The interest of photovoltaic (PV) water pumping systems with standard components is increasing as a low cost and independent solution over dedicated systems. However, one of the challenges of this alternative is the fact that small power systems to drive power pumps require a small number of PV modules and the PV string voltage is, usually, not enough to feed the frequency converter. This paper presents an approach to the drive, using a DC/DC converter with maximum power point tracking (MPPT). The overall system has been tested on a real
experimental platform.info:eu-repo/semantics/publishedVersio

Batista, José

Ferreira, Ângela P.

Goedtel, Alessandro

Leite, V.

Maidana, Wellington

Roman, Dionízio

Tangerino, Bruno

English

Tangerino, Bruno Henrique Boschetti

Roman, Dionizio José Vargas

Biblioteca Digital do IPB

Photovoltaic Water Pumping System for SmallPower Conventional AC PumpsBruno Tangerino1,2, Dion´ızio Roman1,2, Vicente Leite1,3, Alessandro Goedtel2,Aˆngela Ferreira1,3, Jose´ Batista1, and Wellington Maidana1,21 Instituto Polite´cnico de Braganc¸a, Braganc¸a, Campus Santa Apolo´nia, 5300-253Portugal2 Universidade Tecnolo´gica Federal do Parana´, Campus Cornle´lio Proco´pio, Parana´,Brasil3 Research Centre in Digitalization and Intelligent Robotics (CeDRI)tangerino.bruno2@hotmail.com; dionizioroman@hotmail.com; avtl@ipb.pt;agoedtel@utfpr.edu.br; apf@ipb.pt; jbatista@ipb.pt; maidana@ipb.ptAbstract. The interest of photovoltaic (PV) water pumping systemswith standard components is increasing as a low cost and independentsolution over dedicated systems. However, one of the challenges of thisalternative is the fact that small power systems to drive power pumpsrequire a small number of PV modules and the PV string voltage is,usually, not enough to feed the frequency converter. This paper presentsan approach to the drive, using a DC/DC converter with maximum powerpoint tracking (MPPT). The overall system has been tested on a realexperimental platform.Keywords: Water Pumping System, Conventional Components, LowPower Pumps, Maximum Power Point Tracking1 IntroductionThe use of photovoltaic energy for water pumping systems is a solution thathas been widely researched and implanted [1], [2]. DC motor driven pumps arealready in use in several countries, but some problems (mostly maintenance duethe presence of commutator and brushes) have made researchers to find othersolutions [3].One of this solutions is a water pumping system equipped with AC motorsdue to their advantages, mainly their reliability and low cost [2]. However, oneproblem is the fact that the market is being controlled by few manufacturers ableto afford the continuous technology development, causing low spare availabilityand relatively high prices for dedicated systems [4]. Hence, AC drive systemswith fully standard components become attractive [4], [5].Dedicated PV water pumping systems are formed typically by a power con-verter, DC motor and PV string for power generation. Low power PV waterpumping systems based on standard AC motors are not usual, because a higher285voltage is needed to power the motor, which requires a string with a large num-ber of PV modules. Standard Frequency Converters (SFCs) and AC motors areextensively used in industrial applications and they have been seldom used in PVwater pumping systems [4], [5]. The main advantages of this approach in com-parison to dedicated systems include manufacturers’ independence and bettercomponent availability, lower cost because the components are manufactured inlarge quantities and increased reliability of the system because they are designedto work in industrial environment [5].SFCs are produced for AC standard voltage of the grid (single or three-phase) and, therefore, needs a minimum voltage level on their DC-link for properoperation. One initial problem is the fact that a large number of PV modulesare needed to reach this minimum operating voltage. For small power systems,where the power of the motor is below 1,5 kW, this large number of PV modulesimplies a high value of surplus power installed. On the other hand, the numberof necessary PV modules to generate the rated power of the pump implies aundervoltage value to operate the SFC. Another problem, pointed by Ramos[5], is the lack of maximum power point