AN205346 F²MC-8FX Family, MB9500 Series Power Factor Correction.pdf

```AN205346
F²MC - 8FX Family, MB9500 Series, Power Factor Correction
This document describes the principle and usage of PFC along with Power Factor. Power Factor is a parameter that
gives the amount of working power used by any system in terms of the total apparent power. Power Factor becomes
an important measurable quantity because it often results in significant power savings.
Contents
1
2
3
Introduction ..................................................................1
1.1 Purpose...............................................................1
1.2 Document Overview............................................1
Significance of Power Factor .......................................2
2.1 Overview .............................................................2
2.2 Harmonic Introduce.............................................3
Principle of PFC...........................................................4
3.1 Overview .............................................................4
1
1.1
3.2 Power Factor Correction Topologies................... 4
PFC Implementation.................................................... 7
4.1 Smart Power Module of PFC .............................. 7
4.2 PFC Implementation ........................................... 9
Document History............................................................ 12
4
Introduction
Purpose
This document describes the principle and usage of PFC.
1.2
Document Overview
The rest of document is organized as the following:
Chapter 2 explains the Significance of Power Factor.
Chapter 3 explains Principle of PFC.
Chapter4 explains the PFC Implementation.
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2
Significance of Power Factor
Significance of power factor
2.1
Overview
Power Factor is a parameter that gives the amount of working power used by any system in terms of the total
apparent power. Power Factor becomes an important measurable quantity because it often results in significant
power savings.
Typical waveforms of current with and without PFC are shown in Figure 1 below.
Figure 1. Waveform with/without PFC
These waveforms illustrate that PFC can improve the input current drawn from the mains supply and reduce the DC
bus voltage ripple.
The objective of PFC is to make the loading for a power supply look like a simple resistor. This allows the power
distribution system to operate more efficiently, reducing energy consumption.
When Power Factor deviates from a constant, the input contains phase displacement, harmonic distortion or both,
and either one degrades the Power Factor.
The remaining power that is lost as Reactive Power in the system is due to reasons:

Phase shift of current with respect to voltage, resulting in displacement.

Harmonic content present in current, resulting in distortion.
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2.2
Harmonic Introduce
Current harmonics are sinusoidal waves that are integral multiples of fundamental wave.
Source of current harmonics:

Power Electronic Equipment

Auxiliary Equipment

Saturable Inductive Equipment
Problems created by current harmonics:

Erroneous operation of control system

Damage to sensitive electronic equipment

Nuisance tripping of circuit breakers and blowing fuses

Excessive overheating of capacitors, transformers, motors, lighting ballasts and other electrical equipment

Interference with near electronic equipment
To reduce these problems, the current drawn from main supply needs to be shaped similar to that of voltage wave
profile.
By making power converter appear as a linear resistance to the main supply voltage, the input current shape can be
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3
Principle of PFC
Principle of PFC
3.1
Overview
In order to making power converter appear as a linear resistance despite having reactive passive elements like
inductors, capacitors and active switching elements like MOSFETs and IGBTs, the answer lies in the fact that PFC is
a low-frequency requirement. Therefore, the converter need not be resistive at all frequencies, provided a filtering
mechanism exists to remove the high-frequency ripples.
The basic elements present in a converter are an inductor and a capacitor, which are zero order elements. This
means that these elements cannot store energy in a single switching cycle due to their fundamental properties.
Active PFC must control both the input current and the output voltage. The current is shaped by the rectified live
voltage so that the input to the converter appears to be resistive. The output voltage is controlled by changing the
average amplitude of the current programming signal.
3.2
3.2.1
Power Factor Correction Topologies
Boost PFC Circuit
The boost converter produces a voltage higher than the input rectified voltage, thereby giving a switch(MOSFET)
voltage rating of Vout. Figure 2 shows the circuit for the boost PFC stage. Figure 3 shows the boost PFC input
current shape.
