Iam working on a transistorized sinewave inverter using a tranistor oscillator, a buffer amplifier tranformer coupled o/p and a push pull o/p all transistors are BJT's. one may ask why?.... I'm just fed up with noise from rectangular and modified sinewave inverters.
May one assist me on how to wind a coupling tx and what determines o/p driving power.
May one assist me on how to wind a coupling tx and what determines o/p driving power.
Karakacha said:
Your best option is to buy a True-sinewave inverter instead of building your own. The cost to design, build and test will greatly exceed the cost of buying one. Efficient True Sinewave inverters are tricky to design and build. Thats why they are expensive and the majority of inverters are squarewave\modified sinewave output.
You can actually do quite well by taking a modified sine or square inverter and adding filtering to it. Use inductance first as connecting capacitance directly to the output really loads down the inverter.
You can also delta sigma a sine wave to generate signals for driving the H bridge. Then just add a simple LC filter to get a sine wave. (The interesting part is, that is very common in motor control, but there is no separate filter. The motor windings act as the filter.)
If you're looking for a cheap and easy way to get a sine wave inverter, find a discarded UPS with sine wave output (it's usually the batteries that are bad) and use it as an inverter.
You can also delta sigma a sine wave to generate signals for driving the H bridge. Then just add a simple LC filter to get a sine wave. (The interesting part is, that is very common in motor control, but there is no separate filter. The motor windings act as the filter.)
If you're looking for a cheap and easy way to get a sine wave inverter, find a discarded UPS with sine wave output (it's usually the batteries that are bad) and use it as an inverter.
star882 said:
Using an inductor to smooth a squarewave into a sinewave does work:
1. A large enough inductor will just limit the current flow. A small inductor will just round off the edges but it waveform will still be square. An inductor will also increase the noise because the inductor will release its energy each time the output switches. It will create voltage spikes (ie inductance leakage).
2. You would need a low pass filter consisting of an inductor and a capacitor. But this would also filter out 30 to 40% of the power to the output device. You would basically reduce a 1KVA inverter into a 700 to 600 VA inverter. All that filtered energy is also going to make the filter cap run hot (very short life before all the electrolyte evaporates).
If it was as simple as adding a LC filter to a squarewave inverter to make it into a sinewave, then all of the manufacturers would have done it.
The main problem is that a suitable filter will be too bulky. The inductor will be rather big, and so will the capacitor. Electrolytics cannot be used anyways as it's AC - use motor run capacitors, which are even bulkier. If you put that into a modified sine inverter to make it a sine wave inverter, the resulting inverter will be much heavier and bigger. Not exactly desirable for a device that is often designed to be portable. And a small microcontroller operating as a DDS is cheaper than a large LC filter anyways and will make a better sine wave. (The newer UPSes use microcontrollers to generate PWMed sine waves or a series of pulses that approximate a sine wave better than a modified sine.)TechGuy said:
Therefore, a good starting point would be to just connect some inductors (about 500uH to 1mH) in series with each line and connect a 1-5uF motor run capacitor in parallel after that. You won't get a pure sine but it might be close enough.
Karakacha said:
What you will be buildig is a class D amp followed by a large low pass filter. Given a class D amp you don't even need to really create a small alalog sine wave. All you need is to synthisize the digital switching pattern to send to the switch transisors. Think of the signal as a stream of binay numbers with as many bits as you have switches
The output filter can be simple too because you already know to cut off frequency. OK that is one way.
For those who need even cleaner power, use a "motor generator". this is just what it sounds like. You connect the shafts of a motor and a generator with a flexible coupling and a big flywheel.
Ferroresonant Transformers provide another good way to filter the output of the class D amp. Basically what yuo do is rather thaen us a simple low pass you use a use an oscilator with a inductor and cap. It's a transformer and capasitor that are tunned for 60Hz.
None of these are easy to engineer if you need more than a few watts of power
Might I suggest that you look into the Linear Technology low-noise switcher chips -- like the LT3439, LT1533 etc. -- there are probably 5 0r 6 slew controlled chips by LLTC -- you can also do this with discrete devices if you stare at the product folders long enough.
...and they do live up to their descriptions
...and they do live up to their descriptions
sine wave inverter design
my problem just lies on the coupling tx otherwise I still have hopes of succeeding in one. let powerloss not be a factor.
I do not have a software to show you the cct that I'm working on should i get, i would draw it thanks.
. one never fails in design .. he only discovers how many ways the project cannot work.
my problem just lies on the coupling tx otherwise I still have hopes of succeeding in one. let powerloss not be a factor.
I do not have a software to show you the cct that I'm working on should i get, i would draw it thanks.
. one never fails in design .. he only discovers how many ways the project cannot work.
Well, do read the product folders on the Linear Tech devices -- a sine inverter will be much less efficient than a pulse width modulated one -- as you seek to reduce the noise in the LLTC devices heat issues start to dominate the economics.
Reading the product folders will get you much further along in not reinventing the wheel.
Reading the product folders will get you much further along in not reinventing the wheel.
