VFD Wiring Diagram with Motor, Switches, and External Devices

Hey, in this article we are going to see the wiring diagram of VFD or Variable Frequency Drive and its connection with the Motor, External Switches, and External Devices such as HMI, PLC, Computer, etc. VFDs are mainly used to operate three-phase induction motors with variable speeds by varying the frequency.

We know that when we vary the frequency of the applied power supply to the induction motor, the speed of the motor also varies. It is the easiest and most economical way to vary the speed of an induction motor.

VFD or Variable Frequency Drive is built with power semiconductor devices such as SCR, IGBT, etc. Basically, the VFD first converts the input AC supply into a controlled or uncontrolled DC supply. Again it converts the DC supply into a Controlled AC supply where we can change the frequency and other parameters as per our requirement.

A practical VFD unit has different terminals and ports for its connection. It also has a user panel including a display, keypad, and switches for operating.

Anyway, first of all, let's see the wiring diagram so we can further discuss about its connection in detail.

Wiring Diagram

There are two types of VFD available in the market - 1. Single Phase to Three Phase VFD and 2. Three Phase to Three Phase VFD. Here, we have shown the connection diagram of the Three Phase to Three Phase VFD. The connection of Single Phase to Three Phase VFD is also the same just you need to connect a single-phase supply instead of a three-phase supply at the input.

Connection Procedure

Before making the connection terminal identification is very important. So, read the manual given by the manufacturer and identify all the terminals properly and their functions.

In the above wiring diagram, we have shown a few terminals that are most important but your VFD may have more additional terminals.

Power Connection

Here, we have shown a three-phase to three-phase VFD. So, all three phases(R, Y, B) are to be connected to the power input terminals of the VFD. Here, a neutral connection is not required. For safety purposes, a circuit breaker can be connected to the input side of the VFD.

Motor Connection

Find out the power output terminals of the VFD and connect them with the Motor Terminals with proper R, Y, and B connections. If you interchange phases the motor will rotate in the wrong direction.

**Power Connection and Motor Connection is enough to run a motor with the VFD. We can set parameters on the VFD as per our requirement**

Now, the control terminals of the VFD can be used for additional features such as remote controlling, automation, data collection, etc. So, let's know the VFD control terminal connection and its function.

Some VFDs operate in PNP mode, some in NPN mode, and some have both features. When the VFD operates in NPN mode we need an external DC supply(generally 24V DC) for control operation. But if the VFD operates mode, we do not need any external power supply as the VFD provides output DC supply itself.

The VFD shown in the above wiring diagram operates in the NPN mode which is why we used a 24V external DC supply from an SMPS.

Start/Stop Operation

An external switch can be used to start or stop the motor. Here we have a DI1 terminal for this function. When we apply the 24V supply the motor will start running and when we remove the supply the motor will stop. And it can be done by connecting a NO switch between the 24V power supply and the DI1 terminal.

Forward/Reverse Rotation

VFD also has Digital Input terminals to change the rotation of the motor. Here, D2 is for Forward Rotation and D3 is for reverse rotation.

Frequency/Speed Varying

Some VFDs have digital inputs and some VFDs have analog inputs for varying speeds or frequencies. The digital input can be provided by a switch or other external devices such as PLC. Digital input gives very limited settings values to set the speed or frequency whereas using analog input any values can be set. The analog input can be given by a potentiometer or PLC. Here, in the above wiring diagram, we have two terminals GND-AI and AI1 that can be connected to PLC.

VFD Status

The analog output terminal of the VFD can be used to share the VFD running status with the PLC.

VFD Connection With External Device

VFD can be connected with the PLC using terminal connections such as Analog Input/Output and Digital Input/Output terminals. Even, VFD can be connected with PLC using RS485 or RJ45 connector for serial communication.

VFD Can be connected with HMI(Human Machine Interface) using an RS485 connector.

VFD can be connected to the PC/Laptop/Computer using an RJ45 or RS485 connector.

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