Modular multilevel converter sub-module observation method and device

Abstract

The invention discloses a method and device for observing a submodule of a modularized multilevel converter. The method includes: establishing an interphase total input submodule voltage observer based on an extended state observer and an interphase circulation current model; establishing an interphase circulation Current observer: calculate the circulating current between phases of the converter through the current measured by the current sensor, and obtain the change rate of the circulating current between the phases; obtain the observation of the total input sub-module voltage between the phases according to the change rate of the circulating current between the phases and the circulating current model between the phases value; through the measured value of the upper bridge arm voltage measured by the voltage sensor, the upper bridge arm sub-module voltage observer is established; using the difference between the observed value of the phase-to-phase total input sub-module voltage and the measured value of the upper bridge arm voltage, Correct the observed value of the voltage observer of the sub-module of the lower bridge arm, and establish the voltage observer of the sub-module of the lower bridge arm. By adopting the above technical solution, the number of sensors is reduced, and at the same time, the observation of the voltages of all sub-modules of the converter is realized.

Description

technical field [0001] The invention relates to the technical field of power electronics, in particular to a method and device for observing sub-modules of a modular multilevel converter. Background technique [0002] Modular Multilevel Converter (MMC) expands the number of sub-modules according to the required number of levels and voltage levels. This multi-module feature makes MMC naturally have strong redundancy; and At the same time, the multi-level feature of MMC also simplifies the filtering on the AC side. As a topology that is easy to expand, MMC has a wide range of applications in high-voltage frequency conversion, power management, HVDC (High Voltage Direct Current), and traction converters. Among them, HVDC is one of the most concerned application fields of MMC. [0003] However, when the number of sub-modules of the MMC is large, it will also bring challenges to the practical application of the MMC, such as the problems of the capacitor-voltage balance of the s...

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Problems solved by technology

[0003] However, when the number of sub-modules of the MMC is large, it will also bring challenges to the practical application of the MMC, such as the capacitor voltage balance of the sub-modules, the circulating current between phases, etc.

In order to carry out sub-module capacitor voltage balance control and phase-to-phase circulating current suppression, voltage sensors are required to obtain sub-module capacitor voltages, but more voltage sensors will increase the complexity of conditioning circuits and data communication

At the same time, the measurement accuracy and communication delay of the voltage sensor will affect the closed-loop control, reducing the safety and reliability of the system

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