Three Phase Induction Motor Dynamic Modeling and Behavior Estimation

Lauren Atwell

1

, Jing Wang

2

, and Leon M. Tolbert

2

Auburn University

1

, University of Tennessee

2

Introduction

• Induction motors are widely used for industrial applications because they are reliable, rugged, and very efficient.

• Rotor speed and torque characteristics of induction motors are usually controlled by a motor drive for smoother transitions, more accurate behavior, and stable operations.

• While testing power electronics motor drives, an induction motor “dyno set” requires a mechanical load for different operating points, meaning it requires not only the motor to be tested, but also a second motor mechanically coupled to the first. These two motors have a large footprint in a lab, and also do not allow for variations in motor parameters.

• Induction motor dynamic modeling will allow for much more flexible testing of motor drives.

Research Goals

• Mathematically model a three-phase squirrel-cage induction motor.

• Verify model with MATLAB Simulink’s inherent integrated induction motor model.

• Test by simulating various loads to verify correct functionality of mathematical model.

Methodology

Figure 1 shows the implementation of the induction motor model from Simulink library driven by the inverter bridge output with motor rated voltage and frequency.

Results

T L

= 0.5

Fig. 3. Torque of all three models (mathematical ideal, mathematical with PWM inverter, and MATLAB), with increased torque load at t = 0.5 seconds.

T L

= 0.5

Fig. 4. Rotor speed of all three models (mathematical ideal, mathematical with PWM inverter, and MATLAB) with increased torque load at t = 0.5 seconds.

Fig. 5. dq-axis stator voltage of MATLAB model.

Fig. 6. dq-axis stator voltage of mathematical model.

T L

= 0.5

Fig. 7. Three phase AC current of mathematical model with increased torque load at t = 0.5 seconds.

T L

= 0.5

Fig. 1. MATLAB Simulink inherent integrated induction motor model.

The mathematical model of an induction motor is split into several sub-models, including: electrical and mechanical systems expressed within dq0 domain. This realization in Simulink is shown in Figure 2. The model was tested first under ideal voltage conditions, and then powered by a PWM inverter. Both results were then compared to the MATLAB model.

Fig. 8. dq-axis current of mathematical model with increased torque load at t = 0.5 seconds.

Conclusions

Behaviors of the built induction motor have been verified for torque and rotor speed characteristics, regardless of supply (ideal constant supply versus PWM inverter).

However, the built mathematical model allows for flexible voltage filtering resulting in more accurate inputs for the motor model. It produces much more steady dq axis voltage inputs in the per-unit system, as evidenced by the results comparison between Figures 5 and 6.

Fig. 2. Mathematical model of a three phase squirrel-cage induction motor .

This work was supported primarily by the Engineering Research Center Program of the National Science Foundation and the Department of Energy under NSF Award Number EEC-1041877 and the CURENT Industry Partnership Program.