Induction Motor Drives Fed by an NPC Inverter with Unbalanced DC-Link

Abstract

Neutral Point Clamped (NPC) converters with n levels are traditionally controlled in such a way that the DC-link capacitors operate at 1/(n−1) of the total DC-link voltage level. The voltage level across the DC-link capacitors has to be properly regulated by the capacitor unbalance control to contain the harmonic distortion of the converter output voltages. State-of-the-art modulation techniques address the problem of the DC-link voltage regulation for NPC inverters. However, they highly show reduced performance when unbalanced DC-link voltages are considered. In this paper, a novel Space Vector Modulation (SVM) is proposed for NPC converters with an unbalanced DC-link. At every modulation interval, the technique defines the optimal switching pattern by considering the actual unbalanced DC-link conditions. The proposed modulation allows improving the harmonic content of the NPC converter output voltage with respect to a traditional ML-SVM, when the same operating conditions are considered. As an extension, the proposed modulation technique will guarantee the same output voltage quality of a traditional ML-SVM with unbalanced DC-link, while improving the conversion efficiency thanks to a reduction of switching frequency.

Four-Level Hysteresis-Based DTC for Torque Capability Improvement of IPMSM Fed by Three-Level NPC Inverter

“…In addition to the abovementioned high-performance techniques applied to improve the operation of the classical DTC, multilevel inverters could reduce the torque and flux ripples, if replacing the standard two-level inverter. Among the multilevel inverter topologies used in DTC drives, the three-level neutral-point clamped (NPC) inverter was the most widely used inverter [25][26][27][28][29][30]. In DTC fed by a three-level NPC inverter (3L-DTC), the selection of the applied voltage vectors was expanded because of employing a higher-level (HTC), which was capable of utilizing all voltage vectors of the three-level NPC inverter; thus, different speeds of stator flux linkage could be achieved to have a predominant control of torque and flux [31][32][33][34][35][36].…”