The inverter power stage performs the function of converting the DC link voltage to the grid AC voltage. This inverter stage can be of two types depending on grid connectivity – if it is used for powering only an isolated grid (like only a building) on its own, it is called an off-grid inverter and if it connects to a larger grid sharing the load from other sources, it is called a grid-tied inverter.

An off-grid inverter could be used as a back-up source or as a main power source, but while it is active, it is the only source in the micro grid it powers. Therefore, this type of inverter need not have to address the burden of synchronizing with other sources in the grid. They are used only in smaller capacity systems with lesser need to communicate with other systems.

A grid-tied inverter has the additional task of synchronizing in amplitude, frequency, and phase with the existing grid comprised of multiple sources and loads. It also needs to address the situation of detecting and isolating itself from the grid in the event of any faults in the grid like black-out, brown-out, overvoltage, and so forth. This is called anti-islanding protection. Grid-tied inverters tend to be of comparatively higher power than off-grid inverters. Since there could be multiple grid-tied inverters in a typical application, the need for communication is more important with them.

Various buck derived non-isolated topologies modulated with a sine PWM are used as inverters. These include two-level H-bridge, HERIC, three-level TNPC, three-level NPC, and three-level ANPC.