The role of grid-connected inverter

Grid-connected PV inverters have traditionally been thought as active power sources with an emphasis on maximizing power extraction from the PV modules. While maximizing power transfer remains a top priority, utility grid stability is now widely acknowledged to benefit from several auxiliary services that grid-connected PV inverters may offer.

As aforementioned, the inverter is interconnected to the grid, so it should fulfill the grid standards as well. These standards includes power quality, grid ride through capability and islanding prevention . Power quality is mainly measured on the basis of Power Factor (PF) and Total Harmonic Distortion (THD).

For instance, a network of small solar panels might designate one of its inverters to operate in grid-forming mode while the rest follow its lead, like dance partners, forming a stable grid without any turbine-based generation. Reactive power is one of the most important grid services inverters can provide.

The grid-connected inverter can distribute the active and reactive power according to the control. Therefore, the control objectives are designed as tracking active power and reactive power. The parameters of devices and circuits are shown in Table 13.1.

Grid-forming inverters can start up a grid if it goes down—a process known as black start. Traditional “grid-following” inverters require an outside signal from the electrical grid to determine when the switching will occur in order to produce a sine wave that can be injected into the power grid.

This mismatch has not been a problem until now. Inverters have assumed that the grid is strong and will provide a stable and clean voltage and that they are able to inject real power into the grid without undue impact on its operation. The electric power grid is in transition.