A starting method of grid-connected inverter

Abstract

The invention relates to the technical field of grid-connected inverters, in particular to a method for starting a grid-connected inverter, which compares the effective value of the inverter phase voltage with a preset first reference voltage value to judge the grid-connected inverter Whether the relay is bonded, in a mains cycle, the relay is controlled by comparing the difference between the collected current inverter phase voltage value and the instantaneous value of the mains phase voltage with the preset third reference voltage value Turn off, to realize the accurate detection of the effectiveness of the inverter switch tube and the grid-connected relay before the inverter is connected to the grid, and at the same time eliminate the inrush current when the relay is closed and the inrush current caused by the switching tube driving wave when the grid is connected, and finally make the Photovoltaic grid-connected inverters can be successfully connected to the grid and have long-term stable grid-connected power generation.

Description

technical field [0001] The invention relates to the technical field of grid-connected inverters, in particular to a method for starting a grid-connected inverter. Background technique [0002] Before all grid-connected inverters are connected to the grid, they are faced with the failure of the inverter semiconductor switch tube and the failure of the grid-connected relay. A series of problems such as inrush current caused by improper duty cycle initialization. [0003] At present, the mainstream method of starting the grid-connected inverter before grid-connection is: [0004] Step 1: Turn off the relay and the inverter drive, and check whether the voltage at the inverter terminal is close to 0. When the voltage at the inverter terminal is greater than a certain value, it is considered that the relay is bonded, and an error is reported for the relay failure; [0005] Step 2: The inverter detects the phase of the grid in real time, and according to the time Tr required from...

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Problems solved by technology

[0007] However, the current mainstream practice of grid-connected inverters does not test the effectiveness of the inverter power switch tube before grid-connected startup, and there is a risk of safety accidents caused by continuous operation when the inverter switch tube or its drive circuit fails; The mainstream practice of the current grid-connected inverter is to detect the relay bonding fault before the grid-connected start-up, and not detect the open-circuit fault when the relay is driven but the relay is not closed; considering the relays, relay drive circuits, There is a certain deviation between the actual closing point of the grid-connected relay and the zero-crossing point of the mains voltage due to the differences in the components of the phase-locked circuit and the mains voltage sampling circuit. There is still a potential difference between the two ends of the relay at the closing time, and the inrush current still exists.

In the three-camera system, it is even more difficult to close each relay at the zero-crossing point; the current mainstream practice of grid-connected inverters does not optimize the duty cycle of the inverter drive before the grid-connected startup, which makes the inverter drive Due to the unreasonable duty cycle, a large inrush current is generated when starting

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