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Modeling and Simulation of High-Efficiency Interleaved Flyback Micro-inverter For Photovoltaic Applications
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 10417–10421
www.materialstoday.com/proceedings
ICEMS 2016
Modeling and Simulation of High-Efficiency Interleaved Flyback Micro-inverter For Photovoltaic Applications P. Elanchezhian1*, V. Kumar Chinnaiyan2 2
1 Senior Research Fellow, Central Power Research Institute, Bangalore-560080, India Professor & HOD, EEE Department, KPR Institute of Engineering and Technology, Coimbatore-641407, India
Abstract
PV generation is one of the fast growing renewable generation system, it helps to meet the ever-growing power demand. Among the various PV generation techniques available, the micro inverter system which finds its application in roof top systems is rated as one of the best option for maximum energy harvest from each solar panel. High step up dc-dc boost converter with Interleaved Fly back boost converter topology and Maximum power point tracking method (MPPT) can used to vary the duty cycle so as to improve the efficiency and extract maximum available power from each panel in both healthy and partial shading condition. With this background, this paper discusses the advantage of micro-inverter system over the existing string-inverter technology and tries to validate the advantage of fly back boost converter technology with hardware results. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS-2016). Keywords: MPPT; Micro-inverter; AC Panel; Flyback; Interleaved; SFBI, IEC61683
1. Introduction One of the main objective of Solar inverter systems is to extract max energy from each panel and to effectively synchronise with grid. In central inverter system, a single MPPT is used for entire string to harvest energy. Therefore during partial shading condition [1] if panel output is reduced, then the entire string output is reduced [2]. But if a separate micro inverter is attached with each panel then it is possible to extract maximum available power from each panel even in partial shading condition [3]. This entire system is also called AC panel.
* Corresponding author. Tel.: +91-9994111441 . E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS2016).
10418
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
Advantages of a solar micro-inverter system vis-à-vis the central inverter system include: • Central Inverter fail may cause system fail. • Partial shading reduces total output by 25% - 50%, sometimes even by 100% in central inverter. • Micro inverter gives the same output but has 5% to 20% more energy harvest when compared to central installations • Micro inverter avoids dangerous DC cabling system on roof top. • Incidentally its cost of Micro inverter decreases as AC breakers cheaper than DC breakers. 2. Interleaved Flyback Converter The basic structure of the interleaved flyback converter is shown in Fig.1
Fig.1. Interleaved Flyback Converter
2.1
On-State Equations
When switch S1 is ON, the primary side voltage of the transformer V1, is connected in parallel with Vinput. The primary current, i1, is equal to the magnetizing current ima, and is described as
di m a Vinput = dt Lma
(1)
This can be seen to cause a linear increase in ima with an increase in time. The secondary current, i2, is zero during the on time because the diode, D, is reversed biased. The secondary voltage is related to the primary voltage by the turn’s ratio.
N2 (2) ×V1 N1 The output voltage can be determined by the output capacitor, Cout, The output current, iout is observed as the negative of the output capacitor current ica, since isw is equal to zero [4]. V2 =
dVout i = − out dt Cout
(3)
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
10419
2.2 Off-State Equations When switch S1 is off, the primary current, i1, is equal to zero since Switch(S) blocks the current. The primary and secondary voltage will flip polarity due primary side turns T1’s magnetic field decreasing, forcing Diode (D) to become forward biased and the secondary current i2 to conduct. The secondary current i2 can be related to the magnetizing current ima flowing between the ideal transformer and Lma by the turn’s ratio [5].
i2 =
N1 × ima N2
(4)
The output voltage Vout will be reflected back to the primary by the turn’s ratio [6]. Note that Vout is equal to –V2.
