An inverter is a voltage converter that transforms an input AC voltage into another AC voltage with higher or lower amplitude and higher or lower frequency. So it is an AC/AC converter made of voltage converter or current converter and frequency converter.
In principle, converters are electronic devices that convert AC voltage into DC voltage. The unsmoothed DC voltage is smoothed in an intermediate circuit, a filter circuit, and then converted back into an AC voltage with a different frequency and amplitude in an inverter. Technically, it is a series connection of rectifier, DC link and inverter. The conversion of the DC link voltage can use pulse width modulation( PWM) or pulse amplitude modulation( PAM).
Inverters are used, among other things, in power electronics for controlling production machines and motors, for converting 50 Hz three-phase current to 16.66 Hz traction current, and in HVDC technologyfor converting alternating current to direct current and direct current to alternating current.
Two converter methods are usedin HVDC technology: the classic HVDC converter as a line commutated converter( LCC) and the modern HVDC converter as a voltage source converter( VSC).