Field Weakening Methods for Axially Displaceable Brushless DC Machines

Brushless DC (BLDC) machines are known to have a high torque/power density but it is still a challenge to design a BLDC with a wide extended speed range while keeping its torque/power density high. A mechanical field weakening method, in which the active axial length of a BLDC machine is reduced on run by axially displacing its rotor with respect to its stator, was proposed to achieve a wider extended speed range with a limited DC-link voltage. However, its effectiveness and optimal application are not considered in detail. The aim of this study is to analyze the extended speed range of an axially displaceable rotor brushless DC (ADR-BLDC) machine. First of all, factors that limit the speed range of an ADR-BLDC machine are discussed. Afterwards, rotational speed limits of the analyzed ADR-BLDC machine are compared for different field weakening approaches. Based on these results a combined field weakening approach that combines both the electrical and mechanical field weakening methods is proposed

Çocukluk Çağı Pankreatı̇t Hastalarının Tanı, Tedavı̇ ve Klı̇nı̇k İzlem Sonuçları

The number of patients diagnosed with pancreatitis has been increasing in recent years due to the understanding of the physiopathogenesis of pancreatic diseases, developments in diagnostic methods and the increased awareness of physicians. Acute pancreatitis (AP) cases usually resolve without complications but in some AP cases, recurrent pancreatitis episodes (acute recurrent pancreatitis-ARP) are seen and may cause chronic pancreatitis (CP). In this retrospective study, we aimed to identify the demographic, etiologic, clinical and laboratory features, clinical follow-up results and prognosis of patients with AP, ARP and KP who were admitted to Hacettepe University İhsan Doğramacı Children's Hospital, Pediatric Gastroenterology-Hepatology and Nutrition, Pediatric Surgery and Pediatric Emergency Clinics between 01.01.2016 and 01.09.2018 or who were diagnosed with pancreatitis while being followed at the General Pediatric Services. 52 patients (33 female (63,5%) and 19 male (36,5%)) were included in the study. 44.3% of the patients included in the study were AP, 38.4% were ARP and 17.3% were CP. The age at diagnosis varied between 1-17 years (mean 9.1 ± 4.9 years). Etiological causes were grouped according to the type of pancreatitis. In 30% of the patients with AP, drug use was found to cause pancreatitis attack. The most common cause of ARP was pancreaticobiliary system anomaly (pancreatic divisum, pancreaticobiliary junction anomaly) (45%) and the most common cause of CP was genetic mutations (44%). The most common complaint was abdominal pain (94%) and nausea/vomiting (67%). When evaluated according to age groups, the rate of nausea/vomiting, diarrhea and fever in the 1-5 year old age group was higher compared to the 6-17 age group, while there was no significant difference (p>0.05). According to the laboratory findings, mean amylase level 656±663,2 U/L (136-2953 U/L), mean pancreatic amylase level 524,2±559,8 U/L (83-2764 U/L), mean lipase level 1182±1447,3 U/L (83-4932 U/L) were found to be. The mean value of C-reactive protein (CRP) was 3,24 ± 6,64 mg/dL and high in 33(63,5%) patients. It was found statistically significant that patients with CRP had longer hospital stay than those with normal CRP values (p = 0.01). The CRP values of the patients who developed complications were higher than those without complications and no significant difference was found (p> 0.05). Genetic tests were evaluated, genetic mutation analysis was performed in 10 (20%) patients. CFTR mutation was detected in four patients with CP and SPINK-1 mutation was detected in one patient with ARP. When radiological tests were evaluated, it was observed that 94% of the patients were examined with ultrasonography (US), 36.5% with computed tomography (CT), 82.6% with magnetic rezonance cholangiopancreatography (MRCP) and 30.7% with endoscopic retrograde cholangiopancreatography (ERCP). The frequency of MRCP and ERCP was found to be significantly higher in patients with ARP than in AP patients (p<0.05). Paracetamol was the most commonly used analgesic during the episode of pancreatitis and the frequency of opioid use was 9.6% in all patients. When the frequency of antibiotic administration was evaluated, it was seen that 61,5% of all patients received single or multiple and 42% of them received multiple antibiotic treatment. The most commonly used antibiotics were sulperazone (62%), amikacin (51.4%) and ornidazole (28.8%). When the amount of maintenance fluid given during the episode of pancreatitis was analyzed, it was seen that 54% of the patients were given 2000 cc/m2/day and more. Patients who received 1500 cc/m2/day and 2000 cc/m2/day and more fluid were not found to be significantly different in terms of duration of hospitalization, normalization times of amylase and lipase levels and the risk of developing complications (p<0.05). The mean follow-up period for stopped enteral nutrition (EN) was seven days (1-30 days) for all patients. The duration of