tracking (MPPT). This paper presentsan approach with a DC/DC converter as a solution of these two problems. Theproposed solution integrates a step-up converter with MPPT which has beenimplemented is implemented using a real platform.2 Photovoltaic Water Pumping SystemAs demonstrated by Abella [4], a PV array can be directly connected to aSFC to drive an AC pump. The SFC needs a minimum DC-link voltage levelto operate in normal conditions. This value varies depending on the type ofconverter (single-phase or three-phase). Table 1 presents the AC and DC linkvoltage ranges, for rated power, of the single-phase SFC ACS355. The DC valuesare, approximately, the peak values of the AC voltage. For lower power (i. e.,lower radiation), the DC voltage will also be lower, and, consequently, the speedof the AC motor will be smaller than the rated one, due to scalar control. Thesystem proposed is shown on Figure 1.Fig. 1. Configuration of proposed PV water pumping system.286Table 1: Single-phase SFC ACS355.AC Supply voltage [Min-Max] 200 - 240 VDC-link voltage (on DC Bus) [Min-Max] 280 - 340 VFor proper functioning, the DC-link voltage obtained from the PV stringmust attend the minimum value of the SFC and the input voltage must be closeto the maximum power point voltage of the PV string [5]. To attend the requiredvoltage at the DC-link of the SFC, a DC/DC step-up converter which rises thevoltage level at its output is the proposed solution in this paper. The step-up converter is controlled by a Proportional-Integrative (PI) controller whichgenerates the Pulse-Width Modulation (PWM) pulses. The reference voltage(Vref ) is defined by a MPPT algorithm as described later.For the SFC operation, the so-called PID Macro is utilized for control. Thismacro, which has a pre-parametrized list of parameters, is available from themanufacturers for closed-loop process control. In this application, the processvariable is the DC-link voltage. So, the SFC imposes the DC voltage accordingto an external reference value (set-point). This reference is set to 300 V. Thismeans that the SFC works with a fixed DC-link voltage and the reference voltageof the PV string is imposed by the step-up converter according to the MPPTalgorithm.To operate in this way, the SFC requires the configuration of a set of param-eters, such as the operation method that will be used, analog and digital inputand output terminals, acceleration and deceleration times, and mainly the PIDparameters: Proportional Gain (Kp), integral time (Ti) and derivative time (Td)[5].2.1 Maximum Power Point TrackingA general issue in PV generation is tracking the maximum power availableat the PV string output. The need of an algorithm to track the Maximum PowerPoint (MPP) comes from the non-linearity of the I-V curve of a PV module.The MPPT technique consists in adjusting the output voltage of the PV stringto extract the maximum power independently of any changes in the irradiationor temperature.In this work, the MPPT method implemented was the P&O algorithm, dueto its simplicity and low computational resources [6]. P&O is the most commonmethod of MPPT algorithms, since it is widely used in the control of the powerconverters in PV applications and does not require any information about thePV modules characteristics to perform the maximum power point tracking [8].Basically, the P&O algorithm perturbs the voltage and analyses the changeon the power value. These perturbations on the voltage are successive steps onthe operation point that creates a change in power. If this change is positive,the perturbations are applied on the same direction, otherwise the perturbationsare applied on the opposite direction. The steps followed by the algorithm are287Bruno Tangerino, Dionízio Roman, Vicente Leite, Alessandro Coedtel, Ângela Ferreira, José Batista & Wellington Maidana.illustrated on the flow chart of the Figure 2 with the variables defined in theTable 2.Fig. 2. State flow chart of P&O MPPT algorithm [6].Table 2: Description of variables presented in flow chart of Figure 2 [6].Variable DescriptionVpv Voltage measured from the PV PanelIpv Current measured from the PV PanelP (k), V (k) Power and Voltage in present iterationP (k − 1), V (k − 1) Power and Voltage in past iteration∆V Voltage incrementk + + Change for next iterationThe