invention actively shapes the voltage waveform through optimized switching parameters, achieving ripple reduction without increasing physical converter components.
2Stability of the object's composition
If DC-link capacitance is increased to reduce DC-link voltage ripple, then voltage ripple is reduced, but converter cost increases
Solution Approach 1:
The invention changes the operational parameters (pulse patterns, switching sequences) of the converter to achieve ripple reduction through control optimization rather than hardware escalation. This approach maintains manufacturing simplicity and cost-effectiveness while achieving the desired voltage stability.
3Power
If converter operates at high current to increase power output, then power output increases, but DC-link voltage oscillation exceeds permissible values
Solution Approach 1:
The patent employs dynamic pulse pattern optimization that adapts to operating conditions. The converter dynamically adjusts its switching behavior based on real-time parameters, enabling it to maintain voltage stability across varying power output levels including high current operation, where static control methods would fail.
Solution Approach 2:
The optimization of pulse patterns inherently incorporates feedback mechanisms where the converter monitors its operating state and adjusts switching sequences accordingly. This closed-loop approach ensures that even at high power output, the DC-link voltage oscillation remains within permissible bounds through active compensation.
4Power
If converter operates at high modulation index to increase power transfer, then power transfer increases, but interharmonics on grid-side increase violating standards
Solution Approach 1:
The patent optimizes pulse pattern parameters to fundamentally change the harmonic spectrum characteristics of the converter. By carefully selecting and adjusting switching sequences and timing, the invention suppresses interharmonic generation mechanisms while maintaining high modulation index operation, enabling compliant power transfer even at elevated levels.
Data Source
AI summary
The present disclosure provides a method for controlling an energy conversion system. The system includes a rotating electrical machine, a machine-side converter, a DC-link, and a grid-side converter. The method includes modulating the machine-side converter for converting an AC voltage of the rotating electrical machine into a DC voltage supplied to the DC-link, and modulating the grid-side converter to convert a DC-link voltage at the DC-link into an AC output voltage to be supplied to an electrical grid, wherein the machine-side converter is modulated with first optimized pulse patterns, which have been optimized such that a peak value of the DC-link voltage or of a DC-link voltage component of the DC-link voltage is constrained to a predetermined value.