Self-power power supply frequency-hopping control based modular multilevel current converter voltage-sharing method

Abstract

The invention relates to a self-power power supply frequency-hopping control based modular multilevel current converter voltage-sharing method. A charging-discharging principle of series-wound sub module capacitors is analyzed, and a capacitor charging-discharging mathematic model for series-wound power modules is established; controlled parameters affecting the capacitor voltage balance are determined; the capacitor voltage of each module is sampled and obtained for a large number of series-wound power modules, then an average value is obtained from the obtained capacitor voltages; the average value is the voltage-sharing target of each power module; when the capacitor voltage of the corresponding power module is greater than the average voltage value, the high-order energy-taking power supply (refers to the self-power power supply) is controlled to carry out continuous operation; when the capacitor voltage of the corresponding power module is lower than the average voltage value, a modulation signal for controlling the operation of the power supply is calculated firstly; then the frequency and the duty ratio of a triangular wave signal are calculated and determined; and finally the modulation signal is compared with the triangular wave signal to obtain an execution signal for controlling the operation of the power supply. By adoption of the method provided by the invention, the voltage-sharing control of a large number of series-wound power modules can be realized.

Description

【Technical field】 [0001] The invention relates to the field of flexible direct current transmission, in particular to a voltage equalization method for a modular multilevel converter based on frequency hopping control of a self-energy source. 【Background technique】 [0002] With the development of high-power power electronics technology, fully-controlled power electronic devices are more and more widely used in DC transmission systems, especially flexible DC transmission systems with IGBT, IGCT, etc. as the main switching devices have become domestic and foreign related enterprises. and the mainstream of university research. Modular multilevel converter (MMC) has been widely used in high-power wind power generation, solar power generation, island power supply, offshore power supply and other DC transmission systems due to its advantages of low switching frequency and low loss. At present, the sub-modules used to form the MMC topology mainly include H-MMC (half-bridge sub-mo...

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Problems solved by technology

[0003] Due to the many advantages of MMC, there are more and more scholars or experts studying MMC. Regarding the research on voltage equalization of modular multilevel converter modules, many papers or journals have proposed related control methods. However, now The essence of many methods is still according to the positive and negative of the bridge arm current of the system. When the module voltage is low, the IGBT action is controlled to charge the module, and when the module voltage is high, the module is discharged. This control method can complete voltage equalization. requirements, however, tend to result in more power device losses and lower system efficiency

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