Stirling cycle power conversion is an enabling technology that provides high thermodynamic efficiency but also presents unique challenges with regard to electrical power generation, management, and distribution. The High Power Linear Alternator Test Rig (HPLATR) located at the NASA Glenn Research Center (GRC) in Cleveland, OH is a demonstration test bed that simulates electrical power generation from a Stirling engine driven alternator. It implements the high power electronics necessary to provide a well regulated DC user load bus. These power electronics use a novel design solution that includes active rectification and power factor control, active ripple suppression, along with a unique building block approach that permits the use of high voltage or high current alternator designs. This presentation describes the HPLATR, the test program, and the operational results

Birchenough, Arthur G.

Gardner, Brent G.

Hervol, David S.

NASA Technical Reports Server

Test Results From a High Power Linear
Alternator Test Rig
Arthur G. Birchenough and David S. Hervol
QinetiQ North America Operations LLC, Cleveland, OH 44135, USA
Brent G. Gardner
NASA Glenn Research Center, Cleveland, OH 44135, USA
Abstract:
Stirling cycle power conversion is an enabling technology that provides high
thermodynamic efficiency but also presents unique challenges with regard to electrical
power generation, management, and distribution. The High Power Linear Alternator Test
Rig (HPLATR) located at the NASA Glenn Research Center (GRC) in Cleveland, OH is a
demonstration test bed that simulates electrical power generation from a Stirling engine
driven alternator. It implements the high power electronics necessary to provide a well
regulated DC user load bus. These power electronics use a novel design solution that
includes active rectification and power factor control, active ripple suppression, along with
a unique building block approach that permits the use of high voltage or high current
alternator designs. This presentation describes the HPLATR, the test program, and the
operational results.
https://ntrs.nasa.gov/search.jsp?R=20100041271 2019-08-30T13:19:37+00:00Z
National Aeronautics and Space Administration
Test Results from a High Power Linear
Alternator Test Rig
Arthur G. Birchenough and David S. Hervol
QinetiQ North America Operations LLC, Cleveland, Ohio 44135, USA
Brent G. Gardner
NASA Glenn Research Center, Cleveland, OH, 44135, USA
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Introduction
• In support of a future Fission Surface Power (FSP) system, a
pair of commercial pressure wave generators were
pneumatically connected with a pair of linear alternators to
create the High Power Linear Alternator Test Rig (HPLATR).
• The HPLATR simulates some of the dynamics found in the
alternator of a free piston Stirling engine
• The PMAD architecture used in the HPLATR is meant to
demonstrate a proof of concept.
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Driven PWG
(Alternator)
Driving PWG
(Motor)
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HPLATR Description - Stirling Simulator
• Utilizes two commercially procured Pressure Wave Generators
(PWGs)
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HPLATR Description - PMAD Design
• A Stirling based PMAD design has unique requirements
– converts single phase AC power
– Instantaneous power goes through zero twice every cycle
– Low frequency alternator output
– Relatively high alternator inductance
• Classical Stirling PMAD employs a passive system consisting of a
full bridge rectifier and an output filter
– prohibits independent voltage regulation and stroke control
functions
– requires a (potentially large) series tuning capacitor placed
between the alternator and the rectifier for power factor
compensation
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HPLATR Description - PMAD Design
An active rectifier with active power factor correction (PFC):
– eliminates the large tuning capacitor while maintaining
optimum power factor on the alternator,
– has low current harmonics with minimum distortion and,
– allows for regulation of the output bus voltage to be performed
independently of the Stirling engine stroke control.
¥
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HPLATR Description - PMAD Design
1	 AC Input Module	 1
Stirling	 1
Alternator , 1	 1
.,.
1	
Current
 Feedback	 1
l	 I1 Voltage ... 	 PFC Controller -mm.•.	 Power	 11	 Sense	 Compensation	 Stage	 1
L_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ I
• The HPLATR PMAD system consists of three major elements
• These elements rectify and filter the power output, provide constant
engine loading, electrically isolate the load, and regulate DC bus
voltage.
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HPLATR Description – AC Input Module
• An active rectifier providing power factor control (PFC)
• Consists of a full bridge converter using pulse-width modulated (PWM)
controlled field effect transistors (FETs) to modulate the input current
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HPLATR Description – DC-DC Convertor
Module
-------------------------------	
--------------------------
--------------------------- -------------------------------------
I	 ,I
Full Bridge Inverter Transformer	 i i
	
