Variable frequency variable voltage VVVF

Variable frequency variable voltage VVVF

Introduction :- The motor used in any machine need to be operate at variable speed.Earlier DC motor was used for applicatios where speed control is requred. The speed of ac motor is considered as fixed speed because the speed is depend upon number of pole and frquency of supply. But now a day with invent of VVVF drive it becomes easy to control speed of motor by producing variable voltage variable frequency supply for motor.
Working:-

In VVVF drive three phase voltage is converted in to dc voltage generally 500  v dc. Then three phase inverter circuit is used to produce 3 phase ac supply of  varable frequency and variable voltage. Voltage to frequency ratio remains constant.It uses digital control system for firing control of IGBT and inverter parameter setting. All the data of motor (such as voltage current rpm)  and operational requirements are  stored in parameters of drive.  VVVF drive has a display and key pad which are used for parameter setting. During running of motor running data load current and fault candition is also displayed on display. Drive key pad has buttons for start stop local remote forward reverse etc. In addition to this external push buttons can also be connected in control terminal block for start stop speed increase decrease etc. drive has three power terminal nuetral terminal and earth terminal for input connection. similarly three power terminal and one earth terminal for motor connection.

different makes of drive has some difference in control terminal block connection but basically all are same. With the help of instruction manual given with drive and following all instructions care fully it is easy to use VVVF drive for speed control of ac motor application. please see my blog for more articles. your comment and suggestions are welcome.