A solar PV-DRIVEN BLDC pumping system employing M-SEPIC converter using ANFIS controller

Transcription

1 A solar PV-DRIVEN BLDC pumping system employing M-SEPIC converter using ANFIS controller Kshatriya Vamshi Krishna Varma 1, A. Ramkumar 2 1 Research Scholar, Department of EEE, Kalasalingam University, Krishnakoil, Tamil nadu, India. 1 Sr. Assistant Professor (Training & Placement Officer), Department of EEE, 1 G. Pulla Reddy Engineering College (Autonomous), Kurnool, Andhra Pradesh, India. 2 Associate Professor, Department of EEE, Kalasalingam University, Krishnakoil, Tamil nadu, India. Abstract: Efficient, cost-effective, and simple structure of pumping system for irrigation application is utilized by the erratic power conditioning stages; with assisted knowledge of intelligent controllers. Based on the summarized merits & demerits of existed high-voltage gain DC-DC converters, a single-switch high voltage gain M-SEPIC converter is greatly suitable for practical application due to non-presence of coupled inductor, low switch stress, low EMI issues, and low complex design. A novel single switch M-SEPIC type DC-DC converter fed VSI based brushless-dc motor drive (BLDC) is controlled and powered by solar PV system methodology is introduced. This paper recommends the Adaptive Neuro-Fuzzy Inference Systembased (ANFIS) prediction methodology for generation of optimal switching states to enhance the BLDC motor speed and reduction of electromagnetic torque ripples. The identified effectiveness of the proposed scheme is validated under constant and variable speed situations by real-time operating conditions which are demonstrated through Matlab /Simulink tool; and simulation results are conferred with proper conclusion & comparisons. Keywords: ANFIS Controller, BLDC Motor, M-SEPIC Converter, Solar-PV System. 1. Introduction Dispensing the safe and clean water in abundant quantities, achieving sustainable development and securing the health are prime issues for farmers in irrigation applications, domestic and house-hold applications. Surplus water source in remote areas is needed to establish the evenly ruminated regardless of established such massive pumping systems and available information till date. Several challenges come-up with a simple, efficient, low-cost and reliable ways are influenced by present research methodology towards the Renewable Energy Sources (RES) fed pumping system. The PV-power generation plays a significant role and becoming indeed prominent over the several renewable sources being used in many applications due to ample in nature, noise-free, virtuous and non-toxic [1]-[2]. The energy coming from PV source is interfaced to pumping system by utilizing power-conditioning systems [3], in that DC-DC converter and voltage source inverter (VSI) plays a key role. The evaluation of DC-DC converters with incredible voltage gain in the RES is attaining more & more recognition. Photo-voltaic (PV) arrays, Fuel Cells (FC), Super-Capacitors (SC) are generally acquiring as low outcome voltage about 10V-38V. This low outcome voltage is transformed to high voltage up to 380V-415V and then interfacing to load/micro-grid system through DC-bus with attractive Maximum Power Point Tracking (MPPT) algorithm to track the maximum efficiency. Unfortunately, formal DC-DC converters are not preferable because of extreme duty ratios. So as to implement a high voltage gain DC-DC converter,

