STM32 digital PFC

AN3165

10/31

Doc ID 17180 Rev 1

Figure 2.

STM32 digital PFC: connections for the boost and control stages

The "voltage error compensator" regulates the output DC voltage at the target reference

VDCREF. Its output is then used as a scaling factor for the input Vac. This product

constitutes the current reference input IACREF for the "current error compensator",

operating at 40 kHz. The output of this last PI is the actual duty cycle applied at the gate of

the power MOSFET transistor Q.

The "voltage error compensator" uses a frequency of 100 Hz, in line with the Vdc ripple that

has this frequency.

The "current error compensator" uses a frequency of 40 kHz, which is the frequency at

which the system gets the new converted values of all the necessary signals.

2.4

STM32 peripheral utilization

The following peripherals are used to implement the digital PFC.

●

TIM3: its frequency is fixed at 80 kHz. CH4 is used to drive the PFC MOSFET whereas

CH3 is used as the start trigger for ADC1_2.

●

ADC1: converts the output DC voltage (Vdc) and inductor current (Iac) alternatively.

●

ADC2: converts a dummy value and input AC voltage (Vac) alternatively. ADC2 is set

as the slave of ADC1 for simultaneous conversions. The dummy value is replaced with

the sub-motor bus voltage when this firmware is merged with the MC firmware.

●

DMA1: stores the converted values by means of its CH1. As soon as all values have

been converted (with a frequency of 40 kHz), an IRQ is generated and the PFC routine

is executed.

●

EXTI_LINE1: retrieves overcurrent information from the power section. An IRQ is

generated and the digital PFC is stopped if an overcurrent condition is detected.