Alternating current charging control strategy suitable for different working conditions of hybrid MMC (modular multilevel converter)

Abstract

The invention discloses an alternating current charging control strategy suitable for the different working conditions of a hybrid MMC (modular multilevel converter). The alternating current chargingcontrol strategy comprises the following steps that: an alternating current circuit breaker is switched on, and full-bridge sub-modules and half-bridge sub-modules are subjected to uncontrollable charging; after the full-bridge sub-module enter controllable states, and the average voltage of the full-bridge sub-modules is greater than a certain value, and the T2 switching tubes of the all full-bridge sub-modules are switched on; when the average voltage of the full-bridge sub-modules and the half-bridge sub-modules reaches a set value, a sub-module voltage-sharing control strategy is enabled,the full-bridge sub-modules and the half-bridge sub-modules are sorted in a unified mode, a certain number of full-bridge sub-modules and half-bridge sub-modules are switched off step by step, the voltage of the full-bridge sub-modules and the half-bridge sub-modules is charged to approximate a rated value, and charging is completed. With the charging control strategy adopted, an MMC control system does not need to additionally judge the operation mode of the MMC, the access state of the MMC does not need to be judged, and therefore, controller program design can be simplified, and the reliability of the successful charging startup of the hybrid MMC is improved.

Description

technical field [0001] The invention relates to flexible DC transmission technology, in particular to an AC charging control strategy adapted to different working conditions of a hybrid MMC. Background technique [0002] Compared with conventional DC transmission technology, flexible DC transmission technology does not require reactive power compensation, has no commutation failure problem, convenient active and reactive power adjustment, low harmonic level, and is suitable for forming multi-terminal DC systems. It has developed rapidly, among which the flexible direct current transmission system based on MMC (modular multilevel converter) topology is the most representative and has technical advantages. Hybrid MMC has a broad application prospect in the field of flexible DC transmission due to its outstanding advantages such as DC side fault clearing capability, step-down operation capability, relatively low cost and loss, and is very suitable for UHV flexible DC transmissi...

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Problems solved by technology

[0003] (1) AC charging, when the DC side of the valve group is not short-circuited, the charging rate of the full and half bridge sub-modules is inconsistent:

[0013] To sum up, the current AC charging method for hybrid MMC can only be effective under specific operating conditions. At the same time, the implementation of these methods must rely on the control system to pre-determine the current wiring mode of the valve group (starting with short-circuit on the DC side or starting without short-circuiting on the DC side), and select according to the current operating mode. Different charging start control strategies require the control system to access the switch position signal (such as valve group bypass switch position signal, etc.) for judging the MMC state, and design the program valve group state judgment logic and charging mode selection logic, adding The complexity and design difficulty of the control program, and there is a risk of MMC charging startup failure due to misjudgment of the charging startup method

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