How to make block arrangements in Simulink to convolute 2 continuous input signal?
For some reason, I have to be able to reset the convolute integral accumulation. Hence, I can't use the conv block in Simulink. Nor can't I use a transfer function block.
This is what I have tried so far. But it only match with the conv block for the first 0.5 second. It then jumps up and down randomly. I know that the implementation I have tried is not continuous, but I don't know how to implement it continuously: whether it is possible to integrate with respect to some other variable other than time in Simulink.
What is the added value of simscape physical signals compared to normal simulink signals? As far as I can see, from a functional perspective there is no difference between the two types of signals: I can add units to both types, they both have a direction of flow, and they both have similar function blocks like adding, substracting... Only for physical signals the available types of blocks is very limited. Why didn't the matlab guys just use normal simulink lines instead of the physical signals?
Physical signals, unlike Simulink signals, have units associated with them. This means that they follow a number of rules, for example to ensure that the right unit is used (e.g. you can't add kg and m/s). From the documentation:
Using the Physical Signal Ports
The following rules apply to Physical Signal ports:
You can connect Physical Signal ports to other Physical Signal ports with regular connection lines, similar to Simulink signal
connections. These connection lines carry physical signals between
Simscape blocks.
You can connect Physical Signal ports to Simulink ports through special converter blocks. Use the Simulink-PS Converter block to
connect Simulink outports to Physical Signal inports. Use the
PS-Simulink Converter block to connect Physical Signal outports to
Simulink inports.
Physical Signals can have units associated with them. Simscape block dialogs let you specify the units along with the parameter
values, where appropriate. Use the converter blocks to associate units
with an input signal and to specify the desired output signal units.
Any sensor block in Simscape (in whatever physical domain) will output a physical signal. You can then convert it into a normal Simulink for feed to your controller. Similarly, any source block in Simscape (in whatever physical domain) will take a physical signal as input.
I suggest you just read the Simscape product page
In particular,
Simscape components represent physical elements, such as pumps, motors, and op-amps. Lines in your model that connect these components correspond to physical connections in the real system that transmit power.
Accompanying that description is the following image, which shows how Simscape models can be far more intuitive to build than a model which uses standard signal. This means models are far more maintainable and clearer to, for example, engineers who may not have a comp-sci background.
Let's delve into what a "physical connection" is somewhat.
[Simscape] employs the Physical Network approach, which differs from the standard Simulink modeling approach and is particularly suited to simulating systems that consist of real physical components.
[ ... ]
Each system is represented as consisting of functional elements that interact with each other by exchanging energy through their ports.
You stated in your question that both methods have a flow direction. This is wrong!
Simscape blocks try and balance the energy between the inlet(s) and outlet(s). For instance a fixed orifice in a fluid system may have high pressure on one side. Simscape will try and solve the pressure balance each iteration. You would need some custom Simulink subsystem to achieve this if not for Simscape.
What is the added value of simscape physical signals compared to normal simulink signals?
What is it that you think Simscape physical signals provide? Is it one number? How do you solve a mass-spring-damper system with just position? It's position AND it's speed AND it's acceleration.
I can add units to both types
No you can't. You put whatever you want in Simulink. You don't get to choose anything about what's in the physical signal in Simscape. You can specify units in the blocks that the signals connect, but you don't get to pick what the pipe itself is carrying.
they both have a direction of flow
No they don't. Your head and your torso are connected. There's no directionality to this. They're just connected. The physical signal is likewise just showing that (things) are physically connected. Again, the mass-spring-damper system: If the damper points to the mass, and the spring points to the mass, then is there any possibility that the damper could affect the spring? Yes, of course. The damper affects the spring because the damper affects the mass and the mass affects the spring.
The spring affects the mass, and the mass affects the spring. The signal is bidirectional. You're confusing signal directionality with kinematic chains.
they both have similar function blocks like adding, substracting
If you're on a train that's going 30 mph, and you're walking forward at 3 mph, how fast are you going relative to the world frame? What if you're walking backward? There is a physical meaning in adding and subtracting physical signals.
[For] physical signals the available types of [function blocks are] very limited
What is it that you're thinking they're missing? Can you also provide a description of what the physical meaning of that function block would be?
Why didn't the matlab guys just use normal simulink lines instead of the physical signals?
Because they're not the same. The biggest point is probably that Simscape is signal + derivative + second derivative, but again they're just conceptually different. Simulink is an easy way to write code - do this step, move along the arrow, do the next step, etc. Simscape is a pictorial representation of a physical system. The physical signal lines just show that things are connected. The system gets solved simultaneously.
