# Download International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726

Electronic engineering wikipedia , lookup

Electromagnetic compatibility wikipedia , lookup

Power engineering wikipedia , lookup

Three-phase electric power wikipedia , lookup

Electrification wikipedia , lookup

Mains electricity wikipedia , lookup

Voltage optimisation wikipedia , lookup

Commutator (electric) wikipedia , lookup

Utility frequency wikipedia , lookup

Alternating current wikipedia , lookup

Rectiverter wikipedia , lookup

Solar micro-inverter wikipedia , lookup

Dynamometer wikipedia , lookup

Power electronics wikipedia , lookup

Brushless DC electric motor wikipedia , lookup

Power inverter wikipedia , lookup

Pulse-width modulation wikipedia , lookup

Electric motor wikipedia , lookup

Brushed DC electric motor wikipedia , lookup

Stepper motor wikipedia , lookup

Electric machine wikipedia , lookup

International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives Khadim Moin Siddiqui, Kuldeep Sahay, V.K.Giri [email protected] Abstract— AC asynchronous electrical motors especially squirrel cage induction motor presents the greater advantages on cost and energy efficiency as compared with other industrial solutions for varying speed applications. The force-commutated power electronics switches (GTOs, MOSFETs, and IGBTs etc) based inverters are widely employed these days in the conversion of constant speed into variable speed induction motors. Due to the invention of these advanced power electronics switches (GTOs, MOSFETs, IGBTs etc) with improved characteristics, the PWM inverter fed induction motors are widely replacing DC motors and thyrister bridges day by day in the industries. The torque control or field control method may be used with PWM inverter fed induction motors jointly and can achieve the same flexibility in speed and torque control as with DC motors. In this present paper, an IGBT inverter fed squirrel cage induction motor with torque control technique is developed and simulated in the recent MATLAB/Simulink environment and observed the transient characteristics of the used motor. Many motor parameters have been used for induction motor analysis purpose. Further, V/f control and Total Harmonics Distortion (THD) analysis has also been carried out. Though, the stator current parameter of the motor has been widely used from last three decades with Motor Current Signature Analysis (MCSA) technique. Therefore, in the THD analysis, only stator current motor parameter has been analysed. Index Terms— Squirrel cage induction motor Induction Motor (IM), Pulse width modulation Insulated Gate Bipolar Transistor (IGBT), Time Analysis, Direct Torque Control (DTC), V/f MATLAB/Simulink (SCIM), (PWM), Domain Control, I. INTRODUCTION Earlier, the DC motors were widely employed in industries to achieve variable speed for many applications by changing the field and armature current. Consequently, its flux and torque controlled efficiently. But this method requires frequent maintenance, high cost, unable to use in the explosive environment. By using DC motors, large variation in the motor’s speed is not possible. Therefore, for wide range of speed control purpose induction motor fed PWM inverter is preferred these days. Nowadays, induction motor has become the heart of industries with modern power electronics devices. By using this combination, IM can control the wide range of speed with very competitive pricing. Therefore, the induction motor has become the “workhorse” of the motion industry [1-4,13]. In the past, the induction motors were widely employed in constant speed applications because of the unavailability of the variable- frequency voltage supply. The variablefrequency voltage can achieve by the advanced power electronics semiconductor devices based inverters. These inverters widely called Pulse Width Modulation (PWM) Inverters. These inverters provide us capability to vary the frequency of the voltage supplies in the relatively easy way. As a result, the induction motor can be used in the variable speed drive applications. The PWM inverter may control the large amount of speed of the induction motor[1,4,7,13]. The PWM inverters covered many applications in the electrical engineering field such as UPS, AC electric drives, HVDC reactive power compensators in power systems and communications to power control and