I frequently see comments to the effect that portable generators, aka noise and fume makers, don't have true sine wave output. If this is true, from an electrical perspective, I am curious as to why? When I Google this subject I get a lot of hits to non sine wave inverter output (more below) but not generator.
It seems to me that an engine driven generator would turn a winding / rotor shaft in a magnetic field. The output would be a sinewave with a voltage and frequency determined by the number of magnetic poles, the field strength, and the rotor RPM. Unless they are rectifying or have some other sort of electronic output, they're not going to get a sqaure-ish wave and even harmonics should be minimal. What causes these to be non sinusoidal?
* - with respect to inverters there are a few ways to generate the output. One would be to switch pass devices (FET's IGBTs, GTOs, etc) in such a manner as to generate a stair step waveform that approximates the sine wave. This is going to have A LOT of harmonic content to it because of the non linear wave shape. This used to be the old school way of making inverters. Thanks to advancements in semiconductors .....
The other way is to PWM a DC voltage on and off and modulate the pulse width with a 60Hz reference and then low pass filter the output. This will generate a sine wave. This is where the semiconductor advancement has come in to play in that the speed at which they turn on and off has improved (they dissipate significant power during the transition) as well as the current handling capacity. The key to this design is in the filtering and this is where things will get expensive as you will need filter elements that can handle the voltage and more importantly the current. You also need steep filter cut off to pass 60 Hz and remove or sufficiently attenuate 180Hz (and up) or you will get a "fuzzy" sine wave that has an envelope approaching 60Hz made up of a lot of little wiggles - kind of like a poorly demodulated AM radio signal. I am certain that the massive adoption of variable frequency motor drives has pushed a lot of improvement in this area.
It seems to me that an engine driven generator would turn a winding / rotor shaft in a magnetic field. The output would be a sinewave with a voltage and frequency determined by the number of magnetic poles, the field strength, and the rotor RPM. Unless they are rectifying or have some other sort of electronic output, they're not going to get a sqaure-ish wave and even harmonics should be minimal. What causes these to be non sinusoidal?
* - with respect to inverters there are a few ways to generate the output. One would be to switch pass devices (FET's IGBTs, GTOs, etc) in such a manner as to generate a stair step waveform that approximates the sine wave. This is going to have A LOT of harmonic content to it because of the non linear wave shape. This used to be the old school way of making inverters. Thanks to advancements in semiconductors .....
The other way is to PWM a DC voltage on and off and modulate the pulse width with a 60Hz reference and then low pass filter the output. This will generate a sine wave. This is where the semiconductor advancement has come in to play in that the speed at which they turn on and off has improved (they dissipate significant power during the transition) as well as the current handling capacity. The key to this design is in the filtering and this is where things will get expensive as you will need filter elements that can handle the voltage and more importantly the current. You also need steep filter cut off to pass 60 Hz and remove or sufficiently attenuate 180Hz (and up) or you will get a "fuzzy" sine wave that has an envelope approaching 60Hz made up of a lot of little wiggles - kind of like a poorly demodulated AM radio signal. I am certain that the massive adoption of variable frequency motor drives has pushed a lot of improvement in this area.