2 several types of converters are already proposed and reviewed. For example, the formal type DC-DC converters are regular boost converter [4], buck-boost converter [5], switched capacitors type [6], [7], cuk converter [8], SEPIC converter [9] etc., are already utilizing the several PV array applications. The best selection of DC-DC converter for pumping system application is SEPIC converter, wide range of output voltage gain is achieved in both step-up/step-down converter and it suffers from high current and voltage stress. Due to this dis-advantage, SEPIC converter is un-popular and eliminated by modified topology named as M-SEPIC converter by accomplishing additional diode and capacitor devices [10]-[13]. The M- SEPIC converter is allowing high voltage gain, low voltage-current stress, low EMI, high efficiency, reliable, low complex, low operating cost, etc. On the flip side, the DC motors have high maintenance factor due to brushes and commutator. The specified issues related with DC motor, by employing induction motor due to its, low cost, robustness, low maintenance cost and availability in global markets. Several limitations of the induction motor for pumping system like liable to overheating under low voltage condition. The Brushless DC motor (BLDC) motor is obtained more popularity owing to superb advantages and desirable functioning features for pumping application [14]. The attractive merits of BLDC over formal DC/AC motors are incredible efficiency, more ruggedness, greater reliability, low EMI loss, simple control, high torque-weight ratio s and low maintenance factor, basically operated at low voltages and superior performance under wide speed ranges [15]-[17]. Figure.1. Schematic Diagram of Proposed BLDC Driven Solar-PV Fed Pumping System Employing M- SEPIC Converter In this paper, a PV-based single switch M-SPEIC high-voltage gain DC-DC converter fed BLDC drive is proposed by utilizing Adaptive Neuro-Fuzzy Inference System (ANFIS). The main characterization of ANFIS control scheme is constituted by emblematic path along with knowledge proficiency for prediction of optimal switching states to VSI. The main intension of the ANFIS controller is regulated the speed responses under sudden disturbances and minimizes the torque ripples over the formal PI and fuzzy controllers. Finally, the well-recognition of proposed pumping application under several PI and intelligent controllers are validated 228

3 under the real-time operating conditions which are demonstrated through Matlab/Simulink tool and results are conferred with proper comparisons. 2. Proposed System The configuration of the proposed PV based single-switch high voltage gain Modified-SEPIC DC-DC converter fed BLDC motor drive is depicted in Figure.1. From left to right position, the proposed configuration comprises of a solar-pv array, an M-SEPIC DC-DC converter and VSI based BLDC motor with effective ANFIS control objective. The solar-pv supplies the electrical energy and feeds the M-SEPIC DC- DC converter. The M-SEPIC DC-DC converter is functioning through an MPPT control objective such that the PV power is optimized and BLDC motor to be soft-started. This converter is operated in both Discontinuous Conduction Mode (DCM) and Continuous Conduction Mode (CCM) operations. But the requirement of switching components and switch stress is very low in CCM operation. The M-SEPIC converter transforms the power to BLDC motor through VSI topology which is operated by proper switching sequence. The switching sequence for the VSI is provoked by current control objective with respect to electronic commutation for decoding the Hall Effect signals which accords to the rotor position and ANFIS control objective. The implementation of the proposed solar-pv based M-SEPIC DC-DC converter fed BLDC motor drive with ANFIS control scheme is described in the following sub-sections. 2.1 Solar PV-System A solar-pv array with the rating of 1.5 KW is not affected by the associated converter and motor losses and it relies on the photo-electric effect to produce the electrical energy [4]. In the dark circumstances of the PV cell is akin of normal diode, when the sun-light energy is higher than the semi-conductor energy gap which provides the cell electrons becomes free and existed current travels through external circuitry. As PV cell have low voltage and more fragile, formed as modules and securing with an enclosed metallic case. Based on the requirement power levels, the PV cells are integrated as series and/or parallel to form as solar PV-array. The mathematical model of the PV cell is extracted by single-diode model as depicted in Figure.2. The outcome of the PV cell resulted based on the physical attraction of the PV cell is relating with the I sv, I phv, R sv, from the irradiation & temperature over the other. Figure.2. Mathematical Model of Solar PV System The Eqn.1 illustrates the current equation of single PV cell, Where, I phv - Photovoltaic current in amps (A) I sv - Diode s reverse saturation current in amps (A) K - Boltzmann s constant value (1) 229

