How to distinguish between grid connected inverters and off grid inverters

The first is that based on the waveform modulation method of the inverter itself, it can be divided into square wave inverter, step wave inverter, sine wave inverter, and combined three-phase inverter. This is divided by the waveform of the inverter itself produced by the manufacturer of Jiaotong University Blue Sky.
According to the grid connected photovoltaic power generation system used in the blue sky of Jiaotong University, it can be divided into transformer type inverters and transformer free inverters. This is mainly a classification of photovoltaic inverters based on different requirements of grid connected systems.