Digital Power Factor Correction                                  Handling the corner cases                    Superior THD...
Power Factor primer                                                                 Inductive - Lagging                   ...
Calculating Power Factor  Power factor = Real power / Apparent power             = (Vrms * I1rms * CosΦ) / (Vrms * Irms)  ...
PF Degradation                                            Voltage                                                         ...
Power factor correction  •      Reduce energy loss in transmission lines  •      Improve power quality  •      Cost  •    ...
Useful Power                 Useful Power                        Negative Power                                           ...
Digital PFC system                                                               Boost                 AC Supply          ...
Boost Topology                                                         Average Inductor Current      IL                   ...
Challenges   Ideally ……   • Low THD & high PF over entire 90 -265 Vac input   • Low THD & high PF over entire 10 -100 % lo...
Typical specs   Load(%)                        THD(%)   •   (Typical Desired) State of the art                            ...
State of the art review  Approach 1           •     Determine Discontinuous/continuous conduction mode                  op...
State of the art review  Approach 2           •     Harmonic injection  Challenge           •     Trial and error         ...
State of the art summary  •     Computationally complex (MIPS, code size)  •     Fixed point implementation hard !!  •    ...
Proposed solution features  •      Good THD at all operating conditions  •      Plug and play  •      Just enter parameter...
Proposed solution features .  •      No if-else ladder  •      Small extra code size  •      Low MIPS requirement ~ 12-14 ...
Proposed solution features ..  •      System independent /scalable to any rating  •      Relevant for Interleaved PFC and ...
Switched mode Simulation Results  •      Fixed frequency operation ~100 KHz  •      Vac = 220V rms ac, Vdc = 400 V        ...
Simulation Results:  •      Left plot:               Average inductor current  •      Right plot:              Switched mo...
100 % load  •       THD ~ 3%copyright 2011 controltrix corp   www. controltrix.com
50 % load  •         THD ~ 5%copyright 2011 controltrix corp   www. controltrix.com
10 % load  •       THD ~10%copyright 2011 controltrix corp   www. controltrix.com
Comparison of Specifications        IPFC reference design from microchip       2.4 KW server power supply from delta      ...
Experimental results  (IPFC board 89 W only single phase enabled)      Voltage                                         90...
Scope shots (87 W load , 400 Vdc output)  110 Vcopyright 2011 controltrix corp          www. controltrix.com
Scope shots (87 W load , 400 Vdc output)  220 Vcopyright 2011 controltrix corp          www. controltrix.com
Classical PI control w/o FF  110 Vcopyright 2011 controltrix corp   www. controltrix.com
Classical PI control w/o FF      220 Vcopyright 2011 controltrix corp   www. controltrix.com
Results with AN1278 from microchip  Input voltage: 220 V, Load: 180 W (50%) dual phase   180 W for IPFC is equivalent to 9...
Thank You                                  consulting@controltrix.comcopyright 2011 controltrix corp                      ...
Upcoming SlideShare
Loading in …5
×

Digital Power Factor Correction - Handling the corner cases

612 views

Published on

Published in: Technology
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
612
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
18
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

