STM32 digital PFC

AN3165

8/31

Doc ID 17180 Rev 1

2

STM32 digital PFC

2.1

Introduction

A power factor correction (PFC)–also known as a power factor controller–is a feature that

reduces the amount of reactive power generated by a non-linear load. Loads such as

electrical motors distort the current drawn from the system and, in such cases, a power

factor correction may be used to counteract the distortion and raise the power factor.

Reactive power operates at right angles to true power and energizes the magnetic field.

Reactive power has no real value for an electronic device, but electric companies charge for

both true and reactive power, resulting in unnecessary charges. PFC is a required feature

for power supplies shipped to or within Europe.

In a PFC, the power factor is the ratio of the true power divided by the reactive power. The

value of the power factor is between 0 and 1. If the power factor is above 0.8, the device is

using power efficiently. A standard power supply has a power factor of 0.70 to 0.75, and a

power supply with PFC has a power factor of 0.95 to 0.99.

PFC equipment is used to reduce the reactive power produced by fluorescent and high bay

lighting, arc furnaces, induction welders and equipment that uses electrical motors.

2.2

System overview

This demonstration board implements a digital control for a high-power PFC controlled by an

STM32. It has been designed to offer high performances in terms of PF, THD and DC output

voltage ripple.

Contrarily to monolithic ICs, this digital approach facilitates the application of a sophisticated

control algorithm and makes it easier to adjust system parameters to meet customer

requirements.

The STM32 digital PFC hardware system is composed of two boards: a digital PFC board

(STEVAL-ISF002V1) that implements the boost stage of the PFC, and a control board

(STEVAL-IHM022V1) based on the STM32F103ZE microcontroller that implements the

control stage of the PFC.

The digital PFC board can be connected through an MC connector to several evaluation kits

available from STMicroelectronics, in particular those designed for motor control.

An on-board OFF-line switched mode power supply (SMPS) based on the VIPER12 is used

to generate the 15 VDC voltages necessary to supply the drivers inside the power board.

This board provides 5 volts to any control stage supplied via the MC connector.

Note:

Refer to user manual UM0877 for a description of the STM32 digital PFC and an application

example.

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Main system features

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Maximum output power:1400 W

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Input voltage range: 185 ÷ 230 Vrms / 50 Hz

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Output voltage: 415 Vdc / 5% ripple

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PF up to 0.998 (at nominal rated power)