📋 Case Study
Data Center UPS Output Harmonic Resonance with PDU Capacitor Banks
25th harmonic resonance between UPS output impedance and PDU input capacitors caused 3.2 kV peak voltage oscillations on 400V bus, tripping breakers and damaging SSD power supplies
🏗️ Project Overview
Colocation facility deploying 400 kW modular UPS with active harmonic filters
🎯 Challenge
25th harmonic resonance between UPS output impedance and PDU input capacitors caused 3.2 kV peak voltage oscillations on 400V bus, tripping breakers and damaging SSD power supplies
🔧 Design Approach
Performed impedance sweep modeling (using ETAP); re-tuned harmonic filter Q-factor from 30 to 12; added passive damping resistors in parallel with capacitor banks
📐 Design Diagram
AI-generated project design illustration
📐 Key Calculations
Resonant Frequency
f_r = 1/(2π√(LC))
Result: 1250 Hz (25th harmonic of 50 Hz)
Confirmed root resonance mode
Damping Ratio
ζ = R/(2√(L/C))
Result: 0.41
Achieved critical damping to suppress overshoot
📊 Results
Harmonic voltage distortion (THDv) reduced from 12.7% to 2.1%; zero breaker trips over 18 months of operation💡 Lessons Learned
- •Harmonic resonance can occur even when individual components meet standards—system-level modeling is non-negotiable
- •Active filters require precise coordination with passive elements to avoid destabilization
✅ Key Takeaways
- 1Harmonic resonance can occur even when individual components meet standards—system-level modeling is non-negotiable
- 2Active filters require precise coordination with passive elements to avoid destabilization