IDENTIFICATION OF THE OPTIMAL CONVERTER TOPOLOGY FOR SOLAR WATER PUMPING APPLICATION

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 9, Issue 13, December 2018, pp , Article ID: IJMET_09_13_008 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed IDENTIFICATION OF THE OPTIMAL CONVERTER TOPOLOGY FOR SOLAR WATER PUMPING APPLICATION P.R. Chandrasekhar PG student, Energy and power electronics, SELECT, VIT University, Vellore , India Chitra A, Razia Sultana W and J. Vanishree Associate Professor, School of Electrical Engineering, VIT University, Vellore, India ABSTRACT This paper envisages to identify an optimal topology of DC-DC converter for the solar pump application, by comparing the performance indices of the three advanced non-isolated converters namely Landsman converter, Luo converter and Zeta converter. The identified best topology of the non-isolated DC-DC converter, which basically operates in the mode of buck-boost converters cascaded to a three phase voltage source inverter (VSI), which is connected to a permanent magnet brushless DC (PMBLDC) motor. The whole system is front ended to a PV panel. In order to obtain the maximum power transfer to the load, a popular maximum power point tracking (MPPT) technique, Perturb and Observe (P&O) has been implemented. The whole system is simulated under the environment of PSIM. Keywords: PV system, Perturb and Observe, MPPT, PMBLDC, DC-DC converter Cite this Article: P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree, Identification of the Optimal Converter Topology for Solar Water Pumping Application, International Journal of Mechanical Engineering and Technology, 9(13), 2018, pp INTRODUCTION Extinction of the fossil fuels globally making world to concentrate on the renewable energy sources. Non-conventional energy sources being pollution-free, almost does not affect the environment. The initial installation cost may be more, but the running cost will be very low compared to the non-renewable energy sources. Upcoming concepts like distributed generation, smart grid and micro grid can be easily implemented with the renewable energy sources. Solar energy being more economical and stable compared to the remaining sources of renewable energy, may be the scope of power for the future [11]. The solar power generated 63 editor@iaeme.com

2 Identification of the Optimal Converter Topology for Solar Water Pumping Application is DC. The switching power converters have to be employed in order to have control over the generated power and to operate at MPP. There are many MPP techniques such as P&O [15], [21-24], incremental conductance [19-20], hill climbing, etc. [17-18]. Depending on the application, the controlled DC power is directly used or can be converted to AC, employing the DC-AC converters [4]. There are a lot of applications for the DC-DC switching power converters in the solar power based applications [1] - [3]. This gives scope for the development of various topologies of the switching power converters. Topologies based on isolation, interleaving, etc., are developing to ensure the safety of the consumer [6], [12]. As it is a known fact that the running cost of the conventional DC motor is more because of the presence of the brushes and the commutator. Generally the induction is widely used for the water pumping application, because of its ruggedness and other factors. But the same doesn t hold good for this type of solar applications. The reason is that, it requires an intricate control and is liable to be overheated if the voltage levels are too low. These demerits of the above mentioned two machines can be eliminated by the PMBLDC motor which exhibits low voltage handling capacity, operation at higher range of efficiencies, less impact of EMI issues, simple control strategies, ability to operate in a different range of speeds etc., and hence it is chosen for this type of application [5], [7] -[10], [13]-[14]. 2. BLOCK DIAGRAM OF THE SYSTEM The DC-DC converter is front-ended with a solar photo voltaic panel. The DC-DC converter is cascaded with the 3-ɸ VSI which drives the PMBLDC motor. The BLDC motor requires the position sensors for sensing the rotor position. The outputs of the position sensors are fed back to the 3-ɸ VSI. The operation of the DC-DC converter in the optimum power point is ensured by the MPPT. The MPPT technique, Perturb and Observe (P&O) is implemented here. Figure 1 Block diagram of the system 3. SOLAR PV DESIGN The PV panel has been designed to deliver a wattage of P pv = 6.8 V pv = V and I pv =23.26 A. The design of the solar PV is done with reference to the data sheet BYD_ P. A panel of the power rated at 250W has been chosen from the data sheet, whose specifications are given below in the Table editor@iaeme.com

