Derya Ahmet Kocabas

Derya Ahmet Kocabas
Istanbul Technical University · Department of Electrical Engineering

Electrical Engineer, BSc, MSc, PhD

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58
Publications
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340
Citations

Publications

Publications (58)
Article
Full-text available
Presents corrections to the paper, Optimization and Design Considerations of GaN-Based Multi-Level TP PFC Converters.
Conference Paper
Full-text available
Calculation of MMF and winding factor of electric machines is a tedious task. Additionally, there is not a common unified method to calculate the winding factors of different types of electric machines. This is due to the lack of a universal formula for the calculation of the winding factors of both Fractional Slot Concentrated Windings (FSCWs) and...
Article
Full-text available
Cite this article as: T. Dayioglu, M.O. Gulbahce, A. Lordoglu and D. Ahmet Kocabas, "Design of a high-efficiency micro-inverter with TO-220 packaged gallium nitride-high-electron-mobility transistors," Electrica, 10. ABSTRACT Since solar power panels generate direct current (DC) voltage, inverters are needed to provide DC/alternating current (AC) c...
Article
Full-text available
LLC rezonans dönüştürücü tasarımı, Lm, Lr, Cr ve kalite faktörünün gerilim kazancının karmaşık bir fonksiyonu olması ve uygulamaya bağlı olarak gerilim kazançlarını kapsayan Sıfır Gerilimde Anahtarlama’yı (SGA) sağlayabilecek anahtarlama frekansı aralığı seçiminin zorluğundan dolayı elektrikli araç şarj uygulamaları için hayli zorlu bir tasarım pro...
Article
Full-text available
LLC converter design optimization remains a challenging task for varying loads such as in battery chargers. There are numerous L-L-C combinations to choose from a design space that can satisfy the required voltage gains of the application. An accurate magnetic model is essential to optimally size the passive components according to the application...
Article
Full-text available
Latest developments in low voltage wide-bandgap semiconductor technology have increased the popularity of single-phase multi-level (ML) totem pole (TP) power-factor correction (PFC) converters. Phase shifted flying capacitor based power stages offer several advantages, such as higher input current ripple frequency, smaller size inductor and differe...
Article
Full-text available
The passive components of LLC resonance converters are traditionally designed based on a resonance frequency and switching frequency range considering required voltage conversion rate while ensuring zero-voltage-switching of the primary side power devices. Afterwards, the sub-elements such as transformer, power stage, and heat-sink are locally desi...
Article
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Turbogenerators driven by high-speed turbines are frequently used in electrical power generation. Power quality of a synchronous generator is directly associated with its excitation field harmonics. Conventional method to eliminate the most prominent harmonics is to distribute the slots to 2/3 of the rotor perimeter with equal slot pitches and iden...
Article
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There are several benefits of fully utilization of DC link voltage in railway traction applications in terms of increasing inverter output voltage, satisfying power-torque demand and component sizing. To meet traction system requirements; mostly space vector pulse width modulation (SVPWM) is preferred since it has lower harmonic contents and larger...
Conference Paper
Full-text available
LLC converter design remains a challenging task as it is not straightforward to choose the switching frequency range that can provide ZVS covering application dependent voltage gains, considering the fact that it is a complex function of L m , L r , C r , and quality factor. This paper provides a new methodology to choose L-L-C components in favor...
Conference Paper
Full-text available
LLC resonant converters are designed with a specified resonant frequency that is usually determined based on the experience of the designers while impacting the losses and the dimension of the converter. In this paper, a systematic design framework is proposed that attempts to determine the resonance frequency by considering system loss, volume and...
Article
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Although the performance of an Induction Motor (IM) can be maximized for any speed by use of an inverter, there is still room to contribute by optimizing the rotor slot shape while decreasing the mechanical disturbing effects and acoustic noise. This paper focuses on the effect of different individual rotor slot shapes on the performance of an IM i...
Article
AC-AC converters have a wide range of use in industrial applications mostly with installed silicon switches. In last decade, GaN’s are served to market with their high efficiency and fast on-off times, hence implementation of GaN’s to any conventional power electronic circuit is a focus of interest. In this paper, effects of both GaN and MOS switch...
Article
Full-text available
