Economical single-ended cascade hybrid DC transmission system with bidirectional flowing of flow

Abstract

The invention discloses an economical single-ended cascade hybrid DC transmission system with tidal current bidirectional flow. The system comprises a rectifier station and an inverter station. The DCsides of the rectifier station and the inverter station are connected by a DC transmission line. The rectifier station and the inverter station comprises interconnected thyristor converter LCC and modular converter and also comprises a transmitting end AC grid and a receiving end AC grid, and the thyristor converter LCC and the modular converter are respectively connected to the transmitting endAC grid and the receiving end AC grid through a double-winding transformer. The present invention proposes a new LCC-MCSM(monopole current sub-module)-HVDC type hybrid converter valve, and the bidirectional flowing of DC power flow can be achieved by using the voltage polarity reversal of a DC port.

Description

technical field [0001] The invention relates to the technical field of direct current transmission, in particular to an economical single-end cascaded hybrid direct current transmission system in which power flow can flow in both directions. Background technique [0002] Conventional DC transmission system, also known as line-commutated DC transmission system (LCC-HVDC), is composed of thyristor valve group, which has the characteristics of large transmission capacity, high voltage level, low cost and low loss, and has been widely used; but Thyristors are limited by their own semi-controlled characteristics, and are easily affected by voltage fluctuations and sags in the connected AC system, resulting in commutation failures, resulting in blockage of the transmission system and interruption of power flow, which in turn causes voltage stability problems in the AC system at the receiving end. The flexible direct current transmission system (VSC-HVDC) is composed of voltage sou...

AI Technical Summary

Problems solved by technology

However, in this LCC-HBSM-HVDC hybrid DC transmission system, the LCC type converter valve only allows unidirectional current to pass through, and its power flow reversal depends on the reversal of the DC voltage; while the HBSM-MMC type soft DC converter valve allows Bidirectional current flows, but DC voltage cannot be reversed

Secondly, when one end of the DC system (such as the transmitting end or the rectifying end) adopts the LCC-HBSM-HVDC converter valve, if the other end (the receiving end or the inverter end) is affected by an AC fault and causes the DC bus voltage at this end to suddenly When it drops significantly, the LCC-HBSM-HVDC converter valve cannot quickly control the large-scale drop of the near-end DC voltage, so that it cannot suppress the rise of the DC system current

[0010] Although the existing LCC-HBSM-HVDC single-ended cascaded hybrid DC transmission system has advantages in overall operating characteristics and project cost, it is only suitable for The unidirectional power flow operation mode under the unidirectional current constraint cannot realize the bidirectional flow of power flow

At the same time, for the LCC-HBSM-HVDC converter valve, the LCC converter valve is limited by the response speed of the phase control system and cannot quickly control the DC voltage, while the DC voltage fluctuation range of the HBSM-MMC flexible DC converter valve and its Limited, usually the DC voltage drops below 0.9 times the rated voltage and cannot operate. Therefore, the LCC-HBSM-HVDC converter valve composed of the two cascaded with each other cannot control the wide range of DC voltage changes

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