This document discusses an interleaved discontinuous conduction mode flyback converter for a 2 kW grid-connected photovoltaic system. It begins with an introduction to electricity demand and solar energy. Then it describes the flyback converter topology, challenges at high power, and how interleaving cells addresses these challenges. The document outlines the converter description, analysis, simulation results, experimental setup and results. It achieves 2 kW power by interleaving three 700W flyback cells and demonstrates high efficiency and power quality within specifications.

1. Guided by ; Presented by
Mrs. DEEPA M U Ajmal khan N
Asst. Pro., EEE Dept. Roll. No: 03
EEE, S7
1

2. CONTENTS
 INTRODUCTION
 FLYBACK CONVERTER
 CHALLENGES OF FLYBACK CONVERTER
 DISCONTINUOUS CURRENT MODE
 BLOCK DIAGRAM
 CONVERTER DESCRIPTION AND OPERATING PRINCIPLE
 CONVERTER ANALYSIS
 FLYBACK TRANSFORMER DESIGN
 CONTROL SYSTEM DESIGN
 SIMULATION RESULTS
 EXPERIMENTAL RESULTS
 CONCLUSION
 REFERENCES
2

3. INTRODUCTION
 Electricity is the most versatile and widely used form of
energy.
 It’s global demand is increasing.
 The solar energy is considered as the most renewable
and freely available source of energy.
 The research and development in the solar field is in rise.
 The low cost is greatly important.
3

4. FLYBACK CONVERTER
 It’s the lowest cost converter among the isolated
topologies-it uses least number of components.
 It combines the inductor with the transformer.
 In other type of isolated topologies the inductor and
the transformer are separate elements.
 Inductor is responsible for energy storage , while the
transformer is responsible for energy transfer.
4

5. CHALLENGES OF FLYBACK
CONVERTER TO HIGH POWER
 Transformer with relatively large energy storage is
always a challenge.
 For large energy storage it needs large air gap.
Large
air
gap
Magnetizing inductance
Leakage inductance
Poor coupling
Poor energy transfer efficiencyLeads to
5

6. Discontinuous Current Mode
 Advantages
 Very fast dynamic
response-better
stability.
 No reverse recovery
problem.
 No turn on losses
 Easy control.
 Small size of the
transformer.
 Disadvantages
 Higher form factor.
 More power loss.
 Current pulses-large peak ,high
discontinuity.
6

7. What is the solution?????
 INTERLEAVING OF CELLS
 Interleaving of high power flyback stages-increases the
ripple component at the waveform-proportion to the no.
of interleaved cells.
 Which leads to easy filtering and using smaller sized
filtering elements.
 current in each cells –less peak but same amount of
discontinuity.
7

8. BLOCK DIAGRAM
Figure 1. Block diagram of the proposed grid connected PV inverter system
based on interleaved DCM flyback converter topology 8

9. CONVERTER DESCRIPTION AND
OPERATING PRINCIPLES
Figure 2. Circuit schematic of the pr0posed PV inverter system based on three cell
interleaved flyback converter topology .
9

10.  OPERATION
 When flyback switches are turned on-current flows from
PV to magnetizing inductance of flyback transformer-
energy is stored.
 During on time no current flows to the output
 Therefore energy is supplied by the capacitor Cf &
inductor Lf.
10

11.  When switches are off ,energy stored is transferred
into the grid in the form of current.
 To reduce the variations at the terminal volatge a
decoupling capacitor is placed at the flyback converter
output.
 The full bridge inverter used for unfolding the
sinusoidally modulated dc current back to ac at the
right moment of the grid voltage.
11

12. CONVERTER ANALYSIS
 A . Flyback switch is turned on
Figure 3.Flyback switch control signal ,flyback
transformer primary v/g and magnetizing current over
switching period when grid v/g is at its peak.
𝑖1 =
𝑉𝑝𝑣
𝐿𝑚
𝑡 = 𝑖𝑚…………………………………………..(1)
Lm=flyback transformer magnetizing inductance
𝑖1𝑝𝑒𝑎𝑘 = 𝑖𝑚𝑝𝑒𝑎𝑘 =
𝑉𝑝𝑣 𝐷𝑝𝑒𝑎𝑘
𝐿𝑚𝑓𝑠
.....................(2)
Fs=switching freq.; Dpeak=duty ratio
𝐼1 =
𝐼𝑝𝑣
𝑛𝑐𝑒𝑙𝑙
=
𝑉𝑝𝑣 𝐷²𝑝𝑒𝑎𝑘
4𝐿𝑚 𝑓𝑠
………………………………..(3)
I1=average dc current
Ppv=Vpv Ip=
𝑛𝑐𝑒𝑙𝑙 𝑉²𝑝𝑣 𝐷²𝑝𝑒𝑎𝑘
4𝐿𝑚 𝑓𝑠
………………………(4)
ncell= no. of interleaved cells
Ppv= PV source o/p power. 12

