A motor–generator is a device for converting electrical power to another form. Motor–generator sets are used to convert frequency, voltage, or phase of power. They may also be used to isolate electrical loads from the electrical power supply line. Large motor–generators were widely used to convert industrial amounts of power while smaller motor–generators were used to convert battery power to higher voltages.
Nowadays, motor–generators have largely been replaced by semiconductor devices. Examples include rectifiers for converting alternating current (AC) to direct current (DC) and inverters for converting DC to AC.