A Generac GP2500i Portable Inverter Generator at a parking lot tailgate party before the the game.
The inverter generator combines the efficiency of DC power generation with a controlled DC to AC inverter to provide clean electrical power similar to the power produced by electric utilities or larger standby home generators. Its efficiency saves fuel, lowers emissions, and reduces noise levels, all of which make it suitable for use in places like campgrounds, neighborhoods, or to power sensitive electronic equipment.
Electrical Power
The electrical power we are all familiar with in our homes is alternating current, or AC, which means the current flow alternates direction rapidly. The standard in North America is sixty times per second, and fifty times per second on most other continents including Europe and Australia. As the current changes directions, the voltage rises and falls to provide an average voltage of 120 or 240 volts.
The power the electric utility companies supply to homes and businesses is usually very clean. If viewed on an oscilloscope. a device for viewing electrical signals, it appears as a very smooth and consistent sine wave.
Power Quality
The electric utility power is quite smooth and doesn’t vary much because the supply is large enough that the continuously changing load does not substantially affect the voltage except during times of extreme demand. The utility’s power also passes through a number of transformers on the way to businesses and residences which helps to smooth the final product.
Small generators don’t have the luxury of a seemingly infinite supply of power. The amount of current drawn places a load on the engine driving the generator and causes it to vary speed, which changes the average voltage and the frequency of the current. As the total power consumed nears the generator’s capacity, the voltage will also drop. These small variances won’t harm most appliances or lighting, but can cause problems with sensitive electronic equipment.
Inverters
Direct current, or DC, is the type of current supplied by a battery or by a DC generator. It is very steady, doesn’t fluctuate much under a constant load, and is quite efficient. It does not change direction and there is no rising or falling of the voltage level. Viewed on an oscilloscope, it appears as a straight line.
DC current cannot be used on appliances or motors that require AC current, but a device called an inverter changes DC current into AC current.The simplest inverters don’t mimic clean alternating current very well. Even the power supplied by a small and inexpensive generator is cleaner. However, if the inverter is controlled by a microprocessor, it does a much better job and the converted signal appears as a near-perfect sine wave.
In fact, modern inverters handle the job so well, the difference between an inverter generator output and a perfect sine wave is virtually indistinguishable.
Inverter Generators
An inverter generator creates AC power through a threestep process.
- Generate a variable frequency alternating current.
- Convert the variable frequency current to Direct Current (DC).
- Invert the DC to 60 Hertz AC using a microprocessor controlled inverter.
The beauty of the inverter generator is that engine must only turn fast enough to provide the power required at any given moment. Higher alternator output frequencies allows the inverter to produce more power.
In practice, generators have a variable speed engine that runs at different speeds for different power levels instead of a continuously varying engine speed.
As the demand on the inverter generator increases, the microprocessor can push the engine speed up to match the demand. During periods of low use, the engine speed drops almost to idle and uses far less fuel than a conventional generator which must run at the same speed, no matter how low the load.
Conventional generators with a low idle mode must speed up to full speed before they can provide 60 Hertz alternating current.
