A start-up strategy for full-bridge modular multilevel converters

Abstract

The invention discloses a starting strategy suitable for a full-bridge modular multilevel converter of the power transmission and distribution technology field. A technical scheme is characterized in that a starting process is divided into two processes of uncontrolled starting and controllable charging; in the uncontrolled starting process, a converter is locked and a starting resistor is used so that a condition that a device is damaged because a starting current is too heavy is avoided; an alternating current system provides power and carries out first phase charging on upper and lower bridge arm submodules, and at this time, a direct voltage maximumly reaches an alternating current system phase voltage peak value; in the second phase of the controllable charging process, the converter is locked, T4 in each phase bridge arm submodule is triggered and is conducted according to a certain frequency; through above process, each phase of the upper and lower bridge arms is continuously charged so that a direct voltage and a submodule capacitance voltage are further increased. In an uncontrolled charging phase, each converter is unlocked and an alternating current system side starting resistor is bypassed. A control system emits a direct voltage and active power normal rise instruction. Each index of the system gradually reaches a rated value and then a starting process is completed.

Description

technical field [0001] The invention belongs to the technical field of power transmission and distribution, and in particular relates to a start-up strategy of a modular multilevel converter based on a full-bridge sub-module. Background technique [0002] Modular multilevel converters are gradually becoming a trend in the field of DC transmission in the future. Due to the small number of components used and the simple topology, half-bridge sub-modules are used as the first choice in the construction of converters in many DC transmission projects. However, due to the existence of its short-circuit current conduction path, the half-bridge sub-module does not have the DC fault ride-through capability, so when a fault occurs, it can only block the converter and trip the AC side switch, resulting in time for fault removal and system recovery. It is too long, and for the multi-terminal DC transmission system, the ability to transmit power after a fault is lost. In order to solve...

AI Technical Summary

Problems solved by technology

The charging method of the full-bridge sub-module is different from that of the half-bridge sub-module. If the rated value is reached only through simple uncontrolled charging and controllable charging process, the DC voltage will increase rapidly, so that the DC cable can withstand large voltage changes. rate, seriously affecting the normal operation of the system

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