Azeem Khan

PM wind generator topologies

The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 to 200 kW. The basis for the comparison is discussed and implemented in detail in the design procedure. The criteria used for comparison are considered to be critical for the efficient deployment of PM wind generators. The design data are optimized and verified by finite-element analysis and commercial generator test results. For a given application, the results provide an indication of the best-suited machine.

PM wind generator comparison of different topologies

The objective of this paper is to provide a comparison among permanent magnet (PM) wind generators of different topologies. Seven configurations are chosen for the comparison, consisting of both radial-flux and axial-flux machines. The comparison is done at seven power levels ranging from 1 kW to 200 kW. The basis for the comparison is discussed and implemented in detail in the design procedure. The criteria used for comparison are considered to be critical for the efficient deployment of PM wind generators. The design data are optimized and verified by finite element analysis and commercial generator test results. For a given application, the results provide an indication of the best-suited machine.

Development of an HT PEM Fuel Cell Emulator Using a Multiphase Interleaved DC–DC Converter Topology

This paper presents a new emulator topology for a high-temperature (HT) proton-exchange membrane (PEM) fuel cell (FC). Emulators are used to predict FC behavior and facilitate development of the power-conditioning subsystems. In this paper, the high-temperature system is modeled and emulated both in the steady state and transient domains. The model is tailored to operate effectively in real time on the emulator hardware and to deliver acceptable performance during steady-state and dynamic conditions. In particular, a two-stage approach is applied to the design of the emulator hardware. The first stage is based on a multiphase interleaved converter, capable of maximizing ripple cancellation, while ensuring rapid dynamic performance through the use of reduced filter components. These benefits are only apparent by operating the converter at its critical duty ratio. This is achieved through the introduction of a power-stage converter, which tracks the steady-state behavior of the FC, allowing the multiphase converter to account for the rapid transient behavior. This operating principle improves the quality of the output dc voltage and dynamic performance beyond that achieved by conventional emulator topologies. The experimental results of the FC stack, HT PEM FC model and emulator are presented to confirm the performance of the proposed system.

Detecting faults in inverter-fed induction motors during startup transient conditions

This paper presents a fault detection methodology for inverter-fed induction motors during startup transients. The most popular detection technique for steady state analysis is based on the Fast Fourier Transform (FFT). The inverter switching operation affects the harmonic content of the current. Thus, it becomes more difficult and demanding to detect faults in inverter-fed motors using the classical approach, furthermore it cannot be applied when the inverter-fed motor is not in steady state. This detection methodology is based on detecting the transient evolution of the fault related harmonics and may be used to complement the classical approach. This detection methodology has been successfully applied to a low voltage inverter-fed healthy motor and a motor with an inter-turn fault.

Autonomous detection of interturn stator faults in induction motors

The development of non-invasive and more reliable diagnostics techniques for detecting faults in electrical motors is still an on-going process. Motor current signature analysis (MCSA) is a most commonly used technique for detecting faults due its non-invasive quality. The challenge arises when accurately detecting slip dependent fault characteristic components under different loading conditions in absence of speed information. Non-intrusive sensor-less speed estimation technique using MCSA has been developed in literature. This technique is employed in this paper to compute speed thus slip in an attempt to track the inter-turn fault component autonomously under different loading conditions and different operating frequencies. This offers the possibility of incorporating this technique to inverter-fed in future.

Emulation of high temperature PEM fuel cell electrical dynamics and operational phenomena

This paper presents a new emulator system for a high temperature proton exchange membrane fuel cell (HT PEMFC). Many models and emulators for low temperature (LT) PEM fuel cells exist, however these need to be adapted specifically for the representation of the high temperature systems. Specific consideration was given to the development of the model for integration with the emulator system in order to replicate transient phenomena. The emulator hardware is based on a two stage approach to enable the system to deliver accurate outputs in the steady state and transient domains. The design of the two stage emulator system is presented. The power stage converter produces the controllable DC link that tracks the polarization curves as predicted by the model. A multiphase interleaved topology was implemented as the control stage converter to accurately reproduce the dynamic effects of the high temperature fuel cell system. The experimental results of the fuel cell stack, HT PEM FC model and emulator are presented to confirm the performance of the proposed system.

Analysis of a three phase five-level dual tapped inductor quasi impedance source-nested neutral point clamped converter

Further growth in renewable energy integration would be dependent on reliability and cost-effectiveness. These two factors can be achieved through power converter topologies that enable transformer-less connection of renewable energy based technology to the grid. This paper presents a three phase five level dual tapped inductor quasi impedance source (qZS)-nested neutral point clamped (NNPC) topology for medium voltage, renewable energy applications. This topology is based on the high boosting factor of the dual tapped inductor quasi source network with minimal shoot-through period and the multilevel feature of the nested neutral-point clamped (NNPC) converter. The steady-state analysis of the proposed topology is presented to illustrate the performance of the converter at continuous conduction mode (CCM). The theoretical analysis has been verified.

Efficiency estimation of induction machines using nonintrusive no-load low voltage test

Efficiency of induction machines can be determined using international efficiency test standards such as the IEEE standard 112, IEC 60034-2-1 and JEC 37. The methods presented in these standards involve tests such as the no-load test, lock rotor test and a dynamometer test. Performing the no-load test is simple with fewer requirements in terms of equipment. The dynamometer test and the locked rotor test are however not usually simple and involve expensive equipment that may not be available in motor repair/rewound workshops. Efficiency estimation after motor repair or rewound is vital in order to assess the quality of work. This paper presents a simple nonintrusive method for efficiency estimation using only no-load test measurements. The method is based on equivalent circuit parameter identification from a no-load low voltage test and the application of the identified parameters in efficiency calculation. The equivalent circuit parameters are determined by solving a nonlinear least square minimization problem using Artificial Bee Colony (ABC) optimization algorithm. Two induction motors of sizes 7.5kW and 11kW are tested and the results are compared to the IEEE std 112-B1efficiency test method. Error of less than −0.83% and −0.95% on a load range of 50% to 100% are obtained for the 7.5kW and 11kW test motors respectively.

Reclosing transients in standard and premium efficiency induction machines in the presence of voltage unbalance

The impact of restarting an induction machine, while coasting, is investigated in this paper. When restarting a motor, high peaking currents and torque transients appear. As a result, possible damage to the rotor shaft could occur together with destabilising the power system which could lead to a fluctuating supply voltage levels. This paper investigates the restarting of two different efficiency class induction machines and analyses how a shift in phase between the supply and residual voltage affects the restarting transients. Previous studies have been carried out on standard efficiency induction machines (SEIM), however this paper aims to compare the impact of restarting on the standard and premium efficiency induction machines (PPEIM). A further contribution is made by studying the impact of restarting these machines in the presence of voltage unbalance.