Elgar TerraSAS
1kW-1MW
Programmable Solar Array Simulator
• Simulate dynamic irradiance and temperature
ranging from a clear day to cloud cover conditions
• Ramp the voltage, temperature or irradiance level
over a programmed time interval
• Readback of voltage, current, irradiance level and
temperature setting
• Tests for inverter Maximum Power Point Tracking
(MPPT)
• Provides programmable I-V curves for PV Inverter
testing
• Simulates different types of solar cell material
• Multi-Channel, Up to 1MW
Why power supply is critical for PV simulations
Many solar inverters generate AC ripple on their
DC input, which is connected to the photovoltaic
array. For single phase inverters, the frequency
of this ripple is twice the line frequency (120 Hz
for US models). The simulator’s power supplies
must not supress this ripple as a function of
their regulation loop. An increasing number
of inverters (and virtually all micro-inverters)
accurately measure amplitude and phase of the
ripple voltage and current to quickly track the
MPP of the array. This approach allows tracking
the MPP at a much higher speed when compared
to conventional dithering techniques (also called
perturbate-and-observe). Faster tracking of the
MPP results in a much higher overall efciency
in cloudy conditions, where the irradiance is
constantly changing. It is likely that all solar
inverters will use this approach in the near future,
since end users are very sensitive to the overall
efciency of their solar energy installations.
To satisfy this requirement, the PV simulator must
be capable of reproducing the voltage / current
behavior of a solar array at the ripple frequency.
Most standard switching power supplies employ
very large output capacitors and inductors in
their output circuits and are unable to deliver the
required performance - regardless of the response
speed of the I/V curve controller.
Elgar’s line of PV simulators are based on high
speed versions of our standard products, where
output capacitors and other speed-limiting
components have been adjusted. This results
in a speed improvement of 10 times or better.
Proprietary features built into the PV controller
hardware and rmware, combined with our
high speed power supplies, deliver the required
performance. This technology was extensively
tested on micro-inverters and is ready to test the
next generation of inverters.
Strengths of using DSP signal processing
Our technology avoids using linear ampliers,
which are fast but bulky and inefcient. The
required performance is delivered by high speed
switching power supplies and advanced DSP
signal processing techniques. Competitors data
sheets mentions that speed requirements may
not be met in some conditions, “...depending
also on the type of MPP tracking principles”. An
additional linear module is required to satisfy
the new requirements. Some competitor’s
power supplies specications say that it uses “...
innovative IGBT and transformer technology”.
Our power supplies use Power MOSFETs, which
typically switch ten times as fast as the most
recent IGBTs. Higher switching frequency
translates to smaller output capacitors and
inductors - which is the key to a successful high
speed power supply design.
Product Overview
The Elgar TerraSAS System, (TSAS) provides
an easily programmable means of simulating
the characteristic behavior of a PV array. The
system provides a turn-key approach to testing
the maximum peak power tracking (MPPT)
characteristics for grid-tied inverters and DC
charge controllers. The ability to simulate virtually
any ll factor or solar cell material allows the
customer to validate the MPPT algorithm with a
power source. Hardware control is accomplished
by an application running on the local controller
that communicates directly to the PV simulator
using RS422, which operate as a dedicated IV
curve generation processor. The local Graphical
User Interface (GUI) is accomplished via another
application that provides all of the user controls
to the TerraSAS system. Imbedded in the
application is the Ethernet (LAN) parser for
remote communication and control. All of the
80-1000 V
115 208 400
480
AMETEK
Programmable Power
9250 Brown Deer Road
San Diego, CA 92121-2267
USA
858.458.0223
sales@ProgrammablePower.com
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Elgar TerraSAS
functions available locally through the controller
are also available remotely.
Description
As shown in the rack drawing, the TerraSAS
consists of programmable DC power supplies,
a rack mounted controller, keyboard and LCD
display with control software and GUI interface,
output isolation and polarity reversing relays and
a unique PV simulation engine that controls the
power supply. This combination of hardware
allows the TerraSAS to simulate most test
protocols or combination of events that a solar
installation will be subjected to. Power supplies
are available in 1-15KW increments to simulate
arrays up to 1MW.
The included software, as displayed below, allows
modeling of a PV panel without an extensive
knowledge of solar array parameters. The only
parameters required for a simulation are the open
circuit voltage and short circuit current. The slope
of the VI curve can then be modied by the peak
power parameters, Vmpp and Impp. Changes to
these parameters will allow the shape of the VI
curve to be adapted to any ll factor between
0.5 and 1. Once an IV curve has been generated,
changes to the irradiation level or temperature
can be changed on the y so that the behavior
of a grid tied inverter can be tested under realistic
conditions for cloud shadowing and panel
temperature rise. Long term weather simulations
can be run to determine the amount of energy
delivered in a given situation. Inverters can be
optimized for real MPP search modes, because
shadowing and temperature changes can be
simulated realistically.
The PV simulation software allows denition of
key parameters like Voc, Isc, Vmpp and Isc at 25
°C and 1000W/m2, so that the resulting VI curve
is calculated according to a standard solar cell
model.
The PV simulator has the ability to simulate
ideal IV curves as well as irregular characteristics
for peak power tracking that result when solar
panels with different output characteristics are
paralleled as shown on the following two graphs
below. With the simulator programmed for
different values of irradiance or temperature,
the characteristic “multiple hump” IV curve will
result. By programming the changes in irradiance
and temperature in a table, dynamic simulation
of compressed time proles of a 24 hour day can
be run in a loop to simulate the day and night
periods for extended periods of time.