hospitalization of the patients who started EN after the 72th hours was found to be significantly longer than those started before 72th hours (p=0.01). Pancreatitis may be diagnosed in all age groups and complaints may vary according to age group. Laboratory and radiologic findings important for the differential diagnosis and give some clues about prognosis of patients. It is important to diagnose and prevent recurrent attacks in patients with ARP and KP due to disease burden. Developing a standardized approach to the treatment of patients will improve the prognosis.Pankreas hastalıklarının fizyopatogenezinin anlaşılması, tanısal yöntemler konusunda kaydedilen gelişmeler ve hekimlerin artmış farkındalığına bağlı son yıllarda pankreatit tanısı alan hasta sayısı giderek artmaktadır. Akut pankreatit (AP) vakaları genellikle komplikasyon gelişmeden düzelirken, bazı AP vakalarında tekrarlayan pankreatit atakları (akut rekürren pankreatit-ARP) görülüp, kronik pankreatit (KP) gelişimine neden olabilmektedir. Bu çalışmada 01.01.2016 ile 01.09.2018 tarihleri arasında Hacettepe Üniversitesi İhsan Doğramacı Çocuk Hastanesi Çocuk Gastroenteroloji-Hepatoloji ve Beslenme, Çocuk Cerrahisi, Çocuk Acil Polikliniği’ne başvuran ya da Genel Pediatri Servisi’nde takip edilen AP, ARP, KP tanılı hastaların retrospektif olarak demografik, etiyolojik, klinik ve laboratuvar özelliklerinin, klinik izlem sonuçlarının ve prognozunun belirlenmesi amaçlanmıştır. Çalışmaya pankreatit tanısı alan 33’ü (%63,5) kız, 19’u (%36,5) erkek 52 hasta dahil edilmiştir. Hastaların %44,3’ü AP, %38,4’ü ARP, %17,3’ü KP’dir. Hastaların tanı yaşları 1-17 yıl (ort. 9,1±4,9 yıl) arasında değişmektedir. Pankreatit türüne göre etiyolojik nedenler gruplandırılmıştır. AP’li hastalarda %30 sıklıkta ilaç kullanımı pankreatit atağından sorumlu bulunmuştur. ARP’li hastalarda en sık neden pankreatikobiliyer sistem anomalisi (pankreatik divisum, pankreatikobiliyer birleşim anomalisi) (%45), KP’nin en sık nedeni genetik mutasyonlar (%44) olarak saptanmıştır. Hastaların en sık başvuru şikayeleri karın ağrısı (%94) ve bulantı/kusma (%67) olarak saptanmıştır. Yaş gruplarına göre değerlendirildiğinde 1-5 yaş grubunda bulantı/kusma, ishal ve ateş şikayeti 6-17 yaş grubu ile karşılaştırıldığında artmış sıklıkta görülürken, istatistiksel olarak anlamlı farklılık görülmemiştir (p>0,05). Tanı anındaki laboratuvar bulgularına bakıldığında ortalama serum amilaz değeri 656±663,2 U/L (136-2953 U/L), serum pankreatik amilaz değeri 524,2±559,8 U/L (83-2764 U/L), serum lipaz değeri 1182±1447,3 U/L (83-4932 U/L) olarak saptanmıştır. Ortalama C-reaktif protein (CRP) değeri 3,24 ± 6,64 mg/dL olup, 33 (% 63,5) hastada yüksek saptanmıştır. CRP yüksekliği olan hastaların hastanede kalış sürelerinin CRP değeri normal olan hastalara göre daha uzun olduğu istatistiksel olarak anlamlı bulunmuştur (p=0,01). Komplikasyon gelişen hastaların CRP değerleri komplikasyon gelişmeyenlere göre daha yüksek olup, istatistiksel anlamlı saptanmamıştır (p>0,05). Genetik tetkikler değerlendirildiğinde 10 (%20) hastaya genetik mutasyon analizi yapılıp KP’li dört hastada KFTR mutasyonu, ARP’li bir hastada SPINK-1 mutasyonu saptandığı görülmüştür. Radyolojik tetkikler değerlendirildiğinde hastaların %94’ünün ultrasonografi (US), %36,5’inin bilgisayarlı tomografi (BT), %82,6’sının manyetik rezonans kolanjiyopankreatografi (MRKP), %30,7’sinin endoskopik retrograd kolanjiyopankreatografi (ERKP) ile tetkik edildiği görülmüştür. MRKP ve ERKP yapılma sıklığı ARP’li hastalarda AP’li hastalara göre istatistiksel anlamlı olarak daha yüksek bulunmuştur (p<0,05). Pankreatit atağı sırasında en sık kullanılan ağrı kesici parasetamol olup, opioid kullanım sıklığı tüm hastalarda %9,6 olarak saptanmıştır. Antibiyotik verilme sıklığına bakıldığında tüm hastaların %61,5’inin tekli ya da çoklu, %42’sinin çoklu antibiyotik tedavi aldığı görülmüştür. En sık kullanılan antibiyotikler sulperazon (%62), amikasin (%51,4), ornidazol (%28,8) olarak saptanmıştır. Pankreatit atağı sırasında verilen idame mayi miktarına bakıldığında hastaların %54’üne 2000 cc/m2/gün ve üzeri hacimde mayi verildiği görülmüştür. 1500 cc/m2/gün mayi alanlar ve 2000 cc/m2/gün ve üzeri mayi alan hastalar hastanede kalış, amilaz ve lipaz değerinin normal seviyeye gelme süreleri ile komplikasyon gelişme riski açısından karşılaştırıldığında anlamlı fark bulunmamıştır (p>0,05). Enteral nutrisyon (EN) verilmeyen izlem süresi tüm hastalar için ortalama yedi gün (1-30 gün) olarak bulunmuştur. EN’ye 72. saatten sonra başlanan hastaların hastanede kalış süresi EN 72. saatten önce başlanan hastalara göre anlamlı olarak daha uzun bulunmuştur (p=0,01). Pankreatit hastaları her yaş grubunda tanı almakta ve başvuru şikayetleri yaş grubuna göre değişiklik gösterebilmektedir. Başvuru anında bakılan laboratuvar bulguları ve radyolojik görüntülemeler pankreatit ayırıcı tanısında ve hastalığın prognozu konusunda ipucu vermektedir. ARP ve KP hastalarının hastalık yükü nedeniyle akut dönemde tanı konulması ve rekürren atakların önlenmesi önem taşımaktadır. Hastaların tedavisi konusunda standart yaklaşım oluşturulması prognozu iyileştirici etkide bulunacaktır

