Control method for improving flexible DC power transmission AC side fault ride-through capability

Abstract

The invention discloses a control method for improving flexible DC power transmission AC side fault ride-through capability, The method comprises the steps: the mathematical model of the upper and lower bridge arms of a modular multi-level converter station is established through mathematical modeling by using equivalent capacitance with variable capacitance, the analytic relationship between thereal-time power value of the AC/DC side of MMC converter station and the voltage value of the DC side of the MMC converter station is obtained according to the mathematical model, the relationship between the imbalance degree between AC and DC side power of the converter station and the DC side voltage sag is deduced according to the analytic relationship, and then the real-time target value of converter station power adjustment is determined according to the relationship. The AC/DC side power imbalance degree of the converter station is obviously reduced, the power adjustment pressure of theexisting outer loop power control and the inner loop current control is reduced, the control effect of the existing control strategy is indirectly improved and the stability of the DC voltage can be greatly improved.

Description

technical field [0001] The invention belongs to the technical field of two-terminal or multi-terminal flexible direct current transmission systems based on MMC converters, and in particular relates to a control method for improving the fault ride-through capability of the AC side of flexible direct current transmission. Background technique [0002] my country's energy distribution and load distribution do not match, and the distance between energy-rich areas and heavy-load areas is relatively long. In order to achieve efficient allocation and full utilization of energy, it is necessary to develop large-capacity long-distance transmission technology. At the same time, DC asynchronous interconnection also avoids large-scale chain links. Faults occur, eliminate low-frequency oscillation problems, and will not aggravate the short-circuit current of the AC power grid. Modular multi-level flexible DC transmission technology has many excellent characteristics such as small footprin...

AI Technical Summary

Problems solved by technology

These control methods all have a controllable margin in power adjustment. When a serious fault occurs on the AC side, the switching power of the AC and DC side of the converter station will be greatly unbalanced at the moment of the fault, and the degree of this imbalance will exceed The power adjustment controllable margin of the existing control method has insufficient adjustment ability, resulting in voltage instability on the DC side and the shutdown of the converter station

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