Electromagnetics and Electric Machines

Stefan Holst, CD-adapco

Electric machines intro

Designing electric machines with SPEED

Links to STAR-CCM+ for thermal modeling

Electromagnetics in STAR-CCM+

Overview

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 basic definitions and function

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

• Electric machines may be classified by • the source of electric power, • their internal construction, • their application, or • the type of motion they give.

The Electrical Machine – classification

• 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 smallest electric motors are mostly found on electric wristwatches.

The Electrical Machine – Scale: From a few mW to several GW

• Medium-size motors of highly standardized dimensions and characteristics provide convenient mechanical power for industrial uses.

Small watch motor vs. big hydroelectric generator mW & mm diameter Three Gorges Dam: 22,500 MW & several m dia.

• The very largest electric motors are used for pipeline compressors, propulsion of ships and water pumps and of course as generators.

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 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

The SPEED software programs

SPEED – The design process

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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 – range of graphical feedback available

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

Initial design with SPEED

PC-FEA: Loss table calculation

Reading the SPEED geometry and the loss distribution Running the final advanced thermal calculation.

Temperatures impact life time, reliability, cost & size

STAR-CCM+

THERMAL 2D/3D EMAG

SPEED

PC-FEA

time

analytical

STAR-CCM+

SPEED analytical

ELMAC

THERMAL 2D/3D EMAG

PC-FEA

SPEED Development

STAR-CCM+ Development

STAR- CCM+ EMAG only

• Analytical calculations • Geometry templates of electrical machines • Winding schemes • Power electronic circuits • Switch control • Scripts to drive the EMAG/Thermal calculations • …

SPEED and STAR-CCM+ – future: ELectrical MAchine Capability

STAR-CCM+ Electrical Machine Capabilities – Geometry setup

Adding end winding Different rotor types 2D to 3D extrusion

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:

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STAR-CCM+ Electrical Machine Capabilities – Simplified Winding for Cooling Simulations

Tub end windings for Cooling Simulation for BDC Motor

What does low frequency EMAG mean

Low frequency regime is valid for cases with 𝝏𝒕𝑫 ≪ 𝑱 – Displacement current 𝝏𝒕𝑫 = 𝝏_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 = curl𝐴, and div𝐴 = 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 non-magnetic 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

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)

Link to other physics model in STAR-CCM+

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

Lorentz force acting on charged particles

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 field and circuit simulation

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 (𝜕𝑡Ψ)𝐼

Data exchange via minimal exchange protocol, transmitted over TCP connection between programs, – Allows running Simulink and STAR-CCM+ on different machines

Coupling STAR-CCM+ to Simulink®/MATLAB®

Start simulation •Open port

Macro connects to

Simulink port

Specify reports

Store list of reports

Specify input: • field functions • time step size

Run Step •Send reports

Update circuit time step

Protocol Design

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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 𝑋𝑆 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 𝑋𝑀 as (𝑋𝑆 − 𝑋𝑀)/𝑑𝑑

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

Coupling Summary