Comparison of Two-Level and Three-Level NPC Inverter Topologies for a PMSM Drive for Electric Vehicle Applications

Multidimensional comparison of two-level and three-level DC/AC converters for a 120 kW permanent magnet synchronous machine (PMSM) drive is carried out in this study. Comparison of two topologies with Sinusoidal Pulse Width Modulation (SPWM) and Space Vector Pulse Width Modulation (SVPWM) by means of output current THD, conduction and switching losses, thermal stresses on semiconductors and switching frequency limitation are investigated at various operating points. Electro-thermal simulation of both topologies are achieved using PLECS tool with Silicon IGBT and diode pairs from SEMIKRON. Results of these analysis show the limitations of two-level inverter topology in terms of the switching frequency and point out the advantage of three-level inverter in high speed PMSM drives

Influence of Phase Magnetic Couplings on Phase Current Characteristics of Multiphase BLDC Machines with Overlapping Phase Windings

Multiphase brushless dc (BLDC) machines are implemented in electric and hybrid electric vehicle applications due to their high torque/power density, good fault tolerance capability, and low torque ripple. Moreover, the per-phase converter rating can be reduced by increasing the phase number. However, the number of magnetic couplings between phases increases with the phase number, and these magnetic couplings can have an important influence on the machine performance. Therefore, they need to be considered in simulation models and their effect should be considered in control algorithms. Accordingly, the objective of this paper is to analyze the effect of magnetic phase couplings on the performance of multiphase BLDC machines with an overlapping phase winding configuration. First, a detailed electric machine model, in which the machine parameters that are determined by 2-D finite-element method analysis are implemented, is developed. Using this model, the influence of mutual inductances on phase current characteristics with pulse amplitude modulation (PAM) and pulsewidth modulation (PWM) controls is investigated. In addition, a novel PAM-based control strategy, in which the effect of phase mutual inductances is considered, is proposed and analyzed. After demonstrating the influence of mutual inductances on phase current characteristics, the dependence of mutual inductances on the winding configuration is studied. Finally, experimental results with the PAM control and the new PAM-based control are used to validate the simulation results

Optimal design of synchronous reluctance machines

Electric machines are optimized to the extent of their magnetic configuration and manufacturability. Thanks to recent advances in development of composite material (SMC), 3-D printing, and programmable magnets, manufacturing capabilities have changed dramatically. Introducing of cloud computing and impressive computational resources has opened new opportunities in virtual prototyping in a multi-physics environment. These enabling technologies present a potential for a transformative approach in optimal design, evaluation, and manufacturing of the next generation of electric machines and adjustable speed drives. This paper proposes a new design approach applied to optimal design of synchronous reluctance machines. The proposed technique removes all the conventional constraints posed by traditional designs of classic magnetic configurations and only keeps a minimum airgap length and shaft diameter as the boundary conditions. The fabric of the rotor is based on a mesh whose elements can be air or SMC. A genetic algorithm is used for optimal placement of rotor configuration

How Often is Chest Radiography Ordered for Patients with Pediatric Asthma?

