• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.5
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• pp.54-60
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• 2004

With the proliferation of nonlinear loads such as commercial facilities in all of modern society high neutral harmonic currents have been observed. High neutral currents in three-phase four-wire distribution systems can cause lots of harmonic problems. The most common solution of neutral harmonic currents reduction is a zero phase sequence filter using zig-zag transformer. This paper analyzes a commercially available neutral line zero sequence currents reduction device and applies the equipment to commercial office loads for eliminating harmonics. Experimental results m compared numerically and graphically with simulation results through the use of MATLAB.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.3
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• pp.59-64
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• 2004

With the proliferation of nonlinear loads such as lighting facilities in all modern society high neutral harmonic currents have been observed. High neutral currents in three- phase four-wire distribution systems can cause lots of harmonic problems. The most common solution of neutral harmonic currents reduction is a zero phase sequence filter using zig-zag transformer. This paper analyzes a commercially available neutral line zero sequence currents reduction device and applies the equipment to lighting loads for eliminating harmonics. Experimental results are compared numerically and graphically with simulation results through the use of MATLAB.

• Proceedings of the KIEE Conference
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• 2002.07b
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• pp.715-719
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• 2002

Recently, Dangers due to harmonics emanated from all sorts of machinery have been on the increase with the development in industry. One of them is that Zero Sequence harmonic currents flow from the neutral wires in 3 phases - 4 wire systems. The flowing of harmonic currents in neutral wires brings about the superheating and falloff in output of transformer, the overheating of them, a rise in ground potential and the wrong movement of machinery, so has a bad influence on this system. To develop the machinery to decrease neutral wires Zero sequence harmonic currents and apply it help solve these problems and bring about the effects of a improvement in power factor and energy savings.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.48 no.2
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• pp.75-82
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• 1999

A compensation method of the motor parameters using zero sequence third harmonic voltage is presented for the speed sensorless vector control of the induction motor considering saturation of the flux. Generally, the air-gap flux of the saturated induction motor contains the space harmonic components rotating with the synchronous frequency of the motor. Because the EMF of the saturated induction motor contains the zero sequence harmonic voltages at the neutral point of the motor, those harmonic voltages can be used as a saturation index. In this work, the rotor flux observer is firstly designed for the speed sensorless vector control of induction motor. And a novel measurement method of the space harmonic voltage and a compensation method of th LPF(Low Pass Filter) are proposed. For compensating the non-linear variations of the magnetizing inductance depending on the saturation level of the motor, the dominant third harmonic voltage of the motor is used as a saturation function of the air-gap flux. And the variation of the stator resistance owing to the motor temperature can also be measured with the phase angle between the impressed voltage vector and the zero sequence voltage. The validity of the proposed parameter compensation scheme in the speed sensorless vector control using rotor flux observer is verified by the result of the simulations and the experiments.

• Proceedings of the KIPE Conference
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• 2008.06a
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• pp.472-474
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• 2008

According to the development of power switching device technology, the power conversion system is used from the small electric power units to the large industrial instruments. These instruments are operated as harmonic sources in the grid and the harmonics cause zero sequence harmonics in the neutral line. To reduce zero sequence harmonics, the zigzag transformer is used conventionally. But the zigzag transformer can reduce only 60~70% of harmonics. In this paper, hybrid power filter for zero sequence harmonics reduction and the harmonic detection method are proposed.

• The Transactions of the Korean Institute of Power Electronics
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• v.7 no.6
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• pp.596-603
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• 2002

In this paper a new harmonic reduction method of three-phase diode rectifiers is proposed to improve input current performance using the zero-sequence harmonics injection technique. The proposed mothed, based on the third-harmonic injection, employs two half-bridge inverters and two single-phase transformers to independently shape the positive and negative dc rail currents of the diode rectifier. The actively shaped zero-sequence harmonic currents are t]ten circulated through the ac side of the rectifier using a zigzag transformer This results in pure sinusoidal input currents in the three-phase diode rectifier. Experimental results on a 1.5kVA prototype are provided to validate the proposed technique.

• Proceedings of the KIPE Conference
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• 1998.07a
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• pp.388-394
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• 1998

In this paper, we propose a speed sensorless control of the saturated induction motor using the zero sequence third harmonic voltages and a compensation method of the stator resistance variations. The air-gap flux of the saturated induction motor contains the space harmonic components rorating synchronous frequency. As a function of the air-gap flux saturation, the dominant third harmonic voltage is used to compensate the non-linear variations of the mutual inductance depending on the saturation level of the motor. and also the stator resistance variations can be measured with the phase angle between the voltage vector and the zero sequencial voltages. The validity of the proposed compensation scheme in the speed sensorless control using rotor flux observer is verified by simulations.

• Journal of Power Electronics
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• v.3 no.3
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• pp.151-158
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• 2003

Three-phase four-wire electrical distribution systems are widely employed in manufacturing plants, commercial and residential buildings Due to the nonlinear loads connected to the distribution system, the neutral conductor carries excessive harmonic currents even under balanced loading since the triplen harmonics in phase currents do not cancel each other This may result in wiring failure of the neutral conductor and overloading of the distribution transformer In response to these concerns, a cost-effective neutral current harmonic suppressor system has been proposed. This paper proposes an improved control method for the harmonic suppressor system under unbalanced load conditions The proposed control method compensates for only the harmonic components in the neutral conductor, and the zero-sequence fundamental component due to unbalanced loading is prevented from flowing through the harmonic suppressor system This remedies overloading and power loss of the system The experimental results on a prototype validate the proposed control approach.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.63 no.7
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• pp.896-902
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• 2014

As the various kinds of load who generate higher harmonics increases according as the power electronics technology develops, harmonic treatment standard is proposed by IEEE and IEC. Because establishment of harmonic reduction device is required for existent installment to satisfy harmonic treatment standard, the problem of investment charge and installation space increasing may be occurred. In order to solve these problems, a novel transformer connection method using principles of PCT and ZED is suggested.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.273-274
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• 2012

This paper investigates control algorithms for a doubly fed induction generator(DFIG) with a back-to-back three-level neutral-point clamped voltage source converter in medium voltage wind power system under unbalanced grid conditions. Two different control algorithms to compensate for unbalanced conditions are proposed. Evaluation factors of control algorithm are fault ride-through(FRT) capability, efficiency, harmonic distortions and torque pulsation. Zero regulated negative sequence stator current control algorithm has the most effective performance concerning FRT capability and efficiency. Ripple-free control algorithm nullifies oscillation component of active power and reactive power. Ripple-free control algorithm shows the least harmonic distortions and torque pulsation. Combination of zero regulated negative sequence stator current and ripple-free control algorithm control algorithm depending on the operating requirements and depth of grid unbalance presents the most optimized performance factors under the generalized unbalanced operating conditions leading to high performance DFIG wind turbine system.