subject: Electric Inverters [print this page] An electrical inverter converts direct current (DC) to alternating current (AC). The alternating current can then be used for all household appliances and at any voltage and frequency with the help of transformers, switching and control circuits.
Electrical inverters are high-power electronic oscillators, which means they can work in reverse, therefore converting DC to AC or AC to DC.
There are a few basic types of electric inverters. In one of the simpler circuits, the DC power is connected to a transformer. A switch is then rapidly switched back and forth to allow current to flow back and forth to the DC source, which then follows two alternate paths through one end of the primary winding and then the other. This creates an alternating circuit.
There is also an electromechanical version of the switching device. Two stationary pieces work with a spring to provide support. The spring holds the contact against one of the stationary contacts. This allows the current to be interrupted by the movement of the switch, thus creating a vibration as it moves back and forth. This alternates the current.
Inverters are integral to the use of solar panels. A solar panel needs an inverter to switch the direct current from the sun's rays to an alternating current which is used for all household appliances. There are three basic types of solar inverters: stand-alone inverters, grid-tie inverters, and battery backup inverters. All three are easily interchangeable.
Stand alone inverters are used in isolated systems (cabins, cottages, RVs, etc). This type of inverter draws DC energy from batteries and other sources such as wind turbines, hydro turbines, and engine generators. They also often incorporate battery chargers to help replenish the battery from the AC source.
Grid-tie inverters allow users to complement their grid power with solar energy. The inverter regulates the voltage and the current received from the DC solar panels and then converts them into alternating current. Grid tie inverters allow power to be sent back to utility companies by making certain that the power is in phase with the grid power. Grid-tie inverters do not provide power during a power outage.
Battery backup inverters draw power away from a battery. They also are able to recharge a battery with alternating currents.
It is necessary to use anti-islanding protection with most electrical inverters. Islanding occurs when the utility company powers down. The power company circuits may resonate an electrical current similar to an AC current. The inverter is capable of detecting this current. Thus, the inverter does not realize the power is down and will continue to send out currents. This is called islanding. It is very dangerous for utility workers who may not realize there is still power since the utility service is shut down. Anti-islanding protection emits small pulses that offset resonation from the circuits and allow the inverters to turn off.
