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Preventive maintenance of electric drive systems with induction motors involves monitoring of their operation for detection of abnormal electrical and mechanical conditions that indicate, or may lead to, a failure of the system. Intensive research effort has been for sometime focused on the motor current signature analysis (MCSA). The MCSA techniques utilize the results of spectral analysis of the stator current. Reliable interpretation of the spectra is difficult, since distortions of the current waveform caused by the abnormalities in the drive system are usually minute. In this paper, an alternate medium for the motor signature analysis, namely the instantaneous power, is proposed. By theoretical analysis, computer simulations, and laboratory experiments, it is shown that the instantaneous power carries more information than the current itself. Utilization of the instantaneous power is thus enhancing the reliability of diagnostics of induction motor drives.

A novel concept of application of neural networks for generation of optimal switching patterns in voltage-controlled inverters is described. The pulsewidth modulator (PWM), based on hardware analog neural networks, responds with high accuracy to any desired value of the modulation index. No microprocessor or large memory typical for the existing optimal PWM schemes is required. Theoretical analysis of the proposed so-called sparse neural network is provided, and experimental results that confirm the high performance and technical advantages of the developed modulator are presented.

A novel disc-crawling motor (DCM), utilizing the forces of magnetic attraction, magnetic adhesion, and material resiliency is described. The motor is characterized by high-torque low-speed stepped rotational motion. Microprocessor control of the motor allows it to be used as an accurate positioning actuator. Principle of operation, description of a prototype, and experimental results are presented.

Results of a comparative experimental investigation of various media for noninvasive diagnosis of rotor faults in induction motors are presented. Stator voltages and currents in an induction motor were measured, recorded, and employed for computation of the partial and total input powers and of the estimated torque. Waveforms of the current, partial powers PAB and PCB, total power, and estimated torque were subsequently analyzed using the Fast Fourier Transform. Several rotor cage faults of increasing severity were studied with various load levels. The partial input power PCB was observed to exhibit the highest sensitivity to rotor faults. This medium is also the most reliable, as it includes a multiplicity of fault-induced spectral components. Index Terms--Diagnostic media, fault diagnosis, induction motors, rotor faults.

Results of a study on the use of instantaneous electric power for diagnostics of mechanical abnormalities in induction motors are presented. The instantaneous power can be measured as the so-called product power, i.e., a product of one line-to-line voltage and one line current, or as a total input power to the stator. Theoretical analysis, computer simulations, and laboratory experiments described demonstrate the superiority of the instantaneous power as a diagnostic medium over the traditionally used stator current. It is shown that in the practical environment the product power is at least as indicative of the mechanical health of an induction motor as is the total power, which is more expensive to measure. A simple method of filtering noisy spectra of the product power is proposed. Keywords: induction motors, diagnostics, mechanical abnormalities, instantaneous power.