Phase sequence identification and phase locking method for three-phase grid-connected inverter

Abstract

The invention provides a phase sequence identification and phase locking method for a three-phase grid-connected inverter. The method comprises the following steps: configuring a power grid phase sequence identifier which is identified by a phase lock; configuring switching frequency sampling, configuring switching frequency sampling interruption, sampling the three-phase power grid voltage, and obtaining the three-phase power grid voltage for phase locking according to the three-phase power grid voltage; performing coordinate transformation on the three-phase power grid voltage for phase locking to obtain a component Uq on a Q axis under a rotating coordinate system; configuring a sampling circuit to obtain a power grid zero-crossing signal, and judging a power grid identifier; and determining a phase-locked identifier according to the zero-crossing time of the zero-crossing signal, the technical problem that in the prior art, a common phase sequence identification method fails in environments with large power grid harmonics such as a weak power grid, the phase sequence cannot be normally identified, and phase locking cannot be performed is solved, so that the grid-connected inverter can normally operate in the weak power grid and a non-weak power grid, and the applicability of the grid-connected inverter is improved.

Description

technical field [0001] The invention belongs to the technical field of grid-connected inverters in electric power equipment, and in particular relates to a phase sequence identification and phase-locking method of a three-phase grid-connected inverter. Background technique [0002] Before the grid-connected inverter is connected to the grid, it is necessary to detect the phase sequence of the three-phase sine wave voltage of the grid, so that the correct phase sequence can be used as a prerequisite for correct phase-locking of the grid, and then synchronization with external signals or phases can be achieved. [0003] In the earlier technology, since the grid-connected inverter lacks the phase sequence automatic detection function, it is necessary to confirm the phase sequence before assembly and wiring to prevent phase sequence errors. Obviously, considering the many conveniences brought by the actual field application of the phase sequence automatic identification technolo...

AI Technical Summary

Problems solved by technology

However, in actual on-site applications, especially when the number of distributed energy sources increases, the on-site power grid is a weak power grid. At this time, the grid harmonics are relatively large, and the grid voltage may cross zero multiple times. The rising edge may also be on the falling edge, which makes it difficult to accurately identify the phase sequence by using the grid voltage zero-crossing judgment method for phase sequence identification in the aforementioned prior art, so that phase locking cannot be performed.

On the other hand, due to the relatively large low-order harmonics of the grid voltage, the error of the Uq component of the grid voltage always exceeds the set error range, resulting in the judgment of the phase sequence of the grid voltage being always in an error state

In the end, the above-mentioned judgment results in the grid-connected inverter will directly lead to the abnormal failure of the machine to be connected to the grid or the abnormality of the drive when connected to the grid, resulting in machine failure or damage

[0006] In view of this, the existing technology should be improved to solve the technical problem that the rising and falling edges of the sampling circuit have multiple zero crossings, which leads to the wrong identification of the phase sequence of the existing power grid.

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