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designing a charge controller for hybrid system

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diksha.k

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i want to design a charge controller for soar cum wind
Wherein solar panel specifications:
pmax 110W
OC voltage:17.25V
Max current=5.79A
OC voltage=21.7V
Short circuit current=%.90A
wind turbine:
has a PMDC generator
voltage =90V
rpm 2500
current=3.90A
these are the specifications given by the developer who wants a hybrid charge controller to charge his 150Ah smps battery.
I want to take this as my college project.How do i start with this any inputs??
 

Short circuit current=5.90A.
 

It seems that the Vmpp of the panel lies around 17V. You need to design a buck converter with its nominal input voltage at the Vmpp of the panel. While converter design, Vinmax will be Voc, whereas Vinmin can be considered around Vmpp - 0.3Vmpp to be in the range in case the MPP of the panel changes due to lighting conditions.
You can design the converter's output voltage to be minimum 13.8V (Considering 2.30V/cell)

If you consider the charging cycle of a battery, when the battery is not charged, you will need to run the converter in a constant current mode in order to control the charging current through it.
In this mode, the mcu will run the converter in the MPPT mode, so that you extract the maximum current out of it.
For the topping charge, you will gradually need to decrease the charging current depending upon the SOC of the battery.
After the battery has reached 90% of the SOC, you can run the converter in the voltage control mode, just to apply the float voltage to avoid self discharge of the battery.

For more about lead acid battery charging,
 

You really need two controllers, one for solar, and one for wind because the characteristics of each are completely different.

Taking the solar controller first.

The solar panel will produce a current which varies from zero (at night) to a maximum short circuit current in bright direct sunlight.
If you experiment with a power meter under various lighting conditions with an adjustable load, you will find that the maximum power output from the solar panel always occurs around a particular voltage.

So what you really want to do is pull as much power out of the solar panel as possible with a suitable loading, but not overloading it so that the voltage is pulled down below the voltage that produces maximum output power.

What is needed is a buck regulator that regulates its INPUT voltage.
If the solar panel voltage tries to rise, the duty cycle increases feeding more current into the battery. If a cloud passes in front of the sun, solar voltage will try to fall, but the buck regulator reduces its duty cycle, reducing the load on the solar panel, always holding the panel voltage at the optimum point for maximum output power. Power will obviously decrease with a cloud, but it will always be at the maximum that the panel can produce at the time.

This holds the solar panel voltage constant, but the current into the battery rises and falls throughout the day charging the battery, always using as much current as becomes available from the sun.

That takes care of the solar panel.

The next thing to think about is the battery.
Putting maximum solar charge current into the battery all the time is good, until the battery is fully charged. You then need to start thinking about holding the battery voltage at some safe maximum by over riding the control of the solar buck converter.

There are some very clever battery charger control chips that can be used for monitoring the battery. The control output of this chip should be arranged to limit the output of the solar buck converter as required.

The wind machine is more complicated, because like a solar panel, it too can be overloaded. Once again you take your trusty power meter and your adjustable load and set it all up. At a certain wind speed and no load, the wind machine will turn and produce an open circuit output voltage.

As you increase the load, the rotor will slow down, and you will get a certain power reading. More load will slow the rotor even more, and the power will further increase. More load still and the rotor rpm will drop further, but the power will DECREASE. You have just overloaded and stalled the blades.

The problem with this, is that there will be an optimum loading for the wind turbine that varies with wind speed, and every wind turbine is different. Its not as simple as with the constant voltage solar panel, although the idea of optimum peak power loading is the same.

There are several ways to go about this, but the simplest is to use an anemometer to measure wind speed and use that to control the buck regulator that charges the battery. Some kind of lookup table in software where wind speed X generates a particular PWM value for the buck regulator, which you will have to set experimentally for max power output.
Or maybe some kind of maximum peak power self learning algorithm ?

Anyhow, as with the solar controller, the wind controller will need to be over ridden once the battery reaches full charge.
 
