The paper presents a five-level inverter scheme with reduced power circuit complexity for an induction motor drive. The scheme is realized by cascading conventional two-level and three-level neutral point clamped inverters in conjunction with an open-end winding three-phase induction motor drive. An inverter control scheme with common-mode voltage (CMV) elimination, along with a simple DC link voltage control, is developed by using only switching states with zero CMV for the entire modulation range. Theoretical considerations are experimentally verified for a variety of operating conditions.

This paper develops a seven-level inverter structure for open-end winding induction motor drives. The inverter supply is realized by cascading four two-level and two three-level neutral-point-clamped inverters. The inverter control is designed in such a way that the common-mode voltage (CMV) is eliminated. DC-link capacitor voltage balancing is also achieved by using only the switching-state redundancies. The proposed power circuit structure is modular and therefore suitable for fault-tolerant applications. By appropriately isolating some of the inverters, the drive can be operated during fault conditions in a five-level or a three-level inverter mode, with preserved CMV elimination and DC-link capacitor voltage balancing, within a reduced modulation range.

Three-phase ac filters occupy more than 30%–40% of the total power electronics (PEs) system volume. With interleaved operation, the size of three-phase line harmonic filters can be reduced at the expense of high circulating current between channels. Additional filter for circulating current mitigation is required, which contributes to incremental volume. The challenge is to achieve a truly optimized and modular solution for interleaved converters, while effectively blocking circulation. Two concepts are considered, i.e., magnetic and electrical interconnection between filter blocks for parallel converters. These interconnecting methods are integrated with conventional filter structures, such as the LCL filter, to achieve filter building block (FBB) configurations. A design procedure is formulated for the two FBB configurations to compare the loss-volume map of each FBB. Brief experimental and analytical comparison is performed to distinguish between the two topologies. It is found that from modularity point of view, the electrically interconnected FBB can be a favorable option and candidate for high power applications.

This article presents the analysis and realization of a modular interconnected filter building block (FBB) operating under a single and multichannel (parallel three-phase converter blocks) configuration without loss of attenuation to any harmonic components. Emphasis is on the design of coupled inductor (CI) and boost inductor. In order to achieve a modular scheme with interleaved operation, indirect coupling between converters is realized using the secondary loop (SL)-based interconnection with inserted impedance. Here the “SL” serves as an additional pass for average grid side currents for N channels. A building block type configuration has been proposed using this topology, inspired by the power electronics building block (PEBB) nature. The purpose of the loop is to interconnect the parallel converters in series using an arrangement of CIs. In addition, a boost inductor has been introduced in the SL to realize a power factor correction rectifier operation. The CI serves as the circulating current filter while reflecting channel currents toward the SL. To meet conducted electromagnetic interference (EMI) limits, a two-stage LCLC filter has been integrated with the FBB by introducing the point of common coupling (PCC) connection between two stages for filter size reduction. A design procedure is presented to meet power quality, circulating current, and EMI limits as per industry standards (EN-55011 and IEEE-519/1594). The proposed FBB has been characterized using 3L-NPC converters enabled with 1.2 kV Silicon Carbide based modules with comprehensive performance validation up to three channels in parallel with 15-kW power rating per channel.

Due to the limit in current-rating of SiC MOSFETs, a number of SiC-based modular ac-dc converters requires paralleling to increase power-capacity. On the other hands, paralleling diversifies paths of current, and complex filter topologies such as integrated inductors may complicate analysis. To enhance understanding of N-paralleled ac-dc converters, and to provide an insight for filter design, four per-phase equivalent circuits are proposed. Any voltage on the frequency spectrum can be classified into 4 groups by two criteria; Firstly, positive- and negative-sequence vs. zero-sequence, and, secondly, circulating, vs. in-phase. By extending symmetrical component theory to the parallel converters, the N-paralleled three-phase converters can be represented by 4 single-phase circuits. Thanks to the simplicity, complex issues such as an impact of the magnetic integration or change of harmonic attenuation for different N can be easily understood for any N by sinlge-phase equivalent circuits.

Common-mode voltage generated by the PWM inverter causes shaft voltage, bearing current and ground leakage current in induction motor drive system, resulting in an early motor failure. This paper presents a common-mode elimination scheme for a five-level inverter with reduced power circuit complexity. The proposed scheme is realised by cascading conventional two-level and conventional NPC three-level inverters in conjunction with an open-end winding three-phase induction motor drive and the common-mode voltage (CMV) elimination is achieved by using only switching states that result in zero CMV, for the entire modulation range.