DESIGN AND SIMULATION OF IMPROVED DC- DC CONVERTERS USING SIMULINK FOR GRID CONNECTED PV SYSTEMS

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1 International Journal of Electronics and Communication Engineering and Technology (IJECET) Volume 8, Issue 6, November-December 2017, pp , Article ID: IJECET_08_06_006 Available online at ISSN Print: and ISSN Online: IAEME Publication DESIGN AND SIMULATION OF IMPROVED DC- DC CONVERTERS USING SIMULINK FOR GRID CONNECTED PV SYSTEMS Dr. Y. L. ChandraShekar Professor, Dept. of E&C Engineering, Mysuru Royal Institute of Technology, Mandya, Karnataka, INDIA Dr. P.S. Puttaswamy Professor, Dept. of E&E Engineering, PES College of Engineering, Mandya, Karnataka, INDIA ABSTRACT In this paper Maximum Power Point Tracking (MPPT) based Buck-Boost converter for battery charging is proposed for extracting maximum power from the Photo Voltaic (PV) system. There are number of MPPT tracking methods available to operate the PV system at maximum power point. In this proposed work Perturb & observe (P&O) MPPT algorithm is used for design and implementation, which provides the maximum power point irrespective of varying irradiance and temperature. Previously P&O MPPT is used for MPPT based Buck converters, but here much of interest is shown towards the design & simulation of MATLAB Simulink based Buck-Boost regulator system for PV array. This work also presented the improved methods of DC to DC conversion. Key words: Buck-Boost converter (BBC), Maximum Power Point Tracking (MPPT), Buck-Boost Regulator (BBR) Algorithm, Pulse width Modulation (PWM), Photovoltaic (PV) cells. Cite this Article: Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy, Design and Simulation of Improved Dc-Dc Converters Using Simulink For Grid Connected Pv Systems. International Journal of Electronics and Communication Engineering and Technology, 8(6), 2017, pp INTRODUCTION India is the second largest energy consuming nation. In order to avoid energy crisis, it is necessary to utilize renewable resources like solar energy in an efficient manner. Solar charge controllers help in this regard, which mainly consists of dc-dc converters such as buck-boost regulators. Maximum Power Point Tracking (MPPT) is used to detect maximum power that 62

2 Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy can be transferred from a Photo Voltaic (PV) panel. Although the terminal voltage from the solar panel is usually designed to be higher than the voltage required at the load terminal, the DC voltage from the PV panel varies with light intensity, temperature, shaded PV panels; angle of incidence (tilt angle) also affects the dc voltage. Similarly on the battery end the voltage varies depending on the load connections. For the optimal power delivery it is important that the voltages of PV panel and current matches the battery charging state at any instant. Most of the battery chargers on the market today step down/buck their input but it is also necessary to boost the input voltage in some situations. This is achieved by dc-dc buck-boost converters which are also known as switching regulators. The active switches such as MOSFETs are more efficient with their switching efficiency. Duty cycle plays an important role in switching action and will be one of the major design aspects. Dc-Dc converters such as buck, boost, buck-boost, SEPIC converters do not produce power, in fact some of the input power will be consumed by these converters based on their efficiency. MPPT techniques are used in the PV systems to maximize the PV array output power by tracking continuously the maximum power point which depends on panel s temperature and on irradiance condition. The P&O MPPT parameters must be customized to the dynamic behaviour of the specific converter adopted. It can also be used for developing and evaluating new maximum power point techniques, especially for shaded condition. This paper mainly focuses on the design, calculation and simulation of a solar Buck-Boost converter, also the control strategy and power regulation using power convertors. The output of the converter will be such a way that it is designed to match the power ratings of the batteries. 2. SYSTEM DESCRIPTION 2.1. Proposed System CURRENT SENSOR MOSFET BUCK BOOST REGULATOR LOAD SOLAR PANEL ISOLATION CIRCUIT VOLTAGE REGULATOR PWM GENERATOR DISPLAY Figure 1 Block Diagram of Proposed System 2.2. Buck-Boost Converter The design of Buck-Boost converter is one of the main aspects of this work. It involves choosing the values of operating frequency of inductor, capacitor and also the duty cycle of the switching signal. Buck-Boost Converter is a Dc Converter in which the output voltage can be increased or decreased than the input voltage [2]. One of the striking features of this regulator is that it provides output voltage polarity reversal without the use of transformer. It is also called an Inverting Regulator. [2] It is highly efficient and the output short circuit protection can be 63 editor@iaeme.com