13. B.Flyback switch is turned off
ni2=im=
𝑉𝑔𝑟𝑖𝑑
𝑛 𝐿𝑚
𝑡………………..(5)
Vgrid=peak of the grid voltage
n= flyback transformer turns ratio
I2=
𝐼𝑔𝑟𝑖𝑑
𝑛𝑐𝑒𝑙𝑙
=
𝑉²𝑝𝑣 𝐷²𝑝𝑒𝑎𝑘
2 𝐿𝑚 𝑓𝑠 𝑉𝑔𝑟𝑖𝑑
………(6)
I2=max. value of the grid current.
oComparing eqa.(4) &(6)-the average power from PV panels equal to
the active power transferred to the grid assuming an ideal converter.
Ppv=Vpv Ipv=
𝑛𝑐𝑒𝑙𝑙 𝑉²𝑝𝑣 𝐷²𝑝𝑒𝑎𝑘
4 𝐿𝑚 𝑓𝑠
=
𝑣𝑔𝑟𝑖𝑑 𝐼𝑔𝑟𝑖𝑑
2
= 𝑃𝑔𝑟𝑖𝑑……….(7)
13

14. c. ANALYSIS FOR SIZING OF DECOUPLING CAPACITOR
 The control system has no feedback loop for the
regulation of o/p current.
 Since the PV source is not an ideal v/g source it’s o/p
voltage is fluctuating-we provide a decoupling
capacitor –i/p of the flyback converter.
 Major sizing criterion is the effectiveness in diverting
double line freq. away from PV source.
14

15.  Peak to peak voltage ripple across the decoupling capacitor,
ΔVpv=ΔVc= Xc ΔIc………..(8) ΔIc= current ripple
 CONVERTER ANALYSIS
 Switching freq. is 40khz-higher efficiency with smaller sized
magnetics.
 A clamp or a snubber is provided to keep switching transients
within safe operating area .
 Flyback transformer will use the most optimum winding
strategy for the lowest leakage inductance practically
possible.
𝑐 ≥
2𝐼𝑝𝑣
2𝜋100 𝛥𝑉𝑝𝑣
…………….(9)
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16. Flyback Transformer Design
 Air gap length of the flyback transformer can be found
using….
 Lowest leakage inductance can be achieved by……
 Making coil & core heights longer
 Reducing the number of winding layers –less space b/t layers.
 Using sandwiched windings –magnetic field inside the
window area is reduced-reduces leakage inductance.
𝑙𝑔 =
𝑁²µ˳ 𝐴𝑐𝑜𝑟𝑒
𝐿𝑚
16

17. Figure 4. PLECS model of the proposed PV inverter system including the power stage and the controller.
oThe PLECS software comes with a 65w PV model developed
by plexim engineers based on the commercial BP365 part
numbered PV panel. 17

18. CONTROL SYSTEM DESIGN
 The control system is designed for two functions
simultaneously without feedback loop.
 Harvesting the max. power & pump the power to utility
grid with high quality.
 Because of implementation simplicity, the perturb and
observe (P&O) method is selected .
 Figure 6 shows the flow chart of the P&O algorithm
implemented in the DSP controller.
18

19. Figure 6. flow chart of P&O algorithm 19

20.  Besides the magnitude regulation for max. power transfer,
the controller should achieve synch. Of current with grid
v/g
 For this purpose the o/p of MPPT block is multiplied by the
PLL o/p.

 T=fundamental period of the grid signal.
Figure 7. PLL structure based on T/4 transport delay technique.
20

21.  Another control signal that
is also synch. With PLL o/p
is used to control H-bridge
IGBT inverter for unfolding
purpose.
 The whole control system is
implemented in
TMS320F2335 Texas
Instrument’s DSP controller.
Figure 8. Flowchart of the DSP firmware
21

22. SIMULATION RESULTS
Figure 10. simulated wave form of the grid v/g and current.
Figure 11. simulated waveforms of the PV module terminal v/g
& the grid current.
22

23.  EXPERIMENTAL SETUP
Figure 12. Experimental Setup
Figure 13. Exp.wave form of grid v/g(purple)
& grid current(green).
23

24. EXPERIMENTAL RESULTS
 The energy harvesting effi. Of the MPPT algorithm at
the nominal power is 98.5%.
 The power delivered to the load-grid interface is
measured as 1732.4 W.
 The THD of the grid current & v/g is measured as
4.42% and 2.49% respectively.
 The pf is measured as .9975.
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25. CONCLUSION
 The 2 KW power level is achieved by interleaving of
three flyback cells each rated at 700w.
 The power harvesting effi. of the MPPT controller is
measured as 98.5%.
 The THD of the grid current is 4.42% & pf =.998.
 Interleaved flyback topology is practical at high power
as central type PV inverter.
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26. REFERENCES
[1] Solar energy (2013, July 23). [Online]. Available: http://www.conserveenerg
future.com/SolarEnergy.php.
[2] Europe Photovoltaic Industry Association (EPIA) (2013, July 23) Global market
outlook for photovoltaics 2013–2017.
[3] Y. Xue, L. Chang, S. B. Kjaer, J. Bordonau, and T. Shimizu, “Topologies of
single-phase inverters for small distributed power generators: An overview,”
IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1305–1314, Sep. 2004.
[4] S. B. Kjaer, J. K. Pedersen, and F. Blaabjerg, “A review of singlephase grid-
connected inverters for photovoltaic modules,” IEEE Trans. Ind. Appl., vol. 41,
no. 5, pp. 1292–1306, Sep. 2005.
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