Sensorless control offers many advantages for the operation of electrical machines. Being able to operate the machine via field-oriented control without relying on the encoder greatly increases the reliability of the drive. In the low to zero speed region, saliency based control strategies are well suited. For several standard industrial motor designs, induction machine can exhibit multiple inherent spatial saliencies linked to position. For such multi-salient induction machines, the intermodulation saliency has shown good characteristics for sensorless control. Transient excitation can be used to extract said intermodulation saliency. However, it requires intervention in the current controller pulse-width-modulation sequence and greatly oversampled current. Alternatively, rotating high frequency injection can be used to extract the intermodulation saliency, which offers simpler implementation possibilities. The rotating voltage space vector can simply be superimposed onto the current controller output. Additionally the current does not need to be oversampled. However, since the resulting high frequency current is not controlled, it is distorted by the inverter nonlinearities. Compensating the unwanted saliencies and inverter-related harmonics, the intermodulation saliency will be used in this paper to extract the rotor positon of multi-salient induction motors from the high frequency current. The experimental position estimation quality is tested at different stationary loads and transient load steps. Applicability is verified on a traction machine designed for railway application.

In electric rail transportation, traction motors are responsible for propulsion and transmit torque to the bogie wheelsets through a gear drive system. Typically, each traction motor is fixed to the bogie frame using a suspension system and thus motors might withstand a large amount of shock and vibration arising from wheel to track contact. With developing fatigue, the motor-bogie suspension might fail. To prevent destructive contact between motor and track, bogies are often equipped with an additional safety apparatus: a safety bar fixed to the bogie frame that is axially aligned with a motor-fixed safety catch when suspension is healthy. This is the last protective measure that prevents the motor from falling to the track and, thus, it is of tremendous importance to reliably and quickly determine suspension faults. While the motor-bogie suspension is broken, the motor can move up or down within the safety catch. This results in small but abrupt angular movements of the rotor after torque transients take place. Thus, detection of motor-bogie suspension fault can be detected by inspection of the shaft encoder signal or speed sensor signal under load changes. In this work, a novel detection method for motor-bogie suspension fault is presented, using spatial saliency information extraction thus only requiring current transducers and no traditional shaft encoder nor additional sensors. The transient spectra of the motor saliencies are used to define a trigger that serves to detect motor suspension failure during a test. The method is experimentally validated in a test bench equipped with a 1.6MW locomotive traction motor and a suspension-fault emulation system.

Due to the fast slew rates of modern power switching devices, inverter-fed motors experience intensified insulation stress. In addition, inverter switching with fast slew rates excites several high frequencies including multiple antiresonance frequencies of the winding and supply cable, further suffocating winding insulation at localized winding spots. As a result of the wide range of excited frequencies, high frequency currents and voltages can be used to track insulation state. In particular, the voltage at the star point of inverter-fed motors can show the degree of motor ground-wall insulation aging. However, accessing star point might not be feasible in some applications. In this paper, a special switching scheme is proposed, turning the star neutral voltage visible at the terminal voltage without the need for additional equipment or disassembling. Via solely sensing the terminal voltage, ground-wall insulation will be monitored. In addition, the proposed switching scheme elicits additional motor resonance modes, which extends the variety of current and voltage analysis for insulation condition monitoring. Experimental validation using an inverter-fed 2MW medium-voltage traction induction motor is provided.

The extraction of motor spatial saliencies permits stable control at standstill and nearby speeds. One technique to extract saliencies is to excite the motor with voltage steps and process the resulting phase current slopes to form a saliency vector. Yet, the additional voltage steps produce unwanted current ripple and increase audible noise. Therefore, voltage steps have been recently integrated into the space vector PWM symmetrical switching scheme, defined at each period by two adjacent active states and two inactive states. In this paper, only the longest active state is used for saliency extraction. The novelty of this paper lies in the application of the one-active SVPWM excitation to a parallel dual motor configuration supplied by a single inverter and using a reduced current sensor configuration. This configuration consists of only three current sensors, two sensors attached to two phases of one motor, and a single sensor attached to the second motor. A novel signal processing scheme is presented in this paper to extract the saliencies of each motor individually under one-active SVPWM excitation. Experimental results demonstrate the ability of the proposed technique for dual motor saliency extraction under one-active space vector PWM excitation and using the special current sensor configuration.