Analysis of Input Voltage Switching Ripple in Three-Phase Four-Wire Split Capacitor PWM Inverters

Abstract

Three-phase, four-wire split capacitor inverters are currently employed in many applications, such as photovoltaic systems, battery chargers for electric vehicles, active power filters, and, in general, in all grid-tied applications that deal with possible grid voltage and/or current unbalances. This paper provides a comprehensive evaluation of the capacitor-switching voltage ripple and dc-link switching voltage ripple for the three-phase, four-wire, split capacitor inverters. Specifically, analytical formulations of the peak-to-peak and rms values of the voltage ripples are originally pointed out in this paper and determined in the case of balanced three-phase and unbalanced (two-phase and single-phase) output (ac) currents. The obtained results can help in designing the considered inverter and sizing of the dc-link capacitors. Reference is made to the sinusoidal PWM modulation and sinusoidal three-phase output currents with an almost unity power factor, representing a grid-connected application. Extensive numerical simulations have been carried out to thoroughly verify all the analytical developments presented in this paper. Furthermore, some experimental tests, having balanced output currents on the ac side, have been accomplished, validating numerical simulations and analytical developments.

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

“…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:…”

“…which can be employed for finding pulse timings of Equation (19). Employing the timings of Equation (19) together with the voltage ripple definition of Equation (16), the following noticeable voltage ripple peaks (depicted in Figure 4) can be found:…”

“…Following the approach introduced in [19], it is possible to calculate the voltage ripple RMS based on the ripple waveform discussed above. As displayed in Figure 4, the voltage switching ripple assumes an irregular waveform that should be treated considering the RMS components on the piecewise function intervals.…”

“…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.…”

“…A detailed analysis of positive, negative, and zero symmetric voltage components for the same topology is provided in [2]. An exhaustive study of the DC-link voltage ripple with respect to the switching frequency was given for both the total DC-link voltage and the capacitor voltages in [19]. Differently from the current manuscript, no mention of the single-phase connection typical of domestic applications (for instance, V2G/V2H) has been presented.…”