An inverter is an electrical circuit that converts electrical power from direct current (DC) to alternating current (AC).  Inverters are found in systems where a DC source is required to be converted to a fixed voltage/frequency AC source (110V/60Hz in North America) for use by household appliances etc. Solar inverters, for example, convert a variable DC source from solar panels to a fixed voltage/frequency AC source. Another example is Uninterruptable Power Supply (UPS) systems that convert a DC battery backup source to a usable AC source for running computing clusters, communications infrastructure, etc. in case of failure of the power grid. Inverters are also found in AC motor drives. A fixed AC input is rectified by the drive to a DC intermediate voltage and then inverted back to a variable voltage/variable frequency AC source that is capable of adjusting the speed and torque of an AC induction motor. AC drives are used primarily for controlling industrial motors but are becoming increasingly prevalent in household appliances (white-goods) due to the ever increasing energy efficiency demands.