A Five-Level Converter in a Three-Level Mode for Common-Mode Leakage Current Suppression in PV-Generation Systems

Aleksey V Udovichenko,Evgeny V Grishanov,Sergey V Brovanov,Svetlana M Stennikova

doi:10.3390/electronics10192382

Aleksey V Udovichenko, Evgeny V Grishanov + Show 2 more

Open Access

https://doi.org/10.3390/electronics10192382

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Journal: Electronics	Publication Date: Sep 29, 2021
Citations: 3	License type: CC BY 4.0

Affiliation: Novosibirsk State Technical University

Abstract

Power generation systems (PGSs) based on renewable energy sources are finding ever-widening applications, and many researchers work on this problem. Many papers address the problem of transformerless PGSs, but few of them aimed at conducting research on structures with multilevel converter topologies as part of a PGS. In this paper a grid-tied transformerless PV-generation system based on a multilevel converter is discussed. There are common-mode leakage currents (CMLCs), which act as a parasitic factor. It is also known that common-mode voltage is the main cause of the common-mode leakage current in grid-tied PV-generation systems. This paper considers the space vector pulse-width modulation (PWM) technique, which is used to suppress or reduce common-mode leakage current. The proposed PWM technique with the reduction of common-mode leakage current for a generation system based on the multilevel converter controlled with a PWM technique was verified experimentally. The experimental results accurately confirmed the mathematical model and the compensation achieved without errors. In the experiment, there was an approximately six-fold decrease in the common-mode leakage current (10.3 mA in rejection mode and 61 mA in non-rejection current). This can lead to the elimination of CMLC in a multilevel semiconductor converter only by changing the modulation mode. This suggests the possibility of using these devices as part of transformerless generation systems. Suppression of CMLC can only be carried out by changing the PWM algorithm. Both considered topologies can implement this mode of operation. The proposed converter has a higher efficiency up to a frequency multiplicity of 2000.

Highlights

Today, renewable energy sources (RESs) are widespread and are becoming more attractive compared with systems based on fossil fuels such as oil, coal and gas [1]
The structure of the PV power generation system (PVPGS), which includes a multilevel semiconductor converter proposed by the authors, as well as the control algorithm was tested
A vector-based pulse-width modulation (PWM) strategy to be used in this type of multi-level semiconductor converters was developed, which allows the formation of the common-mode voltage having the character of a constant signal

Summary

Introduction

Renewable energy sources (RESs) are widespread and are becoming more attractive compared with systems based on fossil fuels such as oil, coal and gas [1]. VSC voltage components v∗di f and vcm are the main cause of the CMLC presence. As can be seen in Equation (1), the common-mode leakage current has a polyharmonic character with different frequency content It is defined by the spectral composition of the common-mode voltage. It is obvious that the common-mode voltage acquires the character of a constant signal and takes into account the capacitive character of the common-mode leakage current that provide a CMLC value equal to zero. This condition is achieved when the current frequency is equal to zero. (b) The voltage level of vcm is defined by a voltage step of the multilevel semiconductor

A Single-Phase Multilevel Converter with Current Cancelation

Conclusions