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MPPT Solar and Wind Power Boost Charge Controller Jump to: navigation, search
This circuit matches a low voltage solar or wind turbine input to a higher voltage battery. An analogue circuit will measure incoming current and voltage inputs to set the maximum power point tracking (MPPT) and boost the output voltage up to charge a higher, or equal voltage, battery. Input voltage range: 9v through 60v. Output battery voltages: 9v through 60v. MPPT will work only if the battery is higher than the input source. Otherwise, the circuit will act like a direct connection, source to output. It is based on the LTC3703 boost converter IC.
http://vimeo.com/tag:ltc3703
I still have more testing to do. Later, I think I will sell my nine extra boards with one LTC3703 soldered in place, for $59.95US if you want to try the circuit. After they are gone, I might release the board layout diagram, which is critical to success. I burned up a lot of parts with spikes, before succeeding.
It is 9v through 60v MPPT boost to a 48v nominal lead-acid battery. It needs more testing after I attach a wind turbine. Otherwise, it seems to work, so far. How much power can it handle? I am not sure yet. I think 500 watts minimum and maybe 1K watts with more copper over the traces.
This circuit is an analogue computer, when run without a microprocessor. As rpm voltage rises, current is allowed to rise proportionally. The variable loading math is P = I(V-offset) and (V-offset)/I = R (like a fixed resistor load) and I x constant = V. The op amp pegs I equal to V. It is suitable for solar. Wind is a cubed relation, not squared extraction, like this analogue calculation will yield in wind; eg. 2I and 2V = 4P. So, it will likely need the microprocessor for optimizing wind MPPT, but without a microprocessor will be interesting. It will be better than feeding my very high voltage battery, directly because my generator rarely gets above threshold volts, which is 48v to 59v, depending on how full. So it needs a boost converter. It is doing integration math, via the op amp. I added a pin header for optional microprocessor control, which I have not tested, yet.
Page 1: Input from 3 Phase and powering ICs.
Temporary list (I'll source them from digikey.com with their part numbers later)
Simple Solar MPPT Circuit Using IC555 - PWM Maximum Power Point Tracker Posted by Swagatam Majumdar
A simple yet effective solar panel MPPT charger circuit can be built using a couple of 555 ICs and a few other linear components. Let's learn the procedures.
An MPPT or Maximum Power Point Tracker for solar panels is a method which enables deriving maximum available current from a solar panel throughout the day without disturbing its specified voltage, thus allowing greatest efficiency from the panel.
As we all know, acquiring highest efficiency from any form of power supply becomes feasible if the procedure doesn't involve shunting the power supply voltage, meaning we want to acquire the particular required lower level of voltage, and maximum current for the load which is being operated without disturbing the source voltage level, and without generating heat.
Briefly, a concerned MPPT should allow its output with maximum required current, any lower level of required voltage yet making sure the voltage level across the panel stays unaffected.
One method which is discussed here involves PWM technique which may be considered one of the optimal methods to date.
We should be thankful to this little genius called the IC 555 which makes all difficult concepts look so easy.
In this concept too we incorporate, and heavily depend on a couple of IC 555s for implementing the MPPT effect.
Looking at the given solar mppt circuit using IC555 we see that the entire design is basically divided into two stages.
The upper voltage regulator stage and the lower PWM generator stage.
The upper stage consists of a p-channel mosfet which is positioned as a switch and responds to the applied PWM info at its gate.
The lower stage is a PWM generator stage. A couple of 555 ICs are configured for the proposed actions.
IC1 is responsible for producing the required square waves which is processed by the constant current triangle wave generator comprising T1 and the associated components.
This triangular wave is applied to IC2 for processing into the required PWMs.
However the PWM spacing from IC2 depends on the voltage level at its pin#5, which is derived from a resistive network across the panel via the 1K resistor and the 10K preset.
The voltage between this network is directly proportional to the varying panel volts.
During peak voltages the PWMs become wider and vice versa.
The above PWMs are applied to the mosfet gate which conducts and provides the required voltage to the connected battery.