MPPT algorithm generates the reference voltage value (Vref ) for thestep-up converter. This value is the reference for the PI controller, which readsthe actual voltage value of Vpv, the reference voltage (given by MPPT algorithm)and generates the pulses of the duty-cycle for the switch of the step-up.3 Proposed SolutionAs an approach to solve the problems referred in previous sections, a DC/DCstep-up converter is applied to implement the MPPT and operate the PV stringwith a large range of voltages.288DC/DC converters are power electronic circuits for power processing thatconvert a DC voltage value to another level, higher or lower, depending on theconverter. There are many types of converters, which are used in large scale indifferent areas, like UPS, electrical drives, renewable energy systems, DC motorcontrol systems and so on [7]. The step-up converter, or booster converter, is aswitching circuit that elevates the value of the input voltage to the output. Theelectrical scheme of this type of converter is shown on Figure 3.Fig. 3. Step-up converter.The electric scheme of the proposed PV water pumping system is shown inFigure 4. The step-up is installed between the PV string and the DC-link of theSFC. It is composed by an inductor, a diode and a power switch (IGBT). Theblock diagram of step-up control with MPPT implemented is shown on Figure5.Fig. 4. Proposed PV water pumping system.289Bruno Tangerino, Dionízio Roman, Vicente Leite, Alessandro Coedtel, Ângela Ferreira, José Batista & Wellington Maidana.6 Tangerino et al.Fig. 5. Step-up control with MPPT.One challenge is the adjust of the dynamics between the two power stages:the step-up converter and the SFC. The step-up performs the MPPT algorithmwith a determined frequency, and the PID macro of the SFC adjusts the speedof the pump to maintain the voltage on the DC-link equal to reference (VSP ).Hence, the PID macro parameters Kp and Ti, acceleration and decelerationtimes of the SFC, must be adjusted to match the dynamics between these twopower stages. According to the tests achieved on the experimental platform, thevalues of these parameters used in this work are show on Table 3.Table 3: Experimental parameters of the step-up and SFC.Parameter ValueStep-up PI Controller Kp = 500x10−6; Ki = 0,10SFC PID Controller Kp = 0,2; Ti = 2 s; Td = 0SFC Acceleration time 0.1 sSFC Deceleration time 0.1 s3.1 Experimental PlatformTo evaluate the functioning and performance of the system proposed in thiswork, a solar photovoltaic water pumping system at the Polytechnic Institute ofBraganc¸a has been used. The system is composed by the elements described onTable 4.Table 4: Components of the system.Component DescriptionPump Termar B20 3∼ 1.5 kW - SubmersibleStandard Frequency Converter ABB ACS355-01E-07A5-2Step-up Power Switch and Diode Two IGBTs of Mitsubishi PM75RLA120Step-up Inductor Mundorf BT140 12 mH/0,45 OhmPhotovoltaic Modules Fluitecnik’s FTS-220P290The experimental platform components utilized in this work are shown onFigure 6. The PV modules are installed on the roof of the laboratory. The step-up was implemented in Simulink and the real time control was performed usingthe 1103 controller board from dSPACE.Fig. 6. Experimental platform, (a) PV string, (b) step-up converter, (c) single-phaseACS355, (d) water tank and pump.The experimental results were carried out with 4, 6 and 8 PV modules avail-able on the roof of the laboratory. All tests were performed under same solarradiation and temperature levels, acquired by the measuring system present onthe laboratory. These values are shown on Table 5.Table 5: Tests conditions.Condition ValueRadiation level G = 810 W/m2Ambient Temperature Ta = 28◦CPV Module Temperature Tpv = 45◦C291Bruno Tangerino, Dionízio Roman, Vicente Leite, Alessandro Coedtel, Ângela Ferreira, José Batista & Wellington Maidana.4 Practical Implementation of the System and Evaluationof the ResultsFigures 7, 8 and 9 show the Vpv, Vdc, Ipv and Ppv curves for 4, 6 and 8 PVmodules, respectively. VSP is set 300 V and the MPPT is running two times persecond with voltage increment of 1 V.Fig. 7. Vpv, Vdc, Ipv and Ppv for 4 PV modules.Fig. 8. Vpv, Vdc, Ipv and Ppv for 6 PV modules.292Fig. 9. Vpv, Vdc, Ipv and Ppv for 8 PV modules.For all conditions Vdc is 300 V and Vpv varies according to