๐ Case Study
Solar Farm Design: 220 MW PV Plant Weak Grid Interconnection Study
Subsynchronous resonance (SSR) risk and voltage instability during morning ramp-up and cloud-edge transients
๐๏ธ Project Overview
Utility-scale solar farm in rural New Mexico connected to 69 kV rural feeder with SCR = 1.9
๐ฏ Challenge
Subsynchronous resonance (SSR) risk and voltage instability during morning ramp-up and cloud-edge transients
๐ง Design Approach
Grid-forming inverters with virtual inertia + adaptive Q(V) droop + real-time stability monitoring using synchrophasors
๐ Design Diagram
AI-generated project design illustration
๐ Key Calculations
SCR at Point of Interconnection
Short_Circuit_MVA / Inverter_MVA
Result: 1.92
Classified as 'weak grid' requiring GFM control
SSR Frequency Band Estimate
f_ssr โ 1/(2ฯโ(L_eq ร C_eq))
Result: 32.7 Hz
Aligned with 3rd harmonic of 60Hz โ triggered filter resonance
๐ Results
Zero SSR events in 2-year operation; passed FERC 693 compliance audit๐ก Lessons Learned
- โขWeak-grid solar plants require GFM inverters โ GFIs alone are insufficient for stability
- โขCloud-edge transients excite resonant modes more than steady-state conditions
โ Key Takeaways
- 1Weak-grid solar plants require GFM inverters โ GFIs alone are insufficient for stability
- 2Cloud-edge transients excite resonant modes more than steady-state conditions