diy solar

diy solar

Practical implementation of a MPPT algorithm

In real world, the higher wattage peak would have more heating so more current leaking through the photodiodes, which could shift Vmp to a lower voltage than what 25 degrees C gives (but lower illumination could be at still lower voltage).
Yeah! Real-Life(TM) can be quite different than lab conditions.
Vmp is heavily dependent on temperature, which is not a constant.
When you have a succession of sunshines / clouds the Vmp is really dancing: the cells will cool-down then warm up following the irradiance with a few minutes delay. Any MPPT algorithm will have a real hard time to deal with that.
I have decided to catch this situation and switch over to 90% of Voc, which is a good approximation of Vmp for 5 minutes before returning to MPPT.
After 5 minutes I might get another collapse, but one collapse for 15 seconds every 5 minutes is not really impacting the day harvesting.
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When you have a hard shade on a few cells across sub-strings, the span between Voc and Vcollapse gets very narrow.
Then it depends again on whether the remaining sub-strings are generating more voltage than the battery or not.
If the shade comes from a bird, the situation changes that fast that a sweep will return wrong results anyhow.
A hard time for MPPT algorithms again...
The modern half cell panels with 2 strings in parallel within a single panel are really superior with respect to bird shading.
 
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We usually think of shaded panels getting bypassed by current through a diode.
Shading is not shading...
It heavily depends on:
-Is it a hard shade (birds, chimney's, wall's shades on bright sun) or a soft shade (clouds).
-if it is a hard shade, is a complete sub-string shaded or only a few cells over more than one sub-string...
 
??? I cannot really believe that.
It would mean that with short wires, the mosfets would short the panel?
The would also mean that the external wires would carry the huge current pulses of the boost conversion and become powerful antennas for massive RF interference.
Never would any FCC accept such a design!
Were did you get that info from?
Aren't the two mosfets at the input just the usual ideal diode for a flowback protection?
Yes it's the usual ideal diode with pwm design o_O

Sorry i will don't explain again what i seen on my repaired mppt and what my digital scope showed at the screen.
You simply can't make antenna with a dc current souce dipole
 
Yes it's the usual ideal diode with pwm design o_O

Sorry i will don't explain again what i seen on my repaired mppt and what my digital scope showed at the screen.
You simply can't make antenna with a dc current souce dipole
Not DC current!

If you pulse 30A 70V at 50Khz to 150Khz over 30m cables (like a boost converter "using the wires as inductance" would do), your radio noise would probably be noticed in Moscow and you would get within days a pretty unfriendly visit at home, believe me!

Moreover a boost converter, which would not have good strong caps at the inductance side opposite to the FETs would be VERY ineffective.
These caps would have to be on the panel side of the power cables.
It's just silly...

Sometimes what a digital scope shows in the immediate vicinity of high power DC-DC converters (a SCC is just that) is far from being a reliable image of the measured point. Current loops are very common...
 
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Not DC current!

If you pulse 30A 70V at 50Khz to 150Khz over 30m cables (like a boost converter "using the wires as inductance" would do), your radio noise would probably be noticed in Moscow and you would get within days a pretty unfriendly visit at home, believe me!

Moreover a boost converter, which would not have good strong caps at the inductance side opposite to the FETs would be VERY ineffective.
These caps would have to be on the panel side of the power cables.
It's just silly...

Sometimes what a digital scope shows in the immediate vicinity of high power DC-DC converters (a SCC is just that) is far from being a reliable image of the measured point. Current loops are very common...
Maybe it's just a boost topology at the input (pretty sure of topology) just for perturbing the voltage at the input, deactivate mosfet lowering solar voltage by 0.6V step easy without change duty cycle on buck module and see what's happen on mppt.
I'm sure im seen pulse on gate on the mosfet so it's not a dumb ideal diode.
It's can also protect input for high voltage with lowside mosfet and made reverse polarity protection
 
Maybe it's just a boost topology at the input (pretty sure of topology) just for perturbing the voltage at the input, deactivate mosfet lowering solar voltage by 0.6V step easy without change duty cycle on buck module and see what's happen on mppt.
I'm sure im seen pulse on gate on the mosfet so it's not a dumb ideal diode.
It's can also protect input for high voltage with lowside mosfet and made reverse polarity protection
I know the Victrons have a PWM mode in the low voltage realm (less than 3V difference to bat voltage) where MPPT does not work any more.
 
