Post on 22-Oct-2019
transcript
Department of Electrical and Electronic Engineering
Electromagnetic actuation
technologies
Prof Phil Mellor
2 Overview
• Review developments in electromagnetic actuation– More electric aircraft– Our research experience
• Back of envelope system discussion
3 Static performance capabilities
Huber, J.E., Fleck, N.A., and Ashby, M.F., The selection of mechanical actuators based on performance indices. Proceedings of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences, 1997. 453(1965): p. 2185-2205.
4 Why consider electrical actuation?
• Benefits include– High efficiency– High reliability– Low maintenance and easy to replace– Easy to control with good dynamic response– Low infrastructure and running costs
• Challenges– Realising high specific force– Fault tolerance and benign failure modes– Technology maturity: bespoke designs needed for
each application
5 Technology advances
Source: Group Arnold
• Permanent Magnets
• Digital Control
• Power Electronics
• Sensors
Source: Texas Instruments
Source: International RectifierSource: SIKO GmbH
6 Developments in the more-electric aircraft
Elevator
Rudder
Slat
Aileron• Rudder• Aileron• Elevator• Flaps• Slat• Landing gear• Brakes
Flap
7 Aircraft primary surface actuator
30
140
0
Force (kN)
Speed (mm/s)50 80
8 EHA (Electro-Hydrostatic Actuator)
• The EHA consists of an hydraulic pump driven by an electric motor as part of an actuator based around an hydraulic ram.
• Control is achieved by running the motor at varying speeds and directions and driving a fixed volume pump
• Poor static load holding leads to reduced thermal performance and low speed rotation of pump can give rise to high pump wear rates
• Typically powered by permanent magnet synchronous machines (PMSM) with power electronic control
• High inertial losses due to frequent motor reversals
9 EHA actuator schematic
Electronic control
Existing hydraulictechnology
DemandedSurfacePosition
SurfacePositionControl
MotorControl
M
P
Accumulator
ControlledSurface
Actuator
CrossportRelief
By-PassValve
SurfacePosition
Feedback
ShaftPositionFeedback
motor
pump
10
pivot
Inertialmass
Resistiveforce
EHA
EHA on an inertia simulator
- 350kN peak force - <2Hz response
11 EMA (Electro-Mechanical Actuator)
• The EMA consists of a gearbox driven by an electric motor. The resultant output may then drive a rotary to linear conversion e.g. a ballscrew or roller screw
• Control is achieved by running the motor at varying speeds and directions
• Significant static load holding will lead to reduced performance
• Typically powered by permanent magnet synchronous machines (PMSM) requiring power electronic control
• High inertial losses due to frequent motor reversals
12Typical EMA/EHA actuator motors
40kW Brushless PM25kW Brushless PM
5kW Switched Reluctance20kW Brushless PM
13 Electromagnetic direct-drive actuators
Advantages Disadvantages Simple construction Higher cost
Good positioning accuracy No mechanical advantage
Good dynamic performance More complex specification
Reconfigurability Non-standardised
14 PM linear actuator topologies LINEAR MACHINES
LEVITATION MACHINES
ATTRACTION TYPE REPULSION TYPE SHORT ARMATURE LONG ARMATURE
LONG STROKE SHORT STROKE
MOVING ARMATURE STATIONARY ARMATURE
TUBULAR MOTOR
PLANAR MOTOR
SINGLE SIDED DOUBLE SIDED
TRANSVERSE FLUX LONGITUDINAL FLUX
LINEAR INDUCTION MOTOR
LINEAR SYNCHRONOUS MOTOR
COMPOSITE SECONDARY SHEET SECONDARY
BRUSHED DC
STEPPER
SWITCHED RELUCTANCE
RELUCTANCE HYBRID
AC DC
THRUST MACHINES
PM BRUSHLESS
LADDER STRUCTURE
15 PM linear actuator topologies
z (direction of travel)r
θ
TUBULAR
y
x
z (direction of travel)
PLANAR
16 Tubular construction
+ Balanced electromagnetically (single-sided planar has up to ~1000% normal force to continuous
force capability)
+ No end windings leads to a better utilisation of copper and hence improved motor constant
- Limited length and sag of tubular rod
- Radial field orientation makes it difficult to laminate back iron
17Tubular topologies - armature options
(a) Slotless motor with magnetic sleeve (c) Conventional slotted motor
(d) Longitudinal flux motor topology(b) Slotless motor without magnetic sleeve
18 Tubular topologies - magnetisation options
(b) Radially magnetised primary(a) Axially magnetised primary
(c) Ideal Halbach array (d) Discretised Halbach array
19Air-cored or Iron-cored
Air-cored Iron-cored No cogging force Cogging force Small or zero saliency force Saliency force Lower force per amp and per volume Higher force per amp Lower mass per volume Higher mass per volume Higher acceleration (up to 100g) Lower acceleration (up to 22g) Lower thermal resistance Higher thermal resistance
20 Pros and cons of tubular PM linear actuators
• Good force per amp capability (>50N/A)
• High peak force capability (~400%)
• Zero normal (attraction) force
• High force bandwidth
