MPPT solar battery charger

[theFob]

Hi iw,
I'm impressed of your work.
I played once with mppt converters and i know how crazy is.
the attachments show dc simulation of 21V@8A photovoltaic. May be will be useful for you. I have dozens simulations of buck, boost and sepic converters, but i didn't finish the work because the 'client' give up. Now i have 3kg prototype but no panel to play
Allow me to ask you what mppt algorithm you use ?
Some of them are:
* perturb and observe (P&O - sign dP)
* incremental conductance (dP/dV=0)
* constant voltage or current (CV,CI)

May be i'm too lazy to read all your code and find out, sorry.

I suggest reading of this:

Comparative Study of
Maximum Power Point
Tracking Algorithms
D. P. Hohm and M. E. Ropp*,y
Electrical Engineering Department, South Dakota State University, Brookings, SD 5700-2220, USA

It helps me a lot, amazing study.

[iw2fvo]

Thanks TheFob,
I think that the trick to get a stable MPP tracking is that the "Perturbation" must generate a delta power that is greater than the " noise Power ".
If the VP and IP acquisistion by the PIC ADC has some noise, then the power has a noise too. The perturbation created by " DUTY_step" must generate a delta power response bigger than the noise power.
If the hardware is good then and the noise low we could use a duty_step=1 . If you have a sensible noise you could increase it to 2, 3 , 4 ...
The piece of program is this:

MPPT: '................................................. ..............

' PANEL DATA CHANGE

IF WP>WP_OLD THEN ' POWER INCREASES
DP=1
ELSE
IF WP<WP_OLD THEN ' POWER DECREASES
DP=0
ENDIF
ENDIF

if wp=WP_OLD THEN RETURN

IF VP>VP_OLD THEN ' VOLTAGE INCREASES
DV=1
ELSE
IF VP<VP_OLD THEN ' VOLTAGE DECREASES
DV=0
ENDIF
ENDIF

' HILL CLIMBING.... FOR MPP SEARCH

' CLIMBING FROM LEFT

IF DV=1 AND DP=1 THEN
DUTY=DUTY-DUTY_S ' DECREASE LOAD TO INCREASE P_VOLTAGE
ENDIF

'DESCEND TO THE RIGHT

IF DV=1 AND DP=0 THEN
DUTY=DUTY+DUTY_S ' INCREASE LOAD TO REDUCE P_VOLTAGE
ENDIF

' CLIMBING FROM RIGHT

IF DV=0 AND DP=1 THEN
DUTY=DUTY+DUTY_S ' INCREASE LOAD TO REDUCE P_VOLTAGE
ENDIF

' DESCEND TO THE LEFT

IF DV=0 AND DP=0 THEN
DUTY=DUTY-DUTY_S ' DECREASE LOAD TO INCREASE P_VOLTAGE
ENDIF

GOSUB SET_PWM

WP_OLD=WP
VP_OLD=VP

RETURN

Thanks for the interest,
Regards,
Ambrogio
IW2FVO
North Italy

[theFob]

Thanks iw,
I suppose the first chart explains your code. I found it in the net. But i'm still out of focus.
Why is the measurement of dV? As is shown on the simulation, the voltage of the panel
is almost constant up to 90% of available current. So there is "constant voltage" and "constant current" methods. The voltage remain the same even at night, of course with almost no load. The photons flow become electrons flow, i.e. available current. So the panel is kind of current generator.
And of course, measured dV will be small and inaccurate, may be the noise is from there.
I used hardware circuit similar as algorithm in second chart. So i'm interested of your work. I will try to find my circuits, but unfortunately they are on almost dead HDD ...

Regards

[theFob]

ok, i answered myself. I did simulation again.
The voltage have little change indeed and can be used to determine the direction of duty. But this can be done without this too.
Iw, if i find some time i will make Proteus simulation with your code.
Will be nice to check some other algorithms before the fire of soldering iron



PS I don't know how to resize the images, sorry

[iw2fvo]

Thanks theFob,
I am interested in seeing the simulation of my program when you have time .
The mpp_tracking code I am using works well . My program allow to find out the MPP manually using the potentiometer. It also allows to scan the duty cycle to search the MPP : this is automatic.
The normal mode of the program continuously tracks the MPP. There is a very minor difference among them.
Thanks again,
regards,
Ambrogio
IW2FVO
North Italy

[theFob]

Hi iw,
I'll be glad to do this Had no such fun from long time.
I need the nominal voltage and maximum current values of the panel or just the model.
I noticed the lack of general decoupling diode in your circuit. Is needed for reverse current protection. May be the panel have such internally.
Also a small input filter will be good idea, because the input current of the buck is trapezoidal and is very stressful for the panel.
So the preferred converters are boost (when is possible) or sepic. The input currents there are triangle in continuous mode.
I allowed myself to check your CQ on the net. How far you've come with SG3525 inverter ? I guess it will work with this converter .... ?

Regards

[iw2fvo]

TheFob:
panel data are:
max power 50 w
open circuit volt: 21.6 Vdc
short circuit current : 3.04 A
Max pp volt: 17.6 Vdc
Max pp current : 2.84 A
There is a reverse protection diode ( see D1 on buck converter schematics ).
There is 220 uF at the buck input . Could it be too small ?
The panel keeps the SLA battery charged and so I do not have any inverter to produce line alternate power. I just need 12 VDC nominal.
CQ: >> I have a fully working homemade SDR rx tx for the HF. I have to re_install the antenna that went out completely during the last windy thunderstorm.
I plan to do that at the beginning of the next month.
Thanks.
73, IW2FVO.
Ambrogio