Using the AMESim MATLAB/Simulink Interface - NUPET

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Using the AMESim MATLAB/Simulink Interface5.1. IntroductionThe main difference between the two interfaces is that co-simulation interface uses two (ormore) solvers, while the standard interface uses only one. This means that AMESim andSimulink use their own solver for the co-simulation interface whereas they both use theSimulink solver for the standard interface. Another difference is that with the standardinterface the AMESim part is seen as a time continuous block in Simulink and in the cosimulationit is a time discrete block. Since the co-simulation block is seen as a discreteblock it makes this interface very suitable for discrete controllers implemented in Simulinkcontrolling an AMESim model.The figure below shows in more detail how the interfaces work. In the standard interfacethe AMESim part of the system gets state variables and input variables from Simulink andcalculates state derivatives and output variables. The process of exchanging thisinformation is controlled entirely by the Simulink solver. In this case one could say that weimport the equations into Simulink.In the co-simulation case, the only exchanged variables are the input and output variables.The rate of exchange is in this case decided by a parameter that the user decides. As thename indicates the model is not entirely in the hands of one software (Simulink) but it is aco-operation between two (or more) software. It is important to realize that by exchangingonly input and output variables at a certain sample rate there is a loss of information.Figure 16: The two AMESim-Simulink interfaces, exchange of information.State derivativesAMESimsubsystemOutput variablesInput variablesSimulinksubsystem+solverState variablesNormal interfaceAMESimsubsystem+solverOutput variablesInput variablesSimulinksubsystem+solverCo-simulation interfaceThis can be compared with the difference between a continuous and a sampled controller.Normally the smaller sample rate used the closer to the continuous result we get. Anotherpossible problem is that the we loose information about possible cross couplings betweenthe system since we do not communicate information about states and state derivatives.18
MATLAB/Simulink interface 4.2User ManualAll these factors mean that co-simulation can be difficult to set up if the two separatesystems are continuous. You should in that case try to find an interface between thesystems where the coupling is as weak as possible.The obvious situation where co-simulation may be used is of course when the interfacebetween the system is sampled, for instance when using a sampled controller.5.2. Usage of the co-simulation interfaceWe will reuse the AMESim system created earlier (Figure 1: The model in AMESim.).Save the system as skyhookcosim. Now we add the interface block. The process is similarto the process creating the standard Simulink interface, except that we select SimulCosimin the field labeled Type of interface instead of Simulink. See Figure 17:Figure 17: Creating the icon for co-simulation.Go into Parameter mode and then Run mode. Next we create the Simulink system asshown in Figure 18: Simulink model - Co-simulation. We use the same basic system asbefore with the difference that the name of the S-Function is now skyhookcosim_.19
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Using the AMESim MATLAB/Simulink Interface - NUPET

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