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B5.1 Development of a Reliable, Efficient, Lightweight and Compact Cryocooler
Combined April and May 2007 Monthly Report
PI: Dr. Louis ChowCo-PIs: Drs. Jayanta Kapat, Thomas Wu and Faissal Moslehy Postdoc: Dr. Lei ZhouGraduate Students: Shaohua Lin and Gavin Barnes
Principal Authors: Dr. Lei Zhou and Shaohua Lin
Project overview1. Compressor Rotor design completed
• Rotor with attached impeller and embedded magnet.
• Rotor-dynamic analysis confirms critical speed > 160k RPM
2. Motor design completed
• Stator, magnet and winding are ordered
• Motor controller hardware is acquired
• Motor controller software development has started
3. Compressor test rig structure design completed
• Detailed compressor structural design completed in 3-D model with Pro/E
• Prepare detailed 2-D drawings of parts for machine shop
SECTION I
Motor and controller design
Digital Control Design of PMSM
1. Principles
2. Implementation
Principles
• Open Loop V/f Control
• Block Diagram of the V/f Controller
• Driver Circuit
• Conclusion
Main Idea of V/f Control
Torquef
Vm
m is flux linkage per phase
m
mm
mmm
LI
fL
V
L
VI
2
Neglect the winding resistance
The goal is to maintain a constant voltage to frequency ratio
Ideal V/f Control Profile
frequency
voltage
frated
vrated
Constant torque Constant power
TP
Torquef
Vm
Actual V/f Control Profile
voltage
frated
vrated
Compensationvoltage
Block Diagram of Controller
accelerationdeceleration Programm-
ableSVPWM
signalgenerator
Interface
3- phaseswitchmodepowersupply
Programmable deadtime generator
PMSM
Motor
f * f
f
V
DSP
Driver Circuit
• DC to AC inverter
M1
M2
M3
M4
M5
M6
VaVb
Vc
a
a'
b c
b' c'
Va
t
M1 on
M2 on
Pros and Cons of open loop control
• Pros:– easy to implement
• Cons:– no feedback, unstable compared to closed
loop control
Implementation of Open Loop V/f controlUsing SD Ez DSP 2812 board
Implementation
Hardware Features
• TMS320F2812 Digital Signal Processor in socket operating at 150 Mhz.
• 18 K on chip RAM • 128 K on chip FLASH ROM • 64 K words on board RAM • Expansion Connectors (unpopulated) • Onboard embedded IEEE 1149.1 JTAG controller • +5 volt operation with supplied adapter • Onboard IEEE 1149.1 JTAG emulation connector • Compatible with eZdsp Wire Wrap Prototype Card
Software Features
• Compatible with C2000 Code Composer from Texas Instruments (Includes 'C' compiler, assembler, linker, debugger)
• Compatible with SD Flash programming utility from Spectrum Digital
Program Flow Chart
Code Composer Studio Setup
Code Composer Studio Setup Workspace
Main Function of the Control Program
SECTION II
Compressor design
Compressor assembly appearance
Inlet
Top cover
Base Board
Compressor assembly appearance
Bearing support Bearing
Outlet
Compressor structure
Bearing
Intake volute chamber
ImpellerDe-swirler and
diffuser
Outlet volute chamber
stator
Motor wire and cooling
channel
Base board and frames (I)
Inlet frame Outlet frameDwelling
hole
Bolt holes
Base board and frames (II)
Compressor base holes
Frame bolts
Dwelling hole
Base board and frames (III)
Material: carbon steel
Functions:
1. Provide sturdy support of compressor rotor
2. Provide accurate tip-gap controls
Features:
1. High stiffness support
2. Self-aligned
3. Dwelling holes and pins provide high assembling accuracy
Rotor designMaterial:
High stress stainless steel
Impeller attachment:
Tight fit
Total length: 107mm
Span length: 99mm
Shaft diameter: 18mm
Impeller diameter: 51mm
Critical speed: >160k RPM
Permanent Magnet
Bearing housing
Dwelling hole
Material: Brass
Features:
1. Dwelling holes ensure high alignment accuracy
2. Brass provides good heat spreading and wear resistance
3. Side threads for seal cover to ensure compressor’s complete sealing
4. Attach water cooling accessory for bearings if necessary
Threaded for seal cover
Bolt holes
Main sub-assembly (I)
•Main sub-assembly includes all the major functional components of the compressor
•This sub-assembly will be installed into the base-frame with dwelling pins and bolts
Bolt hole
dwelling hole
Main sub-assembly (II)Inner structure of the
main sub-assembly
1. Motor stator and wire
2. Diffuser
3. Impeller
4. Intake volute
5. Outlet volute
6. Rotor and bearing
1
2
3
45
6
Assembling procedure (I)
Base bolts
Fixing the frames on the base board is the first step to assemble the compressor
Assembling procedure (II)
Insert the main sub-assembly into frame and insert the bearing support at both sides
Insert the dwelling pins and tighten the bolts
Final assembly
6.1 inch
5.9 inch
4.9 inch
Place the top cover with bolts to finish the assembling
Future work
• Develop and test open-loop controller codes
• Deliver compressor parts drawings to machine shop
• Develop new de-swirler and diffuser