Reduced Losses in PV Converters by Modulation of the DC Link Voltage

Alex Van den Bossche1, Jean Marie Vianney Bikorimana2 and Firgan Feradov3

1 Department of Electrical Energy, Systems and Automation

Ghent University

E-mail: alex.vandenbossche@ugent.be2 Department of Electrical and Electronics

University of Rwanda

E-mail: jbikorimana@nur.ac.rw3 Faculty of Electronics

Technical university of Varna Bulgaria

E-mail: firgan@mail.bg

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Outline Introduction• Problem • Proposed solution

Losses in a PV converter link• Active components • Passive components

Current control• Constant off time peak current control

o Simulation o Experment results

• Current control with a PWM high pass filtero Simulation

Conclusions Questions

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Span life of the PV system• PV panel life span =

30 years• PV converter life = 10

years

PV system Cost • Grid cost connection

= high• Labor work cost =

high [4],• Converter = expensive

Converter materials and topologies• Electrolytic capacitors

=less efficient• Polypropylene film

capacitors=high efficient

• No general standard control and topology

• Controls are complex

Introduction- What is the problem?

ConverterPanels Converter Panels

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C1

C2

C3

Q1

Q2

Q3

Q4 Q6

Q5

L1

L2

H-bridge inverterBuck-Boost Converter

EMC Filter

Introduction- What is the proposed solution?

Fig.1 Single phase PV converter using a three-phase bridge

PV Grid

Advantages of the topology:

o Lower current ripple o C1 = a typical 150-250 V capacitoro The voltage @ C2 = constant

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Introduction- What is the proposed solution?(cont’d)

δ6

t

δ1

δ3

δ5

δ4

δ of the switches

0

Fig.2 Control voltage across C2 capacitor

Fig.3 The PV converter switches behavior

C1

C2

C3

Q1

Q2

Q3

Q4 Q6

Q5

L1

L2

Fig.1 Single phase PV converter using a three-phase bridge

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Losses in a PV Converter LinkLosses

Profits

Capacitors losses Capacitor losses

Switching and conduction losses

Switching and conduction losses

=Total losses =Total losses

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Current control

t0

Ip

Toff Toff

Fig. 4. Constant off Time Peak Current Control

Constant off time peak current control” (COPCC): protection and control combined

Current control at constant frequency: Instability @ 50% duty cycle

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Material Type Value

Capacitor, C1 electrolytic 2200 µF

Capacitor, C2 Polypropylene film 20 µF

Capacitor, C3 Polypropylene filmelectrolytic

2200 µF

Inductor, L1 Amorphous iron 600 µH

Inductor, L2 Amorphous iron 1400 µH

IGBT APTGF50X60T3G -DC source V1 100V

Load Resistive 50 Ω

Constant off Time Peak Current Control

Power stage Current control

Overvoltage protection

Fig. 9. Buck-Boost Converter Step Up

Table I. Converter materials

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0.027 0.028 0.029 0.03 0.031 0.032 0.033 0.0341

2

3

4

5

6

7

8

Time[seconds]

Var

iabl

es

Vc2

IL1

Iref

0.047 0.048 0.049 0.05 0.051 0.052 0.053 0.0542

3

4

5

6

7

8

Time[seconds]

Var

iabl

es

Vc2

IL1

Iref

Simulation and Lab experment work

Fig. 8 &10. Constant Off time Peak Current Control without HP feedback

Fig. 9 &11. Constant Off time Peak Current Control with HP feedback

Distortion frequencies

No distortion frequencies (Fig.9 &11)

COPCC with HP filter:

+ fast and protection included

- not easy for DSP or µcontroller

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Current control with High pass filter feedback

Continuous

pow ergui

c3c2c1

v+-

v +-

To

V2V1

Signal 1

In<Lo> S/H>=

PID

PID

g DS

Lf2Lf1

L2L1

du/dt

i+ -i+ -

-C-

Cf2

Cf1

Fig.13. The PV converter current mode control block diagram

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Simulation results

0.064 0.066 0.068 0.07 0.072 0.074 0.0762

2.5

3

3.5

4

4.5

5

5.5

6

Time[seconds]

Cur

rent

IL2

Iref

0.008 0.01 0.012 0.014 0.016 0.018 0.022

2.5

3

3.5

4

4.5

5

5.5

6

Time[seconds]

Cur

rent

IL2

Iref

Fig.14. Iref and IL2 of the Boost converter

Fig.14. Iref and IL2 of the Boost converter

COPCC with second order HP filter:+ fast and protection included

- Possible for DSP or µcontroller

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Conclusions

Cost effective

PV system

Polypropylene Capacitors

in DC link

Topology in Fig.1

Current Control with HPF makes

the grid stable

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Questions

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References[1] S. Michael and B. Joe “Selecting Film Bus Link Capacitors for High Performance Inverter Applications,” Electronic Concepts Inc. Eatontown, NJ 07724[2] M.H. Bierhoff, F.W. Fuchs, “Semiconductor Losses in Voltage Source and Current Source IGBT Converters Based on Analytical Derivation,” [3] http://www.digikey.com/product-detail/en/APTGF50X60T3G/APTGF50X60T3G-ND/1920455[4] Lucas Laursen, “Production of Solar Panels Outpaced Investment Last year”, 1 Oct 2013.http://spectrum.ieee.org/energywise/energy/renewables/production-of-solar-panels-outpaced-investments-last-year[5] Rajendra Aparnathi and Ved Yvas Dwived, “LCL Filter for three Phase Stable Inverter Using Active Damping Method (Genetic Algorithm)”,[6] Antonio Coccia, “Control Method for Single-Phase Grid Connected LCL Inverter”[7] Daniel Wojciechowski, “Unified LCL Circuit for Modular Active Power filter”, International Journal for Computation and Mathematics in Electrical and Electronics Engineering,Vol.31 Iss:6,pp.1985-1997.[8] Jian Li, “Current-Mode Control: Modeling and its Digital Application”, Blacksburg, Virginia, 2009[9] Alex Van den Bossche, Dimitar Vaskov B.,Thomas V, and Vencislav Cekov V., “Programmable Logic Based Brushless DC Motor Control” EPE 2011-Birmingham