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the international conference on renewable energies icre 2010 april 5 8 2010 damascus syria

The International Conference on Renewable Energies“ICRE-2010”April 5 – 8, 2010 Damascus, Syria

slide2

Design of High Efficiency DC-DC Converter for Photovoltaic Solar Home ApplicationsDiary R. Sulaiman Hilmi F. Amin Ismail K. Said Department of Electrical Engineering, College of Engineering, University of Salahaddin-Hawler, Iraq

slide3

Topics- Introduction to DC-DC converters- Analysis of the Buck-Boost Converters- Design of the Buck-Boost Converters - The converter control loop- Simulation Results- Conclusion- References

slide4

Introduction

- The solar energy conversion system is very interesting alternative on supplement the electric system generation, due to the persistent cost reduction of the overall system and cleaner power generation.- Buck-boost converters make it possible to efficiently convert a DC voltage to either a lower or higher voltage.

- This paper analyzes and describes step by step the process of designing, and simulation of high efficiency low ripple voltage buck-boost DC-DC converter for the photovoltaic solar conversion system applicable to a (typical) single family home based on battery-based systems. The input voltage can typically change from (20V) initially, down to (5V), and provide a regulated voltage within the range of the battery (12V). The simulation results provide strong evidences about the high efficiency, minimum ripple voltage, high accuracy, and the usefulness of the system of the proposed converter when applied to either residential or solar home applications.

slide5

Introduction Cont`d

The Solar cell, module and array

slide6

Introduction Cont`d

  • There are two different types of solar energy systems that will convert the solar resource into electricity;
  • one method is by collecting solar energy as heat and converting it into electricity using a typical power plant or engine;
  • the other method is by using photovoltaic PV cells to convert solar energy directly into electricity
slide7

Introduction Cont`d

The basic block diagram of the solar energy

conversion system

slide8

Introduction Cont`d

-The solar energy conversion systems can be connecting to a large electrical transmission grid, or to the storage or auxiliary energy supply. If the photovoltaic route is chosen, extra electricity may be stored, usually in storage batteries, thereby extending the operating time of the system, the (typical 12V) storage batteries are ordinary used in the home solar conversion systems to satisfy its operation and maximize power tracking purpose.

-The converter and switching topology of the proposed buck boost DC-DC converter would result in higher efficiency, lower ripple voltage, and significant increase in the overall available power even in a sun lighting condition. Although a small amount of power is generated, given enough time, a battery will reach its full charge.

slide9

Analysis

The basic schematic structure of the buck-boost converter, and the two operation states switch on and switch off are shown:

slide10

Analysis Cont`d

Current and voltage waveforms of the buck-boost converter are shown below:

slide11

Analysis Cont`d

Under the steady state operation of the converter in the CCM, the analytical expression of (Vo/Vg), (iL), and (Vo) can be obtained. Equating the integral to zero of the integral voltage over one time period yields [12,13],

--------(1)

--------(2)

--------(3)

--------(4)

slide12

Analysis Cont`d

For the buck-boost converter,

slide13

Analysis Cont`d

The inductor current at the beginning of the cycle is zero, its maximum value at (t=DT) is

And, during the off period (iL) falls to zero at the end of the off-state, and then, the load current (Io) equal to average diode current (ID,av), and the diode current equal to the inductor current during the off-state, therefore, (Io) is equal to,

slide14

Analysis Cont`d

Both (Vo/Vg), and (Io/Ig) are equal to

Therefore, the output voltage gain (Vo/Vg) in the continuous or CCM mode depends on the duty cycle (D) only, but in the DCM mode depends on the duty cycle (D), inductor value (L), input voltage (Vg), and the output current (Io) [12].

slide16

Design Cont`d

When MOSFET switch is on the voltage across the inductor is equal to (Vg) and when diode switch is on it is equal to (Vo). Then the duty ratio can be related to (Vo) by equation 3. The input and output currents are determined by the switching states of equation 4, [IoD=Ig(1-D)]. Theoretically, if (D=0), the output is zero, if (D=1) the output is infinity, and if (D=0.5), then the output is equal to the input voltage [14].

slide17

Design Cont`d

To find the switching frequency (f) for which (L>Lcr), the (Io) values, the time period, and (D) must be known, because the value of (Lcr) is dependant upon them. To determine (Io), the uses of analytical equations are possible [15]. For a typical (12V) batteries, and (1kW) home devices shown in table 1, the output current of the converter will be (83.34A). Then the calculated results of duty ratio (D) and inductor current (IL=Io/1-D) of table 2 are obtained.

slide19

Design Cont`d

To make the regulator operate in continuous mode and the design will have a good load transient response with an acceptable output ripple voltage, and according to the simulation results, the (iL) considered to be (≤3%), so we can select its value equal to (3%)

slide20

Design Cont`d

The switching frequency of high efficiency buck-boost converters applicable in solar systems typically will be between (20kHz-100kHz) [14]. Choosing the minimum and maximum input voltage values for only these two frequencies to determine the inductor value is shown in table 3.

slide21

Design Cont`d

The minimum or critical capacitor value (Ccr) for a desired output ripple and load current/voltage is

Then, the critical value of the capacitor (Ccr) operating on the frequency (46kHz) and minimum/maximum input voltages (5-20V) regarding the output ripple voltage (vo50mV), using (vo=40mV) is calculated as shown in table 4

slide22

Design Cont`d

The possible capacitance value for our design should be (C>Ccr), So, we can choose (C=1000F). The complete design parameters values of the proposed DC-DC converter are shown in table 5.

slide23

The converter control loop

Digital PWM (DPWM) controllers can offer a number of advantages over analog controllers, including flexibility, lower sensitivity, high frequency switching, and programmability without external components

slide24

The converter control loop cont`d

block schematic of DPWM, (b) The control signals

slide27

Conclusion

The simulations have demonstrated that, the design can achieve (88.20%) efficiency at (5V) input, scaled up to (96.55%) efficiency at (20V) input, producing acceptable ripple voltage (<11mV) for the inputs (5-20V), all at (46kHz) switching frequency under a (83.34A).

