DC-DC Converter fed BLDC Pumping system with MPPT based Solar PV System

Transcription

1 International Journal of Electrical Electronics Computers & Mechanical Engineering (IJEECM) ISSN: Volume 8 Issue 12 ǁ Dec IJEECM journal of Electrical and Electronics Engineering (ijeecm-jee) DC-DC Converter fed BLDC Pumping system with MPPT based Solar PV System K V Gopalachary Electrical and Electronics Engineering Department, RVR & JC College of Engineering, Chowdavaram, Guntur (Dt), A.P., India Abstract: This paper describes about design and integration of solar photovoltaic (SPV) array. The power generated from PV system is fed to brushless DC (BLDC) motor driven water pump through a DC-DC boost converter to enhance efficiency of solar system. Voltage regulator is used in inverter control system to get soft switching and to regulate the voltage given to BLDC motor to get desired speed. The speed control of BLDC motor is performed by PWM (Pulse Width Modulation) control of the voltage source inverter (VSI) using DC link voltage regulator. The test system performance is analyzed in MATLAB/Simulink software environment. Index Terms MPPT, solar PV array, BLDC motor, Water pump, Voltage source inverter (VSI) I. INTRODUCTION In present day by day improvement of Renewable Energy resources are decline the interest of power because of consistent consumption of nonrenewable assets. Presently a days sunlight based and wind vitality control ages are quickly developed when contrast with the other inexhaustible sources. Wind age isn't appropriate for every one of the spots so broadly sun based vitality age is utilized. Essentially sun oriented boards are utilized to produce the sun oriented power. Solar panel-absorb the sun light as a source of energy to generate electricity or heat. Solar panel work by allowing photons of light, to knock electrons free from Atoms, generating a flow of electricity. Solar panels have number of solar cells which is used for the solar power generation. A constant decrease in the expense of the sunlight based photovoltaic (SPV) boards and the power gadgets has empowered the specialists furthermore, the businesses to use the sun based PV array produced control for various applications. SPV cluster created power is broadly utilized for water system in the fields, family unit applications and mechanical use. The water system segment is one of the significant segments where sunlight based PV (photovoltaic) control is broadly utilized for water siphoning. Sun oriented PV water siphoning has been acknowledged utilizing the DC motor. A three-phase induction motor (IM) is widely used in SPV array fed water pumping for irrigation and domestic purposes due to its suitability for applications. A DC motor is also used in, but it requires high maintenance caused by the presence of brushes and commutator, it is not preferred for water pumping. However, a complicated control of IM and high efficiency of a permanent magnet synchronous motor (PMSM) than an IM has motivated the researchers to employ a PMSM drive where a high power water pumping system. A three-phase induction motor (IM) is widely used in SPV array fed water pumping for irrigation and domestic purposes due to its suitability for applications. A DC motor is also used in, but it requires high maintenance caused by the presence of brushes and commutator, it is not preferred for water pumping. However, a complicated control of IM and high efficiency of a permanent magnet synchronous motor (PMSM) than an IM has motivated the researchers to employ a PMSM drive where a high power water pumping system. Because of numbers of benefits of a permanent magnet brushless DC (BLDC) motor drive such as high efficiency, long life, high reliability, low radio frequency interference, noise and no maintenance, various researchers are focusing on this drive for SPV array based water pumping and so opted in this work. A BLDC motor is employed to drive the water pump based on SPV array in, which manifests its suitability for water pumping. A DC-DC converter is usually set between the SPV array and VSI (voltage source inverter) sustained BLDC motor siphon so as to follow the ideal working purpose of the SPV array utilizing a maximum power point tracking (MPPT) technique. Non-isolated DC DC buck, boost, buck boost, Cuk and SEPIC (Single Ended Primary Inductor Converter) converters used for MPPT in SPV applications are reviewed and compared. DC-DC converter to optimize the operating power point of a PV array. This power conversion causes an increased cost, size, complexity and reduced efficiency. As

