12vdc - 240vac power Inverter

[Karl88]

Hi All,

Have been given this project and have to show the 3 different types of inverters: Square wave, modified sine and pure sine. Must also be rated at 1KW.

I must then make a judgement as to what type of inverter to use but it must meet the following specifications:

Total harmonic Distortion: <5%
Output voltage should be free from harmonics within the range of 150Hz - 1.5KHz.

From my experience I guess the pure sine wave is the only inverter that can achieve this but I have to investigate all possible methods.

Anyone got any useful tips or links. Even some examples would be appreciated.

Thanks

 

[bepobalote]

yes, indeed.
The only one solution to your requirements is a sinusoidal inverter.

Added after 49 minutes:

I think also that 1kW from 12Vdc will be really difficult to be obtained for efficiency reasons (cable sections/on resistance of switches in bridge, ...).
I suggest you to use 2 batteries in series, so your start voltage will be 24Vdc.

 

[Karl88]

I realised this from the outset but it states in my project that it must be a 12Vdc source. Any ideas on how this can be achieved? Thanks

 

[bepobalote]

It is not easy but maybe you will be able to do it using:
1) a PCB with copper traces of at least 105um of height
1a) maybe with the help of a specific done soldermask and an heavy tin coating (something like those used by the cheapest UPSs)
2) paralleled MOSFETs with the lowest RDSon like the Infineon IPB009N03L G (0.95 mOhm 180A max)
3) some good way to dissipate the generated heat
4) a custom built transformer
5) really thick cables from battery to bridge/transformer

but I think it will be better for you to ask your professor to change the requirement of your project to a 24V battery power supply.

I also hope this inverter is NOT for continuous usage!!! If yes, please remember to design it taking care of the worst environment hazards, especially temperature.

 

[Karl88]

Thanks for the advice, I'm having a few problems on how to start my schematic as my knowledge in power electronics is not as high as I'd like. Will ensuring the waveform does not contain harmonics between 150Hz to 1.5KHz be difficult? Thanks

 

[bepobalote]

It will depend on the resolution (and frequency) of your PWM generator.
Unfortunately I do not know what will you use for generating it, so it will be a bit difficult to help you.

I suggest you to start to search for a microcontroller which permits you to generate the "typical" signals for a triphase sinewave (to drive an inductive motor): almost any new 16/32 bit microcontroller will be good.
If you are able enough, you can use also an 8 bit micro, but I really do not know your expertise and if your project is price constrained.

The filters (L/C) set to the output of the inverter will filter out the high frequency component of the PWM.

I can assure you that if you have the right experience it is not so difficult to reach very low levels of distortion.

The problem is that the developement of an inverter is not so easy if you want to satisfy all of the (security/EMC/...) norms like: EN 62040, EN 60950, EN 50091 and the other ones which at this moment I do not recall.

I also think a single person will take several months of full time developement to create a perfectly working prototype which can be sent to the production line.

Almost any of the "free" projects I have seen on the web (on edaboard too) do not take care at all about the safety rules in their projects: please remember that we are talking about hundreds of A and working with those kind of energies can be really dangerous (do not forget to always wear safety goggles!).

 

[Karl88]

Is a good job I have 4 weeks to design it then before any of the dangerous stuff. Is there schematics from other projects that I could perhaps modify for this project?

 

[bepobalote]

Sorry, but I do not know of any schematics in the public domain which is good enough to start working with...
BTW, I continue to say that using only 12V for 1kW output is a really though task!

but as I previously wrote, I even do not know if this inverter should be made for continued working or not... so at this moment I can't help you anymore.

 

[Karl88]

Ok, thanks for your help. They've set me a very tough task . If anyone else can help that would be great but if not I'll let you know how I got on.

 

[Karl88]

Hi all, I've found a bubba oscillator for generating the waveform, is this suitable for an inverter. Does anyone have any ideas as to how can I produce it for 1KW, am finding it very tough!

 

[Karl88]

Does anyone know of a similar IC to the SG3524 which is also in ISIS 7/proteus software?

Thanks

 

[Karl88]

I'm having problems trying to get a spice model for a SG3524, can anyone help? If not what components do you recommended to build it, I have the block diagram but am unsure what components would be suitable for it.

Someone please help, I've been looking for the last week and I'm getting absolutely nowhere with my project because of it.

 

[mathsolvesit]

It sounds like this is either a homework assignment, or your company didn't hire a power conversion specialist to design an inverter.

Which is it?

This is definetly not something which an inexperienced person can design in 4 weeks.

 

[Karl88]

You're right with the first one lol.

 

[ntais]

Good evening i would like to make a question about an inverter which i have to construct that converts 12vDC to 220 AC.I have the following diagram.The question is what kind o resistors should i choose?Yesterday i went to an electronic shop to buy the materials an he asked me how many watts resistors.Does anyone know anything about this???

Thank you very much

The diagram is the following.

 

[Mr.Cool]

@ntais

for resistor of 1K or more, you can use 1/4watt resistors.

for the others it is more specific. calculate how much current flows through the resistor in your circuit in a worse case scenario. then use formula: P = I^2*R to get the applied power.

then pick a power rating that is double this to make sure it can survive (hopefully without a fan).

Mr.Cool