• Title/Summary/Keyword: distortion grid

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The Compensation of the Grid Current Distortion caused by the Grid Voltage Unbalance and Distortion for 3-Phase Bi-Directional DC to AC Inverter (3상 양방향 인버터의 계통전압 불평형 및 왜곡에 의한 계통전류 보상)

  • Yang, Seung-Dae;Kim, Seung-Min;Choi, Ju-Yeop;Choy, Ick;Song, Seung-Ho;Lee, Sang-Cheol;Lee, Dong-Ha
    • Journal of the Korean Solar Energy Society
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    • v.32 no.spc3
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    • pp.228-234
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    • 2012
  • This paper presents the algorithm of the 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 sugest simple method to solve the problem. PSIM simulation is used to validate the proposed algorithm.

A Compensation of the Grid Current Unbalance and Distortion caused by the Grid Voltage Unbalance and Distortion in 3-Phase Bi-Directional DC to AC Inverter (3상 양방향 인버터의 계통전압 불평형 및 왜곡에 의한 계통전류 불평형 및 왜곡 보상)

  • Yang, Seung-Dae;Kim, Seung-Min;Choi, Ju-Yeop;Choy, Ick;Song, Seung-Ho;Lee, Sang-Cheol;Lee, Dong-Ha
    • The Transactions of the Korean Institute of Power Electronics
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    • v.18 no.2
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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.

Control Method for Reducing the THD of Grid Current of Three-Phase Grid-Connected Inverters Under Distorted Grid Voltages

  • Tran, Thanh-Vu;Chun, Tae-Won;Lee, Hong-Hee;Kim, Heung-Geun;Nho, Eui-Cheol
    • Journal of Power Electronics
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    • v.13 no.4
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    • pp.712-718
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    • 2013
  • This paper proposes a control method for reducing the total harmonic distortion (THD) of the grid current of three-phase grid-connected inverter systems when the grid voltage is distorted. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for the minimum point of the THD. Both the gain and angle of the compensation voltage at the minimum point of the THD of the grid current are derived with the variation of cut-off frequencies of the hardware LPF. Simulation and experimental results show the validity of the proposed control methods.

Voltage Feedforward Control with Time-Delay Compensation for Grid-Connected Converters

  • Yang, Shude;Tong, Xiangqian
    • Journal of Power Electronics
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    • v.16 no.5
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    • pp.1833-1842
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    • 2016
  • In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter's grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

Study on the Influence of Grid Voltage Quality on SVG and the Suppression

  • Yi, Guiping;Hu, Renjie
    • Journal of international Conference on Electrical Machines and Systems
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    • v.3 no.2
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    • pp.155-161
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    • 2014
  • Industrial Static Var Generator (SVG) is typically applied at or near the load center to mitigate voltage fluctuation, flicker, phase unbalance, non-sine distortion or other load-related disturbance. Special attention is paid to the influence of grid voltage quality on SVG current, the non-sine distortion and unbalance of grid voltage causes not only the AC current distortion and unbalance but also the DC voltage fluctuation. In order to let the inverter voltage contain the fundamental negative sequence and harmonic component corresponding to the grid voltage, a new dual-loop control scheme is proposed to suppress the influence in this paper. The harmonic and negative sequence voltage decomposition algorithm and DC voltage control are also introduced. All these analyses can guide the practical applications. The simulation results verify the feasibility and effectiveness of the present control strategy and analyses.

Grid Current Control Scheme at Thee-Phase Grid-Connected Inverter Under Unbalanced and Distorted Grid Voltage Conditions (계통전압 왜곡 및 불평형시 3상 계통연계인버터의 계통전류제어 기법)

  • Tran, Thanh-Vu;Chun, Tae-Won
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.62 no.11
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    • pp.1560-1565
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    • 2013
  • This paper proposes the control method for compensating for unbalanced grid current and reducing a total harmonic distortion (THD) of the grid current at the three-phase grid-connected inverter systems under unbalancd and distorted grid voltage conditions. The THD of the grid current caused by grid voltage harmonics is derived by considering the phase delay and magnitude attenuation due to the hardware low-pass filter (LPF). The Cauchy-Schwarz inequality theory is used in order to search more easily for a minimum point of THD. Both the gain and angle of a compensation voltage at the minimum point of THD of the grid current are derived. The negative-sequence components in the three-phase unbalanced grid voltage are cancelled in order to achieve the balanced grid current. The simulation and experimental results show the validity of the proposed control methods.

