ISSN: 2454-132X Impact factor: 4.295 (Volume3, Issue2) Simulation of MPPT based Multi-level CUK converter Nikunj B Patel Electrical Engineering department L D College of engineering and technology Ahmedabad, India nikunj079@yahoo.com, nikunj079@gmail.com Abstract Renewable energy sources are now a days becoming increasingly prevalent in distribution and generation systems. Most of the nations are installing significant solar power capacity in their grids as a supplement or alternative to other power sources. Photovoltaic ( PV) energy is one of the most important energy resources since it is clean, pollution free, and endless. Maximum Power Point Tracking (MPPT) is used in photovoltaic (PV) systems to maximize the photovoltaic output power, irrespective the variations of temperature and radiation conditions. This project presents P V module with M u lt i l e v e l CUK converter for electrical applications especially for dc load application. In this project t h e Multilevel CUK converter and PV system is simulated AND hardware and results are presented Keywords PV module, DC-DC converter, Multilevel, MPPT, P&O algorithm. I. INTRODUCTION Due to the demand of the fossil fuels, the photo voltaic technology was developed during the past two decades. Solar panel is the device used for the conversion of sun radiation to the electrical energy. It has the advantages of less maintenance, no wear problem and there is no noise pollution[1]. Nowadays in smart grid, solar power system plays important role even though the initial cost of the solar power system is high. Generation of the solar power is depending upon the PV array. A single PV cell generates very low power. So a series of PV cell is connected in series which gives maximum power output. In order to reduce the number of PV cell intermediate dc -dc converter are used to obtain maximum utilization of PV power. The solar power is increased Maximum power point tracking. A converter which operating in both the mode by varying the duty cycle of the switch is the CUK converter provides continuous input and output dc current. In recent years the MPPT technique is achieved by CUK converter. In this study, MPPT is achieved by power matching scheme i.e. Perturb & Observe algorithm.. The PV array is connected to the CUK converter and the maximum voltage is obtained by varying the duty cycle of the IGBT Switch II. Figure 1 Solar Panel integrated CUK converter MODELLING OF DC-DC CONVERTER A. Single level DC-DC CUK converter : CUK converter is obtained by using the duality principle on the circuit of buck-boost converter. Similar to buck-boost converter, the CUK converter provides a negative-polarity regulated output voltage with respect to the common terminal of the input voltage [1]. 2017, www.ijariit.com All Rights Reserved Page 421
The CUK converter is shown in the Fig 2 Fig 2 Single Level CUK converter configuration Here, the Capacitor Ci acts as the primary means of storing and transferring energy from input to the output. In steady state, the average inductor voltages VL1 and VL2 are zero. Therefore, by inspection of fig 3 V c1 = V d + V 0. (1) Therefore, VC1 is larger than both Vd and Vo. Assuming C1 to be sufficiently large, in steady state the variation in vc1 from its average value VC1 can be assumed to be negligibly small (i.e., vc1 ~VC1), even though it stores and transfer energy from the input to the output. When the switch is off, the inductor current il1 and il2 flow through the diode. The circuit shown in fig 3.8 (A). Capacitor C1 is charged through the diode by energy from both the input and L1. Current i L1 decreases, because Vc1 is larger than Vd. Energy stored in L2 feeds the output. Therefore, i L2 also decreases. When the switch is on C1 reverse biased the diode. The inductor currents i L1 and i L2 flow through the switch, as shown if fig 3.8 (B). Since VC1 > V0, C1 discharges through the switch, transferring energy to the output and L2. Therefore, i L2 increases. The input feed energy to L1 causing i L1 to increase. The inductor currents i L1 and i L2 are assumed to be continuous. Fig 3 Single level CUK Converter waveform : (A) switch off ( B) switch on The voltage and current expression in steady state can be obtained in two different ways. If we assume the capacitor voltage VC1 to be constant, then equating the integral of the voltages across L1 and L2 over one time period to zero yields.(2) 2017, www.ijariit.com All Rights Reserved Page 422
