Design of an Automatic Control Algorithm for Energy-Efficient ...

11 Matlab implementation 115
tion are given by function pointers. This allows easy integration of additional objectives
or different system simulations. The objective and system functions are called by the
IMEA_evaluateObjective function. The data structures and the complete code of the
optimiser is found in Appendix E.
The disturbance estimator is integrated directly into one S-function. The carbon
dioxide concentration simulation is programmed graphically in Simulink since it only
contains standard elements, which allows a faster execution.
11.4 Real-time requirements
Matlab Simulink is mainly designed as a simulation tool. However, with special in- and
output blocks the models can be compiled with a tool called Real-Time Workshop and
used on micro-controllers and other targets. This allow fast testing and implementations
for prototypes.
The model built for the MUTE car has a sample time of 0.01 seconds. Running
all subsystems at this speed would most certainly lead to overruns, i.e. longer calculation
times than one sample. Sensor signals are read at a slower speed. Therefore, a suitable
sample time has to be found for each system. These can be assigned to every subsystem
marked as “atomic” as well as to external S-functions.
For the climate controller a general sample time of 0.1 second was chosen. Input
values are updated at this frequency via the CAN bus. The optimiser does not need
to run that often. Since the timescale of the cabin-system is in the range of several
seconds (see Section 3.1.5), a sample time of two seconds was chosen. The speed for the
disturbance estimator is also set independently. Here, one second was chosen in order to
run slower than the rest but include all new values that are coming from the multiplexer
every 0.8 seconds. To connect these systems running at different speeds, rate transition
blocks are needed. They assure the data transfer by providing zero-order-hold or a delay
functionality depending on the sample time difference.