Slide 1: Deep Dive into PFC Topologies
logo-signature Deep Dive into PFC Topologies September 2024 Session 1 Starts: 1 AM PDT | 4 AM EDT | 10 AM CEST Session 2 Starts: 9 AM PDT | 12 PM EDT | 6 PM CEST rev 20180504
Slide 2: Agenda
Agenda • Introduction: Power Factor Correction • Boost PFC Control • Boost PFC Improvements (Efficiency, PF, Distortion) • Bridgeless PFC • Questions and Answers
Slide 3: Power Factor Correction (PFC)
Power Factor Correction (PFC) • PFC stands for power factor correction. • The power factor (PF) is the ratio of active (real) power over apparent power: Active Power [W] PF = = Apparent Power [V𝑥A] • A PF of 1 corresponds to a pure resistive load VIN IIN IIN VIN o The current is sinusoidal and in…
Slide 4: The Basic Concept of PFC
The Basic Concept of PFC PFC stage Adding PFC The input current follows the voltage (sinusoidal). PFC can be passive (e.g. inductor, valley fill) or active (e.g. buck, boost, flyback). When considering the tradeoffs between performance, efficiency, size, and cost, the boost PFC is the most widely us
Slide 5: Agenda
Agenda • Introduction: Power Factor Correction • Boost PFC Control • Boost PFC Improvements (Efficiency, PF, Distortion) • Bridgeless PFC • Questions and Answers
Slide 6: Boost PFC
Boost PFC • Simple implementation (1x inductor, 1x switch, 1x diode) • High efficiency • Can operate at low input voltage • Step-up
Slide 7: Boost PFC Control Methods
Boost PFC Control Methods • Depending on the market, the type of converter, and the region of the world, the standard minimum PF requirements may be different, ranging from not necessary to a high value. There may also be additional requirements, such as the amount of distortion or minimum PF at dif
Slide 8: Boost PFC Control Method: CoT BCM
Boost PFC Control Method: CoT BCM Constant-on-Time (COT) Boundary-Conduction Mode (BCM) / Critical-Conduction Mode (CrM) CrM (Constant-On-Time) IL Operation Mode tON t • Simple architecture (no need to measure VIN) VAC ( ) VAC ( ) • Zero-current switching (and valley switching) Input Current IIN1(
Slide 9: Boost PFC Control Method: CCM
Boost PFC Control Method: CCM IL IPK IREF Continuous Conduction Mode (CCM) OFF_CUR_REF n-1 n n+1 t SET t PWM t tON tS • Lower RMS current (IIN average is very close to IPK) (from HR12xx digital PFC) ➢ Can be used for higher power up to 1kW (more with interleaving) • More complex architecture (VIN is
Slide 10: Agenda
Agenda • Introduction: Power Factor Correction • Boost PFC Control • Boost PFC Improvements (Efficiency, PF, Distortion) • Bridgeless PFC • Questions and Answers
Slide 11: Efficiency Improvement – BCM + DCM
Efficiency Improvement – BCM + DCM Allowing Discontinuous Conduction Mode (DCM) when the Output Power (POUT) Decreases In BCM, the switching frequency (fSW) goes DCM (Variable-On-Time) up when POUT decreases. This results in IL high switching losses. Operation Mode Inserting a dead time to force it
Slide 12: Efficiency Improvement – CCM + BCM + DCM
Efficiency Improvement – CCM + BCM + DCM Multi-mode control: all 3 modes (CCM, BCM, and DCM) are used by the PFC controller under different output load conditions, depending on the instantaneous input voltage level ∆ICCM • CCM or BCM at high loads. • Different DCM modes at light loads to optimize ef
Slide 13: THD Performance Improvement with Variable-On-Time
THD Performance Improvement with Variable-On-Time At light loads, the input filtering capacitor does not fully discharge around the zero crossing of the input AC. A constant-on-time (COT) controller may also reach the max frequency limit around zero-crossing This is the cause of high distortion (hig
Slide 14: PF Enhancement with Input Capacitor Current Compensation
PF Enhancement with Input Capacitor Current Compensation A boost PFC shapes its input current to be sinusoidal, but the input filter placed in front of iL the PFC can degrade the Power Factor by L introducing a phase shift. iIN RBG + REMI iCz iCz iCz M1 Vbus • Compensating for the input capacitor VI
Slide 15: Agenda
Agenda • Introduction: Power Factor Correction • Boost PFC Control • Boost PFC Improvements (Efficiency, PF, Distortion) • Bridgeless PFC • Questions and Answers
Slide 16: Rectifier Bridge Losses
Rectifier Bridge Losses The bridge rectifier adds 2 diodes in series with the boost PFC at all times, => conduction losses I I 𝑃𝐷 𝐶𝑂𝑁𝐷 = 𝑉𝐹 𝑥 𝐼𝑅𝑀𝑆 With the use of GaN switches and control optimization, the boost PF ’s efficiency alone has increased greatly, such that the rectifier…
Slide 17: Bridgeless PFC – Concept
Bridgeless PFC – Concept In a conventional boost PFC, there is already a diode blocking the reverse conduction — why not utilize this diode to remove the diode bridge rectifier? When using one boost PFC on each AC line, they work in turns, one for each alternance of the sinusoidal input voltage. I I
Slide 18: Totem-Pole PFC
Totem-Pole PFC The evolution of the bridgeless dual-boost PFC is the totem-pole PFC. I Fast Switching Slow Switching fSW = 100kHz fSW = fGRID • Reduced to one inductor. • Diodes replaced by MOSFETs. • Rearranged to work as a synchronous boost (fast switching leg) with polarity-selection switches (sl
Slide 19: Totem Pole PFC – Operation
Totem Pole PFC – Operation A+C • Fast switches connected to inductor A G1 G4 B • Work as a synchronous boost Load B+D • Slow switches D D • Select input polarity C G2 G3 A G1 G4 B Load C+A C G2 G3 D A+C
Slide 20: Totem Pole PFC – Operation
Totem Pole PFC – Operation A+C • Fast switches connected to inductor A G1 G4 B • Work as a synchronous boost Load B+D • Slow switches • Select input polarity C G2 G3 D B A G1 G4 B Load C G2 G3 D C+A A+C
Slide 21: Totem Pole PFC results
Totem Pole PFC results Topology Totem Pole PFC Normal PFC Freewheeling diode - 1x fast recovery Fast MOSFET/SiC MOSFET/GaN 2x GaN FET * 2 1x GaN FET Rectifier bridge - 1x Slow MOSFET/Diode 2x Si MOSFET - Efficiency@90V/300W 97.6% 95.8% 100.0% 90Vac 115Vac 230Vac 265Vac 99.5% Efficiency (%) Measured
Slide 22: Agenda
Agenda • Introduction: Power Factor Correction • Boost PFC Control • Boost PFC Improvements (Efficiency, PF, Distortion) • Bridgeless PFC • Questions and Answers
Slide 23: Thank you!
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