An Interface System for Photovoltaic Based on Dual Cascaded Inverter

Abstract

The power electronics converters are coming into wide scale in different fields due to their capability andflexibility of control, and high dynamic response tovariable change of the load. Power electronics converters provide precise control over wide range of applications, such as electric drive systems, electric traction, ship propulsion and automotive application. In addition, these converters are used widely for energy conversion, grid connection, manufacturing, mining and petrochemical industry. All of these applications require cost reduction, high production rate, high performance and efficiency, which could be served by power electronics systems. This thesis presentsan interface system for photovoltaic based on dual cascaded inverter. This system is based on using dual cascaded inverter, consisting of main and auxiliary inverters. The PV array is connected to the main inverter through a boost converter for maximum power extraction, while the dc-side of the auxiliary inverter is connected to a capacitor bank. The main and auxiliary inverters are controlled to deliver the harvested maximum power from the PV array to the grid and to simultaneously regulate the dc-side voltage of the auxiliary inverter at a constant ratio from the dc-link voltage of the main inverter. Four Hysteresis controllers are proposed for the three-phase currents fed to the grid and the dc-side capacitor voltage of the auxiliary inverter. Two switching control methods are adopted for the dual cascaded inverter: the conventional Hysteresis Current Control (HCC) and the Space Vector Modulation (SVM) based HCC. The later technique offers reduced switching numbers for both inverters compared with the conventional HCC. The system has been also studied during fault / voltage sag condition. A low voltage ride through (LVRT) controller is adopted to fulfill the E.ON grid code requirements. The E.ON grid code ensures that the proposed PV interface system supplies reactive power to the grid according to the value of voltage at the point of common coupling. The proposed dual cascaded inverter for the PV interface system is studied using