conversion. In the present time, the PWM inverter fed asynchronous motor drives are widely used in the industries because it provides more variable and offer in a wide range of speed control with better efficiency and higher performance compared to constant frequency motor drives[4-6,14]. The induction motor with advanced power electronics inverters not only controls the motor speed but can also pick up motor’s dynamic as well as steady state characteristics. Subsequently, these devices can reduce the system's average power consumption and noise generation of the induction motor [1,7]. The three phase Squirrel Cage Induction Motor (SCIM) is simple, efficient and robust asynchronous motor and often a natural choice as a drive for industries with a very competitive pricing. Squirrel Cage Induction motors (SCIM) are the most 1716 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ extensively used electric motors for appliances, industrial control, automation and transportation. The SCIM widely employed these days as variable speed induction motor with PWM inverters and replacing DC motors and thyristor bridges in industries [1, 3, 5]. It has been seen that many researchers proposed various IM models with different power electronics devices based inverters and control the speed of the IM. But harmonics always creates problems in the currents, voltage and developed electromagnetic torque. Therefore, the modeling of such motors is still being the challenging task [1, 8-12,14]. The IM with PWM inverters has been delivering challenging competition with D.C motors these days and given the cause for replacement of D.C. motors from very fast speed in the industries. This technique is cheap and safe to achieve variable speed efficiently with less power consumption and minimum maintenance. Consequently save many dollars for industries. The IM cost per KVA is approximately one fifty than DC motors. Therefore, it seizes higher appropriateness in antagonistic atmosphere [1-3]. In the present paper, we have proposed and developed an SCIM fed PWM inverter model in the recent MATLAB/Simulink environment. We have used IGBT inverter and torque control method with induction motor jointly for better results with reduced harmonics. The V/f control has also been carried out for the proposed model. The transient behavior of the induction motor has been deeply observed. In future, this model may be used in the various power electronics and drive applications. II. MATHEMATICAL MODELLING of INDUCTION MOTOR The traditional per-phase equivalent circuit is used for induction motor mathematical modelling purpose. The basic diagram of per phase equivalent circuit for q and d-axis is as shown in Fig. 1. The equations are derived in the Clarke or αβ (stationary) reference frame by d and q variables. The d-q transformation is widely used because it reduces three AC quantities into two imaginary DC quantities for balanced circuits. The simplified calculations may be carried out on these two imaginary DC quantities for recovering the actual three-phase AC results by performing inverse transformation. (a) (b) Fig. 1 Per- Phase Equivalent Diagram of IM, (a) q-axis, (b) d-axis The stator circuit voltage equations in the Clarke or αβ (stationary) reference frame transformation is as follows: V s qs Rsi s qs p s qs (1) d dt s Rsi ds p s ds (2) Where, V s ds p The stator voltage equations involved in the conversion of rotating reference into stationary reference frame are as follows: V s qs cos s V ds sin sin cos Vqs Vds (3) The variable stationary reference and variable rotating reference frame expressed by the following equations (4 & 5): V s qs Vm cos Where, t V s ds Vm sin (4) (5) The q-axis and d-axis stator voltage equations are as follows: Vqs Rsiqs pqs ds (6) Vds Rsids pds qs (7) The q-axis and d-axis rotor voltage equations are as follows: V qr R r i qr p qr dr Where, (8) r 1717 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ V dr R r i dr p dr qr (9) For simulation of an open loop model, following flux linkage equations (10 to 13) would be considered. (10) qs Lsiqs Lmi qr ds Lsids Lmi dr qr L r i qr Lmiqs dr L r i dr Lmids (11) (12) ds (Vds Rsids )dt (14) qs (Vqs Rsiqs )dt (15) (13) In our case, for closed loop model following flux linkage equations (14 to 16) will be considered. s ( 2 ds 2 qs ) tan 1 ( qs ) ds (16) The total stator and rotor inductances may