• 전력전자학회논문지
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• 제18권2호
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• pp.161-168
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• 2013

This paper presents an algorithm of a compensation of the grid current distortion caused by the grid voltage unbalance and distortion in 3-phase bi-directional DC to AC inverter. Usually 3-phase grid system has unbalance and distortion because of connecting 1-phase and non-linear load with 3-phase load using same input node. Controlling 3-phase inverter by general method under the unbalanced and distorted grid voltage, the grid current has distortion. This distortion of the grid current cause the grid voltage distortion again. So, it need to control the grid current balanced and non-distorted, even the grid voltage gets unbalanced and distorted. There are some complex method to compensate the gird current distortion. it suggest simple method to solve the problem. Simulation and experiment is used to validate the proposed algorithm.

• 플랜트 저널
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• 제4권3호
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• pp.66-72
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• 2008

The vibration of steam turbine is caused by Mass unbalance, Shaft misalignment, Oil whip and rubbing etc. But in turbine which is normally operated and maintained, the Mass unbalance component possesses the greatest portion. Our power plant has two steam turbines in capacity of 200 MW and 135 MW respectively and each turbine is supported by 6 journal bearings. However, we had many difficulties because the vibration amplitude of #3 and #4 Bearings was high during the start-up and operation mode change of steam turbine. But, with this study, we completely solved the vibration problem caused by the mass unbalance of #1 steam turbine. Until a recent date, #3 and #4 bearings which support high pressure turbine for #1 steam turbine had shown about $135{\mu}m$ in vibration amplitude (sometimes it increased to $221{\mu}m$ maximum. alarm: 6 mils, trip: 9 mils) at base load. After applying the study, they decreased to about $45{\mu}m$ maximum. It is a result from that we did not change the setting value of bearing alignment and only changed the assembly position of internal parts in Synchro clutch coupling rachet wheel which links between high pressure turbine and low pressure turbine, and increased the internal gap and machining of the Pawl cage surface. In the operation of steam turbine, if the vibration value increases by 1X, we should reduce the vibration of bearing by weight balancing. However, unless the vibration of bearing is declined by the balancing, we will have to disassemble and check the component and find the cause. In this study, we researched the way to lower mass unbalance that is 1X vibration component which has the greatest portion of vibration generated by steam turbine and we got good result by applying the findings of this study.

• 전기학회논문지
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• 제66권3호
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• pp.587-592
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• 2017

In the three-phase four-wire low-voltage power distribution equipment, single-phase and three-phase load have been used mainly mixed. Also linear and nonlinear loads have been used together in the same conditions. In a three-phase four-wire distribution line, the current distribution of three-phase linear load is almost constant in each phase during driving or stopping, but the single-phase load is different from each other for each phase in accordance with the operation and stop. So that the voltage unbalance is caused by the current difference of each phase. In the three-phase four-wire distribution system, non-linear load is used with linear load. The presence of single-phase nonlinear loads can produce an increase in harmonic currents in three-phase and neutral line. It can also cause voltage unbalance. In the present study, we analyzed for the voltage unbalance fluctuations by the operation pattern of the single and three-phase linear and non-linear load in three-phase four-wire low voltage distribution system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 제37회 하계학술대회 논문집 D
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• pp.1885-1886
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• 2006

The thermal energy from nuclear fission is transferred to the steam generator which is a kind of a large heat exchanger. After the feedwater is injected into the steam generator and absorbs the thermal energy, it is converted into the steam. This steam goes into the turbine. The balance between the generated energy and the consumed energy is required for the nuclear power plant to be stable. For the purpose of which, the feed water, a parameter for energy transfer, should be controlled in stability. Usually, the nuclear power plants are operated in base load in the view of power system for the stability of fission system. Therefore, though there will be almost no unbalance, there can be some instability from unbalance in case of startup/shutdown or disturbance. In this case, the controllability of feedwater pump is very important for the quick recover of stability.