The wind generator should always have a load on it. With no load the turbine spins freely, wearing out the bearings. Therefore as you taper charging current to the battery, you should divert excess power to a load (example, to heat water).

Look for Youtube videos of a wind turbine spinning out of control. Eventually the blades fragment and fly away as much as a quarter mile.
 

The solar panel and wind turbine co-gen unit is setup by the developer and we need to do the charger without having them in actual (ridiculous i know) But, can i make a arrangement at lab to test my charger say: I make chopper circuit which will help give variable DC voltage and then charge the batteries at lab.
 

I doubt if its possible to design one small part of such a complex system in isolation and expect it to work properly over the required very wide range of operating conditions.

Everything interacts, and the charger is totally dependant on other parts of the system over which you have absolutely no control.

Both the solar panels and the wind generator need very careful load control to achieve maximum output, and have to work together with the battery charger as a complete integrated system.

I think you are going to be faced with enormous difficulties, a major part of which I suspect will be the attitude of this "developer".
 

You want to draw power from a PV panel at the maximum Ampere level it can put out, continuously (spec is 5.79 A). That is efficient use of the panel, and fastest way to charge. A 150 A-Hr battery can easily absorb 5.79 A as the bulk charge rate.

Therefore your charge controller input should be able to draw maximum continuous Amperes from the panel. Internally it may have a different waveform. That does not need to be at a constant level, but can be triangular which is typical in a buck converter.

- - - Updated - - -

After posting I see Warpspeed brings up the developer's attitude (post #7). The developer probably has some knowledge of storebought charge controllers. He probably expects you to deliver similar performance, at very little cost. It is wise for you to learn what are his expectations, as well as your obligations and liabilities.

It is odd that he does not provide equipment for you.
 

This holds the solar panel voltage constant, but the current into the battery rises and falls throughout the day charging the battery, always using as much current as becomes available from the sun.
That takes care of the solar panel.
The next thing to think about is the battery.
Putting maximum solar charge current into the battery all the time is good, until the battery is fully charged. You then need to start thinking about holding the battery voltage at some safe maximum by over riding the control of the solar buck converter.

thank you,
But would the concept of keeping voltage constant and increasing or decreasing the current flowing in the battery remain same irrespective of the kind of battery(i.e wet or sealed)? Because the charger developed for wet batteries are not supposed to charge sealed batteries as they may damage the battery.And i suppose the charging cycle you mentioned is to charge a sealed battery.
 

thank you,
But would the concept of keeping voltage constant and increasing or decreasing the current flowing in the battery remain same irrespective of the kind of battery(i.e wet or sealed)?
Well yes, the initial problem is trying to get as much power from the solar panels in all seasons, and in highly changing weather conditions.
That requires very carefully adjusting the load on the solar panels.
It has nothing to do with the state of battery charge, or type of battery.
You may have a dead flat battery, and wish you had thirty amps, but there may only be 20mA in a dense fog.

Because the charger developed for wet batteries are not supposed to charge sealed batteries as they may damage the battery.And i suppose the charging cycle you mentioned is to charge a sealed battery.
Usually solar systems struggle, especially in winter.
But in summer there may be a lot more power than the battery needs for recharging, and the charger MUST be designed to ensure the battery operates within its safe working range. And that includes safe maximum charging current and voltage.

The strategy is to always put as much current as is available into the battery, unless there is a definite reason to limit it, which the often is.
 

hi,
As you mentioned i may require to design a buck converter for solar as well as wind but, what i found was the location where the windmill is placed as per the weather forecast the max wind speed is about 4.5m/s and then calculating voltage developed by wind turbine (from formula) we get around 10.99V to 11.75V but not 12V and above so assuming if wind turbine is to be operated in these conditions then, i need to design a boost converter as well..
This is how i am going to start with:
I know there are two sources and which source is providing greater voltage will be checked, After this whether the voltage lies below 12V or above 12V then according to the condition switching for boost conversion/buck conversion respectively.
 