4 N - Ideality index factor of diode q - Electron charge R shv - Shunt resistance of PV cell in ohms (Ω) R sv - Series resistance of PV cell in ohms (Ω) T - Junction wise temperature V PVv - Terminal voltage of the diode in volts (V) 2.2 Proposed M-Sepic DC-DC Converter The main intension of DC-DC converter is, to transform the low voltage of solar PV array to highvoltage with respect to gain factor. The proposed single-switch M-SEPIC converter is acquired from a regular SEPIC converter with additional switching devices. The extra devices are inductor L b, capacitor C c, and diodes D a, D b combine to form as extra boost sub-modules. The clamping diode D c and capacitor C c are acting as a voltage clamping of switch S M. The proposed M-SEPIC boost converter is operated in both CCM as well as DCM modes, when the I La, I Lb, I Lc inductor currents are continuous then converter operates in a CCM mode. The operating modes of M-SEPIC converter are shown in Fig.3 (a), (b). Mode-I (t 0 -t 1 ): When the time t=t 0, the switch S M is conducted by activating the gate pulse generation and the diode D a is conducted, while D d, D c, D b are non-conducted as well as the current direction in a mode-i is depicted in Fig.3(a). During this mode, the inductor L a, L b, and L c are charging based on input voltage V in and capacitor C a and C c voltages through switch S M and diode D a. The voltage across the inductor L a is V La & L b is V Lb which are same as input voltage V in and the voltage across inductor L c is V Lc which is equal to VC c -VC b. Although, the current flowing in inductors I La, I Lb, I Lc are linearly increased and the capacitor C 0 supplies the energy to the BLDC motor drive through VSI and maintains the outcome voltage V 0 as a constant. The time reaches to t=t 1, the switch S is in non-conduction mode. Figure.3. Operating Modes of Proposed M-SEPIC Converter Mode-II (t 1 -t 2 ): When the time reaches to t=t 1, the switch S M and diode D a is non-conducting due to disactivation of gate pulse generation, while D d, D c, D b are conducted as well as the current direction in a mode- II is depicted in Fig.3(b). The capacitor C a is charged due to input source voltage as V in and L a through D b as well as V La is equal to V in -V Ca. Other-side, the capacitor C c is charged with respect to input source V in and inductors L a, L b through diode D b, then V Lb is equal to V Ca -V Cc. Furthermore, the pertained energy of V in, L a, L b, and L c are transferred to C 0 and DC-link voltage, as well V Lc is same as V Cb. And also, inductor currents i La, I Lb, I Lc linearly declined. When the time t=t 2, switch S M is turned-on, and the modified SEPIC converter enters into the next switching mode. In Mode-I and Mode-II, the performance of M-SEPIC converter discussions should be referred in Fig

5 Based on the voltage-second balance principle of inductor is, Where D represents the duty ratio of the switch S M, assumed the capacitor voltage is maintained as constant under the steady state region, with respect to Eqn.(2), the relation of capacitor voltages are defined as follows; As V 0 is same as the addition of capacitor voltages of V Cb and V cc during mode-ii, the outcome voltage gain of the proposed M-SEPIC converter under CCM operation can be evaluated based on the duty ratio, the output voltage gain of the proposed M-SEPIC boost converter is greater than the regular boost converter under non-isolated manner. (2) (3) (4) 2.3 BLDC Motor Drive Switching Angles Figure.4. Typical Waveforms for Operating Modes of M-SEPIC Converter Sequence Table.1. Switching States for BLDC Drive Phase Hall Sensors ON Switches Current Direction HA HB HC A B C 0º~60º S S1 S6 +ve -ve 0 60º~120º S S1 S2 +ve 0 -ve 120º~180º S S2 S3 0 +ve -ve 180º~240º S S3 S4 -ve +ve 0 231

