Monitoring of induction motor faults based on stray flux measurement has been investigated by many researchers due to its potential benefits in cost and simplicity. Although it was shown that flux based monitoring can provide sensitive fault detection comparable to that of motor current signature analysis (MCSA), the lack of “remote” monitoring capability has limited its practical use. The performance and reliability of stray flux-based detection of induction motor rotor cage faults is evaluated in this paper. It is shown for the first time in this work that spectrum analysis of the radial stray flux can provide reliable detection of rotor faults immune to the influence of rotor axial air ducts, which is the most common cause of false rotor fault alarms. The reliability and sensitivity of stray flux based rotor fault detection is demonstrated through experimental testing on laboratory and 6.6 kV field motors.

In permanent magnet synchronous machine (PMSM) design, a limited number of stator and rotor slots distorts the air-gap flux distribution and its effective length. It causes machine parameters to vary with the rotor position. The rotor flux linkage harmonics introduce non-sinusoidal back-EMF, which causes current harmonics when conventional PI current controller is adopted. Those machines suffer from high frequency torque ripple due to air-gap flux harmonics in low speed region. However, in high speed region, where the torque ripple is filtered out by the mechanical system, the torque ripple may be disregarded. In this case, torque-ripple suppression methods and the associated harmonic current components generate losses. Therefore, a sinusoidal current control is required to reduce undesired harmonic losses. In this manner, this paper focuses on the sinusoidal current control strategy based on harmonic voltage injection, which requires knowledge of rotor magnet flux linkage harmonics. This paper also proposes both offline and online schemes for identification of rotor magnet flux linkage harmonics. These methods do not require any proprietary machine design details such as the shape of stator or rotor for finite element analysis (FEA). Commonly used PI plus resonant (PIR) controller is also designed and its disadvantages in terms of speed-dependent gain and stability, in comparison to the proposed scheme, are highlighted. Finally, experimental results are presented to compare the proposed scheme with the conventional method at different operating conditions.

Fast switching characteristic of wide bandgap devices enables high switching frequency of power devices and thereby, can facilitate high fundamental frequency operation of electrical machines. However, with the switching transition times in orders of tens of nanoseconds, the high dv/dt is observed across the switching device. The high dv/dt experienced by the switches, and consequently by the machine, can degrade winding insulations or bearings over a period of time. Therefore, it is imperative to maintain the dv/dt below recommended values depending on the machine insulation. The dv/dt across the devices can be adjusted by varying the gate resistance. A high value of gate resistance, however, introduces additional switching losses on the device. Using different dv/dt filtering techniques can also help to control the dv/dt on the machine terminals. These techniques do not increase the switching losses on the device. However, it introduces additional losses in the filter resistors and also increases the cost of the system. In this paper, an analysis based on the impact of gate resistance on the dv/dt across the machine, and the corresponding losses is carried out. An analytical dv/dt filter design strategy is proposed to limit the dv/dt to a particular value. With the proposed design scheme, the value of each filter component can be easily obtained, and filter losses can be estimated accurately. Lastly, a comparison is performed on the basis of efficiency between these two techniques.

Current measurement offset errors occur in current sensors and related circuits, because of various factors, such as thermal drift, aging, and nonlinearity. The current offset error results in undesired torque ripples, which deteriorate the speed and torque control performances of vector-controlled drive systems. This study proposes an online current measurement offset error compensator for vector-controlled surface permanent magnet synchronous motor (SPMSM) drive systems. The proposed compensator requires only phase current sensors and no additional hardware. This method is applicable for all systems using two and three phase current sensors. The current offset error is estimated using the motor parameters, stator current, and command voltage in the stationary reference frame. This scheme can continuously adjust the current offset during motor operation. In addition, this study analyzes the effect of parameter errors and confirms that the proposed method is robust to variations in the machine parameters. Simulation and experimental results are provided to verify the performance of the proposed current measurement offset error compensation method.

The induction motor drive with indirect field-oriented control (IFOC) is widely adopted due to its simple structure and easy implementation. The rotor time constant plays the most crucial role in IFOC. However, the rotor resistance varies with temperatures, and the rotor inductance changes with the current magnitude in practice. Furthermore, an accurate estimation of such parameters is challenging. The parameter mismatch between the actual and the estimated rotor time constant deteriorates the performance of the IFOC vector control due to an error in the estimated rotor flux position. This paper presents the theoretical analysis of the effects of the inductance errors in the conventional Q-MRAS method, which is widely used to compensate for the rotor time constant. Next, this paper proposes the dual MRAS consisting of a novel stator flux-based MRAS and the conventional Q-MRAS. The proposed dual MRAS method can simultaneously compensate for the error of inductance and rotor time constant, thereby improving the performance of IFOC. The robustness and effectiveness of the proposed method have been validated through simulations and experiments.