Monitoring Circuit (Miniature Remote Controlled Solar Car)

This absolutely will not work, because your output goes to a battery and you start from a solar cell. Either one of these components makes voltage feedback impractical.

Click to expand...

Just to reconfirm, so, you're saying that I shouldn't tap a feedback from the battery to control the PWM signal? And have a fix PWM signal?

devonsc said:

This absolutely will not work, because your output goes to a battery and you start from a solar cell. Either one of these components makes voltage feedback impractical.

Click to expand...

Just to reconfirm, so, you're saying that I shouldn't tap a feedback from the battery to control the PWM signal? And have a fix PWM signal?

Click to expand...

A fixed PWM period will do a poor job of tracking the mpp of the solar cell. It'll work so-so, your system is low on power already so it may be close to nonfunctional if you lower performance any more.

You can use the battery voltage to shutoff the source to prevent overcharge, but it is not as useful as measuring current in order to provide PWM feedback to track the mpp.

A fixed PWM period will do a poor job of tracking the mpp of the solar cell. It'll work so-so, your system is low on power already so it may be close to nonfunctional if you lower performance any more.

Click to expand...

Will the following incease the efficiency of the DC/DC converter?

I have a PWM signal that varies according to the voltage output at the solar panel instead of according to the 12V battery.

Meaning, example:
If the output voltage of the solar panel is 7.5V, I will step-up to 13.5V.
If the output voltage of the solar panel is 8.5V, I will step-up to 13.5V.

In the second case, where I step up the voltage level of 8.5V to 13.5V, meaning, I step-up lesser. Does this mean that I will obtain a higher value of current at the output of the converter? Is this known as increasing the efficiency of the DC/DC converter? Meaning, I'm close to the max. power point?

By the way, do you mind suggesting what should I do to enhance my DC/DC converter if as mentioned above is wrong?

Thanks in advance...

devonsc said:

A fixed PWM period will do a poor job of tracking the mpp of the solar cell. It'll work so-so, your system is low on power already so it may be close to nonfunctional if you lower performance any more.

Click to expand...

Will the following incease the efficiency of the DC/DC converter?

I have a PWM signal that varies according to the voltage output at the solar panel instead of according to the 12V battery.

Meaning, example:
If the output voltage of the solar panel is 7.5V, I will step-up to 13.5V.
If the output voltage of the solar panel is 8.5V, I will step-up to 13.5V.

Click to expand...

That's varying the PWM based on the output voltage, keeping it constant as the input voltage changes - not based on the input voltage.

In the second case, where I step up the voltage level of 8.5V to 13.5V, meaning, I step-up lesser. Does this mean that I will obtain a higher value of current at the output of the converter? Is this known as increasing the efficiency of the DC/DC converter? Meaning, I'm close to the max. power point?

By the way, do you mind suggesting what should I do to enhance my DC/DC converter if as mentioned above is wrong?

Click to expand...

As you probably have gathered by now, it's a very complex subject, I suspect you may need to do considerable experimentation to try and get optimum power from your solar panel.

Thank you very much for all the guidance...

At this moment, I'll do some reading about obtaining mpp from my panel and complete my PWM signal PIC code.

The other thing is the PWM freq could probably be adjusted by solar cell voltage too, though this may seem odd. The mpp voltage changes somewhat with different light levels, but not a whole lot.

As you may have noticed, if the solar cell voltage is high, you're not loading it enough to take all the power it can give, and if it's low, you're taking too much current and the voltage suffers badly. So you know if you hit the mpp voltage, you're in the area of optimum load. It seems to me it won't accomodate the efficiency issues in the boost converter itself so it won't be as good as current feedback at the load.

The other thing is the PWM freq could probably be adjusted by solar cell voltage too, though this may seem odd. The mpp voltage changes somewhat with different light levels, but not a whole lot.

Click to expand...

Would like reconfirm with about the above statement. It seems that it would be a lot easier for me to tap the output voltage of the solar panel for me to determine the duty ratio of my PWM signal. Are you saying that it is sufficient to perform such feedback to manipulate my PWM signal?

Thanks in advance...