6 240º~300º S S4 S5 -ve 0 +ve 300º~360º S S5 S6 0 -ve +ve A VSI topology is used to control the BLDC motor through electronic commutation process of BLDC motor drive regulates the optimum function of pumping system. An electronic commutating process is required for commutating the currents flowing via BLDC windings in a pre-requisite manner by utilizing the decode circuitry. It should be placed symmetrically at the DC source current component which is mid-point of every phase voltage for 120º. The generation of six-switching states based on the feasible conjunction of three hall sensing elements such as H a, H b, H c and these signals are generated by pre-defined encoder circuit tender to rotor position. A specific integration of Hall-signals is generated for defined range of rotor angle at interval of 60º. The six switching states are provoked based on rotor-position estimation as illustrated in Table.1. It is recognizable, only dual switches are turned-on at a time, to form as 120º switching operation of VSI and although minimize the conduction losses. Moreover, the electronic commutation furnishes the fundamental switching frequency of the VSI; for associated losses with high switching frequency based gate-pulses are eradicated. 2.4 ANFIS Control Objective Several artificial intelligent control schemes are highly used in several applications, in that ANFIS controller has been greatly recognized due to enhanced performance over the classical PI and Fuzzy controllers [18]. The eminent characteristics of intelligent controller is that they comprising as symbolic notation of inference system along with expertise knowledge. It is more requisite for optimal performance of BLDC drive in a solar-pv pumping system; the best suitable controller for this application is ANFIS which is predominantly regulates the current component to attain torque ripples and better speed controllability. It is the unique integral approach for respective task and yields the outcome switching sequences to the BLDC drive. In ANFIS, the knowledge system is acquired from supervised learning algorithm by utilizing the hybrid method or back-propagation algorithm [19]. The role of the ANFIS controller is to provide the optimal switching sequences to M-SEPIC converter fed BLDC drive through VSI. It can improve the over-all system performance in many ways such as good stability index, better reduction of torque ripples, smooth operation, more reliability, better speed regulation, etc. It has incredible ability to attain a supported group as an optimal membership functions are highly used for clustering and deducting the acquired outcome within nominal epochs. The principle of ANFIS structure at initial state is; system provides the test data fuzzy rules which are transformed to attractive training methodology for generation of optimum membership functions and rules [20]. It any violations occurs or doesn t reach the predefined error value, the second process is initiated. It is nothing but, based on provided rules/membership functions, ANFIS generates the new FIS configuration with respect to system error and change in error quantities. The membership functions for error (E) and change in error (CE) quantities of speed variations in BLDC drive are depicted in Figure.5. (5) (6) 232

7 (a) Error e(s) (b) Change in Error Figure.5. Membership Functions Where, represents the reference speed and represents the actual speed coming from the speed estimator, e(s) defines the error value and specifies the change in error value. Several membership functions are EZ-Zero Error; PS-Positive Small; PB-Positive Big and NS-Negative Small and NB-Negative Big value respectively. Several rules of the ANFIS structure are illustrated as below in Table.2. The flowchart of the ANFIS Controller is illustrated in Figure.6. / e(s) Table.2. Rules for ANFIS Structure NB NS EZ PS PB NB R1 R 2 R 3 R 4 R 5 NS R 6 R 7 R 8 R 9 R 10 Z R 11 R 12 R 13 R 14 R 15 PS R 16 R 17 R 18 R 19 R 20 PB R 21 R 22 R 23 R 24 R

8 3. Matlab/Simulink Results Figure.6. Flowchart of ANFIS Controller The Matlab/Simulink modeling of proposed system is carried under the both fixed and variable speed conditions, which are operated, based on certain specifications, are placed in Appendix-IV and depicted in Table Evaluation of Several Controllers in a proposed BLDC Driven Solar-PV system under Constant Speed Condition. 234

9 (a) PV Input Voltage & M-SEPIC Output Voltage (b) Stator Currents (c)stator Back EMF (d) Rotor Speeds in PI, Fuzzy, ANFIS Controller (e) Electro-magnetic Torque in PI, Fuzzy, ANFIS Controller Figure.7 Performance of BLDC Drive under Constant Speed Condition by Several Controllers in a proposed Solar-PV system Figure.7 shows the simulation outcomes of several controllers in a proposed BLDC driven solar-pv system under constant speed condition. In this Case-A, the speed of the BLDC motor is maintained at 2000 rpm. With this constant speed, the following parameters is, such as (a) Input PV voltage and M-SEPIC converter output voltage, (b) Stator Currents, (c) Back EMFs, (d) Rotor Speeds in PI, Fuzzy and ANFIS controllers, (e) Electro-magnetic Torque in PI, Fuzzy and ANFIS Controllers are analyzed. Under steady state condition, motor develops the rated torque at constant speed condition. Due to electronic commutator, the BLDC motor provokes the pulsated electromagnetic torque, makes the mal-function of BLDC motor drive. The performance evaluation of BLDC drive under several controllers under constant speed situations, PI 235

