Modular multilevel converter sub-module simulation model of considering secondary loop

Abstract

The invention relates to a modular multilevel converter sub-module simulation model of considering a secondary loop. The modular multilevel converter sub-module simulation model comprises two IGBTs, two diodes, an energy storage capacitor, an equalizing resistor, an energy taking power supply and a central control board, wherein input ends of the equalizing resistor and the energy taking power supply are connected with two ends of the capacitor in parallel; the energy taking power supply converts capacitor voltage into low-voltage DC for supplying the central control board with electricity by using a DC / DC switching power supply topology; and equivalent resistance of the energy taking power supply dynamically changes according to the differences in working state and voltage value. The influence of secondary loop parameters of the efficiency of the equalizing resistor, the efficiency of the energy taking power supply, the power of the central control board and the like on voltage and current of a sub-module are expressed by using a switch function, so that the simulation model is closer to the actually used sub-module in a flexible DC power transmission project. The modular multilevel converter sub-module simulation model aims at reflecting the influence of the secondary loop in a practical project on the sub-module through one simulation model, especially voltage and current waveform simulation in the startup and shutdown processes of a converter is achieved, so that the simulation result is closer to the engineering practice.

Description

technical field [0001] The invention relates to the technical field of flexible direct current transmission, in particular to a sub-module simulation model of a modular multilevel converter considering a secondary circuit. Background technique [0002] The flexible DC transmission projects that have been put into operation in China all use modular multi-level converters. Each phase bridge arm is composed of multiple sub-modules with the same structure in series. The output voltage of the converter is the cascaded voltage of multiple working sub-modules. form. As the core component of the converter, the sub-module's electrical characteristics directly affect the performance of the flexible DC transmission project. In the design stage of flexible HVDC projects, modeling and simulation methods are usually used to analyze and verify the design parameters of each equipment. The simulation model of the sub-module is the basis of the overall modeling of the converter, but the exi...

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Problems solved by technology

However, according to the actual operation data of the flexible direct current transmission project, it is found that the voltage of the sub-module is polarized and the voltage equalization effect is poor during the start-up process.

[0005] 2. The voltage fluctuation range after unlocking does not match the actual situation

[0006] The above limitations are all due to the fact that the existing simulation model does not consider the influence of the secondary circuit on the electrical characteristics of the sub-module.

During the actual operation of the sub-module, the voltage equalizing resistors connected in parallel at both ends of the energy storage capacitor and the energy harvesting power supply directly consume the power of the energy storage capacitor, and the equivalent resistance of the energy harvesting power supply is a variable that changes with the capacitor voltage, which eventually causes the sub-module to start During the process, the voltage is polarized, and the voltage fluctuation range becomes larger during unlocking operation.

[0007] When it is necessary to simulate the phenomenon of voltage polarization during the start-up process and sub-module voltage fluctuations when the converter is zero-power, the existing sub-module simulation model is not applicable, so the present invention designs a modular multi-level circuit considering the secondary circuit The simulation model of the sub-module of the converter, by introducing secondary circuit parameters such as voltage equalizing resistance, energy harvesting power efficiency, central control board power, etc., enables the model to simulate the voltage polarization phenomenon in the start-up process on the one hand, and accurately simulate the unlocking on the other hand Voltage fluctuation range during operation

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