V1 = −Vout ×
N1 N2
(5)
Therefore, Lma’s magnetization inductor derived from this equation
−Vout ×
di m a = dt
di N1 = Lma m a N2 dt
Vout ×
(6)
N1 N2
(7)
Lma
The output voltage Vout is again determined by the output capacitor Cout.
i2 − iout = Cout ×
dVout dt
(8)
N1 × ima − iout dV0 N 2 = dt Cout
(9)
3. Hardware Design and Component Selection Source pins of MOSFETs are connected to ground and the high frequency transformer connected to drain. When input indictor current interrupted Voltage limited by the zener diode connected between drain and source [7]. Two switching transitions are controlled by gate resistance. At stage 1 the fly back MOSFET1 and MOSFET2 turns ON and energy stored in inductor at that time secondary side diode D1 and D2 in reverse bias due to secondary winding voltage and out is supplied by a capacitor C4, Primary of transformer behaves like an inductor and primary current rises linearly [8]. At stage 2 MOSFET1 and MOSFET2 turn off stored energy in primary side is transferred to secondary winding so diode D1 and diode D2 gets forward bias. During this time current to load directly supplied through secondary winding and capacitor C4 charged. Short-circuit hardware protection is given by two zero Ohm shunt resistors [9] .Hardware setup of microinverter shown in Fig .2.(b). 4. Efficiency test and waveforms Weighted energy efficiency is calculated by considering energy consumption at 100 % (Full load), 75 % (3/4th load), 50 % (1/2th load) and 25 % (1/4th load) for a duration of one minute. The no load loss is also considered for a period of one minute.
ηWT =
POi.Ti
P .T Ii
i
=
P .T + P O1 1
O2
.T2 + PO3.T3 + PO4.T4
PI 0.T0 + PI1.T1 + PI 2.T2 + PI 3.T3 + PI 4.T4
=
E
O1
+ EO2 + EO3 + E4
EI 0 + EI1 + EI 2 + EI 3 + EI 4
(10)
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"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
Where EO1, EO2, EO3 & EO4 AC energy output for one minute for full load, 3/4th load, 1/2th load and 1/4th load respectively in Wh, EI0 is the no load DC energy for a period of one minute and EI1, EI2, EI3 & EI4 DC energy Output for one minute for full load, 3/4th load, 1/2th load and 1/4th load respectively in Wh.
Fig .2. (a) Full load efficiency test;
(b) Microinverter
Fig.3.Full load efficiency test output waveform 4.26 *100 4.26 *100 ηWT = = = 86.22 % 0.05 + 4.88 4.94 Where 0.05 No load power efficiency[11].
(11)
Table 1. Measured power at AC & DC side and efficiency at peak power
Sl. No. 1 2 3 4 5 6
Testing, % load 120% 100% 75% 50% 25% 10%
AC Power, W 118.93 102.50 76.36 51.26 25.50 10.26
DC Power, W 139.78 118.73 87.07 58.00 29.76 13.77
Efficiency, % 85.09 86.33 87.70 88.37 85.69 74.48
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
10421
Test was conducted for 10% load to 120% load and efficiency calculated [9], instantaneous readings calculated, full load efficiency graph shown in Fig.3 and Measured power, efficiency at peak power shown in Table 1[12-14] 5. Conclusion Proposed system is flyback boost DC-DC converter to improve efficiency and isolation. Due to reduction in the number of components, the overall converter is cheaper as compared to other state-of-the-art converters. MPPT control algorithm used to extract maximum available power from each PV panel. Efficiency test for various loads has been done as per IEC61683 and values and output discussed. In future work to improve micro inverter efficiency >95% Acknowledgements The authors gratefully thank the Central Power Research Institute for supporting this research work. References [1] Cheng-Li Chenga, Ling-Mei Liaoa, Chia-Peng Choub, “A study of summarized correlation with shading performance for horizontal shading devices in Taiwan”, Solar Energy 90(2013) 1–16. [2] Wagner Teixeira da Costaa, Jussara Farias Fardinb, Lauro de Vilhena B. Machado Netoc,” Estimation of irradiance and temperature using photovoltaic modules”, Solar Energy 110(2014) 132–138. [3] Brian Goss, Ian Cole, Thomas Betts, Ralph Gottschalg,” Irradiance modelling for individual cells of shaded