NASA Proof-of-Concept 1-W Stirling Convertor Development ...
Transcript of NASA Proof-of-Concept 1-W Stirling Convertor Development ...
NASA Proof-of-Concept 1-W Stirling Convertor
Development for Small RPS
AIAA Propulsion and Energy (P&E) Forum and
Exposition, International Energy Conversion and
Engineering Conference (IECEC)
August 19-22, 2019, Indianapolis, IN
National Aeronautics and Space Administration
www.nasa.gov
Session: ECD-02
Authors: Nick Schifer1, Scott Wilson1, Daniel Goodell1, Michael
Casciani2
1. NASA Glenn Research Center, 2. Vantage Partners, LLC
•
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Small nuclear power systems that would provide electricity to
probes, landers, rovers, or communication repeaters for space
missions• Operate in vacuum or on planetary surface (ie. Moon, Mars, more...)
• Use conversion technology to convert heat to electricity for powering spacecraft
sensors and communications • Fractional GPHS (General Purpose Heat Source) offers around 60 watts of thermal input
• LWRHU (Light Weight Radioisotope Heater Unit, often called RHU) offers around 1 watt of
thermal input for each unit and multiple units could be used
Why Low Power RPS?
Development Goals• Sufficient power for spacecraft functions
• Long-life and low degradation to ensure power at
EOM
• Robust to critical environments (vibration, shock,
constant acceleration, radiation)
• Thermal capability and high efficiency
Dynamic Power Conversion• 12-16% overall system efficiency possible
from 1 to 10 watts electrical power output [Ref 1] Conceptualization of Seismic Monitoring
Stations Being Deployed from Rover [JPL Pub 04-
10, Sept-2004]
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Design Goals• Long life design (no wear mechanisms)
• 3 kg system mass
• Envelope of 11 cm diameter X 32 cm length
• Performance• Heat from multiple LWRHU
• At least 1 We power output
• At least 12% system efficiency
• Maximum of 400 ºC acceptor temperature
• Maximum of 50 ºC rejection temperature
• Robustness• Overstroke collision tolerant (limited time)
• Operates in vacuum or atmosphere
• Launch vibration
• Constant accelerations
• Shock
• Compliance• Minimize exported force
• EMI
Low Power Dynamic RPS Concept
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Low Power Dynamic RPS Concept
Electrical
Controller
Stirling
Engine
Multi-Layer
Metal Insulation
Heat
Source
Linear
Alternator
Stirling Convertor
Radiative Coupling Heat Rejection Flange
: -----------------' ' ' ' ' ' ' ' ' ' -------
' ' ' ' ' ' ' ' ' ' ' __ ,
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Proof of Concept – 1 We design
• Split-Stirling, gas duct between engine and alternator compression space
• Gap regenerator – no porous matrix
• Flexure bearings for piston and displacer
• Laboratory design did not minimize mass
• Simulating heat from 8x RHUs using electric heater, 350 ºC hot end temp
• Fluid loop heat rejection, 50 ºC cold end
• 100 Hz, 94 psig helium, 4.0 mm Xp, 2mm Xd
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Test Setup(insulation not shown)
Stirling Convertor
Heat addition
Engine
Heat rejection
Gas duct
Alternator
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Convertor Instrumentation
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Instrumentation
• Piston hall effect sensor
• Displacer hall effect sensors
• Dynamic CS pressure transducer
• Hot end temperature (1x)
• Cold end temperature (1x)
• Alternator housing temperature (1x)
• Electrical heat input
• Alternator output
Displacer Hall sensor
Piston Hall sensor
....----Displacer
----- Tait housing
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Testing Sequence
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• Flexure Stiffness Characterization
• Displacer & Piston Resonance Characterization
• Displacer & Piston Position Sensor Calibration
• Convertor Characterization
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Displacer Flexure Stiffness
Characterization
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Finite element model over predicted
displacer flexure stiffness by 7% at
full 2 mm amplitude
Force applied using
calibrated masses
> 4x flexures {installed as it will
operate)
Displacement measured using laser sensor
z
3.00
2.50
2.00
~- 1.50 '-0
LL
1.00
0.50
0.00 0
y = 0.1714x2 + 0.7683x + 0.0028
y = 0.1374x2 + 0.7601x + 0.0109
y = 0.1434x2 + 0.7464x + 0.012
.. -~:::. .... :·.:·::::::::~------·····
✓~-··
...........
......... .:~·· --..................
... -····· ......
0.5 1 1.5
Displacement, mm
• FEA Results • Test 1 • Test 2
2
.... ···
2.5
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Piston Flexure Stiffness
Characterization
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Finite element model over predicted
piston flexure stiffness by 13% at full
4 mm amplitude
Force applied using cal ibrated masses
l 2x flexures {insta lled as it w ill
pera te)
Displacement measured using laser sensor
14.00
12.00
10.00
z 8 .00 Q) u ....
6 .00 0 u..
4.00
2.00
0.00
0
y = 0.2137x2 + 1.8025x + 0.1865 .. ····
.·· y = 0.1471x2 + 1.7781x + 0.0915 .. ••· •
y = o.mx' + 1837x ~:.~::~;_::.'.:~t:::::::-::::1/
•···
.. -;::•· . ,,,,,::• .. ... ,.:.::.:--1 2 3
Displacement, mm
• FEA Results • Test 1 • Test 2
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•
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Displacer Resonance Characterization
10Displacer amplitude (Xd) versus frequency.
Test setup used for characterizing displacer
resonance.
