Starting method of grid-connected inverter

Abstract

The invention relates to the technical field of grid-connected inverters. The invention relates to a starting method and particularly relates to a grid-connected inverter starting method. Whether a relay of the grid-connected inverter is bonded or not is judged by comparing the collected effective value of the inverter phase voltage with a preset first reference voltage value, in a commercial power period, a difference value between a collected current inversion phase voltage value and a mains supply phase voltage instantaneous value is compared with a preset third reference voltage value to control the on-off of the relay. The effectiveness of an inverter switch tube and a grid-connected relay is accurately detected before grid connection of the inverter, meanwhile, the impact current generated when the relay is closed and the impact current generated when the switch tube is driven to generate waves during grid connection are eliminated, and finally, the photovoltaic grid-connected inverter can be successfully connected with the grid and stably connected with the grid for a long time for 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...

AI Technical Summary

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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