Capacitive voltage balancing method for MMC type direct current transformer with asymmetric bridge arms

Abstract

The invention discloses a capacitive voltage balancing method for an MMC type direct current transformer with asymmetric bridge arms. The method comprises the following steps: based on a main circuitstructure of the MMC type direct current transformer and a bridge arm current mathematical model, setting up a differential mode current equivalent loop and a common mode current equivalent loop for currents of the bridge arms of the transformer; based on the differential mode current equivalent loop and the common mode current equivalent loop, respectively calculating a first difference value between input power and output power of an upper bridge arm as well as a second difference value between input power and output power of a lower bridge arm; by adopting PI control, acquiring in real time, and based on a difference value between capacitive voltages of the upper bridge arm and the lower bridge arm, adjusting the first difference value and the second difference value, thus capacitive voltage balance is realized. The method disclosed by the invention builds a power transmission model in an equipment operation process, a reason for unbalance of the capacitive voltages of an upper bridge arm module and a lower bridge arm module when an energy transmission direction is asymmetric bridge arm inductance can be accurately obtained, and the first difference value and the second difference value are adjusted by adopting the PI control, so that the method is simple and can effectively inhibit the unbalance, due to the asymmetric bridge arm inductance, of the capacitive voltages of themodules.

Description

technical field [0001] The invention belongs to the field of transformer operation control, and more specifically relates to a bridge arm asymmetrical MMC type DC transformer capacitor voltage balancing method. Background technique [0002] Compared with the traditional DC transformer with dual active bridge structure, the MMC type DC transformer has the advantages of modular design, easy voltage expansion, and simple redundant design, and is more suitable for application scenarios with higher voltage levels. In order to suppress the fluctuation of the bridge arm current, the bridge arm inductance of the same size is set on each bridge arm, but in actual engineering, it is difficult to achieve the same parameters of the bridge arm inductance, and the asymmetrical bridge arm inductance will cause the gap between the bridge arms The energy flow of the module makes the capacitor voltage of the module unbalanced, and finally causes the transformer to fail to operate normally. F...

AI Technical Summary

Problems solved by technology

[0004] The invention provides a bridge arm asymmetrical MMC type DC transformer capacitor voltage balance method, which is used to solve the problem that the existing MMC type DC transformer capacitor voltage balance method cannot obtain the energy flow between the bridge arms due to the equivalent model based on the double active bridge structure The technical problem of high computational complexity due to the asymmetric interaction with the bridge arm inductance

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