Solar MPPT Output Voltage Constant

[SACHIN C]

MPPT Parameters are as follows,
1)Power : 300Wp
2)Vin : 36Voc
3)Iin : 10A

Selected P&O Algorithm accordingly edited code.But,the question is how we can achieve Constant or Regulated Voltage at the Output side of MPPT?
Generally if we go with Flyback or Forward or with any other Isolated Topology for MPPT Technique we are not using any feedback from output in MPPT case.But we use feedback in general DC-DC or AC-DC Converter to keep Output Voltage Constant.

Thanks & Waiting For Knowledge Enhancement,:thinker:
Sachin

 

[Tahmid]

Why can't you have a feedback for the MPPT case? You can't do any kind of control without feedback. Surely you'd want to read back the output voltage and current to calculate the power and then change the output parameters to maximize the power.

I assume that by P&O you mean perturb and observe. What specifically is your algorithm doing? Or are you doing the perturbing and observing by manually changing drive parameters?

 

[SACHIN C]

We are calculating the PV Power by measuring Voltage & Current then adjust Duty Cycle accordingly in Perturb & Observe method.But,the worry part is how to regulate the output Voltage of MPPT if we are going with Isolated Topology as the duty cycle depends on Input i.e PV Panel parameters.


Thanks & Waiting For Knowledge Enhancement,:thinker:
Sachin

 

[chuckey]

If we presume that your solar array is charging a 24V battery. If the battery is disconnected the output voltage must not rise above 26.5V, so as to protect any low current equipment still connected. If the battery gets flattened then the current output must be limited to the maximum allowed by the battery design, say 6A. As the battery voltage rises say to 18V, the battery load can be made operative, so the output current can now be 6A + output load. As the battery voltage rises, the battery current should be reduced, so with a system voltage of 26.5V the output current is the load current.
So it looks with my figures that under Vbatt=18V, the MPPT point is limited to Ibattmax. So you need a battery current monitor. At Vbatt = 18V the load should be switched on, so you need a Vbatt voltage detector and an output to switch the load on. Then as Vbatt rises the Ibatt should be tapered off until it is zero at Vbatt = 26.5V, when the MPPT should be limited.
So if you have a control line or a variable, it should be set to 100% for Vbatt < 18 V and limited to by Ibatt max, and then should equal (26.5 - Vbatt)X 100/8.5 %.
Frank

 

[naseerak]

MPPT is not about regulating voltage, rather it extracts maximum power from the array and is mostly used in charging a battery, however if the battery voltage is reached to the specified level the MPPT algo is paused and charging algo is initiated. and The MPPT Algo is again initiated after the fall of battery terminal voltage.

 

[Tahmid]

We are calculating the PV Power by measuring Voltage & Current then adjust Duty Cycle accordingly in Perturb & Observe method.But,the worry part is how to regulate the output Voltage of MPPT if we are going with Isolated Topology as the duty cycle depends on Input i.e PV Panel parameters.


Thanks & Waiting For Knowledge Enhancement,:thinker:
Sachin

If you're doing MPPT, then you don't want to regulate the voltage. That defeats the purpose of trying to implement MPPT. You'll have a variable voltage since the maximum power point will vary and be at different voltages depending on the illumination and temperature of the solar panel(s). You want to maximize power which will need voltage to be a variable.

 

[chuckey]

If you run your solar array into a low pass filter then chop the DC output to convert it to AC, then if you monitor the SOLAR array current and voltage, you can change the on/off time of your chopper, to present a changing input impedance to the array to find the MPPT. But this is meaningless unless the available power is doing some thing useful. i.e., bright sunshine, the array can produce 36V at 10 A, battery is charged, load is very small. Err what is your MPPT going to do?, it can't find any current? so does it wind up the volts until the battery is charging again? and boil of its electrolyte?
Frank

 

[Tahmid]

If you run your solar array into a low pass filter then chop the DC output to convert it to AC, then if you monitor the SOLAR array current and voltage, you can change the on/off time of your chopper, to present a changing input impedance to the array to find the MPPT. But this is meaningless unless the available power is doing some thing useful. i.e., bright sunshine, the array can produce 36V at 10 A, battery is charged, load is very small. Err what is your MPPT going to do?, it can't find any current? so does it wind up the volts until the battery is charging again? and boil of its electrolyte?
Frank

Of course there should be checking to determine if the battery should be charged or not, or if a load is being driven. In that case only, the MPPT algorithm should be implemented. Otherwise you'd need to either cut off the load or present a constant output voltage. I see now. Is this the regulation that was being talked about? In that case there can be a simple feedback circuitry (such as in DC-DC converters) using a zener-opto combination or for more precision, a TL431 based one. Using an optocoupler will help achieve the required isolation. And if isolation isn't required, a simple voltage divider based circuit can suffice.

 

[naseerak]

Why I said that the battery charging algo is initiated, that means a lot more from trickle charging to keeping the Batt. voltage at standby level of 13.8v or whatever value you wish or dictated by the specs of the battery.

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BASCOM for AVR has a nice function called MAX which picks up the highest value from an array. and is best suited for MPPT.