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

Document Type : Original Article

Authors

1 Aswan Faculty of Engineering, Aswan university, Aswan, Egypt

2 Tanta University, Faculty of engineering, Tanta, Egypt

Abstract

This paper presents a photovoltaic system as a standalone system. The proposed system
consists of photovoltaic (PV) module, battery energy storage system (BESS), high frequency
transformer, and multilevel inverter (MLI). The MLI consists of two H-bridge single phase inverter
per arm (phase) with unequal dc voltages which needs 6 isolated de sources for the conventional
MLI. 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 module
accompany with a BESS. A high frequency transformer (HFT) is proposed in this paper to generate
the dc bus voltage of the auxiliary inverter from the main inverter dc bus voltage. As a result of that
the number of isolated dc bus voltages required is reduced by half which is reflected in reducing the
number of PV required and thus reducing the cost of the overall system. In addition, a natural
balancing between the main and auxiliary inverters dc bus voltages of each arm will be attained due
to the HFT turns ratio which result in simplifying the overall control of the whole system. In order to
reduce the size of the HFT a judicious modulation index (MI) will be chosen. The proposed system
has been simulated using static inductive load. Analyses and simulation have been proposed to
validate the proposed control scheme.

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