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International Journal of Electrical Engineering Technology (IJEET),ENGINEERING ISSN 0976 – 6545(Print), INTERNATIONAL JOURNAL OFand ELECTRICAL & ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME TECHNOLOGY (IJEET) ISSN 0976 – 6545(Print) ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 310-320 © IAEME: www.iaeme.com/IJEET.asp Journal Impact Factor (2014): 6.8310 (Calculated by GISI) www.jifactor.com IJEET ©IAEME AN ADVANCED POWER ELECTRONICS INTERFACE FOR PHOTOVOLTAIC POWERED INDUCTION MOTOR BASED ELECTRIC VEHICLE P.Tulasi Rao 1, CH.Krishna Rao2, K.B.Madhu Sahu3 1 P.G Student, Dept. of EEE, AITAM Engineering College, Andhra Pradesh, India, Associate Professor, Dept.of EEE, AITAM Engineering College, Andhra Pradesh, India, 3 Professor, Principal Dept.of EEE, AITAM Engineering College, Andhra Pradesh, India, 2 ABSTRACT Interfacing of power electronics is the key concept for clean electrical vehicle technology. In this paper a new integrated power electronics interface (IPEI) with battery electric vehicles (BEVs) is proposed to improve the performance of vehicle, to manage the power-flow for each operating mode and to realize the amalgamation of the DC-DC converter, battery charger, and an inverter in the BEV. In this paper lithium ion battery is used. The efficiency and reliability of the system are improved with this proposed idea and also can effectively reduce the current ripples and voltage ripples. With this proposed model the components (active and passive) size is reduced therefore cost is reduced and also this technique reduces the stress in switching devices.The proposed model and its controlling strategy are analyzed and designed by using MATLAB/Simulink. Index Terms: Battery Electric Vehicles (Bevs), Dc/Dc Boost Converter, Induction Motor, PI Controller, Power Train Control Strategies, Power Train Modeling, Small-Signal Model. I. INTRODUCTION The climate changes due to rising environmental pollution, therefore automobile manufacturers are pay attention toward pollution free electrical vehicle technologies. Due to several advances of battery technology with power electronics interfaces (PEIs), and control strategies, these Battery electric vehicles (BEVs) can replace the IC engines. In general, the BEVs are needs to be recharged. It reduces dependency on energy because of stumpy energy consumption and zero local emissions therefore BEVs are called zero-emission vehicles. However, the challenges of BEVs still have to be solved are driving range is limited, it takes long time to charge, battery should be replaced over the lifetime, the performance depends on power electronics equipments, and finally high initial 310 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME cost. The major components which are used in EV vehicle system are motor, power source, controller, charger and drive train. So far the majority of EV system is developed based on dc machines but due to the disadvantages of dc machines, EV developers explore various types of ac machines. The induction motor is one which requires less maintenance, low cost; simple in construction and ruggedness therefore it attracts developers in EV system. [22]. Fig. 2 illustrates the schematic diagram of the BEV power train. A. Proposed model of battery electrical vehicle Fig.1 battery vehicle Fig.2. illustrates the schematic diagram of the BEV power train. B. DC-DC Boost Converter The boost converter converts the available fixed DC supply into variable DC voltage. Usually the dc-d converters are used to step up the voltage therefore these converters also called boost converters. These boost converters are under the category of non-isolated converters. The reason for versatile use of boost converters is because of its continuous current high output voltage mode of 311 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME operations. In this paper DC-DC boost converter is used [17]. The operation of boost converter Operates either in charging mode or in discharging mode depends on switching controlling i,e ON and OFF of switches. Boost Circuit consists of inductor, high frequency switch MOSFET, diode and a filter across load as depicted in below fig.3 The relation between load voltage and source voltage is given as VS (1 − D ) t D = on T V0 = MPPT panel array voltage is the input voltage to the Boost converter. The boost converter output voltage (Vo) depends on the source voltage (Vi), the duty cycle (D) [17].Where, D = duty cycle, ton = total time interval. The DC-DC Boost converter