10 controller attains the rated speed at sec and Fuzzy, ANFIS controller attains rated speed at 0.03 sec and sec, respectively. The starting torque is very high at motor starting period and requires nearly 20 N-m and running condition the electromagnetic torque is stabled at 2 N-m. The back EMF also maintained as constant nearly 110V and stator current is 1.8A. The torque ripples also reduced with respect to possible control objective, while using PI controller torque ripples factor is 8.88%, Fuzzy controller 10.24% and ANFIS controller 12.28% is decreased as shown in above Figure.7 (e), (f),(g). 3.2 Several Controllers in a proposed BLDC Driven Solar-PV system under Variable Speed Condition. (a) Stator Currents (b) Stator Back EMF (c)rotor Speed in PI, Fuzzy, ANFIS Controller (d) Electro-magnetic Torque in PI, Fuzzy, ANFIS Controllers Figure 8: Performance of BLDC Drive under Variable Speed Condition by Several Controllers in a proposed Solar-PV system. Figure.8 shows the simulation outcomes of several controllers in a proposed BLDC driven solar-pv system under variable speed condition. In this Case-B, the speed of the BLDC motor is varied with respect to time such as, at time (t) 0 sec speed (N) is 1500 rpm, at time (t) 0.15 sec speed (N) is varied to 1500 rpm to 2000 rpm, at time (t) 0.25 sec speed (N) is varied to 2000 rpm to 1400 rpm, at time (t) 0.35 sec speed (N) is varied to 1400 rpm to 2500 rpm, at time (t) 0.45 sec speed (N) is varied to 2500 rpm to 2000 rpm, respectively as maintained as constant. The performance evaluation of BLDC drive under several controllers under variable speed situations (1400 rpm to 2500 rpm), PI controller attains the rated speed at 0.25 sec and Fuzzy, ANFIS controller attains rated speed at 0.02 sec and sec. The starting torque is very high at motor starting and requires nearly 20 N-m and running condition the electromagnetic torque is changed with respect to variable speed condition such as 30 N-m to -30 N-m. The back EMF is also changed with respect to speed such as nearly 140V to 180V and stator current is nearly 31 A to 28.5 A. the torque ripples are produced due 236

11 to electronic commutation unit, these torque pulsations are affecting the motor performance and possible eradication by utilizing proposed ANFIS controller. Table.4. Comparison of Settling Time & Torque Ripple Reduction in a BLDC Drive System Controlled by Several Controllers under Fixed/Variable Speed Conditions Parameters Under Fixed Speed Situation (2000 rpm) Under Fixed Speed Situation (1400 rpm to 2500 rpm) Settling Time of Speed Torque Ripple Reduction Settling Time of Speed Torque Ripple Reduction PI Controller sec 8.88% 0.25 sec 8.84% Fuzzy Controller 0.03 sec 10.24% 0.02 sec 10.21% ANFIS Controller sec 12.28% sec 2.24% The torque ripples also reduced with respect to pertained control objective, while using PI controller torque ripples factor is 8.84%, Fuzzy controller 10.21% and ANFIS controller 12.24% is decreased as shown in above Fig.8 (d), (e),(f). The performance analysis of proposed BLDC motor drive is evaluated under several control strategies with fixed and variable speed situations is clearly illustrated in below Table.4. The effective control objective makes the better action to control the on-going and off-going currents of the VSI. These currents components are utilized to operate the BLDC drive under several speed situations. The key component for better speed regulation is the reference current magnitude which is attained from the effective control objective. Several converter topologies are compared with respect to voltage gain factor as clearly illustrated in Table.5, in that proposed M-Sepic converter has high step-up voltage gain function and more advantages. The proposed control schemes generates the precise and error free value of reference magnitude for better regulation of BLDC motor speeds and torque ripple minimization. Table.5. Comparison of Several Converter Topologies S.No Converter Type Voltage Gain Factor 01 Regular Boost Converter [4] 2% 02 Novel DC-DC Converter [21] 3% 03 Switched Capacitor [6] 4% 04 Switched Inductor [7] 4% 05 Proposed M-Sepic Converter 5% to 8% 4. Conclusion The solar-pv integrated BLDC driven pumping system is characterized by utilizing high voltage gain M- SEPIC converter with several controllers such as PI, Fuzzy, and ANFIS to regulate the torque ripples and improve the stability index under different speed variations. The proposed system has been modeled and its performance is evaluated by using Matlab/Simulink tool. The performance evaluation of proposed system has been encouraged based on well operating statistics in both constant/variable speed conditions by using proposed ANFIS controller. The proposed M-SEPIC converter achieves the greater voltage without any couple inductors and requires only one switching device, high efficiency, and low stress on components are the key advantages of the M-SEPIC converter. All the features of the M-SEPIC converter topology are more suitable for pumping application by utilizing the BLDC motor drive. The high reduction of speed error & very 237

