Available in English and French
A new web-based technical presentation from Cobham Technical
Services helps designers of electric motors and generators use
finite element analysis (FEA) techniques to accelerate product
development and improve design accuracy. The presentation will also
be of interest to electromagnetic and electromechanical analysts,
as well as engineers who are currently using analytical design
packages for rotating machines. First shown live to a
pre-registered audience as a webinar, the 47-minute audio/visual
presentation is now available - in English and French - for
on-demand playback via Cobham's dedicated motor design software
website: http://www.motor-design-software.com.
Titled 'Introduction to Rotating Electrical Machine Design using
Opera', the presentation outlines how Cobham's low frequency
electromagnetic simulation software enables designers to improve
the performance of motors and generators to meet specific economic,
efficiency and operating environment targets. Making extensive use
of graphics, it covers all key areas of FEA and is ideal for people
who are new to the subject.
After outlining the fundamental principles of FEA, such as
defining model geometry, creating finite elements (meshing) and
specifying or importing material properties such as B-H curves, the
presentation takes a detailed look at aspects especially relevant
to rotating electrical machines. These include hysteresis loss, the
demagnetization effects of short-circuits and other faults, and the
critical importance of obtaining an accurate representation of the
magnetic field in the rotor-armature air gap. Engineers modeling
highly complex magnetic gearing systems involving concentric
rotating and static magnetic paths are shown how Opera simplifies
the task by allowing the definition of multiple air gaps.
The presentation discusses how by setting suitable periodicity
boundaries, users can reduce the size of the electrical machine
model - and therefore the number of equations that need to be
solved - significantly, leading to much faster computation times.
This is especially important for designers of high pole count
machines, because it enables the analysis model to be a fraction of
the full device.
In Opera, current carrying conductors are represented using
coils; Opera 3D provides a comprehensive library of standard coil
forms such as solenoids, racetracks and bedsteads. If the required
coil is not in the library, it can be represented by a continuous
combination of bars, arcs and bricks. Scripting facilities enable
users to create libraries of commonly used coils for a particular
machine very easily.
The increasing complexity of electrical devices means that a
model of a motor or generator may not be sufficient to obtain an
accurate representation of its behavior under all operating
conditions. The presentation therefore describes how Opera's
standard circuit editor enables power electronics and switching
circuits to be defined, which then interface with the conductors in
the model of the device itself. Simple 'drag and drop' techniques
are used to position general circuit representations of voltage and
current drives, and components such as resistors, diodes,
capacitors, inductors, switches and windings. Specific
configurations can be defined in minutes, and used to create a
library of common test circuits for use during subsequent
analyses.
Mechanical coupling in full rotating machine analyses is
functionally similar for 2D and 3D - the coupling data can include
the moment of inertia and the frictional speed-varying or fixed
applied torque. For solving system-level design problems, rotating
or linear motion simulations can be included using Opera as part of
the system. Co-simulation with Simulink allows the two simulations
to exchange data at each Opera time step, and multiple Opera
simulations can be included in the same system simulation. The
presentation provides an example of two separate Opera 2D models,
for the exciter and generator parts of a system, with Simulink
ensuring that both rotate at the same speed, as though they were
mounted on a common shaft in real life.
Opera allows users to define any shape of device, magnets and
coils - as well as generic electrical circuits - which makes it
possible to create 2D or 3D models of virtually any type of linear
or rotational electrical machine. These include ac induction,
brushed and brushless permanent magnet, ac wound rotor induction
and switched reluctance motors, as well as induction, permanent
magnet and doubly-fed generators. Specific solvers are chosen to
maximize accuracy with the computing hardware that is available;
the results file is post-processed automatically, to generate
graphic displays of the points of interest. Compared to traditional
testing or analytical calculations, these provide a much more
powerful tool for making design decisions based on detailed
assessment of each component part. Forces, torque, hysteresis and
eddy current losses can be calculated automatically, as can
variables such as flux linkage, cogging torque, fields and
saturation, iron loss, demagnetization, etc.
The presentation also highlights Opera's multi-physics
capabilities, showing how the software can perform thermal and
structural analyses, and describes how by use of multiple
goal-seeking algorithms it helps optimize the design process,
automatically 'homing in' on the best solutions. Designers are also
shown how the Optimizer tool can be used within Cobham's Machines
Environment - an application-specific extension to Opera - to
further accelerate the design process. By making extensive use of
templates, drop-down menus and Wizard-style dialog boxes, the
environment enables users to fully quantify the motor or generator
they wish to design, very quickly and easily.
The presentation concludes with a real-world example of FEA,
using the Machines Environment to simulate the permanent magnet
motor fitted to the Toyota Prius hybrid vehicle. The simulation
results are compared to the test results obtained by the Oak Ridge
National Laboratory (ORNL) in the USA, which carried out an
experimental characterization of the motor and its drive system. In
order to demonstrate the Machines Environment's ease of use, the
simulation task was performed by a relative novice in FEA
techniques. After selecting basic design data, such as the type and
sizes of magnets, rotor, stator and windings, the user amended the
profiles of the magnets, rotor and stator manually, to provide a
representative example. The first analysis shows the static torque
that the motor generates for various drive currents, which
correlates closely with the test results from ORNL, while the next
run obtains the cogging torque and torque ripple. The magnetic flux
density images obtained from 2D and 3D models of the motor also
exhibit a high degree of conformity, demonstrating the accuracy of
the simulation.