Atec TerraSAS User Manual
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
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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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