3 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Table 1 Specifications of PV system from the data sheet Specification Open-circuit voltage (Voc) Maximum operating voltage (Vmpp) Short circuit current (Isc) Maximum operating current (Impp) Maximum power in STC (Pmpp) value V V 8.98 A 8.22 A 250 W No. of cells 60 The no. of panels connected in the series =( ) = 10. The no. of panels connected in parallel = ( ) = Design of the series connected panels Total no. of cells = (60) 10 = 600 cells The maximum power, P max = (250) 10 = 2500 W The voltage at P max = (30.40) 10 = 304 V The open-circuit voltage, V oc = (38.00) 10 = 380 V 3.2. Design for the parallel panels The maximum power, P max = (2500) 3 = 7500 W The current at P max = (8.22) 3 = A The short- circuit current I sc = (8.98) 3 = The solar physical model gives the better real time designing experience compared to the solar functional model in the PSIM [16]. Selecting the solar physical model in PSIM, the above designed values are to be entered in the solar module given in the utilities icon of the PSIM software. The values of the series resistance (R s ), saturation current (I SO ), temperature coefficient (C t ), etc., can be calculated in the solar module itself. By adjusting the values of R s, I SO, C t, etc., in the solar module we can obtain the desired P-V and I-V curves. The whole design of the PV panel is done at the standard operating conditions of irradiance and temperature, S =1000 W/m 2 and T= 25 o C respectively. The I-V and P-V curves of the designed PV panel are shown in Fig. 2 and Fig editor@iaeme.com

4 Identification of the Optimal Converter Topology for Solar Water Pumping Application Figure 2 I-V curve of the PV Panel Figure 3 P-V curve of the PV panel The screen shot of the solar physical model designed in PSIM for the above specifications is shown in Fig. 4. Figure 4 Screen-shot of the solar physical model with all the designed data. Hence the PV panel is developed in PSIM which is to be interfaced with the DC-DC converter. 4. COMPARISON OF THE CONVERTER TOPOLOGIES AND THEIR PERFORMANCE INDICES The three advanced DC-DC non-isolated converters namely Landsman converter, Luo converter and Zeta converter are chosen for the comparison of their performance indices and their topologies. In order to perform the comparative studies for the three converters, all three 66 editor@iaeme.com

5 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree converters have to be designed on a common platform viz. the switching frequency f sw, inductor current ripple I L and the capacitor voltage ripple V C, etc., have to be same respectively for all the converters. The switching frequency, f sw is chosen 20 khz and the inductor current ripple, I L is maintained at 3% and the capacitor voltage ripple, V c is maintained at 10%.The PV panel is also designed for the standard operating conditions of S =1000 W/m 2 and T= 25 o C respectively The specifications of the chosen converters The power rating of all the three converters, P pv = 6.8KW. The input voltage to the converters, V pv = V and The input current, I pv = A. All the three converters are designed for, An output voltage of V dc =310 V and The output current, I o = A respectively. The switching frequency of the converters, f sw = 20 KHz. So the duty ratio of the converters, δ = = = The inductors current ripples are fixed at 3% and the output voltage ripples are fixed at the 10%. The circuit diagrams, design equations and simulated results of the performance indices of all the three selected converters are given below Circuit diagrams and the design of the chosen converters The three converters are of the Buck-Boost topology LANDSMAN CONVERTER The circuit diagram of the landsman converter developed in PSIM is shown in Fig. 5. C1 L1 V Ppv 1000 S Cpv L2 C2 R T 25 Figure 5 Circuit diagram of the Landsman converter The design equations of the Landsman converter are I dc = A, = 0.514, f sw = 20 KHz, V pv = V, V dc = 310 V 67 editor@iaeme.com