be expressed by the following equations: Ls L1s Lm (17) L r L 1r Lm (18) The developed electromagnetic torque may be written by the following equation: Te 3P ( ds iqs qs ids ) 2 (19) The rotor acceleration equation may be expressed by the following equations: pm (Te Tm ) (20) 1 Where, , Fm and m p m 2H The abc to dq reference frame transformations in the phase-to-phase voltage may be expressed by the following equations. The q-axis transformed stator voltage equation is as follows: 1 Vqs (21Vabs 2Vbcs ) 3 Where, 1 cos , 2 cos 3 sin (21) (22) The q-axis transformed rotor voltage equation is as follows: 1 V qr (2 1V abr 2V bcr ) 3 cos , 2 cos 3 sin The d-axis transformed rotor voltage equation is as follows: 1 V dr (21V abr 2V bcr ) 3 Where, 1 sin , 2 sin 3 cos (24) In the preceding equations, θ is the angular position of the reference frame, while δ= θ - θr is the difference between the position of the reference frame and the position (electrical) of the rotor. Because the machine windings are connected in a three-wire Y configuration, there is no homopolar (0) component. This also justifies the fact that two line-to-line input voltages are used inside the model instead of three line-to-neutral voltages. The dq to abc reference frame transformations applied for the phase currents may be expressed by following equations: The phase a current in the stator side may be expressed by the following equation: ias 1iqs 2ids (25) Where, k1 cos , k2 sin The phase b current in the stator side may be expressed by the following equation: ibs 3iqs 4ids (26) Where, k3 cos 3 sin 3 cos sin , k4 2 2 The phase a current in the rotor side may be expressed by the following equation: ii ar 1i qr 2i dr Where, 1 (27) cos , 2 sin The phase b current in the rotor side may be expressed by the following equation: ii br 3i qr 4i dr (28) Where, The d-axis transformed stator voltage equation is as follows: 1 Vds (21Vabs 2Vbcs ) 3 Where, 1 sin , 2 sin 3 cos Where, 1 (23) 3 cos 3 sin 3 cos sin , 4 2 2 The phase c current in the stator side may be expressed by the following equation: ics ias ibs (29) The phase c current in the rotor side may be expressed by the following equation: i cr i ar i br (30) 1718 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ The complete mathematical modelling of the used induction motor may be understood by equations (1 to 30). III. PROPOSED DIRECT TORQUE CONTROL INDUCTION MOTOR FED PWM INVERTER The force-commutated electronic switches are widely employed these days to convert constant speed asynchronous motors into variable speed asynchronous motors. Power electronics switches such as MOSFETs, GTOs and IGBTs efficiently controls the induction motor. The Pulse Width Modulation (PWM) voltage source(VSC) inverter-fed induction motor are widely used these days and gradually replacing DC motors and thyristor bridges. With PWM inverter, combined with advanced control strategies such as field-oriented control or direct torque control, we can achieve the same flexibility in speed and torque control as with DC machines. Since, it has been observed that the IGBTs inverter fed into induction motor give better results rather than other power electronics switches based inverters fed induction motor in many power applications with reduced harmonics. Therefore, in the present work, the torque control simulation model has been developed in the MATLAB with PWM inverter fed induction motor. The Insulated Gate Bipolar Transistor (IGBT) inverter has been used in the conversion of DC voltage into AC voltage. The proposed inverter fed induction motor simulation model is as shown in Fig. 2. The positive load torque ought to be applied on the shaft, if electric motor operates in the motoring mode or negative for generating mode. The nominal full load positive torque is applied on the machine’s shaft is 15 Nm for motoring mode. The SCIM block available in the MATLAB/Simulink having three inputs and one output. The three phase supply would be given in the three inputs and output side one bus selector has been used. The bus selector de-multiplexes many outputs of induction motor. There are 21 motor signatures are hidden in induction motor’s one output. We can de-multiplex these signals as per our requirement. In our case, we have been de-multiplexed only maximum six parameters for analysis purpose. Fig. 2 Proposed DTC Control SCIM Fed PWM Inverter Simulation