Method for calculating droop coefficient of flexible DC power grid converter station

Abstract

The invention relates to a method for calculating a droop coefficient of a flexible DC power grid converter station. The method comprises the steps of defining a generalized power sharing coefficient, selecting a preset common reference end, and using a DC voltage as a common voltage reference signal of a droop control station; expanding a steady-state working point of a VSCi-end active power balancing relation before DC network interference according to one-order Taylor's series, and writing a matrix form; calculating a linear analytic relation between a DC voltage change amount and a power step amount of a random converter station end in a system; calculating a least square problem of a generalized power sharing coefficient vector T for obtaining an optimal solution of the generalized power sharing coefficient vector T, and calculating the droop coefficient of each droop control station.

Description

technical field [0001] The invention relates to the technical field of high-voltage flexible direct current transmission, and in particular to a control strategy for the direct current voltage of a flexible direct current grid in response to a converter station N-1 failure or a large power step disturbance. Background technique [0002] A converter station in the flexible direct current transmission network has a large power step disturbance or is out of operation due to a fault, resulting in an internal power imbalance in the entire direct current system, causing a large change in the rise or fall of the direct current voltage of each converter station, so It is extremely important to control the stability of the DC voltage inside the system [1] . Droop control has technical advantages such as small DC voltage fluctuation, fast dynamic response, and high stability [2,3] , has received more attention in the existing DC network voltage control methods. Its control idea is: ...

AI Technical Summary

Problems solved by technology

At present, the droop control adopted by the flexible DC grid mainly includes three types: one is the droop control with fixed droop coefficient [3-5] , the value of the droop coefficient is determined by the rated capacity of the converter station. Since the difference in the actual available transmission capacity of each converter station is not considered, the power adjustment is performed according to the fixed droop coefficient, which may cause some converter stations to operate at full load, while some Light-load operation of the converter station

The second is droop control with variable droop coefficient [6-8] , the droop coefficient is adaptively adjusted according to the power margin of the converter station or the size of the DC voltage. Since the value of the droop coefficient depends on the current operating state of the system, the calculation of the droop coefficient is cumbersome and complicated, and the real-time adjustment of the droop coefficient will be frequently Changing the power distribution method of the DC system, causing frequent fluctuations in the DC voltage

The third is droop control with proportional sharing characteristics [9] , the DC voltage at one end is selected as the public voltage reference signal of the droop control station. Under the premise of ignoring the change of DC network loss, the droop coefficient of the converter station is determined by the load sharing coefficient, the system power step and the maximum allowable DC voltage deviation. However, the determination of the droop coefficient still faces the problem of artificially setting the maximum allowable DC voltage deviation

In view of the above analysis, a fast, direct and general calculation method for the droop coefficient of the droop control station has not yet been formed. In view of the N-1 fault of the converter station or the large power step disturbance, it is necessary to propose a fast and direct calculation of the droop coefficient of the converter station A new method to realize the rapid stabilization of the DC voltage of the flexible DC grid under the goal of ensuring that the voltage fluctuation of the DC grid is as small as possible

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