An On-line Diagnostic Method for Open-circuit Switch Faults in NPC Multilevel Converters

On-line condition monitoring is of paramount importance for multilevel converters used in safety-critical applications. A novel on-line diagnostic method for detecting open-circuit switch faults in neutral-point-clamped (NPC) multilevel converters is introduced in this paper. The principle of this method is based on monitoring the abnormal variation of the dc-bus neutral-point current in combination with the existing information on instantaneous switching states and phase currents. Advantages of this method include simpler implementation and faster detection speed compared to other existing diagnostic methods in the literature. In this method, only one additional current sensor is required for measuring the dc-bus neutral-point current, therefore the implementation cost is low. Simulation and experimental results based on a lab-scale 50 kVA adjustable speed drive (ASD) with a three-level NPC inverter validate the efficacy of this novel diagnostic method

Saliency Ratio and Power Factor of IPM Motors Optimally Designed for High Efficiency and Low Cost Objectives

This paper uses formal mathematical optimization techniques based on parametric finite-element-based computationally efficient models and differential evolution algorithms. For constant-power applications, in the novel approach described, three concurrent objective functions are minimized: material cost, losses, in order to ensure high efficiency, and the difference between the rated and the characteristic current, aiming to achieve very high constant-power flux-weakening range. Only the first two objectives are considered for constant-torque applications. Two types of interior permanent magnet rotors in a single- and double-layer V-shaped configuration are considered, respectively. The stator has the typical two slots per pole and phase distributed winding configuration. The results for the constant-torque design show that, in line with expectations, high efficiency and high power factor machines are more costly, and that the low-cost machines have poorer efficiency and power factor and most importantly, and despite a common misconception, the saliency ratio may also be lower in this case. For constant-power designs, the saliency ratio can be beneficial. Nevertheless, despite a common misconception, when cost is considered alongside performance as an objective, a higher saliency ratio does not necessarily improve the power factors of motors suitable for ideal infinite flux weakening

Effects of Load Magnitude on Diagnosing Broken Bar Faults in Induction Motors Using the Pendulous Oscillation of the Rotor Magnetic Field Orientation

The effects of load level on the ability to diagnose broken bar faults in squirrel-cage induction motors are studied in this paper. The pendulous oscillation of the rotor magnetic field orientation is implemented as a fault signature for rotor fault diagnostic purposes at steady-state operations. Moreover, the effects of load level on the low-side band component of the stator current spectrum, and associated diagnostic difficulties in this approach particularly in the presence of motor operation from pulsewidth-modulation drives, are reported as well. These investigations were performed through testing 2-hp and 5-hp induction motors over a wide range of load levels and control drives. The results of these tests and investigations demonstrate the efficacy of the pendulous oscillation signature as a diagnostic means that can be used for a wide range of motor operating conditions

Diagnosis of Inter-Turn Short Circuit for a Polyphase Induction Motor in Closed-Loop Vector-Controlled Drives

The main objective of this paper is to develop and experimentally verify a new technique to detect an inter-turn short circuit in one phase of a stator winding of an induction motor energized from a vector-controlled drive. This is in order to overcome the fault masking difficulties associated with the concept of depending on the actual magnetic field pendulous oscillation between the conventional voltage and current space vectors with respect to a reference that is unaltered by the compensation action of the drive. This technique is based on the flux pendulous oscillation phenomenon. This flux pendulous oscillation is also described in this paper, this in addition to the magnetic field pendulous oscillation previously addressed in prior publications. The new approach has been verified through experimental results which are represented here

Computer-aided modeling and prediction of performance of the modified Lundell class of alternators in space station solar dynamic power systems

The main purpose of this project is the development of computer-aided models for purposes of studying the effects of various design changes on the parameters and performance characteristics of the modified Lundell class of alternators (MLA) as components of a solar dynamic power system supplying electric energy needs in the forthcoming space station. Key to this modeling effort is the computation of magnetic field distribution in MLAs. Since the nature of the magnetic field is three-dimensional, the first step in the investigation was to apply the finite element method to discretize volume, using the tetrahedron as the basic 3-D element. Details of the stator 3-D finite element grid are given. A preliminary look at the early stage of a 3-D rotor grid is presented

Induction Machine Broken-bar Fault Diagnosis Using the Rotor Magnetic Field Space-vector Orientation

