[General] Impedance matching in MPPT

[thahseen.claysy@gmail.com]

Hi,

I have designed buck converter, planing to take to next stage - MPPT converter.

The designed buck converter is for 30V input(max) from a 24V panel to 12V output.

How can I implement impedance matching in buck converter.

 

[Easyrider83]

What for? MPPT alghorithm based on maximum power point tracking. Impedance mathing actual only for RF I suppose.

 

[BradtheRad]

By impedance matching, I suppose you mean maximum power transfer?

MPPT is often performed by an algorithm called 'perturb and observe'. A microcontroller is the normal method. It tries different duty cycles, watching to see how to produce greatest Ampere flow.

 

[Warpspeed]

MPPT is a kind of impedance matching, although both source and load impedances will both change over a very wide range during normal operation.

The peturb and observe software algorithm has proven to be a very good solution.

If you test your solar panels with a wide range of loads and a power meter, you might be surprised to find that the power always peaks at very close to the same panel voltage from twilight to full sun.

If your 12v output voltage is being held fairly constant by a very large battery, a very simple approach would be to arrange the pwm duty cycle to regulate the input voltage to the buck converter instead of regulating the the output voltage.
This works backwards, a high input voltage must increases the duty cycle.
Usually a high output voltage must decrease the duty cycle.
So changes to your error amplifier circuit will be required by swapping around the reference and sense inputs.

This is all possible because the input is from a current source.
The output from the buck regulator must be tied to a battery load for this to work properly.

Your buck regulator will also need a very large input capacitor to smooth out the narrow current pulses and provide a constant dc load for the solar panels, especially under very low solar output conditions.

A shunt regulator placed across the battery will prevent overcharging.
All this is the simplest possible (all hardware) solution.

If software is "more your thing" then the "peturb and observe" algorithm is the recommended approach.

 

[thahseen.claysy@gmail.com]

Ya. I meant the same Maximum power point tracking(MPPT).
I am using the micro controller for controlling the buck converter already I have.
My question is how can implement MPPT to that circuit.
What is the concept of MPPT algorithm? impedance matching? Any one please help me...

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Thank you Toni.

 

[Warpspeed]

I am using the micro controller for controlling the buck converter already I have.
My question is how can implement MPPT to that circuit..

The basic idea of "perturb and observe" is you set some initial PWM duty cycle and measure the power being transferred into the load.
Power equals volts times amps.

You then make some small change to the PWM duty cycle, and again measure the power into the load.

If power has increased, you make another small change in the same direction.
If the power has decreased, you make the next small change in the opposite direction.

That way, the software continually adjusts the duty cycle in the direction of maximum power transfer into the load.

 

[Arya Kumar]

@warpspeed has explained MPPT P&B technique very welll.
I will just say in other words. If u see graph of V(voltage) vs I (current) you will notice if you increase current you will loose voltage and if you increase voltage you will get less current.
On the extremes open circuit panel has 0 current but ideally infinite voltage(actually 21 volts if it is 12 volt system).. and if you short circuit you have infinite current but 0 voltage.
So if we cross V X I either places you have zero power.

but we are interested in getting maximum power. So we have to look for a point in the curve which gives maximum value for V X I.
So lets keep our starting operating point at 0 current and maximum voltage. Use a micro controller to get value of V and I.
now you have to decrease the resistance so use a Mosfet between souce and load and using PWM technique change the resistance.
change in PWM .....change in resistance .....change in V/I.
keep changing the PWM till ur power keeps on increasing.
after a particular point on further increment of PWM your power will decrease so stop at that point that will come out to be your MPPT point.
Keeping checking for MPPT point at regular interval cos sun radiation may change the MPPT.
after you do this there are many ways to improve ur design