Modular multilevel converter (MMC) valve loss calculation method applicable to different sub-module types

Abstract

The invention discloses an MMC valve loss calculation method applicable to different sub-module types. The method comprises firstly, calculating time domain characteristic curves of alternating current side phase currents, bridge arm currents and bridge arm voltages of the converter in the fundamental frequency cycle according to system basic operation conditions and major loop parameters; then, selecting types of sub-modules, and calculating the switching state and related electric parameters of each sub-module by using recent level modulation and sub-module optimization balance control strategies, involving effects of the sampling frequency; performing data fitting by extracting manufacturer data of insulated gate bipolar transistor (IGBT) and antiparallel diodes to build loss models about the IGBT and antiparallel diodes; uniformly performing loss estimation and soling based on given parameters. The converter power loss and device junction temperature distribution under various operating conditions can be calculated on the basis of the method, the process is easy and clear, the calculation universality is high, rapid calculation can be performed on the different sub-module types, the method is quite suitable for system planning and scheme check at the initial stage, and the accuracy is greatly improved compared with existing algorithms.

Description

technical field [0001] The invention belongs to the technical field of power system performance evaluation, in particular to an MMC valve loss calculation method suitable for different sub-module types. Background technique [0002] The Modular Multilevel Converter (MMC) adopts the form of cascading basic operating units, avoiding the direct series connection of a large number of switching devices, and there is no problem such as dynamic voltage equalization and consistent triggering. It is especially suitable for high-voltage direct current transmission occasions. A number of planning or construction projects at home and abroad have verified the application value and development prospects of the MMC-based high-voltage direct current transmission system (MMC-HVDC). At the two international power electronics conferences in 2010 and 2011, R.Marquardt, a scholar at the Bundeswehr University in Munich, Germany, further proposed the concept of generalized MMC, which uses sub-modu...

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Problems solved by technology

The electrical operating conditions of MMC are very complex, so it is difficult to achieve loss measurement with direct electrical measurement methods

[0005] At present, the research on fast loss calculation of modular multilevel converters is not in-depth. Y. Liu et al. titled Loss calculation method of modular multilevel HVDC converters (Electrical Power and Energy Conference, 2011IEEE:2011, 1-5) Introduced an analytical formula method based on the idea of ​​current averaging in the literature, which introduces the concept of current averaging, deduces the analytical formula of the average current of each device in the sub-module, the calculation is simple and fast, and is suitable for the initial evaluation of loss; but this method It cannot reflect the nonlinear modulation characteristics of MMC. The calculation of switching loss is usually estimated by artificially setting the switching frequency (such as 150Hz). It is difficult to effectively take into account the switching loss caused by additional balance control, and it is also impossible to calculate the voltage and current of each sub-module. Analytical calculation of the change, the loss distribution characteristics of each sub-module of the bridge arm cannot be obtained

General loss reduction measures are mainly aimed at the transient losses caused by the switching process, such as turn-on loss and turn-off loss, and only relying on analytical formulas cannot effectively evaluate the benefits of loss reduction strategies

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