scholarly journals Control Strategies of Full-Voltage to Half-Voltage Operation for LCC and Hybrid LCC/MMC based UHVDC Systems

Energies ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 742 ◽  
Author(s):  
Gen Li ◽  
Wei Liu ◽  
Tibin Joseph ◽  
Jun Liang ◽  
Ting An ◽  
...  
Keyword(s):  
High Voltage ◽  
Low Voltage ◽  
Control Strategies ◽  
Control Process ◽  
Voltage Control ◽  
Load Shedding ◽  
Long Distance ◽  
High Voltage Direct Current ◽  
Bulk Power ◽  
The Time Domain

With the increasing demand of transmitting bulk-power over long-distance, the ultra high-voltage direct-current (UHVDC) transmission systems become an attractive option. Nowadays, not only the line commutated converter (LCC) based systems, but also the modular multilevel converter (MMC) based systems have reached UHVDC levels. The converter stations of UHVDC systems normally utilize two series-connected valve-groups to reduce the difficulties of device manufacturing and transportation. This high-voltage and low-voltage valve-group configuration allows the UHVDC systems to achieve a full-voltage to half-voltage operation which increases the flexibility of the systems. However, the existing research only focuses on the full-voltage to half-voltage control of LCC-UHVDC systems. The control strategies for hybrid LCC/MMC UHVDC systems are underresearched. Moreover, the approaches to reduce the load-shedding caused by the full-voltage to half-voltage control for both LCC and hybrid LCC/MMC based UHVDC systems have not been investigated. In this paper, full-voltage to half-voltage control strategies for both LCC and hybrid LCC/MMC based UHVDC systems have been proposed. Moreover, to avoid load-shedding caused by the half-voltage operation, a power rescheduling method that re-sets the power references of the half-voltage operating and full-voltage operating poles has been proposed. The proposed full-voltage to half-voltage control strategies and power rescheduling method can achieve a stable and fast control process with a minimum power loss. The proposed methods have been verified through the time-domain simulations conducted in PSCAD/EMTDC.

scholarly journals Novel Enhanced Modular Multilevel Converter for High-Voltage Direct Current Transmission Systems

Energies ◽  
2020 ◽  
Vol 13 (9) ◽  
pp. 2257
Author(s):  
Dimitrios Vozikis ◽  
Fahad Alsokhiry ◽  
Grain Philip Adam ◽  
Yusuf Al-Turki
Keyword(s):  
High Voltage ◽  
Low Voltage ◽  
Modular Multilevel Converter ◽  
Multilevel Converter ◽  
Medium Voltage ◽  
High Voltage Direct Current ◽  
Current Transmission ◽  
The Cost ◽  
Voltage Harmonics ◽  
Chain Links

This paper proposes an enhanced modular multilevel converter as an alternative to the conventional half-bridge modular multilevel converter that employs a reduced number of medium-voltage cells, with the aim of improving waveforms quality in its AC and DC sides. Each enhanced modular multilevel converter arm consists of high-voltage and low-voltage chain-links. The enhanced modular multilevel converter uses the high-voltage chain-links based on medium-voltage half-bridge cells to synthesize the fundamental voltage using nearest level modulation. Although the low-voltage chain-links filter out the voltage harmonics from the voltage generated by the high-voltage chain-links, which are rough and stepped approximations of the fundamental voltage, the enhanced modular multilevel converter uses the nested multilevel concept to dramatically increase the number of voltage levels per phase compared to half-bridge modular multilevel converter. The aforementioned improvements are achieved at the cost of a small increase in semiconductor losses. Detailed simulations conducted in EMPT-RV and experimental results confirm the validity of the proposed converter.

Medium and low voltage control strategies for a smart distribution grid

2016 ◽  
Author(s):  
Kamil Korotkiewicz ◽  
Philippe Steinbusch ◽  
Marcel Ludwig ◽  
Felix Dorsemagen ◽  
Marcus Stotzel ◽  
...  
Keyword(s):  
Low Voltage ◽  
Control Strategies ◽  
Voltage Control ◽  
Distribution Grid ◽  
Smart Distribution Grid

scholarly journals DESIGN AND CONSTRUCTION OF A LOW-COST 30KV VARIABLE DC POWER SUPPLY UNIT

