A mmc flexible DC system

Abstract

The invention discloses an MMC flexible direct-current system. The MMC flexible direct-current system comprises a first converter station and a second converter station, wherein the first converter station and the second converter station are connected through a direct-current circuit and each comprise an alternating-current system, a main circuit breaker, a transformer and multiple bridge arms, each alternating-current system, the corresponding main circuit breaker and the corresponding transformer are sequentially connected in series, every two corresponding bridge arms are connected in series to form a phase of bridge arms, the number of the phases of the bridge arms is three, and the phases of bridge arms are connected in parallel and then are connected with the transformers in series; each bridge arm comprises a bridge arm reactor and a valve bank which are connected in series, each valve bank comprises multiple sub-modules, in the open circuit state, the sub-modules are equivalent to a series circuit of a resistor and a capacitor, and in the short circuit state, the sub-modules are equivalent to an inductive circuit. During real-time digital simulation, inversion does not need to be conducted on an admittance matrix again, in this way, a large amount of calculation time can be saved, the real-time simulation step size is reduced to smaller than several microseconds according to requirements, and accurate simulation of the MMC flexible direct-current system is achieved.

Description

technical field [0001] The invention relates to the technical field of modular multilevel (MMC) flexible direct current transmission, in particular to an MMC flexible direct current system. Background technique [0002] Modular multilevel (MMC) flexible DC transmission technology is one of the key and difficult points in the field of high-power power electronics research at home and abroad. It adopts controllable shutdown power electronic devices, which can not only realize the independent control of active power and reactive power, but also supply power to passive systems. When the power flow is reversed, the direction of the DC current is reversed while the polarity of the DC voltage remains unchanged, and there is no need for communication between the converters, which is conducive to the construction of a parallel multi-terminal DC transmission system that can control the power flow conveniently and has high reliability. with broadly application foreground. [0003] Fo...

AI Technical Summary

Problems solved by technology

In the real-time simulation digital, the typical simulation step size is 50-80 microseconds, which is enough for the electromagnetic transient simulation analysis of the conventional power system, but for the MMC flexible DC system, the sub-module switching frequency is very high, if the traditional real-time digital simulation is used method, and every time the sub-module switch state changes, the real-time digital simulation needs to invert the admittance matrix again, which takes a lot of computing time, so it is impossible to reduce the real-time simulation step size to less than a few microseconds , so that it is impossible to accurately simulate the MMC flexible DC system

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