Review of high step-up dc-ac power electronics solutions without galvanic isolation

Abstract

Urgency of the research. Energy storage technologies are heavily related to electric vehicles. The fast charging station together with the wireless power station potentially makes the electric vehicle more attractive and user-friendly.

Target setting. The main problem in this area is the large size and low battery life, as well as the limited loading speed of electric vehicles. It is also important to optimize power density with the greatest possible efficiency.

Actual scientific researches and issues analysis. The analysis of publications shows that a lot of attention has been paid to this topic of research, there are a large number of publications by leading institutes and world-renowned scholars. Therefore, in the current article, a comparison of two main families of non-isolated converters with reference to articles and domestic scientists is also shown. The first family, based on one-step solutions, is presented and classified. Also shown is an analysis of two-stroke converters based on the intermediate DC converter with a high increase.

Uninvestigatigated parts of general matters defining. Many problems with the power industry should be solved to increase the implementation of technology and accelerate the transition from traditional charging to electric mobile charging stations. In the case of a simplified solution without the use of galvanic isolation and the use of low voltage batteries, the gain of the DC converter of the converter plays a very important role.

The research objective. The main task of this work is to review high-frequency DC converters without galvanic isolation to charge the battery from the network.

The statement of basic materials. In the analysis of solutions based on single-stage dc converters and the review of topologies, it was found that among the several groups of impedance networks most suitable for use are high-gain networks based on magnetic connected inductive components or a transformer. With proper implementation, this will result in an increase in the voltage gain through the rotational factor. The same circuitry based on an inverter with a Z-Source Inverter (ZSI) and a SEPIC converter, even with more modified solutions, is limited in practical implementation and operation. These circuits contain many passive components and have additional losses in semiconductors.

In the review of two-level DC converters with a high degree of amplification without galvanic isolation on the basis of high-frequency DC converters, a review and comparison of several solutions was performed. The most interesting circuit is a switched capacitor bidirectional converter consisting only of semiconductor switches and capacitors. An efficiency ratio ranges from 95 to 98.5 % over the entire download range. The intermediate concept of this solution has become quite popular in recent years, thanks to such benefits as high efficiency over a wide range of loads, reduced conduction losses, high power density.

Conclusions. High step up dc-ac converters are one of the key elements for battery charging from the grid. They provide a flexible power processing interface between energy storage device and the rest of system. Two main families of non-isolated converters are considered. The first family based on single-stage converters can be interesting because of reduced amount of elements. At the same time the complex control is a disadvantage.