AN3392 datasheet(19/57 Pages) STMICROELECTRONICS

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AN3392

SPV1020 functions

Doc ID 018749 Rev 1

19/57

the perturbation of the DC. The resolution of the duty cycle perturbation is 0.2 % over most

of its range.

An increase or decrease of the DC depends on the update done in the previous step and by

the direction of the input power.

The MPPT algorithm compares the current input power (Ptn) with the input power computed

in the previous step (Ptn-1). If the power is increasing then the update is in the same

direction as in the previous step. Otherwise the update is swapped (from increasing to

decreasing or vice-versa).

When the system is at the MPP, the user can see the duty cycle oscillating between three

values within a time window of 256*3 = 768 times the switching period (7.68 ms).

Figure 18 shows the sampling/working points (red circles) set by the SPV1020 and how they

change (red arrows) during normal operating mode.

Figure 18.

MPPT concept flow diagram

The input for the MPPT algorithm is the incoming power but its computation depends on the

working mode of the application, either DCM or CM.

The SPV1020 discriminates between DCM and CM by the zero crossing blocks (ZCB), refer

to Section 3 (Figure 9) for details.

The SPV1020 moves between DCM and CM states implementing a sort of hysteresis,

depending on how many of the four ZCBs (Figure 9) have their own outputs activated.

Figure 19 shows the related finite state machine (FSM) implementation within the

normal/MPPT mode:

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