6 Identification of the Optimal Converter Topology for Solar Water Pumping Application V C1 = V pv + V dc = ( ) = V I L1 = I pv = A I L2 = ( ) = A Capacitor, C 1 C 1 = = 9 F (1) Inductor, L 1 L 1 = =1mH (2) Inductor, L 2 L 2 = = 6mH (3) Capacitor,C 2 C 2 = = F; h= (4) N = speed of the BLDC machine; P= No. of poles The simulated results of the performance indices of the Landsman converter namely, the inductor currents (I L1, I L2 ), output voltage (V o ) and output current (I o ) are shown in Fig IL IL2 Vo Io Time (s) Figure 6 Simulated results of the performance indices of the Landsman converter Luo Converter The circuit diagram of the Luo converter developed in PSIM is shown in Fig editor@iaeme.com

7 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Ppv L2 V S 1000 C1 L1 C2 R T 25 Figure 7 Circuit diagram of the Luo converter The design equations of the Luo converter are I dc = A, = 0.514, f sw = 20 KHz, V pv = V, V dc = 310 V V C1 = V dc = 310 V I L1 = (I pv + I dc ) = ( ) = A I L2 = A Inductor, L 1 L 1 = = 5.509mH (5) Inductor, L 2 L 2 = = mH (6) Capacitors,C 1, C 2 C 1 = C 2 = = F; h= (7) N = Rated speed of the PMBLDC machine P= No. of poles The simulated results of the performance indices of the Landsman converter namely, the inductor currents (I L1, I L2 ), output voltage (V o ) and output current (I o ) are shown in Fig editor@iaeme.com

8 Identification of the Optimal Converter Topology for Solar Water Pumping Application IL1 IL2 Vo Io Time (s) Figure 8 Simulated results of the performance indices of the Luo converter Zeta Converter The circuit diagram of the zeta converter developed in PSIM is shown in Fig. 9. V Ppv C1 L2 S 1000 Cpv L1 C2 R T 25 Figure 9Circuit diagram of the Zeta converter The design equations of the zeta converter are as follows I dc = A, = 0.514, f sw = 20 KHz, V pv = V, V dc = 310 V V C1 = V dc = 310 V I L1 = I pv = A I L2 = I dc = A Capacitor,C 1 C 1 = = (8) Inductor, L 1 L 1 = = mh (9) 70 editor@iaeme.com

9 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Inductor, L 2 L 2 = = mh (10) Capacitor,C 2 C 2 = = F; h= (11) N = Rated speed of the PMBLDC machine P = No. of poles The simulated results of the performance indices of the Landsman converter namely, the inductor currents (I L1, I L2 ), output voltage (V o ) and output current (I o ) are shown in Fig IL IL2 Vo Io Time (s) Figure 10 Simulated results of the performance indices of the Zeta converter Topological comparison of the three converters There are two inductors, two capacitors, a diode and a switch in all the three converters. The total no. of components is six which is evident from Fig.5, Fig.6, and Fig Comparison of the output voltage ripple The output voltage ripple value of the Zeta converter is very high compared to the two converters which is observed from the Fig editor@iaeme.com

10 Identification of the Optimal Converter Topology for Solar Water Pumping Application Vo Vo_(luo converter simulation - Copy) Vo_(zeta converter simulation) Time (s) Figure 11 Waveforms of the output voltages (V O ) of the three converters Red- Landsman converter; Blue Luo converter; Green Zeta converter 4.4. Comparison of output current ripple The output current ripple value of the Zeta converter is very high compared to the remaining two converters which is seen from the Fig.12. Io Io_(luo converter simulation - Copy) Io_(zeta converter simulation) Time (s) Figure 12 Waveforms of the output currents (I o ) of the three converters Red- Landsman converter; Blue Luo converter; Green Zeta converter 4.5. Comparison of source current ripple The input current ripple value of the Landsman converter is also very low compared to the remaining two converters in Fig editor@iaeme.com

