Hello,
If a wind turbine is running in isolation and feeding a load then what will be the variations in parameters at the connection point if the load changes without any change in wind conditions (speed and direction)? Can we estimate the limits within which these perturbations do not impact the stability of turbine?
Thanks Akshan for your reply.
I was studying the DFIG's dynamic model available in literature with converters and did not find anywhere a scenario where the loads are changed in isolation functioning of Wind turbine. Since in DFIG the rotor side control will follow the MPPT and the Grid side converter will keep the dc voltage constant how the DFIG will see this change in load at the terminal ?
Also since the DFIG is decoupled, will there still be similar impact as SCIG and will it be felt only on the voltage? Will there be impact on the angle of the voltage as well?
The main difference between grid operation and isolated operation is the setting of Q reference value for the GSC (default operation at unity power factor), in addition it is always required to know whether the load requires a fixed frequency or not. However, if we assumed a fixed frequency (as the case of grid connection), then the load variation will change the reference P and Q values (through load current magnitude and phase measurements). As long as the available wind power is sufficient to cover the load and the converter ratings are not violated the machine will stabilize at the new operation point. Otherwise, if the load is higher for example, the WTG starts to extract its kinetic energy until it completely stops, or converter threshold is reached. Keep in mind that dramatic drop in load might cause over-speeding (machine runs away) as the electrical torque drops deeply below the mechanical torque trying to follow the load variations. Therefore, most of controllers contain a rate limiter to avoid the previous drawbacks. The response time for normal load variations is very fast (depends on the speed pf power electronics converters; ms), but the mechanical response of WT takes longer time based on its inertia, and severity of load change.
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