As discussed previously, during peak sunshine the panel generates higher level of voltage, higher voltage means IC2 generating wider PWMs, which in turn keeps the mosfe switched OFF for longer periods or switched ON for relatively shorter periods, corresponding to an average voltage value that might be just around 14.4V across the battery terminals.
When the sun shine deteriorates, the PWMs get proportionately narrowly spaced allowing the mosfet to conduct more so that the average current and voltage across the battery tends to remain at the optimal values.
The 10K preset should be adjusted for getting around 14.4V across the output terminals under bright sunshine.
The results may be monitored under different sun light conditions.
The proposed MPPT circuit ensures a stable charging of the battery, without affecting or shunting the panel voltage which also results in lower heat generation.
Note: The connected soar panel should be able to generate 50% more voltage than the connected battery at peak sunshine. The current should be 1/5th of the battery AH rating.
Note: The input from the solar panel which connects with pin5 of IC2 must be fed via a BJT stage (wired as common collector), it should be done in the following manner.
Solar feedback input at pin5 of IC2 is disconnected and connected with the base of a BC547 transistor, collector of this transistor is connected with the supply pins of the ICs (pin4/8), while the emitter is joined with pin5 of IC2.
The above is necessary because pin5 of IC555 needs relatively more current to respond, and may not work satisfactorily if the input lacks sufficient current.
How to Set up the Circuit
It may be done in the following manner:
Initially keep S1 switched OFF.
Expose the panel to peak sunshine, and adjust the preset to get the required optimal charging voltage across the mosfet drain diode output and ground.
The circuit is all set now.
Once this is done, switch ON S1, the battery will start getting charged in the MPPT mode.
Adding a Current Control Feature
A careful investigation of the above circuit shows that as the mosfet tries to compensate the falling panel voltage level, it allows the battery to draw more current from the panel, which affects the panel voltage dropping it further down inducing a run-away situation, this may be completely against the MPPT law.
A current control feature as shown in the following diagram takes care of this problem and prohibits the battery from drawing excessive current beyond the specified limits. This in turn helps to keep the panel voltage unaffected.
RX which is the current limiting resistor can be calculated with the help of the following formula:
RX = 0.6/I, where I is the specified minimum charging current for the connected battery
A crude but simpler version of the above explained design may be built as suggested by Mr. Dhyaksa using pin2 and pin6 threshold detection of the IC555, the entire diagram may be witnessed below:
I/V Tracker Circuit for Solar MPPT Applications Posted by Swagatam Majumdar
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.
So far I have tried to present a number of different solar MPPT simulator circuits, however these have been just ordinary solar optimizer kind of designs, and not actually a solar MPPT because these circuits never involved the tracking of the I/V curve or the optimum "knee" of the curve. You may want to have a look at these circuits, as given below:
Poor mans MPPT
PWM based MPPT Simulator
Incremental Conductance MPPT Simulator
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:
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.
DIY MPPT Solar Charge Controller
MPPT Block Diagram
The holy grail of solar charge controllers is the maximum power point tracker (MPPT). How easy would it be to design one that’s both cheap and efficient?
The PWM controller is pretty much finished now, so we’ll use it as a building block and add on MPPT functionality. The sketch shows a few components added to the PWM controller block diagram; a capacitor across the solar panel input, an inductor in line with the battery connection and a Schottky diode to ground.
These additional components would have very little effect at the PWM controller’s switching frequency of around 100Hz, but increase that frequency into the tens of kiloHertz range and the circuit would start to behave as a switched-mode DC-DC buck converter. It should be possible to hold the solar panel input at a different voltage to the battery output.
What about maximum power? How do we measure both the voltage and current from the solar panel. Well, we don’t. We just assume that at maximum solar panel power, we’ll get maximum charge current flowing into the battery. We’ll simply look for maximum battery voltage as we tinker with the PWM duty cycle (otherwise known as peturb and observe).
Just one caveat. I have absolutely no idea if this will work, but I’m keen to give it a try!
