Hybrid converter topological structure based on controllable turning off and control method of hybrid converter topological structure

Abstract

The invention relates to a hybrid converter topological structure based on controllable turning off and a control method of the hybrid converter topological structure. The topological structure is a three-phase six-bridge-arm circuit; the three-phase six-bridge-arm circuit is connected to an alternating current power grid through a converter transformer; the upper bridge arm and the lower bridge arm of each phase of the three-phase six-bridge-arm circuit are respectively composed of valve modules. Each valve module is composed of a main branch and an auxiliary valve which is connected with themain branch in parallel and has forward current controllable turn-off and forward and reverse voltage blocking capacities. Each main branch is composed of thyristor valves which are connected in series, and a turn-off valve which has forward current controllable turn-off and forward voltage blocking capabilities. According to the hybrid converter topological structure provided by the invention, the current turn-off characteristic of a turn-off device is fully utilized; commutation current can be quickly transferred; the commutation voltage time area of the thyristor valves is flexibly controlled; and it can be ensured that the thyristor valves have enough reverse recovery time to be reliably turned off; and meanwhile, the problem of commutation failure of a direct-current system can be fundamentally solved by utilizing the turn-off valves to assist commutation.

Description

technical field [0001] The invention relates to the technical field of commutation in power electronics, in particular to a hybrid converter topology and a control method thereof. Background technique [0002] The traditional line commutated converter high voltage direct current (LCC-HVDC) transmission system has the advantages of long-distance large-capacity transmission and controllable active power, and is widely used in the world. As the core equipment of DC power transmission, the converter is the core functional unit to realize the conversion of AC and DC power, and its operation reliability largely determines the operation reliability of the UHV DC grid. [0003] Since traditional converters mostly use semi-controlled device thyristors as the core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multi-level thyristors and their buffer components connected in series. Commutation failures are prone to occur under conditions suc...

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Problems solved by technology

[0003] Since traditional converters mostly use semi-controlled device thyristors as the core components to form a six-pulse bridge commutation topology, each bridge arm is composed of multi-level thyristors and their buffer components connected in series. Commutation failures are prone to occur under conditions such as faults, resulting in a surge in DC current and a rapid loss of DC transmission power, which poses more severe challenges to the stable and safe operation of the power grid

[0004] Aiming at the problem of commutation failure in traditional DC transmission, many scholars have done a lot of research work and invented a variety of converter topologies with the function of resisting commutation failure. For example, one is the capacitor-commutated converter topology (CCC) , increase the time area of ​​the valve commutation voltage through the capacitor voltage to ensure its reliable shutdown; based on the basic principle of the capacitor commutation circuit, a variety of topological structures have evolved, and the controllable capacitor module is composed of a power electronic switch and a capacitor to realize the capacitor. Input and voltage direction are controllable; but the above-mentioned topology engineering based on capacitive commutation is difficult to realize

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