⚡ CARRIER FREQUENCY IN VARIABLE FREQUENCY DRIVES (VFD)
A guide to understanding carrier frequency, its role, setup parameters, and how to select the right value for your application.
Carrier Frequency is the switching frequency of power components (IGBT/MOSFET) when a VFD generates PWM waveforms to control a motor.
Note that carrier frequency is different from the output frequency supplied to the motor.
- Example: Output frequency is 50 Hz, while carrier frequency may be 4 kHz, 8 kHz, or even 12 kHz.
🎛️ Impact on Waveform Quality
- Higher carrier frequency → smoother voltage output, reduced motor vibration.
- Lower carrier frequency → more noticeable voltage steps but better for heavy loads.
🔊 Noise & Vibration
- 2–4 kHz: Audible whine from the motor is common.
- ≥10 kHz: Quieter operation, ideal for noise-sensitive environments.
🔥 Heat & Losses
- Higher frequencies → more switching losses → hotter IGBTs.
- Balance smooth operation with device longevity.
📊 Typical Carrier Frequency Ranges
| Frequency Range | Recommended Application |
|---|---|
| 2 – 4 kHz | Heavy loads, high-power motors (cranes, mills, rolling systems) |
| 6 – 8 kHz | Medium loads (pumps, fans, conveyors) |
| 10 – 16 kHz | Light loads, quiet environments (HVAC, laboratories) |
🛠️ Parameter Settings (Examples)
- AC10: Carrier Frequency parameter (e.g., F153) – range 0.8–10 kHz.
- AC20/AC30: Switching/Stack Frequency 1–16 kHz (model dependent).
- AC690: Freq Select – select switching level based on application.
Note: Some VFD models automatically derate (reduce available output capacity) at higher carrier frequencies.
🧭 How to Choose Carrier Frequency
By Load Characteristics
- Heavy, high-inertia loads → 2–4 kHz.
- Balanced, medium-duty loads → 6–8 kHz.
By Environment
- Noise-sensitive (HVAC, offices) → ≥10 kHz.
- Hot environments → lower frequencies preferred.
By Motor & Cable Condition
- Older motors or weak insulation → lower frequency to reduce dv/dt.
- Cable runs >30 m → lower frequency to minimize voltage reflection.
⚠️ Common Issues with Incorrect Settings
- Overheated IGBTs → OH/OC error alarms.
- Motor noise/vibration → carrier frequency too low.
- Reduced equipment life → excessive frequency without proper cooling.
- Higher EMI/EMC noise → improper grounding or filtering.
💡 Recommended Practices
- Only increase carrier frequency when necessary for noise reduction or current ripple control; monitor drive temperature.
- Ensure proper ventilation; consider auxiliary cooling for harsh environments or heavy loads.