...(3).(4) From above two equations Assuming P d = P o gives Where IL1 = Id and IL2 = Io V 0 /V d = D/(1-D) I 0 / I d = (1-D) / D.(5) (6) B. Multilevel DC-DC CUK Converter : Single level CUK converter has limitation of output voltage up to certain voltage only, So where voltage is require more-then the output the of single level at that time multilevel CUK converter is used[5]. Negative voltage is obtained from multilevel CUK converter. The gain of the multilevel converter can be increases by adding number of capacitors and diodes without disturbing the main circuit. Multilevel converter are used to improvement of voltage regulation of the output as well overcome the limitation of single converter. There are few advantages of the multilevel converter which as listed below: Bandwidth of output is high. Reduce the huge ratings of components as they are divided into small groups. Minimum to maximum value different increases which can provides better voltage regulation. Output voltage and current ripples can be reduced. Fig 4 Multilevel CUK converter configuration III. PV MODULE A. Mathematical modelling of PV Module: In the Fig 5 In first model does not take into account the internal losses of the current. A diode is connected in opposite to parallel with the light generated current source. The output current equation is obtained by Kirchhoff s law[6] 2017, www.ijariit.com All Rights Reserved Page 423
Fig 5 Ideak single diode model I = I ph - I d..(7) Where Iph = photocurrent Id =diode current which is proportional to saturated current Which is given by equation, Where, V = imposed voltage on the diode. I 0 = reverse saturation or leakage current of the diode(a) N s = number of PV cells in series A = ideality factor which is depend on PV cell technology Where, VT = 26mV at 300 K for silisium cell, In Fig. 6 Tc = actual cell temperature ( K) k= Boltzman constant 1.381*10-23 J/K q = electron charge (1.602*10-19 C) VT = k. Tc /q (8) (9) Fig 6 :Practical model with Rs and R p In practically it is impossible to neglect the series resistance Rs and the parallel resistance Rp because of their impact on the efficiency of the PV cell and the PV module. When Rs is taken into account the equation of Id should take the next form. By applying Kirchhoff s current law, current will be obtained by the equation: I = I ph I d I p (10) I p = current leak in parallel resistor So according to the above equations the output current of a module containing N s cells in series will be : I = I ph I 0 [exp ( V+IR s ) 1] V+IR s...(11) a R p B. PV model Development in MATLAB According to the equation above, a dynamic model for a PV module consisting of 36 cells in series has been developed using MATLAB/Simulink. Figure shows the sub system of the PV model. The input quantities ( solar irradiance and the ambient temperature ) together with manufacturer data are used to calculate the parameters. The models parameters used in the simulation are given in table which is based on the values reported in [6]. 2017, www.ijariit.com All Rights Reserved Page 424
Table : Datasheet of Solar Panel Parameters Maximum Power (Pmax ) Current at Pmax (Imax) Voltage at Pmax (Vmax) Short circuit current (Isc) Open Circuit Voltage (Voc) Series Resistance ( Rs ) Total Number of Cells in Series (Ns) Total Number of Cells in parallel(np) Values 49 W 2.88 A 17 V 3.11 A 21.8 V 0.55 Ω 36 01 Temperature Co-efficient 0.0013 Band Gap Energy (Eg) 1.12Ev Ideality Factor(A) 1.3 A. INTRODUCTION Fig 7 PV module in MATLAB/Simulink Fig 8 Subsystem of PV module in MATLAB/Simulink IV PERTURB AND OBSERVE ALGORITHM A typical solar panel converts only 35 to 40 percent of the incident solar irradiation into electrical energy. Maximum power point tracking technique is used to improve the efficiency of the solar panel module. According to Maximum Power Transfer theorem, the power output of a circuit is maximum when the Thevenin impedance of the circuit (source impedance) matches with the load impedance. Hence our problem of tracking the maximum power point reduces to an impedance matching problem. The P&O algorithm states that when the operating voltage of the PV panel is perturbed by a small increment, if the resulting change 2017, www.ijariit.com All Rights Reserved Page 425
