# Inverter Design

1. Jan 29, 2009

### kiamzattu

Hello every1

I hav a basic question bout Design of inverters(Voltage source inverters). Wel Actually what does designing mean?
I hav to design a inverter whose output Peak voltage is 50v. The input DC voltage wil b around 55V.I'm using single phase full bridge inverter And i'll b using R load in one case and RL in another case. Now wat r the other parameters tat r needed in designing an inverter. My output frequency is 50 Hz and i'm using sinosoidal PWM to trigger my switching devices(MOSFETS). Now how should i calculate wat is my load current?How do i determine the rating of my switching devices and power rating of my whole inverter? I'm entirely clueless. Is ther any step by step procedure for inverter design? any help is greatly appreciated.

Last edited: Jan 29, 2009
2. Jan 29, 2009

### ravioli

First of all, please proofread your post. If every single sentence has multiple grammatical and structural mistakes, then it appears that you are not being serious. It shows your lack of care for the particular problem at hand.

Secondly, since this is appears to be a design project, most of your parameters will be logically determined by yourself. This allows you to view the design process, which is all about requirements and trade-off's. What are some trade-offs that can be associated with an inverter? What are some requirements for the particular design? I'm sorry to say, but for the most part a design project does not have detailed steps for you to take.

3. Jan 29, 2009

### Staff: Mentor

I agree with both of ravioli's points. anbullet -- check your PM box.

As to the questions, I'm not sure that you understand what a "power inverter" is. It generally is a device that takes in a DC voltage, and generates an AC output voltage, usually at AC Mains voltage levels (50Hz, 220Vrms, for example). The quality of the output "sine wave" waveform depends on how much you are willing to spend on the intermediate circuitry, and also on the character of the load impedance.

I don't know what you mean by "I'm using single phase full bridge inverter". By bridge, do you mean an H-bridge output stage? And what do you mean by sinusoidal PWM?

You could search at wikipedia.org for some background on inverter design, and use google to get the basics. If you have specific questions, point us to the page you are studying, and ask the specific question. And please take care to type carefully, and explain yourself clearly.

4. Jan 29, 2009

### kiamzattu

@ravioli
I'm really sorry for my grammar and spellings. English is not my mother tongue.
@ Berekman
Yes full bridge inverter is H-bridge inverter. Sinusoidal PWM means i'm comparing a sine wave and a triangular wave for generating PWM pulses.
I have my input voltage and output voltage values.
I understand the above point. But before actually going into the output waveforms, I need to determine the ratings of my switches.what is the way to do that?

Hope i'm clear. Forgive me if not. Its the best of my grammar. took nearly 15 min to post it.

5. Jan 29, 2009

### Staff: Mentor

Thank you for the effort, anbullet, that makes it so much easier to understand your question.

I'm still a little hazy on the PWM part, though. Could you point me to a reference that describes how the PWM is used with the H-bridge to generate an output sinusoidal power waveform? I don't know enough about inverter design to know what is being done in the comparison you mention.

As for your switch ratings, they will need the V and I ratings to be large enough, and you will also need to check their Safe Operating Area (SOA) specifications, as the max I and max V ratings may not necessarily be used at the same time.

6. Jan 29, 2009

### ravioli

I appreciate the effort. I'll try to post something tomorrow that will help you out. I don't necessarily have the greatest expertise with PWM, but I can look it up during the day tomorrow.

I do have one question, though. Will your inverter supply only real power, or will the inverter have to supply reactive power?

7. Jan 30, 2009

### kiamzattu

@ Berekman
PWM is just for switching the MOSFETS. When i compare a sine and a triangle,square pulses are generated. These pulses are used as switching signals and are given to the gates of MOSFETS.I've attached a pdf file giving a overview of how PWM is used in inverters to obtain output waveforms.

@ ravioli

My inverter needs to supply only real power.

#### Attached Files:

• ###### PWM.pdf
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8. Jan 31, 2009

### ravioli

Anbullet, check out a few datasheets for IBGT's over at Mouser. They are fairly informative and will give you a few clues on what is out there, and what capabilities IGBT's have. Since PWM deals primarily with, well, pulses, you can assume that the resistive load will see the 50 volts at once at the during the pulses. From there, once you know the expected characteristics of the load, you can easily calculate what kind of pulsed current you should be expecting to go through the IGBT's.

Another note, I believe that the 55 Vdc source, and a 50 Vac peak output is fairly important. Since two transistors will usually be on, you will need to pay particular attention to the graphs in the datasheets. By symmetry of the circuit, you will only have a budget of about 2.5 Volts for Vce per transistor when the transistor is on.

Lastly, unless told otherwise, don't underestimate heat.

9. Jan 31, 2009

### kiamzattu

Thank you all for the help.
Will check out informations about IGBT and others.I still have some doubts, will post it after going through the datasheets.
Thanks again

10. Feb 7, 2009

### kiamzattu

Hi everyone
Before implementing the hardware part of my inverter i simulated my circuit using Simulink(MATLAB). I used a DC input source of value 55v, MOSFETS as my switching devices,PWM method for triggering them and output load of 50ohm. I've attached a screenshot of my output voltage.
Now i have some doubts in it. First of all my output peak value must be only 50volts. But i'm getting voltage spikes which cause my output to be around 54volts. Is there any way of eliminating these voltage spikes so that my peak output value is reduced (Preferbly 50volts)?

Secondly as you can see my output is not sinusoidal. I haven't added any filters in my circuit as of now. Can i add an LC filter ?Will a LC filter help in eliminating the switching frequencies so that my output is sinusoidal ( or atleast square) with a frequency of 50 hertz?
Is there any rule of thumb or steps to design LC filter so that it eliminates all the switching frequencies and allows only 50 hertz?

I know i'm asking too many questions, sorry for that.

#### Attached Files:

• ###### Output.jpg
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11. Dec 26, 2010

### bhavin_nair

hi,
well before i suggest u anything i wld like to knw the basic circuitry in your simulink.
may be i could help u with it because i too use MATLAB and as far as i knw u could be optimistic about ur output.
And yes with ur filter circuit try adding some reactive components in ur load.
Basically L & C, they work well for an approximate sinosuidal output.
Hope this may help u