A mmc charging strategy for hybrid DC
A hybrid DC, charging method technology, applied in the direction of AC power input conversion to DC power output, electrical components, power transmission AC network, etc., can solve the problem that the charging resistance cannot be centrally configured, and the MMC cannot independently complete the black start process, etc. The effect of reducing primary equipment requirements
Active Publication Date: 2020-11-24
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.
Method used
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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 an MMC charging strategy suitable for mixed DC. Each MMC does not need to be equipped with charging resistors and corresponding CTs and bypass switches on the AC side, and only needs to be connected in parallel at the neutral bus of pole 1 and pole 2 Resistor; when starting normally, unlock the LCC to charge the bipolar poles of each MMC at the same time, and limit the charging current of the MMC DC side by controlling the firing angle of the LCC to release the phase shift; when the online drop station or black start, charge pole 1 and pole 2 successively And limit the charging current of the MMC DC side through the charging resistor. In the MMC charging strategy of the present invention, during the charging process, the pole bus CT, neutral bus CT and neutral bus switch can be used to replace the special CT and bypass switch for the charging circuit. Compared with the existing AC side configuration charging resistor The charging strategy greatly reduces the primary equipment requirements of the MMC start-up loop, and at the same time enables the MMC to have the ability to independently complete the black-start 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...
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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