Figure 2. BOOST PFC
Figure 3. Boost PFC input current shape
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Closing or opening switch with a fixed rate as Figure 2. But the duty is based on the value of input voltage and
voltage on capacitor. When input voltage is higher than capacitor voltage, the duty is small. When input voltage is
lower than capacitor voltage, the duty should be large enough for the inductor having a way to discharge.
3.2.2
Buck PFC Circuit
In a buck PFC circuit, the output DC voltage is less than the input rectified voltage. Large filters are needed to
suppress switching ripples and this circuit produces considerable Power Factor improvement. The switch(MOSFET)
is rated to Vin this case. Figure 3-3 shows the buck PFC input current shape. Figure 3-4 shows the buck PFC input
current shape.
Figure 4. Buck PFC circuit
Figure 5. Buck PFC input current shape
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3.2.3
Buck/Boost PFC Circuit
In the buck/boost PFC circuit, the output DC voltage may be either less or greater than the input rectified voltage.
High Power Factor can be achieved in this case. The switch (MOSFET) is rated to (Vin + Vout). Figure 6 shows the
circuit for the buck/boost PFC stage. Figure 7 shows the buck/boost PFC input current shape.
Figure 6. Buck/Boost PFC circuit
Figure 7. Buck/Boost PFC input current shape
Regardless of the input line voltage and output load variations, input current drawn by the buck converter and the
buck boost converter is always discontinuous. However, in the case of a boost converter, input current drawn is
always continuous if it is operating in Continuous Conduction Mode. This helps to reduce the input current harmonics.
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4
PFC Implementation
This section provides notes on PFC implementation
4.1
Smart Power Module of PFC
FPAB30BH60 is an advanced smart power module of PFC that Fairchild has developed and designed mainly
targeting mid-power application especially for a conditioner. It combines optimized circuit protection and drive IC
matched to high frequency switching IGBTs. System reliability is further enhanced by the integrated under-voltage
lock-out and over-current protection function.
Figure 8. Pin configuration
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Figure 9. Pin description
Figure 10. Internal equivalent circuit and input/output pins
FPAB30BH60 datasheet: http://www.fairchildsemi.com/pf/FP/FPAB30BH60.html
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4.2
PFC Implementation
In this part, it mainly talks about the implementation in hardware and software.
4.2.1
Block Diagram for PFC Implementation
Figure 11. Block diagram for PFC implementation
4.2.2
PFC hardware interface
PFC hardware interface is shown in Figure 12 below.
Figure 12. PFC Hardware interface
The dotted line frame in Figure 12 is integrated into FPAB30BH60.
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4.2.3
PFC software arithmetic
Software block is shown below in Figure 13.
Figure 13. PFC software block
Vavr’ :Vavr(the average value of Vac)multiply 1/(Vavr*Vavr).
Output of PPG is to control the duty of IGBT integrated in FPAB30BH60.
4.2.4
PFC software arithmetic implementation
This part mainly mentions functions:
Function Name: Init_PFC
Description:
Initialize PFC
Input:
None
Output:
None
Function Name: PFC_Stop
Description:
Initialize PFC
Input:
None
Output:
None
Function Name: PFC_Start
Description:
Start PFC
Input:
None
Output:
None
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http://www.cypress.com/cypress-microcontrollers
http://www.cypress.com/cypress-mcu-product-softwareexamples
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F²MC - 8FX Family, MB9500 Series, Power Factor Correction
Document History
Document Title: AN205346 – F²MC - 8FX Family, MB9500 Series, Power Factor Correction
Document Number: 002-05346
Revision
**
*A
ECN
-
5267119
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Orig. of
Change
Submission
Date
Description of Change
Jason Lv.
03/17/2011
V1.0, First Draft
Mona Chen
06/06/2011
Change the document format
WJLV
05/09/2016
Migrated Spansion Application Note “MCU-AN-500016-E-12” to Cypress format.
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F²MC - 8FX Family, MB9500 Series, Power Factor Correction
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