• High speed operation (>5m/sec)
• No backlash - bearing friction only
• Accuracy (<5µm) & repeatability
• Quiet
21 Pros and cons of tubular PM linear actuators
• Finite length (not for planar)
• Vertical operation problematic (failure)
• Cost
• Cogging force (high accuracy displacement)
• Environmental sealing
22 Moving secondary
Stator
Position sensors
Traversing guide stripsEnd
stop
Pipe adapter
Magnet array
WindingKevlar fibre composite
Coolantrz
10Hz Yarn traverse:Max acceleration >50gMax speed 2ms-1
Traversal 0.2m
23 External armature
• Longitudinal flux motor• 2-phase BLAC machine• Max speed 5 ms-1
• 1.0kN pk force• 10g self acceleration• Traversal 600mm
iron sleevecoil
magnet
24 Electrodynamic shakers
50mm displacement90kN peak force (sine)3m/s max velocity
• Large voice coil actuators• High bandwidth• Limited displacement• Big and expensive
25 Electromagnetic control surface actuator
• 500N force
• ~1.2kg, >10J/kg
• 21Hz operation
• +/-3mm displacement
26 Force capability
Magnetic flux density B (Tesla)
Ampere stream Q (A/m)
Magnetic flux density B (Tesla)
Ampere stream Q (A/m)
Magnetic stress σ = Ku B Q
L
D
σ
Achievable values:– B = 1T for a PM armature– Q = 50,000 A/m rms cont. for a
liquid cooled actuator, peak values x5 cont. not uncommon 60Longitudinal flux PM
80-100Transverse flux PM
40Radial field/linear PM
15Induction
σ (kPa)
60Longitudinal flux PM
80-100Transverse flux PM
40Radial field/linear PM
15Induction
σ (kPa)
27 Composite realisation of transverse flux
28 The route to increased specific outputs
• Novel topologies– >B: improved magnetic properties, multipole magnetisations– >Q: better winding utilisation, improved cooling
• Higher operating stresses– mover mechanical integrity, use of composites
• Higher operating temperatures– high temperature magnets and insulation– better understanding of thermal behaviour and loss
mechanisms
29 Typical table actuator requirements
• 6 axes with 8 actuators
• 50Hz maximum bandwidth
• 40kN force
• +/-150mm displacement
• 1ms-1 peak speed
• 6g acceleration
• Around 20kW rms power per actuator
10
40
0
Force (kN)
Speed (m/s)0.5 1.0
30 Moving magnet tubular actuator example
• 40kN peak, 28kN rms• 0.56m2 active surface: D=0.3m, L=0.6m• 40mm pole pitch with 10mm thick magnet array• Magnet mass 45kg• Composite carrier 25kg mass including bearings• 58g self acceleration
– Accel=ω2x x=0.15m ωmax=61.7rads-1; 9.8Hz– vmax=ωx=9.2ms-1
31Possible system configuration
• Key issue is dynamic energy storage• Capacitors or flywheels are possible solutions• 10 ton at 1ms-1 = 5kJ
– 100V excursion on a 600V dc link = 77mF– 300rpm variation in 3000rpm flywheel = 0.53kgm2
x100 installed filter capacitor
< inertia of a pump motor
Actuator(s)
Active rectifier(supplies losses only)
Commercial induction motor drive acting as a flywheel
415V ac
32 Typical commercial power electronic drive
• 8-16kHz inverter switching
• 1kHz current/force control loop
• 100Hz speed loop
• 10Hz position loop
• Same controller regardless of scale
• ~100Euro/kVA (excludes actuator)
600kVA installation
33Observations
• Bespoke actuator design is required – A typical test cycle is less that 1 minute hence thermal
issues may not be a problem– PM machines have a high peak to mean capability 10:1
possible, performance ultimately thermally limited
• Commercial industrial power electronic equipment would be suitable. – A standard induction motor could be used for load levelling– Power draw from mains supply limited to losses
34 Piezoelectric solutions
• High stress per volume/weight• Unidirectional
– Back to back arrangement– Piezo element must always be in compression
• Low strains – mechanical gearing required• High voltage operation• Low energy density• Stored energy in field comparable to work done
(Similarly issue with electromagnetics where inertia of armature/rotor is significant)
• New high strain materials on there way
35 Conclusions
• A range of direct drive and geared electric actuation technologies are available
• Examples exist with demonstrated performance elements that exceed typical earthquake table requirements:– x10 force capability– x5 maximum speed– x10 acceleration
• Whilst an a specific actuator solution does not exist which can meet the full performance, although challenging, indications are that such a device would be feasible
36 Comparison (source: CLD Inc)
Tubular motors Mechanical Hydraulics Pneumatic Speed 100 in./sec 10 in./sec 10 in./sec 20 in./sec Accuracy 0.001 in. 0.001 in. 0.01 in. 0.1 in. Stiffness High Medium Medium Low Friction Medium Medium High High Temperature 125°C 125°C 50°C 50°C Shock loading High Medium High High Efficiency 50% 40% 25% 25% Noise 40dB 80dB 120dB 120dB Environmental None Minimal Oil
leaks/disposal Oily air mist
Controllability Fully (no backlash)
Fixed move profiles (cams)Backlash
Limited move profiles
Mostly bang/bang