V/F control of the Induction Machine Using MATLAB

 To study the V/F control of the Induction Machine

Software Used: MATLAB R2018a

Theory:

V/F is abbreviated from voltage/frequency. V/F control is an induction motor control method which ensures the output voltage proportional with the frequency, so it maintains a constant motor flux, preventing weak magnetic and magnetic saturation phenomenon from happening.

V/F control principle is to produce a circuit called voltage-controller oscillator with oscillator frequency. It is a voltage-dependent capacitance when subjected to a change in voltage, its capacity will change, and then the change in capacity will cause changes in the oscillation frequency, resulting in variable frequency. This controlled frequency is used to control the frequency of the output voltage, in order to achieve speed changes of the controlled electric motors.

 

Simulated Diagram:

V/F CONTROL WITH CLOSED LOOP:

Fig 1: V/F Closed Loop Final Simulated Diagram

Fig 2: Closed-Loop Logic Implementation Simulated Diagram

 

Fig 3: Dynamic Model of Inverter

Function Block:

function [Van,Vbn,Vcn] = fcn(s1,s3,s5,Vdc)

Van=Vdc*(2*s1-s3-s5);

Vbn=Vdc*(-s1+2*s3-s5);

Vcn=Vdc*(-s1-s3+2*s5)

 

Fig 4: Induction machine Dynamic Model

 

Fig 5: Induction machine Output Torque

 

Fig 6: Induction machine Speed

 

V/F OPEN LOOP

Fig 7: V/F Open Loop Final Simulated Diagram

Fig 8: Dynamic Model of Inverter

Function Block:

function [Van,Vbn,Vcn] = fcn(s1,s3,s5,Vdc)

Van=Vdc*(2*s1-s3-s5);

Vbn=Vdc*(-s1+2*s3-s5);

Vcn=Vdc*(-s1-s3+2*s5)

Fig 9: Induction machine Dynamic Model

 

Fig 10: Induction machine Output Torque

Fig 11: Induction machine Speed

Observations:

1.    The torque in transient condition rises to high value and in 0.2 sec it comes to steady-state i.e zero.

2.    Speed rises slowly and when the torque becomes zero, the speed reaches to 1500 rpm.

3.    In closed-loop we compare the reference speed which is converted to frequency and that to w and ma which makes the calculation easy and output stable and does not change with change in any circuit conditions.

Conclusion:

Hence the open-loop and closed-loop V/F control of the induction machine is studied with the dynamic model and the waveforms are also plotted.