Speed control of 3-phase induction motor using volt/hertz control for automotive application Sachin Hegde, Sachin Angadi, A.B.Raju Electrical and Electronics Department B.V.B College of Engineering and Technology, Hubballi, India Email:sachinparameshwar@gmail.com Abstract—The induction machine is the work horse of the industry It has rugged construction and is suitable for many high power applications It has also been a key aspect in revolutionizing the locomotive and the automotive industries For such automotive applications speed control becomes the driving factor Hence in this we discuss controlling the speed of 3-phase induction motor using constant volt per hertz profile The motor is controlled using 3-phase inverter SPWM technique is used to control the inverter voltage Modelling of the induction motor is done in stationary reference frame and the system in simulated using MATLAB (simulink) and hardware implementation is done for the same using TIs F28069M launch pad under varying speed and load torque conditions Index Terms—SPWM (sine pulsewidth modulation), 3-phase induction motor (IM), 3-phase inverter, F28069M launch pad I I NTRODUCTION Induction motors were used in the past mainly in applications requiring constant speed because conventional methods of IM speed control has either been expensive or inefficient Variable speed applications have been dominated by DC drives Availability of thyristors, IGBT, GTO have allowed the development of variable speed induction motor drives The presence of commutator and brushes is the main disadvantage of DC motor, which require frequent maintenance and make them unsuitable for environments which involve explosive and dirt On the other hand, induction motors, particularly squirrelcage are rugged, cheap, light, small, and more efficient, require lower maintenance and can operate in dirty and explosive environments Although speed control of induction motor drives are generally expensive than DC drives, they are used in number of applications such as pump, steel mills, cranes, hoist drives, conveyors, traction etc because of the advantage of induction motor Dominant of them is the traction system which is used in auto mobiles and locomotives [1].Induction motor drives have gained equal importance as BLDC motor drives in automotive industries Both have their advantages and disadvantages in this we try to see the better parts of induction motor drives In auto mobile applications speed control is the most important crucial part Hence in this we have discussed efficient way of controlling induction motor which is discussed in later sections Following methods are employed for speed control of induction motors: i Pole changing ii Supply frequency control iii Stator voltage control iv Rotor resistance control In this we go for frequency controlled induction motor drive There are again two types of variable frequency drive: a) Scalar control b) Vector control In this we discuss scalar control of induction motor due to its simplicity compared to vector controlled methods We go for Volt/hertz control which is a scalar control method for variable frequency drive II VOLT / HERTZ CONTROL Due to the advancement in solid state power devices and microprocessors, speed control of Induction motor controlled by switched power converter are getting popular Switched power converters offer an easy way to regulate both the frequency and magnitude of the voltage applied to a motor As a result higher efficiency and performance can be achieved by these motor drives with less noise The most common principle of this is the constant V/Hz principle which requires that frequency and the magnitude of the voltage applied to the stator of a motor maintain a constant ratio So by this, the magnetic field in the stator is kept almost constant for all operating points Thus, constant torque is maintained Also allows the motor to achieve faster dynamic response Fig 1: Block diagram of closed loop v/f control of induction motor 120fs (1) P From eqn (1) we can see that synchronous speed is directly proportional to supply frequency So by changing frequency of stator terminal voltage we can control the sped of induction motor.Apart from frequency, the applied voltage should also be varied, to keep constant air gap flux and not let it saturate [2] The air gap induced rmf in ac machine is given by ns = E = 4.44kw ϕm fs T (2) where kw is the stator