Derya Ahmet Kocabas

In previous studies, the first method to eliminate unwanted space harmonic effects in asynchronous motors is chording. However, it is possible to make winding changes in a way that can target a single harmonic within chording and only covers a certain amount of winding change while causing a decrease in the fundamental. There are other techniques that can further reduce the harmonic content in cores having evenly distributed symmetrical slots by altering the winding distribution, slot and teeth shape both in stator and rotor sides. Furthermore, there are previous studies using unevenly distributed slots and number of turns per slot for single layer windings. This manuscript presents a new approach to further reduce winding harmonics in unevenly distributed slots and number of turns per slot for multi-layer windings those obtained by the prepared optimization algorithm that introduces the use of unequal coil-pitches at least for 2 winding layers. It was shown that the optimization method obtains new slot positions and the number of turn values for each slot for the specified ampere-turn value to obtain a magnetomotive force (MMF) distribution that contains fewer harmonics than any traditional or special winding arrangements while still maintaining a high fundamental winding factor. The new technique was applied to the design of a 3-phase, 36-slot 2 pole 4 kW squirrel cage induction motor and important features of the design are given in comparison with those of a standard machine, demonstrating the pros and cons of the method.

This paper introduces the FRATERNAL TWIN MACHINE concept for Fractional Slot Concentrated Windings (FSCW), which alters the initial number of slots, resulting in a different visible topology to maximize the winding factor of the working harmonic while preserving the same harmonic families after optimization. The concept takes its name from the fact that, although they look different, the essence of the altered and unaltered windings is the same due to the identity in their phase spread. Despite offering advantages such as high torque density and simplified end connections, FSCW have relatively high torque ripple and limited performance due to the high space harmonic content in their magnetomotive force (MMF). Considering the winding factors of different harmonics, it is possible to achieve improvements by focusing on the winding function. In this study, a novel approach regarding this was developed and utilized for both existing and novel windings. Three relative three-phase windings with nine slots and different pole numbers are introduced and modified using the proposed method. Unconventional, unique winding solutions are obtained by analytical evaluation of different harmonic families to achieve improved harmonic spectra. Both the number of turns and slot position angles are processed with the proposed method, enabling stator core designs with unequal slot widths and different numbers of turns for a concentrated winding configuration. New solution sets serving increased winding factors for the related working harmonic components with a similar total harmonic distortion (THD) were obtained. The results were implemented in the designs, which led to an increased electromagnetic torque and almost the same torque ripple. Validation of the harmonic performances of proposed topologies and different slot/pole combinations by finite element analysis (FEA) is planned for future work.

Presents corrections to the paper, Optimization and Design Considerations of GaN-Based Multi-Level TP PFC Converters.

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 designed. However, this may only lead to locally optimized designs. In this paper, a systematic design framework is proposed that attempts to determine the resonance frequency by considering non-linear battery load profile, power loss, volume and cost of all main components. To achieve smaller sized transformer, a series connected primary and parallel connected secondary windings with a multi-core configuration is also considered. The proposed algorithm aids designers to optimally size the LLC, and provides a step-by-step design methodology. An LLC stage of a light electric vehicle battery charger converting 370 V- 430 V to an output voltage range of 36 V- 54 V rated at 3700 W with a peak efficiency of 98.2% has been designed validating the proposed design procedure.

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 differential mode (DM) filter, and usage of low voltage Gallium Nitride (GaN) devices with better figure-of-merit. Even though it has been proven that ML TP PFC converters have good power density and efficiency, the determination of optimal voltage levels and switching frequency requires a system-level optimization. This paper proposes an optimization framework for ML TP PFC converters, taking the power stage, thermal, DM filter, and magnetic designs, as well as practical design considerations, into account to determine the voltage-levels and switching frequency that minimize the power losses, cost and volume of the total system. To process output power of 3700W, the optimization tool suggests using a 4-Level GaN TP PFC topology switched at 45 kHz. The outcome of the tool has been compared with other fixed inductor current ripple designs, as well as optimized designs for 3-Level and 5-Level TP PFC converters in terms of cost, volume, and power losses. In accordance with the optimization results, a prototype of a 4L TP PFC rated at 3700 W is designed, which achieves a peak efficiency of 99.6% at 1 kW and >99.1% efficiency under the full power range.

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 problemidir. Bu çalışma, hava aralıklı manyetik bileşenler için birden fazla tasarım bileşenini ve kısıtını bir arada değerlendirebilen, doğadan esinlenen matematiksel yöntem tabanlı yeni bir tasarım yöntemi sunmaktadır. Önerilen yeni yöntem Parçacık Sürüsü Algoritması ile, oluşturulan çekirdek veri tabanındaki birçok çekirdek arasından en uygun tasarımı seçmektedir. Geleneksel tasarım algoritmalarından farklı olarak önerilen algoritma, manyetik bileşenlerin kaybını, maliyetini ve hacmini içeren bir amaç fonksiyonunu en aza indirerek en uygun manyetik akı yoğunluğunu belirlemektedir. Sunulan yöntem hafif bir elektrikli araç şarj cihazındaki 3700W, 48V LLC rezonans dönüştürücü için denenmiştir. Algoritma içinde birincil ve ikincil sargılarda sırasıyla seri ve paralel çoklu bağlamaların uygulandığı çok çekirdekli yapılar dikkate alınarak bir tasarım çalışması yapılmıştır. Tasarlanan manyetik bileşenler Ansys Electronic Desktop ve Simplorer ortak benzetim ortamında doğrulanmış ve çekirdek veri tabanından en uygun çekirdek yapıları seçilmiştir. Önerilen yöntemin en uygun LLC rezonans dönüştürücü tasarımını bulmak için çoklu kombinasyonların bir arada ve hızla değerlendirilebileceği sistem düzeyinde bir optimizasyon algoritmasının bir parçası olarak kullanılabileceği görülmüştür.