• The Transactions of The Korean Institute of Electrical Engineers
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• v.56 no.3
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• pp.465-471
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• 2007

The one step type pole and two step type pole are used in KEPCO's distribution system. The neutral current increases in three-phase four-wire distribution system due to unbalanced load. Usually, power line and communication line are installed at contiguity by effect of topography in Korea. To this end, the damages such as electrostatic induction, electromagnetic induction and harmonic induction generated by induced voltage and current are occured in power line and communication line. This paper calculates the neutral current in KEPCO's distribution system using EMTP by composing various simulated conditions. Also, these results are verified by vector analysis.

• Journal of Power Electronics
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• v.17 no.3
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• pp.704-715
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• 2017

For three-phase synchronization applications, the synchronous reference frame phase-locked loop (SRF-PLL) is probably the most widely used technique due to its ease of implementation and satisfactory phase tracking performance under ideal grid conditions. However, under unbalanced and distorted grid conditions, its performance tends to worsen. To deal with this problem, a variety of filtering stages have been proposed and used in SRF-PLLs for the rejection of disturbance components at the cost of degrading the dynamic performance. In this paper, to improve dynamic performance without compromising the filtering capability, an effective hybrid filtering stage is proposed and incorporated into the inner loop of a quasi-type-1 PLL (QT1-PLL). The proposed filtering stage is a combination of a moving average filter (MAF) and a modified delay signal cancellation (DSC) operator in cascade. The time delay caused by the proposed filtering stage is smaller than that in the conventional MAF-based and DSC-based PLLs. A small-signal model of the proposed PLL is derived. The stability is analyzed and parameters design guidelines are given. The effectiveness of the proposed PLL is confirmed through experimental results.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1869-1883
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• 2016

In recent years, some converter structures and analyzing methods for the voltage regulation of stand-alone self-excited induction generators (SEIGs) have been introduced. However, all of them are concerned with the three-phase voltage control of three-phase SEIGs or the single-phase voltage control of single-phase SEIGs for the operation of these machines under balanced load conditions. In this paper, each phase voltage is controlled separately through separated converters, which consist of a full-bridge diode rectifier and one-IGBT. For this purpose, the principle of the electronic load controllers supported by fuzzy logic is employed in the two-different proposed converter structures. While changing single phase consumer loads that are independent from each other, the output voltages of the generator are controlled independently by three-number of separated electronic load controllers (SELCs) in two different mode operations. The aim is to obtain a rated power from the SEIG via the switching of the dump loads to be the complement of consumer load variations. The transient and steady state behaviors of the whole system are investigated by simulation studies from the point of getting the design parameters, and experiments are carried out for validation of the results. The results illustrate that the proposed SELC system is capable of coping with independent consumer load variations to keep output voltage at a desired value for each phase. It is also available for unbalanced consumer load conditions. In addition, it is concluded that the proposed converter without a filter capacitor has less harmonics on the currents.

• Proceedings of the KIPE Conference
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• 2001.07a
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• pp.172-176
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• 2001

In this paper, a new detection algorithm of faulted voltages under the unbalanced condition and a control algorithm of the instantaneous voltage sag corrector (IVSC) are proposed. To quantify the unbalance under fault conditions, the voltages are decomposed into two balanced three-phase systems using the symmetrical components of positive and negative sequence voltages, which is defined by magnitude factor (MF) and unbalance factor (UF). New control algorithm based on MF and UF values for instantaneous voltage compensation are proposed and verified through the PSCAD/EMTDC simulation and experimental results.

• The Transactions of the Korean Institute of Power Electronics
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• v.9 no.5
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• pp.420-429
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• 2004

This paper proposes a novel current control strategy on active power filters using PQR instantaneous power theory which can compensate the line current harmonics and the neutral line current under the unbalanced and/or distorted source conditions in three-phase four-wire systems. The characteristics of the inverter ac filters are analyzed and a novel digital controller are proposed to overcome the inherent time delay problem in digital controllers with designed control gain in this paper. The proposed current control method is based on a sinusoidal PWM for fully-digital implementation compared with a conventional hysteresis PWM. PSiM simulation results verify the good performance of the proposed current control strategy on shunt type APFs.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.199-206
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• 2010

Matrix converter is an energy conversion device of controlled power semiconductor switches that directly connects the three-phase source to the three-phase load. With no dc-link components for energy storage in the matrix converter the input current depends directly upon the load currents and the switch state of the converter. Therefore the unbalanced and distorted input voltages can result in unwanted output harmonic currents. This paper presents a current compensator based on neural network to improving output current quality for matrix converter under abnormal input voltage conditions. The effectiveness and feasibility of the proposed technique has been proven through numerical simulations and experimental tests.

