The PV installations can be connected to the power grid or can be a stand-alone installation. Due to this division of installations, inverters are divided into:

• island,
• grid,
• hybrid.

The island inverters provide battery charging and they are not connected to the power grid. Grid inverters have the ability to transmit power to the grid without charging the batteries. With grid-tied inverters, if the grid voltage disappears, the inverter automatically shuts down. This is crucial for safety reasons, e.g. if maintenance work is being carried out, the power distributor stops supplying the grid and it is undesirable to return the current generated by the PV installations. Hybrid inverters can be switched to both modes of operation.
Inverters used in photovoltaic installations are also classified according to their size, i.e. the power of the photovoltaic installation with which they work [1]:

• microinverters, working with only one module of about 0.35 kW,
• string inverters (series), used in small installations built with a number of photovoltaic modules with a power from 1 to 50 kW,
• central inverters, used in large photovoltaic installations such as PV farms, generating power of around several dozen MW.

Depending on the presence of a transformer in the inverter, which is to galvanically separate the DC side from the AC side, inverters are divided into [2]:

• transformer inverter,
  • low frequency LF, where the transformer is at the output and operates at 50Hz,
  • high-frequency HF, where the transformer is at the input of the device and works with a frequency of 20-24 kHz (at the output to the network, the frequency is 50Hz),
• inverter without transformers.

Another classification of inverters is based on the number of phases to which they can be connected. Among them, inverters are distinguished by:

• single-phase, used for small installations of a few kW,
• three phase inverters, dedicated for installations with more than a few kW [1].