Siwei Cheng

An Impedance Identification Approach to Sensitive Detection and Location of Stator Turn-to-Turn Faults in a Closed-Loop Multiple-Motor Drive

A single closed-loop inverter drive with multiple motors connected to it is a type of drive topology commonly used in steel processing industry, electric railway systems, and electric vehicles. However, condition monitoring for this type of drive configuration remains largely unexplored. This paper proposes an impedance identification approach to detect and locate the stator turn-to-turn fault in a multiple-motor drive system. Sensitive and fast fault detection is achieved by utilizing the characteristics of current regulators in the motor controller. Experimental results show that the proposed method can reliably detect and locate the stator turn fault on two shaft-coupled 5-hp induction machines under different operating conditions and fault levels with no need of any machine parameters. Although originally developed for multiple-motor drives, the detection scheme can also be directly applied to most of the conventional closed-loop induction motor drives.

A Nonintrusive Thermal Monitoring Method for Induction Motors Fed by Closed-Loop Inverter Drives

Closed-loop induction motor drives have wide applications in electric traction system and industrial processes. Accurate thermal monitoring not only protects the induction machines from overheating, but also boosts the usage and performance of the overall drive system. State-of-the-art thermal monitoring schemes for induction machines utilize thermal models, which are inaccurate for drive-fed machines and are not adaptive to varying cooling conditions. This paper proposes a nonintrusive thermal monitoring scheme for induction motors fed by closed-loop inverter drives. By applying offsets to the current controllers in the motor drive, dc currents are injected into the stator windings of the machine. The accurate estimation of the injected dc voltage is achieved by carefully analyzing and compensating for inverter nonidealities. The stator winding temperature can thus be monitored based on the estimated dc stator resistance. The method is nonintrusive because it eliminates the thermocouples, requires no hardware change to the existing motor drive, and has minimal impacts on the normal operation of the motor. The proposed method is practically implemented in a programmable inverter drive and is validated both by simulation and real-time experimental results.

Design of a 750,000 rpm switched reluctance motor for micro machining

This paper presents a detailed design process of an ultra-high speed, switched reluctance machine for micro machining. The performance goal of the machine is to reach a maximum rotation speed of 750,000 rpm with an output power of 100 W. The design of the rotor involves reducing aerodynamic drag, avoiding mechanical resonance, and mitigating excessive stress. The design of the stator focuses on meeting the torque requirement while minimizing core loss and copper loss. The performance of the machine and the strength of the rotor structure are both verified through finite-element simulations The final design is a 6/4 switched reluctance machine with a 6mm diameter rotor that is wrapped in a carbon fiber sleeve and exhibits 13.6 W of viscous loss. The stator has shoeless poles and exhibits 19.1 W of electromagnetic loss.

A new method to detect stator turn-to-turn faults in a closed-loop multiple-motor drive system

Multiple motors connected to a single closed-loop inverter drive is a common type of drive topology which has wide application in steel processing industry, electric railway systems and electric vehicles. But condition monitoring for this type of drive configuration remains largely unexplored. This paper proposes a new method to detect the stator turn-to-turn fault in a multiple-motor drive system. The method achieves very high detecting sensitivity yet remains easy to implement by utilizing the characteristics of current regulators in the motor controller. Experimental results show that the method can reliably detect a short circuit of 1 turn out of 216 turns per phase on two 5-hp, shaft-coupled induction machines. Although originally developed for multiple-motor drives, the detection scheme can be directly applied to most of normal closed-loop induction motor drive.

A nonintrusive thermal monitoring method for closed-loop drive-fed induction machines

Closed-loop induction motor drives have wide applications in electric traction system and industrial processes. Accurate thermal monitoring not only protects the induction machines from overheating, but also boosts the usage and performance of the overall drive system. State-of-the-art thermal monitoring scheme for induction machines utilize simple thermal models, which is generally far too conservative. This paper proposes a nonintrusive thermal monitoring scheme for induction motors fed by closed-loop inverter drives. By applying an offset to the controllers in the motor drive, DC currents can be injected into the stator windings of the machine. The stator winding temperature can thus be monitored based on the estimated DC stator resistance. The method is nonintrusive because it eliminates the thermocouples and requires no hardware change to the existing motor drive. This proposed method is validated both by simulation and real-time experimental results.

Detecting and locating the stator turn-to-turn faults in a closed-loop multiplemotor drive system

Multiple motors connected to a single closed-loop inverter drive is a common type of drive topology which has wide application in steel processing industry, electric railway systems and electric vehicles. But condition monitoring for this type of drive configuration remains largely unexplored. This paper proposes a new method not only to detect but also to locate the stator turn-to-turn fault in a multiple-motor drive system. The method achieves very high sensitivity yet remains easy to implement by utilizing the characteristics of current regulators in the motor controller. Experimental results show that the proposed method can reliably detect and locate the stator turn fault on two shaft-coupled 5-hp induction machines under different operating conditions and fault levels with no need of any machine parameters. Although originally developed for multiple-motor drives, the detection scheme can be directly applied to most of conventional closed-loop induction motor drive.

Using only the DC current information to detect stator turn faults in automotive claw-pole alternators

The stator turn fault is an important type of fault in automotive claw-pole alternators. In a typical vehicle electric system, however, it is difficult to access the AC current or voltage information of the claw-pole alternator, making conventional sequence-component-based fault detectors useless. This paper analyzes the effects of a full-bridge rectifier on the three-phase unbalanced system. A novel stator turn fault detector was proposed using only the alternator output current measurement. The performance of the stator turn-fault detector is demonstrated both by finite-element simulation and by extensive experimental results. The effect of the winding layout on stator turn fault detection is also discussed. Although the fault detector is originally proposed for claw-pole alternators, it is also applicable to most poly-phase AC generators with a DC link rectifier.

An analysis and discussion of the voltage and current spectrum of claw-pole alternators for fault detection purposes

The ‘claw-pole’ type synchronous alternator is the heart of virtually all automotive Electric Power Generation and Storage (EPGS) system. Timely and accurate detection of alternator faults will not only decrease “walk-home” incidences for drivers but will also significantly decrease misdiagnoses, thereby resulting in significant warranty cost savings for auto manufacturers. This paper performs a general analysis on the voltage and current spectrum of the claw-pole alternators. Various harmonic components in the spectrum are explained from the first principles. The effect of the built-in rectifier on alternator voltage and current spectrum is also investigated. The analysis leads to a better understanding of claw-pole alternators especially for fault detection purposes.

Interpolated FFT for real-time detection of belt slip in automotive electric power generation and storage system

Belt slip is an important type of mechanical fault in the automotive electric power generation and storage (EPGS) system. This paper proposes a robust and sensorless solution for detecting serpentine belt slip. The speed of the claw-pole alternator is directly extracted from the rectifier ripple frequency from the alternator output voltage. The estimated alternator speed is then continuously compared with the engine speed to detect possible belt slip. The proposed method is implemented in a real-time fashion on an EPGS test bench. The experimental results show that the method is able to estimate the alternator speed accurately even during fast mechanical transients. The belt-slip fault can thus be reliably detected within a wide speed range. Although originally developed for automotive alternators, the sensorless speed estimation method can be also applied to other AC generators with a DC-link rectifier.