A Method for Balancing Capacitor Voltage of Bridge Arm Asymmetric mmc Type DC Transformer

Abstract

The invention discloses a bridge arm asymmetrical MMC type DC transformer capacitor voltage balancing method, comprising: based on the main circuit structure of the MMC type DC transformer and a bridge arm current mathematical model, establishing a differential mode current equivalent circuit of the transformer bridge arm current and Common-mode current equivalent loop; based on the differential-mode current equivalent loop and the common-mode current equivalent loop, respectively calculate the first difference between the input and output power of the upper bridge arm and the second difference between the input and output power of the lower bridge arm; adopt PI control, Real-time collection and adjustment of the first difference and the second difference based on the difference between the capacitor voltages of the upper and lower bridge arms to achieve capacitor voltage balance. The present invention establishes a power transmission model during the operation of the equipment, and can accurately determine that the direction of energy transmission is the cause of the unbalanced capacitor voltage of the upper and lower bridge arm modules when the inductance of the bridge arm is asymmetrical, and adopts PI control to adjust the first difference and the second The method is simple, and can effectively suppress the voltage imbalance of the module capacitor caused by the asymmetry of the bridge arm inductance.

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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