Page 256 - Electric Drives and Electromechanical Systems

Chapter 10 Controllers for automation 253

are becoming increasingly user-friendly and the translation between the physical world
and the simulation environment is undertaken using a text editor, or more commonly
block representations.
A considerable number of simulation programs are available on the market, covering
all aspects of electromechanical system design, including:
Electronic circuit-oriented simulation using applications such as PSpice. In many
cases once the design has been proven, the design can be downloaded to a PCB
layout including ORCAD or Eagle (PSpice, 2018).
CAD packages that in addition support finite element stress analysis and kinematic
modelling, for example AutoCAD (AutoCAD, 2018) and Solidworks (Solidworks,
2018)
Control system can be fully simulated by a number of packages, of which the best
know is MATLAB. With addition of Simulink and Simscape it is possible to fully
simulate the mechanical, electric and electronic aspects of a drive system
(Mathworks, 2018).
It is now possible that many, if not all, aspects of an electromechanical system can be
fully simulated, either directly or through the use of extensions or toolboxes to some of
the applications noted above or by using one of the many standalone packages available
either commercially or as freeware.
A typical MATLAB model for a rotary system is shown in Fig. 10.7, the model is based
on a d.c. brushed motor controlled by a P.W.M. drive as discussed in Section 5.3.4. In this
application the motor drives a rotary load through a 5:1 reduction gear box. The model is
constructed using the standard blocked provided in the Simulink and Simscape library
and can be divided into two section, the controller and the mechanical aspects. In this
application the controller is a conventional analogue PID (Proportional, Integral,
Definitive) controller, the output of which is fed to a PWM generator, the H bridge and
finally the motor. The mechanical output of the dc motor block is followed by the speed
measurement block, simulating the tachogenerator on the motor, a frictional load and
the gearbox. Following the gearbox, frictional load, load inertia and load torque blocks
are added, the final element is a speed measurement block allowing the speed to be
inspected during the simulation period. The results of the simulation are shown in
Fig. 10.8., clearly showing the changes in motor current and terminal voltage as the
speed demand and load torque are changed.
A further example is shown in Fig. 10.9, where a linear system is simulated. In this
case a brushless motor is used. The motor is simulated using a parametric model where
only the details of the speed e torque envelope, as shown in Fig. 6.6 are required,
together with the motor’s mechanical details. In this example the load is rapidly moved
0.4 m in 5s, and remains at this position for 5 s. During stationary period a large external
load is applied. Finally, the leadscrew moves the load back to starting position and re-
mains at rest for 5 s before the cycle repeats, the results are shown in Fig. 10.10.