10KVA inverter Design Project

[FvM]

Yes with 48V the current is 208Amps but the MOSFET IRF150 is capable of handling 40Amps so I am using 6pieces (6X40= 240Amps) at either side making it a total of 12pieces.

Did you look at transistor Rdson and related voltage drops? You will get 4% power losses only by Rdson.

During my simulation i figured out that the output voltage decreased when I connected some loads.

You get out what you put in the simulation. Besides said Rdson losses, transformer windings resistance and leakage inductance will cause output voltage to decrease. Most likely, battery voltage drop will be considerable too.

The inverter has to be designed to gived full output voltage at rated power. At lower load, the effective output voltage can be down-regulated, e.g. by reducing the pulse-width of square wave or "modfied sine" inverter.

 

[Ogu Reginald]

Did you look at transistor Rdson and related voltage drops? You will get 4% power losses only by Rdson.

You get out what you put in the simulation. Besides said Rdson losses, transformer windings resistance and leakage inductance will cause output voltage to decrease. Most likely, battery voltage drop will be considerable too.

The inverter has to be designed to gived full output voltage at rated power. At lower load, the effective output voltage can be down-regulated, e.g. by redu


The Rds on is 0.055ohm. How can I reduce the pulse width of a pulse? I have tried what BawA said above but no result. Please tell me another way to make the output of an inverter constant/regulated. If possible attach circuit diagrams.

 

[--BawA--]

Hii.
U should use sg3525. Now I'll tell u how feedback works in this ic. There is an internal error amplifier in the SG3525. Pins 1 and 2 are the inputs to the error amplifier. They are the inverting and non-inverting pins, respectively.when the pottential on pin 1 is grater than pin2 ,duty cycle is reduced.
When the voltage on pin1 is less than pin 2 ,duty cycle is increased.
Now u hve to set a refrence voltage (say 3v) on pin 2. Now your desired output is 220vac. So use a small transformer to convert 220vac to 12vac ..now rectify the output of the transformer .
After this u have to make a voltage divider circuit using resistors. Such that when input to the small transformer is 220v , the output of the voltage divider should be 3v . Now connect this voltage divider circuit's output to pin 1 . Dont forget to common the grounds..
Now as sg3525 starts the duty cycle will start from 0 and will be keep on increasing untill the pottential on pin 1 reaches 3volts .
It will definetly work for u. And let me know if still u have any confusion?




--BawA--

 

[Ogu Reginald]

Thank you very much. I will get back to you as soon as there is a problem.
It is SG3524 that I am using. But hope with this the output will be maintained to a particular voltage say 220V?
Can the output pulse be modified to a sine wave?
The reistors you made mention of for the fèdback network, what power rating are they?

- - - Updated - - -

Thank you very much. It is SG3524 IC that I am using. Hope if I do what you just said the output will be constant?
Can the output of the IC be modified to a sine wave? The resistor you (BawA) mentioned about for the feedback network earlier, are they of what power?

 

[--BawA--]

To get a pure sine wave u have to use SPWM
If u dont know know what is spwm , I can help u
2-Level PWM
The PWM technique involves generation of a digital waveform, for which the duty-cycle is modulated such that the average voltage of the waveform corresponds to a pure sine wave. The simplest way of producing the PWM signal is through comparison of a low-power reference sine wave with a triangle wave . Using these two signals as input to a comparator, the output will be a 2-level PWM signal . This PWM signal can then be used to control switches connected to a dc bus which will replicate this signal at the appropriate voltage. Put through an LC filter, this PWM signal will clean up into a close approximation of a sine wave . Though this technique produces a much cleaner source of AC power than either the square or modified sine waves, there is a relatively high amount of higher level harmonics in the signal .
3-Level PWM
In order to create a signal which is closer to a true sine wave, a 3 level PWM signal can be generated with high, low, and zero voltage levels. For the resulting 3-level PWM signal to correspond to a sine wave, the signal comparison stage must also be 3-level . A triangle wave is used as it is in the 2-level PWM comparison, but it half the amplitude and summed with a square wave to compare one half of the sine reference signal at a time. The resulting PWM signal is used to control one half of an H-bridge , which controls how long the bus voltage is allowed through to the load. The other half of the H-bridge controls the polarity of the voltage across the load, and is controlled by a simple square wave of the same frequency and in phase with the sine signal. Generally, this square wave can simply be created in a stage of the sine wave generation circuit. The resulting 3-level high-voltage PWM signal can be filtered into a very close approximation of the desired sine wave using lc filter.*
Or u can also use microcontrollers to generate spwm..






-BawA--

 

[Ogu Reginald]

(BawA), What will I connect to the pin2 of SG3524 in this case? Please throw more light.

