How to balance MPPT implementation

MPPT implementation ,how to balance

Hi

I searched a lot for solar MPPT , I know that system search for optimal point of voltage and current to got most power of Panel

I have confused that how to balance duty cycle between MPPT and battery voltage

if we used duty cycle to adjust output voltage from buck converter then we will neglect searching for MPPT , and if we find MPPT how to set output voltage from feedback?

let say if I set duty cycle with load on panel and got MPPT ? how to determine and adjust output voltage, if we adjust voltage let say 14 volt then solar panel not will be in optimal value??

:shock::shock::shock:

Re: MPPT implementation ,how to balance

The aim is to draw the right combination of current and voltage, which utilizes maximum power from the pv panel.
For efficiency You wish to draw continuous smooth current.

Therefore you should filter the waveform which is drawn from from your PV panel. It is common to include an input capacitor in the filter, which stores incoming power.

Then the capacitor releases power in the form of strong bursts of current, as drawn by your buck converter. Duty cycle is adjusted by the MPPT, as it seeks to push maximum current into the battery..

Re: MPPT implementation ,how to balance

Example for what i mean:

If I set PV voltage to 18 and current to 8 , then the buck converter will output voltage less or more than 14, it's mean not adjusted voltage

and if I set output voltage to 14 , then load on panel will change and will lose MPP

Re: MPPT implementation ,how to balance

you can onlly draw peak power as long as the load can take it - if the battery is charged you cannot poke peak power into it - or you will overcharge and damage it, hence peak power is over-ridden by Imax and Vmax to the battery ...

Re: MPPT implementation ,how to balance

Easy peasy said:

you can onlly draw peak power as long as the load can take it - if the battery is charged you cannot poke peak power into it - or you will overcharge and damage it, hence peak power is over-ridden by Imax and Vmax to the battery ...

Click to expand...

you are right, but if I want to add load to battery like inverter , so I need to get max power , and voltage not exceed 14 , with MPP how ?????????

if I set MPP by duty cycle how to grantee output voltage not overvoltage battery or inverter

Re: MPPT implementation ,how to balance

You need an MPPT controller / charger that will allow a higher terminal voltage, i.e. higher than standard float of 13.6V, 14V should be enough if your inverter runs off 12V.

Of course, you can change everything over to 24V or 36 or 48V, less current, smaller wires, ... same power.

- - - Updated - - -

if the sun goes way while you are hoping for peak power then the battery will have to supply the difference... usually people have too small a solar array, and too small batteries for running their loads, leading to no full re-charging of the batteries, and too much drain on the batts, leaving them flat too often, and causing reduced capacity from the batts in a pretty short time ...

Re: MPPT implementation ,how to balance

Hi,

MPPT is very useful with grid tied solar systems, because all the available energy of the sun can be used .. to earn money.
You may use all the solar energy all the time.

But with non grid tied systems ... you can not use all the available sun energy .. as soon as the batteries are (almost) full and charge current has to be reduced.
This occurs when battery voltage is close to 13.6V.
In this case MPPT is of no use.

Load connected or not ... the charge current will be reduced when battery voltage is close to 13.6V.

I doubt that there is a big benefit of an MPPT system vs a non_MPPT system at a non_grid tied system.
It depends on many parameters: sun energy and timing, battery capacity, battery charging efficiency, load behaviour and timing....

Klaus

Re: MPPT implementation ,how to balance

I know if you fully charged battery , no benefit for MPPT

but I assume there is load on panel like inverter that need full panel power, I need the answer how to set duty cycle to get MPP and regulate output voltage in same time

Re: MPPT implementation ,how to balance

Hi,

but I assume there is load on panel like inverter that need full panel power, I need the answer how to set duty cycle to get MPP and regulate output voltage in same time

Click to expand...

Please understand that the MPPT controller doesn´t know about your connected load and how much power it draws.
It just "sees" the battery voltage.

If it is below 13.6V it will push as much power is availabe.
If it is about 13.6V it will reduce power.

***
If [solar_power > load_power] then the battery will be charged, thus the battery voltage will rise, until the battery is full
If [solar_power < load_power] then the battery will provide eletrical energy and thus the battery voltage will drop

Klaus

Re: MPPT implementation ,how to balance

In off grid solar systems you will be able to track the VMP as long as your battery or load is demanding excess or equal power than your PV can deliver. Otherwise your battery will become full and you are forced to limit your pwm width to prevent over charging of your batteries.

Re: MPPT implementation ,how to balance

then if battery full charged and we add load, MPPT system start to search for maximum power that not overvoltage battery ?

Re: MPPT implementation ,how to balance

Hi,

battery full: voltage = 13.6V, no charge current, no MPPT

add load:
* battery voltage drops
* charge current increases
* whether MPPT or not depends on load current (which influences battery voltage) and solar power --> see post#9

Klaus

Re: MPPT implementation ,how to balance

Not surely in all the conditions. When battery is fully charged, the load demand has to be more than the PV power input for the MPPT to start tracking.

Re: MPPT implementation ,how to balance

When it comes to battery charging, there's only three main stages: bulk, absorption and float. Depending on the actual stage (by reading the battery VOLTAGE), your (MPPT) charge controller will adjust the output CURRENT.

That's it, the charger will always act as a variable CURRENT SOURCE. Moreover, the PV panel itself it's a COURENT SOURCE, too.

But, depending on the PV panel output current, the voltage across it will also change.

Now, if you want to maximize the PV panel output power you could

(a) measure the charger input current AND the voltage across the PV panel (the charger input voltage) or

(b) measure the charger output current AND the battery voltage (the charger output voltage).

In practice, it's obvious that the second option is the way to go, as you need to monitor the battery charging process anyway.

So, the charging alghorithm should look like that: the battery needs (could accept) more current? Then increase the charger PWM duty cycle. If the charger output current increase, then you're heading in the right direction (toward MPP). If the output current is decreasing, then you're going in the opposite direction (away from MPP) hence you need to decrease the duty cycle.

In simple terms, that's all about the MPPT alghorithm (P&O - perturb and observe).