POWER FACTOR CORRECTION POWER FACTOR CORRECTION Design - - PowerPoint PPT Presentation

POWER FACTOR CORRECTION POWER FACTOR CORRECTION Design considerations for

• ptimizing performance &

cost of continuous mode boost PFC circuits

by Supratim Basu,Tore.M.Undeland

All rectified ac sine wave voltages with capacitive filtering draw high amplitude discontinuous current pulses rich in harmonics , causing:

Low input power factor High circulating currents

There are many approaches to mitigate this problem : Passive and Active power factor correction Passive and Active filtering of network Accepting non-sinusoidal voltage / current in the system.

Passive Power Factor Correction

Simple inductive input filter Inductor stores energy to maintain conduction throughout half cycle Hence reduces harmonic distortation and improves power factor But size, weight and cost limits it’s application upto 200W

Active high frequency power factor correction

Makes load behave like a resistor Near unity load power factor Load generating negligible harmonics

Types of active PFC circuits with Boost converter topologies

Hard switched Soft switched using ZVT Discontinuous Conduction mode (DCM) Critical Conduction mode (CRM) Continuous Conduction mode (CCM)

Block Diagram of an active PFC Circuit of CCM Boost converter

Mosfet & Diode switching waveforms showing switching losses

Switching loss reduction strategies

RCD Snubber Circuits Magnetic Snubber Circuits Power Switch types - IGBT or MOSFET Boost Diode Options

SiC Schottky Diodes Single Package Series connected diodes PFC specific single diodes

RCD Snubber Circuits

Magnetic Snubber Circuit

Comparison of recovery time of various diodes

Comparision of RECOVERY TIME and COST of various diodes

Diode Type Part Number Rating Typical Recovery time Supplier Cost in USD

Sic Schottky SDT12S60 12A, 600V Zero Infineon 7.69 Single package series connected DSEE 808CC 10A, 600V 30ns IXYS 2.46 Single package series connected STTH806TTI 8A, 600V 30ns ST Micro 1.82 PFC Specific 1SL9R1560P2 15A, 600V 25ns Fairchild 1.42 PFC Specific 15ETX06 15A, 600V 18ns IR 1.03

Experimental Results

PFC Specific Diode Single Package Series Connected Diode SiC Schottky Diodes Input AC Voltage (RMS) 85 – 264V 85 – 264V 85 – 264V Switching Frequency 100kHz 100kHz 100kHz Input Power (W) 652 1076 653 1078 642 1049 Output Power (W) 600 1006 598 998 597 1001 Efficiency 0.92 0.935 0.915 0.925 0.93 0.954

Effect of Diode Recovery Current on the Switching Current at turn-on

The switch turn-on peak current was the lowest for the SiC Schottky Diode and highest for the Single Package Series Diode

Effect of Diode recovery current on Mosfet drain current with a SiC Diode

Effect of Diode recovery current on Mosfet drain current with a PFC specific diode

Effect of Diode recovery current on Mosfet drain current with a single package series connected diode

Conducted EMI generated by the PFC board was measured separately for each of the three diode types:

• Measurements were made at 90V AC input, 600W output load with

a 3mH common mode EMI filter connected at the input circuit

Low freq part of conducted emission spectrum ( 150kHz - 1

MHz) is almost unaffected by different diode types

High freq part of conducted emission spectrum ( 1 MHz -

30MHz) is affected by diode behavior

SDT12S60 SiC Schottky diode generates lower noise Increased EMI caused by STTH806TTI single package series

connected diodes is only about 4dBµV

Low frequency conducted emission

SiC Diode SiC Diode Single package series connected diode Single package series connected diode PFC Specific Diode PFC Specific Diode

High frequency conducted emission

Single package series connected diode Single package series connected diode PFC Specific Diode PFC Specific Diode SiC Diode SiC Diode

OPTIMIZING PERFORMANCE BY DESIGN - A SUMMARY

• Power levels < 200W - Critical conduction mode PFC may be considered
• Power levels > 200W - Hard switched CCM PFC is preferred
• Power levels < 1000W & sw. freq of 100kHz - PFC specific is the best choice
• Power levels > 1000W & sw. freq > 100kHz - Higher initial costs of SiC

Schottky diodes are justified

• Higher efficiency or higher sw. freq - ZVT resonant mode boost converter

may be considered

• Power levels < 600W - Older generation Mosfets like IRF460N(IR) could reduce

costs w/o affecting performance significantly