• Journal of Electrical Engineering and Technology
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• 제10권3호
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• pp.971-982
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• 2015

In order to improve the quality of the billet continuous casting, a two-phase orthogonal power supply (TPOPS) for electromagnetic stirrer is researched, which is composed of three-phase PWM rectifier and three-leg inverter. According to the power analysis of system, the ripple of dc-link voltage is analyzed and its analytical expression is derived. In order to improve the performance of electromagnetic stirring, an integrated control method with feedforward control is proposed for PWM rectifier to suppress the fluctuations of dc-link voltage and provide a stable dc source for inverter. According to the simplified equivalent model, a composite current control method is proposed for inverter. This proposed method can combine the merits of feedforward control with feedback control to effectively improve the dynamic output performance of TPOPS. Finally, a 300kVA prototype of TPOPS is developed, and the results have verified the analysis and control method.

• Journal of Power Electronics
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• 제14권6호
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• pp.1293-1302
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• 2014

A flyback inverter using voltage sensorless maximum power point tracking (MPPT) for photovoltaic (PV) AC modules is presented. PV AC modules for a power rating from 150 W to 300 W are generally required for their small size and low price because of the installation on the back side of PV modules. In the conventional MPPT technique for PV AC modules, sensors for detecting PV voltage and PV current are required to calculate the PV output power. However, system size and cost increase when the voltage sensor and current sensor are used because of the addition of the auxiliary circuit for the sensors. The proposed method uses only the current sensor to track the MPP point. Therefore, the proposed control method overcomes drawbacks of the conventional control method. Theoretical analysis, simulation, and experiment are performed to verify the proposed control method.

• KEPCO Journal on Electric Power and Energy
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• 제2권2호
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• pp.253-257
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• 2016

This paper analyzes voltage control method in order to supply high-quality power for stand-alone microgrid. Stand-alone microgrid is composed of battery bank, stand-alone PCS and controllable loads. The main role of stand-alone PCS is to supply high-quality power to loads as main source by using stable voltage method regardless of load conditions. In particularly, output voltage of stand-alone PCS gets severely unbalanced voltage under unbalanced loads. Fundamental positive and negative sequences are transformed by two coordinates transformation which are rotated in each opposite direction, respectively. Each fundamental d-q voltage is regulated by each fundamental PI control. In addition, low-order harmonics are compensated through resonant controllers. Performance of stand-alone microgrid is tested for feasibility, and it is verified that output voltage of THD is improved to 1% from 2.2% under 50 kW balanced load, and is improved to 1.1% from 2.6% under 50 kW unbalanced load.

• Journal of Electrical Engineering and Technology
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• 제13권2호
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• pp.550-558
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• 2018

This paper presents the current limit strategy of voltage controller of delta-connected H-bridge static synchronous compensator (STATCOM) under an unbalanced voltage fault event. When phase to ground fault happens, the feasibility to heighten the magnitude of sagging phase voltage is considered by using symmetric transformation method in delta-structure STATCOM. And the efficiency to cover the maximum physical current limit of switching device is considered by using vector analysis method that calculate the zero sequence current for balancing the cluster energy in delta connected H-bridge STATCOM. The result is simple and obvious. Only positive sequence current has to be used to support the unbalanced voltage sag. Although the relationship between combination of the negative sequence voltage with current and zero sequence current is nonlinear, the more negative sequence current is supplying, the larger zero sequence current is required. From the full-model STATCOM system simulation, zero sequence current demand is identified according to a ratio of positive and negative sequence compensating current. When only positive sequence current support voltage sag, the least zero sequence current is needed.

• 한국전기전자재료학회논문지
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• 제19권6호
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• pp.586-590
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• 2006

This paper deals with the application of a partial discharge (PD) test on low-voltage electrical and electronic devices, which is recently being accepted as a non-destructive and a effective dielectric test method. A comparative analysis combined with the Withstand Voltage Test (WVT) specified in IEC standards was carried out on low-voltage insulation transformers. The results showed that the WVT causes insulation degradation of the specimen during the test by applying high voltage. However, the PD test can be performed in ranges from 30 % to 50 % of the test voltage specified in the WVT. Therefore, the PD test is successfully applicable for a non-destructive test method on low-voltage electrical and electronic devices as a replacement of the WVT.

