Capacitor voltage balance control method for mmc sub-module based on state observer

Abstract

The invention discloses a state observer-based MMC sub-module capacitor voltage equalization control method, comprising the following steps: S1, sampling the capacitor voltages of all MMC sub-modules, and sorting them in ascending order of voltage; S2, determining that each bridge arm needs to be put into a sub-module Whether the number is 0, if so, bypass all MMC sub-modules, otherwise execute S3; S3, if the observed value of the bridge arm current is non-negative, input the minimum voltage N u or N l MMC sub-modules; if the observed value of the bridge arm current is negative, input the N with the largest voltage u or N l MMC sub-modules; among them, N u or N l Respectively represent the number of MMC sub-modules that need to be put into the upper and lower bridge arms of each phase. The present invention uses a state observer to estimate the bridge arm current, uses the estimated value of the bridge arm current to realize the balanced control of the sub-module capacitor voltage, saves the bridge arm current sensor, simplifies the control system of the MMC, and reduces the flexible DC power transmission and distribution system cost.

Description

technical field [0001] The invention belongs to the field of flexible DC power transmission and distribution, in particular to a state observer-based MMC (modular multilevel converter) sub-module capacitor voltage equalization control method. Background technique [0002] With the development of power electronics technology, voltage source converters (voltage source converters, VSCs) have begun to be used in the field of high voltage direct current (High voltage direct current, HVDC) power transmission. The voltage source converter high-voltage direct current (VSC-HVDC) transmission can independently control the active power and reactive power, and the control mode is flexible and changeable. Existing VSC-HVDC has a variety of topological structures. The two-level and three-level VSC-HVDC are limited by the number of levels, so pulse width modulation (Pulse Width Modulation, PWM) technology must be used, and the switching frequency of the device is high and the loss is large...

AI Technical Summary

Problems solved by technology

In MMC, each sub-module has an energy storage capacitor. If the energy of the capacitor is unbalanced, it will cause the energy imbalance of the upper and lower bridge arms, which will affect the normal operation of the converter. Therefore, it is necessary to control the capacitor voltage of each sub-module to maintain balance

However, the large number of sub-modules on the bridge arm leads to a large number of energy storage capacitors, which is difficult to control. Therefore, it has become a hot spot to find a suitable capacitor voltage equalization control method.

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