Model In the present paper, a three-phase SCIM rated 3 HP, 220 V, 1430 RPM is fed by a sinusoidal PWM inverter has been considered for analysis purpose. The sinusoidal reference wave base frequency is used 50 Hz while the triangular carrier wave's frequency is calculated and set to 1650 Hz. The modulation factor is 33 and ought to be choose as high as possible for better results. Therefore, the triangular carrier wave's frequency corresponding to the given modulation factor is 50×33=1650 Hz. Since, the switching frequency (1650 Hz) is relatively high. Therefore, maximum time step is restricted to 10 µs. This high switching frequency (1650 Hz) is required for the inverter. It is recommended in [2-3] that the modulation factor (mf) ought to be an odd multiple of three and that value has to be as high as possible. The machine's rotor is short-circuited for SCIM. The smoothing reactor has also been placed between the inverter and the electric machine for simulating the effect of a smoothing reactor. Consequently, we have set the stator leakage inductance twice to its actual value. If we use PWM inverter then noise will be introduced in the electromagnetic torque, voltage and currents but the motor's inertia will prevents the noise from appearing in the motor's speed. The Clarke or αβ transformation (stationary reference frame) is used in this work. The reference frame is required for the conversion of input voltages (abc reference frame) into the output currents (dq reference frame). If we are interested to do park transformation then the rotor reference frame ought to be choose. In the stationary reference frame, the rotor angle value is set to 0 and the value of δ is set to -θr. The reference frame affects the simulation speed, waveforms of all dq variables and in some certain cases the accuracy of the obtained results. The brief descriptions of the used SCIM block parameters are given in appendix (Table I). 1719 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ Magnetic Field (RMF) 1430 RPM after 0.4 sec. At the starting, the magnitude of the 50 Hz stator current reaches 96 A peak( 68 A RMS) whereas its steady state value is attained 12.25 A( 8.66 A RMS). The developed electromagnetic torque waveform reveals that the stable condition is achieved after 0.4 sec. the strong oscillations have been observed in the electromagnetic torque waveform at starting. If it is zoomed, the noisy torque will be observed with a mean value of 15 N.m. 100 80 <Stator current is_a (A)> 60 40 20 0 -20 -40 -60 -80 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 0.7 0.8 0.9 1 (a) 100 80 60 <Rotor current ir_a (A)> The snubber circuit is essential with IGBT and provided inbuilt in the MATLAB/Simulink Library. In the used IGBT block, we have set the value of snubber capacitor infinite (short- circuit). It means the purely resistive snubber has been used. Generally, the Insulated Gate Bipolar Junction Transistor (IGBT) do not use snubbers but every non-linear elements are used in the MATLAB/Simulink is modeled as a current source. Consequently, we need to provide a parallel path across each IGBT to allow connection to an inductive circuit (stator of an induction motor). But, the circuit performance would not be affected by choosing high value of the snubber. A pulse generator is employed to control the inverter bridge. In the present work, the torque control method has been used for induction motor controlling purpose with PWM inverter. Since, the field or vector control method is a pretty attractive control method but due to some serious drawbacks is not used in this present work. The field control method relies deeply on accurate acquaintance of the motor signatures. The rotor time constant is particularly hard to measure accurately, and to make matter very inferior because it varies with temperature. The torque control method proficiently controls the IM than field control method. It estimates the stator flux and electric torque by Clarke or αβ transformation and terminal measurements. The mathematical equation of torque control has already been discussed. The approximated stator flux and electric torque are directly controlled by comparing them with their relevant demanded values by using hysteresis comparators. The two comparator’s output will then be used as input signals of an elective switching table. The value of the direct torque