re: power inverters vs generators

Generators have to run at a multiple of 60 rpm to provide 60 Hz power because they are spinning a generator that the load is directly connected to. Generally, this means they run at 3600 rpm, no matter how much load is connected to them. Even when using no power, the engine will be running at 3600 rpm. Also, when load is connected to or disconnected from the generator, the engine feels it because it is mechanically coupled to the generator. Since the whole thing has inertia to overcome, the response to a changing load can't be instantaneous. When a load connects, the whole system slows down slightly until the engine can mechanically respond. The opposite happens when load is shed. Since the engine is mechanically coupled to the generator, and the rotational speed of the generator is linked to the frequency of the electricity it produces, the quality of the electricity is not steady and varies as the machine operates.

Compare this to an inverter generator. These devices don't have just an engine and a generator. The output of the generator goes through a rectifer which turns the AC output into DC. The DC then goes through smoothing capacitors that condition the DC power. The conditioned power then goes through an inverter, which takes the smooth DC power and turns it back into smooth, steady AC power.

Why bother, though? In the inverter setup, the generator is not directly connected to the load. The conversion from AC to DC back to AC means that the rotational speed of the generator has nothing to do with the frequency of the output electricity. The frequency and waveform of the AC are all maintained by the power electronics in the inverter. Since that output section is fed by DC power from the rectifier, no matter what the engine is doing, the output power is unwavering provided the generator is producing enough power to match the load. So that's the first benefit: clean power. The second benefit is related. Since the quality of the output is not coupled to the rotational speed of the generator, there is no need for the engine to run at 3600 rpm regardless of the load. Therefore, the whole system can be designed and controlled to run at the most efficient speed under all conditions, making them MUCH more fuel efficient and quieter.

So why do we still have regular generators? Cost and weight. Those power electronics that do the AC to DC to AC trick aren't cheap and their cost rises quickly as their power handling capability is increased. So, a 4000W inverter generator's output section would cost more than twice the a 2000W, and 8000W power electronics would be more than twice a 4000W, and so on. The weight of the system has a similar behavior. The sheer mass of the electronics required to handle increasing wattage quickly starts shooting up.

Since the cost and weight of inverter generators starts spiking quickly with increasing power, you tend to see them in the lower wattage ranges and fill more of a portable role that might power a few devices that might be finicky about how clean their power is. There are some that go up to several thousand watts, though, and many of them now let you run multiple units in parallel to provide higher total outputs and have some flexibility to avoid having a single giant and horribly expensive inverter generator. That cost and size, though, are why you start seeing mostly traditional generators when you start getting up into the higher wattages. They can power more powerful machines that might not care as much if their electricity's frequency fluctuates a couple of Hertz and they can do it at a much more reasonable cost, weight, and footprint than an equally powerful inverter generator.