simulating passive Hybrid Energy Storage System but getting weird values in scope

Hello, I was simulating a passive Hybrid Electric Storage System in Simulink but by Scope for battery and Supercapacitor shows weird graphs, like shown in attachments.The current of battery starts from a 400 and then drops to zero and the supercapacitor starts from -400 and then drops to zero.

What am I doing wrong here? Is it related to battery and SC parameters or do I need to make some changes to the simulation model?

Answer 1

[Joel Van Sickel]

One of the primary problems is that your step size isn't small enough for what you are modelling. Since you are modelling the switching behavior of your boost converter, and using a fixed step simulaiton, you need to set your step size to at least 100 times smaller than your switching period. Or you could try a solver like ode23tb which is variable step and not worry about it. You can also set up your boost convert to use an average approach (feed in the duty cycle instead of the pwm signals) to have a faster simulation. (there is a boost converter model that you can use and set to use average mode)

[Irfan]

Hi, I'm not using a fixed step simulation but still I did what you said about using the ode23tb solver, but the graphs didn't change. Also, I tried unlinking the PV panels and Boost converter from the simulation but I still got the same graphs. So now i don't know where the problem is 😭

[Joel Van Sickel]

your power gui block in the shared model is set to disrete, 5e-5 s, so while your global solver may be variable step, you are still simulating the circuit with a fixed step solver. You can change the power gui to be variable step.

[Irfan]

Sorry to ask, how can I change it to variable step? I'm new to matlab so I really don't know how?

[Joel Van Sickel]

no worries! you can double click on the power gui block and select continuous instead of discrete. Also, if you are new, I highly recommend the free onramps. Here is one for Simulink: https://matlabacademy.mathworks.com/details/simulink-onramp/simulink

[Irfan]

Hello, I changed the power gui from discrete to continous but still the graphs in scope show the same values

[Irfan]

Can the problem lie in the design of the model?

Answer 2

[Joel Van Sickel]

Yes, there could be problems with the model. I highly recommend that you get each piece working individually. First get a solar panel discharging into a resistive load, and make sure that does what you expect. THen make a dc/dc converter that is powered by a fixed voltage source, and goes into a resistive load. Get that working too. Once you can build both individually, then you can try bringing them together.

[Irfan]

Thank you, let me try this way.