And low frequency (a few kHz) PWM is not very hard to implement. Some microcontrollers have PWM hardware built in, so a complete implementation would use a DDS in software.
I wonder what modifications, if any, would be required to drive the output H bridge of a common modified sine inverter with PWM at a few kHz...
I wonder what modifications, if any, would be required to drive the output H bridge of a common modified sine inverter with PWM at a few kHz...
bumping the thread.....
I'm planning on making a pure sine wave inverter.
plan is 220V 60Hz. power is 300watts more or less and I will use readily available parts.
so far, my idea is to use a 12V to 300VDC DC-DC converter (no problems there, been making car amp SMPS's for a while now) then use a triangle wave + comparator PWM circuit and feed it from a sine wave oscillator.
here's where my questions start. I'm thinking below 100kHz switching frequency good enough for 60Hz output? probably 50kHz to make things a little easier on layout?
H bridge will probably be needed. it's easier to handle a single 300V rail than a 600V bipolar supply.
planning on useing IRF740 mosfets due to availability and low cost.
I have a few spare MPP toroids that I could use for the output filter. how do you calculate the inductance/capacitance needed for the output filter? its my first time to design a class D based PWM output stage from scratch.
I'm planning on making a pure sine wave inverter.
plan is 220V 60Hz. power is 300watts more or less and I will use readily available parts.
so far, my idea is to use a 12V to 300VDC DC-DC converter (no problems there, been making car amp SMPS's for a while now) then use a triangle wave + comparator PWM circuit and feed it from a sine wave oscillator.
here's where my questions start. I'm thinking below 100kHz switching frequency good enough for 60Hz output? probably 50kHz to make things a little easier on layout?
H bridge will probably be needed. it's easier to handle a single 300V rail than a 600V bipolar supply.
planning on useing IRF740 mosfets due to availability and low cost.
I have a few spare MPP toroids that I could use for the output filter. how do you calculate the inductance/capacitance needed for the output filter? its my first time to design a class D based PWM output stage from scratch.
all repeating signals are made up of the fundamental and higher order harmonics. square, triangle, very distorted sines etc. If you want to clean up your line voltage. You can take the several hundred dollars that will cost to build or buy an inverter and spend that money on a very good line filter. Not an audiophile golden ears filter with cyro oxygen free silver coated wire and organic materials, but a series of pi filters tuned to 60 hz. There was a series of articles in audio express a while back that dealt with this problem. Basically you want to build a 60hz filter with a high Q. You must include the power transformer inductance in your calculations. If you eliminate/filter out the high harmonics you get a pure sine.
sorry, I wasn't clear on my application. I have a 12V 200Ah battery under my workbench and a 40watt and a 75watt solar panels on the roof. I would like to power some bench tools off of it. they don't run that well on my modified sine wave inverter so I want to run a pure sine wave inverter.
I doubt cheap ones would do the work well enough. besides, this is DIY, I want to try build one myself.
I doubt cheap ones would do the work well enough. besides, this is DIY, I want to try build one myself.
Karakacha,
You must have a very small power application, otherwise you wouldn't be interested in doing this linear.
You probably shouldn't bother trying to make your own power transformer for line frequencies. It is too effective to buy one, especially below a couple hundred watts. If your application power is above that then linear is arguably a poor choice. I wouldn't use linear in any case unless I actually needed the sine for something. Since all the loads I drive that actually care about supply cleanliness really need DC anyway, a sine inverter is impractical. In most cases it indicates a needless conversion step.
With what are you loading this inverter? What is the power? What is your inverter input voltage?
Once you have all that straight you just need a transformer of right size with the proper primary and secondary RMS voltages. Your supply voltage will need to be over about 1.5 times higher than the primary RMS voltage, if you intend to hold the secondary at rated voltage through a half bridge running in linear mode with any regulation headroom. (.75 for push-pull)
You must have a very small power application, otherwise you wouldn't be interested in doing this linear.
You probably shouldn't bother trying to make your own power transformer for line frequencies. It is too effective to buy one, especially below a couple hundred watts. If your application power is above that then linear is arguably a poor choice. I wouldn't use linear in any case unless I actually needed the sine for something. Since all the loads I drive that actually care about supply cleanliness really need DC anyway, a sine inverter is impractical. In most cases it indicates a needless conversion step.
With what are you loading this inverter? What is the power? What is your inverter input voltage?
Once you have all that straight you just need a transformer of right size with the proper primary and secondary RMS voltages. Your supply voltage will need to be over about 1.5 times higher than the primary RMS voltage, if you intend to hold the secondary at rated voltage through a half bridge running in linear mode with any regulation headroom. (.75 for push-pull)
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some bench tools only draw 200 watts or less, some draw more than 1KW under load. If your inverter is 100% efficient you will be drawing about 100 amps from your battery. Think of the size of the wires you will need. A 50/60hz sine generator feeding a 1-2kw car stereo driving a transformer backwards might work. You would have to know what the maximum output voltage of the car stereo is ie 2kw mono amplifier driving 2 ohms would provide about 64 volts ac rms, so you would need a 220 volt to 60-65 volt transformer at 1-2kw
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