Dear all,
As you know, one method of maximum power point tracking in wind turbines is to select the reference active power which complies with the maximum power that is achievable (power at MPP).
I wonder what happens if one increases the reference power beyond what is imposed by the value corresponding to MPP? Will it lead to power reduction? (from the control engineering point of view, we can design the power control loop so that the output power will approach the reference power; so, why not increase the reference power beyond MPP?!)
Dear Mohamed Azab ,
Thanks for your prompt response; my point was however regarding the reference power selection: If a PI controller or an on-off controller can finally set the actual active power to its reference value, then what happens if the reference power (P_ref) is set higher than that is imposed by the maximum power point formula (this formula expresses the P_ref should be in proportion with the wind speed cubed).
Kind wishes
Naser
Dear Mohamed Azab
Thanks for your kind response, but I am concerned with MPPT in wind generation systems, such as DFIG, PMSG, etc.
Dear Mohammad,
Firstly:
The maximum power ,which can extracted from the wind at MPP, is related to the operating wind speed. At every wind speed , there is a maximum power. So, the MPPT algorithms are implemented to track this power point in which the power coefficient and tip speed ratio are optimal values. The tracking performance can be obtained by comparing the reference power or speed that acquired from MPPT algorithms with the actual power/speed. The controller objective is reaching the MPP that the ref and actual power are equal so the error equals zero.
Secondly:
Returned to your question,
1- If the wind speed varies below rated wind speed, any change in wind speed makes MPPT algorithm generates new ref power and the optimal power curve is continuously changed until reaching the optimal/ ref power.
2- If the wind speed is above rated wind speed, the ref power is limited to rated power by using pitch controllers which are operated to reduce the mechanical stress on WT blades.
3- Wind speed below cut in or above cut out , the WT is stopped for safety requirements.
To sum up , any change in wind speed makes the optimal power curve is changed.
You can read the following papers,
[1] Hossain MM, Ali MH. Future research directions for the wind turbine generator system. Renew Sustain Energy Rev 2015;49:481–9. [2] Cheng M, Zhu Y. The state of the art of wind energy conversion systems and technologies: a review. Energy Convers Manage 2014;88:332–47. [3] Kumar D, Chatterjee K. A review of conventional and advanced MPPT algorithms for wind energy systems. Renew Sustain Energy Rev 2016;55:957–70. [4] Tripathi S, Tiwari A, Singh D. Grid-integrated permanent magnet synchronous generator based wind energy conversion systems: a technology review. Renew Sustain Energy Rev 2015;51:1288–305.
I hope my comment satisfies your question.
It is not possible to a power higher than MP. if tried, this causes to speed or torque goes beyond the optimal values, which ends up with a lower extracted power than MP.
Dear Murat Karabacak ,
Thanks a lot for your nice and concise response. Do you have a proof or simulation to validate your statement?
Mohammad Naser Hashemnia,
In Matlab (i recommend the last version), there are several demos for PV MPPT applications. They are pretty good simulations, i am sure they will be useful for you. Best regards.
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