Neutral Point Voltage Analysis for Three-Phase Four-Wire Three-Level Grid-Connected Converter Based on CBPWM Strategy

Jinping Wang,Juncan Wang,Weidong Jiang,Mingna Ma

doi:10.1109/access.2020.3022691

Abstract

In order to ensure the safe and reliable operation of three-phase four-wire (3P4W) three-level grid-connected converter (TL-GCC) from the point view of neutral point voltage (NPV) self-equilibrium, a sufficient condition based on carrier-based pulse width modulation (CBPWM) strategy is presented. The analysis of NPV self-equilibrium based on the sufficient condition is presented while different forms of current are outputted. Then, a novel active control method based on producing zero sequence direct current is proposed to balance NPV. The theoretical analysis of NPV self-equilibrium as well as the effectiveness of the proposed active NPV control method are verified by experimental results.

Highlights

With the rapid development of new energy fields such as photovoltaic and wind power generation, grid-connected converter (GCC), as a core component of new energy generation, converts the generated electricity into appropriate electricity that can be fed into the grid [1]
The neutral point voltage (NPV) self-equilibrium is analyzed in Section 3 while different current forms are outputted
For φ = π/2 or 3π /2, uNP corresponds to extreme value, which means NPV increase or decrease with maximum rate

Summary

INTRODUCTION

With the rapid development of new energy fields such as photovoltaic and wind power generation, grid-connected converter (GCC), as a core component of new energy generation, converts the generated electricity into appropriate electricity that can be fed into the grid [1]. Considering the output current form in different applications, such as the grid-connected renewable energy generation (sine fundamental current) and active power filter (harmonics current), the NPV self-equilibrium becomes more complicated. The NPV self-equilibrium is analyzed in Section 3 while different current forms are outputted. Based on CBPWM strategy, the NPV self-equilibrium characteristics under different current forms are discussed . The NPV self-equilibrium characteristics are analyzed while fundamental current, odd harmonic current and zero sequence direct current are respectively outputted. It can be seen that the sufficient condition of NPV self-equilibrium given in (7) is always satisfied while outputting asymmetric fundamental current, and the NPV self-equilibrium period is 2π, which means that. ODD HARMONIC CURRENT For active power filter applications, odd harmonic current is usually outputted In this case, the three-phase currents can be expressed as: ia =.

ACTIVE NPV CONTROL METHOD FOR 3P4W TL-GCC

EXPERIMENTS

CONCLUSION