UM0527 datasheet(32/66 Pages) STMICROELECTRONICS

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General description

UM0527

32/66

1.2.11

Inverter

The inverter is controlled by signals generated by the PWM module. In battery working

mode the microcontroller generates two signals: INV_A and INV_B. The frequency depends

on the firmware version: EU - 50 Hz, US - 60 Hz. The duty cycle is less than 50% and

depends on the voltage of the DC/DC converter. The phase of the INV_B signal has to be

shifted by a half time period to INV_A. The inverter is controlled by a timer interrupt. The

frequency of the interrupt is 32 times higher than the mains frequency: every half-period is

divided into 16 steps, and the number of steps is stored in a global variable.

Before any steps the SHD signals are checked and if they are inactive (H), the inverter

signals are switched off (rise to H).

Buffered working mode

< 26,8

>= 27,8

Table 15.

Battery charge modes (continued)

Step of charge

process

Battery

voltage

CHOFF

Description

Table 16.

SHD signals

Step

SHD

Description

Fall to L

Proper inverter signal falls to L.

2 - 13

In any steps the squared value of the output voltage accumulates. The

accumulated value is compared with the nominal RMS output constant, and if it is

greater, the SHD signal rises to H.

14 - 15

The accumulated value of the output voltage is cleared, the variable storing a step

is not cleared. The inverter phase is changed to the opposite state.

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