DRIVE A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, micro drives or inverter drives. Since the voltage is varied along with frequency, these are sometimes also called VVVF (variable voltage variable frequency) drives. Variable-frequency drives are widely used. For example, in ventilations systems for large buildings, variable-frequency motors on fans save energy by allowing the volume of air moved to match the system demand. Variable frequency drives are also used on pumps, conveyor and machine tool drives.

Power flex 4M drive

Variable frequency drive controllers are solid state electronic power conversion devices. The usual design first converts AC input power to DC intermediate power using a rectifier bridge. The DC intermediate power is then converted to quasi-sinusoidal AC power using an inverter switching circuit. The rectifier is usually a three-phase diode bridge, but controlled rectifier circuits are also used. Since incoming power is converted to DC, many units will accept single-phase as well as three-phase input power (acting as a phase converter as well as a speed controller); however the unit must be de-rated when using single phase input as only part of the rectifier bridge is carrying the connected load

Flux should remain constant in order to produce full load torque which is achieved by maintaining a constant magnetic flux in the motor. This method of magnetic flux control is called the volts-per-hertz ratio. With this method, the frequency and voltage must increase in the same proportion to maintain good torque production at the motor.  For example, if the frequency is 60 Hz and the voltage is 460 V, then the volts per Hertz ratio(460 divided by 60) would be 7.6 V/Hz. So, at half speed on a 460 V supplied system, the frequency would be 30 Hertz and the voltage applied to the motor would be 230 V and the ratio would still be maintained at 7.6 V/Hz.  This ratio pattern saves energy going to the motor, but it is also very critical to performance. The variable-frequency drive tries to maintain this ratio because if the ratio increases or decreases as motor speed changes, motor current can become unstable and torque can diminish. On the other hand, excessive current could damage or destroy the motor.   In a PWM drive the voltage change required to maintain a constant Volts-per-Hertz ratio as the frequency is changed is controlled by increasing or decreasing the widths of the pulses created by the inverter. And, a PWM drive can develop rated torque in the range of about 0.5 Hz and up. Multiple motors can be operated within the amperage rating of the drive (All motors will operate at the same frequency). This can be an advantage because all of the motors will change speed together and the control will be greater.  

Catalog no. explanation

Drive connection

Installation connection

Program for speed control

For speed control we have to given three input, one is for forward run, one for reverse run & one for speed control. The forward run & reverse run are of digital type while speed control in analog type that is 0 – 10 V or by current control from 0 to 10 mA. The program is shown below.

SCADA Coding

Proximately sensor

Allen-Bradley proximity sensors set the standard for ruggedness, reliability and application flexibility. Choose from one of the industry’s widest selections of inductive, capacitive and ultrasonic proximity sensor models, all of which offer you no-touch object detection

The most commonly-used proximity sensor is the inductive type, which generates an electromagnetic field to sense metal objects passing close to its face. This is usually the easiest sensing technology to apply in applications where the metal object to be detected is within an inch or two of the sensor face. The diverse Allen-Bradley offering serves the full spectrum of customer needs, from light-duty packaging applications to the punishing environments on automotive welding equipment or the harsh wash downs in food processing plants.

Proximately sensor

Program me relative to sensorWAP to measure speed of motor by proximity sensor

For this connect a metallic arc (of iron) with the shaft of motor & place a sensor near it. The programme is shown below.