A Comprehensive AC Current Ripple Analysis and Performance Enhancement via Discontinuous PWM in Three-Phase Four-Leg Grid-Connected Inverters

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.

Prediction of DC-Link Voltage Switching Ripple in Three-Phase Four-Leg PWM Inverters

“…In grid-connected applications, the set of grid currents, whether balanced or not, might have pretty small variation in the modulating signals of Equation (1). Indeed, as highlighted in [8,13], a small voltage unbalance can cause a considerable current unbalance. For this reason, the modulating signals can be approximated as sinusoidal and balanced waveforms if such a grid voltage is considered.…”

“…Following a similar approach to the one introduced in [19] for split-capacitor inverters, the voltage switching ripple can be computed from Equations (8) and 15as:…”

“…In the case of unbalanced AC loads, four-wire topologies are employed in place of the classical three-wire inverters due to their built-in feature to handle zero-sequence components of both voltages and currents [1]. Typical applications for this kind of topology are grid-forming converters [2,3], shunt power filters [4,5], active rectifiers [6][7][8][9][10], electric drives [11], and battery chargers for electric vehicles [12][13][14]. Recently, these converters have been considered for trending smart EV chargers that are featuring vehicle-to-grid (V2G), vehicle-to-home (V2H), or even vehicle-to-vehicle (V2V) operating modes.…”

“…Recently, these converters have been considered for trending smart EV chargers that are featuring vehicle-to-grid (V2G), vehicle-to-home (V2H), or even vehicle-to-vehicle (V2V) operating modes. Several configurations exist and have recently been studied in the literature, such as four-leg topologies with [15,16] and without [8,13,17] a neutral inductor, and four-wire split capacitor inverters, also with [18] and without [19] a neutral inductor.…”

“…All these findings are helpful to estimate the main parameters for the correct design of the converter through straightforward equations. The authors of [8] optimized three-phase four-leg inverter harmonic performances by employing discontinuous PWM (DPWM) techniques.…”