Optimizing power by tracking is the key feature which makes solar MPPT concept so unique and efficient, where the complex and non-linear I/V curve of the solar panel is tracked and switched for creating maximum optimal conditions for the connected load.
The Circuit Concept
I have been trying hard to design something that would in true sense track the I/V curve or the power curve of the panel, and correct it automatically whenever it drifts from the optimal points.The proposed design is based on the same grounds, but here I have included only the I (current) tracking stage in order to keep things simple.Actually it's the current that really matters and is directly proportional to power of the panel so I thought keeping this parameter in control could fulfill the job.
Let's try to understand the design with the following observations:
How the Circuit Functions
Looking at the proposed solar MPPT I/V curve tracker circuit diagram, the BC547 at the extreme right along with the 10k resistor and 1uF capacitor forms a linear ramp generator.
The central stage comprising the two 555 ICs form a variable PWM controlled output generator, while the IC 741 stage becomes the actual current tracker stage.
When the voltage from the solar panel connects across the BC547 collector and ground, due to the presence of the base 10k/1uf network, the emitter follower provides a gently rising voltage to the 555 PWM generator stage.
The ramp activates IC2 and forces it to generate a correspondingly rising PWM output at its pin#3 which goes to the gate of the driver mosfet.
The mosfet responds to these pulses and gradually increases its conduction and provides current to the battery in the same incremental order.
As soon as the current intake across the battery begins rising, an equivalent voltage level is translated across the current sensing resistor Rx which gets applied a pin#3 of the 741 IC.
The above potential also hits pin#2 of 741 via the dropping 1N4148 diode so that pin#2 follows this potential in tandem with pin#3 but lags behind by about 0.6V due to the presence of the series diode.
The above condition allows the opamp to begin with a high output which keeps the diodes at its pin#6 reverse biased.
As long as the current keeps climbing with the ramp, opamp pin#3 continues to be higher than pin#2, thus keeping the output higher.
However at some point of time, which might be after the I/V curve has just crossed, the current output from the panel starts dropping or rather drops abruptly across Rx.
This is sensed by pin#3 immediately, however due to the presence of the 33u capacitor, pin#2 is unable to sense and follow this drop in potential.
The above situation instantly forces the pin#3 voltage to become lower than pin#2, which in turn reverts the output of the IC to zero, forward biasing the connected diode.
The base of the ramp generator BC547 is dragged to zero forcing it to switch OFF, and reset the whole procedure back to the original state. The process now begins afresh.
The above procedure continues and ensures that the current is never allowed to fall or cross the inefficient region of the I/V curve.
This is just an assumption, a concept which I have tried to implement, it might require a lot many tweaking and alignments before it can become truly result oriented.
The output from the mosfet may be integrated with an SMPS based converter for even higher efficiency.
Anonymous says
Hi Swagatam,
I'll take a look on proposed solutions and if I have any questions will ask them here or there.
Regards
Lubo
Swagatam says
Sure Lubo, you are most welcome!
Anonymous says
Hi,
I'm currently looking for a MPPT curcuit for water heater.
I have 4 260 Wp panels in series. Could order water hater element wth virtually any resistance.
Is it possible to use any of proposed circuit diagrams?
Thanks
Swagatam says
Hi, an MPPT can be much complex to build, instead you can simply hook up the coils directly with panel's output.
by the way a more sensible approach would be to use concave mirrors for the heating purpose…
Anonymous says
Hi Swagatam,
I use PV panels with dula purpose – electricity suply and heating the water.
But instead of adding more bateries and bigger inverter, I want to heat the water directly from PV.
Because direct connection is not so efficient, I'm looking for simple MPPT, so to have more time for charging the batteries.
Regards
Swagatam says
Hi, I have a kind of MPPT desin published in this website, you can find it below
https://homemade-circuits.com/2015/11/simple-solar-mppt-circuit-part-2.html
instead you can simply incorporate a buck converter in order to generate electricity more efficiently.
If turning the solar panel manually according to the sun rays is possible, then you could also think about the following design with great efficiency….
https://homemade-circuits.com/2013/04/solar-water-heater-with-battery-charger.html
Anonymous says
which software do you use to draw this circuits? much appreciations and thanks.
Anonymous says
Hello sir, i want to make solar based submersible motor which are used in farm..because of in farm there is lots of problem of main supply..thnks and regards.. chirag hirani
Swagatam says
Hello Chirag,
I'll try to design it, and post it soon.
alex says
thank u for your reply. Why I asked about inreasing the current is when u look on the display of say an outback mppt display u see incoming current say 10amps and out current say 15amps so i thought the mppt controler was increasing the the incoming current. i am now confused with what to build because u are saying adding another 741 as voltage tracer would help. Should we wait until u complete that part of the circuit because I am sure there are a lot of people folowing your links on making a mppt controller we need a final circuit please help us here Mr Swagatam
Swagatam says
If you compare the input and output power levels, you will find it to be equal, in short the MPPT power can never exceed the panel power output.
The voltage tracker stage will be also simiar to the current tracker stage except the input supply which will be received from the emitter follower at pin#5 of IC2, the diode cathode outputs of the two opamps may be then made into and connected with the 547 base, however as discussed in one of my posts an MPPT will be most efficient when its output is isolated and dropped via an SMPS circuit.
alex says
Mr Swagatam I have been following ur post for months especially on the mppt controllers i appreciate ur improvement here. The operation sounds complex but I am willing to give it a try. So will this controller increase the current that the panel is putting out
Swagatam says
No MPPT in this world can increase current, they are designed only for extracting the most from the panel in terms of voltage and current, it can never exceed the instantaneous maximum current production of the particular panel.
If you can make the 741 work correctly then it's done, you would definitely be able to make the above circuit work as per the expectations.
I think an identical 741 voltage tracker also needs to be added here, because tracing and optimizing voltage of the panel is also crucial.