• 전력전자학회논문지
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• 제20권1호
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• pp.91-103
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• 2015

This paper investigates control algorithms for a doubly fed induction generator with a back-to-back three-level neutral-point clamped voltage source converter in a medium-voltage wind power system under unbalanced grid conditions. Negative sequence control algorithms to compensate for unbalanced conditions have been investigated with respect to four performance factors: fault ride-through capability, instantaneous active power pulsation, harmonic distortions, and torque pulsation. The control algorithm having zero amplitude of torque ripple indicates the most cost-effective performance in terms of torque pulsation. The least active power pulsation is produced by a control algorithm that nullifies the oscillating component of the instantaneous stator active and reactive power. A combination of these two control algorithms depending on operating requirements and depth of grid unbalance presents the most optimized performance factors under generalized unbalanced operating conditions, leading to a high-performance DFIG wind turbine system with unbalanced grid adaptive features.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
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• pp.586-590
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• 2001

In this paper, a novel control scheme compensating source voltage unbalance and harmonic currents for hybrid active power filters is proposed, where no low/high-pass filters are used in compensation voltage composition. The phase angle and compensation voltages for source harmonic current and unbalanced voltage components are derived from the positive sequence component of the unbalanced voltage set, which is simply obtained by using digital all-pass filters. Since a balanced set of the source voltage obtained by scaling the positive sequence components is used as reference values for source current and load voltage, it is possible to eliminate the necessity of low/high-pass filters in the reference generation. Therefore the control algorithm is much simpler and gives more stable performance than the conventional method. In addition, the source harmonic current is eliminated by compensating for the harmonic voltage of the load side added to feedback control of the fundamental component.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 학술회의 논문집 정보 및 제어부문 A
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• pp.87-90
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• 2003

There are generally two temperature control methods using ac voltage regulators - the phase control method and the on-off control method. The phase control method uses thyristor's angles of extinction for the output power regulation and the on-off control method uses the control of on and off times for the output power regulation. Both of methods have the problems that are the unbalance of the three phase and surge current caused system's destruction. The main object of this study proposes a solution of problems of surge currents and unbalance of three phase when thyristor voltage regulator is switching. To solve the problem, It is proposes that the solution of surge currents is using a tap transformer and an additional switch with adjustable resistance and applies zero crossing of switching voltage of two input line to power load. This method is discuss and verified by computer simulations and experiments.

• 전력전자학회:학술대회논문집
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• 전력전자학회 2001년도 추계학술대회 논문집
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• pp.49-52
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• 2001

This paper presents a new partial excitation method of the moving magnet type linear synchronous motor(MMLSM) and proposes a new way of implementation for multi-mover MMLSM. Originally, partial excitation circuit which excites the coils only under the magnet is necessary for proper operation of MMLSM. In conventional partial excitation method there is inevitably impedance unbalance situation. So a new partial excitation method Is proposed to solve this impedance unbalance problem. Based on this partial excitation method, a novel control method for multi-mover MMLSM is proposed. The validity and performance of the proposed partial excitation method and multi-mover MMLSM is verified by experimental results.

• 한국전기전자재료학회논문지
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• 제19권4호
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• pp.391-397
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• 2006

We present investigations of a hybrid type superconducting fault current limiter (SFCL), which consists of transformers and resistive superconducting elements. The secondary windings of the transformer were separated into several electrically isolated circuits and linked inductively with each other by mutual flux, each of which has a superconducting current limiting element of $YBa_2Cu_3O_7$ (YBCO) stripes as a current limiting element. Simple connection in series of the SFCL elements tends to produce ill-timed quenching because of power dissipation unbalance between SFCL elements. Both electrical isolation and mutual flux linkage of the elements provides a solution to power dissipation unbalance, inducing simultaneous quench and current redistribution of the YBCO films. This design enables to increase the voltage rating of SFCL with given YBCO stripes.

• 전력전자학회:학술대회논문집
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• 전력전자학회 1999년도 전력전자학술대회 논문집
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• pp.41-44
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• 1999

The main purpose of the UPS is to supply independent and stable power to connected equipment. In installing and operating the UPS system, songle module, three phase UPS in more benefit than multi module, songle phase UPS in the point of volume and cost. However, when supplying Rectifier with output power form three phase UPS, by connecting auto-transformer, occurred harmonic and ripple current makes output filter damaged and leads to nonlinear current coasted by unbalance load. Therefor, in this paper the aim of concentring compound-wound transformer and harmonic filter is supplying liner current by reducing harmonic and ripple current and improving unbalance in voltage and distortion in current wave.