| 1. |
- Farhan, Muhammad, et al.
(författare)
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Pattern of neurosurgical cases and procedures in Gilgit Baltistan : two-year experience at a newly established neurosurgical department
- 2022
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Ingår i: Hospital Practice. - : Informa UK Limited. - 2154-8331 .- 2377-1003. ; 50:5, s. 368-372
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundIn Pakistan, there are a total of 160 neurosurgeons that constitute a ratio of one neurosurgeon for a 5.5 million population. Gilgit Baltistan being a backward region does not have a single tertiary care facility. A new department of neurosurgery was established at Regional Headquarter City Hospital (RHQ) Gilgit with only one neurosurgeon. This study aimed to determine which neurosurgical diagnoses are common and which surgical interventions were performed at RHQ.MethodsThis is a retrospective cross-sectional study conducted at Regional Headquarter Hospital (RHQ) Gilgit in which data of patients operated for neurosurgical diseases between January 2020 and January 2022 was collected from patient record books.ResultsOf the total of 223 patients, 148 (66.3%) were males and 75 (33.6%) were females. A total of 92(41.2%) belonged to the pediatric age group. The top most diagnosis included Neurotrauma (46.6%), NTDs (13.9%) and CSDH (10.3%) while the most routinely performed procedures were craniotomy & hematoma evacuation (22.9%), debridement & elevation of DSF (20.6%), and burrhole evacuation (13.9%). In the pediatric age group, the top diagnosis was Neurotrauma (43.5%), NTDs (32.6%), and Hydrocephalus (19.6%) while in adults, neurotrauma (48.9%) was the leading diagnosis followed by CSDH (17.6%). In the pediatric age group, repair of NTDs (32.6%) was the most frequently performed procedure.ConclusionThis study shows different kinds of neurosurgical cases but because of a lack of diagnostic and therapeutic facilities, very limited operations were performed and many cases were referred to metropolitan cities. The hospitals in the region need further up-gradation to cater to the presenting burden.
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| 2. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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A 2x3 Reconfigurable Modes Wide Input Wide Output Range DC-DC Power Converter
- 2021
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Ingår i: IEEE Access. - 2169-3536. ; 9, s. 44292-44303
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Tidskriftsartikel (refereegranskat)abstract
- There is an increasing demand for efficient and low-profile power converters in almost all industrial applications. Some require stable performance over a wide range of input voltages, whereas others require converters with a stable performance over a wide range of output voltages. In this regard, little work has been done to combine both requirements into one solution. This work suggests a unique solution that addresses both requirements at once. A power converter with 2x3 reconfigurable modes has been presented, able to operate with DC gains of 1, 2 and 4, which can be further extended to 8. The converter shows stable performance for the extended range of both input and output voltage. The flexible reconfigurable feature of the proposal can be applied in a variety of applications. Two reconfigurable modes on the input side can be configured following the variation in the line voltage to maintain a stable performance, and three reconfigurable modes for the output voltage, which raises the output voltage from 24V to 48V and 96V. The proposal is applied in an example application of a phase shifted full bridge converter. The converter is characterized for Vin = 100-400Vdc, Pout = 1kW. CCBY
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| 3. |
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| 4. |
- Bakar, Muhammad Abu, et al.
(författare)
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A phase shifted full bridge converter with novel control over the leakage inductance
- 2016
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Ingår i: 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16 ECCE EUROPE). - : Institute of Electrical and Electronics Engineers (IEEE).
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Konferensbidrag (refereegranskat)abstract
- The electronics industry is progressing towards the high density board solutions due to the requirement of compact and intelligent electronic systems. In order to meet the industry demands, the power system is required to be of high power density. This article proposes one of the solution to improve the power density for the medium power applications. In phase shifted full bridge converter, the intrinsic leakage inductance of the main transformer is not high enough to obtain the zero voltage switching of the power switches for the entire operating conditions. An additional shim inductor is usually connected in series with the primary winding of the main transformer to increase the collective leakage inductance. This additional shim inductor degrades the power density of the converter. This paper proposes a method to embed and control the resonance inductance inside the main transformer. In addition to the increased inter-winding spacing, this paper proposes a practical approach to integrate the ferrite rods inside the main transformer for further increase in the leakage inductance. A power transformer is constructed and investigated by using the modelled equations to estimate the leakage inductance. A prototype phase shifted full bridge converter is also developed to investigate the performance of the proposed transformer. The converter is designed for the switching frequency of 400kHz, and tested up to 600watts output power at the input voltage of 200Vdc. The performance of the proposed converter is also compared with the converter of using an external inductor. The investigations show that, in addition to the improved power density, the converter with the proposed transformer is more efficient than the converter with the traditional transformer.
