Frequency Inverters (VFDs)
Aluminum Electrolytic Capacitor Solutions for Variable Frequency Drive Applications
Summary: HUAYU provides aluminum electrolytic capacitor solutions for variable frequency drives (VFDs) and frequency inverters. Our snap-in (CD294, CD295) and screw terminal (CD13HL, CD13NH) series handle DC-link filtering, bus support, and braking circuits in VFD applications from 220V to 690V input.
Capacitor Functions in a VFD
DC-Link Smoothing
The primary role — smooths the 6-pulse rectified AC into stable DC. The capacitor bank must absorb the 300 Hz (50 Hz input) or 360 Hz (60 Hz input) ripple from the rectifier stage while also handling the high-frequency ripple from the inverter PWM output stage.
Energy Buffer
Provides ride-through capability during brief power interruptions and absorbs energy during motor deceleration (regenerative braking). Insufficient capacitance leads to DC bus voltage collapse during transient loads.
Braking Absorption
In VFDs without regenerative front ends, the capacitor bank absorbs regenerated energy during motor braking. For high-inertia loads, a dedicated braking chopper and resistor are used, but the DC-link capacitor must still handle the current pulses.
dv/dt Filtering
Output filter capacitors (often in LC filter configurations) reduce the dv/dt of the PWM output waveform to protect motor insulation and reduce electromagnetic interference (EMI).
Voltage Selection Guide
| VFD Input Voltage | Nominal DC Bus Voltage | Peak DC Bus Voltage | Recommended Capacitor Voltage Rating |
|---|---|---|---|
| 220V AC (1-phase) | ~280V DC | ~311V DC | 400V |
| 380V AC (3-phase) | ~510V DC | ~537V DC | 400V (series pair) or 600V |
| 440V AC (3-phase) | ~591V DC | ~622V DC | 400V (series pair) or 600V |
| 690V AC (3-phase) | ~930V DC | ~976V DC | 500V (series pair with balancing) |
Recommended Series
HUAYU series best suited for VFD applications
| Series | Type | Key Features | Typical VFD Application |
|---|---|---|---|
| CD294 | Snap-In | Ultra-low ESR, extended life | Small VFD DC-link (<7.5kW) |
| CD297 | Snap-In | Load-life optimized, high ripple | Medium VFD DC-link (7.5–37kW) |
| CD13NH | Screw Terminal | High temperature, compact | Medium-large VFD DC-link (37–110kW) |
| CD13HL | Screw Terminal | 105°C, 10,000h+ life | Large VFD DC-link (110kW+) |
| CD135 | Screw Terminal | Large can, high capacitance | High-power VFD DC-link (250kW+) |
| CD17FX | Snap-In | Miniature, high reliability | VFD output filter (dv/dt filter) |