Management of a PEM Electrolyzer in Hybrid Renewable Energy Systems - Fuzzy Modeling and Control: Theory and Applications - page 210

constitutes a control signal because it determines the voltage and current that feed
the electrolyzer, regulating its operating point as well as the hydrogen production.
This voltage level varies in the range 4-8.5V, which has been studied during the
characterization of the electrolyzer. The voltage of the analogue output goes from 0
to 10 V, so fits the proposed objective. This control signal is generated from the output
signal of a fuzzy controller designed specifically for this application, which will be
described in detail in the Sect. 12.3 . Figure 12.2 outlines the scheme of connections
described before.
Next, the software applications and communication protocols involved in the
proposed control architecture are briefly described.
Configurations of PLC program, hardware and communication parameters have
been performed by STEP7 Professional of Siemens. WinCC flexible plays the role
of a Human-Machine Interface (HMI) to solve tasks like visualization, acquisition
and data storage and control of automated processes. WinCC flexible Runtime is a
HMI based on PC and OPC communication is one of its functionalities.
The fuzzy logic controller has been implemented with the Fuzzy Logic Toolbox of
Simulink/Matlab environment, which communicates with the management PLC via
OPC technology. Matlab includes the required OPC Toolbox. Integration of PLC and
Matlab/Simulink environment is a very interesting approach due to the programming
ability to develop different types of controllers of the latter one.
OLE for Process Control, OPC, is a series of seven specifications defined by
the OPC Foundation to provide open connectivity and reliable communication in
industrial automation. The specification of OPC technology contains Server and
Client, using the Client/Server mode. The Server is the supplier of data and Client is
the user of data. They establish a complete set of rules between hardware supplier and
software developer. An OPC client is able to connect to one or more OPC Servers,
and several OPC clients are also allowed to simultaneously connect to the same OPC
Server.
AWinCC flexible Runtime software application has been developed. It runs in the
computer connected to the PLC via Ethernet by using the communications processor
CP343-1 Advanced. Operation as OPC Server is not started by default, so it has
to be activated as a service of runtime in the Operator panel Configuration menu
when designing the application. Figure 12.3 shows the activation of the OPC Server
function.
This application accesses to data blocks in the PLC memory where both sensors
measurements (electrolyzer current, pressure, etc.) and calculated values are stored
(battery state of charge, averaged irradiance, etc.). So, these values are available for
the OPC client. In this case, the OPC Toolbox of Matlab allows the communication
with Simulink acting as OPC client. Figure 12.4 outlines the communication structure
between the PLC, Simulink and WinCC.