Electromagnetics and
Electric Machines
Stefan Holst, CD-adapco
Overview
Electric machines intro
Designing electric machines with SPEED
Links to STAR-CCM+ for thermal modeling
Electromagnetics in STAR-CCM+
The Electrical Machine
– the basic definitions and function
Basic definition:
• A motor is a machine that converts electrical energy into mechanical energy.
• A generator (also alternator or dynamo) is a machine that converts mechanical energy into
electrical energy.
• This can be due to rotation or translation.
• A traction motor on a vehicle may perform both tasks. Electric motors and generators are
commonly referred to as electric machines.
Basic function:
Most electric motors operate through the interaction of magnetic fields and current-carrying
conductors to generate an electromagnetic force.
The Electrical Machine
– the main parts
A simple Electric motor has the following main parts:
• Rotor (turning part) carrying either
• an excitation DC winding or permanent magnets or
• a three phase winding or a squirrel cage or
• an armature winding
• Stator (fixed part) having
• a stator winding (single, 2-, 3-, n-phase) or
• exictation permanent magnets
• a commutator: a rotary mechanical switch, which reverses
the current between
the external circuit
and the rotor along
with the
• brushes,
• a shaft with bearings
and bearing shields,
• a cooling system
• a housing
The Electrical Machine
– classification
• Electric machines may be classified by
•
•
•
•
the source of electric power,
their internal construction,
their application, or
the type of motion they give.
• They may be powered by
• direct current (DC), e.g., a battery
powered portable device or DC source
(rectified AC) or
• alternating current (AC) from a central
electrical distribution grid or inverter.
The Electrical Machine
– Scale: From a few mW to several GW
• The smallest electric motors are mostly found on electric wristwatches.
• Medium-size motors of highly standardized dimensions and characteristics provide convenient
mechanical power for industrial uses.
• The very largest electric motors are used for pipeline compressors, propulsion of ships and water
pumps and of course as generators.
Small watch motor
mW & mm diameter
vs.
big hydroelectric generator
Three Gorges Dam: 22,500 MW & several m dia.
SPEED
– What does SPEED has to do with electrical machines?
SPEED is the leading design software
for
electric machines
• Detailed analytical analysis with finite-element links or finite-embedded solver
for
• Motors, Generators and Alternators
• including inverters and other electronic controls
• Over 150 corporate accounts
• Over 1500 users
• A Worldwide CD-adapco Direct Sales Team and additional a Distributors
Network including support
• Operating in all industrialized countries
The SPEED software programs
• The following machine types are available:
– brushless permanent magnet and wound-field AC
synchronous
• PC-BDC
– induction
• PC-IMD
– switched reluctance
• PC-SRD
– direct current (PM)
• PC-DCM
– wound field and
PM commutator
• PC-WFC
SPEED
– The design process
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2
7
3
4
6
5
8
SPEED in use: Definition of the winding – The
winding editor
SPEED in use: The Template editor – input data for
calculation options, temperature, control parameters, etc.
SPEED in use: Graphical Output –
graphical feedback available
range of
SPEED in use: Output design sheet –
large range of numerical values available
SPEED in use: GoFER
Go to Finite-Elements and Return
… or use the embedded FE-solver directly (PC-BDC)
SPEED and STAR-CCM+
– the combined workflow for Electrical Machines
PC-FEA: Loss table
calculation
Reading the SPEED
geometry and the loss
distribution
Running the final
advanced thermal
calculation.