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| 5. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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Characterization of phase shifted full bridge converter along with GaN devices and series-connected hybrid transformers for medium power applications
- 2020
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Konferensbidrag (refereegranskat)abstract
- Compact power converters are the major concern of today’s power industry. This article proposes GaN devices based isolated dc-dc phase shifted full bridge converter along with the configuration of four series-connected hybrid transformers. The series connection of transformers reduces the applied volt-second on each transformer which reduces the proportional losses and simplify thermal management. This configuration also reduces the required turn’s ratio as well as bringing down the stress on the secondary devices and filters. The converter is characterized in a compact prototype up to the load power of 2.2 kW for Vout=48 Vdc at Vin=400 Vdc. The converter reports satisfactory performance with a maximum efficiency of 96%.
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| 6. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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Dual-mode stable performance Phase-Shifted Full-Bridge converter for wide-input and medium power applications
- 2021
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Ingår i: IEEE transactions on power electronics. - 0885-8993 .- 1941-0107. ; 36:6, s. 6375-6388
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Tidskriftsartikel (refereegranskat)abstract
- Power converters with an extended range of line voltage are the main requirement in today's industrial applications like photovoltaic and supercapacitors based energy systems. The variation in the line voltage severely degrades the performance of power converters, because of the extended freewheeling interval, more circulation current, narrow range of zero voltage switching and increased EMI. This work suggests a modified Phase-Shifted Full-Bridge converter that cuts the freewheeling interval and minimizes these problems. It extends the input voltage range by keeping the operational duty cycle of the converter high over the wide range of input voltage while maintaining the performance stable. The proposed converter consists of four low profile transformers having reconfigurable interconnection structure. There are two distinct reconfigurable modes, a series mode and a parallel mode, which can be configured with changes in the operational conditions. The operation of the proposed converter with high switching frequency improves power density. Additionally, the use of multiple transformers minimizes heat management efforts and reduces the overall volume of the converter. The proposed work is validated in hardware characterization for a wide range of input voltage 100-400Vdc and up to the load power of 1kW. The measured energy efficiency of the proposed converter remains stable over the complete range input voltage 100-400Vdc.
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| 7. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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Modeling and Characterization of Series Connected Hybrid Transformers for Low-Profile Power Converters
- 2020
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Ingår i: IEEE Access. - : IEEE. - 2169-3536. ; 8, s. 53293-53306
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Tidskriftsartikel (refereegranskat)abstract
- Compact and low profile power converters are the main business of today's power industry. A significant volume of a power converter is occupied by the power transformer. This article proposes a unique solution that would make the power converters low profile. Instead of designing a power converter by using a single bulky transformer, the solution proposed is to split the main bulky transformer into a number of low profile transformers. This not only reduces the total weight and volume of the converter but also the total transformer losses. The use of more than one transformer in series reduces the applied voltage on the transformers, which minimizes the required turns ratio and decreases the stress on the secondary rectifiers and filter elements. Moreover, the decrease in the applied voltage reduces the proportional loss per transformer and makes it possible to design a hybrid transformer by combining Litz wire and traces of a printed circuit board. The reduced copper loss and lower heat dissipation per transformer simplify thermal management. An analytical comparison is made between the utilization of a single transformer or a number of transformers. The procedure of splitting a volume of a single transformer into a number of small transformers has been comprehensively discussed. The idea is investigated both experimentally and in computer simulation for an example application of a phase shifted full bridge dc-dc converter. The converter is characterized up to a load power of 2.2 kW at Vin = 400 Vdc and Vout = 48 Vdc. To make the approach more practical, the transformers are modeled using the traditional analytical method. The design of the example application using the split transformer approach reduces the total transformer weight by 45%, compared to the traditional approachwith a single transformer. The converter also shows good performance with a maximum efficiency of 96%.
