Page 281 - Design of Solar Thermal Power Plants

4.4 CONTROL DESIGN OF THE HELIOSTAT FIELD 263

lower limit of the deviation correction range, the deviation-
correction process finishes, and the azimuth deviation angle and
elevation deviation angle are recorded as the corrected values of X
and Y separately in the database while recording the completion
date and time of deviation correction.
In the case that the absolute value of deviation is greater than
the upper limit of the deviation correction range and the number
of deviation corrections is less than the maximum number of
deviation corrections, new coordinates are calculated based on the
current deviation and sent to the heliostat control system; when the
heliostat once again reaches the deviation-correction point, the
camera is initiated. In the event that the absolute value of deviation
is less than the lower limit of the range, the deviation correction
process finishes, and the azimuth deviation angle and elevation
deviation angle are recorded as the corrected values of X and Y
separately in the database while recording the completion date and
time of deviation rectification. In the event that the number of
deviation corrections is equivalent to the maximum number of
deviation corrections and the absolute value of deviation is still
greater than the upper limit of the range, it means that the
deviation correction fails, and the respective data will not be
recorded in the database.
After completion of deviation correction, the deviation-correction
heliostat number will be automatically reset, and the system returns
to the status of “deviation correction to be performed.” The control
program will then select the next heliostat mirror number for
deviation correction and initiate the next deviation correction
process; the cycle repeats.
3. Special circumstances. If no tracking deviation angle is recorded in
the respective daily time interval, the tracking deviation angle
inspected in the respective time interval of the previous day, several
days before, or from the previous month shall be used as the
tracking deviation angle for that day. If there is no inspection result
for the current time interval, the tracking deviation angle shall be 0.
Then the tracking deviation angle inspected in the previous time
interval shall be applied as the tracking deviation inspection result
of the current time interval.
To achieve higher tracking precision, according to database
records, the tracking deviation curve of the heliostat
corresponding to any given daily time can be obtained through
interpolation based on modifying the current angle of the heliostat
so that the heliostat’s concentrated solar image can be precisely
projected to the target position.