Jo Apr 23, 2022
A research team led by Hong Yong Jun, a researcher at the Institute of Electric Engineering, has developed and introduced a single-phase grid connected VSI(Voltage Sourced Inverter). It can not only transfer active power to the national power grid by converting the DC power generated by PV(Photovoltaic) modules into AC active power and synchronizing it with the voltage and frequency of the grid, but also control reactive power independently.
They realized the control of reactive power in the grid-connected VSI by applying the IRP (instantaneous reactive power) theory, the base of the FACTS(flexible AC transmission system). For this control, they had to ensure the exact tracking of the frequency of the grid voltage by introducing the fictitious phase by the SOGI(second-order generalized integrator) and FLL(frequency locked loop).
Then, they took control of grid injected current by a PR(proportional resonant) regulator with proper parameters, and added anti-islanding detection by active frequency drift.
The THD(total harmonic distortion) of grid-injected current is 3.6% and the time required for anti-islanding detection is less than 0.1s.
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Jo Apr 21, 2022
A research group led by Jang Ki Ho, a section head at the Faculty of Heat Engineering, has developed a 10kV electric boiler designed to use the electricity from a power system directly, and they are now working hard to make further achievements in their research.
Boilers are largely divided into two types, i.e. a low voltage electric boiler (LVEB) and a high voltage electric boiler (HVEB).
In a LVEB, heat is generated by Joule heating effect in an electrical resistor as an electrical heating element below 380V and is transferred to fluids. Usually, the electrical heating element used in a LVEB produces several kilowatts of thermal power.
However, hundreds or thousands of kilowatts are needed to heat various kinds of liquid for swimming pools, ponds used for aquaculture, sensitive products used in chemical and agro alimentary processes and buildings. The heat power output of boilers used for controlling the load in a wind power station or a nuclear power station is the same. Even if several heating elements below 380V can be used as one, it remains uneconomic, because it needs a transformer that maintains the supply system voltage at 380V, and it also causes a considerable energy loss.
On the contrary, an HVEB(10kV) offers several advantages: it produces thousands of kilowatts of high electro-thermal power, it needs comparatively low investment, it is easy to make, and it can be operated without a transformer from the direct supply from an electric power system.
The problem is the safety of a high-voltage electric boiler. It is difficult to predict the amount of thermal power in the step of its design because it depends on the temperature, velocity and specific resistance of the fluid that are also changed in relation to each other. To solve these problems, they proposed a 10kV electric boiler equipped with a ceramic insulation tube inside and determined its geometrical sizes and operation parameters through a numerical analysis of coupled thermal, hydro mechanical and electrical fields in the water heating process. On the basis of this, they completed it through tests and practices.
The investment of an 10㎸ electric boiler is under ½, and the installation area under ¼, compared to a LVEB of the same capacity. And there is no consumed power due to the operation of a transformer.
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Jo Apr 14, 2022
A research group led by Ri Ju Hyok, a section head at the Faculty of Heat Engineering, has invented a vaporizer that vaporizes cryogenic liquid oxygen to supply to consumers.
It is an atmospheric source cryogenic vaporizer that turns cryogenic liquid oxygen into gas by cryogenic distillation method.
In practice, the demand for oxygen is unpredictable. To meet this flexible demand, liquid oxygen is usually stored in the cryogenic tank and is vaporized whenever needed. The vaporization of liquid oxygen is conducted by means of a cryogenic vaporizer.
The vaporizer is a vertical heat exchanger, its cross section is of an 8-pointed star type and it vaporizes cryogenic liquid by atmospheric heat.
To determine the optimal parameters of a vaporizer, they studied 4 items: growth process of frost on the surface of the heat exchanger when liquid oxygen is vaporized, the property of frost, the pulse phenomenon in the heat transfer pipe and the destruction of frost on the surface, and the characteristics of air flow in the surrounding of a heat exchanger.
The cryogenic oxygen liquid vaporizer is extruded of aluminum alloy of good conductivity.
As its heat source is based on only the air in the atmosphere, environmental problems such as pollutant emission and noises are not arisen.
It is also applicable to the vaporization of other cryogenic liquids like nitrogen, argon, etc. as well as oxygen.
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Jo Apr 13, 2022
Choe Yong Son, a researcher at the Faculty of Physics, realized the computerization of an experiment device to measure the characteristics of glow discharge plasma.
Compared to the previous devices with analog meters, the computerized device is equipped with an embedded system and a touch-panel interface, which makes it possible to supervise and analyze experimental processes, and to display the results. It also ensures high accuracy in measurement and short time of measurement along with intuitiveness and effectiveness of experiments.
The device consists of a power supply, a probe voltage stabilizer, a triangular signal generator, a discharge current sustainer, a current-to-voltage converter, a voltage signal detector, a matching unit, and a computer. The main characteristics to measure are electron density and electron temperature. A linearly increasing voltage is applied to the electrostatic probe, which is placed in the discharge region, and the current to the probe is captured at a regular interval, in order to gain voltage-current measurement points of the probe.
These measured data are treated by 3-order spline interpolation and then by weighed polynomial method to obtain a voltage-current curve of the probe. Necessary features are to be derived from the characteristic curve, and these features are utilized to determine electron temperature and electron density. All these operations are automatically performed through its embedded system and touch-panel interface.
