AN3392 datasheet(7/57 Pages) STMICROELECTRONICS

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AN3392

Application overview

Doc ID 018749 Rev 1

7/57

Inverters are complex systems normally providing three functions (DC-DC conversion, DC-

AC conversion and Anti-Islanding) managed by a main controller typically implemented by a

microcontroller or DSP and executing the following actions:

●

Anti-Island control, a safety control forcing the system to disconnect from the grid when

it is OFF for maintenance.

●

Inverter control, for converting the DC power generated by the PV field to AC power

compatible with the power on the public grid (voltage and current amplitude, frequency

and phase).

●

The MPPT (maximum power point tracking) control, allowing the extraction of the

maximum amount of power possible from the PV field in order to maximize the power

sourced to the grid.

A limitation of the architecture in Figure 2 is that the MPPT control performs properly only

when the PV field is uniformly irradiated.

A first evolution of the above architecture is shown in Figure 3 (string-distributed), where the

inverter includes more DC-DC converter sub-blocks, each implementing its own MPPT

algorithm.

Figure 3.

Photovoltaic system with multi-string inverter

Even though this architecture provides for a different shadow on each string, it doesn’t solve

the problem of the partial shading on each panel.

AN3392 Datasheet(PDF) 7 Page - STMicroelectronics