Jo Oct 12, 2023
Pak Se Yang, a researcher at the Science Engineering Institute, has proposed a new control technique to realize the maximum torque per ampere (MTPA) in direct torque control (DTC) of a permanent magnetic synchronous motor (PMSM).
Because MTPA condition is provided by the relation between d-axis and q-axis components of the stator current, rotor position has to be known for frame conversion. Therefore, he chose to employ the estimation method of rotor position for realization of MTPA.
For the sake of rotor position estimation, he formulated the recursive least square problem for online estimation of back electro-magnetic force by using a motor model based on the rotational reference frame, and then determined the rotor position. In order to minimize the torque ripple of conventional DTC system, he synthesized the 3 phase output voltages by using the space vector pulse width modulation (PWM) technique.
His paper was presented in the “10th International Conference on Advanced Technologies”.
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Jo Oct 11, 2023
From ancient times, our people enjoyed Chusok (Harvest Moon Day) playing a variety of folk games altogether.
The most interesting of them was ssirum. On the day, it was played on a large scale in every part of the country for a bull prize. Ssirum in Pyongyang was particularly well known across the country.
When ssirum was attracting men, swinging was popular among women. Swinging was widely spread in the care of our people and it was played on public holidays everywhere in the country.
Another popular pastime was singing and dancing where thirty or forty neatly-dressed women dance in a circle singing “Kanggang Suwollae”.
Thanks to our Party’s policy of protecting national heritage, the custom of all folk games on Chusok including archery, yut game, janggi (Korean chess) and tug of war is still being carried forward and developed in line with the socialist lifestyle and aesthetic tastes of the times.
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Jo Oct 9, 2023
Generally, rotary angular sensors can be classified into two types ― sensors based on changes in an electric field and a magnetic field, and optical sensors ― according to the physical principle used for measurement. Among them, optical sensors that operate on visible light or infrared light offer advantages of contactless measurement and insensitivity to electric and magnetic fields.
Yu Nam Chol, a researcher at the Science Engineering Institute, has proposed an absolute rotary angular sensor with a nonlinear transparent disc between light source and light dependent resistors (LDR).
In this sensor, the absolute rotary angle is measured by the output resistance of double LDRs which has a linear change by nonlinear transparency of the disc in a range of 0~360° according to the characteristics of LDR’s resistance via irradiance.
This sensor’s advantage is that it is immune to shock and vibration as it has a nonlinear transparent disc instead of a binary coded disc and it has a large gap between the disc and the optical sensor. It means that it is easy to make a sensor. The disc is made of fiber glass and covered up by a self-adhesive tape whose transparency changes nonlinearly in a range of 0~360°.
Another advantage of this sensor is that its resolution is determined by an AD converter in the signal processing circuit as the output signal of LDRs is analogue. Therefore, this rotary angular sensor is provided with a high resolution in a range of 0~360°.
For more information, please refer to his paper “Improving of Characteristics of Rotary Angular Sensor Using Nonlinear Transparent Disc” in “International Journal of Sensors and Sensor Networks”.
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Jo Oct 6, 2023
The Pyongyang Bell, which was founded during the feudal Joson dynasty, is a precious legacy of national culture indicative of high creative wisdom of our people of those days.
The bell is 3.1 metres tall and about 13 tonnes heavy, with a 1.6 metre-wide mouth.
The present bell is said to have been refounded of bronze for approximately four months in 1726.
The bell looks harmonious, well-balanced and stately. The ring at the head that is shaped like a blue dragon and a yellow dragon entangled together looks so sophisticated and vigorous. With the most charming shape and the most solemn peal of the bells during the feudal Joson dynasty, the Pyongyang Bell has been known as the “attraction of Pyongyang” from olden times.
It was used for telling the time and sounding an alarm to the Pyongyang citizens.
President
The Pyongyang Bell serves as a precious national cultural legacy that gives a glimpse into the high-level metal processing and formative arts of our people and as a witness conveying the history of change of our country.
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Jo Oct 5, 2023
The Shockley-Read-Hall (SRH) lifetime is a very important parameter in silicon bipolar power devices that determine switching characteristics.
As for carrier lifetime control, recombination center levels in impurities-doped silicon are dependent on the properties of impurities and silicon materials, but not on the amount of impurities.
Preceding researchers studied diffusion of impurities and radiation action for recombination center levels by means of Au, Pt, electron irradiation, proton irradiation, etc.
Yu Nam Chol, a researcher at the Science Engineering Institute, has determined new recombination center levels in n-type silicon with gold and platinum, and investigated the effectiveness of the levels for low-level and high-level injection lifetime control.
At injection levels below 3×1013cm-3, reverse recovery technique was used, while open-circuit carrier decay (OCCD) technique was employed at levels above 1015cm-3. He performed lifetime measurements in the temperature interval of 303~403K. He studied the deep levels introduced by diffusion using DLTS, and calculated the corresponding SRH lifetime, and finally compared it with the measured values. The comparison suggests that low-level lifetime is mainly controlled by defect B located at 0.54eV below the conduction band, and high-level lifetime by defect A located at 0.25 eV.
The result shows that the recombination center levels estimated from DLTS measurement are dominant levels in n-type silicon doped gold and platinum.
If further information is needed, please refer to his paper “Analysis of recombination center levels in gold and platinum doped n-type silicon” in “Journal of Power electronics and devices”.
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Jo Oct 3, 2023
A good practice of keeping gardens neat and beautiful is one of our people’s traditional customs.
Koryo people liked sinking wells and growing fruit trees and flowers in their gardens.
It was common to plant several kinds of trees like junipers, matrimony vines and willows around wells to landscape gardens.
It is said that those in the central part of Korea round Kaegyong (Kaesong at present), which was the capital of Koryo, would enclose their houses with hedges that often consisted of juniper trees, needle juniper trees or flower trees.
Some of them used to decorate their gardens with odd-shaped rocks and big stones or famous flowers.
Such landscape gardening of the Koryo age was the inheritance and improvement of Koguryo peoples’ landscape gardening practice in accordance with Koryo peoples’ aesthetic feelings and emotions.
The murals in Anak Tomb No. 1, one of the Koguryo tombs, show artificial mounds and pavilions with lotus ponds and rocks of fantastic shape, enclosed by fences or cloisters.
In addition, the eastern wall and the east part of the southern wall of the inner chamber of the Koguryo Tokhung-ri Tomb are painted with lotus ponds and scenes of colourful events, which tells us that dwelling houses used to have gardens with lotus ponds in the east.
Landscaping of front garden, inner garden and back yard that constituted gardens of houses in the Koryo age differed greatly according to class and social positions, but it gives a full description of one aspect of civilized house customs of Koryo people who were good at making their gardens elegant.
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