• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.6
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• pp.497-505
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• 2016

Operating wind turbine generators at maximum power point requires maximum power point tracking (MPPT) control methods. However, conventional methods cannot track the appropriate maximum power point in situations involving wind turbine systems based on a series operation strategy. These systems comprise one or more local maximum power points, and conventional methods can detect only one local maximum power point closed by a current operation point. This study proposes an advanced MPPT method for the series operation strategy of a small, grid-connected wind turbine system. In determining the appropriate maximum point, operations at certain local maximum power points are analyzed. The results show one appropriate point, which is tracked by the proposed MPPT method. The effectiveness of the proposed method is verified by the experimental results.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.372-378
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• 2012

This paper deals with a 3-phase voltage disturbance generator for a performance test of custom power devices such as dynamic voltage restorers (DVR), dynamic uninterruptable power supplies (UPS), etc. The operating principle of the proposed circuit is described in each mode of voltage sag, swell, outage, and unbalance. The main components of the proposed disturbance generator are silicone controlled rectifier (SCR) thyristors, variable autotransformers, and transformers. Therefore, the disturbance generator can be implemented with a considerably low cost compared to the conventional pulse width modified (PWM) inverter and converter type generators. Furthermore, it has good features of high reliability with simple structure, high efficiency caused by no PWM switching of the SCR thyristors, and easy control with a wide variation range. To verify the validity of the proposed scheme, simulations and experiments are carried out.

• Journal of the Korean Institute of Telematics and Electronics S
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• v.35S no.10
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• pp.186-192
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• 1998

This paper presents a high performance low switching PWM technique or the propulsion system of railway such as subway and high speed train. In order to achieve the continuous voltage control to six-step and s low harmonics with low switching frequency under 500Hz, the synchronous technique is combined with a space vector overmodulation and implemented by using DSP. Improved performance and a validation of proposed method are showed by the digital simulation and the experimental results using a 1.65MVA IGBT VVVF inverter and inertia load equivalent to 160 tons railway cars.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.4
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• pp.640-645
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• 2015

Near surface transit system has should be constructed as installation cost of light rail transit with elevated track. So, distance between two substations is longer than conventional system. The long feeding distance results in severe voltage drop. This paper proposes a PWM rectifier instead of diode rectifier. The PWM rectifier has some advantages. This is able to control output voltage constantly to reduce voltage drop and to use regeneration power without additional inverter. This paper analyse on improved voltage profile and cost of substation with PWM rectifier. The analysis of voltage profile use PSIM, and the installation cost of substation with PWM rectifier is compared to substation with diode rectifier.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.65 no.5
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• pp.902-910
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• 2016

This paper presents the overall measurement system for on-line test of super-speed maglev train. The super-speed maglev train is composed of vehicle, propulsion, power, and so on. In order to evaluate and diagnose for sub-system, we made overall measurement system. Just like the other measurement system, it is designed to distributed type. The hardware is consist of SCXI, PXI, Terminal, UPS, and so forth. It is installed on a train, control room, power room and track to collect lots of signals. The software controls hardware system, monitors main data such as inverter current, converter voltage. Using the measurement system, we evaluated a lot of performances for vehicle, track, and so forth. Through the developed system have improved reliability and safety for super-speed maglev train.

• Journal of Power Electronics
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• v.1 no.2
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• pp.117-126
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• 2001

A synchronous motor(SM) with q-axis special field winding of which the q-axis field-current compensates and cancels armature reaction can be driven at unity power factor under the conditions of transient state as well as steady state. The motor operates in high efficiency in all conditions. However, in order to obtain maximum performance of the motor, it is required that the time constant of armature circuit corresponds to that of q-axis field circuit. Inverse LQ(ILQ) design method on a basis of the pole assignment is suitable for this problem:(1) The time constants of the output responses can be designed for desired specifications, (2) Relations between feedback gains and response of closed loop system are very clear and (3) Optimal solutions can be given by simple procedure of ILQ method without solving the Ricaati's equation, compared to the usual LQ design method. Accordingly, the ILQ method can make the responses of armature current and q-axis field-current correspond. In this paper, it is proved by numerical simulations and experiments that the ILQ method is very effective for optimal regulator design of this plant and realizes a high-performance motor with unity power factor and high efficiency.

