ENHANCEMENT OF FAULT RIDE THROUGH CAPACITY OF GRID CONNECTED INVERTER

Abstract

Under the demands of contemporary grid code (GC), the solar PV system should stay attached to the grid for a certain time period depending on the voltage sag level under the fault condition. The voltage of the point of common coupling (PCC) is the same when the fault appears on the grid side due to compensation of voltage by the grid connected system. But the output voltage of inverter is very low when fault occurs in the inverter side resulting in a very high DC connection voltage and very high current through the inverter for the power balance. This high voltage of the intermediate circuit can damage the DC link capacitor and high current during the transient fault may damage the inverter. Moreover, the deflection of the voltage will cause the PV plant to be disconnected from the network based on the modern GCs. But, due to on-growing demand of consumers, it is required to connect the PV system to grid even during faulty condition. This study proposes a DC Braking chopper approach for the two-stage grid-integrated solar PV system to enhance fault ride through (FRT) capability. The proposed DC Braking control approach consists of a resistor in series with IGBT which absorbs the excess energy in the DC link capacitor during the fault, which will regulate the DC-link overvoltage where required PWM signal for IGBT used in DC braking chopper is generated by the principle of power balance between DC side and AC side.