Sine wave power inverter

[sougata]

Hi Mincing,

I was too busy in a project and really coudn't get the time to reply to the thread.

1. For the driver part I use TLP250 from Toshiba. Get the datasheet and everything should be easy.

2. For the bridge you would be using all N-Channel Mosfet perhaps cause they are readily available and have much lower Rds On compared to P-Channel. However switching the high side MOSFETs are a little tricky. You need to have a charge-pump circuit to switch them on. Try the IR2101 it makes your design much easy.

3. To maintain low distortion in the output use a flux reset method when changing cycle. You do this by turning of the high-side mosfet, then turning on the other low side mosfet (both low side mosfets on) and then turning off the one which is not required for the current cycle and finally starting the high side driver of the corresponding cycle.

4. Please note that keep your high-side MOSFETs turned on during the entire cycle and apply PWM to the low side MOSFET. Initially I tried steering the PWMs to all of the four MOSFETs to make up for the conduction switching loss. But it did not produce satisfactory results.

5. Now for the transformer design. Say you are operating on a 12 volts battery. Now when the battery is full charged it is upto 13.8 volts nominal and before the deep-discharge of at around 10.8 volts. You can reduce the voltage with PWM but cannot increase it with the current scheme (boosting can be done, theoritically using a boost PFC like technique but I failed to do so). So keep your transformer primary at around 7.5 to 8 volts. This accomodates conduction loss, battery low, and so on.

6. Now the problem is that the same transformer is being used for charging and you need to boost the voltage during charging. Well a PFC boost method can be applied. See the attached PDF. Note the high side rectifiers are your high side mosfet's body diode.

I am attaching a few more documents links which can be handy during the design process. Sorry for Rapidshare. The documents are more than the allowed 200kb and a multipart zip/rar would have been around 10 parts.

Here are the document links:

http://rapidshare.com/files/34936881...r_with_PFC.pdf

http://rapidshare.com/files/34936883...ter_Design.pdf

http://rapidshare.com/files/34936882...c-inverter.pdf



I am sorry I may not be able to provide active support on this thread due to time limitation but will always try too within my knowledge and scope. (I am a completely self-taught with little or no academic background, So I might not be accurate all the times and ready to learn from others.)

I may start up a project on high frequency double-conversion sine wave inverter that utilizes Ferrite Core Transformers as PsDayama suggested. However it would be based on the dsPIC 30F2020. I still don't know whether I would be able to take up that project. Cause I have very little time left for myself catering to clients.

Anyways its good to see that the thread is alive again and would refresh my knowledge base.

[mincing]

Thanks Sougatha!

However I am building SI with Full bridge and isolation transformer.

My Dc input to bridge is 48V DC.

I am using optically isolated gate drivers.I need a 4 output power supply with isolation.

I am looking for suggestions.

[sougata]

Hi,

I mentioned TLP250 for the gate drivers. They have an optically isolated input and a totem pole output. It works great with IGBTs too. While your DC input is 48 volts be carefull about choosing the MOSFETs . Generally MOSFETs with greater breakover voltage have higher RdsOn. While it may seem logical to use a 100volts MOSFETs for the design. Please note that hard turn off of the MOSFETs connected to inductive load causes ringing in the drain as well as gate. So surges may kill them. Snubbers are recommended and fully avalanche rated MOSFETs should be used. If you keep your PWM frequency lower that will result in lower switching losses however may produce audible noise.

Best of luck in your design.

[mincing]

I have selected Mosfets with very low Rds on about 5mOhmm and 100V, 100A devices.


I also have optically isolated drivers from Avago ,but how about the power supply to these devices on output side i.e.Totempole and ground.I understand that a four out put supply with 18V and current? is required.
Is there any other means or method to escape this!

If you could suggest that Power supply cky that will be great.

[sougata]

4. Please note that keep your high-side MOSFETs turned on during the entire cycle and apply PWM to the low side MOSFET. Initially I tried steering the PWMs to all of the four MOSFETs to make up for the conduction switching loss. But it did not produce satisfactory results.

Hi Charles,

Your system was essentially a double conversion system. Although it has two power stages but the sinewave regulation becomes real easy when you have your DC bus regulated. I had my original design of the DC boost using a SG3525 followed by a PIC driving MOSFETs to produce the sinewave. Now I am trying to utilize a dsPIC (I am in the process of learning it and still a Newbie ) to handle both the conversions as well as battery charging on mains availability. My knowledge in SMPS is very limited till date and I am working hard for those "gotchas". So wish me luck. (I need it for keeping the number of toasted MOSFET/Chopper low, obtained during trial phase)

[Navneet Vinaik]

Hi Charles,

Now I am trying to utilize a dsPIC (I am in the process of learning it and still a Newbie ) to handle both the conversions as well as battery charging on mains availability. My knowledge in SMPS is very limited till date and I am working hard for those "gotchas". So wish me luck. (I need it for keeping the number of toasted MOSFET/Chopper low, obtained during trial phase)

Dear Sougata,

I have a short experience in this domain but have learnt quite a few things. I have developed a UPS on 16F676, square wave inverters on 16F72 and sinewave inverter again on 16F72 based on H bridge..... all in the past one year. Now, I am keen to work on ferrite core...so if you can guide me some thing..please help....I want to grow in this field, presently am working on SMPS designing(low power, upto 200W only)....the fire is there in me, everyone please guide....

[mincing]

Navneet Vinaik,

Dont worry!This field is more of a stabilized now.You will get every kind of information you need.

let me know what exactly you need.If not able to answer directly,I can give you links and sourcs.