12 less torque pulsations are getting in ANFIS controller over PI and Fuzzy controllers. Also, ANFIS controller is the best choice for power-electronic fed BLDC drive system. The steady state error is highly decreased in ANFIS controller and then getting the better speed response and increases the stability index. 5. Appendix Table.3. Operating Specifications S.No Parameters Values 01 PV Input Voltage 112V 02 PV Output Power 1.5KW 03 DC-Link Voltage 520 V 04 Switching Frequency 100KHz 05 Inductors L a =127µH; L b =550µH; L c =295µH 06 Capacitors C a =C 0-470µF; C b =C c -2 µf 07 Rated Power of BLDC 1 KW Motor 08 Variable Speeds 1400 rpm to 2500 rpm 6. Acknowledgement The authors extend their hearfelt gratitude to the management of G. Pulla Reddy Engineering College (Autonomous), Kurnool, Andhra Pradesh, India and Kalasalingam University, Anand Nagar, Krishnakoil, Tamilnadu, India, for their constant and continuous encouragement for this work. References [1] Mapurunga Caracas, J.V., Carvalho Farias, G.D., Moreira Teixeira, L.F., et al, Implementation of a highefficiency, high-lifetime, and low-cost converter for an autonomous photovoltaic water pumping system, IEEE Trans. Ind. Appl., 2014, 50, (1), pp [2] Kim, K.-T., Kwon, J.-M., Kwon, B.-H.: Parallel operation of photovoltaic power conditioning system modules for large-scale photovoltaic power generation, IET Power Electron., 2014, 7, (2), pp [3] Mohammed Ali Elgendy, Bashar Zahawi, David John Atkinson, "Comparison of Directly Connected and Constant Voltage Controlled Photovoltaic Pumping Systems", IEEE Transactions on Sustainable Energy, vol. 1, no. 3, Oct [4] S.-K. Changchien, T.-J. Liang, J.-F. Chen, L.-S. Yang, "Novel high step-up DC DC converter for fuel cell energy conversion system", IEEE Trans. Ind. Electron., vol. 57, no. 6, pp , Jun [5] T.-J. Liang, J.-H. Lee, "Double-deck buck-boost converter with soft switching operation", IEEE Trans. Power. Electron., vol. 31, no. 6, pp , Jun [6] Xiong, Song, Siew-Chong Tan, and Siu-Chung Wong. Analysis and design of a high-voltage-gain hybrid switched-capacitor buck converter, IEEE Trans on Circuits and Systems I: Regular Papers, vol.59, no.5, pp , May 2012 [7] Axelrod, Boris, Yefim Berkovich, and Adrian Ioinovici. Switchedcapacitor/ switched-inductor structures for getting transformerless hybrid DC DC PWM converters, IEEE Trans on Circuits and Systems I: Regular Papers, vol.55, no.2, pp , Feb

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