Project 2 - Modeling of 3 phase Induction Motor Drive

• V / f Control or Frequency Control

  Whenever three phase supply is given to three phases induction motor, rotating magnetic field is produced which rotates at a synchronous speed given by
  
  In three phase induction motor, emf is induced by induction similar to that of a transformer which is given by
  
  Where K is the winding constant, T is the number of turns per phase, and f is frequency. Now if we change frequency synchronous speed changes but with a decrease in frequency flux will increase and this change in the value of flux causes saturation of rotor and stator cores which will further cause an increase in the no-load current of the motor. So, it's important to maintain flux, φ constant and it is only possible if we change voltage. i.e if we decrease frequency flux increases but at the same time if we decrease voltage flux will also decrease causing no change in flux and hence it remains constant. So, here we are keeping the ratio of V/f constant. Hence its name is the V/ f method. For controlling the speed of three phase induction motor by the V/f method we have to supply variable voltage and frequency which is easily obtained by using a converter and inverter set.

  
• 
• 

2. Transfer Function of 3 phase Induction Motor

3. Model 3 phase induction motor with a 3 phase inverter using Direct Torque control using an Average Model, Implement both torque and flux control to achieve desired power.

Design Parameters:

1. Initial Speed = 0 RPM
2. Flux Target = 0.5 webers
3. DC Voltage = 500 V;
4. Fundamental Frequency = 60 Hz
5. Speed Step Time = 0.01 secs
6. Determine fundamental speed based upon fundamental frequency
7. Determine the switching sequence for direct torque control
8. Moment of Inertia = 0.1 Kgm^2
9. Load Torque Initial = 0 Nm
10. Final Load Torque = 50 Nm
11. Torque Step Time = 0.03 secs

Motor Parameters: (Create an Average Model)

1. Stator Resistance = 0.5 Ohms
2. Rotor Resistance = 0.2 Ohms
3. Stator Leakage Inductance = 20 mH
4. Rotor Leakage Inductance = 10 mH
5. Magnetizing Inductance = 200 mH
6. Number of Poles = 4

Simulation results:

The speed and the tprque waveforms. Speed is around 1400 rpm

Reference speed and actual speed and the second waveform is the that of Flux

Gating pulses to the VSI.