For a grid connection wind turbines have to fulfill several requirements at the point of common coupling (PCC). Essential specifications concern frequency and voltage stability, in which wind turbines must take part with their active and reactive power control. Also dynamic characteristics during faults like short-circuits or voltage drops are stipulated in certain limits. Furthermore limits for harmonic distortions like harmonic currents and voltages or flicker must be guaranteed, which has to be proved by certificates. For this task measurements as well as simulations are necessary.
Grid compatibility according to EN 50160 and IEC/EN 61400 is rated by means of disturbance measurements. To be able to determine the capacity of a PCC, methods for grid impedance measurements are developed in two other projects (see context menu).
For the simulations stipulated in the unit certificate a modeling of the wind turbine according to FGW guideline TR8 is necessary. The model must represent the dynamic behavior of the wind energy converter in normal operation as well as during grid faults.
Dynamic behavior in normal operation:
- modeling of the grid-side converter by a controllable voltage source
- fluctuating feeding of active power caused by the renewable energy source
- change of reactive power by reference value inputs of the grid operator (static voltage support)
Dynamic behavior during grid faults
- dynamic voltage support during voltage drops (short-circuit in grid)
- reduction of active power in case of overfrequency
Test bench of a wind turbine with doubly fed asynchronous generator:
- analysis of harmonics at a real and an ideal low-voltage grid
- influence of harmonics on power terms
In this project models are developed for wind turbines with 4-pole, permanently excited synchronous generators and indirect voltage converter as well as such with doubly fed asynchronous generators. Part of this task is the modeling of the converters and the development of control algorithms.
As an example the figure shows the simplified diagram of a wind turbine with permanently excited synchronous generator.
The simulation models are verified at low-voltage test benches in the laboratory.
Letzte Änderung: 19. June 2020