Solar power systems and inverters

AN3152

4/17

Doc ID 17056 Rev 1

1

Solar power systems and inverters

There are a wide variety of topologies employed in the design of converters for solar power

systems, but they can be separated into two main classifications:

●

Grid connected:

–

These are usually isolated residential PV panels or collections of panels, called

“farms”, connected to a central power facility maintained by a private or public

company. Therefore, the energy produced from these photovoltaic modules during

the day can be used immediately on the main grid. These systems do not require

storage batteries or any backup system to store the energy, because the main grid

continues to supply energy at night or in the absence of sunlight.

●

Standalone:

–

These are used on systems typically far from a municipal or public power grid.

These systems use a battery, or bank of batteries, to store the energy produced

during the day by the panels, in order to provide a supply of energy at night or

when solar irradiation is low. Grid connected inverters are generally more complex

than the standalone because they must synchronize with the grid sinusoid and

supply the current within the same phase. However, the first stages of design are

quite the same on both types of inverters. Traditionally, solar systems used to

implement a single, shared inverter for all panels. This is called a “centralized”

system. The trend today is toward a “string inverter” system, in which each panel

is equipped with its own low power and high performance inverter. Each of the

inverters mentioned previously can be designed following two different

approaches with respect to frequency operation. If a low frequency approach is

adopted (typically 100 Hz), very slow devices can be used. However, in this case

very heavy transformers and bulk capacitors are necessary. Generally, newer

designs adopt high frequency operation in order to minimize inverter dimensions

and weight and to maximize performance. It is worth mentioning that in our

example we have performed the tests on a 3 kW grid-connected inverter, but the

same benefits can be obtained in each of the types of inverters previously

mentioned.