Method for detecting failure of relays and protecting filter capacitors of photovoltaic grid-connected inverters

Abstract

The invention relates to the technical field of photovoltaic grid-connected inverters, particularly to a method for detecting the failure of relays and protecting filter capacitors of photovoltaic grid-connected inverters. The method comprises the following steps: before the relays are closed, if the difference of the absolute values of the effective value (Vinv) of one-phase or multi-phase inversion voltage and the effective value (Vgrid) of the same-phase grid voltage is detected to be smaller than the failure voltage threshold (delta V) of the relays, namely the absolute value of(Vinv-Vgrid)is smaller than delta v, judging that the relays in the phase are adhered, otherwise, judging that the relays are normal; similarly, after the detection of the relays on closed inversion sides, the detection of the relays on closed grid sides, and the closed detection of the relays on both sides are successively performed by the same method, if the relays have no failures in every step, grid connection is allowed, if any relay has a failure, machines are stopped, and grid connection is denied. According to the method disclosed by the invention, when every relay is accurately detected to have a failure or not, the filter capacitor voltage output by the inverters is processed, so that the possibility that at the moment of grid connection of the inverters, the grids generate current impact on the filter capacitors is eliminated, the system stability of the inverters is improved, and the service life of the filter capacitors is prolonged.

Description

technical field [0001] The invention relates to the technical field of photovoltaic grid-connected inverters, in particular to a relay failure detection and filter capacitor protection method of a photovoltaic grid-connected inverter. Background technique [0002] In the field of string photovoltaic grid-connected inverters and low-power photovoltaic grid-connected inverters, two sets of relays are used for grid-connection. The relay detection method commonly used in the industry is that the relay pulls in and the inverter is connected to the grid at the moment, and the inverter filter capacitor will not be charged, so that the grid energy is instantly poured into the filter capacitor at the moment the inverter is connected to the grid. This will generate a large current impact on the filter capacitor, which will easily lead to the failure of the filter capacitor and the reduction of its service life. Especially when the power of the inverter is large and the capacity of th...

AI Technical Summary

Problems solved by technology

The relay detection method commonly used in the industry is that the relay pulls in and the inverter is connected to the grid at the moment, and the inverter filter capacitor will not be charged, so that the grid energy is instantly poured into the filter capacitor at the moment the inverter is connected to the grid. This will generate a large current impact on the filter capacitor, which will easily lead to the failure of the filter capacitor and the reduction of its life.

Especially when the power of the inverter is large and the capacity of the filter capacitor is large, this surge current may even cause the machine to fail to start normally.

Images