This example shows the AC3 detailed model and the AC3 average model during speed regulation. The comparison is performed for normal condition and for inverter saturation condition.
O. Tremblay, L.-A. Dessaint (Ecole de technologie superieure, Montreal)
This circuit uses two AC3 blocks of the Specialized Power Systems electric drives library. The AC3 block models a field-oriented control (FOC) induction motor drive with a braking chopper for a 200 HP AC motor. The first AC3 block is set to average value model and the second AC3 block is set to detailed model.
For the detailed model, the induction motor is fed by a PWM voltage source inverter, which is built using a Universal Bridge Block. The average value model uses ideal voltages and currents sources to feed the induction motor. The speed control loop uses a PI regulator to produce the flux and torque references for the FOC controller. The FOC controller computes the three reference motor line currents corresponding to the flux and torque references and then feeds the motor with these currents using a three-phase current regulator.
Motor currents, voltages, speed, and torque signals are available at the output of the block.
Start the simulation. You can observe the motor stator current, the rotor speed, the electromagnetic torque, the DC bus voltage and the magnitude of the rotor flux on the first scope. The speed set point and the torque set point are also shown. On the second scope, the dq currents and voltages are displayed. Note that all signals are multiplexed to compare the two models.
At time t = 0 s, the speed set point is 4000 rpm. Observe that the speed follows precisely the acceleration ramp.
At t = 0.5 s, the full load torque is applied to the motor shaft while the motor speed is still ramping.
At t = 0.65 s, the inverter is saturated due to the limited DC bus voltage. You can observe loss of current tracking which decreases the motor torque.
At t = 1.5 s, the speed set point is changed to -4000 rpm.
At t = 2 s, the deceleration ramp reaches the motor speed. The inverter comes back to normal mode.
At t = 2.5 s, the mechanical load passes from 792 N.m to -792 N.m.
At t = 3.45 s, the inverter is saturated due to insufficient DC bus voltage. You can observe loss of current tracking which decreases the motor torque.
Finally, notice that the results of the average-value model are similar to those of the detailed model except that the higher frequency signal components are not represented with the average-value converter.
To evaluate the speed gain of the average value model, see ac3_example_simplified and compare the simulation speed with ac3_example.