Dear Akhilesh, the pv produces a DC voltage. When converting it to AC, this should have harmonics. Moreover, even if you eliminate the harmonics by using a suitable inverter system, the fluctuation of the solar radiation cause fluctuations to the pv. This affects the DC voltage output of the pv and further the frequency output. Even with a voltage regulator, there will be always present a fluctuation. The point is to reduce it in a tolerate level. 

Dear Paraskevopoulos

Thanks for explaining the things.

As i have simulated the system with taking care of each and every aspects. After the simulation i am getting some of the results of frequency.

So can i conclude the things after your explanation that in the system having the solar PV as one of the source will always have the small signal oscillation. 

When you have renewable generations, like wind, solar etc (which are fickle), are coupled to traditional generation the frequency variations will be more compared to the traditional one. It is obvious.        

Dear Akhilesh,

If I understand your waveform correctly, you have simulated with higher and lower PV penetration. Higher PV penetration has more distortions as compared to lower PV penetration. The reality we have seen is that the ratio between PV and Grid power matters and if PV is a small component of total power needed not much of distortion. You seem to have captured that, also as suggested in earlier responses, harmonics and fluctuations is seen in PV combined power

Thanks for your Answer Mr. Sridhar H V

As mentioned in the last few lines of your answer, I also captured the ratio of PV power to Grid power. As i am increasing the PV power penetration to the grid the ratio is increasing and hence the system is having larger fluctuation.

So as from your answer and with my understanding from the same, the system will always have fluctuation until unless we are not providing the compensator to damp out the system oscillation.

Dear Akhilesh,

We have done some work on finding the effect of PV on low frequency oscillation (0.1-2 Hz) of existing modes. The results are mixed, i.e. the PV influence the low frequency oscillation in positive and negative ways based on location of the PV, size, control strategy put in place at PV  etc. This depends on flow pattern change and loading on synchronous generators as well, 

In order to make this analysis in your simulation results, you can look at the frequency of oscillation and damping ratio, before and after adding PV and make a conclusive remark. It very hard to see the wave form and make judgement. There are ways to do this from your time domain simulation, if you don't have eigenvalue analysis. 

In general, PV as a "non-inertia" generator could contribute in oscillation, though you can emulate inertia by some control measures and add damping on weak modes.

Best wishes,

-Mithulan