How to Build a Variable Frequency Drive for a Three-Phase Motor?

Posted by Mike Collan on March 10th, 2018

The VFD or the Variable Frequency Drive can control the speed of the 3-phase motor. The VFD can increase the efficiency and performance of the motor and provide for energy bill cost reduction. The drive, when applied and installed, reduces the jerks that occur when the motor is started. VFD panels provide easy control of the drive.

Built of the VFD

The VFD controls the AC or alternating current rotational speed, as it can control the frequency at which electric power is supplied to the motor. The 3 basic components of the VFD are the rectifier, DC bus, and inverter.

The electric current that reaches the industries is in the form of AC or alternating current, as the current is transferred to large distances. The rectifier of the motor converts the AC current to DC or direct current. 3 pairs of rectifier combinations are employed for converting the 3 phase alternating current into the DC output. The BUS or the DC BUS contains the capacitors that can store power received from the rectifier and then deliver it to the inverter. The final section of the VFD contains the transistors that deliver the power finally to the motor. Modern VFD uses the IGBT or the Insulated Gate Bipolar Transistor, which can switch itself “on” and “off” multiple thousand times in a second and can control the power delivered to the motor precisely.

VFD features

The features of VFD include: 

• Speed search
• Auto restart
• Torque protection
• Digital or analog protection

Low cost

The cost and the size of the modern semiconductors have reduced, and hence a user can replace the mechanical drive with the VFD at low costs. As all operations do not require the same motor, the VFD helps in reduction of energy consumption and motor wear. Installation of the VFD also provides for the gradual starting of the motor, which reduces the spikes.

Controlling the VF

The supply frequency can be controlled to vary induction motor’s speed. The supply frequency and the applied voltage are directly proportional to the final torque that the motor develops.

Application of the VFD

VFD is used across industries. Some of the most common uses of the VFD are towards:

• Fans, pumps, petrochemicals, well pump and oil field recovery among others
• HVAC pumps and fans
• Metals and mining: cooling beds, reheat furnaces, run out/in tables
• Conveyors for handling materials, hoists, cranes, the small vehicles drives etc.

The concept of VFD is very important towards saving of energy. All machines and processes that can be optimized and improved by varying the speed of the current can use VFD. VFD offers other advantages as well and these include smooth acceleration, better process control, reduction in problems relating to the power supply, reduction of motor stress and heating and many others. You can also buy and install the variable frequency drive panel and control the operations in a convenient way.