Digital Power Factor Correction - Handling the corner cases

  1. 1. Digital Power Factor Correction Handling the corner cases Superior THD over entire operating range www.controltrix.comcopyright 2011 controltrix corp www. controltrix.com
  2. 2. Power Factor primer Inductive - Lagging we r cosΦ = Real Power Po re n t Apparent Power pa Ap Reactive Power = Power Factor Φ Real Power Capacitive - Leading Applies for ideal sinusoidal waveforms for both voltage and currentcopyright 2011 controltrix corp www. controltrix.com
  3. 3. Calculating Power Factor Power factor = Real power / Apparent power = (Vrms * I1rms * CosΦ) / (Vrms * Irms) = cosΦ * ( I1rms / Irms) Power factor = KΦ * Kd Kd = distortion factor (THD) KΦ = displacement factor (D.F) Vrms = AC input rms voltage Irms = AC input rms current I1rms = Fundamental component of Irms cos Φ = Phase angle between input AC voltage and the fundamental current Irms = Sqrt (I12 + I22 + I32+ ………….+In2)copyright 2011 controltrix corp www. controltrix.com
  4. 4. PF Degradation Voltage Resulting CurrentSinusoidal Current with phase shift Voltage Resulting Current Current with harmonic contentcopyright 2011 controltrix corp www. controltrix.com
  5. 5. Power factor correction • Reduce energy loss in transmission lines • Improve power quality • Cost • Regulatory needscopyright 2011 controltrix corp www. controltrix.com
  6. 6. Useful Power Useful Power Negative Power Applied Voltage Region Region Resulting CurrentWithout PFC Φ Φ Applied Voltage Resulting CurrentWith Active PFCcopyright 2011 controltrix corp Useful Power www. controltrix.com
  7. 7. Digital PFC system Boost AC Supply Rectifier Load PFC Vac Iac PWM Vdc DSP/DSC Basic Components of the PFC Converter Switch Capacitor Inductor Diodecopyright 2011 controltrix corp www. controltrix.com
  8. 8. Boost Topology Average Inductor Current IL IL PFC Boost Converter L D tON + IL ID IS IS + vIN S C - ID - VOUT > VIN Average Current Mode Control The average current through the inductor is made to follow the input voltage Ref: AN1274 Interleaved PFC app note from microchipcopyright 2011 controltrix corp www. controltrix.com
  9. 9. Challenges Ideally …… • Low THD & high PF over entire 90 -265 Vac input • Low THD & high PF over entire 10 -100 % load range Low line and high load meeting specifications is EASY !!!! Low load ( < 50%) & Hi Line (> 220 V) spec is HARD !!!! Cause : Change of system dynamicscopyright 2011 controltrix corp www. controltrix.com
  10. 10. Typical specs Load(%) THD(%) • (Typical Desired) State of the art spec. 10 <15 • 2.4 KW bridgeless PFC spec. for 20 <10 power supplies for server 30 <6 farms 50 <5 • Digital (DSP) control 70 <3 • Fixed switching frequency operation 80 <3 100 <3 Gets harder @ Hi linecopyright 2011 controltrix corp www. controltrix.com
  11. 11. State of the art review Approach 1 • Determine Discontinuous/continuous conduction mode operation • Change the control laws Challenge • Computation • If-else ladder • Parameter sensitivity • Non linearity of discontinuous mode of operation is hard • Fixed point implementation is challengingcopyright 2011 controltrix corp www. controltrix.com
  12. 12. State of the art review Approach 2 • Harmonic injection Challenge • Trial and error • Not plug and play / System specific • If-else ladder (discontinuities in code execution and dynamics) • Limited Code size Memory/MIPScopyright 2011 controltrix corp www. controltrix.com
  13. 13. State of the art summary • Computationally complex (MIPS, code size) • Fixed point implementation hard !! • Physical models sensitive to parameter estimates (e.g. inductor saturation ) • Poor convergence • Strange artefacts • Jumps/spikes/kinks/oscillations due to if-else laddercopyright 2011 controltrix corp www. controltrix.com
  14. 14. Proposed solution features • Good THD at all operating conditions • Plug and play • Just enter parameter dependent coefficients • Low parameter and feedback sensitivity • Fast convergencecopyright 2011 controltrix corp www. controltrix.com
  15. 15. Proposed solution features . • No if-else ladder • Small extra code size • Low MIPS requirement ~ 12-14 MIPS (25% of 40 MIPS) @ 50 KHz interrupt frequency (Compares favorably with traditional methods)copyright 2011 controltrix corp www. controltrix.com
  16. 16. Proposed solution features .. • System independent /scalable to any rating • Relevant for Interleaved PFC and bridgeless PFC topologies • Guaranteed convergence/no large scale oscillations • No if -else ladder • Patent pending technologycopyright 2011 controltrix corp www. controltrix.com
  17. 17. Switched mode Simulation Results • Fixed frequency operation ~100 KHz • Vac = 220V rms ac, Vdc = 400 V ( High line is hardest to handle !!! ) • 330 W boost PFC system • 700 uH inductance • 300 uF output capacitancecopyright 2011 controltrix corp www. controltrix.com
  18. 18. Simulation Results: • Left plot: Average inductor current • Right plot: Switched mode inductor current (continuous and discontinuous conduction mode)copyright 2011 controltrix corp www. controltrix.com
  19. 19. 100 % load • THD ~ 3%copyright 2011 controltrix corp www. controltrix.com
  20. 20. 50 % load • THD ~ 5%copyright 2011 controltrix corp www. controltrix.com
  21. 21. 10 % load • THD ~10%copyright 2011 controltrix corp www. controltrix.com
  22. 22. Comparison of Specifications IPFC reference design from microchip 2.4 KW server power supply from delta Switching frequency : 100 KHz Switching Frequency : 65Khz One side max load : 180 W Inductance : 200uH Inductance : 700 uH(much smaller value than equivalent server supply for that rating) • A system for similar specification as server supply for 700 uH, 100 KHz the power rating would be, 2400 * 200 / 700 * 65 / 100 = 445 W • Thus 87 W is effectively 19.5 % load • The results are thus very convincingcopyright 2011 controltrix corp www. controltrix.com
  23. 23. Experimental results (IPFC board 89 W only single phase enabled) Voltage 90 110 160 220 Remarks Method Classical PI controller (over damped) modeled 5.98 7.2 17.0 18.4 PF and THD rapidly degrades on linear dynamics of continuous conduction at low loads mode system Classical PI controller modeled on linear 3.5 6.5 13.5 15.5 Easily ends up becoming (critically damped) unstable / sub harmonic oscillations due to parameter changes Classical P I controller with voltage feedforward 3.35 5.35 7.65 17.75 Works great in CCM. But rapidly degrades in DCM /low load conditions Proposed method 2.9 5.2 6.21 8.5 Works equally well in all regions of operation 89W load when corrected for inductance values and switching frequency is equivalent to 19.5 % load for comparable 2.4 KW system used in server power supply.copyright 2011 controltrix corp www. controltrix.com
  24. 24. Scope shots (87 W load , 400 Vdc output) 110 Vcopyright 2011 controltrix corp www. controltrix.com
  25. 25. Scope shots (87 W load , 400 Vdc output) 220 Vcopyright 2011 controltrix corp www. controltrix.com
  26. 26. Classical PI control w/o FF 110 Vcopyright 2011 controltrix corp www. controltrix.com
  27. 27. Classical PI control w/o FF 220 Vcopyright 2011 controltrix corp www. controltrix.com
  28. 28. Results with AN1278 from microchip Input voltage: 220 V, Load: 180 W (50%) dual phase 180 W for IPFC is equivalent to 90 W with only one phase of IPFC operational.copyright 2011 controltrix corp www. controltrix.com
  29. 29. Thank You consulting@controltrix.comcopyright 2011 controltrix corp www. controltrix.com

×