$H^infty$Control of the Neutral Point in Four-Wire Three-Phase DC–AC Converters

Abstract

Abstract-Inverters used as the interface for a distributed generator in a three-phase four-wire system sometimes operate with a large neutral current because of unbalanced loads and singlephase (possibly nonlinear) loads. Voltage balance within the dc-link of the inverter is important for proper operation of the inverter, and the neutral current is a significant disturbance to this. It is preferable to use fast acting control rather than dissipative balancing or large-valued capacitors. This paper develops a linear model of an actively balanced split dc-link and applies H ∞ control design to provide high-bandwidth robust control. The approach is developed for a conventional two-level inverter, but it remains valid (without change) for a three-level neutral-point clamped inverter. The controller achieves very small deviations of the neutral point (better than 0.5 in 800 V) from the midpoint of the dc source despite the large neutral current (32 A RMS ). The controller design is described and verified first in a PSCAD simulation and second in experimental testing of a 30-kW 415-V (line) inverter.Index Terms-DC-AC power converter, dc-link balancing, fourwire three-phase power system, H ∞ control, multilevel inverter, neutral line.

>tex<$H^infty$>/tex<Repetitive Control of DC-AC Converters in Microgrids

“…Due to the presence of a balanced dc link (see [8], [9]), we may regard this system as three independent single-phase systems, as shown in Fig. 1, and hence there is no need to study here the three-phase behavior of the system.…”

“…Normally, the high-frequency poles can be reduced using various controller/model reduction techniques, which is a topic of wide interest. Here, we use a different approach from that used in [18], [8], [9] to decrease the controller bandwidth: we do not minimize the -norm of but find a suboptimal controller such that (which is larger than the minimal value 17.37). Such a controller (obtained using the hinfsyn routine in MATLAB is (9), shown at the bottom of the page.…”

“…1) DC-link balancing [8], [9]: to provide a neutral line, on which the voltage is balanced w.r.t. the two terminals of the dc link, even when the three-phase system is not balanced and there is a large zero-sequence current compo- This paper concentrates on one of these items only: microgrid voltage control.…”

Digital Control Techniques Based on Voltage Source Inverters in Renewable Energy Applications: A Review

“…In Figure 8, u o represents the output voltage of the LC filter, whereas M represents the point neutral point between two switches, S M and S M . Even though the configuration in this topology does not need expensive and large capacitors and produces lower ripple on the DC link voltage, however, using two extra switches lead to a complex control system [47]. Additionally, the split DC-link voltage is about 15% less as compared to the AC voltage in this configuration [48].…”

Review of Multifunctional Inverter Topologies and Control Schemes Used in Distributed Generation Systems

“…To mitigate the neutral current in a 3P4W system, various shunt inverter configurations have been studied, namely, two-split capacitor (2C) [130], [131], four-leg capacitor (4L) [131]- [141], and three-H bridge (3HB). 6 shows the 3P4W MFI configurations based on 2C, 4L, and 3HB topologies.…”