It sounds like you need two completely separate voltage converters both simultaneously feeding the battery, because you might have both wind and sun together.

Optimise each to correctly load the power source, and feed maximum available current into the battery.

Then when the battery charger decides that the battery has had enough, both systems are throttled down together.
If the battery needs say five amps maximum, it does not matter if that is made up of 1+4 amps, or 3+2 amps or 5+0 amps. The charger just throttles back both systems until the current flowing into the battery is whatever is required to prevent overcharging.

The solar system is easy, just a buck regulator with the duty cycle controlled by the voltage directly at the solar panels.

The wind system will need a boost converter with the PWM duty cycle adjusted by the voltage coming from a wind speed sensor. Power will rise roughly cubed law with wind speed, its a fairly steeply rising curve.

Because there is no linear relationship between wind speed and PWM, you will need to get creative on how best to do that.
A lookup table in software is probably the nicest solution if you are comfortable with that approach.

A hardware approach might be using wind speed to select one of ten preset potentiometers, say every 0.5 M/sec up to 5 meters/sec.
Then manually tweaking each potentiometer for maximum output when each potentiometer becomes the active one. That may be easier, depending on your skills and available resources.

Then the battery charger just over rides the duty cycle in both to decrease total output when a reduction is required.
 
Last edited:

hi,thanks,I know that i need to design two separate converters for each source.
But before all i just thought of something like this:
I know i have already mentioned it but let me explain though what i actually intended to do "before" you suggested of using two converters that is:
I actually wanted to compare the voltages from each sources (which of the source has higher voltage) and then calculate the voltage from the source which has highest voltage. See if "this" voltage is greater than or less than 12V. If greater than 12V use a buck converter and if less than 12V use a boost converter to keep the voltage at battery 12V(though i have not mentioned about the battery charging here).
I actually wanted to have only one circuit in common for both (sources) and to only select the one which can give the maximum and best at that instant.
 

That complicates things, because without a load on either converter, the converter output voltage will just rise up to full maximum.

Consider the solar converter (its simpler), but the wind system will have very similar characteristics when running unloaded.

With no load on the output of the buck converter, the solar panel voltage will rise to maximum open circuit voltage. The converter sees this, and tries to load the panel down to the maximum output power point voltage, but it cannot as there is zero load.

It just goes to 100% full duty cycle in a vain attempt to apply more load.
The output of the buck regulator then becomes the same as the full open circuit output voltage of the solar panels.

Now take the other extreme, a dead short on the output of the buck converter.
The converter will adjust the pwm so the panel voltage is pulled down to the maximum power point output voltage (but no lower).
It will take only a very small duty cycle to do that, because of the short on the output.
The output voltage of the converter will be essentially zero, but the output current will be huge, many times what the solar panel is putting out. Hopefully there is a fast current limit on the buck converter to prevent damage.

The conclusion here is that the solar buck converter adjusts itself to suit both the solar panel operating condition, AND the load condition on the output.

Without a load, measuring the output voltage tells you nothing about how much power might potentially be available.

Its best to keep both systems connected to the battery at all times.
Use all the available battery charging current, right up to the point that the battery has reached either its maximum charging current limit, or maximum terminal voltage limit. Then throttle back both systems together to prevent cooking the battery.
 
What is needed is a buck regulator that regulates its INPUT voltage.
If the solar panel voltage tries to rise, the duty cycle increases feeding more current into the battery. If a cloud passes in front of the sun, solar voltage will try to fall, but the buck regulator reduces its duty cycle, reducing the load on the solar panel, always holding the panel voltage at the optimum point for maximum output power. Power will obviously decrease with a cloud, but it will always be at the maximum that the panel can produce at the time.

This holds the solar panel voltage constant, but the current into the battery rises and falls throughout the day charging the battery, always using as much current as becomes available from the sun.
You have mentioned that the solar panel voltage is constant.
It is solar voltage remains always at maximum power point voltage right?
And to charge a completely discharged battery in it's bulk power mode the charge controller need to charge the battery with constant current mode and if current keeps fluctuating would it be good for battery health?
 

