Distributed-generation three-phase inverter smooth switch control method

Abstract

The invention discloses a distributed-generation three-phase inverter smooth switch control method. The method includes smooth switch control over two parts from isolated island operation to grid-connected operation and from the grid-connected operation to the isolated island operation. A smooth switch control link is mainly composed of a phase-locked loop (PLL) and a switch. When an inverter is switched from the isolated island operation to the grid-connected operation, output voltage of the inverter is subjected to presynchronization by operating the switch, so that the output voltage and grid voltage of the inverter are synchronized, current impacting during grid connection is reduced, and smooth grid connection switch is realized; when the inverter is switched from the grid-connected operation to the isolated island operation, reference instruction controlled by current are gradually decreased to zero form current instruction current by operating the switch, off-grid operations have no effect on a system since the grid-connection current is dropped to zero before disconnection of the grid connection switch, the output voltage of the inverter cannot fluctuate, and off-grid smooth switch is realized. With the method, dual-mode smooth switch operation of the distributed generation system is realized.

Description

technical field [0001] The invention relates to the technical field of three-phase inverter control, in particular to a method for smooth switching control of a distributed power generation three-phase inverter. Background technique [0002] With the increasingly severe global energy crisis and environmental pollution, people pay more and more attention to the development and utilization of distributed energy (photovoltaic, wind power, fuel cells, etc.). The substitution ratio of energy will become larger and larger. At present, distributed energy generation is considered to be the most promising technology in the world, and various countries have invested huge sums of money in research and development, and are vigorously expanding its market applications. [0003] A key technology of distributed energy control is the smooth switching technology. The inverter should have the ability to provide electric energy to the local load and the grid at the same time. Intermittent po...

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Problems solved by technology

When transferring from island mode to grid-connected mode, because the three-phase inverter is not synchronized with the grid, instantaneous overvoltage or over-current will occur; when grid-connected mode is transferred to island mode, due to the power exchange between the two After the grid-connected switch, the active or reactive power is unbalanced, which eventually leads to fluctuations in the output voltage of the inverter, which will affect the normal operation of the load and destroy the reliability and stability of the power supply.

The existing smooth switching control methods often only modify the calculation method of the reference current command during switching, or artificially add virtual impedance to reduce the current impact, and do not fundamentally eliminate the current impact and voltage fluctuations before switching. reason

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