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The direct torque control (DTC) strategy was proposed more than 25 years ago. It is one of the most successful and reliable techniques for AC motors. This paper presents the application of DTC using a four-switch inverter, as one of the non-conventional economic topologies suitable for low power ranges. The experimental prototype proves the validity and effectiveness of the investigated configuration. In addition, for comparison purposes, the DTC technique has been implemented using a conventional six-switch inverter. According to the experimental results, the DTC-based four-switch inverter would be competitive with the conventional topology in low power ranges to achieve an economic AC drive with a satisfactory transient and steady-state performance at moderate costs. [ABSTRACT FROM AUTHOR]

This work describes a frequency-dependent bearing voltage model for squirrel-cage induction motors. Previous research related to bearing voltages commonly considered the bearing voltage ratio (BVR) as a constant. However, it is important to analyze the frequency-dependent behavior of the BVR when dealing with systems excited by high-switching-frequency pulsewidth modulation voltages. First, we measure the BVR characteristic for a 1.5-kW test motor. The measurement data show that, in the mid-frequency range (100 kHz–6 MHz), the BVR values are smaller than the conventional low-frequency constant value, and at higher frequencies, the BVR value increases above the low-frequency value. Considering this BVR characteristic, an equivalent circuit has been built and analyzed from the perspective of the BVR. The proposed equivalent circuit has been verified by comparing simulation data with measurement data. Based on the analysis results of the equivalent circuit, a parametric study was done to examine the effects of motor system parameters on the bearing voltage. For the study, variations of the bearing voltage on the changes of the input voltage waveforms and the winding-to-stator capacitance are analyzed by using measurement and simulation data. [ABSTRACT FROM AUTHOR]

Fault-tolerant control (FTC) solutions are increasingly being used in modern drive systems with AC motors. Such systems provide a higher degree of security and solutions that allow the on-line detection and localization of failures, as well as the switching of the control mode to a mode that allows us to continue the operation or safely stop the drive system. As the current sensors (CSs) are necessary to ensure precise control of the AC motors, in the event of their failure, one of two strategies can be used—hardware or software redundancy. The first strategy requires the use of additional measuring sensors. For this reason, the algorithmic solution, based on the Luenberger Observer (LO), has been proposed in this article as one of the software redundancy methods. In contrast to methods presented in the literature, the proposed solution allows one not only to compensate the stator current in a phase with a faulty CS, but also to adjust the correction of current estimation based on a measured signal in the other phase with a healthy CS. Extensive simulation studies in the direct rotor flux-oriented control (DRFOC) structure with the induction motor (IM) confirm the effectiveness of the proposed method. In addition, the proposed solution allows the drive system to be controlled even if all CSs are damaged. [ABSTRACT FROM AUTHOR]