control feedback constant k has been computed 6.693 . IV. RESULTS in SYMMETRICAL CONDITION (HEALTHY STANDSTILL CONDITION) 40 20 0 -20 -40 -60 -80 -100 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) (b) 1600 1400 1200 Rotor Speed(RPM) The simulation result in symmetrical condition or healthy standstill condition of the motor is as shown in Fig. 3. Six motor parameters of the induction motor have been used for performance and analysis purpose. These are stator current, rotor current, rotor speed, developed electromagnetic torque, q-axis stator/rotor flux. In the standstill condition of the motor, the load torque and slip set at 15 and 1 respectively. The obtained results show that all the considered motor parameters have been reached in the steady state condition after 0.4 seconds. In the starting of the motor, the first transient peak of the stator current and electromagnetic torque waveforms having highest amplitude when it is decreased and reached in the stable condition. The proposed simulation model is simulated only for 1 sec for clear visualization of transient characteristics. Therefore, the transient characteristic of the motor is clearly visualized. The squirrel cage induction motor starts and reached in the steady state condition after 0.4 sec and attained Rotating 1000 800 600 400 200 0 -200 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 (c) 1720 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ 140 100 100 80 80 <Stator current is_a (A)> <Electromagnetic torque Te (N*m)> 120 60 40 20 60 40 20 0 0 -20 -40 -20 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 0 0.1 0.2 0.3 1 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 0.7 0.8 0.9 1 0.7 0.8 0.9 1 0.7 0.8 0.9 1 (a) (d) 80 1 0.8 60 <Rotor current ir_a (A)> <Stator flux phis_q (V s)> 0.6 0.4 0.2 0 -0.2 40 20 0 -20 -0.4 -0.6 -40 -0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 0 0.1 0.2 0.3 1 0.4 0.5 0.6 Time (seconds) (b) (e) 1440 0.6 1420 1400 Rotor Speed(RPM) <Rotor flux phir_q (V s)> 0.4 0.2 0 1380 1360 1340 -0.2 1320 -0.4 1300 0 0.1 0.2 0.3 -0.6 0.4 0.5 0.6 Time (seconds) (c) 60 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 (f) Fig. 3 Motor Parameters in Symmetrical Condition(Healthy Standstill Condition), (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d) Electromagnetic Torque, (e) q-axis Stator Flux, (f) d-axis Rotor Flux If we zoomed stator and rotor current waveforms, the harmonics will be displayed multiple of the 1650 Hz switching frequency. This is filtered by stator inductance. Therefore, we can say that the 50 Hz frequency component is dominant. Similarly, q-axis stator and rotor flux is also attained steady state condition after 0.4 sec. After passing transient time, perfectly sinusoidal signal can be observed. Therefore, finally we can say that the proposed simulation model given expected correct results. Second healthy running condition has also been considered and observed due to the clear revelation of the transient characteristics. In the healthy running condition mode the slip is set at 0.04. At this slip, we can get 1430 RPM rotor speed on full load nominal torque. This is our nominal speed of the 40 <Electromagnetic torque Te (N*m)> -0.8 20 0 -20 -40 -60 -80 -100 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) (d) 1721 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ 1 0.8 0.4 0.2 0 -0.2 -0.4 -0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 (e) 0.6 <Rotor flux phir_q (V s)> 0.4 0.2 0 80 -0.2 60 40 -0.4 -0.6 -0.8 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 <Rotor current ir_a (A)> <Stator flux phis_q (V s)> 0.6 When IGBT inverter frequency is increased or decreased compared to the rated frequency, the large variation in the rotor speed has been achieved. The inverter frequency variation has been considered from 70 Hz to 6 Hz. It may be observed from Table III, that the inverter frequency is able to control the speed up to 1825 RPM to 238 RPM. Therefore, we can say that a wide range of speed control is possible through this proposed inverter fed induction motor with torque control technique by the V/f control strategy efficiently. In the similar way, if we change the power, the same speed variation will be taken place. It has been observed that the motor power will be varied from 2.95 HP to 0.15 HP. Hence, we can say that an efficient V/f control has been successfully implemented in this model. 