• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.28 no.11
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• pp.58-67
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• 2014

A grid-connected inverter used for renewable energy resources produces harmonic components in the switching frequency. To effectively reduce switching harmonic components, several types of filter are generally used in the output stage of the grid-connected inverter. Many research works on LCL filter design have been done to maintain the performance with low cost. However, it is not easy to make the filter design be economical and optimal due to the varying characteristic of magnetic core and redundancy design by experience. In this paper, a design method for a LCL filter is presented through the inductor optimization scheme in view of the size and cost when the inductor is manufactured using the magnetic core. The effectiveness is verified through tests using a 3kW grid-connected inverter by simulations and experiments.

• Journal of Electrical Engineering and Technology
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• v.12 no.1
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• pp.217-224
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• 2017

The analysis and design process of the LCL filter with passive damping circuits for three-phase grid-connected inverter are presented based on the generalized model of LCL filter. Several types of the passive damping circuits in previous studies could be compared and analyzed by using the generalized model considering various design criteria of passive damping circuits. According to the analysis in this paper, a reasonable configuration of passive damping circuits for three-phase grid-connected inverters is proposed. The validity of the proposed design process is verified by informative simulation and experimental results.

• Journal of Electrical Engineering and Technology
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• v.12 no.5
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• pp.1945-1954
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• 2017

In recent years, several LCL filter design methods for different converter topologies have been published, many of which use analytical expressions to calculate the ideal converter AC voltage harmonic spectrum. This paper presents the LCL filter design methodology but the focus is on presentation and validation of the non-iterative filter design method for a grid-connected three-phase two-level PWM-VSC. The developed method can be adapted for different converter topologies and PWM algorithms. Furthermore, as a starting point for the design procedure, only the range of PWM carrier frequencies is required instead of an exact value. System nonlinearities, usually omitted from analysis have a significant influence on VSC AC voltage harmonic spectrum. In order to achieve better accuracy of the proposed procedure, the system nonlinear model is incorporated into the method. Optimal filter parameters are determined using the novel cost function based on higher frequency losses of the filter. An example of LCL filter design for a 40 kVA grid-connected PWM-VSC has been presented. Obtained results have been used to construct the corresponding laboratory setup and measurements have been performed to verify the proposed method.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.6
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• pp.538-541
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• 2016

This paper proposes an LCL-filter design for space vector pulse width modulation (SVM) in grid-connected three-phase inverter systems. Although there are a several studies in progress, the existing methods are erroneous because they do not focus on the other switching methods. This paper presents the design methodology for an LCL-filter that is optimized for SVM switching operations. The design procedure for the LCL-filter is presented step-by-step. The inverter-side inductor was determined by an analysis of the ripple components, mathematically. Based on the reactive power absorption ratio, the filter capacitor was determined. The grid-side inductor was determined by the ripple attenuation factor of the output current. Experimental results verify the validity of the design method for the LCL-filter.

• Journal of the Korean Society of Radiology
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• v.10 no.5
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• pp.313-320
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• 2016

This research has been conducted to investigate the method of reducing patients' radiation exposure during X-ray imaging of Both Hip Ap examination by removing the grid. When using the grid with 60 kV and a non-filter, the Entrance Surface Dose was 4.77 mGy, and the result was highest and 34 times higher than the lowest measurement when removing the grid with 90 kV, and 0.3 mmCu filter. Based on the ICRP Pub. 60 at the level of 70 kV, the Effective Dose of testis and ovary was 0.255 mSv when using the grid, and that result was approximately 5.2 times higher than the 0.049 mSv when removing the grid. Based on the ICRP Pub. 103 at the level of 70 kV, the Effective Dose of testis and ovary was 0.090 mSv when using the grid, and that result was approximately 4.5 times higher than the 0.020 mSv when removing the grid. When using the grid, the range of Exposure Index was 671 to 782, and when removing the grid, the range of Exposure Index was 513 to 606, and both results were at optimal exposure conditions and valid diagnostic imaging after evaluations. Therefore, removing the grid during X-ray imaging of Both Hip Ap will help reduce patients radiation exposure.