solar photovoltaic arrays” , Solar Energy 110,(2014) 410–419. [4] D. Lauria, M. Coppola,” Design and control of an advanced PV inverter”, Solar Energy 110(2014) 533–542. [5] R. C. Variath, M. A. E. Andersen, O. N. Nielsen and A. Hyldgard, "A review of module inverter topologies suitable for photovoltaic systems," in Proc. IEEE IPEC, (2010)310-316. [6] HANSJÖRG GABLER,” Grid-Connected PV/Grid-Connected Photovoltaics”, Solar Energy 70(2001) 455–456. [7] S. Vijayalekshmya, G.R. Bindua, S. Rama Iyer,” A novel Zig-Zag scheme for power enhancement of partially shaded solar arrays”,135(2016) 92-102. [8] Woo-Jun Chaa, Jung-Min Kwonb, Bong-Hwan Kwona,” Highly efficient step-up dc–dc converter for photovoltaic micro-inverter”, 135 (2016) 14-21. [9] Simon J. Buckleb, Ned Ekins-Daukesa, b, Ajay Gambhirb, Jenny Nelsona,” Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India”, may 2016. [10] Aritra Ghosh, Brian Norton, Aidan Duffy,” First outdoor characterisation of a PV powered suspended particle device switchable glazing”, Solar Energy Materials and Solar Cells 157(2016) 1–9. [11] P Elanchezhian, V Kumar Chinnaiyan, R Sudhir Kumar,” Review of three port micro-inverter with power decoupling capability for photovoltaic (PV) systems applications”, Cpri Journal,11(2015)561-570, [12] P.Elanchezhian, V.Kumar Chinnaiyan, R.Sudhir Kumar,” Design Of Lcl Filter For Micro Inverter”, CPRI Journal , 11(2015) 735-740. [13] P.Elanchezhian, V.Kumar Chinnaiyan, R.Sudhir Kumar, “Design of two-stage soft-switched module Inverter for Photovoltaic applications”, 11(2015)145-154. [14] P Elanchezhian, “Soft-Switching Boost Converter for Photovoltaic Power-Generation System with PSO Based Mppt”, International Journal of Communications and Engineering, 06(2012) 121-128.
ScienceDirect Materials Today: Proceedings 4 (2017) 10417–10421
www.materialstoday.com/proceedings
ICEMS 2016
Modeling and Simulation of High-Efficiency Interleaved Flyback Micro-inverter For Photovoltaic Applications P. Elanchezhian1*, V. Kumar Chinnaiyan2 2
1 Senior Research Fellow, Central Power Research Institute, Bangalore-560080, India Professor & HOD, EEE Department, KPR Institute of Engineering and Technology, Coimbatore-641407, India
Abstract
PV generation is one of the fast growing renewable generation system, it helps to meet the ever-growing power demand. Among the various PV generation techniques available, the micro inverter system which finds its application in roof top systems is rated as one of the best option for maximum energy harvest from each solar panel. High step up dc-dc boost converter with Interleaved Fly back boost converter topology and Maximum power point tracking method (MPPT) can used to vary the duty cycle so as to improve the efficiency and extract maximum available power from each panel in both healthy and partial shading condition. With this background, this paper discusses the advantage of micro-inverter system over the existing string-inverter technology and tries to validate the advantage of fly back boost converter technology with hardware results. © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS-2016). Keywords: MPPT; Micro-inverter; AC Panel; Flyback; Interleaved; SFBI, IEC61683
1. Introduction One of the main objective of Solar inverter systems is to extract max energy from each panel and to effectively synchronise with grid. In central inverter system, a single MPPT is used for entire string to harvest energy. Therefore during partial shading condition [1] if panel output is reduced, then the entire string output is reduced [2]. But if a separate micro inverter is attached with each panel then it is possible to extract maximum available power from each panel even in partial shading condition [3]. This entire system is also called AC panel.
* Corresponding author. Tel.: +91-9994111441 . E-mail address: [email protected] 2214-7853 © 2017 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of International Conference on Recent Trends in Engineering and Material Sciences (ICEMS2016).