• Journal of Power Electronics
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• v.5 no.2
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• pp.109-119
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• 2005

This paper deals with the performance analysis of static compensator (STATCOM) based voltage regulator for self­excited induction generators (SEIGs) supplying balanced/unbalanced and linear/ non-linear loads. In practice, most of the loads are linear. But the presence of non-linear loads in some applications injects harmonics into the generating system. Because an SEIG is a weak isolated system, these harmonics have a great effect on its performance. Additionally, SEIG's offer poor voltage regulation and require an adjustable reactive power source to maintain a constant terminal voltage under a varying load. A three-phase insulated gate bipolar transistor (IGBT) based current controlled voltage source inverter (CC- VSI) known as STATCOM is used for harmonic elimination. It also provides the required reactive power an SEIG needs to maintain a constant terminal voltage under varying loads. A dynamic model of an SEIG-STATCOM system with the ability to simulate varying loads has been developed using a stationary d-q axes reference frame. This enables us to predict the behavior of the system under transient conditions. The simulated results show that by using a STATCOM based voltage regulator the SEIG terminal voltage can be maintained constant and free from harmonics under linear/non linear and balanced/unbalanced loads.

• Journal of Power Electronics
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• v.19 no.1
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• pp.89-98
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• 2019

This paper analyzes the input side performance of a conventional three-phase to single-phase matrix converter (3-1MC). It also presents the input-side waveform quality under this topology. The suppression of low-frequency input current harmonics is studied using the 3-1MC plus capacitance compensation unit. The constraint between the modulation function of the output and compensation sides is analyzed, and the relations among the voltage utilization ratio and the output compensation capacitance, filter capacitors and other system parameters are deduced. For a 3-1MC without large-capacity energy storage, the system performance is susceptible to input voltage imbalance. This paper decouples the inner current of the 3-1MC using a Lyapunov function in the input positive and negative sequence bi-coordinate axes. Meanwhile, the outer loop adopts a voltage-weighted synthesis of the output and compensation sides as a cascade of control objects. Experiments show that this strategy suppresses the low-frequency input current harmonics caused by input voltage imbalance, and ensures that the system maintains good static and dynamic performances under input-unbalanced conditions. At the same time, the parameter selection and debugging methods are simple.

• Journal of the Korean Society of Safety
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• v.26 no.2
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• pp.26-31
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• 2011

In this paper, the safety diagnosis using thermal image analysis is described for power equipments. The conventional three-phase comparison method has only provided the results of thermal comparison for the equipments. The proposed method defines the conditions of poor connection by visual checks, and supports the criteria with each thermal rise step. As a result, the thermal difference from $5^{\circ}C$ to $10^{\circ}C$ meant the warning state. In addition, the thermal difference more than $10^{\circ}C$ meant that the connection status was unbalanced. In this case, the countermeasure might be the internal load distribution. If the thermal difference more than $20^{\circ}C$ is observed, it means a hot spot at the poor connection. If the hot spot is observed all over the surface, its cause was the unbalanced load, which made the conductive parts discolored and raised the possibility of oxidization or $Cu_2O$ generation. This diagnostic technology employing thermal image analysis method can be directly applied in the field and ensures the safety of equipments.

• Journal of Industrial Technology
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• v.25 no.B
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• pp.203-210
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• 2005

The PWM(Pulse Width Modulated) converter for the AC to DC rectification has become attractive in the industrial variable-speed drive application and the electric utilities due to the following benefits: Nearly the sinusoidal input current with unity power factor; Controllable DC link voltage; Bidirectional power flow. This paper presents a quantitative analysis of single and three phase PWM converter's input and output characteristics as a function of the input filter inductance under balanced and unbalanced conditions. Also, its performance under the supply voltage including harmonics is investigated by simulation with Matlab Simlulink and experiments. These results provide a reference for selecting the reasonable converter's input filter inductance for given harmonics or power factor criterion.