Dynamic simulation showing changes in Irradiance and Temperature over time
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TerraSAS
IV Curve Control Interface : Parameters are programmable through sliding scale or direct input of value
Control Displays
The graphic above shows the GUI interface
displays. The entered set of IV curves is displayed
as soon as the parameters are entered. The actual
measured data is then overlaid on the screen so
that the operating point can be viewed in real
time. The display times can be set from minutes
to days to allow for long term testing.
Programmable Parameters
Set a specied irradiance level
Set a specied temperature value
Set a specied voltage level
Set a specied current level
Set a specied temperature coefcient
Ramp of voltage, temperature or irradiance level
over a programmed time interval Readback of
voltage, current, irradiance level, and temperature
setting Programmable calibration of system
Curve Formula
The PV curves for the simulator are derived from
the formula shown below.
Io as a function of Vo:
Io=Isc (1-C1 (exp (V/(C2 x Voc))-1))
C1=(1-(Imp/Isc)) (exp(-Vmp/(C2 x Voc)))
C2=((Vmp/Voc)-1)/(ln(1-Imp/Isc))
Where the Reference Irradiance conditions for the
simulated arrays is 1000W/m2 and the Reference
Array Temperature is 25°C
The simulated PV arrays are provided in terms of
array ll factor, Maximum Power Point Voltage
and Maximum Power Point Power. The curves
generated are based on the Sandia Labs simplied
PV Array model dening the relationship between
these values and other parameters as provided
below:
Where:
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TerraSAS - Specications
1kW-1MW
Where:
β Array temperature Coefcient, %/°C
T= Cell temperature, °C
V= Voltage, V
I= Current, A
FF= Fill Factor
Subscripts:
Ref= Reference (i.e., at reference or rated
conditions)
MP= Maximum Power
OC= Open Circuit
SC= Short Circuit
DC Output Connections
The output connections will use nger safe,
pressure type connectors or terminal blocks of
suitable ampacity on the rear I/O panel depending
on output current requirements.
Characteristic “multiple hump” IV curve results when three PV proles are added
“Multiple Hump” IV Curve
Utilizing data gathered from the Solar Advisor
Model (SAM) data base, the TerraSAS allows
the user to model systems made up of two or
more subsystems. For example, a PV system that
consists of three arrays with different orientations,
thus creating a “Multiple Hump” as shown below.
Safety
The system includes a shutdown function that
will disable the output with an open interlock
contact. In the event of an open interlock, the
PV simulator chassis will program down the DC
output and open the output relays, and provides
complete qalvamic isolation
The benet of simulators is simply that they offer
the ability to test and invert without reliance on
a real array and can simulate PV behaviors that a
real array cannot be easily manipulated to do.
This assumes that the PV simulator can behave
like a real panel of course.
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TerraSAS - Specications
Specications
AC Power AC Input Voltage: 115V (for DCS) 208VAC three phase Std, 400VAC and 480VAC three phase are optional
DC Output Open circuit voltage, Voc: 0 - 1000VDC
Programmable Parameters Irradiance level: 0 to 2000 W/m²
Accuracy Voltage Readback: 0.2% of rated max voltage
Programming Interface Ethernet with RJ-45 connector / LAN
AC Input Connections Finger safe, pressure type connectors three phase AC four wire plus safety ground stud AC input circuit breaker
DC Output Connections Finger safe, pressure type connectors positive and negative
Safety The output isolation relay operates as a disconnect relay in the event of a malfunction or an open interlock contact
Output Voltage and Current Ranges
Power (MPP) 1 kW 5 kW 10 kW 15 kW RMS P-P DC Leakage Current
Voc
80V Isc=12.5 Isc=83A Isc=167A Isc=250A 20 mV 100 mV
600Voc Isc=1.6A Isc=8A Isc=16A Isc=25A 60 mV 350 mV 335mA
1000Voc N/A Isc=5A Isc=10A N/A <1mA
MMPT
Scalable (MPPT) 1000W to 1.0MW
Response to MPPT Up to 120Hz
Current Slew Rate 3msec/A
Control Loop Sampling Rate 1usec / 10kHz
Static and Dynamic Programmable PV Array Parameters
Irradiance Level 0-2,000W/m2
Temperature -100 to +100*C
Voltage Level 0-600/1,000V 80V - Consult factory for other voltages
Current level to rated output current 0-Rated Output (see MPP Chart)
Voltage Temperature Coefcient 0 to -2% / *C
Arbitrary VI Curve Up to 4096 data points
Programmable Setpoints
Voc 0-Rated output voltage
Fill Factor 0.5 to 0.95
Vmp 0-Voc
Imp 0-Isc
ISC 0-Rated output current
Over Voltage Protection (OVP) 0.1% to 110% of Voc Max
VI Curve Set Point Accuracy
Voltage <0.1%, FS
Current <0.5%, FS
Programming Resolution
Programming Resolution <0.002% of FS
Voltage / Current <0.002% of FS
(Input current depends on power rating)
Short circuit current, Isc: 0 – 1000A
Maximum output power at MPP: 1MW
(Lower voltage ranges will provide proportionately higher currents) 1-6 channel output, consult factory for additional channels.
Temperature: -40 to 90°C
Temperature Coefcient: 0 to -65,000 mV/°C
Simulation Times: 0 to 65,000 seconds
Isolation relay and polarity relay closure
Current Readback: 0.5% of max current
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TerraSAS
VI Curve Readback Accuracy
Voltage <0.1%, FS
Current <0.5%, FS
Output Sampling Rate 100usec
IV Curve Update Rate 1sec
IV Curve Interpolation rate 7.8msec
Stability
CC 0.05
Temperature Coefcient
CC 0.03
Misc
Simulation PV Array Channels 1-250
Preloaded Formula LUFT
SAM Database Over 100 pre-loaded PV Panels, Series & Parallel capability
Over 100 pre-loaded PV Panels, Series & Parallel capability
1kW-1MW
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