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Many climate change-related extreme weather events are occurring with increasing frequency and intensity, causing catastrophic outages that serve as a powerful reminder of the vulnerability of current power systems[1]. Power system restoration has been well identified as one of the critical strategies to enhance system resilience. Generally, the objective of system restoration is to re-supply load as quickly as possible after an outage. To this end, for large-scale power systems, the generating units have to be restarted first; and then, the delivery systems should be energized to pool and transfer electric power to the demand side; the final stage picks up loads sequentially[2]. As the most critical operating strategy, restoration strategies meet all operating constraints by fully using the available resources. As one of the most widely used emerging transmission technologies, HVDC's contribution for system restoration should be carefully identified.
Few study addresses the HVDC restoration strategy at present, although the importance has been well identified. To fulfill this critical gap, the black-start capability of various HVDC system needed to be identified; and then the operating strategies should be designed. At present, there are two types of HVDC with different power electronic devices, i.e., LCC-HVDC and VSC-HVDC.
Traditionally, LCC-HVDC can't act as a restoration source in a blackout condition when serious faults occur in one side of the AC systems[3]. The classical line-commutated current-source converter (LCC-HVDC) based on the thyristor technology, which has been used for some decades and proven to be superior to the AC transmission in terms of operating cost and reliability[3-4]. Since LCC-HVDC requires commutation current supplied by strong AC systems and the receiving end system should be an active system. However, the latest development demonstrates that LCC-HVDC may be extended with restoration capability by sophisticated control strategies[5-6].
With the development of power electronics technology, novel HVDC technology is available. By using the insulate gate bipolar transistor (IGBT) components, Voltage Source Converter (VSC) technology are proposed. For VSC-HVDC projects, up until now, DC voltage has reached ±320kV and the transmission power reaches about 1000MW. VSC transmission system provides favorable control ability[7-8]. By PWM technology, the desired output voltage amplitude is controlled by modulating the width of constant DC voltage pulses. VSC-HVDC can be restarted without external support. As a result, VSC-HVDC is suggested as a tie line to provide energy for system restoration[9]. When the VSC-HVDC link is charged, the DC voltage across the capacitor rises. VSC can convert the DC voltage into the desired AC voltage by switching on or off converter bridges according to the pre-determined switching mode. By use of PWM, VSC will produce the AC voltage, which contains a fundamental component equal to the AC reference voltage in magnitude, frequency and phase.
HVDC connections doesn't not play a major role in wind power integration so far. The main reason is the traditional LCC-HVDC does not have black-start capability without auxiliary device. Due to the characteristics of VSC-HVDC, it can be used for wind farm restoration. Since wind farms usually behaves as a load during startup, this technology may be critical for the future power systems. A voltage waveform with appropriate amplitude and frequency has to be established to integrate the generators. Recently, it is reported that VSC-HVDC has full black-start capability for wind farms[10].
This paper comprehensively discusses the potential contributions for restoration of HVDC systems, including LCC-HVDC and VSC-HVDC. The wind farm restoration with VSC-HVDC will be studied as well.
HVDC Technology for Power System Restoration
doi: 10.16516/j.gedi.issn2095-8676.2016.02.009
- Received Date: 2016-02-01
- Publish Date: 2020-07-17
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Key words:
- LCC-HVDC /
- VSC-HVDC /
- blackstart /
- wind farm /
- STATCOM
Abstract:
Citation: | Lijuan LU, . HVDC Technology for Power System Restoration[J]. SOUTHERN ENERGY CONSTRUCTION, 2016, 3(2): 47-52. doi: 10.16516/j.gedi.issn2095-8676.2016.02.009 |