Highest current point is Isc. Maximum amps x zero volts = zero power.
The curve hits zero in two places; objective is to find the maximum.

Just like the "matched impedance provide maximum power transfer" we were taught in school. And proved by taking the derivative.
Then I met a PhD and company fellow who actually believed it and used it in his work. I explained why he was wrong (I like to do that!) in the particular application, and his calculation of power was not correct.
Yes, but we will never (hopefully) be running panel into a short circuit so eliminate that point completely. My point is simply that if we dance around a particular duty cycle we will see current go up or down. If current goes up we can (?) assume that cell voltage tended to go up with increased current product with tiny (LiFePO4) ESR. So why is there a need to monitor voltage as well as current?
 
Start with open circuit, current is zero.
As you draw more current, current increases and so does power, and current into battery.
As you continue drawing higher current from PV, power decreases and current into battery decreases.
Eventually, duty ratio = 100%, PV voltage equals battery voltage.

It may be that monitoring current on battery side, not on PV side, is sufficient to find and follow a local maxima in power production.
Of course, you are subject to being confused by variations in current draw from other loads changing battery voltage and therefore MPPT output current.

For some arrays and some shading conditions, you need to explore the entire duty ratio range, see if there is another maxima which is higher than the one you got stuck on.
 
Yes, but we will never (hopefully) be running panel into a short circuit so eliminate that point completely. My point is simply that if we dance around a particular duty cycle we will see current go up or down. If current goes up we can (?) assume that cell voltage tended to go up with increased current product with tiny (LiFePO4) ESR. So why is there a need to monitor voltage as well as current?
Start with open circuit, current is zero.
As you draw more current, current increases and so does power, and current into battery.
As you continue drawing higher current from PV, power decreases and current into battery decreases.
Eventually, duty ratio = 100%, PV voltage equals battery voltage.

It may be that monitoring current on battery side, not on PV side, is sufficient to find and follow a local maxima in power production.
Of course, you are subject to being confused by variations in current draw from other loads changing battery voltage and therefore MPPT output current.

For some arrays and some shading conditions, you need to explore the entire duty ratio range, see if there is another maxima which is higher than the one you got stuck on.
In fact, I am not directly working on duty ratios.
I have on the battery side 2 fast paced (125mS) voltage and current control loops and on the panel side a slower (1s) voltage control loop that modifies the battery control current loop according to MPPT.
I also have the ability to switch over between fixed battery voltage and current control, fixed panel voltage and MPPT operation.
That isn't really useful in productive operation, but gives me the great opportunity to understand deeply what happens in specific situations like shaded panels or bad weather.
In the battery current control mode, I have also the possibility of running a grid-tied converter on the panel and just diverting from the same panel a small fixed part of the energy, just to keep my batteries fully charged afloat, which is a much more efficient, than charging the batteries from AC.
 
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Start with open circuit, current is zero.
As you draw more current, current increases and so does power, and current into battery.
As you continue drawing higher current from PV, power decreases and current into battery decreases.
Eventually, duty ratio = 100%, PV voltage equals battery voltage.

It may be that monitoring current on battery side, not on PV side, is sufficient to find and follow a local maxima in power production.
Of course, you are subject to being confused by variations in current draw from other loads changing battery voltage and therefore MPPT output current.

For some arrays and some shading conditions, you need to explore the entire duty ratio range, see if there is another maxima which is higher than the one you got stuck on.
I'm sorry, yes, I was speaking of battery side current.
 
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