Design and implementation of a single phase modified Z-source inverter topology for photovoltaic/grid interconnected DC charging applications

Abstract

Solar energy has been the most popular sources of renewable energy for residential and semi-commercial applications. Solar energy sources alone cannot be used to charge an electric vehicle (EV). Solar/Grid interconnected charging stations are used to charge EV batteries to reduce the dependency on the grid and enable charging at convenient locations such as a residential garage or a parking lot right next to an office or a shopping mall. The Z-source inverter (ZSI) topology achieves voltage boost and DC-AC power conversion in a single stage. In this thesis, the design and implementation of a modified ZSI (MZSI) based charging topology for PV/EV/Grid interconnected application has been presented. The operation of the proposed topology was verified. The proposed topology reduces the number of conversion stages to charge EVs from a Smart Grid/PV interface (high efficiency). A 3.3 kW MZSI has been designed and simulated using PLECS. Detailed loss modeling was done using PLECS. The peak efficiency of 94% was observed under irradiation and temperature changes. A scaled-down version of the proposed topology has been implemented for proof of concept. In a single-phase 60 Hz inverter, the 120 Hz component has to be suppressed. One way is to size the capacitance in the system to absorb the 120 Hz component which may result in a bulky system. The design of Active Power Filters (APF) for the ZSI topology can be tricky because of the shoot-through state. A new DC side active power filter has been proposed for ZSI topology which suppresses the 120 Hz component completely thereby eliminating the need to use electrolytic capacitors in ZSI systems. The proposed APF can reduce the capacitance by 100 times. Simulation studies have been presented for the proposed topology.