A multi-objective optimization method for high voltage and large capacity flexible direct current transmission system

Abstract

The invention discloses a multi-objective optimization method for a high-voltage and large-capacity flexible direct current transmission system, which includes: monitoring and storing corresponding variables of the flexible direct current transmission system in real time; calculating the submodules that need to be opened for each bridge arm according to the nearest level approach debugging method Quantity; with the working state of the sub-module as a variable, two optimization objective functions of the minimum switching times and the minimum capacitor voltage fluctuation are established; the multi-objective genetic algorithm is used to solve the optimal solution set; the sub-modules of the three bridge arms of the flexible direct current transmission system are obtained Optimal working state: send the optimal working state of the three bridge arm sub-modules of the flexible direct current transmission system to the control system. This method can not only reduce the fluctuation of the sub-module capacitor voltage, but also reduce the switching frequency and switching loss, and the parallel intelligent algorithm can simultaneously calculate the switching states of the three-phase bridge arms, and the calculation efficiency is higher.

Description

technical field [0001] The invention relates to the technical field of new energy power generation, in particular to a multi-objective optimization method for a high-voltage and large-capacity flexible direct current transmission system. Background technique [0002] Modular multilevel converter (MMC), as a power electronic structure with good output characteristics, is a research hotspot in the field of voltage source converter in recent years. The MMC structure has become the optimal solution in the field of HVDC transmission due to its modular characteristics, good scalability, and small output voltage harmonics. MMC's sub-modules are easy to cascade and can be applied to higher voltage levels. However, when MMC is applied in the high-voltage field, it usually adopts the nearest level approximation modulation, which requires a large number of sub-modules to be connected in series. The resulting irregular bridge arm current and irregular switching of sub-modules lead to u...

AI Technical Summary

Problems solved by technology

The direct capacitor voltage equalization algorithm can reduce the DC capacitor voltage fluctuation to a very small range, but its switching frequency is very high. The incremental capacitor voltage equalization algorithm is just the opposite. On-off level

The capacitive voltage equalization algorithm that adds hold factor sorting introduces the hold factor and the voltage threshold, and the required switching frequency or voltage fluctuation can be obtained by adjusting the parameters, but the two are irreconcilable in theory

[0004] To sum up, in the prior art, there is still no effective solution to the unbalanced problem of sub-module capacitor voltage in the high-voltage and large-capacity flexible DC transmission system.

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