Solutions for Frequency Converter Interference Issues

1. Software-Based Anti-Interference Measures

• Adjust Carrier Frequency:

• Reduce the carrier frequency via the converter's HMI to an appropriate range.

• If ineffective, proceed with hardware solutions.

2. Proper Grounding

Effective grounding suppresses external interference and minimizes device emissions.

Implementation:

• (a) Converter Grounding:

• Connect the main circuit terminal PE (E/G) to a dedicated ground rod (not shared with other equipment).

• Ground wire: ≥4mm² cross-section, ≤20m length.

• Keep away from low-voltage device grounding points.

• (b) Other Equipment Grounding:

• Separate protective ground and working ground with independent ground rods.

• Route shielded control and power cables to separate ground points before connecting to the main electrical ground.

3. Shielding the Interference Source

• Converter Housing: Use an iron enclosure to contain EMI.

• Output Cables: Shield with steel conduits.

• Signal Cables:

• Use shielded twisted pairs (STP) for control signals (e.g., 4–20mA).

• Keep signal lines short (≤20m) and physically separate from power lines (AC380V/AC220V).

• Never run signal and power lines in the same conduit or duct.

4. Optimized Cable Routing

• Keep power/signal lines far from converter I/O cables.

• Avoid parallel routing of other equipment cables with converter lines.

If Interference Persists, Apply These Additional Measures:

5. Interference Isolation

• Use isolation transformers between power supplies and sensitive devices (controllers, transmitters).

• Noise isolation transformers block conducted interference.

6. Installing Filters

Filters suppress interference propagation via power lines.

Types of Filters:

• (1) Input Filters

• Line Filter (Inductive): Blocks high-frequency harmonics.

• Radiated Filter (Capacitive): Absorbs high-frequency noise.

• (2) Output Filters (Inductive)

• Never connect capacitors directly to the inverter output (risk of damaging IGBTs).

• In LC filters, connect the capacitor side to the motor.

• Reduces motor harmonic currents and torque ripple.

• Critical Notes:

7. Installing Reactors

Suppresses low-frequency harmonics (5th, 7th, 11th, 13th) that degrade power factor.

Types of Reactors:

• (1) AC Reactor (Input Side)

• Improves power factor (0.75–0.85).

• Protects against inrush current and voltage imbalance.

• (2) DC Reactor (DC Link)

• More effective for power factor correction (up to 0.95).

• Compact and lightweight.

Interference Case Studies

1. External Device Interference

• Symptom: Motor occasionally fails to stop despite proper shielding and filter use.

• Root Cause: Strong magnetic fields from nearby high-current power distribution cabinets.

• Solution: Relocate the converter cabinet away from the power room.

2. Converter-Induced Interference

• Symptom: Motor does not start; 4–20mA signal shows 0Hz.

• Root Cause: Signal interference from the converter.

• Solution: Add a 102 capacitor at the transmitter output to filter noise.

Summary of Best Practices

✔ Input/Output Filters & Reactors
✔ Proper Shielding & Grounding
✔ Isolation & Cable Separation
✔ Carrier Frequency Optimization

For persistent issues, consult Nanjing Oulu’s 24/7 Technical Support: +86 159-5163-6558.