Voltage Source Converter Controller Using Rotating Frame Prediction
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Solution Overview
Problem
Voltage source converters in high voltage power transmission networks face challenges in efficiently converting AC to DC and vice versa with low harmonic distortion, particularly due to the complexity added by increasing switching frequency, which affects the design and performance of the controller.
Innovation Solution
A controller for voltage source converters that utilizes the rotating reference frame space to accurately predict AC voltage demand, allowing for a higher switching frequency without increasing the sampling frequency, thereby reducing complexity and improving harmonic distortion management.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the switching frequency is increased to reduce total harmonic distortion, then the waveform resolution is improved, but the controller complexity increases significantly
Solution Approach 1:
The controller predicts future AC voltage demand values before they are needed, allowing the switching operations to be prepared and executed in advance. This predictive approach enables the system to achieve high waveform resolution without requiring proportionally high switching frequencies, thereby reducing controller complexity while maintaining manufacturing precision.
Solution Approach 2:
A prediction element is introduced as an intermediary component that calculates future AC voltage demand values based on current operating conditions. This intermediary allows the controller to decouple the switching frequency from the sampling frequency, enabling high waveform resolution without the need for high switching frequencies that would increase controller complexity.
2Object-generated harmful factors
If the switching frequency is increased to reduce step changes in output waveform, then the total harmonic distortion is reduced, but the controller design becomes more complex
Solution Approach 1:
The controller performs preliminary calculation of future AC voltage demand values using a prediction element that operates at a lower sampling frequency. This allows the switching frequency to be reduced while still maintaining low total harmonic distortion, as the predictive information enables more efficient switching strategies without requiring high-frequency switching operations.
Solution Approach 2:
The invention changes the operational parameters by decoupling switching frequency from sampling frequency. The prediction element calculates future voltage demands at the sampling frequency, while the actual switching can occur at a lower frequency using this predictive information. This parameter change allows reduction of total harmonic distortion without increasing controller design complexity.
3Measurement precision
If linear interpolation in cartesian space is used to predict future voltage demand, then the prediction accuracy is insufficient, but the rotating reference frame space provides more accurate predictions
Solution Approach 1:
The prediction element transforms the prediction problem from cartesian space to rotating reference frame space, adding a rotational dimension to the analysis. This dimensional transformation allows the system to exploit the periodic nature of AC voltage patterns, providing significantly more accurate predictions of future voltage demand while maintaining manageable control system complexity through the use of standard transformation techniques.
Data Source
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AI summary
A controller for a voltage source converter (VSC), said controller including; an AC vector control element configured to generate an AC voltage demand signal based on a measure of an AC voltage output from the VSC and a demand value, a module selection element configured to determine a module instruction set based on said AC voltage demand signal, said module switch instructions set providing switching instructions for a plurality of modules of the voltage source converter to form an output waveform, said AC vector control element configured to generate said AC voltage demand signal in a rotating reference frame space formed by transformation, using a DQ transform, of said measure of the AC voltage and said demand value into symmetrical sequence rotating reference frame terms, wherein said AC vector control element is configured to generate said AC voltage demand signal comprising at least two AC voltage demand values comprising an AC voltage demand value at a first time and a AC voltage demand value at a future time, calculated from the same symmetrical sequence rotating reference frame terms, said AC voltage demand values determined in said rotating reference frame space, wherein said module selection element is configured to determine a module instruction set for each of the prediction values in accordance with the associated time.