AC Current Ripple in Three-Phase Four-Leg PWM Converters with Neutral Line Inductor

Aleksandr Viatkin,Mattia Ricco,Riccardo Mandrioli,Manel Hammami,Gabriele Grandi

doi:10.3390/en14051430

Abstract

This paper presents a comprehensive study of peak-to-peak and root-mean-square (RMS) values of AC current ripples with balanced and unbalanced fundamental currents in a generic case of three-phase four-leg converters with uncoupled AC interface inductors present in all three phases and in neutral. The AC current ripple characteristics were determined for both phase and neutral currents, considering the sinusoidal pulse-width modulation (SPWM) method. The derived expressions are simple, effective, and ready for accurate AC current ripple calculations in three- or four-leg converters. This is particularly handy in the converter design process, since there is no need for heavy numerical simulations to determine an optimal set of design parameters, such as switching frequency and line inductances, based on the grid code or load restrictions in terms of AC current ripple. Particular attention has been paid to the performance comparison between the conventional three-phase three-leg converter and its four-leg counterpart, with distinct line inductance values in the neutral wire. In addition to that, a design example was performed to demonstrate the power of the derived equations. Numerical simulations and extensive experimental tests were thoroughly verified the analytical developments.

Highlights

Three-phase converters have been extensively employed as an interface between AC distribution networks and the distributed energy sources, such as photovoltaic and wind farms, DC microgrids, and energy storage systems [1]
At total harmonic distortion (THD) ≤ 3%, the lowest LΣ|rms belongs to the “0.5774L” four-leg voltage source converters (VSCs) design
This paper provides a thorough analysis of the instantaneous AC current ripple in the general case of three-phase, four-leg inverters with a neutral line inductor

Summary

Introduction

Three-phase converters have been extensively employed as an interface between AC distribution networks and the distributed energy sources, such as photovoltaic and wind farms, DC microgrids, and energy storage systems [1]. Another popular tendency in the automotive industry is to apply three-phase converters as a power factor correction stage in on- or off-board electrical vehicle (EV) battery chargers [2,3]. There are various three-phase four-wire topologies available in the literature/market, but only three are widely applied: split-capacitor [7,8], four-leg [6,9], and independently controlled neutral module [10,11]. These voltage source converters (VSCs) can either have or not have the fourth wire’s neutral line inductor

Objectives

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Conclusion