Objective: Although many children with asthma can be diagnosed clinically, chest radiographs are routinely requested in asthma attacks. The aim of this study is to determine how often chest radiographs are requested and the factors affecting these requests in pediatric patients with asthma. Methods: This cross-sectional study was performed by studying the electronic radiographic records of pediatric patients with asthma who were referred to our Pediatric Allergy and Immunology Department over a six-month period. A questionnaire was designed to obtain further information from the parents of the patients. Results: The records of 100 children with bronchial asthma, aged 21 to 192 months, were evaluated. The average number of chest radiographs was 3.9±3.8 (between 1-30). Fifty-one percent of the children underwent three or more chest radiographs. There was a positive correlation between the number of chest X-rays before asthma diagnosis and the frequency of antibiotic usage (r=0.222, p=0.026). An inverse correlation was found between the number of chest radiographs and the patients’ ages and the age at which asthma was diagnosed (r=−0.335, p=0.001; r=−0.211, p=0.035, respectively). In contrast, there was a positive correlation between the number of chest X-rays and the number of hospital admissions (r=0.205, p=0.040). A positive correlation between the frequency of antibiotic usage and the annual number of hospital admissions was determined (r=0.428, p=0.000). Furthermore, a positive correlation between the frequency of antibiotic usage and the frequency of asthma attacks was observed (r=0.292, p=0.003). Conclusion: The results of our study show that the use of chest radiographs is high in cases of childhood asthma, especially in younger children

Thermal analysis of switched reluctance motor with direct in-winding cooling system

Demand for compact high torque/power density electric machines necessitates the choice of an effective cooling system. The focus of this paper is to compare the steady-state thermal analysis of a naturally air-cooled conventional 8/6 SRM to the same motor with direct in-winding cooling system. The goal is to determine how much torque increase can be achieved by using direct cooling in the windings slots. The results show that the direct cooling of the winding guarantees lower temperature in the windings by 50% at a given operating point, although the winding slot volume is reduced by 25%. This means current density limit increases with direct winding cooling, hence improving the torque/power density of the machine

Severity Estimation of Interturn Short Circuit Fault for PMSM

This paper presents a novel method to estimate the number of shorted turns in a permanent magnet synchronous machine (PMSM) following the detection of interturn short-circuit (ITSC) fault and its location. In this proposed method, PMSM is excited through a low sinusoidal voltage at standstill condition to obtain the winding resistance and synchronous inductance by current response. It is shown that the ITSC fault introduces variation in the current response, which can be used to calculate the number of shorted turns under zero fault resistance assumption. Using this practical procedure, the fault severity can be estimated directly in a straight-forward manner. In other words, the severity estimation for a given machine can be done without complex machine modeling or experiments on ITSC prototype with multiple taps. The findings in this paper are essential for a comprehensive solution including fault mitigation algorithms and postfault operations. In order to verify the findings, a three-phase equivalent circuit model supported by finite element analysis results is used to take saturation and space harmonics into account. In addition, experimental results are presented to demonstrate the validity and practicability of the severity estimation

Opportunities and Challenges of Switched Reluctance Motor Drives for Electric Propulsion: A Comparative Study

Selection of the proper electric traction drive is an important step in design and performance optimization of electrified powertrains. Due to the use of high energy magnets, permanent magnet synchronous machines (PMSM) have been the primary choice in the electric traction motor market. However, manufacturers are very interested to find a permanent magnet-free alternative as a fallback option due to unstable cost of rare-earth metals and fault tolerance issues related to the constant permanent magnet excitation. In this paper, a new comprehensive review of electric machines (EMs) that includes various new switched reluctance machine topologies in addition to conventional EMs such as PMSM, induction machine, synchronous reluctance machine (SynRel), and PM-assisted SynRel is presented. This paper is based on performances such as power density, efficiency, torque ripple, vibration and noise, and fault tolerance. These systematic examinations prove that recently proposed magnetic configurations such as double-stator switched reluctance machine can be a reasonable substitute for permanent magnet machines in electric traction applications