PLL small signal modeling method in double-end MMC-HVDC system

Abstract

The invention discloses a PLL small signal modeling method in a double-end MMC-HVDC system. The method includes firstly obtaining the conversion relation of the electric quantity of the AC lines at both ends of the converter transformer; according to the control block diagram of a phase-locked loop, taking the voltage phase angle of the common node PCC and the output phase angle of the phase-locked loop as variables to construct a small-signal model of the phase-locked loop; according to the power current equation, obtaining the expression analysis formula of the voltage drop and the voltage phase angle difference at both ends of the AC branch connected with the converter; obtaining the linear expression of the voltage phase angle of the PCC point; and obtaining the small-signal mode complete expression of the phase-locked loop. Taking the voltage phase angle of the common point as the variable, and considering the common point voltage phase angle change caused by the equivalent impedance of the AC network connected with the converter, the change of two-phase synchronized rotation reference coordinate system rotating speed under the small disturbance can be reflected, and the model precision is improved.

Description

technical field [0001] The invention belongs to the field of flexible direct current transmission, and in particular relates to a small-signal modeling method of a PLL (phase-locked loop) in a double-terminal MMC-HVDC (flexible direct current transmission system based on a modular multilevel converter) system. Background technique [0002] In recent years, voltage source converter based high-voltage dc (VSC-HVDC) technology is a new generation of DC transmission technology, because it can realize the decoupling control of active power and reactive power, and there will be no commutation failure, etc. It has broad application prospects in the fields of new energy access and power supply to passive systems. Small-signal stability analysis plays an important role in the construction of flexible DC transmission network. [0003] The most widely used converter-level controller consists of phase-locked loop (PLL) and double closed-loop control. Among them, the phase-locked loop ...

AI Technical Summary

Problems solved by technology

In the case of small disturbances, the phase angle will be affected by the equivalent impedance of the AC network connected to the converter. This effect can be ignored in an AC system with a large enough short-circuit capacity, but it will make The rotation speed of the synchronous rotating coordinate system changes significantly

The existing method transforms the coordinate system of the entire small-signal model, avoiding the error caused by the equivalent impedance of the AC network, but there are many formulas, the calculation amount is significantly increased, and the simulation efficiency is reduced

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