VFD is the acronym of variable frequency drive which is used in the industry to control electric motor, fan, pump and blower.

Benefits of VFD

  1. It helps to vary motor speed to match process requirements.
  2. To reduce motor starting current.
  3. To break the motor in accordance.
  4. To protect the device against overload, under lower voltage and phase loss.
  5. It helps to start motor softly in other to eliminate mechanical, electrical, transient and hydraulic surges.
  6. It helps to consume less energy.

Power flex of VFD

  1. AT1 single phase to three phase
  2. AT2 single phase to single phase
  3. AT3 single phase to three phase
  4. AT4 three phase to three phase

Features of single phase to three

The single phase to three phase has six ports labelled L N W V U where: L and N is for single phase AC with 220V input which serves as the input terminal. W V U is the output terminal connect to three phase (220v-AT1)(380V-AT4)AC motor and the GND which is the grounding terminal.

          Features of single phase to single phase

The single phase to single phase also has six 6 connection ports such as GND, L,N,W,V and U.
Here, the terminal label L and N is single phase AC 220v input terminal and W and V is the 220v main coil which is the output connection to the single phase AC motor and the U is the secondary coil and GND which serves as the grounding terminal.

       Features of three phase to three phase
The three phase to three phase has six ports such as R, S, T for the input and W V U for the output. The R S T serves as the three phase AC 380v input as terminal and W V U as the output terminal connected to the three phase 380v AC motor and also GND for grounding terminal.


They are four basically parts in Variable frequency drive which are as follows with it’s function in the circuit.

  1. Utility power AC
  2. Rectifier
  3. DC Bus
  4. Inverter.

The power supply is the port that enable or give access for current and voltage to enter the circuit.

The rectifier is the part that houses diode or SRC which helps to convert AC to DC.

The DC Bus is made up of capacitor bank whose work is to filter the pulsating DC coming from the source to the rectifier to a pure DC and then transfer it to the inverter.

The inverter is the part that perform the major work in the VFD whose work is to convert the DC back to AC which is required by the motor. The inverter section also give room for variation of frequency and voltage and it Carry’s out this conversation mode with the help of IGBT ( INSULATED GATE BIPOLAR TRANSISTOR) and it also embedded with micro controller which helps to communicate with the PLC and other forms of command.


The terminal description are the port in the VFD which shows where to connect your input and output in the VFD and they are as follows with they function and instructions.

  1. Port (15v /24v or 12v/5v) is for power output port which uses (200MA/5v/24v or 12v/5v) output.
  2. Port X1 is for (section speed 1) whose instruction is to input signal effectively.
  3. Port X 2 is for (section speed 2) whose instructions is to input signal effectively.
  4. Port X3 is for (section speed 3) whose instructions is to input signal effectively.
  5. Port X4 is for (forward rotation control switch) whose instructions is to input signal effectively.
  6. Port X5 is for (reverse rotation control switch) whose instructions is to input signal effectively with com.
  7. Port X6 is for (reversing switch) whose instructions is to input signal effectively with com.
  8. Port 485+/485- is for communication port
  9. Com is for common GND
  10. Vl1 is for external analog voltage input whose voltage range is from 0-5v/10v for analog voltage input.
  11. C1 is for external current signal input whose current range is from 4-20MA for input current.
  12. SP1 is for open collector output 1
  13. SP2 is for open collector output 2.
    5v/10v is for 5v/10v power output whose instructions is to supply 5v/10v and 20MA power output.
  14. TC is for Relay output C
  15. TB is for Relay output B
  16. TA is for Relay output A.
    Note: TA and TB are normally close while TA and TC are normally open with the voltage and current range respectively: 250vac, 5A/30vdc, 3A.
    We also have multi speed input frequency control table that will come with the manufacturer specification which are the speed section that ranges from section speed 1 to 10, it is here that your can select or varies your frequency to it original settings that the output device or components can carry.

Operational panel is the section that has the various port or button used to set or write your program in the VFD and they are 10 main keys in the operation panel such as:

Speed adjustment knob which is used to control the speed of the motor or the frequency that the motor can or will operate.

Reversing/forwarding switch is used to determine how the process or movement of the motor will be.

Run is the start button that helps to start up the process or motor.

Stop or Reset key is the key that helps to stop or Reset the motor.

Function/data/save key helps you to enter your program and data and also save before running the program.
Numerical display is used or it helps you to see the sequence that you are writing.
Shift key helps you to go back and complete your program and as well can also serve as enter button.

Enter or exit program is the key that helps you to bring out the program mode you want to write.

The two arrows helps you to input your program or change your program.

Status indicators are those LED that shows if the program or the system is ON or in a process.
Note: F means frequency setting
H means operating frequency
A means operating current
R/min Revolution per minute.
Program specification: program specification will be given by the manufacturer, which will serve as a guide for you to input all your program that you want your output to exhibit, and they are 127 program that the VFD for perform or work on.
Note: when working on VFD always not when it’s sinking or sourcing so that your output will respond to your input as required by the operator. And not all VFD has the TA, TB and TC which are the port and majorly the analog input.


Note: when working on a ready program VFD, and you want to reset the program, you then need to select P77 and reset the program from 65535 to 54321(which is the factory default).

Question: what is jog?
Answer: Jog is the state in VFD that enables the motor to run at steady gentle pace, which may be required in some factory like bread etc.
Questions: what is my line voltage?
Answers: some common ratings are:

  1. 120v, 1 phase
  2. 200-230v, 1 phase
  3. 200-230v, 3 phase
  4. 380-400v, 3 phase
  5. 500-600v, 3 phase.

Questions: what the motor voltage?
Answers: some common ratings are:

  1. 200-230v, 3 phase
  2. 380-400v, 3 phase
  3. 500-600v, 3 phase.
    Note: if the line voltage is 1 phase, the drive output will be 3 phase.
    Questions: what is my horse power?
    Answers: we have three phase 1/4 horse power(hp) to 80,000 hp.

Questions: Are communication options needed?
Answers: yes, these are some communication networks:

  1. Control Net
  2. Device Net
  3. Ether Net IP
  4. Profibus
  5. modbus and P1.
    Note: Additional option may be needed especially when drives are communicating on a network.
    Questions: why are we using drives?
    Answers: some important information about it.
  6. Process improvement
  7. To reduce the energy wastage.
  8. To increase reliability
  9. To extend the life spam of the system.

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