Carrier Signal Phase Adjustment for Harmonic Reduction
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Solution Overview
Problem
Wind farms and solar power plants generate carrier sideband harmonics at the point of common coupling with the electrical grid, which are undesirable and must be kept below regulatory thresholds to ensure power quality, despite existing methods not effectively addressing this issue.
Innovation Solution
A method that adjusts the phase of the carrier signal of selected converters using a search algorithm to invert the carrier signal by 180°, minimizing harmonic magnitudes in the electrical output, allowing real-time reduction or cancellation of harmonics at the point of common coupling, utilizing stochastic hill-climbing or other search algorithms to optimize converter states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If pulse width modulation scheme is used by converters to generate electrical output, then electrical power conversion efficiency is improved, but carrier sideband harmonics are generated at the point of common coupling
Solution Approach 1:
The invention uses the harmful carrier sideband harmonics generated by PWM converters and transforms them into a beneficial effect by adjusting carrier phases to create destructive interference. The harmonics that were previously harmful are now utilized as a mechanism for harmonic cancellation, where the same harmonics from multiple converters interfere destructively at the point of common coupling, reducing total harmonic distortion without sacrificing conversion efficiency
Solution Approach 2:
The invention changes the phase parameter of the carrier signals in selected converters to achieve harmonic reduction. By adjusting the carrier phase shift (particularly 180-degree inversion), the harmonic components from different converters are transformed to interfere destructively at the point of common coupling, thereby reducing the magnitude of carrier sideband harmonics while maintaining the PWM conversion process
2Object-generated harmful factors
If phase of carrier signal is adjusted to reduce harmonics, then harmonic distortion is reduced below threshold, but device complexity increases due to search algorithm requirements
Solution Approach 1:
The system performs self-configuration by automatically determining the optimal carrier phase shifts for each converter through a search algorithm. The control system autonomously iterates through possible phase combinations, measures the resulting harmonic distortion at the point of common coupling, and selects the configuration that minimizes harmonics. This eliminates the need for manual tuning or complex external intervention, allowing the system to self-optimize its harmonic performance
Solution Approach 2:
The invention implements a feedback mechanism where the harmonic distortion level at the point of common coupling is continuously measured and used to guide the search algorithm. The measured harmonic magnitudes provide feedback information that directs the optimization process, allowing the system to iteratively adjust carrier phases based on actual performance and converge to the optimal configuration that minimizes total harmonic distortion
3Object-generated harmful factors
If carrier signal phase is inverted by 180° in selected converters, then harmonic cancellation is achieved at point of common coupling, but timing synchronization becomes critical
Solution Approach 1:
The invention performs preliminary determination of the optimal carrier phase shifts for each converter before implementing the harmonic cancellation scheme. The search algorithm pre-calculates the required phase adjustments based on system characteristics, and this preliminary configuration is then applied to the converters. This preliminary action ensures that when the 180-degree inversion is implemented, the timing and phase relationships are already optimized for destructive interference, reducing the criticality of real-time synchronization precision
Data Source
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AI summary
The invention relates to a method to reduce harmonics in the electrical output (i.e. voltage and current) of a power plant. The power plant is connected via a point of common coupling with an electrical grid. Converters of the power plant provide respective electrical converter output by an applied pulse-width modulation scheme, which is used in the respective converter. The electrical output of the respective converters are summarized to generate the electrical output of the power plant. The electrical output of the power plant is provided via the point of common coupling to the electrical grid. Carrier sideband harmonics, which are generated by the converters, are measured in the electrical output of the power plant. A carrier signal of at least one selected converter is adjusted in its phase until specified and characteristic harmonics in the electrical output of the power plant are reduced below a given threshold.