How to chose pwm and buck converter parameters?

Hello.

I am looking at this example https://uk.mathworks.com/matlabcentral/fileexchange/73115-mppt-solar-charge-controller-model of a MPPT Solar charge controller model. I would like to simulate it for irradiance variations during a day of around 12 hours (12*3600 seconds of simulation time). The simulation becomes very slow. Is there anything that can modify in order to increase the simulation speed? I was wondering if I can change the buck converter's parameters, or the PWM frequency, or sampling time. I am a beginner so any answer would be very helpful.

Thank you

[NAZAR Nihad]

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Answer 1

[Joel Van Sickel]

Hello Eleni,

following up on your new question, you can model the buck converter using an average model to remove the switching. There is an SPS block that works with powergui. You could then switch to a larger fixed step for a discrete powergui or switch to continuous.

https://www.mathworks.com/help/physmod/sps/powersys/ref/buckconverter.html

To do this, you will need to modify the MPPT algorithm to instead of outputting the PWM signal, to output the duty cycle, between 0 and 1 and feed this into the average model of the block in the link above.

Regards,

Joel

[Eleni.T]

Thank you very much for your answers. I use the average model and connected it to the duty coming from the MPPT. My problem is that i dont know much about circuits and how to connect the buck converter block with the PV module and the battery. I have the +/- terminals of the PV array block, the battery block and the buck converter block adn also the 1 terminal of the buck converter and i am not sure how they should all be connected.

Answer 2

[Zhao Wang]

Simulating the behavior of a solar charging system with this detailed model would be very slow. This is because of the sample time (1e-5 s) used in the 'powergui' block, which is required in the switching buck converter circuit. What you can change would be very limited in this case.

To conduct a simulation for a day or 12 hours, typically you will need a simplified system, such as the one in https://www.mathworks.com/help/releases/R2020a/physmod/sps/examples/simplified-model-of-a-small-scale-micro-grid.html. As you can see in the model, the 'powergui' block's simulation type of this simplified model is 'Phasor'. Phasor simulation mode allows you to simulate the solar charging behavior over a long period of time.

There would be a gap between the two simulation types because of the different modeling details. To bridge this gap, you will need to match the behaviors of the two circuit models.

[Eleni.T]

Thank you for the answer. Before I move to the simplified model, I would like to check any possible solution because I need the MPPT algorithm and charge controller for my PV panel. Is there any other way to model the buck converter so that it does not need a discrete powergui? I mean does the MPPT and charge controller always need a switching method?

[Zhao Wang]

For your two questions:

1) No, you can use an averaged-value model for the buck converter. For example, you can replace the buck converter elements with a buck converter block: https://www.mathworks.com/help/physmod/sps/powersys/ref/buckconverter.html. After inserting the block, remember to change the model type to use: "Average model (D-controlled)". You do not need the PWM signal to drive the buck converter block.

2) The MPPT control algorithms should also work in phasor mode.

Besides the buck converter and the MPPT controller, you may also need to change the pv array with a simplified model to speed up simulation.