2 a unique solution of these problems, the present work proposes a single stage solar energy conversion system which demonstrated through its steady state, starting and dynamic functionalities, using MATLAB based simulation and an experimental system. It operates satisfactorily under the desired circumstances without sacrificing its performances, specially the MPP operation of PV array. II. DESIGN OF PROPOSED SYSTEM Fig. 1 shows a detailed schematic of proposed PV array fed BLDC motor driven water pump. This system constitutes a SPV array, boost DC-DC converter, VSI, BLDC motor and water pump. An incremental conductance (INC) MPPT method is applied for efficiency enhancement of PV array through boost converter operation. On the other hand, the speed controls of BLDC motor and electronic commutation are Fig.1 Configuration of PV array fed BLDC motor-pump. performed by PWM control of the VSI. An inbuilt encoder, mounted on the BLDC motor itself, provides three Hall signals following the rotor position which are further converted into six pulses. Following sections elaborate design and control methodologies of proposed system. A. Design of SPV Array: The elimination of DC-DC power conditioning stage makes the system simple and can categorized only in two parts, i.e. PV array and DC link capacitors converter fed BLDC drive coupled with water pump system. B. PV Array Modeling: The equivalent circuit models of PV cells are connected in series and parallel combination to reach the fixed output voltage and power of PV array. Fig 3. Equivalent circuit of PV ell An equivalent circuit consists of an ideal current source IL in parallel with an ideal diode. Two Resisters Rs and Rsh connected is series and parallel respectively. The values of those resistance depends upon the number of PV cells connected in series and parallel. And its output is constant under constant temperature and constant incident radiation of light. Current from the current source is denoted as short circuit current Ish. Thus, Iph=Isc Assume that output is in open-circuit, the current from the source is shunted internally by the intrinsic p-n junction diode. This gives the open circuit voltage Voc. The output current I from the PV cell is found by applying the Kirchoff s current law (KCL) on the equivalent circuit Ish Id Vd/ Rp Ipv = 0 Where, I sh is the short-circuit current that is equal to the current from the source I d is the current shunted through the intrinsic diode V d is the voltage across the diode (V) R P =R SH is Parallel Resistance (ohm) The parameters V, I, i o, and i pv as input to it. Where, V=Operating voltage of PV cell, I=Net cell current, i PV = PV current at MPP and io=leakage current. The MPP power of PV array, Pmp = (ns*vmp)*(np*imp) We know, voltage of the PV panel VPV = ns * Vmp, From above equation we can calculate the number of panel connected in series ns = VPV/Vmp The current at MPPT is given as, ipv = PPV/ (VPV) The formula for calculate the parallel number of panels connected Np =Ipv / Imp PV modelling is done by considering the above calculations. C. Design Of DC Link Capacitor:

3 The DC link capacitor of Voltage source Inverter(VSI) connected across the PV array. It is a small, capacitor it carries the ripple current and it is Given as, DESIGN OF SPV ARRAY ic = ipv idc Where, ipv is the PV array current and idc the dc link current of the VSIUnder the various conditions, dc link current idc is kept zero to estimate the ripple current in the capacitor current, i.e. ic = ic,max = ipv The capacitor required is given by, TABLE III DESIGN OF BOOST DC-DC CONVERTER C = ic, max/ fsw*δvpv fsw is the switching frequency of thevsi and ΔVpv is the ripple content in PV array voltage The switching frequency, fsw is selected under the factors like component size, system response, noise disruption and conversion efficiency. Switching frequency directly affecting these factors. High switching frequency make the reduction in the size of dc link capacitor. It also improves the transient response, and avoids the frequency bans in noise. High switching frequency also cause the low conversion efficiency and also the switching losses is increased. The capacitor value is quite low when compare to existing topologies D. Design of Boost DC-DC Converter The MPP voltage of SPV array, vpv = Vmpp = 238 V is boosted to the DC bus voltage of VSI, Vdc = 310V. This offers a minimum duty ratio, D, resulting in the merits mentioned in previous section. Table III summarizes the estimation of inductor, L [4] and capacitor, C [1], where fsw is the switching frequency of boost converter; IL is the average inductor current; ΔIL is ripple contents in the inductor current; TABLE I SPECIFICATIONS OF BLDC MOTOR ΔV dc is ripple contents in the capacitor voltage; Idc is average current flowing through the DC bus of VSI; f and ω are the input voltage frequencies of BLDC motor in Hz and rad/sec. respectively. The poles of BLDC motor are denoted by P, and speed of the BLDC motor is denoted by Nr. The values of converter parameters are selected such that the proposed system performs satisfactorily even at the bad weather condition also. E. Design Of Water Pum: A water pump is acting as a load and it is coupled to the shaft of BLDC motor. This pump is designed by its powerspeed characteristics as, KP = P/ w3r A suitable water pump with these data is selected for the system. III. PROPOSED SYSTEM CONTROL TABLE II The control techniques used at various stages of proposed water pumping system are divided into following three parts. A. MPPT of Solar PV Array