Although the operating principles of eddy current brakes are well known, no generalised torque/speed equation that covers the entire speed range in terms of the various machine parameters has yet been produced. This limitation is overcome in the present paper that develops a torque/speed equation valid throughout the complete speed range. The appro...
Article
Full-text available
With its simple construction, excellent mechanical and thermal capabilities to withstand stress, solid rotor induction motors (SRIMs) have become widely used in the areas of high-speed and high-pressure application fields. In this study, a novel solid rotor structure with slits in axial directions, of which the top of the rotor iron teeth is coated...
Article
Full-text available
“Tesla's Egg of Columbus” is the name given to the experiment conducted in 1893 by Nikola Tesla that proved the existence of rotating magnetic field produced by two-phase AC winding. In this study, a generalized mathematical magnetic field model for m-phase “Tesla's Egg of Columbus” is presented in detail, and a novel 3-phase model of “Tesla's Egg...
Article
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Depending on its mechanical and thermal advantages, solid rotor induction motors (SRIMs) are widely used in demanding high-speed applications. Since eddy currents are set free in SRIMs, great part of rotor losses is caused by space harmonics created in the air-gap. Rotor losses are increased tremendously in high-speed applications with the remarkab...
Article
Full-text available
Synchronous and non-synchronous buck converters are uninsulated DC-DC converters which are widely used in any application that needs low voltage and high current. In ideal case, switches are accepted as ideal during simulations of these converters in order to simplify the analysis. Non-ideal case can be analyzed by adding the resistances of switche...
Conference Paper
In this study, the power extraction from oscillating water column device is done by using three level active rectifier and three level inverter which is controlled by using NTV-SV-PWM method. The mid-point balancing of the DC-link is achieved by using a look-up table, aiming to improve the efficiency, the response time of the system and the quality...
Article
Full-text available
OZET Günümüzde elektrik motorları günlük hayatın gereksinimlerini karşılamak amacıyla hemen hemen her alanda kullanılmaktadır. Endüstriyel uygulamalara yönelik olarak üretilen birçok elektrik motoru olduğu gibi eğitim ve araştırma amaçlı olarak üretilen elektrik motorları da bulunmaktadır. Manyetik yataklı güneş motoru da bunlardan birisidir. Bu ça...
Conference Paper
Full-text available
In recent years, improvements in the manufacturing, transport and process industries have brought about an increase in the optimum operating speed for drive systems. In this respect, the recently developed, high-speed, gearless or direct electrical drives are currently very popular, because of the reduction in the total structural volume of the dri...
Conference Paper
Full-text available
Solid rotor induction motors (SRIM) became increasingly prominent in high-speed drive applications with the development of efficient power electronics systems. These types of motors are easier to manufacture compared to conventional caged rotor induction machines (CRIM). In addition to that their high material integrity and high thermal properties...
Conference Paper
Full-text available
Axially-Slitted Solid Rotor Induction Motor (ASSRIM) has a better electric and electromagnetic performance in comparison to Smooth Solid Rotor Induction Motor (SSRIM) in high-speed drive application. A better flux penetration into rotor and increased rotor cooling capability can be performed with axial slits on rotor. The main drawbacks of the axia...
Conference Paper
This paper presents a novel design containing design constraints and analysis of a radial-flux salient pole Eddy current brake whereby performance characteristics and design principles are given. In order to obtain an optimal brake design, different design models based on different parameters are all analyzed by using finite element method (FEM). E...
Conference Paper
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Ocean wave energy is one of the high potential renewable energy sources. Due to the recent progresses in the OWEC devices higher power extraction is possible which also brings the need of using multilevel converters to increase the voltage together with power. In this study, adaption of a sophisticated NTV-SV-PWM method to the multilevel converter...
Conference Paper
Full-text available
A voltage multiplier (DC-DC converter) is tested in simulated space environment to establish a benchmark result for further studies. The literature includes a variety of methods to design such systems; however, test results are very rare.
Conference Paper
Full-text available
The principle of electromagnetic braking involves the conversion of kinetic energy into thermal energy. When a non-magnetic or magnetic conductive material rotates into static magnetic field, eddy currents are induced in material. Paths of induced eddy currents depend on the geometrical configuration of moving conductive material and also its elect...
Conference Paper
Full-text available
