DC-Link Capacitor Selection Guide

Introduction to DC-Link Capacitors

DC-Link capacitors are critical components in inverter and power supply applications, serving to smooth the DC bus voltage and absorb ripple current. This guide covers the key selection criteria for choosing the right DC-Link capacitor.

Key Selection Parameters

1. Voltage Rating

Select a capacitor with a voltage rating at least 1.5 times the nominal DC bus voltage. For example:

• 380V AC input → 540V DC bus → Select 700V or higher capacitor
• 480V AC input → 650V DC bus → Select 900V or higher capacitor

2. Capacitance Value

The required capacitance depends on:

• Acceptable voltage ripple
• Load current
• Switching frequency

Typical formula: C = I / (2 × f × ΔV)

3. Ripple Current Rating

Ripple current is often the limiting factor in capacitor selection. Calculate the expected ripple current and select a capacitor with at least 1.5x margin.

4. Temperature Considerations

Capacitor lifetime is strongly dependent on temperature. Every 10°C reduction doubles the lifetime.

Application Guidelines

Application

Typical Capacitance

Voltage Rating

Key Considerations

5kW Motor Drive	10-20uF	600-700V	High ripple current
30kW Motor Drive	50-100uF	900-1100V	Thermal management
Solar Inverter	100-200uF	1100V	25-year lifetime
EV Charger	20-50uF	900-1200V	AEC-Q200 qualification

Design Best Practices

Voltage Margin: Always operate at 80% or less of rated voltage for extended lifetime

Thermal Management: Ensure adequate cooling - capacitor temperature should not exceed 85°C

Ripple Current: Size for 1.5-2x calculated ripple current

Series/Parallel: Use parallel connection for higher capacitance, series for higher voltage

Conclusion

proper DC-Link capacitor selection requires careful consideration of voltage, capacitance, ripple current, and temperature. Contact our FAE team for application-specific guidance.