 

[--BawA--]

Well I didn't understand your question. Which case are u talking about?
You cant generate pure sine wave through sg3524
, however u can generate modified sine wave from sg3524.. if u want to generate modified sine wave , just increase the deadtime b/w the signals.
And for feedback , the same thing will also apply here. Just give a refrence voltage (<5v) to pin no2.





--BawA--

 

[Ogu Reginald]

Using SG3524 to generate modified sine wave, how can I reduce or increase the deadtime? Thank you.

 

[--BawA--]

Add a small resistance RD b/w pin 5 and 7.generally the values of RD are in the range 10Ω to 47Ω. The range of values that can be used is 0Ω to 500 ohm. As given in datasheet. .
So add a sufficiently large resistance b/w 5 and 7.
But it should be lie in the range 0 to 500

 

[Ogu Reginald]

BawA,Thank you I have tried it and it is working.

 

[Ogu Reginald]

The project is working, I have designed and constructed a good change over unit but I have a question.
Remember I am using 96V (8X12V), please can you help me with a circuit that will be used to charge the battery. Will the charging circuit produce 12V or 96V?

 

[Ogu Reginald]

What I mean is: should the charging voltage be a bit higher than 12V or a bit higher than 96V?

 

[kyrietec]

It depend on battery.If it is deep cycle ,108v- 112v without using battery full cutoff cct. .You cannot use 12v to charge 12v battery.

 

[--BawA--]

As u are using batteries in series , so ofcourse u hve to make a charger of output greater than 96v.

 

[Ogu Reginald]

If I use a charger of output 120V, is it too much? And what current should I use to charge the battery so that it can be fully charged at 5hrs.
Remember that the battery I am using is 8X 12V 65Ah.

 

[ch wazir]

If I use a charger of output 120V, is it too much? And what current should I use to charge the battery so that it can be fully charged at 5hrs.
Remember that the battery I am using is 8X 12V 65Ah.

hello,u are using 96 volts having 8 battery bank therefore u need output 135v to charge the same.now if ur battery have 65AH u should use the formula c/10 approx.@6.5A .Regads

 

[FvM]

Maximum voltage for cycle charging is about 15V for a 12V battery = 120V for the 96V battery. The power supply should implement constant current control.

 

[Ogu Reginald]

Ch Wazir, Please I don't get the formular you said I should use, can you throw more light.

FVM, thank you. Please help me with the formular through which you got the values and please if am charging 12V 65Ah battery with a constant current of 5A, how may hours will it take to get fully charged. If possible please show me the formular.

 

[schmitt trigger]

Lead acid batteries ( I assume you are using deep discharge flooded lead acid) have a multiple charging regimen:

But first, you have to determine how many individual cells are in series.
For 96 volt (nominal) each with a nominal voltage of 2 volts, there will be 96/2 = 48 cells.

Bulk Charge: In the first stage of the process, current is sent to the batteries at the maximum safe rate they will accept until voltage is brought up to nearly 80-90 percent full charge level. There are limits on the amount of current the battery and/or wiring can take, usually C/10, where C is the battery's amp-hour capacity.

Absorption Charge: In the second stage, voltage peaks and stabilizes and current begins to taper off as internal resistance rises. The charge controller puts out maximum voltage at this stage, 2.35 volt per cell. In 48 cells, this means 112.8 volt.

Float Charge: This can also be referred to as trickle charging or a maintenance charge. In this stage, voltage is reduced to lower levels (2.15 volts per cell) in order to reduce gassing and prolong battery life. This means 103.2 volt.

Now, in addition to that, batteries have a temperature dependent charging correction applied to the voltage. The above voltages are for 25C, if the temperature deviates from that, you have to adjust the voltage approximately -6mV/cell/degree C...this may appear insignificant, but in 48 cells and an ambient temperature of 0C, the charging voltage would have to be increased 7.2 volt.

Now, I know many people will suggest that I'm crazy and that this method is waaaay too complicated. But I worked as a field service engineer for a large battery manufacturer, and later worked at a company that designed large power electronic systems, including UPS and battery chargers. I can tell you, from over a dozen years of actual field experience, that poor charging techniques are by far the biggest cause for early life battery failure. When a single cell fails, you cannot just replace that single cell, but the whole battery bank (for many reasons too long to explain here), so you have to replace everything. This becomes VERY EXPENSIVE, very quickly.

Now, and this is important...one cannot determine a battery's health from voltage readings alone. You need to buy an cheap hydrometer and take specific gravity readings. A healthy, fully charged battery will have a specific gravity of 1.277 +/- .007 at 25C, an example of such a hydrometer can be found here:
http://www.diseno-art.com/products/tools/battery_hydrometer.html

 

[Ogu Reginald]

With this can anybody help me on how to monitor the voltage of the battery (96V) and tell me when it is below(80V). If possible inlcude circuit diagram, thank you.