Abstract
A complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections.
Highlights
The capability to handle neutral current is gaining interest in grid-connected power applications such as distributed generation systems [1,2], active rectifiers [3,4], and power filters [5]
This paper provides a detailed analysis of the switching ac current ripple in three-phase, four7
This paper provides a detailed analysis of the switching ac current ripple in three-phase, fourcurrents have been analyzed detail. ac current ripple in three-phase, fourThisripple papercharacteristics provides a detailed analysis of theinswitching
Summary
The capability to handle neutral current is gaining interest in grid-connected power applications such as distributed generation systems [1,2], active rectifiers [3,4], and power filters [5]. Neither average switching frequency nor switching losses, in the case of DPWM, have not been taken into account to optimize the performance of four-leg inverters The target of this manuscript is to provide a thorough analytical description of the phase and neutral current ripple characteristics in three-phase, two-level, four-leg, grid-connected inverters for the most popular PWM schemes, such as SPWM, CPWM, DPWM, and third harmonic injection (THIPWM). The aim of this assumption is to simplify computation efforts while preserving the applicability of the derived expressions in grid-connected applications Another contribution given by this work is a comparison of the considered modulation strategies in terms of different metrics, i.e., switching losses, average switching frequency, rms and peak-to(usually 0.05–0.08 p.u.), relevant unbalanced currents can be driven by slightly asymmetric inverter peak of voltages.
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