Voltage Source Inverter (VSI)
•Inverter is device which converts Direct Current (DC) to Alternating Current (AC).
•There are two types of inverters one is Voltage source inverter (VSI) and second is current source inverter (CSI).
•Voltage source inverter keeps the voltage constant.
•Current source inverter keeps the current constant.
•Voltage source inverter (VSI) consists of one dc voltage source, transistors for switching, and one large dc link capacitor.
•DC source may be a battery, Dynamos or Solar cell.
•Transistor may be IGBT, BJT, MOSFET, or GTO.
•For Direct Current the large DC link capacitor acts like open circuit and for high frequency AC the capacitive impedance is low.
•VSI may be single phase bridge circuit or three phase bridge circuit.
•Single phase bridge circuit consist of two legs of switches each leg consist of upper and lower switch.
•Antiparallel diode is use to allow non-unity power factor load at output.
•The single phase VSI consist of two load terminals and three phase VSI consist of three load terminals.