the MPPT algo-rithm, validating the parameters of PID controller of the SFC and the requireddynamics between these two power stages. The PV power curve as well as thewater pump operation are in agreement with the expected results, showing thatthe step-up controls the PV string voltage using the MPPT algorithm applyingsuccessive steps in order to operate in MPP. The SFC PID macro controls theDC-link voltage indirectly by adjusting the speed of the motor.These results show that the step-up allows driving low power pumps (up to1,5 kW) minimizing the necessary number of PV modules. For comparison, Table6 shows the power and voltage (in MPP) provided by each set of PV modulestested.Table 6: Comparison of the power and voltage for each set of PV modules.Size of PV string Power and Voltage4 PV modules P = 880 W and Vpv = 117 V6 PV modules P = 1320 W and Vpv = 176 V8 PV modules P = 1760 W and Vpv = 235 VFrom the analysis of the results of Table 6 and Figure 9, with 8 PV modules,it is possible to verify that the power is greater than the 1,5 kW (beyond thenecessary) and the PV voltage level is less than the minimum value requiredfrom the SFC, i. e., 280 V (Table 1): Vpv varies between 200 V - 210 V and Vdc isfixed at 300 V for rated operation of the SFC, validating the solution proposed.293Bruno Tangerino, Dionízio Roman, Vicente Leite, Alessandro Coedtel, Ângela Ferreira, José Batista & Wellington Maidana.5 ConclusionsSFCs can be used in PV pumping applications driven by AC motors. Thisalternative offers significant advantages compared with those based on PV dedi-cated controller and pumps. Indeed, SFCs are widely available all over the worldat significantly lower costs than those of PV dedicated power inverters. To solvethe problem of the number of PV modules on low power systems and the im-plementation of a MPPT, the addition of a DC/DC converter has been provento operate as expected. The validity of these proposals have been evaluatedexperimentally in a real system.6 AcknowledgementsThe authors wish to thank Polytechnic Institute of Braganc¸a, JG ElectricalInstallations and the Research Center in Digitalization and Intelligent Robotics(CeDRI), for the experimental set-up available.References1. Rohit, K. B., Karve, G. M., Khatri: ”Solar Water Pumping System”, InternationalJournal of Emerging Technology and Advanced Engineering, Volume 3, Issue 7,July, 2013.2. Miladi, M., Abdelghani-Bennani, A. B., Slama-Belkhodja, I., M’Saad, H.: ”Improvedlow cost induction motor control for stand alone solar pumping,” 2014 InternationalConference on Electrical Sciences and Technologies in Maghreb (CISTEM), Tunis,2014, pp. 1-8.3. Malla, S. G., Bhende, C. N., Mishra, S.: ”Photovoltaic based water pump-ing system,” 2011 International Conference on Energy, Automation and Signal,Bhubaneswar, Odisha, 2011, pp. 1-4.4. Abella, M. A., Lorenzo, E., Chenlo, F.: ”PV Water Pumping Systems based on stan-dard frequency converters”, Progress in Photovoltaics Research and Applications 11,179-191.5. Ferna´ndez-Ramos, J., Narvarte-Ferna´ndez, L., Poza-Saura, F.: ”Improvement ofphotovoltaic pumping systems based on standard frequency converters by meansof programmable logic controllers”, Solar Energy, Volume 84, Issue 1, 2010.6. Zamora, A. C., Vazquez, G., Sosa, J. M., Martinez-Rodriguez, P. R., Juarez, M.A.: Eciency based comparative analysis of selected classical mppt methods, in2017 IEEE International Autumn Meeting on Power, Electronics and Computing(ROPEC), Nov. 2017, pp. 16.7. Hart, D. W.: Introduction to power electronics, Prentice Hall, 1997.8. Jiang, J. A., Su, Y. L., Kuo, K. C., Wang, C. H., Liao, M. S., Wang, J. C., Huang,C. K., Chou, C. K., Lee, C. H., Shieh, J. C.: On a hybrid mppt control schemeto improve energy harvesting performance of traditional two-stage inverters used inphotovoltaic systems, Renewable and Sustainable Energy Reviews, vol. 69, pp. 11131128, 2017.9. Narvarte, L. , Poza, F., Lorenzo, E.: ”Specification and testing of PV pumps for aMoroccan project”. Prog. Photovolt: Res. Appl., 14: 733-741, 2006.294

Photovoltaic water pumping system for small power conventional AC pumps

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Photovoltaic water pumping system for small power conventional AC pumps

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