4 In order to enhance the efficiency of a SPV array, MPPT is mandatory due to variable weather condition. The proposed system adapts an INC type of MPPT technique [2, 14-15]. This technique is less sensitive to the system dynamics and noise. The direct duty ratio control is used because it offers good stability characteristics and simplicity. The initial duty ratio is set as zero in view of soft starting of the motor. Likewise, the perturbation size is in order to get reduced swing around the optimum operating point. B. Electronic Commutation of Brushless DC Motor The VSI which feeds the brushless DC motor is switched in a predefined sequence to perform the so called electronics commutation [1, 6]. It is a procedure of converting the three Hall signals into the six switching signals, s1,-s6,. The three Hall signals are generated by the encoder, mounted on the shaft, according to the rotor position. The conduction of only two switches at a time results in a reduced conduction losses. C. Speed Control of Brushless DC Motor-Pump The speed control of BLDC motor-pump is accomplished by PWM switching of VSI while regulating its DC bus voltage. As illustrated in Fig. 1, the reference and sensed DC bus voltage, Vdc* and vdc respectively, are compared and the error is passed through voltage regulator which is a PI (Proportional-Integral) controller. Further, the output value of voltage regulator is compared with the maximum possible value of duty ratio i.e. 1 to get the final duty ratio, Do. The comparison of Do and a high frequency carrier wave results in a PWM signal, s. Finally, the PWM switching signals for VSI are generated by modulating s1,- s6, with s using AND logic. The duty ratio of the switches of VSI, Do varies following the variation in weather condition, resulting in the BLDC motor-pump speed control. This proposed method of speed control completely eliminates the motor current sensing elements and requires only a voltage sensor at the DC link, resulting in a reduced complexity, cost and size. the time motor develops the rated torque. A small ripple appears in the torque because of current commutation and sensor-less operation of the motor. It causes vibration in the motor at low speed. The system is designed to run motorpump in high speed range in order to done the successful water pumping. The motor pump is usually installed in submerged area or in agriculture field, and the noise don t cause any disturbance in the surroundings. The torque ripple reduction may lead to an enhancement in the efficiency of motor. Motor phase current sensors and front end converters provides various solutions for the torque ripple reduction. It cause the complexity of the system and torque ripple becomes uncontrollable at higher speed range. Fig.2 Starting and steady state performances of solar PV array IV. SIMULATION RESULTS The performance of the system is simulated in MATLAB/Simulink under various static and dynamic conditions. A. Steady State Performance At 1000w/m2 Steady state and starting performance of BLDC motor and PV array are shown in fig 5 B. Solar PV Array Performance: The voltage Vpv current Ipv and power Ppv exhibits in fig 5 at an irradiance, S of 1 kw/m2. The starting duty cycle and its step size are chosen properly to obtain safe starting motor. At steady state the six fundamental frequency have no modulation and the value of D is one. C. BLDC Motor Pump Performance: Fig 5 exhibits back emfea, winding current Isa, speed N, Torque Te and TL of BLDC motor. The pump is operated in full speed at Fig.3 Starting and steady state performance of boost DC-DC converter

