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Square wave = cheap but useless for driving inductive loads.
Modified sine wave = cheap but not efficient at driving inductive loads.
Sine wave = more expensive and drives almost any load.
PWM is normally used to generate pure sine signals. Square wave cannot be used to generate sine signals without huge filtering losses.
Hi izzu91
As i can see name of this thread is how power inverter DC to ac works . well ?
ok it is simple to understand it . but it depends on what kind of out put wave are you referring to ? sine wave or just square wave ? are you referring to the commercial inverters which are simply available and you can use them for homes too ? sine wave out put ? if you mention it exactly then i can describe it in detail .
Best Wishes
Goldsmith
Hi izzu91
As i can see name of this thread is how power inverter DC to ac works . well ?
ok it is simple to understand it . but it depends on what kind of out put wave are you referring to ? sine wave or just square wave ? are you referring to the commercial inverters which are simply available and you can use them for homes too ? sine wave out put ? if you mention it exactly then i can describe it in detail .
Best Wishes
Goldsmith
yea, what i mean is the commercial inverters. i just bought 300 watt power inverter. i just wonder how it produce sine wave? is that a pure sine wave inverter or modified sine wave inverter?
It should have it marked on it somewhere. Without an oscilloscope it's difficult to tell what the waveform is. A modified sine wave is like a square wave with a step half way down and half way up the wave edges and it has a flat top and bottom. Apart from the natural rise and fall limitations of the components it has no sloping or curved edges.
A pure sine inverter produces a waveform closely resembling a sine wave and should have no straight parts in it's waveforn.
Both systems use high frequency step-up generator to produce a voltage equal to the peak of the output waveforrm (in theory - most don't!) then use a switching circuit to connect it to the output socket. In a modified sine system it follows these steps:
1. connect the output to the high voltage
2. disconnect the output (the step in the waveform.
3. reconnect the output with the connections reversed
4. disconnect the output (the other step in the waveform)
5. back to 1.
Pure sine converters use a high frequency PWM stream and modulate the mark/space ratio of the output switches to control the voltage. This gives far better control and hence can produce enough steps in the waveform for it to look close to a sine wave.
yea, what i mean is the commercial inverters. i just bought 300 watt power inverter. i just wonder how it produce sine wave? is that a pure sine wave inverter or modified sine wave inverter?
Hi izzu91
many of the sine wave inverters are based on this theorem :
A first stage will be voltage increasing section like H bridge or push pull converter or perhaps a half bridge for lower powers .
after converting a low voltage into the high rated DC voltage ( of course with High frequency transformer and circuit ) there will be another stage which is usually an H bridge . it will be drove with a SPWM ( unlike the first stage which has been drove with PWM ) and there won't be any transformer in the latest stage . it will have a simple 2nd order filter , and then perhaps a feedback into the 1st stage .
it is whole idea . of course there are plenty of ideas for inverter design . i've just noticed you about one of the ideas which is so popular .
Best Wishes
Goldsmith
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