Initial design with
SPEED
Temperatures impact
life time, reliability, cost & size
SPEED and STAR-CCM+
– future: ELectrical MAchine Capability
SPEED Development
SPEED
SPEED
analytical
analytical
• Analytical calculations
• Geometry templates of electrical machines
• Winding schemes
• Power electronic circuits
• Switch control
• Scripts to drive the EMAG/Thermal calculations
•…
PC-FEA
STARCCM+
PC-FEA
EMAG
only
STAR-CCM+ Development
ELMAC
STAR-CCM+
2D/3D
EMAG
THERMAL
STAR-CCM+
2D/3D
EMAG
THERMAL
time
STAR-CCM+ Electrical Machine Capabilities
– Geometry setup
2D to 3D extrusion
Adding end winding Different rotor types
Different machine types
STAR-CCM+ Electrical Machine Capabilities
– Symmetries and Periodicity
STAR-CCM+ Electrical Machine Capabilities
– Stator and rotor skewing
Stator skewing
Rotor skewing,
stepped:
linear, V:
STAR-CCM+ Electrical Machine Capabilities
– Simplified Winding for Cooling Simulations
Tub end windings for Cooling Simulation for BDC Motor
20
What does low frequency EMAG mean
Low frequency regime is valid for cases with
𝝏𝒕 𝑫 ≪ 𝑱
– Displacement current 𝝏𝒕 𝑫 = 𝝏_𝒕(𝜺𝜺) is
growing with highly fluctuating fields
• Radar signals (low conduction current)
• Electric machines in contrast are driven by
conduction currents
STAR-CCM+ solves for potentials
– Formulation simplifies by using electric
potential 𝜙 and magnetic vector potential 𝐴
𝐸 = 𝛻𝜙, 𝐵 = curl 𝐴, and div 𝐴 = 0
Transient mode, magnetostatic, and
magnetostatic and motion
Solver Status v7.06
Formulation is validated for 2D
simulations
– For transverse magnetics (current
normal to simulation plane)
equations reduce to solving for 𝜙
and 𝐴𝑧
In 3D simulation stability issues
arise along magnetic to nonmagnetic material interfaces
– Proximity effect simulation in
copper wire are possible
– Molten metal looses magnetic
properties
Excitation Coils available in v8.02
Current driven simulation
– Magneto-static situation
– Current strength & orientation
Modeling coil as bulk region
– Orientation given by contour
– Winding parameter Number of
Turns multiplied by Electric Current
defines applied current density
Post processing
– Specific Magnetic Flux linkage FF
– Volume integral delivers flux
linkage of region
Link to other physics model in STAR-CCM+
Electrically conducting fluids  Magneto hydrodynamics
– Plasma simulation
– Mixing of molten metal
STAR-CCM+ v8.02 will bring one way coupling
– Given magnetic field forces as momentum source for the fluid
Hartmann channel validation
– Magnetic flux aligned to y-axis leads to secondary flow pattern
– For strong B-field, velocity profile looks like in turbulent flow (more mixing)
Lorentz force acting on charged particles
Lorentz force currently requires field function
cross($$MagneticFluxDensity,$$Velocity)
cross($$MagneticFluxDensity,$$ParticleVelocity)
For Lagrange phases this is specified as an external force field
Applications
– Particle tracing due to field change
– CRT
Coupling field and circuit simulation
Electromagnetic field calculations are costly
Circuit modeling helps reducing the EMAG simulation domain
considerably
– Electric machines can for the most part be simulated in 2D in the design
stage of product development
– Circuit modeling will deliver currents to be applied in the winding regions
– Field simulation provides flux linkages
– Applied voltages are an input parameter
or stem from more complex controller
models
Coupling STAR-CCM+ to Simulink®/MATLAB®
Simulink is a block diagram environment for designing general control
flow diagrams including electrical circuits
– Simulink handles discrete or continuous states
• Continuous state handling is needed for the circuit coupling
– Model is transferred internally into a differential algebraic equation
• Solution method can be auto-selected or user specified
Transient STAR-CCM+ can provide individual post-processed values at
every time step
– Supply of flux linkage Ψ𝐼 or even its time derivative (𝜕𝑡 Ψ)𝐼
Data exchange via minimal exchange protocol, transmitted over TCP
connection between programs,
– Allows running Simulink and STAR-CCM+ on different machines
Protocol Design
Start
simulation
•Open port
Specify input:
Specify
reports
Update circuit
time step
• field functions
• time step size
……
Macro
connects to
Simulink port
Store list of
reports
Run Step
• Send reports
Test case
Coupling STAR-CCM+ to Simulink®/MATLAB®
Simulink data enters STAR-CCM+ via Java Macro scripting
– Macro listens for input parameters
Field Function,CurrentPhase1,<0.3 A>
Field Function,CurrentPhase2,<0 A>
Field Function,CurrentPhase3,<10.3 A>
– Step protocol element leads to time step with a specified size (0.1s)
Step,0.1
The STAR-CCM+ representation within Simulink
– Level 2 Matlab functions
• Provides function hooks for link initialization and data update
• Matlab language easily interfaces with Java  one language protocol
implementation
– STAR-CCM+ provides state value 𝑋 𝑆 directly in SI units
Report,FluxLinkagePhase1,0.7
– In Continuous state integration Simulink requires derivative at each time step
• Derivative is calculate with respect to last Simulink value 𝑋 𝑀 as (𝑋 𝑆 − 𝑋 𝑀 )/𝑑𝑑
Coupling Summary
STAR-CCM+ and Simulink communicate over sockets
Offers continuous state coupling of field simulation to circuit
– Explicit Euler Simulink solver needed
Current approach only uses scripts
– Soon on http://javahut.cd-adapco.com
Protocol extends to any application
– Anything in STAR-CCM+ that can be defined as a field function can be an
input
– Any report value can be an output to Simulink/Matlab