Design of medium-power dynamic electrical load simulator has been extended to permit simulation of ac as well as dc loads and to provide for operation at higher power levels. Simulator is internally protected against reverse voltage, overvoltage, overcurrent, and overload conditions

Birnbach, S.

Bruce, L. D.

Joncas, K. P.

Smith, L.

English

NASA Technical Reports Server

I Multiplier I 
No Control	 w Vc 
RIun	 Indicator I	 - 
Current 
Sink 
Overvoltage	 ltage I"-	
Fail Wave 
I Bridge 1°'--I	 Butter Indicator	 Detector
ACIDC	 NOV5 
Gain	 I Indicator VDetector 
June 1975	 B75-10108 
NASA TECH BRIEF S	 Lyndon B. Johnson Space Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High-Power AC/DC Variable Load Simulator 
The design and development of electrical power 
distribution and conditioning systems is highly 
dependent on the characteristics of power sources and 
loads. A significant factor in the design of these 
systems is the effect of the transient, or dynamic, 
characteristics of the various loads reflected back into 
the systems. This dynamic behavior, if not identified 
and accommodated, can result in faulty operation or 
catastrophic failure of the power sources and the other 
loads connected to these sources.
Earlier development (described in NASA Tech 
Brief B73-10305) has produced a medium-power 
dynamic electrical load simulator capable of repre-
senting both the transient and steady-state character-
istics of electrical equipment operating on dc 
powerlines. The design of this device has been 
extended to permit the simulation of ac as well as dc 
loads and to provide for operation at higher power 
levels. 
.
Power
CA
V8 ACIDC 
+15V 
Line Voltage 
115 V. 60Hz	 + 5V . 15 V 
Blower 
Control
Vc
E.'0-.U"0:- 
No Control 
Override
Overcurronl 
Detector
V0 or External Control I Crossing 
On/Off Control
	
ACIOC	 Gain 
	
Gain	 Ampliller	 - 
-,
	
I	 Power	 I
	
1.	 1 
Power-
Overload 
Indicator 
Overload	 I lllerOnll:i	 ACIOC Multiplier	
1 Amplifier	 Gain 
	
MI	
Current
Monitor 
Control Signal Path 
Source Current Path 
Source Current Monitor 
Source Voltage Monitor 
Block Diagram of AC/DC Variable A Dynamic Electrical Load Simulator
(continued overleaf) 
This document was prepared under the sponsorship of the National 	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	
information contained in this document, or warrants that such use 
Government norany person acting on behalf of the United States 	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19750000108 2020-03-19T20:06:07+00:00Z
The new simulator, called •a high-power ac/dc 
variable R (variable resistance) simulator, responds to 
control signals over a wide frequency range and is 
capable ' of dissipating high power. The prototype 
operates over a frequency range of from dc to 10 kHz 
and up to 500 W continuous power in load voltage 
ranges of 20 to 60 V dc and 30 to 130 V ac. A variable 
R load-simulator operating at higher levels may be 
constructed by adding more output stage modules. 
The system, as shown in the illustration, operates as 
follows: A control voltage Vc is applied to an input 
isolation stage and from there to the input of a 
multiplier. The second input to the multiplier is 
obtained from a full-wave bridge circuit which 
samples an applied source voltage .V 5 through a buffer 
stage. The output of the multiplier, a product of the 
two inputs, is then used to drive the power stages. 
This feature makes the load current Is proportional to 
the applied load voltage Vs and, therefore, simulates 
a true resistance. The unit provides a separate system 
gain for ac and dc operation to assure optimum 
dynamic range for each mode. 
The simulator contains an npn power stage for all 
positive load voltage inputs and pnp power stage for 
all negative load voltage inputs. Each power stage is 
comprised of four power modules, each of which 
consists of an operational amplifier and driver 
transistors in a voltage follower configuration. The 
source current is monitored through series resistors 
that provide feedback to the operational amplifiers. 
Additional power modules may be used, as necessary, 
to allow each power stage to accommodate larger 
power requirements. The source currents through the 
power modules are summed providing a' current flow 
proportional to control voltage Ye and source voltage 
vs.
The general form of the variable R transfer 
characteristic is:
IS 
VsVc 
=
where Is is the source current, Vs is the source 
voltage, Vc is the control voltage, and K is a scaling 
constant. The output resistance R is given by 
K 
R5 = - 
Vc 
The simulator is internally protected against reverse 
voltage, overvoltage, overcurrent, and overload 
conditions. 
Notes: 
1. The simulator is described in the following report: 
High Power AC/DC Variable R Dynamic Elec 
trical Load Simulator 
NASA CR-140331 (N75-12199) 
Copies of this report may be obtained at cost from: 
Technology Application Center, 
University of New Mexico 
Albuquerque, New Mexico 87131 
Telephone: (505) 277-3622 
Reference: 0540108 
2. Specific technical questions may be directed to: 
Technology Utilization Officer 
Johnson Space Center 
Code AT3 
Houston, Texas 77058 
Reference: B75-10108 
Patent status: 
NASA has decided not to apply for a patent. 
Source: K. P. Joncas, S. Birnbach, 
L. D. Bruce, and L. Smith of 
Avco Corp. 
under contract to 
.Johnson Space Center 
(MSC-14788)
. 
. 
B75-10108	 Category: 02 (Electronics Systems)


High-power ac/dc variable load simulator

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