I don't think it's mainly about the enforcement of physical signal units, nice though this is.
I think it's about the solver - and before it gets to the solver, about the choice of states and equation causality - rearranging the equations ready to be solved.
Simulink doesn't have any truck with this and just gets straight on with integrating signals as a succession of samples. I know it gets complicated with variable step solvers, but they are only doing extra fancy numerical analysis with the sampled data. Integration and the here-and-now is what it's all about!
Simscape just starts with a bucket of variables and a bucket of equations that variously depend on said variables. A 'bipartite graph', I believe they call it.
Just as we have to navigate a route through simultaneous equations to pick off the simple ones and substitute (or the matrix equivalents of this) Simscape has to do likewise in software so wants to keep alive augmented info on signals like which equations they are in and whether it knows or can easily obtain their derivatives, what they are, etc. Physical signals behave for us users just like Simulink signals, but I reckon they are there to provide the valuable service to Simscape of keeping this augmented info alive and linked between blocks so that one massive matrix equation can be formed for the whole system, not separate ones that get sampled as Simulink systems between Simulink blocks.
This rearrangement of equations ready for the more conventional solver getting stuck in is a black art indeed! We learn very little of how Simscape does it from the MathWorks docs, but you can install OpenModelica for free and see how that does it.
Can I connect an RC circuit from the Simscape library (as a feedback) to an s-function block and apply a time series as input? I am trying to use the Linearize tool from Control Design to obtain the frequency response of the whole system.
Yes, you can. You need to use the PS-Simulink Converter block to convert the physical signals from your electrical sensor blocks to Simulink signals, and the Simulink-PS Converter block to convert the Simulink signals from your S-function into physical signals to feed into electrical source blocks. Beware of creating algebraic loops though.
Is there a way to create an input/output port in Simulink (some workaround)? The port would be a bus and some signals are set from outside the block while some signals are set by the block. Here is an example:
Given the following bus:
Flow (scalar)
Composition (vector)
Enthalpy (scalar)
I would like Flow to be set from outside the block (there's a pump downstream which sets this value). Composition and Enthalpy are computed by the block.
My solution so far: Make Flow an input into the block and with direct feedthrough set it on the outport. I don't find this solution intuitive because from a graphical point of view the outflow becomes an input into the block (which is true from a math point of view - but I would like to make the Simulink diagram intuitive). I've seen in Modelica the possiblity to create input/output ports (RealPort) and the signal could be read or written by the block. I would need such a feature in Simulink.
It sounds like you need to use Simscape and SimHydraulics, which do excatly what Modelica does, but within Simulink. Each physical domain is represented with through and across variables, which are flow rate and pressure for the hydraulic domain. However, that's extra $$/££/€€ and a new modelling paradigm (you don't think in terms of inputs and outputs anymore)...
If you stay with Simulink blocks, there isn't much else you can do above what you've already done, although I assume you mean the flow is set on the input, not the output.
I tried to rotate the revolute joint of a machine in SimMechanics. The actuator is from SimElectronics, so I use the Revolute - Rotational Interface block to connect the motor and the joint together. The whole block model is as follows (also available here)
But when I tried to run the simulation, I got the following error:
Not enough input derivatives were provided for one or more Simulink-PS Converter blocks associated with the highlighted Solver Configuration block, for the solver chosen. Implicit solvers (ode23t, ode15s, and ode14x) typically require fewer input derivatives than explicit solvers, and local solvers never require any. You can provide more input derivatives by selecting different options (including turning input filtering on or increasing the number of user-provided input derivatives) on the Input Handling tab of Simulink-PS Converter blocks linked below:
...'R0x2D1000iA80F_1joint_motor/Revolute - Rotational Interface/Simulink-PS Converter' (1 required, 0 provided)
I've tried to control the machine using SimMechanics Joint Actuator, which gives a correct result. The error occurred when I tried to control it with the motor from SimElectronics.
What's the problem with the model and how to solve it? Thanks
A few suggestions to try out:
Try removing the Joint Initial Condition block and see if it allows the model to run
In the DC motor block, try setting the rotor inertia parameter to 0 (as the inertia is provided by the SimMechanics part of the model). See the Warning on the Revolute-Rotational Interface documentation page
Make sure the initial condition specified in the Joint Initial Condition block is consistent with the initial condition specified in the DC Motor block
I would change how you connected your interface block to the DC Motor so that port B is connected to R, and F to C. This is because your Follower in the SimMechanics is welded to ground, whereas the Base if free to move.
Arnaud