Low-voltage ride-through control method for grid-connected inverter

Abstract

The invention discloses a low-voltage ride-through control method for a grid-connected inverter. Whether a power grid works properly can be judged through a dropping state judgment device, so the method has the advantage of being fast in power grid judgment. In specific configuration, the method includes the steps of controlling a given current calculation module to calculate given current target values of the power grid in a normal working state and in a dropping state, and controlling a feedforward weight calculation module to distribute reasonable specific gravity of different voltage feedforward quantities according to the voltage state of the power grid agine. Consequently, current impact at the instant of voltage drop of the power grid can be restrained, and the recovery rate of the current waveform after voltage drop of the power grid can be increased so that the balance of three-phase current output by the inverter during voltage drop of the power grid can be maintained. Thus, it is guaranteed that the grid-connected inverter is in a fault ride-through state and accords with national standard inverter grid-connection requirements.

Description

technical field [0001] The invention belongs to the technical field of inverters, and more specifically relates to a low-voltage ride-through control method suitable for grid-connected inverters. Background technique [0002] As a large number of distributed power sources are connected to the power grid, affected by severe weather or sudden start of large loads (such as large motors, steelmaking electric arc furnaces, etc.), the voltage of the grid bus connected to the load will drop, affecting the normal work of other users state. Statistics show that more than 60% of voltage drops are related to severe weather (such as lightning strikes, storms, etc.), and the damage lasts for a short time. [0003] Under normal circumstances, when the power grid fails, the grid-connected inverter will immediately disconnect from the grid, regardless of the duration and severity of the fault, so as to protect the safety of the grid-connected inverter to the greatest extent. Lower values ...

AI Technical Summary

Problems solved by technology

However, when distributed power generation accounts for a large proportion, taking the method of immediate off-grid will increase the difficulty of the recovery of the entire system, and may even aggravate the failure, and eventually cause all grid-connected inverter systems of other distributed power sources in the system to go off-grid , so effective low-voltage ride-through control measures must be taken to maintain grid stability

[0004] The voltage drop of the power grid will cause an instantaneous current impact on the distributed power supply. In the existing technology, one is to solve the problem through hardware solutions by increasing the capacity of power devices to withstand several times the current impact, such as IGBT , AC contactors, molded case circuit breakers, etc., increase the hardware cost of the equipment

The second is to use the feedforward control method to suppress grid disturbance through an algorithmic solution, and the feedforward item uses the average value of the positive sequence component of the fundamental wave of the grid voltage However, the voltage average as a feed-forward item has sampling delay, control delay, and large filtering delay, so that the feed-forward item cannot track the grid voltage well, and the purpose of suppressing voltage fluctuations cannot be achieved. When the grid voltage drops There is still a large current impact in an instant

In addition, when the power grid fails due to unbalanced voltage drop, the three-phase current output by the inverter will be unbalanced, resulting in negative sequence current components.

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