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 5 Additional Information ................................................ 11 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. Chapter5 explains Additional Information. www.cypress.com Document No. 002-05346 Rev. *A 1 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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. www.cypress.com Document No. 002-05346 Rev.*A 2 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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 made to follow the input voltage wave. www.cypress.com Document No. 002-05346 Rev.*A 3 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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 www.cypress.com Document No. 002-05346 Rev.*A 4 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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 www.cypress.com Document No. 002-05346 Rev.*A 5 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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. www.cypress.com Document No. 002-05346 Rev.*A 6 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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 www.cypress.com Document No. 002-05346 Rev.*A 7 F²MC - 8FX Family, MB9500 Series, Power Factor Correction Figure 9. Pin description Figure 10. Internal equivalent circuit and input/output pins FPAB30BH60 datasheet: http://www.fairchildsemi.com/pf/FP/FPAB30BH60.html www.cypress.com Document No. 002-05346 Rev.*A 8 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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. www.cypress.com Document No. 002-05346 Rev.*A 9 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 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 www.cypress.com Document No. 002-05346 Rev.*A 10 F²MC - 8FX Family, MB9500 Series, Power Factor Correction 5 Additional Information For more information on Cypress Semiconductors Products, please visit the following websites: http://www.cypress.com/cypress-microcontrollers http://www.cypress.com/cypress-mcu-product-softwareexamples www.cypress.com Document No. 002-05346 Rev.*A 11 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 www.cypress.com 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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