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