A fault tolerant dual inverter configuration for islanded mode photovoltaic generation system

In this paper a fault tolerant dual inverter configuration is proposed for a islanded mode PV generation system. The proposed system is capable to maintain the desired output voltage even under any fault in one of the PV string and/or corresponding inverter. In the dual inverter configuration the DC link voltage requirement of each inverter is half compared to single centralized inverter configuration. So the number of series connected PV panels in each PV string is half compared to single PV string of centralized inverter which in turn increases the reliability of the generation system. The voltage rating of switches will also reduce to half compared to a conventional centralized inverter. In the proposed system the primary windings of a three phase transformer (center tapped) are fed by dual inverters from both ends. The center tapings are connected through mechanical relays in order to provide fault tolerance ability to the system. Under normal operating condition, mechanical relays remain open and the primary windings will have resultant three level voltage profile. In case of any fault in one side of the system, mechanical relays are closed so that center tapings are shorted to connect half of the primary windings in star across the healthy side inverter. This arrangement maintains constant volt per turn in the three phase transformer which in turn maintains desired output voltage even during fault time. Decoupled SVPWM is used to control both the inverters which provide an advantage to control each inverter independently without disturbing other. So during fault condition faulty side inverter is made inoperative without any control complexity. As the healthy side inverter is rated half of the system rating, some less important loads are scheduled to be off during fault condition which avoids the overloading of the healthy side inverter. The proposed system is simulated for total power rating of 8kVA with two 4kVA inverters in dual configuration using MATLAB/Simulink.