In MATLAB simulation model of DFIG grid tied system, why after starting the DFIG, the torque produced by the wind turbine DFIG increases and the rotor speed decreases and why it is not coming under steady state? What is this phenomena called?
There is a lot of information missing from what you are asking.
I will answer with two possibilities.
First, when the DFIG is connected to the grid, the rotational speed of the generator is quite high.
In this case, it may be a process of finding the maximum output point according to the generator's MPPT control. I don't know what the simulation time is for the matlab simulation model, but in this case, a longer simulation time can reach a steady state.
Second, when DFIG's MPPT controller excessively controls the amount of power generation.
In this case, the rotational speed of the generator becomes lower than the minimum speed(approximately 70 to 75% of the synchronous speed in the case of DFIG).
Question needs to be more clear. To my understanding when you refer to rotor speed, it's the speed of turbine rotor and not DFIG rotor speed.
During the DFIG startup, the starting torque required is huge and this is obtained from mainly from turbine rotor inertia which gets converted through mechanical gearbox increasing the rotor speed of high speed shaft attached to generator.
However as soon as the DFIG starts supplies the active power to grid, depending on the grid load / demand conditions, the rotor speed of DFIG decreases and vice-versa. This means whenever the grid load demand is reduced or fluctuating , or in the event of grid fault occurrences, this supply of power is dangerous to turbine components and therefore the turbine/ grid operator regulates the active power inflow from WTG to grid. As this happens it causes the rotor speed of DFIG to increase again due to high inertia of wind turbine rotor getting converted to mechanical energy.
For a more detailed explanation please refer an authoritative text on WTG / DFIG generator operation.
Hope this helps
Cheers
Hello,
I would like to remind you that before DFIG-WT debits its P-Q output on demand, there is a preliminary synchronization and coupling step that takes place.
- Badges
- Science topic