A new technique based on rotor magnetic field space vector orientation is presented to diagnose broken-bar faults in induction machines operating at steady state. In this technique, stator currents and voltages are used as inputs to compute and subsequently observe the rotor magnetic field orientation, which has a more significant swing-like pendulous oscillation in case of broken-bar faults than in healthy operation. It will be shown here that the range of this pendulous oscillation is a function of the number of broken bars. Also in this technique, it was found that an inter-turn shorted stator-winding fault, which exhibits similar pendulous oscillation, could be distinguished from rotor broken-bar faults through the use of a variance index. In order to validate this method, experimental evidence is given here for several broken-bar cases in a 2-hp three-phase two-pole squirrel-cage induction machine

On Innovative Methods of Induction Motor Interturn and Broken-bar Fault Diagnostics

A fault indicator, the so-called swing angle, for broken-bar and interturn faults is investigated in this paper. This fault indicator is based on the rotating magnetic-field pendulous-oscillation concept in faulty squirrel-cage induction motors. Using the swing-angle indicator, it will be demonstrated here that an interturn fault can be detected even in the presence of machine manufacturing imperfections. Meanwhile, a broken-bar fault can be detected under both direct-line and PWM excitations, even under the more difficult condition of partial-load levels. These two conditions of partial load and motor manufacturing imperfections, which are considered as difficult situations for fault detection, are investigated through experimentally obtained test results for a set of 2- and 5-hp induction motors

Rotor Bar Fault Monitoring Method Based on Analysis of Air-Gap Torques of Induction Motors

A robust method to monitor the operating conditions of induction motors is presented. This method utilizes the data analysis of the air-gap torque profile in conjunction with a Bayesian classifier to determine the operating condition of an induction motor as either healthy or faulty. This method is trained offline with datasets generated either from an induction motor modeled by a time-stepping finite-element (TSFE) method or experimental data. This method can effectively monitor the operating conditions of induction motors that are different in frame/class, ratings, or design from the motor used in the training stage. Such differences can include the level of load torque and operating frequency. This is due to a novel air-gap torque normalization method introduced here, which leads to a motor fault classification process independent of these parameters and with no need for prior information about the motor being monitored. The experimental results given in this paper validate the robustness and efficacy of this method. Additionally, this method relies exclusively on data analysis of motor terminal operating voltages and currents, without relying on complex motor modeling or internal performance parameters not readily available

A Fault-Tolerant T-Type Multilevel Inverter Topology with Soft-Switching Capability Based on Si and SiC Hybrid Phase Legs

The performance of a novel three-phase four-leg fault-tolerant T-Type inverter topology is presented in this paper, which significantly improves the inverter\u27s fault-tolerant capability regarding device switch faults. In this new modular inverter topology, only the redundant leg is composed of Silicon Carbide (SiC) power devices and all other phase legs are constituted by Silicon (Si) devices. The addition of the redundant leg, not only provides fault-tolerant solution to switch faults that could occur in the T-Type inverter, but also can share load current with other phase legs. Moreover, quasi zero-voltage switching (ZVS) and zero-current switching (ZCS) in the Si Insulated-Gate Bipolar Transistors (IGBTs) of the main phase legs can be achieved with the assistance of SiC Metal-Oxide Semiconductor Field-Effect Transistors (MOSFETs) in the redundant leg. Simulation and experimental results are given to verify the efficacy and merits of this high-performance fault-tolerant inverter topology

Optimal Design of IPM Motors With Different Cooling Systems and Winding Configurations

Performance improvement of permanent magnet (PM) motors through optimization techniques has been widely investigated in the literature. Oftentimes the practice of design optimization leads to derivation/interpretation of optimal scaling rules of PM motors for a particular loading condition. This paper demonstrates how these derivations vary with respect to the machine ampere loading and ferrous core saturation level. A parallel sensitivity analysis using a second-order response surface methodology followed by a large-scale design optimization based on evolutionary algorithms are pursued in order to establish the variation of the relationships between the main design parameters and the performance characteristics with respect to the ampere loading and magnetic core saturation levels prevalent in the naturally cooled, fan-cooled, and liquid-cooled machines. For this purpose, a finite-element-based platform with a full account of complex geometry, magnetic core nonlinearities, and stator and rotor losses is used. Four main performance metrics including active material cost, power losses, torque ripple, and rotor PM demagnetization are investigated for two generic industrial PM motors with distributed and concentrated windings with subsequent conclusions drawn based on the results