10418
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
Advantages of a solar micro-inverter system vis-à-vis the central inverter system include: • Central Inverter fail may cause system fail. • Partial shading reduces total output by 25% - 50%, sometimes even by 100% in central inverter. • Micro inverter gives the same output but has 5% to 20% more energy harvest when compared to central installations • Micro inverter avoids dangerous DC cabling system on roof top. • Incidentally its cost of Micro inverter decreases as AC breakers cheaper than DC breakers. 2. Interleaved Flyback Converter The basic structure of the interleaved flyback converter is shown in Fig.1
Fig.1. Interleaved Flyback Converter
2.1
On-State Equations
When switch S1 is ON, the primary side voltage of the transformer V1, is connected in parallel with Vinput. The primary current, i1, is equal to the magnetizing current ima, and is described as
di m a Vinput = dt Lma
(1)
This can be seen to cause a linear increase in ima with an increase in time. The secondary current, i2, is zero during the on time because the diode, D, is reversed biased. The secondary voltage is related to the primary voltage by the turn’s ratio.
N2 (2) ×V1 N1 The output voltage can be determined by the output capacitor, Cout, The output current, iout is observed as the negative of the output capacitor current ica, since isw is equal to zero [4]. V2 =
dVout i = − out dt Cout
(3)
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
10419
2.2 Off-State Equations When switch S1 is off, the primary current, i1, is equal to zero since Switch(S) blocks the current. The primary and secondary voltage will flip polarity due primary side turns T1’s magnetic field decreasing, forcing Diode (D) to become forward biased and the secondary current i2 to conduct. The secondary current i2 can be related to the magnetizing current ima flowing between the ideal transformer and Lma by the turn’s ratio [5].
i2 =
N1 × ima N2
(4)
The output voltage Vout will be reflected back to the primary by the turn’s ratio [6]. Note that Vout is equal to –V2.
V1 = −Vout ×
N1 N2
(5)
Therefore, Lma’s magnetization inductor derived from this equation
−Vout ×
di m a = dt
di N1 = Lma m a N2 dt
Vout ×
(6)
N1 N2
(7)
Lma
The output voltage Vout is again determined by the output capacitor Cout.
i2 − iout = Cout ×
dVout dt
(8)
N1 × ima − iout dV0 N 2 = dt Cout
(9)
3. Hardware Design and Component Selection Source pins of MOSFETs are connected to ground and the high frequency transformer connected to drain. When input indictor current interrupted Voltage limited by the zener diode connected between drain and source [7]. Two switching transitions are controlled by gate resistance. At stage 1 the fly back MOSFET1 and MOSFET2 turns ON and energy stored in inductor at that time secondary side diode D1 and D2 in reverse bias due to secondary winding voltage and out is supplied by a capacitor C4, Primary of transformer behaves like an inductor and primary current rises linearly [8]. At stage 2 MOSFET1 and MOSFET2 turn off stored energy in primary side is transferred to secondary winding so diode D1 and diode D2 gets forward bias. During this time current to load directly supplied through secondary winding and capacitor C4 charged. Short-circuit hardware protection is given by two zero Ohm shunt resistors [9] .Hardware setup of microinverter shown in Fig .2.(b). 4. Efficiency test and waveforms Weighted energy efficiency is calculated by considering energy consumption at 100 % (Full load), 75 % (3/4th load), 50 % (1/2th load) and 25 % (1/4th load) for a duration of one minute. The no load loss is also considered for a period of one minute.
ηWT =
POi.Ti
P .T Ii
i
=
P .T + P O1 1
O2
.T2 + PO3.T3 + PO4.T4
PI 0.T0 + PI1.T1 + PI 2.T2 + PI 3.T3 + PI 4.T4
=
E
O1
+ EO2 + EO3 + E4
EI 0 + EI1 + EI 2 + EI 3 + EI 4
(10)
10420
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
Where EO1, EO2, EO3 & EO4 AC energy output for one minute for full load, 3/4th load, 1/2th load and 1/4th load respectively in Wh, EI0 is the no load DC energy for a period of one minute and EI1, EI2, EI3 & EI4 DC energy Output for one minute for full load, 3/4th load, 1/2th load and 1/4th load respectively in Wh.
Fig .2. (a) Full load efficiency test;
(b) Microinverter
Fig.3.Full load efficiency test output waveform 4.26 *100 4.26 *100 ηWT = = = 86.22 % 0.05 + 4.88 4.94 Where 0.05 No load power efficiency[11].