20 0 -20 -40 (f) Fig. 4 Motor Parameters in Symmetrical Condition(Healthy Running Condition), (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d) Electromagnetic Torque, (e) q-axis Stator Flux, (f) d-axis Rotor Flux -60 -80 0 0.2 0.4 0.6 0.8 1 1.2 Time (seconds) 1.4 1.6 1.8 1.4 1.6 1.8 1.4 1.6 1.8 1.4 1.6 1.8 2 (a) 100 The SCIM fed PWM inverter with torque control can control the large amount of speed of the motor. The used induction motor (3 HP, 4 Pole, 50Hz) motor's speed can be controlled efficiently by the V/f control method. The speed can vary from 1825 RPM to 238 RPM by changing the frequency of the inverter. The rotor current, stator current, rotor speed, and electromagnetic torque for various frequencies have been carried out. It may be observed from Fig. 5 and Fig. 6. If we observe only rotor speed waveform for 70 Hz and 30 Hz in Fig. 5 and Fig. 6. The large variation in the rotor speed has been taken place by the inverter frequency. It has been observed from the Fig. 3 that when the motor frequency is 50 Hz then the rated rotor speed is achieved i.e. 1430 RPM. <Stator current is_a (A)> 60 40 20 0 -20 -40 -60 -80 0 0.2 0.4 0.6 0.8 1 1.2 Time (seconds) 2 (b) 2000 1500 Rotor Speed(RPM) V. V/f CONTROL by PROPOSED SIMULATION MODEL 80 1000 500 0 -500 0 0.2 0.4 0.6 0.8 1 1.2 Time (seconds) 2 (c) 70 60 <Electromagnetic torque Te (N*m)> motor. In this mode, we may observe that the transient time has been decreased and flux waveforms give perfectly sinusoidal flux. Therefore, we can say that the motor is given excellent results in the healthy running condition also. The transient variation in the motor parameters is given in the appendix(Table II) for different loading conditions. From Table II, we may observe that how our used induction motor works in the different loading conditions. In the standstill healthy mode, the slip is set at 1. Consequently, the rotor speed is zero but RMF value is shown in the Table II i.e. 1430 RPM for clear comparison purpose. 50 40 30 20 10 0 -10 -20 -30 0 0.2 0.4 0.6 0.8 1 1.2 Time (seconds) 2 (d) 1722 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ Fig. 5 Motor Parameters in Symmetrical Condition for Inverter Frequency f=70 Hz, (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d) Electromagnetic Torque 150 <Rotor current ir_a (A)> 100 50 0 increased or decreased, the motor signatures will be varied correspondingly, as shown in Table III. When the frequency of the inverter is 50 Hz then the stator current, rotor speed and electromagnetic torque are 95.46A, 1430 RPM and 128.17 N-m respectively. These are high values in the first transient peak because of high switching frequency of the inverter. For other frequencies, the variations in the induction motor parameters are as shown in the Table III. -50 300 250 -150 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 (a) 120 100 <Stator current is_a (A)> 80 60 40 <Electromagnetic torque Te (N*m)> -100 200 150 100 50 0 -50 -100 20 -150 0 -200 -20 0 0.1 0.2 0.3 -40 0.8 0.9 1 250 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 200 <Electromagnetic torque Te (N*m)> (b) 1000 800 Rotor Speed(RPM) 0.7 Fig. 7 Electromagnetic Torque vs. Time for f=22 Hz -60 -80 0.4 0.5 0.6 Time (seconds) 600 400 200 150 100 50 0 -50 -100 -150 -200 0 -250 -200 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 Fig. 8 Electromagnetic Torque vs. Time for f=15 Hz (c) 300 <Electromagnetic torque Te (N*m)> 250 200 150 100 50 0 -50 0 0.1 0.2 0.3 0.4 0.5 0.6 Time (seconds) 0.7 0.8 0.9 1 (d) Fig. 6 Motor Parameters in Symmetrical Condition for Inverter Frequency f=30 Hz, (a) Stator Current, (b) Rotor Current, (c) Rotor Speed, (d) Electromagnetic Torque The transient variations in the motor parameters are as shown in Table III(appendix). In the transient analysis only first transient peak has been observed. The transient analysis has been carried out for three motor parameters. These parameters are stator current, rotor speed and electromagnetic torque. When frequency is 50 Hz, we have been achieved rated values of the motor. When the inverter frequency is It has clearly been observed in the Table III, that upto 22 Hz frequency, the electromagnetic torque first transient peak is being increased upto 281.39 N-m. If we further decreases the frequency, the maximum peak electromagnetic torque is being decreased as can observe from Table III and