is shown in the below figure.3 a) Boost converter circuit b) Operating phases c) Fig. 3. DC-DC Boost converter Circuit C. Space-Vector Pulse Width Modulation (SVPWM) SVWPM technique is the idea to generate the PWM signals to increase the output voltage of inverter. This technique was first proposed in -1980s.Now it has become the most essential PWM method for three-phase inverters [9]. In this paper SVPWM technique is used to control the inverter to maximize the performance of drive and minimize the power losses. Microprocessor technology helps to implement Several SVPWM schemes. The switching losses are reduced, harmonic content is lessened, and finally controlling is very precise. SVPWM technique utilizes the DC bus voltage effectively when compared with the SPWM technique, generates less THD [10]. SVPWM inverter capacity is Peak fundamental magnitude is 90.6%. Maximum voltage increased by SVPWM is 15.5% [10]. A reference vector is rotating around the state diagram there by SVPWM is accomplished. A 312 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME circle can be created inside the state map by touching all the maximum points of vectors. There are two regions in the representation of SVPWM, under- modulation region and over-modulation region, these regions depends on modulation the index. Fig.4. Space Vector Representation D. DC-AC Three-Phase Inverter DC to AC converter is called as an Inverter. Inverter generates required voltage or frequency by operate it at proper switching control technique. For high power applications three-phase inverters are commonly used [9]. Three half-bridge units makes this inverter and consists of switching devices like IGBTs, BJTs, GTOs etc. the switching control depends on the power level and desired frequency. The switches on the same leg should not turn on at a time [11]. Gating pulses in 3-ph inverterare delayed by 120 degrees. Six possible modes of operation in each cycle and has time period of 60 degrees. Therefore 3-ph voltages are lag by 120 degrees. The output of inverter is a square waveform when it is not connected to a transformer. This square waveform can be converted to sine waveform by using LC low pass filter. E. Control Strategy of Induction Motor In this literature control techniques of Induction motor drives are proposed. The most popular and advanced one is vector control technique used in automotive applications. In this case, the torque control is extended to transient state and allows better dynamic performances. In this paper DTC is proposed for EV applications due to its simplicity [7]. Speed or position encoders do not involved in DTC and it only measures current to estimate flux, torque. Reference speed as the input to the motor controller, this reference speed is directly applied with pedal of the vehicle. In this model PI controller is used in a closed loop to regulate the speed of the motor and also reduce the steady state error. The error signal is generated in a closed loop system by comparing actual speed of the motor with the reference speed. Difference between the actual and desired speed gives the amplitude and polarity of the error signal. To overcome this generated error signal, the PI controller generates the corrected stator frequency of IM [14]. In DTC the switching loss and torque ripples are high because of the use of hysteresis band. SVPWM technique is used to reduce the ripple and also to control the induction motor in a closed loop manner. The advantage of this closed loop controlling is based on output speed, the frequency and amplitude of the reference signals will change [5]-[8]. II.DYNAMIC MODELING OF POWER TRAIN A. Dynamic Modeling of the Battery System The battery is a device which stores energy in the form of electrochemical form. All EV systems widely use this storage device. In this literature lithium-Ion batteries used as an optimal 313 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME choice for storage of energy in EV applications [17-18]. The mathematical modeling of the Li-Ion battery is used in this paper, Thevenin battery model is defined in simulation program. The Thevenin battery model has an internal resistance Rint, over voltage resistance (Rp, polarization resistance), polarization capacitance Cp, and open circuit voltage Voc[21].The elements which are modeled are the functions of the battery state of charge (SoC). Fig. 5 shows the model of Thevenin battery. In this modelNbatts cells are connected in series and Nbattp cells are connected in parallel. By using look-up tables the parameters of