• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.1
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• pp.53-60
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• 2001

In many applications of power electronics, high frequency resonant inverters are used, and the PAM(Pulse Amplitude Modulation), PFM(Pulse Frequency Modulation) or PWM(Pulse Width Modulation) techniques are used to control the output power of resonant inverters. And the resonant inverters have to control the output frequency for the reliable operation under the variable load conditions. In this paper, a new switching scheme is proposed as a PWM control of resonant inverters. With the proposed method, it can be obtained that optimum resonant frequency and unity output displacement factor under the variable resonant frequency adaptively. The detail algorithm or the proposed PWM switching scheme and its output characteristics are discussed. And the veridity of the proposed method is confirmed with the experimental results.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.2B no.3
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• pp.81-89
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• 2002

The sensorless AC motor drive is a popular topic of study due to the cost and reliability of speed and position sensors. Most sensorless algorithms are based on the mathematical modeling of motors including electrical variables such as phase current and voltage. Therefore, the accuracy of such variables largely affects the performance of the sensorless AC motor drive. However, the output voltage of the SVPWM-VSI, which is widely used in sensorless AC motor drives, has considerable errors. In particular, the SVPWM-VSI is error-prone in the low speed range because the constant DC link voltage causes poor resolution in a low output voltage command and the output voltage is distorted due to dead time and voltage drop. This paper investigates a novel high-performance strategy for overcoming these problems in a sensorless ac motor drive. In this paper, a variation of the DC link voltage and a direct compensation for dead time and voltage drop are proposed. The variable DC link voltage leads to an improved resolution of the inverter output voltage, especially in the motor's low speed range. The direct compensation for dead time and voltage drop directly calculates the duration of the switching voltage vector without the modification of the reference voltage and needs no additional circuits. In addition, the proposed strategy reduces a current ripple, which deteriorates the accuracy of a monitored current and causes torque ripple and additional loss. Simulation and experimentation have been performed to verify the proposed strategy.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.48-52
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• 1988

For the refrigeration system using the reversed Carnot cycle, maximum conditions of effectiveness and available energy output are studied with taking into account of the heat transfer between heat sources and the cycle, and of the heat loss due to heat leakage into the cold heat source. The extremum of the effectiveness exists for variables T$_{l}$ and T$_{L}$. Therefore the desirable results in engineering applications that available energy output is not zero under maximum condition of the effectiveness are obtained. In addition, the extremum of the available energy output does not exist for the variable T$_{l}$ but does for the variable T$_{L}$. As the heat loss increases, the available energy output and the effectiveness decrease, the regions of T$_{l}$ and T$_{L}$ where the refrigeration system is possible to operate become smaller.aller.

• Journal of Korean Institute of Industrial Engineers
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• v.27 no.1
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• pp.47-53
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• 2001

In this paper, we compare the classification performances of both ensemble and clustering algorithms (Data Bagging, Variable Selection Bagging, Parameter Combining, Clustering) to logistic regression in consideration of various characteristics of input data. Four factors used to simulate the logistic model are (1) correlation among input variables (2) variance of observation (3) training data size and (4) input-output function. In view of the unknown relationship between input and output function, we use a Taguchi design to improve the practicality of our study results by letting it as a noise factor. Experimental study results indicate the following: When the level of the variance is medium, Bagging & Parameter Combining performs worse than Logistic Regression, Variable Selection Bagging and Clustering. However, classification performances of Logistic Regression, Variable Selection Bagging, Bagging and Clustering are not significantly different when the variance of input data is either small or large. When there is strong correlation in input variables, Variable Selection Bagging outperforms both Logistic Regression and Parameter combining. In general, Parameter Combining algorithm appears to be the worst at our disappointment.

• The Transactions of the Korean Institute of Power Electronics
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• v.13 no.6
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• pp.461-468
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• 2008

This paper presents a novel series connected DC/DC converter and a proper variable phase shift switching method in order to obtain high voltage ratio for fuel cell system. The proposed series connected DC/DC converter has same rectifier and LC filter for DC output voltage, so it can reduce the number of passive devices regardless of the converter number. In the conventional constant phase shift switching method, the proposed series connected DC converters have inverse bias output voltage. In order to overcome this problem, a simple but proper variable phase shift switching method is proposed in the a novel series connected DC/DC converter. In order to verify the proposed system, simulation and experiments are implemented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.7
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• pp.1405-1410
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• 2009

Output voltage of a DC/DC power converter system is likely to be distorted if variable loads exist in the output terminal. This paper presents a new disturbance observer(DOB) approach to maintain a robust regulation of the output voltage of a boost type DC/DC converter. Unlike the buck-type converter case, the regulation problem of the boost converter is very complicated by the fact that, with respect to the output voltage to be regulated, the system is non-minimum phase. Owing to the non-minimum phase property the classical DOB approach has not been applied to the boost converter. Motivated by a recent result on the application of DOB to non-mimimum phase system, an output feedback control law is proposed by using a parallel feedforward compensator. Simulation results using the Simulink SimPowerSystems prove the performance of the proposed controller against load variation.

• Journal of Institute of Control, Robotics and Systems
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• v.18 no.7
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• pp.613-616
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• 2012

This paper proposes the state observer design for nonlinear systems with delayed output. It is shown that by considering a nonlinear term of error dynamics as an additional state variable, the nonlinear error dynamics with time delay can be transformed into the linear one with time delay. Sufficient conditions for existence of a state observer are characterized by linear matrix inequalities. Finally, an illustrative example is given in order to show the effectiveness of our design method.

• 제어로봇시스템학회:학술대회논문집
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• 1993.10a
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• pp.1213-1218
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• 1993

Variable structure control is applied to the robust output tracking control problem of general nonlinear multi-input multi-output (MIMO) systems. Using the concept of relative degree and minimum phase, input/output(I/O) linearization is undertaken. For I/O the linearized system, a new sliding hyperplanes design method is proposed. In this procedure, we can construct very robust and efficient sliding mode controller for general nonlinear systems of relative degree higher than two. The control results are illustrated by adopting a numerical example.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.12
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• pp.782-790
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• 2011

Typical temperature control methods of a cooler for machine tools are hot-gas bypass and compressor variable speed control. The hot-gas bypass system has been widely used to control the cooler temperature in many general industrial fields. On the contrary, the compressor variable speed control is focused on special fields such as aerospace and high precision machine tools which need high precision control. The variable speed control system usually has two control variables such as target temperature and superheat. In other words, the variable speed control system is basically multi-input multi-output(MIMO) system. In spite of MIMO system, the proportional integral derivative(PID) feedback control methodology that based on single-input single-output (SISO) system is generally used for designing the variable speed control system. Therefore, it is inevitable to describe transfer functions for dynamic behaviors of every controlled variables and decide the PID gains with tremendous iteration process. Moreover, the designed PID gains do not provide optimum system performances. To solve these problems, high performance controller design method based on a state space model is suggested in this paper. An optimum controller is designed to minimize both control errors and energy inputs. This method was more simple to describe dynamic behaviors and easier to design the cooler controller which is MIMO system.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1987-1992
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• 2004

A Variable Structure Model Reference Adaptive Controller (VS-MRAC) using state Variables is proposed for single input multi output systems. . The structure of the switching functions is designed based on stability requirements, and global exponential stability is proved. Transient behavior is analyzed using sliding mode control and shows perfect model following at a finite time. The effect of input disturbances on stability and transients is investigated and shows preference to the conventional MRAC schemes with integral adaptation law. Sliding surfaces are independent of system parameters and therefore VS-MRAC is insensitive to system parameter variations. Simulation is presented to clear the theoretical results.