Browsing by Author "Omoigui, Michael"

Now showing 1 - 8 of 8
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    Analysis of a synchronous reluctance machine with an auxiliary single-phase winding
    (International journal of Electronic and Electrical Engineering, 2003-10-01) Ojo, Olorunfemi; Omoigui, Michael; Dong, Gan
    A three-phase synchronous reluctance machine having an axially laminated rotor structure and an auxiliary DC-source-fed single-phase control winding has utility as either a high-speed generator or a high-torque low-speed motor. This paper provides an understanding of its operation using electric circuit and electromagnetic field concepts in the process of which some insights are provided into the design of the windings, conditions for torque production and generation of electric power when operating in the motoring or generating modes. Some confirmatory experimental results of analytical developments are provided showing performance characteristics of an experimental machine.
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    Analysis of multi-terminal unified power flow controller for power transfer
    (IEEE, 2008-09) Omoigui, Michael; Karugaba, Sosthenes; Ojo, Olorunfemi
    The paper reports the results of analysis of a multi-terminal UPFC used for power transfer and stability improvement of power systems. The analysis employed abc to qd0 transformation technique to obtain a time-invariant equation describing the system. A simulation of a-two transmission network rated at 20 and 15 MVA at 33 kV was investigated. Results confirm that converters rated appropriately can be used to transfer power between the lines. Converter power and current optimization were carried out to determine their operational limits.
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    A control strategy for optimum efficiency operation of high performance interior permanent magnet motor drives
    (IEEE, 2003-11) Ojo, O.; Wu, Zhiqiao; Osaloni, F.; Omoigui, Michael
    This paper, using the concept of input-output linearization with decoupling, sets forth the speed control of the interior permanent magnet motor drives which simultaneously ensures the minimization of the losses-the copper and core losses. This control scheme is unique in that saturation dependent parameters such as the d and q axis inductances and the armature reaction dependent magnet flux linkage are included in the controller structure formulation and implementation. The proposed control scheme differs from known schemes which are either based on perturbation and search methods or on steady curve fitted graphs that map the command q and d axis currents based on reference torque. Unlike these methods, an optimization formulation that dynamically determines the reference currents/voltages required to achieve high performance speed control and total loss minimization is used. The control structure methodology, the nature of the variations of the machine parameters and how they influence the machine efficiency are clearly laid out.
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    Dynamic and steady-state operation of a five phase induction machine with an open stator phase
    (IEEE, 2008-09) Karugaba, Sosthenes; Olorunfemi, Ojo; Wang, Ge; Omoigui, Michael
    The analysis of an open phase fault for a five phase induction motor is presented. A circuit based model is developed which can help to predict not only the steady-state performance but also the dynamics including the pulsating torque and to evaluate the small-signal stability of the faulted machine. This is made possible by the utility of the harmonic balance technique on the model of the machine in the stationary reference frame. The resulting model is used in determining the small-signal stability of the five-phase induction motor under open-phase fault. At low speeds the machine exhibits instability on the rotor flux linkages but it is stable at higher speeds. Simulation results and steady state results are presented which also predict the speed harmonic components as well as the torque pulsations.
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    The influence of magnetic saturation and armature reaction on the performance of interior permanent magnet machines
    (IEEE, 2003) Ojo, O; Osaloni, F.; Zhiqiao, Wu; Omoigui, Michael
    These effects are reflected in the classical qdo equivalent circuit model of the machine in the following fashion: the core loss is represented with a stator flux linkage dependent core loss resistance, the armature reaction effect is accounted for by the changing magnet flux linkage and magnetic saturation effect is reflected in the changing d and q-axis inductances of the machine. The steady-state modeling and analysis of the machine, the nature of the variations of the machine parameters and how they influence the machine torque and efficiency are clearly laid out and eventually confirmed by simulation and experimental results. The balance of the paper provides finite element analysis results for an experimental 2 hp IPM to further validate the conclusions drawn from calculation and experimental results.
