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

Control Method for Reducing the THD of Grid Current of Three-Phase Grid-Connected Inverters Under Distorted Grid Voltages Thanh-Vu Tran*, Tae-Won Chun†, Hong-Hee Lee*, Heung-Geun Kim**, and Eui-Cheol Nho*** *†Dept. of Electrical Engineering, University of Ulsan, Ulsan, Korea **Dept. Of Electrical Engineering, Kyungpook National University, Daegu, Korea ***Dept. of Electrical Engineering, Pukyong National University, Busan, Korea
Abstract 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.
LINK
 http://jpe.or.kr/archives/view_articles.asp?seq=772

The Effect of Transformer Leakage Inductance on the Steady State Performance of Push-pull based Converter with Continuous Current Qian Chen†, Trillion Q. Zheng*, Yan Li*, and Tiancong Shao*

The Effect of Transformer Leakage Inductance on the Steady State Performance of Push-pull based Converter with Continuous Current Qian Chen†, Trillion Q. Zheng*, Yan Li*, and Tiancong Shao* †*School of Electrical and Engineering, Beijing Jiaotong University, Beijing, China Abstract As a result of the advantages such as high efficiency, continuous current and high stability margin, push-pull converter with continuous current (PPCWCC) is competitive for battery discharge regulator (BDR) which plays an important role in power conditioning unit (PCU).Leakage inductance yields current spike in low-ripple current of PPCWCCs. The operating modes are added due to leakage inductance. Therefore the steady state performance is affected, which is embodied in the spike of low-ripple current. PPCWCCs which are suitable for BDR can be separated into three types by current spike characteristics. Three representative topologies IIs1, IIcb2 and Is3 are analyzed in order to investigate the factors on the magnitude and duration of spike. Equivalent current sampling method (ECSM) which eliminates the sampling time delay and achieves excellent dynamic performance is adopted to prevent the spike disturbance on current sampling. However, ECSM reduces the sampling accuracy and telemetry accuracy due to neglecting the spike. In this paper, ECSM used in PPCWCCs is summarized. The current sampling error is analyzed in quality and quantity, which provides the foundation for offsetting and enhancing the telemetry accuracy. Finally, current sampling error rate of three topologies is compared by experiment results, which verify the theoretical analysis.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=735

Design of an LCL-Filter for Three-Parallel Operation of Power Converters in Wind Turbines Hae-Gwang Jeong*, Dong-Keun Yoon**, and Kyo-Beum Lee†

Design of an LCL-Filter for Three-Parallel Operation
of Power Converters in Wind Turbines
Hae-Gwang Jeong*, Dong-Keun Yoon**, and Kyo-Beum Lee†
†*Department of Electrical and Computer Engineering, Ajou University, Suwon, Korea
**Research Group, LG Innotek Co., Ltd., Ansan, Korea

This paper proposes a design scheme for an LCL-filter used for the three-parallel operation of the power converters in high-capacity wind turbines. The designs of the power devices and grid connected filter are difficult due to the high level voltages and currents in huge-capacity wind turbines. To solve these problem, this paper presents three-parallel operation and LCL-filter design techniques optimized by parallel operation. Furthermore, the design of an inverter side inductance of the LCL-filter is discussed in detail considering the switching modulation method. Simulation and experimental results demonstrate the validity of the designed filter and wind turbines.
LINK
http://jpe.or.kr/archives/view_articles.asp?seq=744
https://www.mediafire.com/?f2tlal6acrdao3a

GRAU DE PROTEÇÃO IP PARA EQUIPAMENTOS ELÉTRICOS

Parallel Operation of Three-Phase Four wire UPS using Droop Control ( Hyunseob Kim․Jungho Han․Joong-Ho Song )

Parallel Operation of Three-Phase Four wire UPS using Droop Control

* Main author：Dept. of Railway Electrical and
Signaling Engineering, Seoul National
University of Science and Technology,
Candidate of MS
** Corresponding author：Dept. of Electrical and
Information Engineering, Seoul National
University of Science and Technology,
Professor
Tel：02-970-6415, Fax：02-978-2754
E-mail：joongho@seoultech.ac.kr
 Abstract
A new droop control method which can be applied to 3-phase 4-wire uninterruptible power supply is
proposed in this paper. The droop control method for parallel operation is very attractive one as UPS
parallel operation can be carried out without any data communication devices provided among UPS
systems connected, but it reportedly shows a PnP(plug-and-play) problem. A basic reason why a
circulating current could flow among parallel-connected UPS systems is clearly investigated as well
when droop-controlled-ups systems are operated in the manner of PnP. The proposed algorithm is
deduced from the investigated result and is basically structured to keep a balanced frequency and
balanced voltage profile against power variation. This paper shows that balanced parallel operation of
droop control method can be obtained under unbalanced load as well as balanced load conditions .when PnP operation is needed and load change occurs.
LINK
http://www.koreascience.or.kr/article/ArticleFullRecord.jsp?cn=JMJGCE_2013_v27n4_88

https://www.mediafire.com/?gyedgrq3fd38alx