• The Transactions of the Korean Institute of Power Electronics
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• v.3 no.1
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• pp.8-14
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• 1998

This paper describes a novel real-time based optimal Pulse Width Modulation (PWM) method suitable for microprocessor-based PWM inverters. Optimal switching patterns minimizing the performance index corresponding to the distortion between the reference and the controlled output voltages are decided by on-line calculation using the microprocessor-implemented control system. To show the effectiveness of the proposed PWM scheme, digital simulation studies and experiments using a 16-bit single-chip microcontroller (Intel 80C196KC) are performed. The results obtained from these simulation studies and experiments show that the proposed PWM scheme has better performance than the other methods such as the natural PWM and the direct PWM.

• The Transactions of the Korean Institute of Power Electronics
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• v.20 no.4
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• pp.321-329
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• 2015

The static synchronous compensator (STATCOM) of cascaded H-bridge configuration accompanying multiple separate DC sides is inherently subject to the problem of uneven DC voltages. These DC voltages in one leg can be controlled by adjusting the AC-side output voltage of each cell inverter, which is proportional to the active power. However, when the phase current is extremely small, large AC-side voltage is required to generate the active power to balance the cell voltages. In this study, an alternative zero-sequence current injection method is proposed, which facilitates effective cell balancing controllers at no load, and has no effect on the power grid because the injected zero sequence current only flows within the STATCOM delta circuit. The performance of the proposed method is verified through simulation and experiments.

• ETRI Journal
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• v.36 no.6
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• pp.905-912
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• 2014

In this paper, a new architecture is proposed to achieve complexity efficiency in implementing variable pulse position modulation (VPPM). VPPM, specified in IEEE 802.15.7, can support wireless communication and dimming control simultaneously using visible light. The proposed architecture is based on the VPPM signal property in which the transition point of the modulated output is obtained by counting the sample index and comparing it to both the assigned dimming factor and the transmitting data. Therefore, the proposed architecture can be composed of simple logics, including a counter, a comparator, and an inverter, all of which are insensitive to the dimming resolution in contrast to a conventional codeword-table method. This paper describes the verification of the proposed algorithm through a register-transfer level implementation of the codeword and proposed architectures. In comparison with the codeword-table method, the proposed method gains a nine-fold complexity reduction at a 1% dimming-step resolution.

• Journal of Magnetics
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• v.16 no.3
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• pp.246-252
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• 2011

A high-voltage power supply has been built for activation of the brain via stimulation using a Full Wave Cockroft-Walton Circuit (FWCW). A resonant half-bridge inverter was applied (with half plus/half minus DC voltage) through a bidirectional power transistor to a magnetic stimulation device with the capability of producing a variety of pulse forms. The energy obtained from the previous stage runs the transformer and FW-CW, and the current pulse coming from the pulse-forming circuit is transmitted to a stimulation coil device. In addition, the residual energy in each circuit will again generate stimulation pulses through the transformer. In particular, the bidirectional device modifies the control mode of the stimulation coil to which the current that exceeds the rated current is applied, consequently controlling the output voltage as a constant current mode. Since a serial resonant half-bridge has less switching loss and is able to reduce parasitic capacitance, a device, which can simultaneously change the charging voltage of the energy-storage condenser and the pulse repetition rate, could be implemented. Image processing of the brain activity was implemented using a graphical user interface (GUI) through a data mining technique (data mining) after measuring the vital signs separated from the frequencies of EEG and ECG spectra obtained from the pulse stimulation using a 90S8535 chip (AMTEL Corporation).