Grid Strength Estimation for Weak-Grid Renewable Farm Control
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Solution Overview
Problem
Existing methods for estimating grid strength in renewable energy farms connected to power grids are inadequate, particularly in real-time scenarios, leading to challenges with voltage stability and power evacuation in weak grid conditions, especially when wind farms are closely coupled.
Innovation Solution
A method and system that measure voltage, active power, and reactive power at the point of interconnection, determine sensitivity to these parameters, and dynamically adjust active and reactive power commands based on grid strength, using frequency domain transformations and derivative calculations to assess and manage grid stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If wind farms are connected to grids with reduced short circuit capability (weaker grid), then renewable energy capacity can be increased, but voltage stability and power evacuation capability deteriorate in contingency situations
Solution Approach 1:
The system continuously monitors voltage, active power, and reactive power at the point of interconnection, and dynamically adjusts power commands based on real-time grid strength estimates. This closed-loop feedback mechanism enables the wind farm to adapt to varying grid conditions and maintain voltage stability even when connected to weaker grids with reduced short circuit capability.
Solution Approach 2:
The grid strength estimation system transitions from static offline assessment to dynamic real-time evaluation. By continuously updating grid strength estimates based on current operating conditions (loading level, compensation sub-systems, line outages), the system enables adaptive control strategies that respond to changing grid conditions, thereby maintaining reliability as renewable energy capacity increases.
2Measurement precision
If offline assessment of short circuit ratio is used during planning stage, then grid strength can be evaluated, but real-time variations in grid strength due to operating states are not captured
Solution Approach 1:
The system replaces traditional mechanical/offline grid strength assessment methods with an electronic/digital real-time estimation approach. By using measurements of voltage, active power, and reactive power combined with frequency domain transformations and derivative calculations, the system electronically computes grid strength estimates continuously, capturing real-time variations that offline methods miss.
Solution Approach 2:
The system performs preliminary calculations by establishing the relationship between power injections and voltage changes through frequency domain transformations. This preliminary modeling enables rapid real-time estimation without requiring complex online computations, thus achieving both measurement precision and real-time responsiveness.
3Reliability
If wind turbines perform sacrificial trips to maintain grid stability, then voltage control issues are addressed, but energy production losses increase
Solution Approach 1:
The system enables wind turbines to self-regulate their power output based on real-time grid strength estimates. By dynamically adjusting active and reactive power commands according to current grid conditions, each turbine serves itself to maintain grid stability without requiring sacrificial trips, thereby preventing energy production losses while ensuring grid reliability.
4Adaptability or versatility
If dynamic adjustment of power commands is implemented, then grid strength variations are managed, but control system complexity increases
Solution Approach 1:
The system uses a unified control framework that handles both active and reactive power control through a single grid strength estimation mechanism. By measuring voltage, active power, and reactive power and using frequency domain transformations to estimate grid strength, the system provides a universal solution that manages both types of power commands through the same control logic, reducing overall control system complexity despite the dynamic adjustment requirements.
Data Source
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AI summary
A method for estimating grid strength of a power grid connected to a renewable energy farm having a plurality of renewable energy power systems includes measuring, at least, a voltage, an active power, and a reactive power at a point of interconnection of the renewable energy farm to the power grid. The method also includes determining a sensitivity of the voltage to at least one of the active power or the reactive power at the point of interconnection. Further, the method includes determining the grid strength of the power grid as a function of the sensitivity of the voltage to at least one of the active power or the reactive power at the point of interconnection. In addition, the method includes dynamically determining at least one of an active power command or a reactive power command for the renewable energy farm at the point of interconnection based on the grid strength. Moreover, the method includes distributing at least one of the active power command or the reactive power command to individual controllers of the plurality of renewable energy power systems and a farm-level controller of the renewable energy farm.