DC Optimizer for Multistring Configuration and Fault Detection Localization & Isolation of Solar PV Modules

Abstract

The Renewable energies are the flash point for researchers nowadays. In solar parks where a large number of PV arrays are connected in series and parallel combinations producing large amount of electric power at high voltage levels need proper fault detection and localization mechanisms for their reliable operation. DC Power Optimizer is used which helps each PV Solar panel in string or multistring to operate solely and any faulty panel in said combination doesn’t affect the power of other panels. Multi-level inverters (MLI) are to be developed which can detect and isolate the faulty cells from the series parallel connections to avoid any kind of electrical or mechanical loss. Cascaded H-Bridge (CHB) MLI is prominent in such scenarios as these inverters have high tolerance to fault currents due to huge flexibility at the output terminal voltages of MLIs. A single-phase 7-level 3-cells CHB is selected to simulate healthy and faulty operation. To develop such MLI which can perform fault detection, localization and isolation in case of an open circuit fault a Sliding mode-based differentiator has been studied in this research. MLI is required to ensure continuous and effective operation of large-scale PV array installation. However, an effective operation of a CHB required needs persistent monitoring in order to detect fault and isolate that fault for non-interrupting power supply. Selected MLI is subjected to open circuit fault. The fault detection technique uses 1st order Dynamic Gain Robust Differentiator (DGRD) to detect open-circuit faults. For a proper detection of fault, the estimate of the load current is calculated and then its derivative is amplified to avoid any discrepancies for the detection of fault in case of any small disturbance. This method is an improved version of the sliding mode-based Levant derivation method, where a constant gain is used instead. The fault detected by the MLI through 1st order (DGRD) needs isolation to provide non-stop power supply. The Auxiliary cell is used for the fault isolation in proposed scenarios, the auxiliary cells replaces the faulty cells to ensure the un-interruptible power supply to the grid. In the simulation fault is injected in different cells and that particular faulty cell is replaced by the auxiliary to show the effectiveness of the proposed algorithm for fault detection and isolation.