Li-Ion battery are determined based on experimental data. Here VBatt is the terminal voltage of the battery pack. Fig.5. Thevenin battery model. B. Dynamic Modeling of EM IM is the most suitable choice in automotive industry for EV systems, due to their, ruggedness, reliability and low cost. Stator current of induction motor is decoupled into flux and torque by using field-oriented control (FOC) and it gives independent commands on the motor torque, speed control is more accurate, this controlling is similar to that of a separately excited DC motor [4]-[7]. The main use of the IFOC is that it completely decouples the direct and quadrature currents. That is any change in torque may change the quadrature current and any change in direct current will affect the magnitude of flux linkages. Thereby, to realize the concept of the FOC, the dq model of the IM is required in synchronous reference frame. In induction motor the distribution of mmf is sinusoidal along the air gap. The dq model of 3ph IM in a synchronous reference frame is used in this paper, for a dynamic analysis. As shown in Fig. 6, dq model is considered with core losses and is represented as core resistance Rf [5]–[8]. All machine variables transform into the synchronous reference frame. The synchronous reference frame stator and rotor voltage equations can be written asin this fashion [26]: Fig. 6. The dq equivalent circuit of the induction motor in synchronous reference frame. 314 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME e qs e s qs v = R i + Lls diqse dt vdse = Rs idse + Lls e qr + Lm e diqm dt ( e + we Llsidse + Lmidm ) didse die e + Lm dm − we Llsiqse + Lmiqm dt dt e r qr v = 0 = R i + Llr vdre = 0 = Rr idre + Llr ( (5) ) (6) ) (7) didre die e + Lm dm − wsl Llriqre + Lmiqm dt dt (8) diqre dt + Lm e diqm dt ( e + wsl Llridre + Lmidm ( ) where the magnetizing currents can be given as e e iqm = iqse + iqre − iqfe (9) e e idm = idse + idre − idfe (10) The electrical torque equation can be expressed as 3 p Lm e e iqs idr − idre i qre 2 2 Lr where: P = number of poles of the machine; Vds ,Vqs = dq axes of the stator voltages; idr ,iqr = rotor currents; idm ,iqm = dq axes magnetizing currents; Rs ,Rr = stator and rotor resistances; Lls ,Llr = self-inductance of the stator and rotor [ Te = ] (11) III. SMALL-SIGNAL MODEL OF BMDIC (SSM) To analyze the nonlinear systems such as dc/dc converters, SSM is best method. SSM is essential in manipulating of the closed-loop control for PWM dc/dc converters to attain a definite performance [19], [28]. SSM is derived in continuous current mode (CCM) to model the proper controller using bode plot. The transfer function of the duty cycle and the inductor current has been proposed and also the transfer function of the duty cycle and the output voltage is also presented in this paper. The small-signal transfer functions in CCM are derived as follows: s s 1 + 1 − w v w z 1 z v2 Gvd (s ) = ∧ = Gdv ∆(s ) d (s ) ∧ (12) V0 (s ) s 1 + w z 1 G id (s ) = ∧ = G di ∆ (s ) d (s ) (13) ∧ i L (s ) Here is the assumption that the parameters are ideally the same values to simplify the analysis. That is L1 = L2 = L,RL1 = RL2 = RL, and IL1 = IL2 = IL . Therefore 315 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME Gdv = v0 (14) − 2RL + 2(1 − 2D)2 R0 δRL + 2(1 − 2D)2 R0 (1 − D ) ω zv1 = 1 CRC (15) ω zv 2 = 2(1 − 2 D )2 R0 − 2 RL 2L (16) ∆ (s ) = ς= s2 ω02 + (17) s +1 Qω 0 δL + C (δRL (R0 + RC ) + 2(1 − 2 D )2 R0 RC ) 2 (18) δLC (R0 + RC )[δRL + 2(1 − 2 D ) R0 ] 2 1 2ξ (19) 1 − 2D 1− D (20) Q= δ = Gdi = ω zi = IL = Vo (2 + δ ) δRL + 2(1 − 2 D )2 R0 (21) 1 δR0 C RC + (2 + δ ) (22) V2 V0 , Ro = 0 P0 2(1 − 2 D )R0 (23) Where, L is the inductance, Vo is output voltage, C is the capacitance, RC is the internal resistance of the capacitor, RL is the internal resistance of the inductor, m is the number of the parallel switches per phase, n is the number of phases, Vin is input voltage, Ro is the resistance of the load, Po is the output power andD is the duty ratio. Fig.7. Speed control system. IV. RESULTS AND DISCUSSION The proposed system, advanced power electronics interface for solar powered induction motor drive for electrical vehicle applications, is analyzed on MATLAB Simulink platform; involves modelling of solar modules, design of DC-DC converter with MPPT algorithm, and inverter fed speed control of induction motor. After successful completion of all the above mentioned subsections, results have been captured and presented below. 