5 Fig.4 Starting and steady state performance of brushless DC motor-pump Fig.7 Dynamic performance of brushless DC motor pump V. CONCLUSION This paper describes about design and analysis of SPV system and DC/DC boost converter fed VSI based BLDC motor. The proposed system provides singe stage operation by neglecting DC to DC conversion stage. Here DC-DC boost converter is used to enhance efficiency of solar system. The soft starting and speed control of the motor pump done without any additional circuit. The system is simple and low cost, because of the elimination of phase current sensors. The system has successful operation even at 20% solar irradiance. The proposed system is very useful in farm irrigation, fish farms and street watering systems. ACKNOWLEDGEMENT Fig.5 Dynamic performance of solar PV array I thank the college management of RVR&JC college of Engineering, Guntur for providing library and Internet facilities required to write the research paper. I thank Principal, President, Registrar, Professors for encouraging writing this paper. REFERENCES Fig.6 Dynamic performance of boost DC-DC converter [1] R. Kumar and B. Singh, Solar PV array fed Cuk converter- VSI controlled BLDC motor drive for water pumping, 6th IEEE Power India Int. Conf. (PIICON), 5-7 Dec. 2014, pp [2] M. A. Elgendy, B. Zahawi and D. J. Atkinson, Assessment of the Incremental Conductance Maximum Power Point Tracking Algorithm, IEEE Trans. Sustain. Energy, vol.4, no.1, pp , Jan [3] J.V. Mapurunga Caracas, G. De Carvalho Farias, L.F. Moreira Teixeira and L.A. De Souza Ribeiro, Implementation of a High- Efficiency, High-Lifetime, and Low-Cost Converter for an

6 Autonomous Photovoltaic Water Pumping System, IEEE Trans. Ind. Appl., vol. 50, no. 1, pp , Jan.-Feb [4] N. Mohan, T. M. Undeland and W. P. Robbins, Power Electronics: Converters, Applications and Design, 3rd ed. New Delhi, India: John Wiley & Sons Inc., [5] M. H. Rashid, Power Electronics Handbook: Devices, Circuits, and Applications, 3rd ed. Oxford, UK: Elsevier Inc., [6] B. Singh and V. Bist, A BL-CSC Converter-Fed BLDC Motor Drive With Power Factor Correction, IEEE Trans. Ind. Electron., vol. 62, no. 1, pp , Jan [7] M. Ouada, M.S. Meridjet and N. Talbi, Optimization Photovoltaic Pumping System Based BLDC Using Fuzzy Logic MPPT Control, Int. Renew. Sustain. Energy Conf. (IRSEC),7-9 March 2013, pp [8] Rajan Kumar and Bhim Singh, Buck-boost converter fed BLDC motor drive for solar PV array based water pumping, in IEEE International Conference on Power Electronics, Drives and Energy Systems (PEDES), Dec. 2014, pp.1-6. [9] Rajan Kumar and Bhim Singh, Solar photovoltaic array fed Luo converter based BLDC motor driven water pumping system, in 9 th International Conference on Industrial and Information Systems (ICIIS), Dec. 2014, pp.1-5. [10] Rajan Kumar and Bhim Singh, Solar photovoltaic array fed canonical switching cell converter based BLDC motor drive for water pumping system, in Annual IEEE India Conference (INDICON), Dec. 2014, pp.1-6. [11] M. H. Taghvaee, M. A. M. Radzi, S. M. Moosavain, Hashim Hizam and M. Hamiruce Marhaban, A Current and Future Study on Non-isolated DC DC Converters for Photovoltaic Applications, Renew. Sustain. Energy Rev., vol. 17, pp , Jan [12] Standard Solar PV Module Specifications [Online]. Available: ULEBroucher.pdf [13] W.V. Jones, Motor Selection Made Easy: Choosing the Right Motor for Centrifugal Pump Applications, IEEE Ind. Appl. Mag., vol.19, no.6, pp.36-45, Nov.-Dec [14] Boualem Bendib, Hocine Belmili and Fateh Krim, A survey of the most used MPPT methods: Conventional and advanced algorithms applied for photovoltaic systems, Renew. Sustain. Energy Rev., vol. 45, pp , May Author Profile: K.V.Gopalachary had completed his B Tech degree in electrical Engineering from JNT University in 1979 and M E degree in EEE with control systems specialization from Madras University in1981.currently he is working as an Assistant Professor dept. of EEE,RVR&JC college of Engineering, Chowdavaram,Guntur from August 2018 onwards. He had nearly 16 years of teaching and 14 years of Industrial experience till date. I am interested in doing PhD work in the areas of FACTS, Microgrid. Six research papers got published in International Journals till now.