What is an inverter and what are its main types?

An inverter converts DC to AC by switching DC polarity using semiconductor switches. Main types: Voltage Source Inverter (VSI) - has stiff DC voltage input, most common for motor drives; Current Source Inverter (CSI) - has stiff DC current input via large inductor, used in high-power drives. By phase: single-phase (two or four switches) and three-phase (six switches). Modern inverters use PWM to create sinusoidal output. Applications include motor drives, UPS, grid-tie inverters, and HVDC transmission.