Irfan N. Ali

Turn-Off Time as an Early Indicator of Insulated Gate Bipolar Transistor Latch-up

In this paper, effects preceding a latch-up fault in insulated gate bipolar transistors (IGBTs) are studied. Primary failure modes associated with IGBT latch-up faults are reviewed. Precursors to latch-up, primarily an increase in turn-off time as a consequence of elevated junction temperature, are examined for an IGBT. The relationship between junction temperature and turn-off time is explained by modeling the parasitic properties of an IGBT. A metric is derived from the model to standardize the relative estimates in junction temperature from measurements of turn-off time. To evaluate the effects preceding latch-up in-situ, seeded fault testing is conducted on a three-phase power inverter using aged transistors induced with a fault located in the die-attach solder layer. Experimental results demonstrated the feasibility of using the proposed metric as a precursor to transistor latch-up.

Power electronics health monitoring test platform for assessment of modern power drives and electric machines with regeneration capabilities

This work presents a power electronics health monitoring test platform for assessing modern power drives and electric machines with regeneration capabilities. This versatile platform combines data acquisition of critical system signals that are used for analysis as health indicators for the overall system and individual components such as power semiconductor devices. The test platform combines hardware and software in the loop to allow health monitoring and control techniques for fault tolerance.

On-line motor winding early diagnostic based on dynamic leakage current monitoring

This paper presents a new on-line method for motor winding deterioration diagnostic based on the increase in the high frequency leakage current. A differential current sensor is used for the measurement of the leakage current. Traditionally, differential current sensors are used as a protection device, however, in this work their use is extended for health monitoring. In order to validate the proposed approach, motor windings are aged using the accelerated thermal method. The reduction of the leakage impedance in the aged winding is compared with online measurements for verification purposes. 1 2

Smart phone machinery vibration measurement

This paper presents a computationally economical algorithm that provides RMS value of vibration velocity calculated using the accelerometer measurements embedded in modern smartphones. This measurement extends the use of smartphones to quickly diagnose the health status of machinery. 1 2

Solar cells aging estimation based on impedance characterization

Solar energy generation has been a mainstay in space applications such as the International Space Station and military and commercial satellites. More recently, solar power has gained a lot of momentum for terrestrial commercial and residential applications as a viable alternative source of energy. In the current work, a low cost impedance measurement system was implemented to measure the complex impedance of solar cells. Some of the cells were then thermally aged, and the impedance changes from baseline were observed. It was noticed that the phase of the complex impedance signal (or alternatively, the imaginary part of the impedance) was different for a few of the cells subjected to aging.1, 2

Observer based junction temperature estimator in thermoelectrical aging

Transistor thermal model is nonlinear and highly dependent upon temperature. For reliability assessments, accurate estimation of the junction temperature is especially critical. This paper proposes a novel approach that employs an observer during thermoelectrical aging for estimation of the junction temperature based on available and measurable temperature data. 1 2

Automated Feature Extraction and Tuning of Ringing Characterization for Power Drives Diagnostic and Prognostic

Ringing characterization has been successfully implemented as a health indicator of power transistors in simplified power systems. This paper presents a systematic effort to achieve an automated method to extract the ringing characteristics of the current during transistor switching in a complete power drive system. Baseline patterns and their standard deviations are established from the ringing of the motor current. Four main components of the repeating patterns are identified and all the ringing components are synchronized and un-dampened for frequency extraction and harmonics variation estimation during normal operation. Ringing component(s) are studied to find the most suitable to be used as a transistor health indicator for tracking the characteristic ringing changes in an online manner. Automated feature extraction will enable fabrication of a low cost sensor solution for motor and actuator based applications to evaluate power transistor aging.

New sensing application to diagnose power semiconductor aging in actuator power drive systems

This paper presents a new sensing application to diagnose power semiconductor aging in power drive systems. It has been shown previously that device parasitic characteristics change during the aging process which results in detectable changes in their frequency response. This change is manifested in the current signal at very high frequencies. Therefore, using a wideband AC current sensor, high frequency components of the current can be acquired, providing a way to detect device aging.

Sensing and characterization of EMI during intermittent connector anomalies

This paper presents a new on-line methodology for detecting intermittent disconnection failures. The detection principle operates on the fundamental Lorentz Law that states that sudden changes in flux create a large voltage, resulting in an arc. This arc propagates as a traveling wave through the circuit until all the energy associated with it is dissipated. It is possible to detect that traveling wave as an indication of an intermittent disconnection failure. A test bench was implemented to test and validate the theory. Preliminary results presented in this paper show the feasibility of detecting disconnection failures and the possibility of locating the failing connector based on distance.

On-line intermittent connector anomaly detection

This paper investigates a non-traditional use of differential current sensor and current sensor to detect intermittent disconnection problems in connectors. An intermittent disconnect, often resulting in an arc, creates an imbalance which is manifested in the current. The traveling wave generated due to the perturbation can be detected using current sensors. This paper shows the feasibility to detect disconnection based on this principle.