The advantages of this design are: the ability to choose the constant output voltage and current, the procedure is simple, the converter and controller has a simple structure, improved efficiency – up to (96.55%), reduced output ripple voltage-less than (11mV), the complete converter circuit is small and inexpensive, and finally, the designed converter circuit topology operates effectively for different input and output operating conditions.

It is, therefore, feasible for common solar DC-DC conversion applications.

This design procedure in principle opens the possibility to additional work in converter design and modeling, and could allow further improvements in efficiency, ripple, and usable power range. Other control schemes are also possible, and it could provide a way for controlling other converter topologies.

slide28

References

[1] W. Jianqiang, and L. Jingxin, “Design and experience of grid-connecting photovoltaic power system”, IEEE international conference on sustainable energy technologies ICSET 2008, Pp 607-610, Singapore, 2008.

[2] M. C. Cavalcanti, G. M. S. Azevedo, B. A. Amaral, K. C. de Oliveira, F. A. S. Neves, and Z. D. Lins, “Efficiency evaluation in grid connected photovoltaic energy conversion systems”, IEEE 36th power electronics specialists conference, Pp 269-275, Brazil, 2005.

[3] S. Mekhilef, N. A. Rahim, and A. M. Omer, “A new solar energy conversion scheme implemented using grid-tied single phase inverter”, Proceedings of IEEE TENCON-2000, Kuala Lumpur, Malaysia, 2000.

[4] H. J. Chiu, C. J. Yao, and U. K. Lo, “A DC/DC converter topology for renewable energy systems”, International journal of circuit theory and applications, Vol.37, Issue-3, Pp 485-495, 2009.

[5] H. S. Kim, J. H. Kim, B. D. Min, D. W. Yoo, and H. J. Kim, “A highly efficient PV system using a series connection of DC–DC converter output with a photovoltaic panel”, International journal of renewable energy, Vol.34, Issue-11, Pp 2432-2436, 2009.

[6] J. P. Lee, B. D. Min, T. J. Kim, D. W. Loo, and J. Y. Yoo, “Design and control of novel topology for photovoltaic DC/DC converter with high efficiency under wide load ranges”, International journal of power electronics, Vol.9, No.2, Pp 300-307, 2009.

[7] J. K. Park, w. Y. Choi, and B. H. Kwon, “Step-up DC–DC converter with a resonant voltage doubler”, IEEE transactions on industrial electronics, Vol.54, Issue-6, Pp 3267-3275, 2007.

[8] M. Sippola, and R. Sepponen, “ DC/DC Converter technology for distributed telecom and microprocessor power systems – a literature review”, The report of applied electronics laboratory, department of electrical and communications engineering, Helsinki, University of technology, Finland, 2002.

slide29

References

[9] R. M. Irigo, K. T. Shafik, and C. W. Park, “A solid-state DC-DC converter using n-channel MOSFETs”, IEEE proceedings of southeastcon, apos-91, Pp 997-1000, USA, 1991.

[10] S. M. Wu, C. L. Wu, and C. H. Chang, “A new adaptive mode-switching mechanism with current-mode CMOS DC-DC converter”, International symposium on integrated Circuits ISIC’07, Pp 548-551, Singapore, 2007.

[11] S. L. Liu, J. Li, J. Zhang, “Research on output voltage ripple of boost DC/DC converters”, proceedings of the international multi-conference of engineers and computer Scientists IMECS’2008, Hong Kong, 2008.

[12] K. I. Hwu, Y. T. Yau, “A novel voltage-bucking/boosting converter: KY buck-boost converter”, IEEE international conference on industrial technology, ICIT 2008, Pp 1-4, China, 2008.

[13] Analysis of buck-boost converter,

ftp://ftp.elet.polimi.it/users/Massimo.Ghioni/Elettronica%20di%20Potenza/Convertitori%20DC-DC/buck-boost/AnalysisConverter-buck-boost.pdf

[14] C. A. Ayre, and I. Barbi, “CCM operation analysis of a family of converters”, 27th Annual IEEE power electronics specialists conference PESC 96, Pp 986-992, Italy, 1996.

[15] N.A. Keskar, and G.A. Rincon-Mora, “Self-stabilizing, integrated, hysteretic boost DC-DC converter”, IEEE industrial electronics conference IECON-04, pp. 586-591, Korea, 2004.

[16] F. Baronti, P. C. Adell, W. T. Holman, R. D. Schrimpf, L. W. Massengill, A. Witulski, and M. Ceschia, “DC/DC switching power converter with radiation hardened digital control based on SRAM FPGAs”, 2004 MAPLD international conference, USA, 2004.

[17] A. Prodic, D. Maksimovic, and R. W. Erickson, “Design and implementation of a digital PWM controller for a high-frequency switching DC-DC power converter”, The 27th annual conference of the IEEE industrial electronics society IECON'01, USA, 2001.

[18] B. J. Patella, A. Prodic,A. Zirger, D. Maksimovic, “High-frequency digital PWM controller IC for DC-DC converters”, IEEE transactions on power electronics, Vol.18, Issue-1, Pp 438 – 446, 2003.