Boost converter in micro inverters

[hamed]

Dear Friends,

I am new in this forum and I hope that I could learn from you.
I have a question regarded to DC-DC boost converters in micro inverters and power optimizers.
In most of the micro inverters and power optimizers a DC-DC boost converter for MPP tracking has been applied and as far as I know, boost converters only can increase the voltage level so when there is a decrease on illumination of Sun or an increase on temperature, how this converter can decrease the voltage level and adjust the voltage on MPP ? (I have never seen the producers mention that they use Buck-Boost converters and all of them just have pointed to boost converter).

Cheers,
Hamed

[inetdog]

Dear Friends,

I am new in this forum and I hope that I could learn from you.
I have a question regarded to DC-DC boost converters in micro inverters and power optimizers.
In most of the micro inverters and power optimizers a DC-DC boost converter for MPP tracking has been applied and as far as I know, boost converters only can increase the voltage level so when there is a decrease on illumination of Sun or an increase on temperature, how this converter can decrease the voltage level and adjust the voltage on MPP ? (I have never seen the producers mention that they use Buck-Boost converters and all of them just have pointed to boost converter).

Cheers,
Hamed

Welcome to Solar Panel Talk, hamed!

1. A boost convertor does not have to have a fixed boost ratio. By controlling pulse width and duty cycle into the transformer or inductor you can increase or reduce the amount of boost.
2. Decreasing the amount of light hitting a panel will proportionally reduce the available current, but have little effect on the voltage. That is why you need an MPPT algorithm instead of just a fixed resistance or fixed voltage ratio.
The output voltage or current will be reduced to match the power that is available from the panel.
A microinverter will need to boost, while a charge controller will need to buck. Either can be combined with MPPT.

[hamed]

Welcome to Solar Panel Talk, hamed!

1. A boost convertor does not have to have a fixed boost ratio. By controlling pulse width and duty cycle into the transformer or inductor you can increase or reduce the amount of boost.
2. Decreasing the amount of light hitting a panel will proportionally reduce the available current, but have little effect on the voltage. That is why you need an MPPT algorithm instead of just a fixed resistance or fixed voltage ratio.
The output voltage or current will be reduced to match the power that is available from the panel.
A microinverter will need to boost, while a charge controller will need to buck. Either can be combined with MPPT.

Thank you very much dear friend
I almost understand what's happening but I still have some questions regarded to your answer.
As you mentioned the amount of boost can be controlable by PWM and duty cycle but which points are the minimum and maximum points for this converter ?
Is there a primary increase of voltage (24-48) and after that adjusting the voltage by PWM (so the normal Vmpp of the solar module without converter would be the minimum point) or it just adjusts it by increasing the current and decreasing the voltage (which means that the converter decreases the main voltage level of the module).
in a short sentence, the boost converter always increases the voltage and in high temperatures, there is a decrease on voltage. How it can adjust the Vmpp calculated by MPPT if the maximum points would be the solar modules maximum points?
I hope that I could have my question explained.

Thanks in advance,
Hamed

[inetdog]

Thank you very much dear friend
I almost understand what's happening but I still have some questions regarded to your answer.
As you mentioned the amount of boost can be controlable by PWM and duty cycle but which points are the minimum and maximum points for this converter ?
Is there a primary increase of voltage (24-48) and after that adjusting the voltage by PWM (so the normal Vmpp of the solar module without converter would be the minimum point) or it just adjusts it by increasing the current and decreasing the voltage (which means that the converter decreases the main voltage level of the module).
in a short sentence, the boost converter always increases the voltage and in high temperatures, there is a decrease on voltage. How it can adjust the Vmpp calculated by MPPT if the maximum points would be the solar modules maximum points?
I hope that I could have my question explained.

Thanks in advance,
Hamed

A particular boost (or buck) converter will be designed for a specific range of input voltages yielding a specific range of output voltages. You cannot say much more than that without looking at a specific boost converter circuit.
You are correct that the general principle that limits what it can do is that the output power (volts times amps) must be lower than the input power (volts times amps) by an amount which gives the efficiency of that boost converter.
Using larger, higher priced components can increase the efficiency.

The most common designs of MPPT controller will try a number of different Vin to Vout ratios to see which one produces the highest overall power. There are a lot of different ways of doing that.
The cheap almost MPPT controllers will just measure the open circuit voltage from the panel and then draw enough current to drop the voltage to 80% of that.
For use with a charge controller, you will generally see a buck-only converter used while for grid tied inverter applications either type or a buck-boost converter may be chosen.