(11)
Table 1. Measured power at AC & DC side and efficiency at peak power
Sl. No. 1 2 3 4 5 6
Testing, % load 120% 100% 75% 50% 25% 10%
AC Power, W 118.93 102.50 76.36 51.26 25.50 10.26
DC Power, W 139.78 118.73 87.07 58.00 29.76 13.77
Efficiency, % 85.09 86.33 87.70 88.37 85.69 74.48
"Elanchezhian P" / Materials Today: Proceedings 4 (2017) 10417–10421
10421
Test was conducted for 10% load to 120% load and efficiency calculated [9], instantaneous readings calculated, full load efficiency graph shown in Fig.3 and Measured power, efficiency at peak power shown in Table 1[12-14] 5. Conclusion Proposed system is flyback boost DC-DC converter to improve efficiency and isolation. Due to reduction in the number of components, the overall converter is cheaper as compared to other state-of-the-art converters. MPPT control algorithm used to extract maximum available power from each PV panel. Efficiency test for various loads has been done as per IEC61683 and values and output discussed. In future work to improve micro inverter efficiency >95% Acknowledgements The authors gratefully thank the Central Power Research Institute for supporting this research work. References [1] Cheng-Li Chenga, Ling-Mei Liaoa, Chia-Peng Choub, “A study of summarized correlation with shading performance for horizontal shading devices in Taiwan”, Solar Energy 90(2013) 1–16. [2] Wagner Teixeira da Costaa, Jussara Farias Fardinb, Lauro de Vilhena B. Machado Netoc,” Estimation of irradiance and temperature using photovoltaic modules”, Solar Energy 110(2014) 132–138. [3] Brian Goss, Ian Cole, Thomas Betts, Ralph Gottschalg,” Irradiance modelling for individual cells of shaded solar photovoltaic arrays” , Solar Energy 110,(2014) 410–419. [4] D. Lauria, M. Coppola,” Design and control of an advanced PV inverter”, Solar Energy 110(2014) 533–542. [5] R. C. Variath, M. A. E. Andersen, O. N. Nielsen and A. Hyldgard, "A review of module inverter topologies suitable for photovoltaic systems," in Proc. IEEE IPEC, (2010)310-316. [6] HANSJÖRG GABLER,” Grid-Connected PV/Grid-Connected Photovoltaics”, Solar Energy 70(2001) 455–456. [7] S. Vijayalekshmya, G.R. Bindua, S. Rama Iyer,” A novel Zig-Zag scheme for power enhancement of partially shaded solar arrays”,135(2016) 92-102. [8] Woo-Jun Chaa, Jung-Min Kwonb, Bong-Hwan Kwona,” Highly efficient step-up dc–dc converter for photovoltaic micro-inverter”, 135 (2016) 14-21. [9] Simon J. Buckleb, Ned Ekins-Daukesa, b, Ajay Gambhirb, Jenny Nelsona,” Off-grid solar photovoltaic systems for rural electrification and emissions mitigation in India”, may 2016. [10] Aritra Ghosh, Brian Norton, Aidan Duffy,” First outdoor characterisation of a PV powered suspended particle device switchable glazing”, Solar Energy Materials and Solar Cells 157(2016) 1–9. [11] P Elanchezhian, V Kumar Chinnaiyan, R Sudhir Kumar,” Review of three port micro-inverter with power decoupling capability for photovoltaic (PV) systems applications”, Cpri Journal,11(2015)561-570, [12] P.Elanchezhian, V.Kumar Chinnaiyan, R.Sudhir Kumar,” Design Of Lcl Filter For Micro Inverter”, CPRI Journal , 11(2015) 735-740. [13] P.Elanchezhian, V.Kumar Chinnaiyan, R.Sudhir Kumar, “Design of two-stage soft-switched module Inverter for Photovoltaic applications”, 11(2015)145-154. [14] P Elanchezhian, “Soft-Switching Boost Converter for Photovoltaic Power-Generation System with PSO Based Mppt”, International Journal of Communications and Engineering, 06(2012) 121-128.