Fig. 7 and Fig. 8. The electromagnetic torque waveform has been shown for 22 and 15 Hz frequency respectively for clear revelation purpose. These Figs (7 and 8) show that the first maximum transient peak is being decreased if frequency is decreased. Therefore, we can say that the induction motor parameter variations in the transient conditions are completely controllable by this proposed simulation model. VI. TOTAL HARMONIC DISTORTION (THD) ANALYSIS The harmonic analysis of this proposed simulation model has also been carried in this section for its stator current and line to- line voltage. The stator current waveforms for 1 KHz and 5 KHz maximum frequencies are as shown in Fig. 9 and Fig. 10 and observed small harmonics (1.11 % & 2.26%). 1723 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ THD variation with maximum frequency is as shown in Table IV(appendix). It has been observed from the Table IV when the maximum frequency is being increased then the THD will also be getting increased. Therefore, in the proposed simulation model, we ought to choose the accurate maximum frequency for obtaining the maximum efficiency of the motor. Fig. 12 THD in Input Voltage when Max. Frequency is 5 KHz Fig. 9 THD in Stator Current for Closed Loop when Max. Frequency is 1 KHz Fig. 10 THD in Stator Current for Closed Loop When Max. Frequency is 5 KHz The THD for various maximum frequencies is as shown in Table IV. The fundamental frequency is set at 50 Hz for various maximum frequencies. The THD in the Line-to-Line Input Voltage (LLIV) for 1 KHz maximum frequency is very small. It is because of the reality that IGBT based inverter efficiently control the induction motor upto 1 KHz frequency in spite of disturbance occur in the supply due to inverter. When the maximum frequency again increased, the THD in the LLIV will be increased, but the THD in stator current will be less. It has been clearly observed in the previous recent researches that the THD value obtained relatively high in the LLIV as well as stator current [13]. Therefore, we can say that if upcoming researchers will use IGBT inverter fed induction motor model in the upcoming researches. They may achieve maximum efficiency of the induction motor in various applications. The magnitude of the fundamental frequency is as shown in the spectrum window i.e. 311 V (Fig. 11 & Fig. 12). This inverter voltage 311 V is compared well with the obtained theoretical value 311 V for modulation index m=0.9. This inverter voltage may be find out from the following equation. VLLrms Fig. 11 THD in Input Voltage when Max. Frequency is 1 KHz. m 3 Vdc = m 0.612 Vdc 2 2 (31) The harmonics are displayed in the LLIV in percent of the fundamental component. The harmonics has been observed as multiples of carrier frequency (n×33± k). The 30% highest harmonics visualized at 31st harmonic and 35th harmonic (33+2). These values we already expected. It can be clearly observed in Fig. 10. The THD value in the LLIV has been obtained 1.70 to 62.27 % for 0 to 5000 Hz maximum frequency range. VII. CONCLUSIONS In the present paper, it has been observed that the squirrel cage induction motor with a power electronics device based inverter presents the greater advantages on cost and energy 1724 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ efficiency, compared with other industrial solutions for varying speed applications. The induction motor fed PWM inverter with torque control has been proposed and implemented in the recent Matlab/Simulink environment. From proposed simulation model, the transient performance of the used induction motor has been analysed. It has been observed that the simulation model has been given excellent results with reduced harmonics. The extensive simulation has been performed for 3HP, 4 pole, 50 Hz induction motor with IGBT inverter and torque control technique jointly. The obtained simulation results have given ultimate solution for the wide range of speed control with lower harmonics. Since, the rapid improvement in the power electronics semiconductor devices based inverters enable us to control large speed with reduced harmonics with the care of the induction motor safety also. The V/f control method has also been successfully discussed efficiently. The transient behavior of the motor has been discussed and observed that the maximum transient peak is completely controllable with