Photovoltaic grid-connected inverter low-voltage ride-through control system

Abstract

The invention provides a photovoltaic grid-connected inverter low-voltage ride-through control system. On the basis of double closed-loop vector control of an inner current loop and an outer voltage loop, the system further comprises a low-voltage ride-through control module and a sub module capacitor voltage control module. When that the voltage at a grid connection point drops is detected, the low-voltage ride-through control module injects reactive current and limits active current, and the sub module capacitor voltage control module sends out a sub module capacitor voltage fluctuation range at reactive power under control of a bridge arm ring current optimization unit and / or a sub module capacitor reference voltage regulation unit. With the system, the problem that reactive power injection low-voltage ride-through is not smooth due to sub module capacitor voltage fluctuation is solved. Some inverters cannot achieve low-voltage ride-through properly. There is no need to arrange an additional power device. Low-voltage ride-through of a photovoltaic inverter system based on MMC is realized with low cost. Photovoltaic safe grid-connected operation is ensured.

Description

technical field [0001] The invention relates to the field of power electronics, in particular to the field of low-voltage ride-through control of photovoltaic grid-connected inverters Background technique [0002] With the rapid increase in the proportion of photovoltaic power generation, the grid connection of photovoltaic power stations will also bring security and stability problems to the operation of the power system, especially in the case of voltage drops due to failures at the grid connection points of the system, which will bring low voltage to the grid connection of photovoltaic power stations. Crossing the question. The low-voltage ride-through problem we are facing now has become a difficult point and research hotspot in new energy grid-connected technology. At present, most researches are based on traditional VSC-based photovoltaic grid-connected inverter low-voltage ride-through technology, but with the emergence of new inverters, such as MMC (modular multi-le...

AI Technical Summary

Problems solved by technology

At present, most researches are based on traditional VSC-based photovoltaic grid-connected inverter low-voltage ride-through technology, but with the emergence of new inverters, such as MMC (modular multi-level inverter), VSC-based When the voltage ride-through method is transferred, it will be somewhat inappropriate. For example, when the reactive power injection method is used in the MMC-based system, the sub-module capacitor voltage fluctuation will be affected by the reactive power. When the reactive power emitted by the MMC reaches a certain value, The voltage fluctuation of the sub-module capacitor may exceed the specified value, thus limiting the size of the reactive power output

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