2020 ◽  
pp. 3666-3673
Author(s):  
Bolarinwa H.S. ◽  
Fajingbesi F.E. ◽  
Yusuf A. ◽  
Animasahun L. O. ◽  
Babatunde Y. O.
Keyword(s):  
High Voltage ◽  
Power Supply ◽  
Low Voltage ◽  
High Reliability ◽  
Low Cost ◽  
Scientific Data ◽  
High Voltage Power Supply ◽  
Technology Application ◽  
High Voltage Direct Current ◽  
Current Voltage

A high voltage power supply is a key component in the advancement of science and technology. Application of high voltage power supply requires careful attention to critical variables such as voltage ripple, long and shortterm stability, repeatability and accuracy. These are important factors in the consideration of reliable scientific data. This paper presents the design of a low-cost high voltage power supply from the off-the-shelf electronics components to meet the high-end requirement of high voltage power supply. A 30kV, 63.8mA maximum power supply was constructed at the Fountain University electronics workshop. This high voltage directs current (HVDC) power supply was built around three basic compartments that include an adjustable low voltage power supply (LVPS), a high frequency oscillator, and a line output transformer (LOPT) using flyback transformer, NE555timer, BU508D BJT, and other off-the-shelf components. The current-voltage relationship at the output of the constructed High Voltage Direct Current was found to be linear. This power source will serve any high DC voltage applications such as electrospinning. The constructed 30kV power supply has been tested in the electrospinning laboratory of the Center for Energy Research and Development (CERD) Obafemi Awolowo University (OAU) Ile-Ife. The unit successfully electrospun Zinc-Titaninm polymeric solution into fibers at about 8 kV. The importance of this fabricated device is its high reliability despite its low cost and capability to produce different magnitude of high voltage DC.

scholarly journals Feasibility Evaluation on Elimination of DC Filters for Line-Commutated Converter-Based High-Voltage Direct Current Projects in New Situations

Energies ◽  
2021 ◽  
Vol 14 (18) ◽  
pp. 5770
Author(s):  
Xiaodong Li ◽  
Zheng Xu
Keyword(s):  
High Voltage ◽  
Direct Current ◽  
Power Transmission ◽  
Rapid Development ◽  
Maintenance Cost ◽  
Attractive Alternative ◽  
Stable Operation ◽  
Long Distance ◽  
High Voltage Direct Current ◽  
Feasibility Evaluation

The line-commutated converter (LCC)-based high voltage direct current (HVDC) technology has been widely applied on long-distance and bulk-capacity power transmission occasions. Due to the terrible interferences in the vicinity of communication lines, DC filters (DCFs) are always installed to mitigate the interferences within acceptable levels for almost all in-service overhead line transmission LCC-HVDC schemes. With the rapid development of the communication technology, however, the anti-interference capability of the telephone system has been remarkably improved. Thus, the original purpose of employing DCFs has been virtually absent, and the necessity of the DCFs shall be re-evaluated in sufficient depth not only for new LCC-HVDC projects, but also in the case of refurbishment of older projects. To demonstrate this constructive topic, this paper carries out a commercial ±800 kV/8000 MW LCC-HVDC project as an illustrative example to analyze and discuss those crucial aspects, which may influence the LCC-HVDC stable operation and reliability after removing the DCFs. Then, the paper studies the harmonic voltage/current stresses of the DC equipment, the DC loop low-order harmonic resonances, and the overvoltage under the switching surge and lightning stroke. Finally, it is concluded that the DCF elimination mainly affects the harmonic steady-state stresses of the DC equipment, but has little influence on the transient stresses. For the refurbishment of older projects, the evaluation on the cost between the DCFs’ maintenance cost and the equipment modification is needed for the DCFs’ elimination. For new LCC-HVDC projects, the DCFs’ elimination or at least simplification may be a more economical and attractive alternative, thereby reducing the footprint and cost.

scholarly journals A Study for the Measurement of the Minimum Clearance Distance between the 500 kV DC Transmission Line and Vegetation

Energies ◽  
2018 ◽  
Vol 11 (10) ◽  
pp. 2606
Author(s):  
Kumail Kharal ◽  
Chang-Hwan Kim ◽  
Chulwon Park ◽  
Jae-Hyun Lee ◽  
Chang-Gi Park ◽  
...  
Keyword(s):  
High Voltage ◽  
Transmission Lines ◽  
Power Transmission ◽  
Electrical Power ◽  
Long Distance ◽  
Dc Voltage ◽  
Hvdc Transmission ◽  
High Voltage Direct Current ◽  
Dc Line ◽  
Pass Through

