Phase locking method capable of improving stability during power exchange of VSC and weak AC network

Abstract

The invention discloses a phase locking method capable of improving the stability during power exchange of a voltage source converter and a weak AC network. The phase locking method comprises two parts of estimating infinite bus voltage under the condition of the weak AC power grid and carrying out phase locking by using a phase-locked loop. By using the phase locking method capable of improving the stability when the voltage source converter and the weak AC network exchange power, the stability of a whole system formed by the voltage source converter and the weak AC network when the power istransmitted to the weak AC network by using the voltage source converter or the weak AC network outputs the power outwards by using the voltage source converter can be improved, the possibility of a potential instability failure is reduced and the utilization efficiency of the voltage source converter is improved, thereby reducing the cost.

Description

Technical field [0001] The invention relates to a phase locking method of an AC system, in particular to a phase locking method for improving the stability of power exchange between a VSC and a weak AC power grid. Background technique [0002] Voltage Source Converter based High Voltage Direct Current Transmission (VSC-HVDC) is compared with conventional Line Commuted Converter based High Voltage Direct Current Transmission (LCC-HVDC) It has the advantages of flexible control, no commutation failure, and power supply to weak AC systems and passive networks. It is especially suitable for wind power generation and other new energy grid-connected application scenarios, so it has been widely used. Voltage Source Converter (VSC) mainly has three typical topologies: two-level, three-level, and Modular Multilevel Converter (MMC). [0003] Although the voltage source converter has no commutation failure and can be connected to a weak AC system, the lower the strength of the AC system, the...

AI Technical Summary

Problems solved by technology

When the AC power grid is a strong power grid, when the active power P and reactive power Q injected from the VSC into the AC grid change, the voltage change at the PCC point ΔUs≈0, and the PLL can work normally; when the AC power grid is When the power grid is weak, when the active power P and reactive power Q injected from the VSC into the AC power grid change, the change of the voltage at the PCC point cannot be ignored, ΔUs≈0 is no longer established, and the working performance of the PLL becomes worse

[0006] When the AC power grid is weak, the existing method is to reduce the response speed of the phase-locked loop by reducing ki-pll , to improve the overall stability of the system composed of VSC and AC grid, but the effect is not significant, and the selection method of the parameter ki-pll is complicated

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