316 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME Ambient Irradiation of solar PV modules in W/m2 Irradiation(W/m 2 ) 1000 Irradiation 800 600 400 200 0 0 0.05 0.1 Time(sec) 0.15 0.2 Fig 8. Ambient irradiation of solar PV modules The irradiation shown in fig8 is fed to solar modules, modelled in matlab, produced dc power. This dc natured power supply is fed to dc-dc boost converter, which employed with MPPT algorithm to track maximum power from PV modules, output parameters are presented in figs. 9 and 10 respecively. Fig 9. MPPT based dc-dc converter output voltage MPPT based DC-DC Converter Current 3 2.5 IDC(A) I dc 2 1.5 1 0.5 0 0 0.05 0.1 Time(sec) 0.15 0.2 Fig 10. MPPT based dc-dc converter output current To analyze stability of MPPT based dc-dc converter bode plot is drawn in matlab, found its PM=57.5 and GM=3.92 respectively, revealed that designed converter is fully satble. Fig 11. Bode plot of DC-DC converter 317 International Journal of Electrical Engineering and Technology (IJEET), ISSN 0976 – 6545(Print), ISSN 0976 – 6553(Online) Volume 5, Issue 12, December (2014), pp. 295-309 © IAEME This DC power coming from DC-DC converter is fed to inverter fed induction motor, which operating in closed loop to control the speed. Inverter fed induction motor drive is tested under different loading conditions and its output for 100% loading is presented below. Inverter output currents are shown in Fig 12. Stator Currents 100 Ia Ib Iph(A) 50 Ic 0 -50 -100 0 0.05 0.1 Time(sec) 0.15 0.2 Fig 12. Inverter output currents Actual and Reference Speeds of Induction motor drive 200 W Reference Speed(rad/sec) 150 W Actual 100 50 0 -50 0 0.05 0.1 Time(Sec) 0.15 0.2 Fig 13. Speed of induction motor drive From fig.13, it can be observed that proposed system is driving the induction motor at specified speed. V. CONCLUSION Matlab based simulation reveals that, Modelled solar modules process dc natured power supply fed dc-dc converter with MPPT algorithm tracks maximum power from modules. Bode plot based analysis helped to judge stability of dc-dc converter, found that designed dc-dc converter is fully stable. 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Lee, “Loss minimization control for doubly-fed induction generators in variable speed wind turbines,” presented at the 33rd Annu. Conf. IEEE Ind. Electron. Soc., Taipei, Taiwan, Nov. 5–8, 2007. P.Vishnu, R.Ajaykrishna and Dr.S.Thirumalini, “Recent Advancements and Challenges in Plug-In Diesel Hybrid Electric Vehicle Technology” International Journal of Electrical Engineering & Technology (IJEET), Volume 3, Issue 1, 2012, pp. 316 – 325. M. Daniel Pradeep and S.Jebarani Evangeline, “A Review of Pfc Boost Converters For Hybrid Electric Vehicle Battery Chargers” International journal of Electronics and Communication Engineering &Technology (IJECET), Volume 4, Issue 1, 2013, pp. 85 - 91, ISSN Print: 0976- 6464, ISSN Online: 0976 –6472 AUTHORS DETAILS Mr.P.Tulasi Rao received the B.Tech Degree in Electrical & Electronics Engineering from Aditya Institute of Technology Management,Tekkali, Srikakulam,India in 2012. Currently persuing M.tech in Aditya Institute of Technology & Management,Tekkali, Srikakulam,India. His research interests include power quality, power systems , Power electronics. Sri.CH.KrishnaRao obtained B.Tech Degree in Electrical and Electronics Engineering from College of Engineering, GMRIT Rajam and Srikakulam Dt. He also obtained M.Tech in Power Electronics and Electric Drives from ASTIET Garividi, Vizayanagaram. He has 12 Years of Teaching Experience. Presently he is working as associate professor in the Department of Electrical & Electronics Engineering, A.I.T.A.M, Tekkali, and SrikakulamDt Andhra Pradesh. He has published number of papers in journals, national and international conferences. His main areas of interest are power electronics, switched mode power supplies, electrical drives and renewable energy sources Dr.K.B.Madhu sahu received the B.E. Degree in Electrical Engineering from college of Engineering. Gandhi Institute of Technology &Management, Vicakhapatnam, India in 1985 and the M.E Degree in power systems from college of Engineering, Andhra University and Visakhapatnam in 1998. He obtained his Ph.D from Jawaharlal Nehru Technological university .Hyderabad. He has 26 years of Experience. Currently he is working as a professor & Principal in the Department of Electrical & Electronics Engineering, AITAM, Tekkali, and Srikakulam. Dt.Andhra Pradesh. His research interests include gas insulated substations, high voltage engineering and power systems. He has published research papers in national and conferences. 320