Electrical Converter Harmonic Observer for Pulse Pattern Control
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Solution Overview
Problem
Existing methods for controlling electrical converters using pulse patterns struggle to distinguish between fundamental and harmonic components in ripple current, leading to inferior harmonic performance and limited controller bandwidth, which affects the quality of output voltage and current total harmonic distortion.
Innovation Solution
A method and control unit employing Linear Quadratic Gaussian Selective Harmonic Control (LQG-SHC) that decouples grid current and voltage harmonics, allowing for high-bandwidth linear control by estimating and rejecting individual harmonics, independent of the pulse pattern used, and includes a harmonic observer and controller to determine optimal switching angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If linear controllers are used to eliminate harmonics by feeding back ripple current samples, then harmonic elimination is improved, but controller bandwidth must be severely limited which worsens control performance
Solution Approach 1:
The patent segments the ripple current signal into fundamental and harmonic components using a harmonic observer. This segmentation allows the controller to selectively act on harmonic components without being constrained by bandwidth limitations when processing the entire ripple current signal, thereby resolving the contradiction between harmonic elimination and bandwidth preservation.
Solution Approach 2:
The patent introduces a harmonic observer as an intermediary component that processes the ripple current signal and extracts harmonic components. This intermediary enables the linear controller to work with separated harmonic signals rather than the full ripple current, allowing effective harmonic elimination while maintaining adequate controller bandwidth for stable operation.
2Ease of operation
If pulse patterns are used for driving electrical converters, then switching control is simplified, but the ability to distinguish fundamental and harmonic components in ripple current is lost which worsens harmonic performance
Solution Approach 1:
The patent implements feedback through a harmonic observer that continuously monitors the ripple current and extracts harmonic components. This feedback mechanism works in conjunction with pulse pattern control, allowing the system to maintain the simplicity of pulse patterns while actively compensating for harmonics through observed and fed-back harmonic information, thus resolving the contradiction between control simplicity and harmonic performance.
Data Source
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Figure 3
AI summary
A method for controlling an electrical converter (16) is provided. The electrical converter (16) is coupled to a DC energy source and to an electrical grid and is configured for converting a DC voltage from the DC energy source into an AC voltage and to feed the AC voltage into the electrical grid. The method comprises the steps of: receiving a grid current signal being representative for a grid current (ig,abc) of the grid and a grid voltage signal being representative for a grid voltage (vg,abc) of the grid; determining grid current harmonics (îg,αβ;h) of the grid current (ig,abc) and grid voltage harmonics (v̂g,αβ;h) of the grid voltage (vg,abc) from the grid voltage signal and the grid current signal; determining a pulse pattern ( ui,abcopt) for driving the electrical converter (16) from the determined grid current harmonics (îg,αβ;h), the determined grid voltage harmonics (v̂g,αβ;h), and a given fundamental grid current setpoint ( ig,abc;1∗), wherein the pulse pattern ( ui,abcopt) comprises switching angles ( αi,abcopt) for the electrical converter (16) over a next modulation period of the electrical converter (16); and applying at least the next switching angle ( αi,abcopt) determined from the pulse pattern to the electrical converter (16).