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He J.,Changzhi Power Supply Company | Zhou X.-S.,Tianjin University of Technology | Chen S.-Z.,Changzhi Power Supply Company | Lu Y.-H.,Changzhi Power Supply Company | And 2 more authors.
Gaodianya Jishu/High Voltage Engineering | Year: 2011

Cascaded dynamic voltage restorer (DVR) which is an effective setup in modifying the power quality problems caused by voltage sags has been applied in the power system. Thereby, the carrier phase-shifted modulation technology was used in the cascaded multilvevel inverter. A 5 MVA uncoupled transformer 11-level cascaded DVR was researched for the 6 kV power system. The double loop control strategy was designed which employed a slow outer voltage loop and a fast inner current loop. Voltage sag was simulated at a random time when multi-level DVR was under the control of any control strategy. Results show that the DVR based on voltage shifted pulse width modulation technology can greatly increase the inverter switching frequency and decrease the harmonic distortion and variation rate of voltage, and the system damping ratio and stability and error can be regulated by adjusting relevant parameters. The application of this technology can greatly enhance the performance indicators of DVR and has a high practical value.

Meng H.,Shanxi Electric Power Research Institute | Liang J.,Shanxi Electrical Power Corporation | Xue L.,Shanxi Electric Power Research Institute | Zhou G.,Shanxi Electrical Power Corporation | And 6 more authors.
Dianwang Jishu/Power System Technology | Year: 2013

To investigate the cause of three-phase current unbalance of triple-circuits of 500kV transmission lines from Changzhi to Jiu'an in Shanxi province thoroughly and optimize the renovation scheme, using electromagnetic transient program PSCAD and structural model of the transmission lines different conductor arrangements were simulated and the optimal renovation scheme was recommended, and satisfied renovation effects were achieved. It was discovered from both simulation results and renovation process that for non-transposed double-circuit transmission lines on the same tower, within the 36 kinds of conductor arrangements the minimum current unbalance could be attained by six kinds of reverse phase sequence conductor arrangements and the current unbalance degrees of the six reverse phase sequence conductor arrangements are basically the same; however under the parallel operation of non-transposed double-circuit transmission line on the same tower with incomplete-transposed single transmission line, due to the affection of the single transmission line there were obvious differences among the six renovation schemes adopting reverse phase sequence conductor arrangements, thus there was the optimal one that could be selected.

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