Reduction of Grid Current Harmonic Distortion through a 6th Harmonic Control Method in Grid-Connected Three-Level NPC Inverters (계통연계형 3-레벨 NPC 인버터의 6차 고조파 제어 기법을 이용한 계통 전류 고조파 저감)

  • Sin, Jiook;Bak, Yeongsu;Park, Seong-Soo;Lee, Kyo-Beum
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.66 no.5
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    • pp.778-785
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    • 2017
  • This paper presents a control method for reducing the distortion of the grid current at a grid-connected three-level neutral point clamped (NPC) inverter. The grid current is distorted from the 5th and 7th harmonic components in the stationary frame current also the 6th harmonic component in the synchronous frame current. In this paper, the 6th harmonic component on synchronous frame is controlled by using all-pass filters (APFs) and proportional integral (PI) controllers for distortion of the grid side. When transformed the 6th harmonic component is controlled, the 5th and 7th harmonic components are reduced. The validity of the proposed control method is verified by simulation and experiment results using a 25kW three-level NPC inverter.

Alleviate Current Distortion of Dual-buck Inverter During Reactive Power Support (듀얼벅 인버터의 무효전력 보상 시 전류 왜곡 저감)

  • Han, Sanghun;Cho, Younghoon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.27 no.2
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    • pp.134-141
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    • 2022
  • This study presents a method for reducing current distortion that occurs when a dual-buck inverter generates reactive power. Dual-buck inverters, which are only capable of unity power factor operation, can generate reactive power capabilities by modifying a modulation technique. However, under non-unity power factor conditions, current distortion occurs at zero-crossing points of grid voltage and output current. This distortion is caused by parasitic capacitors, dead-time, and discontinuous conduction mode operation. This study proposes a modified modulation method to alleviate the current distortion at zero-crossing point of the grid voltage. A repetitive controller is applied to reduce this distortion of the output current. A 1 kVA prototype is built and tested. Simulation and experimental results demonstrate the effectiveness of the proposed method.

Optimal Localization through DSA Distortion Correction for SRS

  • Shin, Dong-Hoon;Suh, Tae-Suk;Huh, Soon-Nyung;Son, Byung-Chul;Lee, Hyung-Koo;Choe, Bo-Young;Shinn, Kyung-Sub
    • Progress in Medical Physics
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    • v.11 no.1
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    • pp.39-47
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    • 2000
  • In Stereotactic Radiosurgery (SRS), there are three imaging methods of target localization, such as digital subtraction Angiography (DSA), computed tomography (CT), magnetic resonance imaging (MRI). Especially, DSA and MR images have a distortion effect generated by each modality. In this research, image properties of DSA were studied. A first essential condition in SRS is an accurate information of target locations, since high dose used to treat a patient may give a complication on critical organ and normal tissue. Hut previous localization program did not consider distortion effect which was caused by image intensifier (II) of DSA. A neurosurgeon could not have an accurate information of target locations to operate a patient. In this research, through distortion correction, we tried to calculate accurate target locations. We made a grid phantom to correct distortion, and a target phantom to evaluate localization algorithm. The grid phantom was set on the front of II, and DSA images were obtained. Distortion correction methods consist of two parts: 1. Bilinear transform for geometrical correction and bilinear interpolation for gray level correction. 2. Automatic detection method for calculating locations of grid crosses, fiducial markers, and target balls. Distortion was corrected by applying bilinear transform and bilinear interpolation to anterior-posterior and left-right image, and locations of target and fiducial markers were calculated by the program developed in this study. Localization errors were estimated by comparing target locations calculated in DSA images with absolute locations of target phantom. In the result, the error in average with and without distortion correction is $\pm$0.34 mm and $\pm$0.41 mm respectively. In conclusion, it could be verified that our localization algorithm has an improved accuracy and acceptability to patient treatment.

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Visual Inspection of Tube Internal

  • Choi, Young-Soo;Cho, Jai-Wan;Kim, Chang-Hoi;Seo, Yong-Chil;Kim, Seung-Ho
    • 제어로봇시스템학회:학술대회논문집
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    • 2003.10a
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    • pp.789-792
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    • 2003
  • Pipe inspection has a great importance to ensure safety for the nuclear power plant. In this paper, we designed visual inspection module for the tube internal, which diameter is 15${\sim}$20mm. And we made inspection module which consisted of CCD camera and light. And the relation between image and real world coordinate is established. Image processing is performed to calculate mapping parameter and analyze the size of defect. For the calculation of mapping parameter, experiment is performed using grid type test pattern. Acquired image is processed to extract image coordinate. Edge detection, thresholding, median filtering and morphology filtering is applied to extract grid pattern. Extracted image coordinate is used to calculate image to real world mapping. Lens distortion was considered and corrected to get exact data. Coordinate transformation data is provided for the users to recognize easily. Experiment was performed using grid type test pattern, we extracted lens distortion parameter and real coordinate of defect point. Radial distortion of lens was corrected but tangential distortion was not considered. As continuum to this study, the tangential distortion of lens is considered and improvement of analy zing technique for the tube internal be explored continuously.

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