winding factor, ϕm is the peak air gap flux, fs is the supply frequency, and T is the number of turns per phase in stator Neglecting the stator impedance, the induced emf is approximately equals the supply phase voltage Hence, Vph = E (3) The flux is written as ϕm = Vph Kb fs Fig 2: 3-phase Rectifier and Inverter combination (4) where Kb = 4.44kw T (5) since Kb is a constant, we get ϕm ∝ Vph fs (6) Fig.1 represents the closed loop control of 3-phase induction motor using SPWM technique The actual speed is sensed and is compared with reference speed This is given to PI controller whose output is the slip speed this is given to slip limiter which limits the slip value to rated slip This slip speed is added with the actual speed to give the synchronous speed This is given to V/f controller which gives the frequency and voltage as output According to which SPWM pulses are generated which is given to 3-phase inverter switches which gives voltage of required frequency which is given to stator of induction motor This voltage is fed to induction motor which controls the speed Fig.2 represents the circuit of 3-phase uncontrolled diode rectifier cascaded with 3-phase fully controller inverter which gives variable voltage variable frequency which is used to control induction motor B Induction motor modeling Considering the applied stator voltage and flux linkages the mathematical modeling of the squirrel cage induction motor in the stationary reference frame using standard nomenclature is given as Stator flux, dψds = vds − Rs ids (12) dt dψqs = vqs − Rs iqs dt (13) dψdr = vdr − Rr idr − ωr ψqr dt (14) dψqr = vqr − Rr iqr − ωr ψdr dt (15) III M ODELING AND S IMULATION To simulate the system in matlab (simulink), it is essential to model the system in terms of their mathematical equations A 3-phase inverter modeling In applications such as uninterrupted AC power supplies and AC motor drives, three-phase inverters are commonly used to supply three-phase loads [3] Here we take 3-phase AC supply and give it to 3-phase diode rectifier which gives average output voltage as: Rotor flux, Stator currents, 3Vm(L−L) (7) Vdc = π Now, the output voltages of three phase inverter are given by ψds = Ls ids + Lm idr (16) ψqs = Ls iqs + Lm iqr (17) ψdr = Lr idr + Lm ids (18) ψqr = Lr iqr + Lm iqs (19) Rotor currents, van (2vao − vbo − vco ) = (8) (2vbo − vco − vao ) (9) vbn = (2vco − vao − vbo ) (10) Line to line rms voltage at fundamental frequency, due to 1200 phase shift between the phase voltages is given by √ Vdc VLL = √ ∗ ma ∗ (11) 2 vcn = Electrical torque developed by IM, Te = P ∗ ∗ Lm (idr iqs − iqr ids ) 2 (20) Swing equation representing the speed and torque relation, J dωr = Te − TL dt (21) C Simulation results The induction motor parameters specified in the appendix are considered for the simulation and are carried out in MATLAB (simulink) simulation tool design software which supports all TI launchpads The model developed in Vissim is directly dumped on the F28069M which is designed specially for power control application The hardware setup is as shown in Fig.6 which consists of Induction motor Rectifier and inverter stack F28069M launch pad Regulated power supply Fig 3: Simulation of the System In Fig.3 the block representation of the induction motor system controlled by 3-phase inverter is shown Fig.4 represents the speed response for 1400 rpm at constant load torque of Nm Due to the closed loop control the motor speed remains at constant speed even after the application of load Fig.5 represents the electrical torque developed by induction motor Load torque of Nm is applied on the motor Due to the closed loop control the motor torque developed will settle at Nm Fig 6: Hardware system set-up Fig.7 represents the line to line stator voltage applied to the induction motor at a frequency of 25 Hz constant DC voltage is applied to the inverter using rectifier the inverter gives variable frequency and variable voltage when ma is changed in SPWM Fig 4: Speed response for constant load torque Fig 7: Stator applied voltage waveform Fig 5: Motor torque characteristic IV H ARWARE IMPLEMENTATION In this TI’s F28069M launch pad is used to generate pulses to control the frequency and voltage magnitude of the 3-phase inverter output Vissim is a special model based Now the results plotted are real time graphs taken by hardware in loop system with the help of F28069M launch