Photovoltaic Cluster Virtual Inertia Allocation for Frequency Stability
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Solution Overview
Problem
In large-scale photovoltaic grid-connected systems, a single VSG control unit is insufficient to maintain safety and stability, requiring coordination and cooperation among multiple VSG control units to ensure overall stability, and there is a need to effectively allocate virtual inertia among these units.
Innovation Solution
A method for allocating virtual inertia in a photovoltaic cluster is provided, which involves determining the required virtual inertia based on the frequency change rate, obtaining values of indexes affecting virtual inertia for each VSG control unit, and using a predetermined function equation to determine the allocation proportion of virtual inertia for each unit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple VSG control units are coordinated to maintain stability in large-scale photovoltaic systems, then system stability is improved, but the complexity of virtual inertia allocation increases
Solution Approach 1:
The patent transforms the complex multi-dimensional inertia allocation problem into a simplified one-dimensional problem by changing the parameter representation. It uses a unified objective function that aggregates multiple performance indicators (frequency response, damping, stability) into a single comprehensive metric, allowing straightforward comparison and allocation among multiple VSG units without complex multi-objective optimization
Solution Approach 2:
The patent segments the overall virtual inertia allocation problem into independent unit-level allocations. Each VSG control unit's inertia contribution is calculated independently based on its own characteristics and the unified objective function, then aggregated to achieve the total required virtual inertia, simplifying the coordination complexity
2Device complexity
If traditional power electronic devices are used in photovoltaic systems, then device simplicity is maintained, but inertia control capability is lost during sudden load changes
Solution Approach 1:
The patent introduces virtual synchronous generator (VSG) control as an intermediary layer between the traditional power electronic devices and the grid. This control strategy simulates the inertia characteristics of traditional synchronous generators through virtual physical models, enabling frequency stability without requiring actual synchronous generators or complex hardware modifications
Solution Approach 2:
The patent replaces the mechanical inertia of traditional synchronous generators with virtual inertia generated through control algorithms. By using mathematical models and control theory instead of physical mechanical systems, it achieves inertia control in power electronic-based photovoltaic systems while maintaining device simplicity
Data Source
AI summary
The method includes: determining required virtual inertia based on a frequency change rate monitored at a grid connection point of a photovoltaic grid-connected system; obtaining values of indexes that affect virtual inertia provided by each virtual synchronous generator (VSG) control unit in a photovoltaic cluster of the photovoltaic grid-connected system; determining, by using a predetermined function equation, a function value corresponding to each index; and determining an allocation proportion of the required virtual inertia in each VSG control unit based on the function value corresponding to each index. A problem of difficult conversion between a plurality of kinds of performance during operation of a power system is resolved, the frequency change rate is suppressed to a certain extent, and a stable state is recovered quickly.