📋 Case Study

Puerto Rico PREPA Grid Restoration Post-Maria

Small-signal instability in inter-area modes (0.3–0.8 Hz) due to loss of synchronous inertia

🏗️ Project Overview

Rapid integration of 500 MW distributed solar + microgrids into fragmented 115 kV backbone

🎯 Challenge

Small-signal instability in inter-area modes (0.3–0.8 Hz) due to loss of synchronous inertia

🔧 Design Approach

Synchronous condenser banks (2× 100 MVA) + virtual inertia tuning in BESS inverters per IEEE 2030.7

📐 Key Calculations

Equivalent Inertia Constant

H_eq = Σ(H_i × S_i)/S_base

Result: 1.2 s

Below 2.5 s minimum for stable inter-area oscillations

Virtual Inertia Gain K_f

K_f = 2H_virt × ω₀ / ΔP

Result: 8.4 MW·s/rad

Restored effective inertia to 2.1 s equivalent

📊 Results

Damped inter-area mode eigenvalues moved from −0.01±j0.52 to −0.18±j0.49; eliminated 92% of forced oscillations

💡 Lessons Learned

• •Synchronous condensers provide superior damping vs. pure virtual inertia
• •Microgrid boundary impedance must be modeled in system-wide eigenanalysis

✅ Key Takeaways

• 1Synchronous condensers provide superior damping vs. pure virtual inertia
• 2Microgrid boundary impedance must be modeled in system-wide eigenanalysis