Failure detection method for relay of three-phase grid-connected inverter

Abstract

The invention discloses a failure detection method for relay of a three-phase grid-connected inverter. Under the condition that a relay on each phase of the three-phase grid-connected inverter is driven by the same driving signal, the invention provides the method for detecting the voltage of the three-phase output end of the inverter to a zero line N, and whether the relay on a certain phase is adhered or cannot be attracted can be accurately detected by virtue of the pull-in action of a switching tube of the inverter and the actual photovoltaic panel PV to-ground voltage, false detection isavoided, and 100% accurate detection can be achieved.

Description

technical field [0001] The invention belongs to the field of three-phase grid-connected inverters, in particular to a method for detecting failure of a relay of a three-phase grid-connected inverter. Background technique [0002] Due to safety requirements, the grid-connected inverter must use relays for electrical isolation between the output terminal and the grid terminal. For three-phase grid-connected inverters, relays must be installed between the three phases A, B, and C of the grid and the output terminals of the inverter. When the inverter is not working, the relays must be reliably disconnected to ensure the inverter There is no electrical connection to the grid at all. If there is a failure of relay adhesion failure, it will bring great safety hazards. Therefore, before the inverter starts to run, it must detect the adhesion failure of the relay to ensure that the relay is in a normal working state. In addition, when the relay fails to close normally, if the inv...

AI Technical Summary

Problems solved by technology

However, in order to reduce the design cost of the inverter, the relays on the A, B, and C three-phase lines often use the same drive signal, which brings troubles to the relay detection. For the conventional three-phase grid-connected inverter, The voltage detected by the inverter includes the voltage at the inverter output terminal and the phase voltage of the power grid. The voltage detection is the voltage of the neutral line N of the power grid A, B, and C. Under normal circumstances, if the potential of Ni is equal to the potential of the neutral line N, the voltage at the output terminal of the inverter can be detected when the relay is disconnected or closed. Whether the phase voltage of the grid is equal or not is used to determine whether the relay has failures such as adhesion or failure to pull in normally. However, the potential of the Ni point is suspended when the inverter is designed, and it may be equal to the N potential of the neutral line, or it may not be equal. In this way, When the relay is disconnected, it is possible that the detected voltage at the inverter output terminal is equal to the phase voltage of the power grid due to the floating potential of the Ni point, which may cause a false report of relay adhesion failure. It may be that the potential of the Ni point is not equal to the N potential of the zero line, and the relay is mistakenly considered to be closed and the alarm is reported by mistake, so that the inverter cannot operate normally to generate electricity.

[0004] Chinese patent CN108761319B discloses "Relay failure detection method, device and system of photovoltaic grid-connected inverter". This patent is aimed at detecting relay failure of three-phase grid-connected equipment, which requires additional detection of voltage at other points, making the system complicated. And it can only detect a group of relays with the same driving signal to fail at the same time, and cannot detect the failure of a single relay to fail

[0005] Chinese patent CN107957546B discloses "a detection method and equipment for inverter grid-connected AC relay". This patent is also for relay failure detection of three-phase grid-connected inverters, but the technical problem to be solved is the short circuit of the power grid to the ground wire The problem of lower relay detection failure is completely different from the technical problem to be solved in the present invention

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