11 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Is Is_(luo converter simulation - Copy) Is_(zeta converter simulation) Time (s) Figure 13 Waveforms of the source currents (I s ) of the three converters Red- Landsman converter; Blue Luo converter; Green Zeta converter 4.6. Comparison table for the three converters Table 2gives the information about the calculated values of the three converter components, input current ripple comparisons, output voltage and current ripple comparisons. Table 2 Comparison of the value of the components and the performance indices of the three converters. PARAMETER LANDSMAN LUO ZETA Inductor current ripple (3%) Intermediate capacitor voltage ripple Input current ripple Output voltage ripple Output current ripple L1 1 mh mh mh L2 6 mh mh mh C1 9 F F F Is A A A Vo A A V Io A A A The calculated values of the components are based on the design equations mentioned in the previous section. The values of the components of the Landsman converter components are very low compared to the other two converter components. Even though the output voltage and current ripples of the Luo converter are very low compared to the remaining converters, the cost of the intermediate capacitor will be very high because of its higher value compared to the remaining two converters. The cost of the components of the Landsman converter is very low because of its lesser values compared to the other converters editor@iaeme.com

12 Identification of the Optimal Converter Topology for Solar Water Pumping Application Based on the above conclusions, it can be inferred that the Landsman converter is the one, which is best and ideal for the solar pumping application. 5. MAXIMUM POWER POINT TRACKING (MPPT) The maximum power point tracking (MPPT) helps the system to operate at the maximum value of the power that is to be delivered to the load. The MPPT facilitates the load impedance to be equal to the source impedance, by adjusting the duty ratio of the converter. Perturb and Observe (P&O) method is used for tracking the optimum operating point of the PV panel Flowchart of Perturb and Observe (P&O) method The voltage and current are sensed with the help of voltage and current sensors respectively and the power is calculated. If the calculated value of power is greater than the previously calculated value of power, check with the voltage whether the present value of the voltage is greater than the previous value of the voltage. If yes, increase the duty ratio. If not, reduce the duty ratio. The flow chart for the P&O technique is shown in Fig.14. Figure 14 Flow chart of the P&O technique The pictorial view of the P&O technique is shown in Fig

13 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Figure 15 Portrayal of the PV curves for the operation. Starting from an operating point A, if atmospheric conditions stay approximately constant, a perturbation V in the PV voltage V will bring the operating point to B and the perturbation will be reversed due to a decrease in power. However, if the irradiance increases and shifts the power curve from P 1 to P 2 within one sampling period, the operating point will move from A to C. This represents an increase in power and the perturbation is kept the same. Consequently, the operating point diverges from the MPP and will keep diverging if the irradiance steadily increases Analog circuit implementation of the (P&O) technique in PSIM software The P&O technique is implemented using the analog switches in the PSIM software. The circuit implementation is given below. Figure 16 Analog implementation of the (P&O) technique in PSIM 75 editor@iaeme.com

14 Identification of the Optimal Converter Topology for Solar Water Pumping Application The step- size is initially chosen to be 0.1 so as to facilitate the soft- start of the BLDC motor. The variation of the duty ratio is being done and the switching frequency of f sw = 20 KHz is set for the carrier triangular wave, so as to operate the DC-DC converter with the same frequency that is designed to perform Landsman converter with MPPT Perturb and Observe (P&O) technique [16] is applied to the Landsman converter in order to deliver the maximum power to the load. The results of the Landsman converter output power and output voltage are shown in Fig.17and Fig.18 respectively. Po Po_(landsman converter simulation) with MPPT 6.8K 6.798K 6.796K 6.794K without MPPT 6.792K Time (s) Figure 17 Steady- state waveforms of the output power of Landsman converter with and without MPPT Figure 18 Steady- state waveforms of the output voltage of landsman converter with and without MPPT It is evident from the result that the PV system with MPPT is working satisfactorily Cascading the Landsman converter with the PMBLDC motor The Landsman converter is connected to the PMBLDC motor through a simple 3-ɸ VSI, operating in the 120 o mode of conduction. The control of the VSI is done with the help of the signals generated from the hall-sensors that are embedded in the machine editor@iaeme.com

