Method of improving low voltage crossing performance of large-scale photovoltaic system

Abstract

The invention discloses a low voltage crossing method of a DC outward transmission system of a large-scale photovoltaic power station. When an AC power grid has different types of faults, the whole system has problems such as grid-connected current distortion and DC bus overvoltage in a basic voltage current double closed-loop control strategy and cannot realize low voltage crossing. Under the condition, a novel low-votlage control method combining a dynamic switching control method of a photovoltaic power generation module MPPT mode with current converter positive and negative sequence doublecurrent loop control of VSC of an optimized DDSRF-PLL (Decoupling Dual Synchronous Reference Frame based Phase-Locked Loop) is provided. Via coordination of a front-stage photovoltaic power station and a back-stage VSC current converter, influence from overvoltage and a negative sequence component of the DC bus to grid-connected current is suppressed efficiently. Low-voltage crossing operation ofthe large-scale photovoltaic power station is realized successfully and the capacity of stable operation of a large-scale photovoltaic power station accessing system is greatly improved.

Description

technical field [0001] The invention belongs to the technical field of photovoltaic power generation, and in particular relates to a method for improving the low-voltage ride-through performance of a large-scale photovoltaic system. Background technique [0002] In recent years, due to the low-voltage DC output characteristics of photovoltaics, the continuous development of high-power DC / DC converters, and the increasingly mature development of high-voltage DC grids, photovoltaic power generation technology must have the ability to connect to DC grids. And with the large-scale clustering of photovoltaics, the interaction between the photovoltaic DC grid-connected system and the AC grid at the receiving end is becoming more and more significant. In order to ensure uninterrupted grid-connected operation of photovoltaic power plants during grid failures and improve the stable and reliable operation of the entire system, the State Grid stipulates that photovoltaic grid-connected...

AI Technical Summary

Problems solved by technology

[0003] Most of the existing LVRT control strategies are used in medium and low-voltage AC grid-connected systems, and are not suitable for large-scale photovoltaic power station DC step-up and external transmission systems. In addition, the VSC control strategy in the current photovoltaic DC grid-connected scheme is relatively basic and does not consider AC Impact of grid failure

When the AC power grid fails, under the basic voltage and current double closed-loop control strategy of the entire system, problems such as DC bus overvoltage and grid-connected current distortion will occur, resulting in LVRT ride-through failure of the outgoing system

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