Abstract
Three-phase four-leg voltage-source converters have been considered for some recent projects in smart grids and in the automotive industry, projects such as on-board electric vehicles (EVs) chargers, thanks to their built-in ability to handle unbalanced AC currents through the 4th wire (neutral). Although conventional carrier-based modulations (CBMs) and space vector modulations (SVMs) have been commonly applied and extensively studied for three-phase four-leg voltage-source converters, very little has been reported concerning their pollution impact on AC grid in terms of switching ripple currents. This paper introduces a thorough analytical derivation of peak-to-peak and RMS values of the AC current ripple under balanced and unbalanced working conditions, in the case of three-phase four-leg converters with uncoupled AC-link inductors. The proposed mathematical approach covers both phase and neutral currents. All analytical findings have been applied to two industry recognized CBM methods, namely sinusoidal pulse-width modulation (PWM) and centered PWM (equivalent to SVM). The derived equations are effective, simple, and ready-to-use for accurate AC current ripple calculations. At the same time, the proposed equations and diagrams can be successfully adopted to design the conversion system basing on the grid codes in terms of current ripple (or total harmonic distortion (THD)/total demand distortion (TDD)) restrictions, enabling the sizing of AC-link inductors and the determination of the proper switching frequency for the given operating conditions. The analytical developments have been thoroughly verified by numerical simulations in MATLAB/Simulink and by extensive experimental tests.
Highlights
Three-phase four-wire voltage-source converters (VSCs) are becoming increasingly popular in different power applications, such as grid-connected generation systems [1,2], shunt active power filters [3], active front-end rectifiers [4], renewable energy sources, and electric drives [5] applications. This kind of topology has started to be widely adopted as active front-end of dual stage electric vehicle (EV) battery on-board chargers (OBCs) in order to enable vehicle-to-grid (V2G), vehicle-for-grid (V4G) and vehicle-to-X
The most adopted modulation strategies to control three-phase four-wire converters are carrier-based pulse-width modulation (CBPWM) [14] and space vector modulation (SVM) [15]. They have been broadly employed thanks to their simple implementation, fixed switching frequency, and well-known harmonic spectrum [16,17]. These features assist the evaluation of the switching losses, which allows the converter design to be more accurate
The aim of this paper is to extend the analysis introduced by Viatkin et al [23] that has been done only for SPWM, and to present a complete mathematical formulation of envelopes and RMS values of AC
Summary
Three-phase four-wire voltage-source converters (VSCs) are becoming increasingly popular in different power applications, such as grid-connected generation systems [1,2], shunt active power filters [3], active front-end rectifiers [4], renewable energy sources, and electric drives [5] applications. The most adopted modulation strategies to control three-phase four-wire converters are carrier-based pulse-width modulation (CBPWM) [14] and space vector modulation (SVM) [15] They have been broadly employed thanks to their simple implementation, fixed switching frequency, and well-known harmonic spectrum [16,17]. These features assist the evaluation of the switching losses, which allows the converter design to be more accurate
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