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| 8. |
- Bakar, Muhammad Abu, 1969-, et al.
(författare)
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Reconfigurable three state dc-dc power converter for the wide output range applications
- 2019
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Ingår i: IECON 2019 - 45th Annual Conference of the IEEE Industrial Electronics Society. - Lisbon : IEEE. - 9781728148786 ; , s. 4911-4916
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Konferensbidrag (refereegranskat)abstract
- Improving the dc voltage gain of power converters has been the primary focus of the current and past research in the area of power electronics. This work presents another solution to widen the range of the output voltage. It proposes three reconfigurable steps for the output voltage. The range of theoutput voltage varies up to four times the base level. These configurations together vary the output voltage from 15 to 96 volts. A soft switched dc-dc power converter is built with the traditional topology of phase shifted full bridge converter along with improved characteristics. For better management of thetransformer loss, a configuration of four transformers has been employed. The proportional gate drive approach is implemented to obtain four similar isolated blocks of the output voltage. This makes it possible to either configure these blocks all in series,parallel or in series/ parallel combination of two. The concept is verified in a low-profile prototype. The hardware is characterized up to the load power of 1kW for the input voltage of 400Vdc. The converter reports better efficiency over the complete range of output voltage.
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| 9. |
- Akram, Shazad, et al.
(författare)
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Capacitive and optical sensing for automatic detection and characterization of cleaning sponges in fiber optic microduct installations
- 2019
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Ingår i: Proceedings - 2019 8th International Workshop on Advances in Sensors and Interfaces, IWASI 2019. - : IEEE. - 9781728105574 ; , s. 274-278
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Konferensbidrag (refereegranskat)abstract
- Optical fiber duct installation requires blowing of cleaning sponges for dirt and moisture removal before blowing the fiber cables. The traditional method requires one operator that blows the sponge and one operator in the receiving end that manually evaluate the sponges until a dry sponge is received. The proposed system eliminates the need of a second operator by introducing a solution for automatic sponge detection and characterization of moisture in sponges at the receiving end. An optical sensor is used for detection and a capacitive sensor is developed to measure the sponge's wetness. Sensor data is automatically transmitted back to the operator at the feeding end via a mobile phone. The system is characterized to work with sponges ranging from saturated with wetness to what is deemed as dry.
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| 10. |
- Akram, Shazad, et al.
(författare)
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Design and Development of a Battery Powered Electrofusion Welding System for Optical Fiber Microducts
- 2020
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Ingår i: IEEE Access. - 2169-3536. ; 8, s. 173024-173043
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Tidskriftsartikel (refereegranskat)abstract
- At present, optical fiber microducts are coupled together by mechanical types of joints. Mechanical joints are thick, require a large space, and reduce the installation distance in multi-microduct installation. They may leak or explode in the blown fiber installation process. Mechanical joints are subjected to time dependent deterioration under long service times beneath the earth's surface. It may start with a small leakage, followed by damage due to water freezing inside the optical fiber microduct. Optical fiber microducts are made up of high-density polyethylene, which is considered most suitable for thermoelectric welding. For thermoelectric welding of two optical fiber microducts, the welding time should be one second, and should not cause any damage to the inner structure of the microducts that are being coupled. To fulfill these requirements, an LTspice simulation model for the welding system was developed and validated. The developed LTspice model has two parts. The first part models the power input to joule heating wire and the second part models the heat propagation inside the different layers of the optical fiber microduct and surrounding joint by using electro-thermal analogy. In order to validate the simulation results, a battery powered prototype welding system was developed and tested. The prototype welding system consists of a custom-built electrofusion joint and a controller board. A 40 volt 4 ampere-hour Li-Ion battery was used to power the complete system. The power drawn from the battery was controlled by charging and discharging of a capacitor bank, which makes sure that the battery is not overloaded. After successful welding, a pull strength test and an air pressure leakage test were performed to ensure that the welded joints met the requirements set by the mechanical joints. The results show that this new kind of joint and welding system can effectively replace mechanical joints in future optical fiber duct installations.
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