• The Transactions of the Korean Institute of Power Electronics
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• v.21 no.2
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• pp.168-174
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• 2016

In this paper, current control using PI controller in the synchronous reference frame is analyzed through the relationship among bandwidth, resonance frequency, and sampling frequency in the grid-connected inverter with LCL filter. Stability is investigated by using bode plot in frequency domain and root locus in discrete domain. The feedback variable is the grid current, which is regulated by the PI controller in the synchronous reference frame. System delay is modeled as 1.5Ts, which contains computational and PWM modulator delay. Two resonance frequencies are given at 815 Hz and 3.16 kHz from LCL filter parameters. Sufficient phase and gain margins can be obtained to guarantee stable current control, in case that resonance frequency is above one-sixth of the sampling frequency. Unstable current control is performed when resonance frequency is below one-sixth of the sampling frequency. Analysis results of stability from frequency response and discrete response is the same regardless of resonance frequency. Finally, stability of current control based on theoretical analysis is clearly verified through simulation and experiment in grid-connected inverters with LCL filter.

• Journal of the Korean Society for Precision Engineering
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• v.30 no.3
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• pp.308-316
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• 2013

This paper proposes an observation model for a particle filter-based localization using a sonar grid map. The proposed model estimates a predicted observation by considering the properties of a sonar sensor which has a large angular uncertainty. The proposed model searches a grid which has the highest probability to reflect a sonar beam using the following procedures; (1) the reliable area of a single sonar data is determined using the footprint association model; (2) the detection probability of each grid cell in a sonar beam coverage in estimated. The proposed model was applied to the particle filter based localization, and was verified by experiments in indoor environments.

• Journal of Power Electronics
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• v.11 no.4
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• pp.456-463
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• 2011

Grid-connected converters have widely adopted LCL filters to acquire high harmonic suppression. However, the LCL filter increases the system order so that the design of the system stability would be complicated. Recently, sole-loop control strategies have been used for grid-connected converters with L or LC filters. But if the sole-loop control is directly transplanted to grid-connected converters with LCL filters, the systems may be unstable. This paper presents a novel dual-loop power control strategy composed of a power outer loop and a current inner loop. The outer loop regulates the grid-connected power. The inner loop improves the system stability margin and suppresses the resonant peak caused by the LCL filter. To obtain the control variables, a single-phase current detection is proposed based on PQ theory. The system transfer function is derived in detail and the influence of control gains on the system stability is analyzed with the root locus. Simulation and experimental results demonstrate the feasibility of the proposed control.

• Proceedings of the KIEE Conference
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• 1993.07b
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• pp.1016-1019
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• 1993

A low-pass L-C filter has been adopted for conversion of frequency variable 3 phase PWM waveform to a grid power line and it is used for attenuation of harmonics in the VSI PWM Inverter. A optimum design of the L, C parameters was derived. The result of the study show that the inductor L seems to have a certain air gap for linear I-V characteristics and the resonant frequency of the filter must be set below the 5th harmonics of the grid power line. Further, the voltage drop in L must be within a adequate limit compared to grid power voltage.

• The Transactions of the Korean Institute of Power Electronics
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• v.23 no.6
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• pp.440-445
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• 2018

This study proposes a novel control and design method for a grid-connected inverter with an LCL filter without damping. The current resonance phenomenon must be considered when designing the grid-connected inverter system with an LCL filter. Passive or active damping is used in the inverter system to reduce the resonant current. However, passive damping reduces the efficiency of the system, and active damping methods are complex. If the resonant frequency is in a specific region, then the system will be unstable. This study examines the process of stabilizing the entire region without resonant damping. The validity of the proposed method is verified through simulation and experimentation.