MATLAB Examples

AC5 - Comparison Between Detailed and Simplified Models

This example shows the AC5 detailed model and the AC5 average model during speed regulation. The comparison is performed for normal condition and for inverter-rectifier saturation condition.

O. Tremblay, L.-A. Dessaint (Ecole de technologie superieure, Montreal)

Contents

Description

This circuit uses two AC5 blocks of Simscape™ Power Systems™ electric drives library. The AC5 block models a self-controlled synchronous motor drive with active front-end rectifier for a 200 HP motor.

The first AC5 block is set to average value model and the second AC5 block is set to detailed model.

For the detailed model, the synchronous 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 synchronous motor. The speed control loop uses a PI regulator to produce the flux and current references for the vector controller block. The vector controller computes the three reference motor line currents corresponding to the torque reference and feeds the motor with these currents using a three-phase current regulator. The vector controller also computes the flux estimate and compares it with the desired value in order to generate the field excitation voltage.

Since the field flux dynamics of the synchronous machine are relatively slow, it is advisable to establish first the field flux to its nominal value before feeding the stator with three-phase currents. In this example, a high magnetization voltage of 600V is applied to the rotor field during the first 0.2 s of the simulation in order to speed up the rotor field increase. Once the field flux has reached its nominal value of 1.0 weber, the three-phase current regulator associated to the motor stator is switched on.

Motor currents, voltages, speed, and torque signals are available at the output of the block.

Simulation

Start the simulation. You can observe the motor stator current, the rotor speed, the electromagnetic torque 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. Finally, on the third scope, the DC bus voltage, the rectifier current and the inverter current are shown. Note that all signals are multiplexed to compare the two models.

At time t = 1.5 s, the speed set point is 1750 rpm. Observe that the speed follows precisely the acceleration ramp and that the stator current amplitude and frequency increase gradually.

At t = 3.0 s, a resistive torque of -792 N.m is applied to the motor shaft while the motor speed is still ramping. Observe the rectifier saturation on the third scope.

At t = 3.5 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 = 5 s, the speed set point is changed to -1750 rpm.

At t = 6 s, the deceleration ramp reaches the motor speed. The inverter and the rectifier come back to normal mode.

At t = 6.5 s, the mechanical load passes from -792 Nm to 792 Nm.

At t = 9.5 s, observe on the third scope the rectifier saturation.

At t = 10.5 s, the inverter is saturated due to the limited DC bus voltage. You can observe loss of current tracking which decreases the motor torque.

Finally, note how the simplified model reacts well compared to the detailed model.

Notes

To evaluate the speed gain of the average value model, see ac5_example_simplified and compare the simulation speed with ac5_example.