Project 2 - Modeling of 3 phase Induction Motor Drive
1.Model 3 Phase Inverter using Simulink (model the parasitic as well) with a switching frequency of 10Khz using 3 phase Squirrel Cage
Induction motor, using V/F method, open loop - :
- Given - :
- Design Parameters - :
Power = 100 HP
DC Voltage = 800 V
Output Voltage = 460 VRMS – line to line
Initial Speed = 1500 RPM
Final Speed = 1000 RPM
Initial Load Torque = 10 Nm
Final Torque=20 Nm
Torque Step Time = 0.1 secs
- The simulink model is shown below - :
- V/f control is a method to control a ratio between primary voltage (V) to be applied to the induction motor and inverter output frequency (f)
to be constant. This control enables to obtain satisfactory torque characteristics in a wide frequency range by maintaining the magnitude of
the rotating magnetic field vector independently from the inverter output frequency when voltage drop due to a primary winding resistance is
ignored.
- However, as the frequency declines, the voltage drop due to the primary winding resistance becoming too large to be ignored, and
consequently, it becomes impossible to obtain sufficient torque. In such a case, applying a higher voltage than the voltage calculated from
the V/f ratio which was used for a high frequency makes it possible to secure enough torque even at a low frequency.
- 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
f is frequency.
- Now, synchronous speed varies as frequency is changed, but when frequency is decreased, flux increases. This change in flux value results
in saturation of the rotor and stator cores, which further raises the motor's no-load current. Hence, maintaining flux at a consistent value is
crucial, and doing so requires changing the voltage. In other words, if we lower the frequency, the flux will increase, but if we lower the
voltage, the flux will drop as well, creating no change in flux and keeping it constant. Hence, we are maintaining a constant V/f ratio here. As
a result, it is called the V/f approach.
- With the above parameters the simulink is run for a stop time of 0.6 seconds and the output results are shown below - :
2. Use the 3 phase inductor motor theory to derive the 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.
- Given - :
- Design Parameters - :
Initial Speed = 0 RPM
Flux Target = 2.5 webers
DC Voltage = 500 V;
Fundamental Frequency = 60 Hz
Speed Step Time = 0.01 secs
Determine fundamental speed based upon fundamental frequency
Determine the switching sequence for direct torque control
Moment of Inertia = 0.1 Kgm^2
Load Torque Initial = 0 Nm
Final Load Torque = 50 Nm
Torque Step Time = 0.03 secs
- Motor Parameters: (Create an Average Model) - :
Stator Resistance = 0.5 Ohms
Rotor Resistance = 0.2 Ohms
Stator Leakage Inductance = 20 mH
Rotor Leakage Inductance = 10 mH
Magnetizing Inductance = 200 mH
Number of Poles = 4
Torque to Speed
- I have modeled a 3 phase induction motor with a 3 phase inverter using Direct Torque control using MATLAB And Simulink - :
- The three-phase voltage source is fed to the diode rectifier to convert 3 phase to a DC Voltage Source.
- Three-phase two-level inverter is connected to the dc voltage source and then connected to the induction motor.
- The DC source is charged from the grid equivalent and then discharged by the 3 phase inverter.
- To achieve this, a breaking chopper is added.
- Vabc is ranged at approximately -420 to 420V.
- Iabc is approximately -400 to 400 A.
- Vdc is set at 500V.
- The power is 80Kw as shown in the graph.
- Above plots represents speed, torque, Phi value and Current in the Motor respectively.
- From the plot, we can observe the flux and torque and the speed of the induction motor is controlled.
- Conclusion - :
- The Three Phase induction motor Drive is modeled and controlled using both the V/F control method and the Direct Torque Control Method
and also the Transfer Function of the Induction motor based on the Equivalent Circuit is determined.