This example shows the DC5 one-quadrant chopper DC drive during speed regulation.
C.Semaille, Louis-A. Dessaint (Ecole de technologie superieure, Montreal)
This circuit uses the DC5 block of Specialized Power Systems. It models a one-quadrant chopper (buck converter) drive for a 5 HP DC motor.
The 5 HP DC motor is separately excited with a constant 150 V DC field voltage source. The armature voltage is provided by an IGBT buck converter controlled by two PI regulators. The buck converter is fed by a 280 V DC voltage source.
The first regulator is a speed regulator, followed by a current regulator. The speed regulator outputs the armature current reference (in p.u.) used by the current controller in order to obtain the electromagnetic torque needed to reach the desired speed. The speed reference change rate follows acceleration and deceleration ramps in order to avoid sudden reference changes that could cause armature over-current and destabilize the system. The current regulator controls the armature current by computing the appropriate duty ratio of the IGBT 5 kHz pulses (Pulse Width Modulation). This generates the average armature voltage needed to obtain the desired armature current. In order to limit the amplitude of the current oscillations, a smoothing inductance is placed in series with the armature circuit.
Start the simulation. You can observe the motor armature voltage and current, the IGBT pulses and the motor speed on the scope. The current and speed references are also shown.
The speed reference is set at 500 rpm at t = 0 s. Initial load torque is 15 N.m.
Observe that the motor speed follows the reference ramp accurately (+250 rpm/s) and reaches steady state around t = 2.5 s. The armature current follows the current reference very well, with fast response time and small ripples. Notice that the current ripple frequency is 5 kHz.
At t = 2.5 s, the load torque passes from 15 N.m to 20 N.m. The motor speed recovers fast and is back at 500 rpm at t = 3 s. The current reference rises to about 16.7 A to generate a higher electromagnetic torque to maintain the speed reference. As observed before, the armature current follows its reference perfectly.
At t = 3 s, the speed reference jumps down to 350 rpm. The armature current lowers in order for the speed to decrease following the negative speed slope (-250 rpm/s) with the help of the load torque.
At t = 4 s, the speed stabilizes around its reference.
1) The power system has been discretized with a 1us time step. The speed and current controllers use a 100 us and 20 us sampling time respectively in order to simulate a microcontroller control device.
2) In order to reduce the number of points stored in the scope memory, a decimation factor of 25 is used. Some transitions may thus not appear on the scope. To view detailed simulation results, reduce the decimation factor to 1.
3) A simplified version of the model using an average-value converter can be used by selecting 'Average' in the 'Model detail level' menu of the graphical user-interface. The time step can then be increased up to the smallest control system sample time value. This can be done by typing 'Ts = 20e-6' in the workspace in the case of this example. See also dc5_example_simplified model.