Adaptive PR Controller for Grid Inverter Frequency Tracking
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Solution Overview
Problem
Existing control systems for grid-connected inverters face challenges in accurately tracking sinusoidal reference signals due to digital implementation issues, such as deviations in resonant frequency and phase-shift caused by discretization and coefficient truncation, as well as frequency variations in the utility grid.
Innovation Solution
An adaptive proportional-resonant controller with update blocks that continuously adjust coefficients to maintain high gains at the grid frequency and harmonic frequencies, ensuring precise tracking of the sinusoidal reference signal and compensating for grid frequency variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a proportional-resonant controller is used to provide high gain at line frequency, then tracking accuracy of the sinusoidal reference signal is improved, but digital implementation causes deviation in resonant frequency and phase-shift
Solution Approach 1:
The patent applies dynamics by making the controller coefficients adaptive rather than fixed. The update blocks continuously adjust the PR controller coefficients based on the actual grid frequency, allowing the controller to dynamically track frequency variations and maintain accurate resonance at the operating frequency, thereby resolving the contradiction between tracking accuracy and frequency accuracy.
Solution Approach 2:
The patent implements feedback through update blocks that monitor the grid frequency and use this information to adjust the PR controller coefficients. This closed-loop approach ensures that the controller adapts to frequency deviations caused by digital implementation, maintaining both tracking accuracy and frequency accuracy simultaneously.
2Device complexity
If digital truncation is used to implement controller coefficients, then device complexity is reduced, but large deviation in resonant frequency occurs
Solution Approach 1:
The patent uses dynamics to adapt the controller coefficients in real-time based on actual grid frequency measurements. This adaptive approach compensates for the precision losses introduced by digital truncation, allowing the use of simpler fixed-point arithmetic while maintaining frequency precision through continuous coefficient adjustment.
Solution Approach 2:
The patent changes the parameters (controller coefficients) dynamically to compensate for digital truncation effects. By adjusting the coefficients based on measured frequency and the known sampling period, the system maintains accurate resonant frequency despite using truncated digital representations of the coefficients.
3Ease of operation
If fixed coefficients are used in the controller, then ease of operation is improved, but adaptability to grid frequency variations deteriorates
Solution Approach 1:
The patent transforms the static controller into a dynamic one by introducing update blocks that continuously adjust coefficients based on grid frequency variations. This maintains the simplicity of the basic PR controller structure while adding adaptability through automatic coefficient adjustment, resolving the contradiction between ease of operation and frequency adaptability.
Solution Approach 2:
The controller performs self-adjustment through the update blocks that automatically modify the coefficients based on measured grid frequency. This self-service mechanism eliminates the need for manual retuning while maintaining adaptability to frequency variations, combining ease of operation with frequency adaptability.
Data Source
AI summary
Systems, methods, and devices relating to the controlling of a grid-connected inverter. A grid connected inverter is controlled by a proportional-resonant controller which tracks the grid current. To adjust for changes in grid conditions, an update block dynamically and continuously adjusts coefficients used by the controller to ensure high gains provided by the controller at the grid frequency. A harmonic compensator is also provided to ensure that high loop gains at harmonic frequencies of the grid frequency are also provided for. To also adjust for changing grid conditions, a second update block also continuously adjusts the coefficients used by the harmonic compensator.