Grid-Frequency Estimation Control Using Synchronous Current Reference Frame
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Solution Overview
Problem
Conventional power electronics systems lack effective methods for providing accurate and clean grid-frequency control due to challenges in estimating grid frequency from voltage and current measurements, especially in weak grid conditions, leading to instability issues.
Innovation Solution
An active power conversion apparatus (APCA) that estimates grid frequency by converting phase current measurements to a synchronous reference frame, determining direct and quadrature current references, and using these to adjust active power delivery, with a controller that forces zero average current error signals to ensure precise frequency control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If digital signal processing with phase-locked loop algorithm is used to estimate grid frequency, then frequency estimation capability is improved, but reliability deteriorates in weak grid voltage measurement conditions
Solution Approach 1:
The patent introduces an intermediary variable - the q-axis current component in the synchronous reference frame - as a mediator to indirectly estimate grid frequency. Instead of directly measuring voltage frequency (which fails in weak grid conditions), the method uses current measurements transformed to synchronous reference frame, where the q-axis current contains frequency deviation information that can be reliably extracted even when voltage measurements are weak or unreliable.
2Productivity
If synchronous machines are replaced by static power electronics, then productivity and decarbonisation are improved, but stability deteriorates due to reduced system inertia
Solution Approach 1:
The patent implements a feedback mechanism where the estimated grid frequency (derived from q-axis current) is continuously fed back to adjust the active power output of the power electronics system. This closed-loop control enables static power electronics to respond to frequency deviations similarly to synchronous machines, providing virtual inertia and frequency regulation services that compensate for the loss of mechanical inertia when replacing synchronous generators.
Data Source
AI summary
An active power conversion apparatus (APCA) estimates a grid frequency estimation of an electric grid connected to the APCA. The APCA includes a controller for receiving measurements of at least one phase current between the APCA, and the electric grid. The controller converts the at least one phase current to at least one synchronous reference frame, and determines direct and quadrature current references to be used in the grid frequency estimation. The controller determines a use of frequency estimation as a manipulated variable that forces to zero at least one of the average values of current error signals.