Behaviour of an industrial load can be described with the total inertia of rotating parts and load torque. It is important to know both the load torque and power in order to determine the rated values of the electrical motor since the needed power is supplied by the motor during continuous operation. The mechanical behaviour of the electrical motor...
Conference Paper
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Temperature rising test is one of the most important electrical machine tests which used to determine the name plate values of an electrical machine and is a key element in confirming that the machine is designed for use within its designed operating capability. As defined in standards, an induction motor is loaded gradually and winding temperature...
Conference Paper
Full-text available
Eddy currents are induced by the nature of alternating flux related to the frequency of the change. In Eddy currents brakes, no precaution is taken in order to set the currents free to flow. In linear applications, Eddy current brakes are used to slow down a moving object by the produced braking force. In rotating applications, mostly braking torqu...
Conference Paper
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In Eddy current brakes, mechanical energy is converted into thermal energy and the system is mainly an electromechanical conversion device. A rotating conductive disk is placed in front of calculated number of pole surfaces that create a magnetic field which is unchanged according to time. Since the disk rotates, a relatively changing magnetic fiel...
Conference Paper
DC to DC converters are one of the most important components in power systems. The topology of the converter must be chosen depending on the power level to be converted. In this paper, a converter which is isolated by a high frequency transformer will be discussed. Although the converters are widely used and are easy to use, it is very hard to desi...
Conference Paper
Full-text available
This paper presents an overview to main problems that may occur in load sharing of three-phase squirrel cage induction motors in tandem operation including mathematical transformations and dynamic model. In the study, two simulations for two individual problematic situations are performed and results are presented. Data for motors having “the same...
Conference Paper
Full-text available
The eddy current brakes are electromechanical conversion systems which convert mechanical energy into thermal energy. When a conductive disk falls into a time-varying magnetic flux, eddy currents are induced in the conductive disk which go around the disk and these currents produces a magnetic field having an opposite polarity which is generated by...
Conference Paper
This paper presents a mathematical model for an induction motor having a Dahlander connected winding, which has the capability to work in two different number of poles as well as two different synchronous speed levels. Park transformation is used to obtain the mathematical model. The model is built in MATLAB Simulink ® in order to compute the dynam...
Conference Paper
This paper contains a mathematical model of a system including two identical three-phase squirrel cage induction motors and a load driven by these motors. While modeling the drive system, to represent three phases as two phases, d-q transformation was used. Mathematical model of the system was obtained and then built in MATLAB Simulink. In the driv...
Article
Earlier studies have shown that it is possible to reduce the disturbing effects of space harmonics by making changes to the winding arrangement and stator core design. This paper presents the calculation of these space harmonic effects, including the induced harmonic voltages, currents and conduction losses in the rotor by using a linear equivalent...
Article
The familiar method for reducing the space harmonic content of the magnetomotive force (MMF) produced by a distributed polyphase ac winding is by chording, although by itself this can eliminate only one of the major low-order harmonics. Other techniques are available that can further reduce the harmonic content, although these all require a more co...
Conference Paper
Only constructional changes can be used to reduce the negative effects of space harmonics in an electrical machine. In this paper it is shown that eliminating space harmonics by designing a phase winding placed in various shapes of slots and teeth is possible. The analysis is performed for two poles and the results can be extended to any number of...
Conference Paper
In the companion papers, the reduction in the space harmonic effects resulting from constructional changes and new design concepts were explained. In this paper, an induction motor with a novel winding and stator structure and a standard squirrel cage motor are compared, both magnetically and in terms of their operational and constructional data. C...
Conference Paper
This paper complements others by the same authors [1], [2], where the general concepts, design calculations and constructional differences of an induction motor with a novel winding arrangement were presented, together with a magnetic analysis. In the present paper, the equivalent circuit for the space harmonics of the mmf is described and the slip...

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