High voltage direct current (HVDC) transmission is being widely implemented for long-distance electrical power transmission due to its specific benefits over high voltage alternating current (HVAC) transmission. Most transmission lines pass through forests. Around the HVDC lines, an arc to a nearby tree may be produced. Thus, there should be a minimum possible clearance distance between a live conductor and a nearby tree, named the minimum vegetation clearance distance (MVCD), to avoid short-circuiting. Measurement of minimum clearance distance between the conductor and trees is a significant challenge for a transmission system. In the case of HVAC transmission, a large amount of research has been undertaken in the form of the Gallet equation for the measurement of this distance, whereas for HVDC transmission no substantial work has been done. An equivalent AC voltage value can be derived from the DC voltage value in order to use the Gallet equation. This paper presents an experimental measurement technique for determining the MVCD at 500 kV to verify the results obtained from the Gallet equation in the case of DC voltage. Performing the experiment with a 500 kV DC line is not possible in the laboratory due to safety concerns. Therefore, an experiment up to 60 kV is conducted to measure the MVCD for DC voltage. The measured results achieved from the experiment are then extrapolated to calculate the MVCD at 500 kV.

Techno-economic assessment of voltage control strategies in low voltage grids

2015 ◽  
Author(s):  
Thomas Stetz ◽  
Konrad Diwold ◽  
Markus Kraiczy ◽  
Dominik Geipel ◽  
Martin Braun ◽  
...  
Keyword(s):  
Low Voltage ◽  
Control Strategies ◽  
Voltage Control ◽  
Economic Assessment

Low Voltage Skin Burns

PEDIATRICS ◽  
1971 ◽  
Vol 48 (5) ◽  
pp. 831-832
Author(s):  
Charles W. Jarvis ◽  
Donald A. Voita
Keyword(s):  
Cardiac Function ◽  
High Voltage ◽  
Direct Current ◽  
Low Voltage ◽  
Electronic Devices ◽  
Laboratory Safety ◽  
High Voltage Direct Current ◽  
Electrical Devices ◽  
Different Types ◽  
The Subject

The hazards accompanying the increasing use of line-operated electrical devices for diagnosis and therapy as well as the more common hospital appliances such as electrically operated beds, television sets, radio sets, and so forth have been recently reemphasized.1 Most physicians are aware of the dangers of alternating current (60 Hz AC) or of high voltage direct current (DC) , especially in relation to cardiac function. However, few physicians seem to be aware of the hazards of low voltage direct current. A standard text2 on laboratory safety fails to mention the subject. Low voltage direct current is used with many different types of miniature electronic devices and iontophoresis.

Research on DC Voltage Control Strategies for Typical Four-Terminal HVDC System

2014 ◽  
Vol 521 ◽  
pp. 222-228
Author(s):  
Kai Wang ◽  
Hai Shun Sun ◽  
Yu Hua ◽  
Yuan Liu ◽  
Wei Xing Lin ◽  
...  
Keyword(s):  
High Voltage ◽  
Direct Current ◽  
Control Strategy ◽  
Alternative Energy ◽  
Control Strategies ◽  
Future Trend ◽  
Voltage Source ◽  
Voltage Source Converter ◽  
Dc Voltage ◽  
High Voltage Direct Current

The continuous development of alternative energy has put forward higher requirement for electricity transmission. To cope with its fluctuation characteristics, high voltage direct current (HVDC) technology has received more attention. Voltage Source Converter (VSC) based Multi-Terminal High Voltage Direct Current (MTDC) represents the future trend of HVDC technology. This paper mainly focuses on the control strategies of a four-terminal VSC based MTDC power transmission system. The operation characteristic of the system was studied, and the proposed two control strategies, master-slave control strategy and DC voltage droop control strategy, were verified through simulations. The latter control strategy was proved to be performing well under various conditions, including converter station disconnection and faults at AC side of the converter.

scholarly journals Optimal operation of hybrid high voltage direct current and alternating current networks based on OPF combined with droop voltage control

2018 ◽  
Vol 101 ◽  
pp. 176-188 ◽  
Author(s):  
Mònica Aragüés-Peñalba ◽  
Joan Sau Bassols ◽  
Samuel Galceran Arellano ◽  
Andreas Sumper ◽  
Oriol Gomis Bellmunt
Keyword(s):  
High Voltage ◽  
Direct Current ◽  
Voltage Control ◽  
Alternating Current ◽  
Optimal Operation ◽  
High Voltage Direct Current
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