• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.22 no.5
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• pp.64-72
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• 2008

In the three phase four wire system, voltage unbalance caused by the unbalanced load operation, gives rise to current unbalance and de-rates by the increase of machine's loss and eventually enlarges power capacity and besides has a bad effect on power quality. Power capacitor has been used for the power factor correction of inductive load and the voltage stability of power system. And it uses instead of power side for magnetic excitation of induction motor. If voltage unbalance keeps up, it affects on voltage stress at the power capacitor and finally can be caused breakdown. In this paper, we analysed that voltage and current of power capacitor increases by the voltage unbalance factor and its stress is growing more and more.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.7
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• pp.343-350
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• 2005

Conventionally, for transferring the primary power to the secondary one, the high frequency series resonant converter has been widely used for the contactless power supply system. However, the high frequency series resonant converter has the disadvantages such as the low efficiency, the high voltage gain characteristics and deviation of the phase angle in the overall load range. To improve this disadvantages, In this paper, the characteristics of the high efficiency and unit voltage gain as well as in-phase are revealed in the proposed three-level LCLC (Inductor-Capacitor- Inductor-Capacitor) resonant converter. The results are verified on the simulation based on the theoretical analysis and the 4kW experimental Prototype.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.4
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• pp.763-769
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• 2009

A series voltage compensation(SVC) system is a power-electronics controller that can protect sensitive loads from disturbance in the supply system. Especially, voltage sags are considered the dominant disturbances affecting the power quality. This paper dealt with a system of off-line type voltage sag compensation by using a bi-directional DC/DC converter of environmentally friendly ultra-capacitor. This capacitor is attached to the DC link of SVC through the high-efficiency DC/DC converter in order to compensate the DC link voltage drop during short-term power interruption as voltage sags. Therefore, in this paper, a DC/DC converter to control high-efficiency energy of ultra-capacitor and voltage sag detection algorithm of off-line type SVC systems are newly introduced. According to the results of experimental of prototype system, it is verified that the proposed system has effectiveness of voltage sag compensation using an ultra-capacitor.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.59 no.4
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• pp.372-376
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• 2010

Electrolytic capacitors have been widely used in power electronics system because of the features of large capacitance, small size, high-voltage, and low-cost. Electrolytic capacitors, which is most of the time affected by aging effect, plays a very important role for the power electronics system quality and reliability. Therefore it is important to estimate the parameter of an electrolytic capacitor to predict the failure. The estimation of the equivalent series resistance(ESR) is important parameter in life condition monitoring of electrolytic capacitor. This paper proposes a simple technique to measure the ESR of an electrolytic capacitor. This method uses a switching DC/DC boost converter to measure the DC Bus capacitor ESR of power converter. Main advantage of the proposed method is very simple in technique, consumes very little time and requires only simple instruments. Simulation results are shown to verify the performance of the proposed method.

• Journal of Power Electronics
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• v.12 no.1
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• pp.193-200
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• 2012

Previous publications regarding the design and specifications of the interface inductor and the DC side capacitor for a STATCOM usually deal with the interface inductor and the DC side capacitor only. They seldom pay attention to the influences of the interface inductor and capacitor on the performance of a STATCOM system. In this paper a detailed analysis of influence of the interface inductor and the DC side capacitor on a STATCOM system and the corresponding design considerations is presented. Phase and amplitude control is considered as the control strategy for the STATCOM. First, a model of a STATCOM system is carried out. Second, through frequency domain methods, such as transfer functions and Bode plots, the influence of the interface inductor and the DC side capacitor on the stability and filtering characteristics of the STATCOM are extensively investigated. Third, according to this analysis, the design considerations based on the phase margin for the interface inductor and the DC side capacitor are discussed, which leads to parameters that are different from those of the traditional design.

• Journal of Power Electronics
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• v.10 no.1
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• pp.27-33
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• 2010

This paper presents a bidirectional DC-DC converter suitable for low-voltage super capacitor-based electric energy storage systems. The DC-DC converter presented here consists of a full-bridge circuit and a current-fed push-pull circuit with a high frequency (HF) transformer-link. In order to reduce the device-conduction losses due to the large current of the super capacitor as well as unnecessary ringing, synchronous rectification is employed in the super capacitor-charging mode. A wide range of voltage regulation between the battery and the super capacitor can be realized by employing a Phase-Shifting (PS) Pulse Width Modulation (PWM) scheme in the full-bridge circuit for the super capacitor charging mode as well as the overlapping PWM scheme of the gate signals to the active power devices in the push-pull circuit for the super capacitor discharging mode. Essential performance of the bidirectional DC-DC converter is demonstrated with simulation and experiment results, and the practical effectiveness of the DC-DC converter is discussed.

