• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.104-106
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• 2007

In this paper, we propose an approach to design of optimized Cascade controller for Rotary Inverted Pendulum system using Hierarchical Fair Competition-based Genetic Algorithm(HFCGA). GAs may get trapped in a sub-optimal region of the search space thus becoming unable to find better quality solutions, especially for very large search space. The Parallel Genetic Algorithms(PGA) are developed with the aid of global search and retard premature convergence. HFCGA is a kind of multi-populations of PGA. In this paper, we design optimized Cascade controller by HFCGA for Rotary Inverted Pendulum system that is nonlinear and unstable. Cascade controller comprise two feedback loop, parameters of controller optimize using HFCGA. Then designed controller evaluate by apply to the real plant.

• Journal of Mechanical Science and Technology
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• v.19 no.12
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• pp.2303-2311
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• 2005

Super low temperature has many applications nowadays, from the chemical processing, automotives manufacturing, plastic recycling, etc. Considering of its wide application in the present and the future, study of the super-low temperature refrigeration system should be actively carried out. Super low state temperature can be achieved by using multi-stage refrigeration system. This paper present the development and testing of cascade refrigerator system for achieving super-low temperature. On this experiment, two different types of HCFCs refrigerants are utilized, R-22 and R-23 were applied for the high stage and the low-pressure stage respectively. The lowest temperature in the low-pressure evaporator that can be achieved by this cascade refrigeration system is down to $-85^{\circ}C$. This experiment is aimed to study the effect of inlet pressure of the low-pressure stage evaporator and low-pressure stage compressors inlet pressure characteristics to the overall temperature characteristics of cascade refrigeration system.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1001-1008
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• 2011

This paper describes an analysis on performance and exergy of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporation and condensation temperature in the R744 low- and R404A high- temperature cycle, respectively. The main results are summarized as follows : As the evaporation temperature of cascade heat exchanger increases, the COP of R404A high-temperature cycle increases. But the COP of R744 low-temperature cycle decreases, and the COP of total cascade cycle is almost constant. As cascade evaporation temperature increase, the exergy loss in the R404A condenser and the R744 internal heat exchanger is the largest and the lowest among all components, respectively. Therefore, the exergy loss in the condenser and compressor of R404A must be decreased to enhance the COP of R744-R404A cascade refrigeration system.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.4
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• pp.66-72
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• 2005

In this paper, a small supersonic wind tunnel is designed and built to study the flow characteristics of a supersonic impulse turbine cascade. The flow is visualized by means of a single pass Schlieren system. The supersonic cascade with 2-dimensional supersonic nozzle was tested for various blade leading edge shapes and gaps between the nozzle and cascade. Highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions are observed.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.58-63
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• 2013

This paper presents the new cascade liquefaction cycles using $CO_2-C_2H_6-N_2$ and $CO_2-N_2O-N_2$. The performance of the cascade liquefaction cycles with respect to temperature differences in the LNG heat exchangers is analyzed using HYSYS software and then compared the performance of these cycles with phillips optimized cascade liquefaction cycle. The coefficient of performance of the new liquefaction cycles considered in this study decreases with the temperature differences in the LNG heat exchangers, but the compressor work, expander work and heat capacity in the LNG heat exchanger increases, respectively. From the comparison of performance of three cycles, the cascade liquefaction cycles using $CO_2-C_2H_6-N_2$ showed the highest COP. And the cycles using $CO_2-C_2H_6-N_2$ and $CO_2-N_2O-N_2$ presented the second and third highest COP, respectively. In the view of performance, the optimized cascade liquefaction cycle using $C_3H_8-C_2H_4-C_1H_4$ yields much better COP. But, in the environment view, it is found that the cascade liquefaction cycle using $CO_2-C_2H_6-N_2$ shows favorable characteristics.

• Proceedings of the KIPE Conference
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• 2002.07a
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• pp.618-621
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• 2002

This paper proposes a static vu compensator using hybrid cascade 5-level PWM inverter, Circuit DQ transformation is used for modeling and analysis of the system, and it reveals the important characteristics and related equations of the system. Also, a multilevel PWM technique suitable to hybrid structure Is proposed for less harmonics in the input currents of the system. Finally, the validity of tile characteristics analysis is shown through PSIM simulations.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.5
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• pp.225-232
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• 2013

Heat pump systems have been widely adopted in buildings for cooling and heating, due to their higher energy efficiency. Recently, the demand for hot water supply from the heat pump system has been increasing. To increase the water supply temperature with higher system efficiency and reliability, a heat pump water heater adopting cascade cycle was investigated in this study. The cascade heat pump water heater consisted of a low-stage cycle using R410A, and a high-stage cycle using R134a. A simulation program for the cascade heat pump water heater was developed, and verified by comparison with experimental data. The performance of the cascade heat pump water heater was optimized, by varying the compressor rotating speeds of the low- and high-stage cycles. At low ambient temperatures, the performance of the cascade cycle was compared with that of the single-stage cycle. The system efficiency of the cascade cycle was higher than that of the single-stage cycle, showing a lower compression ratio and compressor discharge temperature.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.387-392
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• 2006

A small supersonic wind tunnel was designed and built to study the flow characteristics of a supersonic impulse turbine cascade. Experiments are performed to find flow characteristics of supersonic turbine with the cascade positions and to find factor of expansion loss. The supersonic cascade with a 2-dimensional supersonic nozzle was tested with the cascade positions. Firstly, the flow was visualized by Z-type Schlieren system. Finally, highly complicated flow patterns including shocks, nozzle-cascade interaction and shock boundary layer interactions, flow characteristics of the supersonic turbine were observed.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.6 no.3
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• pp.421-426
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• 2002

Hybrid cascade multilevel PWM inverter has advantages of hybrid structure which enhances the better utilization of power semiconductor switches, that is, both hi호 power-low frequency switch, GTO and low power-high frequency switch, IGBT can be used in the same circuit. In this paper, a static var compensator using hybrid cascade 5-level PWM inverter is presented for high voltage/high power applications. The proposed system is modelled by circuit DQ transformation, and thus an equivalent circuit is obtained which reveals the important characteristics of the system and lead to the related equations. Finally, circuit structure and characteristics is presented and the validity of the characteristics analysis is shown through PSIM simulation.

• Journal of Advanced Navigation Technology
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• v.19 no.6
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• pp.473-483
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• 2015

This paper reports the single-input-single-output cascade control by using 1-axis attitude control test-bench for quad-rotor UAV. The test-bench was designed as a see-saw shape using 2 motors and propellers, and to enable changing the center of gravity with the center of gyration using ballast. The experiment was carried out by constructing a PID-PID controller having a cascade structure with the test-bench. The SIMC based PID gain tuning process, which makes PID gain tuning easy, was grafted to cascade control. To graft SIMC method, the system parameter estimation result was conducted with second order time delay model by using Matlab-Simulink. Gain tuning was conducted by simulating with estimated system parameter. In this paper, the conventional application of SIMC was conducted and improved application was proposed for improving stability at tuning process.