• 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.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.67 no.3
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• pp.155-159
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• 2018

Recently, the expansion or establishment of facilities for the logistics system is increasing. Conveyor facilities play a major role in sorting and transporting logistics. Induction motors are widely used for the operation of these conveyor systems. In the logistics system, a large number of induction motors are used. These motors have a considerable distance from the power source side and have a low power factor. The installation position for the power factor compensation of the induction motor is very important. Since the voltage drop depends on the length of the line, it is an important parameter in capacitor capacity determination for power factor compensation. The capacity of the capacitors installed to compensate the power factor of the inductive load should be designed to the extent that self-excitation does not occur. In this study, we analyze the method of compensating the proper power factor considering the voltage drop and the installation position of the induction motor in the logistics system.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.8
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• pp.632-639
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• 2003

This paper proposes a simple compensation scheme for the time delay caused by measurement, calculation and selection of voltage vector in Direct Torque Control (DTC) of an induction motor. In general scheme, it is difficult to know the exact delay time, furthermore the delay time can be varied by program routines for calculation and processing of measured data. In this proposed scheme, by applying voltage vector at the beginning of next sampling period, a fixed delay time is achieved and its compensation becomes much simpler. Furthermore, with the simple compensation algorithm, an improved performance can be achieved by shortening sampling period. Experimental results prove the feasibility of the proposed scheme in induction motor control.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.39 no.8
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• pp.836-846
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• 1990

This paper presents a Static Var Compensator (SVC) system compensating the reactive power for power system, which consists of a voltage type Pulse Width Modulation (PWM) converter and a reactance linking the converter to the source. The system drives the four quadrant modes. The system determines the magnitude of the input voltage, and then compares it with the magnitude of the source voltage by regulating the phase of the SVC about the source. Therefore, the system generates leading compensation currents when the input voltage is larger than the source in magnitude, and lagging compensation currents for smaller input voltage. Reactive power about voluntary load in power system is smoothly compensated by those compensation currents, and also power factor of source is improved. Furthermore, the SVC system using PWM method may improve the source current waveforms by eliminating the 5th and 7th harmonic components from the input voltages.

• 제어로봇시스템학회:학술대회논문집
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• 2005.06a
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• pp.817-820
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• 2005

Dead-Time is necessary to prevent the shot circuit of the full bridge inverters in pulse width modulation. However the output voltage deviations is the result of the Dead-Time that decrease power from the out put voltage inverters. This paper presents the method that compensate power output voltage inverters loss in Dead-Time circuit for DC Motor Drives with full bridge voltage inverters. The compensation of Dead-Time method is a sample and a low-cost solution. The comparison between the test results and simulation by MATLAB&SIMULINK under the same condition is similar.

• The Transactions of the Korean Institute of Power Electronics
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• v.18 no.1
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• pp.110-116
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• 2013

This paper proposes a current ripple reduction method to improve the control performance of B4 type inverter that is studied for cost-effective drive systems. B4 inverters employ only four switches and they have a center-tapped connection between the split dc-link capacitors and one phase of a three-phase motor or load. In the B4 topology, unbalanced three-phase voltages will be generated due to the dc-link voltage ripple. To solve this problem, this paper presents a voltage distortion compensation method that adjusts the voltage reference with the consideration of dc-link voltage ripple. The validity of the proposed method is verified by simulation and excremental results with an induction machine.

• Journal of Power Electronics
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• v.5 no.4
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• pp.329-334
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• 2005

The DSTATCOM(Distribution Static Synchronous Compensator) is one of the Custom Power Devices that can regulate voltage. The DSTATCOM operates as a shunt connected static var compensator whose capacitive or inductive output current can be controlled independent of the system voltage. The magnitude of the compensated voltage is limited by characteristics of the system and the load. Compensation capability of the DSTATCOM which can inject 1 MVAR reactive power was simulated by EMTDC under several conditions. This paper analyzes the effect of the DSTATCOM's compensation considering the length and kind of distribution line, the power factor and magnitude of the load, and the duration and magnitude of the voltage variation.

• 제어로봇시스템학회:학술대회논문집
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• 1988.10a
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• pp.688-692
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• 1988

The active filter system for harmonic current compensation is presented in this paper. The active filter, composed of a three-phase voltage-type PWM inverter and the capacitor, compensates both the harmonic currents and the reactive power by injecting the PWM current to the ac line. This paper describes the principle of harmonic current compensation, the calculation circuits for the harmonic currents to be injected, the several compensation characteristics. Also the experimental results are shown to verify the theory proposed in this paper.

• Journal of Power Electronics
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• v.17 no.2
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• pp.522-532
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• 2017

This paper presents a novel integrated structure for a cascaded distribution static compensator (D-STATCOM) and distribution transformer for medium-voltage reactive power compensation. The cascaded multilevel converter is connected to a system via a group of special designed taps on the primary windings of the Dyn11 connection distribution transformer. The three-phase winding taps are symmetrically arranged and the connection point voltage can be decreased to half of the line-to-line voltage at most. Thus, the voltage stress for the D-STATCOM is reduced and a compromise between the voltage rating and the current rating can be achieved. The spare capacity of the distribution transformer can also be fully used. The working mechanism is explained in detail and a modified control strategy is proposed for reactive power compensation. Finally, both simulation and scaled-down prototype experimental results are provided to verify the feasibility and effectiveness of the proposed connection structure and control strategy.

• Proceedings of the KIPE Conference
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• 2011.11a
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• pp.71-72
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• 2011

This paper presents a novel and direct dead time compensation method of the 3 phase inverter using space vector pulse width modulation(SVPWM) topology. In the turn on time calculation of the effective voltage, the dead time effect is directly compensated according to the current direction of the midium voltage reference. Since the turn on time of the effective voltage vector is affected by the dead time, the loss time is compensated to turn on time of the effective voltage vector. And the dead time is added to the calculated voltage vector switching times according to the current direction. For the more effective compensation, the direction of the midium phase current is considered by the practical direction and voltage drops in the power devices. The proposed method can compensate the dead time which is considered feedback error or direction of middle phase current without coordinate transform in added controller. The proposed dead time compensation scheme is verified by the computer simulation and experiments of 3 phase R L load.