Should the inverter be connected to DC or AC first?

The input of photovoltaic grid-connected inverter is components, DC power, and the output is AC power. From the perspective of the inverter, there is no order of priority, and it can be connected in any way without affecting the inverter. If we consider it from the system perspective, we can consider three situations: the initial installation of the grid-connected system, the maintenance of the grid-connected system, and the off-grid system.

1. Initial installation of grid-connected system

It is recommended to connect the PV panels first. After connecting the panels, the inverter can start. When powered on for the first time, it will first self-check, and then check the insulation of the panels and the DC side. If there are multiple strings, it is recommended to connect them one by one. After there are no problems, connect the AC power. The inverter detects the AC voltage and frequency. If it is normal, the inverter will start and adjust the voltage and phase sequence. After the voltage of the inverter is completely consistent with the voltage of the grid, the grid contactor is closed and the inverter starts working.

If it is a centralized inverter, it is recommended to connect the auxiliary power supply first, then the PV panels, and finally the AC.

2. Grid-connected system maintenance

If the components and AC are normal, you can connect the AC switch first and then the DC switch. This can save some time because once the AC switch is disconnected, the inverter will start the island protection function, and the grid recovery time is longer, generally 1 minute or 5 minutes. The sooner you close the AC switch, the earlier you can connect to the grid.

3. Off-grid battery system

The off-grid system has an additional battery, and the off-grid inverter needs to be powered by the battery, so you must first connect the battery, start the inverter, complete the self-test, and then connect the components.