Hi everyone, is there anyone who has experience with SPICE simulations of photovoltaic systems?

I have doubts about a SPICE simulation of a circuit where I have a PV panel (represented with the single diode model as in the attached pictures), a capacitor to store the energy given from the panel when the switch on the right (made through two mosfets) is open, a 12 V rechargeable battery (modelled with a voltage generator, a series resistor and a capacitor) and a symbolic 200kOhm load. I'm trying to do a parametric analysis where I evaluate the average power supplied to the battery V(s)*Id(M2) for various duty cycles of the NMOS control PWM signal, varying the Ton of this signal (with a period of 140us) from 0 to 140us with an incremental step of 10 us. Knowing the trend of the power supplied by a PV panel, I would expect the power to increase as the Ton increases, reach a maximum, and then start to decrease. I know it is not the best way to have a MPPT circuit (I should use a buck converter) but It is used only for a simulation. In the analysis, I see that I immediately reach the point of maximum power with an extremely low duty cycle (Ton=10 us), subsequently the power decreases. I would like to know if something like this is possible, why are these power values extremely close to each other and, possibly, where could a possible error be in the circuit?
Thank you all.

 

Hi pep'
Welcome to AAC
Please post your LTS asc file and any models you are using.
E

 

Hi,
this is the asc file.

 

hi pep'
The MOSFET Gate drive circuit needs redesigning.
Look at these plots for two Ton values, 5u and 10u, the highest plot values are the lowest Ton time.
Also, the PWM falling edges are unacceptable.

I am using an SLA battery model, setting values as per the attached image

NOTE: also the PV panel voltage is falling !!!!!!
E
BTW: Do you have any SLA Battery models in your LTSpice.?
The Vtest and Lim resistor are only used to check the SLA charge performance.

 

Hi Eric,
first of all, thank you for your help. As I can see I have a current increasing with a Ton decreasing and it is the opposite of the behavior that I would expect. Actually, I had already observed this trend of the current in these days but I really do not know which models for the two mosfets I should use. For the PWM falling and rising edges, I could increase them but the problem persists. In the end, I've never used a SLA battery in my LT Spice.

 

Hi pep,
An important point is that in your circuit, the PV voltage is falling below the required 13.8V charging voltage.

I can post a copy of my PV panel if you are interested.
Top plot trace.
E

 

Eric, It could be helpful for me to have a copy of your PV panel. In any case, is this one of the motivations of the problem I have in the power values? I think the fact that the PV panel voltage is falling is normal because, increasing the Ton, the PV panel current increases and the Voltage decreases. The goal is to achieve the MPPT. I'd like to show the power supplied to the battery for various Ton, so for various duty cycles.

 

hi pep,
This zip contains the PV and SLA battery files.
Ask if you have a problem.
E

The SOC sets the State of Charge 0.1 through 1

 

It’s not going to work without an inductor.
Your circuit will just clamp the panel voltage to the battery voltage whenever the transistor is on. Energy stored in C1 will then be dissipated in the MOSFET on resistance.

 

hi pep,
This zip contains the PV and SLA battery files.
Ask if you have a problem.
E

The SOC sets the State of Charge 0.1 through 1

Eric, do you have any idea of how can I redesign the MOSFET Gate drive circuit? In particular, should I use other mosfets models?

 

hi pep.
Is this homework or a college assignment?

Check this link
E
https://www.youtube.com/results?search_query=mppt+circuit+design

 

hi pep.
Is this homework or a college assignment?

Check this link
E
https://www.youtube.com/results?search_query=mppt+circuit+design

It is a college assignment.

 

Hi pep,
An important point is that in your circuit, the PV voltage is falling below the required 13.8V charging voltage.

I can post a copy of my PV panel if you are interested.
Top plot trace.
E

Yes please post it I'm interested to see what you have done

 

To repeat Ian's comment that you both seem to have ignored "It’s not going to work without an inductor."
That's a bit fundamental and I should worry about that before the niceties of the switch!
You should also compare your panel against your battery to determine if you need a buck or boost conversion or as is often the case both in which case you likely need a SEPIC or similar converter.
Don't forget you need to be able to extract power/charge at all insolation conditions, not just the maximum and please don't forget shading that may or may not also be important.

 

I would like to know if something like this is possible, why are these power values extremely close to each other and, possibly, where could a possible error be in the circuit?

Hi forty,
If you read the TS's opening post, you will see he is running his simulated circuit, and he is asking will his circuit work, and of course the answer is no.
I ran a simulation of his circuit to confirm his simulation results.

@Ian0 and I are both aware that the circuit requires an inductor, also for full operation a SEPIC convertor is needed.

But this is a College assignment, so it is now up to the TS's to modify his design and repost it.
AAC policy is to only help with assignments, not to give a final solution.
E