Project 2 - Modeling of 3 phase Induction Motor Drive
- 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
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
- For Induction Motor model – use Asynchronous Machine from Simulink with Squirrel Cage Preset Model – 05 , for 100HP Motor
- For back emf to speed relation, assume a linear rate from 0.25 to 1, with speed changing from 500 RPM to 2000 RPM
- Plot speed, stator voltage (line to line) and frequency.
- Plot stator line voltage, phase current.
- The simulink model is shown below :-
- All the parameter blocks are shown below :-
- 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.
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
- The simulink model is shown below :-
- Induction motor block :-
- Parameters script matlab :-
- with the above parameters the simulink model is run and output results are shown below :-
- Summary :-
- DTC :-
- Electrical model :-
- The electrical energy is supplied by a three-phase AC/DC diode rectifier connected to a 460 V, 60 Hz grid equivalent. The DC bus is connected to a three-phase, two-level converter. This converter generates the variable voltage and frequency required for variable-speed operation of the 150 HP induction motor. In addition, a braking chopper is connected to the DC bus in order to dissipate the kinetic energy of the motor during deceleration.
- An inverter-fed induction motor drive can be controlled through various techniques depending on application, desired performance, and controller design complexity. Commonly used schemes are scalar control (V/Hz control or open loop flux control) or vector control (field-oriented control or direct torque control). This example uses a hysteresis-based direct torque control (DTC) technique.
- Direct Torque controller :-
- Direct torque control (DTC) is a technique that allows you to instantaneously control the motor magnetic flux and its electromagnetic torque in a decoupled way. Controlling the torque directly permits accurate static and dynamic speed regulation. The main components of the DTC subsystem are:
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Flux and Torque Calculation — The stator flux linkage is estimated by integrating the stator voltages, and torque is calculated based on the estimated flux and the motor currents.
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Speed Regulator — The regulator compares the actual motor speed with the speed reference and generates the torque reference.
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Hysteresis Control — The calculated flux magnitude and torque are compared with the reference values. When the resulting flux or torque error crosses either the positive or negative hysteresis band value, a control signal is activated in order to correct the error.
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Optimal Switching — Pulses to the motor inverter are produced based on the control signals generated by the hysteresis control and the stator flux linkage position.
- The figure below illustrates the strategy used to determine the best voltage vector when the flux linkage is located in sector 0.
- The image shows four cases:
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V3 is selected when the electromagnetic torque should be increased and the flux should stay unchanged. Selecting the V3 voltage vector speeds up the flux and thus applies an acceleration torque to the rotor while slightly decreasing the flux magnitude.
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V2 is selected when the electromagnetic torque should be increased and the flux should be increased. Selecting the V2 voltage vector slightly speeds up the flux and increases its magnitude.
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V6 is selected when the electromagnetic torque should be reduced and the flux should be increased. Selecting the V6 voltage vector slows down the flux and thus applies a deceleration torque to the rotor while increasing the flux magnitude.
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V5 is selected when the electromagnetic torque should be reduced and the flux should stay unchanged. Selecting V5 the voltage vector applies a deceleration torque to the rotor and slightly decreases the flux magnitude. Note that voltage vectors V1 and V4 are not selected in sector 0. Using these two vectors would have too much negative impact on the desired flux value. Finally, to keep the torque and the flux unchanged, the null voltage vectors V0 or V7 are selected.
- When the flux linkage vector moves to sector 1, the selected voltage vectors become V4 for case 1, V3 for case 2, V1 for case 3, and V6 for case 4, and vectors V2 and V5 are not used. This 60 degree shift in the voltage vectors happens each time the flux linkage vector enters a new sector.