Self-adaptive virtual inertia frequency modulation control method for flexible direct-current power transmission system

Abstract

The invention provides a self-adaptive virtual inertia frequency modulation control method for a flexible direct-current power transmission system. The control method comprises the following steps of:firstly, realizing secondary frequency modulation of an alternating-current side system by controlling a reference value of active power in droop control; secondly, enabling virtual inertia power tobe equal to capacitor charging and discharging power, and establishing a coupling relationship between a direct-current voltage reference value and the active power; adopting self-adaptive virtual inertia control adjusted according to a fitting hyperbolic tangent function, reducing an inertia coefficient when a direct-current voltage is close to a limit value, thereby preventing the direct-currentvoltage from exceeding the limit value; and increasing the inertia coefficient when the direct-current voltage is far away from the limit value, thereby making the frequency more stable. With the method adopted, the overshoot in the secondary frequency modulation process is reduced, the frequency recovery of an instantaneous fault is facilitated, the frequency stability of an AC system is improved, and the stability of an interconnection system is improved.

Description

technical field [0001] The invention relates to the technical field of direct current transmission, in particular to a frequency modulation control method in a flexible direct current transmission system. Background technique [0002] At the end of the 20th century, flexible DC transmission technology has been greatly developed. Due to the advantages of flexible DC transmission technology in centralized transmission of new energy, asynchronous grid interconnection, weak grid and island power supply, so far, there have been a large number of flexible DC transmission projects. successively put into operation. At the same time, the flexible direct current transmission system can easily form a multi-terminal flexible direct current transmission system (MTDC) to realize multi-point interconnection. [0003] Although the flexible DC transmission system has many advantages, as the proportion of the flexible DC transmission system in the power grid is increasing, there are also som...

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Problems solved by technology

[0005] (1) The master-slave control method has higher requirements for inter-station communication and higher requirements for the reliability of the main converter station

[0006] (2) The control method of the virtual synchronous machine has a complex structure, and it is difficult to set parameters

[0007] (3) The droop control with additional frequency adjustment has the advantages of simple control structure, flexible terminal number expansion, and no dependence on communication, and has high engineering practicability; but the frequency modulation effect is relatively general, the transient fluctuation is large during the frequency modulation process, and the DC voltage may also be Overrun occurs

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