pad In Fig.8, time versus speed is plotted The reference speed is set to 1350rpm The motor starts picking up the speed and settles at the given command speed The circled area is zoomed and shown in Fig.9 which shows the response of the system for different loaded conditions The loads are applied and then removed to see the dynamic response of the system Fig 11: Step change in speed with oscillations Fig 8: Speed versus time actual and reference speed TABLE I: Speed and voltages obtained at different frequencies speed (rpm) 430 570 720 880 1030 1182 1330 1484 v 68 90.8 113 136 158 181 203 226 f 15 20 25 30 35 40 45 50 v f 4.53 4.54 4.52 4.53 4.51 4.52 4.51 4.52 Fig 9: Various loads applied at different time interval In Fig.10, the speed command is given through step input The step input varies from 830 rpm to 1380 rpm which is shown in per unit form As the step changes the motor shows dynamic change in the speed and settles at the commanded speed In Fig.11, the proportional and integral values are changed so as to get small oscillations between the reference speeds The system shows very good dynamic response Table I represents the actual speed of the motor at various frequency Also corresponding voltages are shown V/f ratio almost remains constant This represents the dynamic behaviour of control strategy V C ONCLUSION The speed of induction motor is being successfully controlled by a low cost development board from TIs F28069M launch pad This is a promising control theory which is low cost and can be implemented for auto mobiles Due to its low cost and high efficiency induction motor can be a great inclusion in the automotive drives Since in automotive drives varying speed and load conditions are very common and requires dynamic response this system provides the necessary requirement This is highly efficient compared to DC motor drives Also this can handle high load torque and provide good dynamic response Simulation and hardware implementation is carried out successfully A PPENDIX Fig 10: Speed change from 1380rpm to 830rpm Induction motor specification as used in simulation Parameters Power (hp) Voltage (V) Frequency (Hz) Current (A) Connection Rated torque (N-m) Rated speed (rpm) Slip(%) Value 220 60 5.8 delta 11.9 1710 Induction motor parameters at rated frequency: R1 =0.435Ω; X1 =X2 =0.754Ω; R2 =0.816Ω; Xm =26.16Ω; Induction motor specifications as used in hardware implementation Here we have used it in delta connection Parameters Value Power (kW) 0.55 Voltage (V) 415/230 Frequency (Hz) 50 Current (A) 1.4/2.7 Connection Star/delta Efficiency (%) 70 Rated speed (rpm) 138 Slip (%) ACKNOWLEDGEMENT I would like to thank Prof P.G Tewari, Principal, BVBCET, Hubballi I would also express my sincere gratitude to Prof.A.B.Raju, HOD, Mr Sachin Angadi, Asst Prof, Electrical and Electronics Dept for their generous guidance and encouragement throughout the project R EFERENCES [1] Gopal.K.Dubey, Fundamentals of Electrical Drives, second edition, New Delhi, Narosa Publishers, 2001 [2] R Krishnan, Electric motor drives, modeling, analysis and control, first edition, Pearson education inc, 2001 [3] Ned mohan, Tore M Undland, William P Robbins, Power electronics converters, application and design, third edition, John willy,2003 [4] Vijay Babu Koreboina, Shankar J Magajikondi, A B Raju, Modeling, Simulation and PC Based Implementation of a Closed Loop Speed Control of VSI Fed Induction Motor Drive, IEEE 2010 (2011.01.28-2) [5] Prof.S.P.Das, Advanced electric drives, video lectures 1-9, NPTEL, IIT Kanpur [6] Gopakumar, K., Power Electronics and Electrical Drives, Video Lectures 24-35, Centre for Electronics and Technology, Indian Institute of Science, Bangalore [7] Texas instruments, Scalar (V/f) Control of 3-Phase Induction Motors, application report, july 2013 ... circuit of 3-phase uncontrolled diode rectifier cascaded with 3-phase fully controller inverter which gives variable voltage variable frequency which is used to control induction motor B Induction motor. .. is given to 3-phase inverter switches which gives voltage of required frequency which is given to stator of induction motor This voltage is fed to induction motor which controls the speed Fig.2... consists of Induction motor Rectifier and inverter stack F28069M launch pad Regulated power supply Fig 3: Simulation of the System In Fig.3 the block representation of the induction motor system controlled