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    Investigation of the Damping of Electromechanical Oscillations Using Power System Stabilizers (PSS) in Nigerian 330 kV Electrical Network
    (Electrical and Electronic Engineering, 2012-08) Ariyo, Funso; Omoigui, Michael
    Abstract The study simulated the behaviour of power system stabilizer (PSS ) on automatic voltage regulator (A VR) and excitation s ystem. It also developed an algorithm to investigate the transient and dynamic stability of the power systems. This was with a view to providing informat ion of da mping rotor os cillations of s ynchronous generators. Three types of power systems were inves tigated: a single-machine-infinite-bus system with and without PSS, two generato rs conn ected to a load with various types of e xc itation controls and a multimachine powe r system typified by Nigerian 330-kV e lectrical network. Tabu-search technique was used to tune the PSS-parameters for a s ingle machine con nected to an infinite bus operating at three different loading conditions . The objective function allowed the selection of the stabilizer parameters to optimally place the closed-loop eigenvalues in the left-hand side of a vertical line in the complex s-plane. The effectiveness of this suggested technique was confirmed through eigenvalue analysis. Time-do main simulations were a lso carried out o n two generators connected to a load using MATLAB/Simu link. T wo types of PSS we re us ed for these simulat ions: generic and multiban d. The power sy stems were subjected to a balanced three-phas e fault (most severe fault). The inves tigation was further e xtended to Nigerian 330-kV electrical network
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    Precision Measurement of Rotor Angle of a Microsynchronous Alternator
    (IEEE Xplore, 1991) Omoigui, Michael
    A precision instrument used for the measurement of rotor angles of a laboratory microalternator is described. The measurement is performed by integrating digital signals derived from a phase-locked loop (PLL) reference (i.e. laboratory infinite busbar or the terminals of another machine in a multimachine system) and an optical encoder mounted on the shaft of the machine. The integration is executed by synchronous up-down binary counters. A 12-b digital-analog converter enables both transient and dynamic movement of the rotor to be displayed on an oscilloscope or other suitable recorder. When used on a four-pole 3-MVA microalternator, the resolution of the encoder is 0.2 electrical degrees. Relatively slow and fractional movements of the rotor angle arising from dynamic power imbalances as well as fast and large rotor excursions arising from severe transient disturbances, which sometimes result in pole slipping, are reliably and precisely recorded. It is possible to obtain constant information on the stability or lack thereof for the machine under every operating condition. With appropriate transducers, the principle may easily be applied to continuously monitor changes in the rotor angle of large alternators in interconnected power systems
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    Reliability investigation of the Nigerian Electric Power Authority transmission network in a deregulated environment
    (International journal of Electronic and Electrical Engineering, 2003-11-12) Komolafe, Olusola; Momoh, A.; Omoigui, Michael
    The paper presents the findings of reliability investigation carried out on the 330 kV high voltage transmission network of the Nigerian Electric Power Authority (NEPA). The system made up of three hydro generating stations in the north and four thermal stations in the south is loosely tied together by long transmission lines that are basically radial. The system was represented by a 24-bus, 39-transmission line and seven generating stations that made up the grid. The base load was taken as 1776 MW representing approximately 30% of installed capacity of about 6000 MW. Taking into consideration all available VAr injections and voltage control equipment the load was increased by 10% consecutively and the system generating voltages and. available VAr were controlled to make sure that all bus voltages were within tolerance of +5% and -10% of rated values The results show that the system was able to cope with the load demand without problems up to 3500 MW. Although some stations experienced low voltages, these were corrected when the generator voltages were adjusted via reactive power injection. But by the time the load was increased to 3800 MW, all the available VAr injection had been utilized and most stations were at their upper voltage limits. The system response for load above 4160 MW was completely unacceptable. Suggestions are given that will enable the network to cope should the installed generating capacity be increased in order to meet the increasing load demand.