3 Design and Simulation of Improved Dc-Dc Converters Using Simulink For Grid Connected Pv Systems easily implemented. However it shows discontinues input current and high peak current flows through the switch. Buck Boost Converter consists of a switch which may be MOSFET or a Transistor, Inductor, Diode, Capacitor and Load may be resistive or any other. [2] Figure 2 Buck-boost regulator [4] There are two modes of operation in buck boost converter as in the buck converter and the boost converter. Mode 1 [Fig3a]: In this mode the transistor is turned on and diode is reverse biased, the input current rises and flows through the inductor and transistor. Mode 2 [Fig3b]: Transistor is switched off and the current which was flowing through inductor would flow through capacitor, diode and the load. The energy stored in the inductor will be transferred to load and the inductor current would fall until transistor is switched on again in the next cycle. Then the cycle repeats. The output obtained by the buck boost converter has the reverse polarity voltaget. [4] The characteristics of the buck boost converter comparing to Buck and Boost are mainly: The output voltage polarity is opposite of the input voltage polarity. In case of an Ideal Converter the output voltage can vary continuously from 0 to -. The ranges for a buck and a boost converter are respectively 0 to Vi and Vi to. Figure 3a Mode 1 Operation of Buck-Boost converter Figure 3b Mode 2 Operation of Buck-Boost converter 64 editor@iaeme.com

4 Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy 3. DESIGN OF BUCK-BOOST REGULATOR In this work Buck-Boost Converter is used for resistance matching to achieve the optimum output by maximum power point tracking. The PV panel used as a source of input for the DC- DC converter has the following characteristics: Maximum power Pmax=10watt, Maximum voltage Vmax=17.40 volt, Maximum current Imax=0.58Amp, Open circuit voltage VOC=21.20volt, Short circuit current Isc=0.66amp. The design of Buck-Boost Converter starts with the selection of one Inductor and one Capacitor with a resistive load. Input voltage range is 10V-17V, output voltage is 12V and current of 0.58 amps. By using the output equation =, eqn. (1) Where D is the Duty cycle D is calculated to be 0.48.When D > 0.5 it will be Boost mode and D < 0.5 it is Buck mode. Is = source current, 0.66 Amp. Similarly by using this formula =, eqn. (2) Output current is calculated, Io =-0.72Amp. The value of Inductance as calculated is given as =, eqn. (3) L= 1mH, and the value of Capacitance is taken as =, eqn. (4) C= 2.7μF. The switching frequency is chosen as fs = 100 KHz with Time period T = 10*10. eqn. (5) 3.1. Effect of varying inductance & capacitance 1. Inductance Effect: for any constant duty cycle, either in buck or boost mode, (if an inductance value is varied say from 1mH to 10mH) it is observed that the regulated output voltage decreases and experimental results are depicted as follows. Inductance (L) Output Voltage(V o) 1mH to volts 10 mh -8 to -9.8 volts For constant capacitance of C= 2.7µf, 2. Capacitance Effect: for any constant duty cycle, either in buck or boost mode, (if an capacitance value is varied say from 2.7µf to 27 µf) it is observed that the regulated output voltage increases with small change and experimental results are depicted as follows. For constant Inductance of L= 1 mh, Capacitance (C) Output Voltage(V o) 2.7µf to volts 27µf to volts 65 editor@iaeme.com

5 Design and Simulation of Improved Dc-Dc Converters Using Simulink For Grid Connected Pv Systems 4. GENERATION OF PWM SIGNAL Pulse Width Modulation (PWM) is the most effective means to achieve constant voltage battery charging by switching the solar system controller s power devices. When in PWM regulation, the current from the solar array tapers according to the battery s condition and recharging needs. The generation pulse width modulation signal is required to trigger the MOSFET which switches the Buck-Boost regulator. The benefits of PWM are as follows: 1. Ability to recover lost battery capacity and de-sulfate a battery. 2. Dramatically increase the charge acceptance of the battery. 3. Maintain high average battery capacities (90% to 95%) 4. Equalize drifting battery cells. 5. Reduce battery heating and gassing. 6. Automatically adjust for battery aging. 7. Self-regulate for voltage drops and temperature effects in solar systems 5. BUCK-BOOST REGULATOR ALGORITHM There are several techniques for tracking MPP, two algorithms are commonly used to track the MPPT - the Perturb and observe (P&O) method and Incremental Conductance (INC) MPPT.The P&O method has been broadly used because it is easy to implement. Figure 4 presents the control flow chart of the P&O algorithm. The MPP tracker operates by periodically incrementing or decrementing the solar array voltage. If a given perturbation leads to an increase or decrease in the output power of the PV, then the subsequent perturbation is generated in the same or opposite direction respectively. [1] The BBR algorithm periodically increases or decreases the output terminal voltage of the PV system and comparing the power obtained in the current cycle with the power of the previous value. If the power is increased, it is observed power point is moved the operating point closer to the MPP. Thus, further voltage perturbations in the same direction should move the operating point toward the MPP. If the power decreases, the operating point has moved away from the MPP, and the direction of perturbation should be reversed to move back toward the MPP [1]. The result is shown in Fig editor@iaeme.com

