AC Grid Condition Evaluation Using Local Frequency and Equivalent Impedance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for evaluating the condition of AC power grids, particularly in the context of HVDC links, are inadequate due to limitations in estimating grid strength and stability, leading to potential issues like HVDC station trips, overvoltage, and power instability, especially when the AC power grid is weak.
Innovation Solution
A method that captures time series of voltage and current signals, identifies local frequency, transforms these signals, estimates equivalent circuit parameters, and determines a grid condition indicator using a comprehensive equivalent circuit model, enabling improved evaluation of AC power grid conditions and reducing the risk of network contingencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a PLL and fixed phase estimate method is used to evaluate grid condition, then the evaluation process is simple, but the measurement precision deteriorates in the presence of phase deviations due to fast power/current dynamics
Solution Approach 1:
The patent applies dynamics by making the phase estimate adaptive rather than fixed. The phase estimate is continuously updated based on the rotating reference frame transformation and impedance calculation, allowing the system to track phase deviations dynamically caused by fast power/current dynamics, thus maintaining measurement precision while managing complexity through algorithmic adaptation
Solution Approach 2:
The patent changes the parameter of phase estimate from a fixed value to a dynamically calculated value based on the rotating reference frame. By transforming the impedance calculation to account for varying phase angles and using the rotating reference frame transformation, the system adapts to changing grid conditions, improving frequency estimation accuracy during transient events
2Measurement precision
If a comprehensive equivalent circuit model accounting for frequency variations is used, then the measurement precision of grid condition improves, but the device complexity increases
Solution Approach 1:
The patent segments the grid monitoring function into distinct computational modules: rotating reference frame transformation, impedance calculation, frequency variation detection, and grid condition indicator determination. This segmentation allows the comprehensive equivalent circuit model to be implemented in a structured manner, improving measurement precision through detailed modeling while managing complexity through modular computation
Solution Approach 2:
The patent introduces the rotating reference frame as an intermediary transformation that simplifies the analysis of frequency variations. By transforming the three-phase system into a rotating reference frame, the complex time-varying impedance calculations are converted into a more manageable form, enabling accurate grid condition assessment without excessive computational complexity
3Adaptability or versatility
If the AC power grid is weak with high equivalent impedance, then the flexibility of HVDC operation is reduced, but the risk of network instability increases
Solution Approach 1:
The patent implements feedback by continuously monitoring the grid condition indicator (short-circuit ratio) and using this information to assess the interaction between the AC grid and HVDC link. This feedback mechanism allows the system to detect weak grid conditions and adjust operations accordingly, maintaining HVDC flexibility while preventing network instability through real-time condition assessment
Data Source
AI summary
The present disclosure relates to a method and system for evaluating a grid condition of an AC power grid. A time series of voltage and current signals of the AC power grid is captured and a local frequency of the AC power grid is identified. The time series of the voltage and current signals is transformed at the identified local frequency of the AC power grid into transformed signals. Equivalent circuit parameters are estimated from the transformed signals based on a description of an equivalent circuit of the AC power grid. A value of a grid condition indicator is determined based on the calculated equivalent circuit parameters and the identified local frequency of the AC power grid and processed in a grid monitoring system for evaluating the grid condition of the AC power grid.