• 대한전기학회논문지:전력기술부문A
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• 제52권5호
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• pp.257-262
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• 2003

The voltage unbalance factor derived from symmetrical component analysis requires manipulation of complex quantities. To facilitate the calculation of the voltage unbalance factor in field applications, this paper proposes the method for calculating the voltage unbalance factor in terms of the line voltage magnitudes that are readily available in moat practical circumstances. It is shown that the line voltages appear as circular Phasor loci for given voltage unbalance factor, and a graphical chart is developed that can be used to determine the voltage unbalance factor in a straightforward manner avoiding calculation.

• Journal of Electrical Engineering and Technology
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• 제9권6호
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• pp.2187-2193
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• 2014

In this paper, we propose a method for suppressing shaft voltage by modifying the rotor shape and the permanent magnets in interior permanent magnet type high voltage motors. The shaft voltage, which adversely affects the bearing by occurring bearing current, is induced by parasitic components and the leakage flux in motor-driven systems as well as inherent linkage flux between main magnetic flux and shaft according to rotor configuration. Thus, shaft voltage should be analyzed and considered under inverter-driven and non-inverter-driven conditions because inherent linkage flux can analyze under non-inverter-driven condition. In this study, we designed re-arrangement magnet and re-structuring rotor to minimize the shaft voltage. In addition, we optimized the proposed models. The shaft voltage suppression effect of the designed model was validated experimentally and by comparative finite element analysis.

• Journal of Electrical Engineering and Technology
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• 제2권1호
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• pp.35-41
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• 2007

This paper presents the results of investigating harmonic levels on medium voltage motors at loading conditions in air separation plant. The essential results of the measurements of the medium voltage motor harmonics are summarized in the values for the total harmonic distortion (THD). Motors loading case is used to assess the current and voltage harmonic distortions. Proper system analysis is important when adding a new motor starting and controlling the equipment. With the result of the paper it is possible to suggest the most appropriate starting and control method. Two medium voltage motors of air separation unit measurement results and simulations are summarized. Both current and voltage harmonic distortions are fitted by using a linear and exponential regression model. The prediction of THD values can be used for this kind of process for future planning by utilities.

• Journal of Electrical Engineering and Technology
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• 제8권4호
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• pp.938-944
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• 2013

In this paper, we propose a method for suppressing shaft voltage by modifying the shape of the rotor and the permanent magnets in interior permanent magnet-type-high-voltage motors. Shaft voltage, which is induced by parasitic components and the leakage flux in motor-driven systems, adversely affects their bearings. In order to minimize shaft voltage, we designed a magnet rearrangement and rotor re-structuring of the motor. The shaft voltage suppression effect of the designed model was confirmed experimentally and by comparative finite element analysis.

• Structural Engineering and Mechanics
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• 제76권5호
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• pp.619-629
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• 2020

In current study, surface/interface effects for pull-in voltage and viscous fluid velocity effects on dimensionless natural frequency (DNF) of fluid-conveying piezoelectric nanosensor (FCPENS) subjected to direct electrostatic voltage DC with nonlinear excitation, harmonic force and also viscoelastic foundation (visco-pasternak medium and structural damping) are investigated using Gurtin-Murdoch surface/interface (GMSIT) theory. For this analysis, Hamilton's principles, the assumed mode method combined with Lagrange-Euler's are used for the governing equations and boundary conditions. The effects of surface/interface parameters of FCPENS such as Lame's constants (λI,S, μI,S), residual stress (τ0I,S), piezoelectric constants (e31psk,e32psk) and mass density (ρI,S) are considered for analysis of dimensionless natural frequency respect to viscous fluid velocity u̅f and pull-in voltage V̅DC.