Investigating Extreme Oscillations in Low-Inertia Generators within IEEE 39-Bus System with Heterogeneous Inertia Constants

[Barbara258]

Dear Hantao Cui,

I've encountered an interesting phenomenon while simulating load disturbances in the IEEE 39-bus system with different generator inertia settings. I'm seeking your insights on the following behavior:

When generators have significantly different inertia constants (M values), and I apply a sudden load increase disturbance to the system, I observe extreme oscillations in both rotor speed and COI frequency specifically for the low-inertia generators (as shown in Figures 1). The oscillations appear highly erratic and significantly differ from the expected frequency response pattern.

However, when I set the generator inertia constants to be more homogeneous (with smaller differences between units), these extreme oscillations disappear, and all generators show more consistent frequency responses (as shown in Figures 2).

My specific settings in the heterogeneous case were:

• COI 1: M values of 25-30 (ultra-high inertia)
• COI 2: M values of 10-12 (medium inertia)
• COI 3: M values of 3-4 (low inertia)
• COI 4: M values of 2 or lower (extremely low inertia)

While in the homogeneous case, all generators had M values between 6-15.

What causes these extreme oscillations specifically in low-inertia areas under heterogeneous conditions? Is this related to numerical instability in the simulation, or does it represent actual physical phenomena we might observe in real power systems with high penetration of inverter-based resources?

Any insights on the underlying mechanisms and potential mitigation strategies would be greatly appreciated.

Thank you

[cuihantao]

Hi Barbara,

Sorry about the delay. I couldn't find the previous email reply. Looking at the results, I don't think it is a numerical instability issue.

Let's rule out the issue of COI calculation. Can you plot all the generator speed for a) the heterogeneous inertia case, and b) the homogeneous inertia case?

If the heterogeneous case shows fast frequency drops and subsequent oscillations, it is likely due to the low-inertia nature.