15 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree Basically the Landsman converter is operated in the mode of the basic buck-boost converter. The worst case design of the Landsman converter follows the basic buck-book converter s worst case design Need for the worst case design The inductors and the capacitors in the converters will be designed for only one value of the supply current or voltage values. But as far as the solar is concerned, the supply voltage or currents will never be constant as the irradiation levels vary in the wide range throughout a day. If the converter is designed only for a single value of the voltage or current, the desired performance cannot be achieved. So, the converter has to be designed for a wide range (worst case) to achieve a better performance. According to the worst case design, all the components of the Landsman converter are to be designed at the minimum input voltage (V min ) and the maximum value of the duty cycle max. The Landsman converter is designed for the worst case, such that even if the irradiation varies from 1000 W/m 2 to 500 W/m 2, its performance is not deteriorated. 6. RESULTS OF THE BLDC MOTOR INDICES The BLDC motor that is cascaded to the Landsman converter through the 3-ɸ VSI exhibits the following characteristics shown in the Fig. 19 and Fig Vdc Ia nm Tem_BDCM Time (s) Figure 19 Waveforms of the performance indices of the BLDC motor@ the irradiance level of S = 1000 W/m 2 The Fig 15 depicts the waveforms of the performance indices of the PMBLDC the irradiation level of S = 1000 W/m 2. The parameters are as below The DC link voltage is V dc = 306 V. The R.M.S. value of the phase- A current, I a = 23.5 A The speed of the BLDC motor, N = 2562 rpm editor@iaeme.com

16 Identification of the Optimal Converter Topology for Solar Water Pumping Application The electromagnetic torque of the motor, T em = N-m The load chosen for the motor is the general mechanical load which is equivalent to the water pump characteristics. The pump is designed based on the power-speed characteristics as follows K p = = = W/ (rad/sec) 3 Where K p is the proportionality constant, is the speed of the motor and P is the rated power. The Fig 16 depicts the waveforms of the performance indices of the PMBLDC motor@ the irradiation level of S= 500 W/m 2. The DC link voltage is V dc = V. The R.M.S. value of the phase- A current, I a = A The speed of the BLDC motor, N = 1817 rpm. The electromagnetic torque of the motor, T em = N-m Vdc Ia nm Tem_BDCM Time (s) Figure 20 Waveforms of the performance indices of the BLDC the irradiance level of S = 500 W/m 2. The results reveal that the proposed system with PMBLDC motor operates satisfactorily according to the variation of the irradiance and hence it is suitable to drive a pump load editor@iaeme.com

17 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree 7. CONCLUSION The identification of the optimal topology for the solar pumping application has been done. The identified best topology of the DC-DC converter viz., the Landsman converter is designed for the worst case. The Landsman converter is front-ended with solar PV panel and cascaded a with the PMBLDC motor. For operating the converter to operate at an optimum power point, an MPPT technique named Perturb and Observe (P&O) has been employed. The soft start of the motor is achieved by setting the initial value of the duty ratio at 0.1. The performance indices of the whole system are obtained and they are found to be satisfactory. ACKNOWLEDGEMENT I sincerely thank VIT University, Vellore for the support in completing this paper. REFERENCES [1] Kumar, R., & Singh, B. (2014, December). Buck-boost converter fed BLDC motor drive for solar PV array based water pumping. In Power Electronics, Drives and Energy Systems (PEDES), 2014 IEEE International Conference on (pp. 1-6). IEEE. [2] Singh, B., & Kumar, R. (2016). Solar photovoltaic array fed water pump driven by brushless DC motor using Landsman converter. IET Renewable Power Generation, 10(4), [3] Kumar, R., & Singh, B. (2014, December). Solar photovoltaic array fed Luo converter based BLDC motor driven water pumping system. In Industrial and Information Systems (ICIIS), th International Conference on (pp. 1-5). IEEE. [4] Singh, B. (2014). BLDC Motor Driven Solar PV Array Fed Water Pumping System Employing Zeta Converter. IEEE Transactions On Industrial Electronics, 61(6). [5] Singh, B., & Kumar, R. (2016). Simple brushless DC motor drive for solar photovoltaic array fed water pumping system. IET Power Electronics, 9(7), [6] Caracas, J. V. M., Farias, G. D. C., Teixeira, L. F. M., &Ribeiro, L. A. D. S. (2014). Implementation of a high-efficiency, high-lifetime, and low-cost converter for an autonomous photovoltaic water pumping system. IEEE Transactions on industry applications, 50(1), [7] Singh, P. K., Singh, B., &Bist, V. (2016, March). PFC converter based power quality improvement and ripple current minimization in BLDC motor drive. In Power Systems (ICPS), 2016 IEEE 6th International Conference on (pp. 1-6). IEEE. [8] Singh, P. K., Singh, B., &Bist, V. (2016, March). PFC converter based power quality improvement and ripple current minimization in BLDC motor drive. In Power Systems (ICPS), 2016 IEEE 6th International Conference on (pp. 1-6). IEEE editor@iaeme.com

