The "automatic frequency hopping" (or frequency skip) function of a Variable Frequency Drive (VFD) is designed to resolve mechanical resonance issues that occur when equipment operates at specific frequencies.

When the VFD outputs a frequency that matches the natural frequency of the motor or mechanical equipment (such as fans, pumps, or drive shafts), it triggers intense vibration and noise. This not only compromises equipment precision but can also lead to mechanical component damage during prolonged operation. This function allows the VFD to "skip" the problematic frequency points, ensuring smooth operation.

This manifests in the following four ways:

1. Core Function: Eliminating Mechanical Resonance (Hardware Protection)

This is the primary function. All rotating machinery (such as fans, water pumps, and conveyor belts) has a natural resonant frequency. When the VFD operates at this frequency, the equipment shakes violently.

Direct Effect: By "skipping" the resonance point, it prevents fatigue fractures or bearing damage in motor shafts, couplings, pump casings, or fan impellers caused by prolonged resonance.

Typical Case: A centrifugal fan in a workshop emitted a piercing screech and caused the ductwork to shake violently at 28 Hz; after setting a skip frequency range (avoiding 26–30 Hz), vibration levels dropped by over 60% instantly.

2. Indirect Function: Reducing Noise Pollution (Environmental Improvement)

Resonance not only damages equipment but also generates high-decibel mechanical and electromagnetic noise.

Direct Effect: Skipping this frequency band results in a smoother, lower-pitched operating sound, effectively improving the noise environment for the factory or nearby residential areas.

Note: This addresses noise caused by the mechanical structure, not the noise associated with the VFD's carrier frequency.

3. Function in Special Scenarios: Ensuring Process Continuity (Avoiding Downtime)

In continuous production lines where mid-process shutdowns are not permitted (such as in textile or paper manufacturing), if the VFD operates at the resonant frequency point, violent vibrations could trigger overload protection or mechanical limit switches, causing a system trip.

Direct Effect: The frequency hopping function ensures the VFD does not dwell in the resonance zone while passing through it, thereby maintaining production line continuity and preventing raw material waste caused by shutdowns.

4. Protecting the VFD itself (preventing overcurrent)

During resonance, the motor load fluctuates drastically, causing severe current pulsation; this can easily lead to overheating of the VFD module (IGBT) or trigger an "overcurrent" fault.

Direct benefit: By avoiding the resonance zone, the current waveform stabilizes, effectively reducing the VFD's temperature rise and failure rate.

To ensure accurate usage, two points need clarification:

1.It does not solve "unstable frequency commands": If the command signal itself is fluctuating (e.g., due to interference on a potentiometer), causing the output frequency to rise and fall erratically, the "skip frequency" function cannot fix this. That is an issue with analog signal interference, requiring checks on shielded cabling or filtering.

2. It does not affect the acceleration/deceleration process: As previously mentioned, during acceleration or deceleration, the frequency passes rapidly through the skip range without getting stuck. The "skip" action only triggers when the target operating frequency falls within that range.

Practical advice (determining skip values)

If you have identified the resonance frequency point (e.g., 25 Hz), the following settings are recommended:

Skip frequency point: Set to 25 Hz.

Skip amplitude (range): Typically set to ±2 to ±3 Hz (i.e., 22–28 Hz or 23–27 Hz). Setting the range too narrow may fail to fully eliminate resonance; setting it too wide may result in excessive "speed loss," impacting production efficiency and torque output (since a portion of the usable frequency band is skipped).