varying inverter frequency. In future, this simulation model may be employed in various applications and may be diagnosed different motor faults by suitable Digital Signal Processing (DSP) techniques. Appendix Table I Motor Description and Equivalent Parameters Rotor Type: Squirrel Cage Reference Frame: Stationary Motor: 3HP Rotor Speed: 1430 RPM Frequency: 50 Hz No. of Poles:4 DC Voltage: 400 V Stator Resistance: 0.435 ohm S.No. 1 2 3 4 5 6 7 LT MPTSC MPTRC RS MPTEMT (A) (A) (RPM) (N-m) 1 95.46 87.12 1430 (RMF) 128.17 15 0.04 86.76 79.81 1430 54.06 15/2 0.02 87.47 81.81 48.53 N-L 0 1 95.46 87.20 1470 1500 (RMF) N-LR-N 0 0.04 86.97 80.33 1500 50.28 H-YR-N H-L 70 50 30 22 21 10 6 MPTEMT (N-m) (RPM) 80.86 95.46 116.98 127.11 127.13 120.04 142.38 1825 1430 903 792 773 457 238 66.18 128.17 261.39 281.39 279.25 175.48 105.79 Table IV THD Variation with Maximum Frequency S.No. 1 2 3 4 5 5 Fundamental Frequency Maximum Frequency (Hz) (KHz) 50 50 50 50 50 50 1 2 3 4 5 5 THD (%) LLIV SC 1.70 42.52 42.55 58.73 62.27 62.27 1.11 2.08 2.09 2.24 2.26 2.26 ACKNOWLEDGMENT Authors acknowledge Technical Education Quality Improvement Program Phase-II, Electrical Engineering Department, Institute of Engineering & Technology, Lucknow for providing financial assistantship to carry out the research work. [1] [2] [3] 15 H-Y (A) REFERENCES Slip (N-m) Rotor speed MPTSC (Hz) Table II Transient Variation in Motor Parameters MC Inverter frequency 128.17 MC: Motor Condition, H-Y: Healthy, H-Y-R-N: Healthy Running, H-L: Half- Load, N-L: No-Load, N-L-R-N: No-Load Running, LT: Load Torque, MPTSC: Maximum Peak Transient Stator Current, MPTRC: Maximum Peak Transient Rotor Current, MPTEMT: Maximum Peak Transient Electromagnetic Torque, RS: Rotor Speed [4] [5] [6] [7] [8] Table III Transient Motor Parameters Variation with Inverter Frequency [9] K.M.Siddiqui, K. Sahay and V.K. Giri, “Performance and Analysis of Switching Function Based Voltage Source Inverter Fed Induction Motor”, International Electrical Engineering Journal, Vol. 5, No.9, pp. 1545-1552, 2014. P.C. Krause, O. Wasynczuk and S.D. Sudhoff, Analysis of Electric Machinery, IEEE Press, 1995. P.C. Krause, “Simulation of Symmetrical Induction Machinery”, IEEE Trans. Power apparatus Systems, Vol. 84, No. 11, pp. 1038–1053, 1965. N. Mohan, T.M. Undeland and W.P. Robbins, Power Electronics: Converters, Applications, and design, John Wiley & Sons, New York, 1995. R. Krishnan, Electric Motor Drives Modelling, Analysis, and Control, Prentice Hall, 2001. B.K. Bose, Modern Power Electronics and AC drives, Prentice-Hall, N.J, 2002. S.N. Ghani, “Digital Computer Simulation of Three- Phase Induction Machine Dynamics A Generalized Approach”, IEEE Trans Industry Appl., Vol. 24, No. 1, pp. 106–114, 1988. S. Wade, M.W. Dunnigan and B.W. Williams, “Modelling and Simulation of Induction Machine Vector Control and Rotor Resistance Identification, IEEE Trans. Power Electronics, Vol. 12, No.3, pp. 495–505, 1997. K.L. Shi, T.F. Chan, and Y.K. Wong, Modeling of the Three-Phase Induction Motor using SIMULINK, Record of the 1997 IEEE International Electric Machines and Drives Conference, USA, pp. 3-6, 1997. 1725 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives International Electrical Engineering Journal (IEEJ) Vol. 6 (2015) No.1, pp. 1716-1726 ISSN 2078-2365 http://www.ieejournal.com/ [10] K.L. Shi, T.F. Chan and Y.K. Wong, “Modeling and Simulation of Direct Self Control System”, IASTED International Conference: Modeling and Simulation, , pp. 231–235, Pittsburgh, USA ,1998. [11] N.N. Soe, H.T. T. Yee and S.S. Aung, “Dynamic Modeling and Simulation of Three phase Small Power Induction Motor", World Academy of Science, Engineering and Technology, pp. 421-424, 2008. [12] P. Fritzson, Principles of Object-Oriented Modeling and Simulation with Modelica 2.1. Piscataway, NJ: IEEE Press, 2004. [13] K. M. Siddiqui, K. Sahay and V.K. Giri, “Health Monitoring and Fault Diagnosis in Induction Motor- A Review”, International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, Vol. 3,No. 1, pp. 6549-6565, 2014. [14] K.M.Siddiqui, K.Sahay and V.K. Giri, “Simulation and Transient Analysis of PWM Inverter Fed Squirrel Cage Induction Motor Drives”, i-manager’s Journal on Electrical Engineering, Vol.7, No.3, Jan-March, 2014. 1726 Siddiqui et. al., Performance and Analysis of Direct Torque Control Induction Motor FED PWM Inverter Drives