Design and implementation of single‐phase inverter without transformer for PV applications

Abstract

For safety purposes, many photovoltaic (PV) systems are designed using galvanic isolation and transformers. The main problem in the existing topologies is that transformers are expensive, heavy and large. Another problem is that at conversion stage, the overall frequency is reduced. The efficiency of a PV inverter which is equipped with a transformer is usually between 91 and 94%. To tackle this issue, a transformerless (TL) PV system is proposed which has high efficiency and is lighter and cheaper. Due to stray capacitance, harmful leakage current will flow to the grid and PV array. H5, HERIC, H6 and oH5 are different types of existing TL inverter, and may be used to solve this problem. Each configuration has its drawbacks like shoot-through issues of switches, high conduction losses, metal-oxide-semiconductor field-effect transistor reverse recovery issues, or to avoid shoot-through fault when dead time requirements and grid voltage are nearly zero. The efficiency of the proposed TL inverter presented in this study is compared with other existing configurations. It shows that the proposed inverter efficiency is better than the conventional hard switching inverters. Moreover, to increase reliability, the inverters do not contain any shoot-through issues.

H7 three phase transformerless inverter for photovoltaic grid-tied system with maximum power point operation

“…In PV grid-connected systems, a transformer is employed to achieve several targets; (1) raising the PV panels voltage to suitable levels that meet requirements of connection to the grid, (2) preventing the injection of DC currents into the grid and therefore it improves the grid power quality and (3) providing galvanic isolation between the PV panels and the grid thus achieving personal safety where it prevents the leakage current which can flow in the parasitic capacitance between the frame of PV panels and ground. On the other hand, the transformer results in increase in size, weight and cost of PV systems and also the efficiency is decreased [3]- [5]. Transformerless inverters overcome the aforementioned disadvantages of transformers.…”