Voltage balancing in three-level neutral-point-clamped converters via Luenberger observer

Abstract

This paper addresses the problems associated with the dc-link capacitor voltages of the three-level neutral-point-clamped power converter: the imbalance of the capacitor voltages as well as the presence of an ac-voltage low-frequency oscillation in the dc link of the converter. In order to cope with them, a mathematical analysis of the capacitor voltage difference dynamics, based on a direct average continuous model, is carried out, considering a singular perturbation approach. The analysis leads to a final expression where a sinusoidal disturbance appears explicitly. Consequently, the two problems can be handled together using the ordinary formulation of a problem of regulating the output of a system subject to sinusoidal disturbances, applying classical control theory to design the controller. In this way, the controller is designed including the disturbance estimate provided by a Luenberger observer to asymptotically cancel the disturbance, while keeping also balanced the capacitor voltages. Experiments for a synchronous threelevel neutral-point-clamped converter prototype are carried out to evaluate the performance and usefulness of the converter working as a grid-connected inverter under the proposed control law.

Observer-based Switched Control of the Three Level Neutral Point Clamped Rectifier

“…In that context, the transfer function between ∆I αβ and ∆v + = y e − v + can be approximated from the power balance equation. Taking into account (14) and retaining the first order terms, we obtain…”

“…In the same vein, the observation problem has been even less considered for this specific power converter, except in adaptive control schemes [11]- [13], or based on approximated/averaged model [14]. Indeed, the three level NPC converter have a large number of switches and a dynamic reference which are the sources of difficulties when compared to numerous examples of converters usually considered [15]- [17].…”

Two-level inverter and three-level neutral point diode clamped inverter for traction applications: a comparative analysis study

“…The major reason for this unbalance is the flow of average The modulation technique applied should be able to reduce this unbalance issue in case no external circuit is added. Many researchers have reported solutions for the unbalance of the neutral current [23]- [26]. In [26], the neutral point current was reduced by adding a measured zero-sequence voltage signal to the reference voltages, which improved the converter performance that is highly recommended for EVs applications.…”

A High-Gain Observer-Based Adaptive Super-Twisting Algorithm for DC-Link Voltage Control of NPC Converters

“…In the balancing loop, to assure the converter operates normally, the error voltage between the two capacitors is demanded to be near zero, i.e., e * dc = 0. Normally, a simple PI controller is used in this loop to achieve this goal and alleviates the complexity of the whole control system although other techniques can be found in the literature [30,31].…”