PERFORMANCE OF CASCADED H-BRIDGE INVERTER INTEGRATED WITH HFT FOR PV SYSTEM APPLICATIONS

Abstract

This paper presents a photovoltaic system as a standalone system. The proposed systemconsists of photovoltaic (PV) module, battery energy storage system (BESS), high frequencytransformer, and multilevel inverter (MLI). The MLI consists of two H-bridge single phase inverterper arm (phase) with unequal dc voltages which needs 6 isolated de sources for the conventionalMLI. The relative values between the upper (auxiliary) inverter dc voltage and the lower H-bridge(main) inverter is 1/3 resulting in 9 levels MLI. Each isolated dc source comes from a PV moduleaccompany with a BESS. A high frequency transformer (HFT) is proposed in this paper to generatethe dc bus voltage of the auxiliary inverter from the main inverter dc bus voltage. As a result of thatthe number of isolated dc bus voltages required is reduced by half which is reflected in reducing thenumber of PV required and thus reducing the cost of the overall system. In addition, a naturalbalancing between the main and auxiliary inverters dc bus voltages of each arm will be attained dueto the HFT turns ratio which result in simplifying the overall control of the whole system. In order toreduce the size of the HFT a judicious modulation index (MI) will be chosen. The proposed systemhas been simulated using static inductive load. Analyses and simulation have been proposed tovalidate the proposed control scheme.