• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.12
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• pp.65-73
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• 2014

In this paper, the detection scheme of the voltage variation using a two difference voltage is proposed. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on a d-q transformation using an all-pass filter (APF). The APF generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the APF cannot generate the virtual q-axis voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage around the zero crossing is not enough to detect the voltage sag. Therefore, the new detection scheme using the two difference voltage which can detect the sag around the zero crossing voltage is proposed.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.3
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• pp.254-259
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• 2013

We examined the generation of harmonic voltage by a synchronous machine adding d-axis and q-axis harmonic field windings in order to reduce the harmonics in a power line. We derived the expressions of the armature voltage in the case of supplying the currents with the frequency nf to the d-axis and q-axis harmonic field windings. We constructed the synchronous machine adding the harmonic windings. In this paper, the expressions and the experimental results on the generation of harmonic voltages by the synchronous machine are presented.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.157-166
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• 2016

In this paper, a new sag and peak voltage detector is proposed for a single-phase inverter using delta square operation. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on d-q transformations using an all-pass filter (APF). The d-q transformation is typically used in the three-phase coordinate system. The APF generates a virtual q-axis voltage component with a 90° phase delay, but this virtual phase cannot reflect a sudden change in the grid voltage at the instant the voltage sag occurs. As a result, the peak value is drastically distorted, and it settles down slowly. A modified APF generates the virtual q-axis voltage component from the difference between the current and the previous values of the d-axis voltage component in the stationary reference frame. However, the modified APF cannot detect the voltage sag and peak value when the sag occurs around the zero crossing points such as 0° and 180°, because the difference voltage is not sufficient to detect the voltage sag. The proposed algorithm detects the sag voltage through all regions including the zero crossing voltage. Moreover, the exact voltage drop can be acquired by calculating the q-axis component that is proportional to the d-axis component. To verify the feasibility of the proposed system, the conventional and proposed methods are compared using simulations and experimental results.

• Journal of international Conference on Electrical Machines and Systems
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• v.3 no.2
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• pp.132-138
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• 2014

We investigated the harmonic voltages generated by a synchronous machine adding d-axis and q-axis harmonic field windings to reduce the harmonics in a power line. First, electronic circuits such as a frequency multiplier, band-pass filter, and phase shifter were newly designed and made to carry out the experiment. Next, an experimental circuit, for which an AC voltage of frequency 6f synchronized to the power line voltage of frequency f could be obtained, was constructed to examine the generation of harmonic voltage in more detail. Finally, an experiment involving the generation of harmonic voltage was performed using an experimental synchronous generator with harmonic windings in the d-axis and q-axis. In this paper, the power spectrum and the waveforms of the harmonic voltages in the armature winding are presented. Moreover, the values calculated from theoretical expressions of harmonic voltages in armature winding are compared with the values obtained by the experiment.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.6
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• pp.262-270
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• 2003

In this paper, the characteristics of single-phase line-start permanent magnet synchronous motor driven by constant voltage are analyzed on d-q axis vector diagram and compared with that of current controlled motor. The coupled method of symmetrical coordinates and d-q axis voltage equation are applied to the analysis method like the analysis of single-phase induction motor. From the result of the analysis, it is seen that motors driven by constant voltage source have effects on not only the amplitude of current and torque but also current and current phase angle, so overall characteristics such as power factor and load angle are affected by circuit parameters. For precise analysis and design of single-phase line-start synchronous motor, its characteristics should be analyzed on d-q axis vector plan in consideration of the variation of circuit parameters.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.1
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• pp.96-104
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• 2014

The all pass filter generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the virtual q-axis voltage cannot detect the voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage between the current and previous value around the zero crossing voltage is not enough to detect the voltage sag. Therefore, the new detection scheme which can detect the sag around the zero crossing voltage is proposed.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.29-33
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• 1998

In this paper, a new dynamic overmodulation strategy is proposed for vector-controlled induction motor drive, and a comparison experiment with conventional schemes are also performed. In overmodulation region, the proposed overmodulation scheme allocates the output voltage of inverter so that synchronous d-axis voltage is diminished in proposed overmodulation scheme allocates the output voltage of inverter so that synchronous d-axis voltage is diminished in proportion as reference voltage exceeds hexagon boundary. As a result, d-axis current is decreased in the overmodulation region, which improves the dynamic performance of torque control considering the current dynamics of induction motor. The conspicuous improvement of the proposed scheme over conventional ones is observed in experimental results.

• 한국정보디스플레이학회:학술대회논문집
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• 2006.08a
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• pp.286-289
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• 2006

Temporal dual gamma drive technology employing the 120Hz refresh rate was developed to enhance the off-axis viewing quality in patterned vertical alignment mode. The color shift ${\Delta}u'v'$ from on-axis to off-axis (60 deg.) for pale orange color, (R,G,B) = (196,124,96), was below 0.01, and the power exponent of gamma curve for off-axis viewing angle (60 deg.) was about 1.8, when the gamma curve for on-axis was set with power exponent of 2.4. The off-axis image distortion index was below 0.180 in contrast to the normal case ${\sim}0.23$. To elevate the response speed of liquid crystal in the intra-frame, the voltage below threshold voltage of liquid crystals was used.

• Proceedings of the KSR Conference
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• 1998.11a
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• pp.171-178
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• 1998

This paper proposes a new overmodulation strategy to give a better voltage utilization by tracking voltage vector along hexagon sides. This strategy enables the inverter to control both magnitude and angle of current. Therefore, the vector control using this strategy can lead to better output torque dynamics compared to the conventional slip frequency control with six-step voltage, which is widely used in the traction drive. In this strategy, the d-axis output voltage of a current controller to control the flux is conserved and the q-axis output voltage to control the torque is controlled to place the voltage vector on the hexagon boundary In case of overmodulation. The limited q-axis voltage is used for anti-windup of q-axis current controller. This paper also presents a new field weakening scheme which incorporate the proposed overmodulation strategy. In this scheme, the flux level is selected by both required current limit and the available maximum voltage along hexagon sides. The validity of the proposed overall scheme is confirmed by the computer simulations for a typical traction drive with a 210[㎾] induction motor.

• Journal of Power Electronics
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• v.16 no.6
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• pp.2294-2305
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• 2016

The introduction of a high-voltage direct-current (HVDC) system based on a modular multilevel converter (MMC) for wind farm integration has stimulated studies on methods to control this type of converter. This research article focuses on the control of the AC voltage and circulating current for a wind-farm-side MMC (WFS-MMC). After theoretical analysis, emotional learning (EL) controllers are proposed for the controls. The EL controllers are derived from the learning mechanisms of the amygdala and orbitofrontal cortex which make the WFS-MMC insensitive to variance in system parameters, power change, and fault in the grid. The d-axis and q-axis currents are respectively considered for the d-axis and q-axis voltage controls to improve the performance of AC voltage control. The practicability of the proposed control is verified under various conditions with a point-to-point MMC-HVDC system. Simulation results show that the proposed method is superior to the traditional proportional-integral controller.