No it does not need to bulk charge at constant current.

In fact constant current may be impossible on a day with big fluffy clouds passing in front of the sun.

The concept of constant current bulk charging ONLY applies if you have a steady constant source of grid power. If the wind is gusting up and down, the charging current will be up and down too.

All you can do with any alternative energy system is use what is available, when it becomes available, and then make the most efficient use of that.

Think of the battery in your car, from idling stopped at a red light, to changing up through the gears, the charging current is going up and down all the time. The charging current is hardly ever constant, but the battery charges up perfectly well.
 

You want to draw power from a PV panel at the maximum Ampere level it can put out, continuously (spec is 5.79 A). That is efficient use of the panel, and fastest way to charge. A 150 A-Hr battery can easily absorb 5.79 A as the bulk charge rate.

Therefore your charge controller input should be able to draw maximum continuous Amperes from the panel.Internally it may have a different waveform. That does not need to be at a constant level, but can be triangular which is typical in a buck converter.
the bold line i didn't get what are you trying to tell me please can you explain it.
 

Warpspeed, if you have two different systems trying to charge the battery wouldn't they fight each other and tend to oscillate.
 

After reading about MPPT i still have many doubts which i would like to clarify here
The solar panel will produce a current which varies from zero (at night) to a maximum short circuit current in bright direct sunlight.
What is needed is a buck regulator that regulates its INPUT voltage.
If the solar panel voltage tries to rise, the duty cycle increases feeding more current into the battery.
I understand this if the available voltage is maximum then i can always make the panel voltage come back to max power voltage(As voc>vmpp at that irradiance).
If a cloud passes in front of the sun, solar voltage will try to fall, but the buck regulator reduces its duty cycle, reducing the load on the solar panel, always holding the panel voltage at the optimum point for maximum output power.
But then what would be at night? (I guess the PWM duty cycle will be 1)

The next thing to think about is the battery.
Putting maximum solar charge current into the battery all the time is good, until the battery is fully charged. You then need to start thinking about holding the battery voltage at some safe maximum by over riding the control of the solar buck converter.
Ok now say my solar panel can give a max power at 30V and the controller is just making sure that panel operates at max power voltage but,simultaneously when i am doing this i should also check that the voltage of battery is maintained at around 13-14.4V for a 12V battery right?
 

Warpspeed, if you have two different systems trying to charge the battery wouldn't they fight each other and tend to oscillate.
No, that never happens.

- - - Updated - - -

But then what would be at night?

The controller will see that the panel voltage is very low and will remove all load (set the duty cycle to zero), but of course its the middle of the night.

Before true sunrise (glow in the sky only) the panel voltage will begin to rise, but the duty cycle will stay at zero, until it reaches your magic 30v peak power voltage.
But it has only just struggled up to 30v with zero load, and is not yet capable of supporting any load.

As the sun starts to appear above the horizon, the voltage sits steady at the peak power 30v, and both duty cycle and current slowly begin to rise above zero, and continue to increase as the sun strength grows.

The exact reverse happens during sunset. Current and duty cycle fall, still with constant 30v. Once the current and duty cycle both fall to zero, then the voltage begins to drop.
When the last glow on the horizon has gone, the voltage goes right to zero.

Ok now say my solar panel can give a max power at 30V and the controller is just making sure that panel operates at max power voltage but,simultaneously when i am doing this i should also check that the voltage of battery is maintained at around 13-14.4V for a 12V battery right?

Yes that is correct. If it reaches 14.4v or whatever you decide is the fully charged voltage, the battery charger takes over command of the solar buck controller and forces the duty cycle lower to prevent overcharging.

The solar panel voltage will rise above 30v, maybe up to the full open circuit voltage, if the battery is fully charged and there is no other load on the system.
 
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