This device can increase the measurement accuracy of probe voltage and current by more than 20 times and, as a result, as many measurement points as possible are available. Therefore, we can eliminate scale errors, which were indispensable in the past, and decrease random errors down to below 0.5% (in analog meter: 4.2%). In addition, offline experiments may become possible by the combination of serial communication and network communication.
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Jo Apr 12, 2022
From the viewpoint of interpretation and methodology, quantum mechanics as one of the greatest achievements in the field of physics in the 20th century involves two formulations, i.e., the traditional standard formalism and non-standard formalism such as quantum mechanics in phase space, quantum trajectory formulation and path integral method.
Hibert-space formalism as the standard formalism yielded an excellent mathematical formulation for explaining the microscopic world such as atoms and subatomic objects. After that, the trajectory-based quantum mechanics such as Bohmian mechanics was proposed in order to improve mathematical formulation of quantum mechanics. Quantum mechanics in phase space also attracted a great deal of interest from the aspect of mathematical formulation, but the tasks of establishing an alternative independent formalism of quantum mechanics still remained not accomplished.
After as long as 15 years of painstaking effort, Jong Chol has proposed that it would be possible to establish an alternative autonomous formalism of quantum mechanics in phase space by means of a statistical method.
The proposed theory as a new formalism of quantum mechanics in terms of ensemble in phase space leads to obtaining within the framework of its theory the fundamental quantum-mechanical equation without recourse to other formulations of quantum mechanics, and gives the idea for operators pertaining to dynamical quantities.
The theory also demonstrates that the system of operators given by quantum mechanics in phase space is a complete system of quantum operators and it is possible to explain, using the fundamental equation, the structure of quantum mechanics in phase space and the approximation of the fundamental equation of the present formalism to the Schrödinger equation. Therefore, it concludes that quantum mechanics in phase space is the general formulation comprising the formulation in configuration space as a special case.
This formalism provides reasonable results of quantization by dealing with some simple cases such as the quantization of harmonic oscillation, the two-slit interference and the uncertainty relation, which confirms the validity and generality of this formalism.
In particular, this formalism shows that it is possible to easily obtain the relativistic wave equation by making use of the relativistic phase velocity without treating the problem of linearizing the Hamiltonian operator as in the case of the deduction of the Dirac equation.
The ultimate outcome this formalism produces is that it has been confirmed that primary and general matters of quantum mechanics can be studied reasonably within the framework of statistical mechanics.
This information is from the essay “Ensemble in phase space: Statistical formalism of quantum mechanics” presented by Jong Chol, a researcher at the Faculty of Materials Science and Technology, to the SCI Journal “Pramana Journal of Physics” 92:83(2019).
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Jo Mar 25, 2022
When mining penetrates increasingly deeper in open pit mines, the mines take some kind of funnel shape. The deeper the funnel is, the greater the expense for transport gets. In order to accelerate and cheapen transport while maintaining the flexibility offered by truck transport, several types of Trucklift systems have been employed.
These systems are generally similar in structure and operating principle and consist of a slope hoisting plant, platforms, tracks and loading stations. Friction winders or drum winders are used as a hoisting machine and the system can be equipped with either single or double tracks.
When a truck is driven onto and off the platform vertically to the transport direction at the loading station, the platform moves on the rails by the weight of the truck although the winder comes to a halt. Then the truck changing might fail because there may be a difference in the height between the platform and the loading station. So platform arrestors that work when the platform reaches are provided at loading stations, ensuring that the platform is held in the position when the load changes by truck changing.
In addition, when the truck is driven in parallel with the transport direction, the platform also moves on the rails and there appears the varying clearance between the platform and the edge of the loading station. Truck changing may be hindered by this clearance. However, the moving direction of the truck and the platform are the same, so we can avoid the effect of the movement of platforms during truck changing without the help of arrestors by a reasonable design of the structure of loading stations and platforms. For this reason, it is necessary to make a deep study of the moving process of the platform during truck changing.
The moving process of the platform can be simulated with ADAMS and MATLAB/Simulink.
Especially, the simulation of the truck changing process in the Trucklift slope hoisting system where trucks stand parallel to the transport direction on the platform and the analysis of the movement of the platform and the force of rope can provide us with important data for the design of a platform, a loading station and an arrestor.
According to the simulation results, in the Trucklift slope hoisting system with a drum winder, normal truck changing can be realized by making a reasonable design of the platform and the loading station after determining the moving displacement of the platform,
In the Trucklift slope hoisting system with a friction winder, the need to arrange arresters at loading stations must be examined to avoid slipping of ropes in the drum groove due to the movement of the platform during truck changing. If arresters have to be provided at loading stations, the force acting on the platform obtained from the simulation can be used as reference data for the design of arresters.
You can find more information about this in the paper “Simulation for Motion of Platform During Truck Changing in Trucklift Slope Hoisting System in Open Pit Mines Using ADAMS and Matlab/Simulink” by Han Tok Hyong, an institute head at the Faculty of Mining Engineering, presented to the SCI Journal “Arch. Min. Sci.”.
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