Question

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Answer 1

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The basis of constant V/F speed control of induction motor is to apply a variable magnitude and variable frequency voltage to the motor. Both the voltage source inverter and current source inverters are used in adjustable speed ac drives. The following block diagram shows the closed loop V/F control using a VSII. A feedback is used to obtain the actual speed of the motor. It is then compared to a reference speed the motor is fed with variable frequency signals generated by the PWM control from an inverter. the V/f ratio is maintained constant in orderto get constant torque overthe entire operating range. Since only magnitudes of the input variables frequency and voltage are controlled, this is wwwww wwwws known as scalar control Generally, the drives with such a control are without any feedback devices (open-loop control) Hence, a control of this type offers low cost and is an easy to implement solution In such controls, very little knowledge of the motor is required forfrequency control. Thus, this controlis widely used

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