Digital Inverter Generator Technology

[44Kebeck]

I am building a generator which will probably be a straight DC unit but I'm interested in the technology behind the small Honda units which claim to provide pure sine wave AC using inverters etc. I haven't been able to find out much about how they work. Do they invert the rectified DC from an alternator back to AC or what? Has anyone come across a generator head that uses this technology?

From my research I've found that you need about 2HP/KW for an AC generator or about 1HP/25 amps for a DC generator. Does this sound about right? I'm planning on using a small diesel (Kubota).

Thanks for any help on this.

-44Q

Welcome here,

if you are talking about a marine installation, I would recommend to start at:

http://www.victronenergy.com/
see their genny test, dl "achieving the impossible" ,have a deeper insight in this topic. It might save you a few bucks.

Regards
Richard

[CDK]

Originally Posted by 44Kebeck

I am building a generator which will probably be a straight DC unit but I'm interested in the technology behind the small Honda units which claim to provide pure sine wave AC using inverters etc. I haven't been able to find out much about how they work. Do they invert the rectified DC from an alternator back to AC or what? Has anyone come across a generator head that uses this technology?

-44Q

The technology is more or less comparable to that of digital music: sampling.
To make a 50 or 60 Hz sine wave a capacitor/inductor pair is charged with a number of small "bursts" like a switching regulator does, but with varying pulse width. The result is something like a staircase going up and down, then a low pass filter removes the sharp edges and it results in a sine wave.
It sounds simple, but the output must remain at (almost) the same voltage level between zero and full load; that requires an extensive feedback circuit.

[44Kebeck]

I found some information on the Honda web site:

Honda 's inverter technology takes the raw power produced by the generator and uses a special microprocessor to condition it through a multi-step process.

First, the generator's alternator produces high voltage multiphase AC power. The AC power is then converted to DC. Finally the DC power is converted back to AC by the inverter. The inverter also smoothes and cleans the power to make it high quality. A special microprocessor controls the entire process, as well as the speed of the engine.

The AC to DC to AC seems counterintuitive but I guess that's the only way you can get 60 cycle AC from the mulitphase alternator output.

[Tug]

AC1 to DC to AC2 seems like a great idea...if the microprocessor was smart enough to store the excess DC into batteries when not being used by AC2...
But the inverter generators really become efficient at intermittant use....somehow the microprocessor combines the highvoltages together to give you instant amps at a low idle.....then the generator revs up to keep up the demand....
Usually generators run at a set rpm for your HZ to be maintained...never get to idle....
Cheers
Tug

Just the next example:
not worth to contribute....
They know much more than we, they just need to have a stamp on their opinion.

[BTPost]

Tug, it isn't "somehow" it IS the Large Capacitors that ride on the DC Buss and supply the power needed while the Engine Output is ramped up. A battery could also be used if the DC Voltage was designed to stabile enough as to not KILL the battery, with DC Voltage variations, between Idle and Full Output.

[goboatingnow]

AC1 to DC to AC2 seems like a great idea...if the microprocessor was smart enough to store the excess DC into batteries when not being used by AC2...

what.. There isnt any "excess". the alternator on teh engine provides only as much power as the load requires. Energy usnt left floating in the ether or anything.

[jonr]

AC to DC+battery to pure sinewave AC provides a nice clean waveform, surge capability (beyond what some generators could produce) and less running of an engine at sub optimal speeds/loads. But it isn't cheap.

2HP per kw is about right for AC or DC generation.