Environmental Engineering Reference
In-Depth Information
can be represented to good accuracy by a second-order polynomial and the efficiency
equation is solved for the input DC power
p
DC
p
own
+
r
ohm
p
AC
p
AC
p
DC
=
p
DC
−
v
switch
p
AC
+
η
=
p
DC
p
own
p
DC
−
r
ohm
η
2
p
DC
=
1
−
v
switch
η
−
(6.23)
v
switch
)
2
(2
r
ohm
p
DC
)
2
1
v
switch
2
r
ohm
p
DC
±
+
(1
+
p
DC
−
p
own
r
ohm
p
2
DC
η
=
+
(6.24)
The three loss coefficients
p
own
,
v
switch
and
r
ohm
can be calculated from three effi-
ciency values
η
1
,
η
2
and
η
3
given by most manufacturers in technical data sheets for
power ratios of, for example,
p
1
100%of the rated power.
The input to the model is the DC power. Parameters for 500 inverters are provided
in the INSEL database.
=
10%,
p
2
=
50%and
p
3
=
6.3.2 Communication Strategies for Simulation-Based Remote Monitoring
To allow precise system simulation of a PV power plant, monitoring data for the
meteorological boundary conditions such as irradiance and ambient temperature has
to be available. Irradiance data should best be available in the module plane, or can
be calculated from horizontal data to high accuracy. To detect faults in the power
plant, DC voltage and current and AC power should be monitored. If possible the
module temperature should be measured, but it can also be calculated from ambient
temperature and more precisely from temperature and wind speed. All the data need
to be transferred from the data logging equipment to a server, from which clients can
access the data, visualize it and simulate performance.
There are different server technologies with varying degrees of response time: ftp
servers only transfer on request complete data files, which are produced at a set time
interval, for example every hour. Alternatively, a web server provides HTML pages
with included XML data, which are actualized in a given time interval. If monitoring
data is stored locally in a database, which is often the case in BMS, an elegant method is
to access the database server via open database connectivity communication (ODBC).
For real-time access to the measured data, socket servers such as DataSocket from
National Instruments write the data to the computer memory, where it is continu-
ously actualized. Other protocols such as OPC provide the same functionality. The
simulation environment INSEL with its graphical interface VEE already includes the
DataSocket server and client blocks, where monitored data can be easily written to
the memory (server) and read from the server for the simulation process (client or
simulation agent).
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