Full Bridge Output Rectifier
I	 I
I	 I	 I I
	
u	 I	 I
Reduces the PFC output voltage to desired user bus voltage
Attenuates voltage ripple
Provides isolation between the alternator and DC bus
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HPLATR Description – Parasitic Load
Controller (PLC)
• Absorbs Stirling alternator power not required by the user loads.
• By dissipating the excess energy the parasitic load controller
regulates the bus voltage.
• PWM controlled FET switches modulate the power dissipation
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HPLATR Description – Parallel and Series
Architectures
• Each AC input module is paired with a DC-DC converter module –
isolates alternator from DC bus
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HPLATR Description – Design Advantages
• This independence allows for simple and robust connections.
• There is no interaction between modules - no control signal
compensation is required.
• Additional AC input modules can be added to increase system
redundancy.
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Testing -General
• The optimum Stirling engine operating frequency determined by
operating the engine at a constant drive motor voltage and then
sweeping the drive frequency until a maximum alternator piston
stroke was determined.
• Alternator power required for each test sequence obtained by
changing the drive motor voltage and commanding the desired
current drawn by the AC power stage.
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Testing - DC Bus Voltage Control with
Switched User Loads
Linear alternator	 User Load
	
.
—Alternator power	 User Load power 	 current	 current
s a a s s	 ------
	
i	 •
DC bus
voltage
	
User Load DC bus	 Linear alternator
•	 current	 voltage	 stroke
Test Time sequence	 User Load (Watts)
• Shows that the PLC can successfully provide DC bus regulation
• Shows that the alternator voltage and stroke remained unaffected, even
when “overloading” the DC bus.
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Testing –
DC-DC Convertor Ripple Suppression
• Shows effectiveness of the DC-DC convertor current ripple suppression
technique
• HPLATR operated at a constant power level to obtain time traces of DC
link input voltage and DC bus current with the active ripple suppression
operational. The current feedback loop was then disabled and the same
data was taken.
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age
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Testing –
Parallel and Series Module Configurations
Yarallel	 Jeries
• Demonstrated the ability to connect the power modules in parallel or
series
• Showed good power sharing between power modules regardless of how
they were connected.
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Conclusions
• Demonstrated the innovative use of independent controls to divide
the functions of rectification, DC bus ripple suppression, and DC
voltage control.
• The DC bus parasitic load control maintained correct voltage
regulation throughout a wide range of user loading conditions.
• Demonstrated DC bus voltage regulation does not affect linear
alternator voltage.
• The active ripple control on the DC-DC convertor provides good
DC bus ripple suppression.
• This PMAD approach allows flexibility to configure the system for
high current or high voltage alternator designs and allows for
system redundancy.
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Acknowledgments
• The work in this paper was performed for the Exploration
Technology Development Program and the Fission Surface Power
Project. The authors would like to thank Steve Geng for the
HPLATR procurement and installation, and Wayne Gerber, for his
assistance with testing. The opinions expressed in this paper are
those of the authors and do not necessarily reflect the views of the
National Aeronautics and Space Administration.
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Test Results from a High Power Linear Alternator Test Rig

Stirling cycle power conversion is an enabling technology that provides high thermodynamic efficiency but also presents unique challenges with regard to electrical power generation, management, and distribution. The High Power Linear Alternator Test Rig (HPLATR) located at the NASA Glenn Research Center (GRC) in Cleveland, Ohio is a demonstration test bed that simulates electrical power generation from a Stirling engine driven alternator. It implements the high power electronics necessary to provide a well regulated DC user load bus. These power electronics use a novel design solution that includes active rectification and power factor control, active ripple suppression, along with a unique building block approach that permits the use of high voltage or high current alternator designs. This report describes the HPLATR, the test program, and the operational results

Test Results from a High Power Linear Alternator Test Rig

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