in power P is positive, then we are going in the direction of MPP and we keep on perturbing in the same direction. If P is negative, we are going away from the direction of MPP and the sign of perturbation supplied has to be changed. B. FLOWCHART OF P & O ALGORITHM : Start Read V and I P=V.I Yes If Pn>Pn-1 No Yes No Yes If No If Vn>Vn-1 Vn>Vn-1 Increase Duty cycle Decrease Duty cycle Decrease Duty cycle Increase Duty cycle RETURN Figure 9 : Flowchart of Perturb & Observe algorithm C. Simulation of P & O Algorithm in MATLAB/Simulink Fig 10 :Perturb & Observe algorithm simulation in MATLAB/Simulink V. SIMULATIONS AND RESULTS OBTAINED IN MATLAB A. Simulation result for closed loop CUK converter in different supply voltages and loads :(V ref= 50V) V in Load(Ohm) V out I out 24 55 50.11 0.9111 24 27.5 49.51 1.8000 30 55 49.98 0.9087 30 27.5 49.70 1.8070 50 55 49.97 0.9086 50 27.5 49. 89 0.8140 2017, www.ijariit.com All Rights Reserved Page 426
Fig 11 : Waveform foe close loop simulation of CUK converter ( V in, V out, I out ) B. Simulation result for Multi-level CUK converter in different supply voltages and loads :(V ref=250v) V in Load(Ohm) V out I out 25 50 250.1 5.003 25 25 249.5 9.990 50 50 250.3 5.006 50 25 249.6 9.984 75 50 249.9 4.998 75 25 249.6 9.983 Fig 12 : Waveform for simulation of Multi-level CUK converter (V in, V out, I out ) C. Characteristics results for PV module under different Irradiance ( I-V and P-V curve ) 2017, www.ijariit.com All Rights Reserved Page 427
Fig 13 : I-V Characteristic curves of the PV module under different irradiance Fig 14 :P-V Characteristic curves of the PV module under different irradiance D. Simulation of MPPT based Multi-level CUK converter system : Fig 15: Multi-level CUK converter configuration in MATLAB/Simulink E. Simulation result for MPPT based Multi-level CUK converter in different irradiance levels: 2017, www.ijariit.com All Rights Reserved Page 428
Fig 16 : Waveform for simulation of MPPT based Multilevel CUK Converter for irradiance 1000W/m 2 (V in, V out, I out) Fig 17 : Waveform for simulation of MPPT based Multilevel CUK Converter for irradiance 800W/m 2 (V in, V out, I out) Fig 18 : Waveform for simulation of MPPT based Multilevel CUK Converter for irradiance 600 W/m 2 (V in, V out, I out) CONCLUSION Here in this paper, simulation of single level CUK converter and Multilevel CUK converter is done and results are conclude that output voltages of multilevel CUK converter are much more greater than the single level CUK converter. Which can be utilized to run some small dc loads? The output of multilevel CUK converter depends on the number of level (or gain). Photovoltaic module have output of very low voltages so for run dc loads of higher rating the Multilevel CUK converter can be used as step up DC DC converter and which can be utilized to some small DC load applications. Here also output voltages and current results are compared for different irradiance level. 2017, www.ijariit.com All Rights Reserved Page 429
REFERENCES [1] Design of Cuk Converter Powered by PV Array By R. Sriranjani, A.ShreeBharathi and S. Jayalalitha. Research Journal of Applied Sciences, Engineering and Technology 6(5): 793-796, 2013 ISSN: 2040-7459; e-issn:2040-7467. [2] Simulation and Hardware Implementation of Incremental Conductance MPPT With Direct Control Method Using Cuk Converter By Azadeh Safari and Saad Mekhilef, IEEE TRANSACTION ON INDUSTRIAL ELECTRONICS VOL 58 NO. 4 APRIL 2011 [3] Comparison of Mathematical Models of Photo- Voltaic (PV) Module and effect of various Parameters on its Performance By Mamta Suthar, G.K Singh and R.P Saini. International conference on Energy Efficient Technologies for suatainability ( ICEETS), 2013. [4] Review of the maximum power point tracking algorithms for stand- alone photovoltaic systems By V. Salas, E. Olı as, A. Barrado, A. La zaro. Solar Energy Materials & Solar Cells (Elsevier) [5] Non-Isolated Dual Output Hybrid DC-DC Multilevel Converter for Photovoltaic Applications By Mahajan Sagar ranjana, Nandyala Reddy, Repalle Kusala PavanKumar. 2 nd International conference on Devices, Circuit and System ( ICDCS) 2014 [6] A detailed modeling of photovoltaic module using MATLAB By Habbati Bellia, Ramdani Youcef, Moulay Fatima. NRIAG Journal of Astronomy and Geophysics. 2017, www.ijariit.com All Rights Reserved Page 430