6 Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy Start Sense V(k), I(k) P(k) = V(k)*I(k) Yes P(k) P(k-1) = 0 P(k)>P(k-1) Yes No V(k)>V(k-1) V(k)>V(k-1) Yes No Yes No Increase Duty Cycle Decrease Duty Cycle Decrease Duty Cycle Increase Duty Cycle Update V(k-1)=V(k) I(k-1)=I(k) Return Figure 4 Flow Chart of Buck-Boost Regulator 67 editor@iaeme.com

7 Design and Simulation of Improved Dc-Dc Converters Using Simulink For Grid Connected Pv Systems Figure 5 Power v/s Voltage curve for BBR Compared to on-off regulated state-of-charge levels that are typically 55% to 60% efficient. But this proposed work provides more efficient power delivery to load of about 80% to 85%. 6. RESULTS Figure 6 Modelling of BBR System. Simulation results& discussions Matlab Simulink can be used for exploring the behavior of wide range of real world dynamic system including electrical circuit, Electronics and many other Electro-mechanical systems. System that is being built in Simulink is consisting of a number of blocks that are connected with signal lines in uni-functional group. Matlab Simulink (V-2015) library consist of different kinds of blocks such as sources, sinks, subsystems etc. Different blocks are used for presentation of different PV module parameters like solar irradiance, temperature, short circuit current and resistance. With scope block the output of PV module, MPPT circuit and output at the load can be observed. Toolbox required: Simulink (sinks, sources, model verification, and user defined functions), simscape (sim electronics, sim power system, power electronics, foundation library, and 68 editor@iaeme.com

8 Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy additional components), Simulink coder, Simulink control design, Simulink verifier, Simulink extras. The MPPT Buck Boost Regulator MATLAB-SIMULINK model is shown in figure 6. The below Fig7a to Fig 7d shows the simulated waveforms. The input voltage here from the solar panel varies from 5v to 12v.The output voltage varies from v to v which is almost a constant entity, with a ripple of 0.2v, which can be smoothened by increasing the value of the inductance. Figure 7a For inductance of 1mH and Capacitance of 2.7µF Figure 7b For inductance of 10mH and Capacitance of 2.7µF 69 editor@iaeme.com

9 Design and Simulation of Improved Dc-Dc Converters Using Simulink For Grid Connected Pv Systems Figure 7c For Capacitance of 2.7µF and an inductance of 1mH Figure 7d For Capacitance of 27µF and an inductance of 1mH 7. CONCLUSION This work aims at an efficient utilisation of renewable solar energy for battery charging. Typical P & O MPPT based BBR helps in maintaining the output voltage of system a constant entity. The variable solar voltage, whether it is equal, greater, lesser than the desired output voltage is regulated by controlling the switching action of the converter. The present work increases the reliable operation and efficiency of power transfer in comparison to systems without MPPT (direct connection), which provides reducing the size and the cost of the PV system editor@iaeme.com

10 Dr. Y. L. ChandraShekar and Dr. P.S. Puttaswamy ACKNOWLEDGMENT The Author would like to thank Dr. C.Ram Singla, Professor, Department of Electronics and Communication Engineering, Sunrise University, Alwar for giving timely suggestions and technical advice. Author also extend gratitude to Dr.B.Ramachandra, Porfessor, Dept. of Electical & Electronics Engineering, PES College of Engineering, Mandya. Also would like to thank trustee members, Mysore Royal Education Trust, MYSURU, who encouraged and provided the opportunity to carryout research work. REFERENCES [1] Dr.Anil S. Hiwale, MugdhaV.Patil, Hemangi Vinchurkar, An Efficient MPPT Solar Charge Controller, International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering Vol. 3, Issue 7, July [2] Muhammad H. Rashid, Power Electronics, third edition, ISBN , published by Dorling Kindersley (India). [3] Shuchi Shah PG Student [PEMD], Department of EE, Nirma University, Ahmedabad, Gujarat, India, Design and Implementation of DC to DC Buck-Boost Converter Using PIC Controller, International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering Vol. 3, Issue 9, September 2014 [4] Arjydhara Pradhan, Dr.SMali, Chitralekha Jena, Puspapriya Behera, Design and Simulation of Dc-Dc converter used in solar charge controllers, International journal of engineering inventions,volume2,issue 3(February 2013), pp