VFD: Operation

During start - Normal start

During a normal start the VFD will start and operate at given frequency in open loop mode, or operate in
closed loop mode according to parameter settings.

During start - Soft start

Upon start, the VFD will softly start and accelerate to the frequency of power grid regardless of the given frequency. When the output frequency of VFD reaches the power grid frequency (set at installation), then the output of the VFD will become zero. At the same time VFD sends a ‘transfer to power grid' command. This command transfers the power supply of the motor from VFD to the power grid. During the transient transfer, there is a big inrush current. For synchronous operation (requires optional transfer reactor) the VFD and power grid will supply the motor during the transient transfer, creating a small inrush current.

During Operation - Closed loop

In closed loop mode, the VFD will automatically adjust the output frequency to operate at the set parameter value e.g. pressure or temperature.

During operation - Open loop

In open loop mode, the VFD will operate at the given frequency. This frequency can be set via controller, external analog signal, or serial communications module.

During operation - Automatic scheduling

The user can program the VFD to automatically perform a series of tasks set by the parameters for each scheduled time.

During operation - Operation log

Operation logs are automatically recorded. Every operation includes a time/date-stamp.

During operation - Motor protection

The user can modify the default settings of overload and underload protection settings.


The VFD has several monitoring options for comprehensive understanding of the performance of the VFD and associated equipment:

  • Waveform display (optional). By sampling the input/output current/voltage, the VFD will show the waveform and calculate the power factor and input/output power.
  • Easy-to-use, touch screen HMI controls: Output frequency, voltage, current, power; input voltage, current, power, power factor; failure/alarm; log; parameter setup; waveform display, etc.
  • Local or remote control via friendly touch screen interface and buttons. Remote control via PC (optional) or GPRS (optional). With remote control the user can start, stop, emergency stop, reset, set the frequency parameter and read logs. The user can also monitor all the key operating parameters of VFD via computer, i.e. current, voltage, frequency, and reset values of controlled parameters and alarms. One computer can monitor 32 VFDs at once.