18 Identification of the Optimal Converter Topology for Solar Water Pumping Application [9] Singh, P. K., Singh, B., &Bist, V. (2016). Brushless DC motor drive with power factor regulation using Landsman converter. IET Power Electronics, 9(5), [10] Akin, B., Bhardwaj, M., &Warriner, J. (2011). Sensorless Trapezoidal Control of BLDC Motors. Texas Instruments Document, ver, 1. [11] Franklin, T. S., Cerqueira, J. J. F., & de Santana, E. S. (2014). Fuzzy and PI controllers in pumping water system using photovoltaic electric generation. IEEE Latin America Transactions, 12(6), [12] Mishra, A. K., & Singh, B. (2016, July). Solar energized SRM driven water pumping utilizing modified Landsman converter. In Power Electronics, Intelligent Control and Energy Systems (ICPEICES), IEEE International Conference on (pp. 1-6). IEEE. [13] Singh, B., &Bist, V. (2013, November). A PFC based BLDC motor drive using a Bridgeless Zeta converter. In Industrial Electronics Society, IECON th Annual Conference of the IEEE (pp ). IEEE. [14] Saxena, R., Pahariya, Y., &Tiwary, A. (2010, February). Modeling and simulation of BLDC motor using soft computing techniques. In Communication Software and Networks, ICCSN'10. Second International Conference on (pp ). IEEE. [15] Nanshikar, K., & Desai, A. (2016). Simulation of P & O Algorithm using Boost Converter. In Nitte Conference on Advances in Electrical Engineering NCAEE (pp ). [16] Abdul kadir M., A. S. Samosir, and A. H. M. Yatim (Dec. 2012), Modelling and simulation of maximum power point tracking of photovoltaic system in Simulink model, IEEE International Conference on Power and Energy (PECon), (pp ). [17] Kjaer Soren Baekhoj (Dec. 2012), Evaluation of the Hill Climbing and Incremental Conductance Maximum Power Point Trackers for Photovoltaic Power Systems, IEEE Transaction on Energy Conversion, vol. 27, no. 4, pp. (pp ). [18] Reisi, Ali Reza, Mohammad Hassan Moradi, and Shahriar Jamasb. (Mar. 2013), Classification and comparison of maximum power point tracking techniques for photovoltaic system: a review, Renewable and Sustainable Energy Reviews- Elseveir, vol. 19, (pp ). [19] Safari, Azadeh, and Saad Mekhilef. (Apr. 2011), Simulation and hardware implementation of incremental conductance MPPT with direct control method using cuk converter, IEEE Transactions on Industrial Electronics, vol. 58, no. 4, (pp ). [20] Elgendy, Mohammed A., Bashar Zahawi, and David J. Atkinson. (2013), Assessment of the incremental conductance maximum power point tracking algorithm, IEEE Transactions on sustainable energy 4.1 (pp ) editor@iaeme.com

19 P.R. Chandrasekhar, Chitra A, Razia Sultana W and J. Vanishree [21] Tafticht, T., et al. (2008), An improved maximum power point tracking method for photovoltaic systems, Renewable energy 33.7 (pp ). [22] Hua, C., and J. Lin. (2003) An on-line MPPT algorithm for rapidly changing illuminations of solar arrays, Renewable Energy 28.7, (pp ). [23] Mamarelis, Emilio, Giovanni Petrone, and Giovanni Spagnuolo. (2014). A twosteps algorithm improving the P&O steady state MPPT efficiency, Applied Energy 113, (pp ). [24] Femia, Nicola, et al (2012). Power electronics and control techniques for maximum energy harvesting in photovoltaic systems. CRC press, 81 editor@iaeme.com