• Journal of Power Electronics
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• v.15 no.6
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• pp.1468-1479
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• 2015

Renewable energy resources such as wind and photovoltaic power generation systems demand a high step-up DC-DC converters to convert the low voltage to commercial grid voltage. However, the high step-up converter using a transformer has limitations of high voltage stresses of switches and diodes when the transformer winding ratio increases. Accordingly, conventional studies have been applied to series-connect multioutput converters such as forward-flyback and switched-capacitor flyback to reduce the transformer winding ratio. This paper proposes new single-ended converter topologies of an isolation type and a non-isolation type to improve power efficiency, cost-effectiveness, and output ripple. The first proposal is an isolation-type charge-pump switched-capacitor flyback converter that includes an extreme-ratio isolation switched-capacitor cell with a chargepump circuit. It reduces the transformer winding number and the output ripple, and further improves power efficiency without any cost increase. The next proposal is a non-isolation charge-pump switched-capacitor-flyback tapped-inductor boost converter, which adds a charge-pump-connected flyback circuit to the conventional switched-capacitor boost converter to improve the power efficiency and to reduce the efficiency degradation from the input variation. In this paper, the operation principle of the proposed scheme is presented with the experimental results of the 100 W DC-DC converter for verification.

• Journal of Power Electronics
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• v.16 no.5
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• pp.1928-1938
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• 2016

The three-phase four-wire shunt active power filter (APF) is an effective method to solve the harmonic problem in three-phase four-wire power systems. In addition, it has two possible topologies, a four-leg inverter and a three-leg inverter with a split-capacitor. There are some studies investigating DC-link voltage control in three-phase four-wire APFs. However, when compared to the four-leg inverter topology, maintaining the balance between the DC-link upper and lower capacitor voltages becomes a unique problem in the three-leg inverter with a split-capacitor topology, and previous studies seldom pay attention to this fact. In this paper, the influence of the balance between the two DC-link voltages on the compensation performance, and the influence of the voltage balance controller on the compensation performance, are analyzed. To achieve the balance between the two DC-link capacitor voltages, and to avoid the adverse effect the voltage balance controller has on the APF compensation performance, a new DC-link voltage balance control strategy for the three-phase four-wire split-capacitor APF is proposed. Representative simulation and experimental results are presented to verify the analysis and the proposed DC-link voltage balance control strategy.

• Journal of IKEEE
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• v.18 no.3
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• pp.313-319
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• 2014

The objectives of power system operations are to preserve system stability and reliability as well as to supply proper electric power. For an activation of these objectives, voltage and reactive power should be considered. There are a number of types about reactive power sources, and an insertion of shunt capacitor banks are one of the method to support bus voltage adjacent. This paper includes the design procedure to determine the hybrid type capacitor bank configurations on power system to improve stability and reliability. This procedure includes the capacitor bank capacity calculation, reactor type selection, and reactor capacity calculation. The total capacity calculation of capacitor bank is based on the reactive power margin which is calculated through system studies such as, contingency analysis and Q-V analysis. In the second step, the reactor type and its capacity can be determined through the harmonic analysis. This paper shows that the harmonics are decreased by the proposed hybrid type capacitor bank, especially 5th and 7th harmonics.

• Journal of Power Electronics
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• v.12 no.1
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• pp.172-180
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• 2012

Z-source inverters (ZSI) are used to realize both DC voltage boost and DC-AC inversion in single stage with a reduced number of power switching devices. A traditional MPPT control algorithm provides a shoot-through interval which should be inserted in the switching waveforms of the inverter to output the maximum power to the Z-network. At this instant, the voltage across the Z-source capacitor is equal to the output voltage of a PV array at the maximum power point (MPP). The control of the Z-source capacitor voltage beyond the MPP voltage of a PV array is not facilitated in traditional MPPT algorithms. This paper presents a unified MPPT control algorithm to simultaneously achieve MPPT as well as Z-source capacitor voltage control. Development and implementation of the proposed algorithm and a comparison with traditional results are discussed. The effectiveness of the proposed unified MPPT control strategy is implemented in Matlab/Simulink software and verified by experimental results.