By Majeed Ahmad, Contributing Writer
The new system implements three key improvements:
1) a rim drive mechanism for the heliostat that reduces
weight and improves performance, 2) a decentralized
heliostat control scheme that draws its power from a local
photovoltaic supply (with battery storage), and 3) a wireless
heliostat control that reduces cabling costs, simplifies
deployment, and enables better scalability.
This concept required an appropriate software platform
for heliostats that would be highly autonomous. As such, it
should require minimal communication from a centralized
control system and perform all important tasks on its own.
The structure had to be modular and adaptable to different
hardware solutions, distributing the intelligence of the control
server not only across the field, but also within the different
hardware components of the heliostat.
The new heliostat OS was successfully tested with a rim-
drive heliostat prototype in the Solarturm Jülich CSP research
field in Germany. It tracked the sun using a wireless module
that communicates with the centralized field control system
through a mesh network made of similar devices, ensuring that
the mirror facet reflected the sun on the CSP power tower
that contains a central absorber to convert the produced heat
into electrical power via heat exchangers and turbines.
Using the autonomous energy system and wireless remote
control, the commands are sent by the operating system
to two motion control drives that control both axes of the
heliostat’s rims. A photovoltaic panel, battery, and a battery
management unit power for the autonomous system (Figure
1). These components are connected with a wired bus within
each autonomous heliostat. One of the drives is selected
to runs the heliostat OS and act as master controller. It
communicates wirelessly with the centralized field control
system and other devices.
The heliostat OS software can consists of several parts
(Figure 2). The kernel at its center carries out the most
important tasks, e.g. determining sun position, and
coordinating the rest of the modules. It maintains the current
mode of operation as a state machine and allows different
behaviors and actions in the same mode.
The drive abstraction layer sits between the kernel and
each axis, transparently connecting the motion actions of the
kernel with the drives. In AutoR, one axis is connected to the
primary host board, whereas the second axis is controlled via
RS485. The parameter repository centralizes the control of
all variables, storing the values, updating them, and delivering
them to the kernel or the control system.
The command interpreter manages received commands
from the central field control system and connects them
to the matching functions of kernel and repository. It also
manages reply and asynchronous messages.
The heliostat kernel works as an advanced state machine
that executes – either periodically or event-triggered – the
CONTROL SOFTWARE MAKES
SOLAR POWER MORE SCALABLE,
RELIABLE, AND AFFORDABLE
GETTING HUNDREDS, OR EVEN THOUSANDS OF MIRRORS TO
FOCUS THE SUN’S ENERGY ON A SMALL TARGET CAN BE COMPLEX
AND COSTLY. THIS DISTRIBUTED SOFTWARE ARCHITECTURE
PROVIDES A SIMPLER, MORE COST-EFFECTIVE SOLUTION.
Concentrated Solar Power (CSP) has held the promise of producing thermally generated
electricity at a lower cost than photovoltaic or fossil-powered sources, but the promise has yet to be
fulfilled due to several technical challenges. The
AutoR Project (Autonomous Rim drive heliostat),
created under the auspices of the German Federal
Ministry for Economic Affairs and Energy, seeks to
fulfil that promise by developing CSP technologies
that significantly reduce the cost of heliostat fields.
TRINAMIC Motion Control was proud to play a key
role in developing a new heliostat architecture that
achieved this goal.