Goal: Achieve 102-103 Hz at 2 mm amplitude
Procedure:
• 1 W linear alternator was used as an exciter
driven by an AC source
• Frequency swept from 90 to 104.75 Hz
• Displacer (mass-spring) assembly allowed to
resonate
• Adjust number of flexures and mass as needed.
2.50
E E 2.00 (l)-
"C :::,
:t= 1.50 a. E <t: ,_ 1.00 (l) u ro a. -~ 0.50 0
0.00 90.0
y = 0.1552x-13.994
I .... .... • I ... •·•···1··
•······· I
92.0 94.0 96.0
.•... •
98.0
.... .•
. •
r
•••
100.0 102.0
Frequency, Hz
.. -·• .• •••
104.0 106.0
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Piston Resonance Characterization
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Goal: Achieve 95-98 Hz at 4 mm amplitude.
Two Approaches:
• Resonant approach (used for displacer), requires 2x alternators
• Ringdown
• Drive alternator to 4 mm, go open circuit on the alternator.
- A free piston should ring down for >1 second.
- Frequency of oscillation equates to resonance
throughout the ringdown.
~6 seconds
1.5
1
0 .5
E E 0
c 0
·.;;;; -0.5 "cii
0 Cl. C 0 -1 'tii Cl.
-1 .5
-2
-2.5
110 111 112 113 114
Time, Seoonds
115 116 117 118
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Displacer & Piston
Position Sensor Characterization
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Procedure:
• Displacer was excited via harmonic resonance.
• 1 W linear alternator was driven via AC source.
• A laser displacement sensor was used to measure position.
• All signals were recorded and monitored via LabVIEW.
• Correlations of hall sensor voltage amplitude to laser amplitude (in mm) were derived.
Signals are linear over and beyond entire operating range.
10.00
> 9.00 a.,' 8.00
"C
_.; 7.00
E 6.oo <l'. 5.00 fili ro 4.00
.:!: ;; 3.00
ro 2.00 I 1.00
0.00
--. ·----1
0.00 0.50
t-. •
• •
1.00 1.50
Displacer Amplitude, mm
T •
2.00 2.50
>
5.00
4.50
a.,' 4.00 "C _.; 3.50
t 3.00
<l'. 2.50 Q)
~ 2.00 .:!: g 1.50
ro 1.00 I
0.50
0.00 • 0.00
•• • • • • ---+.-• • ~-~
~- -- •~ - - -• - - - -•-- - - - - -+- - - -• - - • - - - - - - -t- - - -• I -- I
1.00 2.00 3.00 4.00 5.00
Piston Amplitude, mm
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Convertor Characterization
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Test process:
- Engine and alternator assemblies were integrated
- Convertor filled with helium
- Used and AC source to drive the piston
- Motor at piston amplitude of 2 mm at frequencies of 95-103 Hz
- Motor at piston amplitude of 4 mm at frequencies of 95-103 Hz
Observations:
- Round 1 of testing w/ non-rigid mount
- Measured case motion: 0.1 mm
- Round 2 of testing w/ rigid mount
- Displacer leads piston by 50-80 degrees
at frequencies of 95-99 Hz.
- Cooling of hot-end observed
- 3.5 W to drive the cooler (rub discovered)
Mode 1 Mode 2
Hot-end Heating Cooling
Xp-Xd Phase Angle ~170 deg ~0 deg
Non-rigid mount
Rigid mount
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Objective: High performance required (~0.001 W/m-K effective thermal conductivity)
- Peregrine Falcon Corp. designed and fabricated multi-layered metal insulation (MLMI)
- The prototype is currently under test at GRC.
Current Challenge: Low conductance of the evacuation port requires long evacuation time.
Insulation – Functional Test
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Fluid Rejector
Stirling Thermal SimulatorInsulation
Evacuation
Port
Multiple layersHeat Source
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Controller design and functionality
• Linear AC regulator controller using a MOSFET H-bridge with analog circuit to control FETs for AC to DC rectification and load control
• Constant power load monitoring allows for load control and shunting of unused power
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ControllerDesign Progression
• LTspice model contains a linear alternator, H-bridge rectifier, constant power circuit, and waveform smoothing circuit for power factor and Total Harmonic Distortion correction
• Model validated with breadboard testing.
• Design finalized and incorporated into a printed circuit board design. Assembly in progress
Alternator Voltage, Vp-p 25.6
Alternator Power, We 1.24
Controller Voltage, Vdc 11.1
Controller Power, We 1.16
AC-DC Conversion Efficiency 93%
Controller Breadboard Testing Results
P P :Cll1 0 ~/OA P P :Clll i¥&, :Cll10 103 WoA RIIS :Cll1
· s1oppe<1----4932 2018/12/13 15 :06 :05 .02974723
2"J_b3V Av1,
137 Ol4nA RHS
10ai1 :11 .11
11 1398V q OH?IV
Ac<lbio •: • Hor lld l--200kS/s 5os/div
Reallime Math
Filter /Delay SetllJ
I ·l Next 1/2
fdge-- c111 •r -----------~ :Hlo ___ _ Auto O .020A 201 8/12/13 15 :07 :•6
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Summary
• Small RPS are being considered for small spacecraft missions
• Enables long-life power for use in darkness
• 1-W Stirling RPS is in development at NASA GRC
• Testing & Demonstration of Subcomponents is Underway:
• Convertor
• High-performance insulation
• Controller
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Special thanks to contributors
• Barry Penswick
• Jonathan Metscher
• Malcolm Robbie
• Cheryl Bowman
• Paul Schmitz
• Roy Tew
Thank you for attending
•