MMC charging strategy suitable for hybrid direct current
A hybrid DC and charging strategy technology, applied in the direction of converting AC power input to DC power output, electrical components, power transmission AC network, etc., can solve the problems that charging resistors cannot be centrally configured, MMC cannot complete the black start process independently, and achieve The effect of reducing primary equipment requirements
Active Publication Date: 2020-02-21
EXAMING & EXPERIMENTAL CENT OF ULTRAHIGH VOLTAGE POWER TRANSMISSION COMPANY CHINA SOUTHEN POWER GRID
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Problems solved by technology
At present, various charging strategies of MMC are based on the premise of configuring charging resistors on the AC side. Since the charging circuits on the AC side of each bridge arm of the MMC are different, the charging resistors cannot be configured centrally. At least three charging resistors must be configured for each pole of the MMC. Three CTs (current transformers) and three bypass switches
At the same time, since the charging resistor is not configured on the DC side, MMC cannot complete the black start process independently, and other MMC stations need to cooperate with charging after they are out of service.
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[0018] In order to make the above objects, features and advantages of the present invention more comprehensible, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.
[0019] Hybrid DC includes several LCC-based conventional DC sites and several MMC-based flexible DC sites. A typical three-terminal hybrid DC system structure is shown in figure 1 , including one conventional DC station and two flexible DC stations. In each flexible DC station, the charging resistor R0 is connected in parallel to the neutral bus of pole 1 and pole 2, and the neutral bus of pole 1 is equipped with switch Q1 and CT (used For measuring the neutral bus current I dCN1 ), the pole 1 pole bus is equipped with a spacer and CT (used to measure the pole bus current I dcH1 ), pole 2 neutral bus is equipped with switch Q2 and CT (used to measure neutral bus current I dCN2 ), the pole 2 pole bus is equipped with a spacer and...
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The invention discloses a MMC charging strategy suitable for hybrid direct current. Each MMC does not need to be configured with charging resistors and corresponding CTs and bypass knife switches on an AC side, and only one charging resistor needs to be connected in parallel to the position of a center line bus of a pole 1 and a pole 2; under normal starting, an LCC is unlocked to charge the double poles of each MMC at the same time, and the charging current of the DC side of each MMC is limited by making the LCC release the trigger angle during phase shifting; and under online station switching or black starting, the pole 1 and the pole 2 are charged in sequence, and the charging current of the DC side of each MMC is limited through the charging resistor. According to the MMC charging strategy, in the charging process, a pole bus CT, a neutral bus CT and a neutral bus knife switch can be used to replace a CT and a bypass knife switch special for a charging loop. Compared with an existing charging strategy in which a charging resistor is configured on the AC side, the primary equipment requirement of an MMC starting loop is greatly reduced, and an MMC is enabled to independently complete a black starting process.
Description
technical field [0001] The invention relates to hybrid direct current transmission technology, in particular to an MMC charging strategy suitable for hybrid direct current. Background technique [0002] With the development of flexible DC transmission technology, the engineering community is actively expanding the application scenarios of MMC (Modular Multilevel Converter), from EHV to UHV, and from back-to-back to hybrid DC and DC power grids. [0003] MMC is composed of multiple half bridge sub-modules (half bridge sub-module, HB-SM) or full bridge sub-modules (full bridge sub-module, FB-SM) cascaded, each sub-module consists of IGBT, anti-parallel diode and Composition of capacitors. In order to drive the switching of each sub-module, it is necessary to charge the MMC before unlocking to increase the capacitor voltage of the sub-modules on average. At present, various charging strategies of MMC are based on the premise of configuring charging resistors on the AC side. S...
Claims
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IPC IPC(8): H02M7/483H02J3/36
CPCH02J3/36H02M7/483H02M7/4835Y02E60/60
Inventor 刘航王海军彭茂兰邹延生
Owner EXAMING & EXPERIMENTAL CENT OF ULTRAHIGH VOLTAGE POWER TRANSMISSION COMPANY CHINA SOUTHEN POWER GRID