MATLAB/Simulink Based Model For 25 KV AC Electric

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 5, May - 2014MATLAB/Simulink Based Model for 25 kV ACElectric Traction DriveShubhra (MIEEE, LMIETE)Assistant ProfessorIndraprastha Engineering CollegeGhaziabad, Uttar Pradesh, IndiaKeywords-- Rectifier, inverter, MATLAB, Simulink, Traction,Induction Motor.I. INTRODUCTIONII. ELECTRIC TRACTION DRIVE SYSTEMBlock diagram for a typical electric traction drive is shown in“Fig. 1”. The electric power is supplied to the locomotivepropulsion drives via overhead lines. Motor-end inverter canbe a current source inverter or a voltage source inverter[3].Thecircuitry of the input converter which provides a DC supplyfor the load side converter depends on the following: Type of input power supply i.e. AC or DC Electricity utility‟s limits on reactive power harmonics. Type of electric brakes; that‟s regenerative, rheostatic orboth.IJERTAbstract-- Advances in power Electronics have permittedVariable Voltage Variable Frequency (VVVF)controlled devicefor induction motors becoming immensely popular. These devicessave power and permit the robust squirrel cage motor to drivefrom the smallest pump motors to fuel efficient hybrid drive carsand buses to the most powerful Diesel loco upto 4000 kW andElectric Locomotives up to 9000kW. This paper presents a novelmethod of modelling AC Traction drive using MATLAB. Powersystem Block set/simulation software focusingon Rectifier –Inverter – Motor systems. Three phase induction motor used inelectric locomotive has been considered for the model. Theinverter has been simulated to operate in two modes i.e. six stepand Pulse Width Modulation (PWM) mode with rectifier block.The inverter fault condition has also been simulated to study theperformance of electric traction drive under loaded condition.The model can be used to evaluate the load torque value for aparticular speed of traction motor drive.Railway electrification emerged as means of electrification inlate years of nineteen centuries & it came to India in 1925 withDC traction. However AC traction started in Indian in latefifties. Major boost of electric traction was provided by theadvancement in power electronics field. The overhead systemsupplies energy to the traction motors in a controlled manner,which is mounted on the electric locomotive. Locomotive inturn develop tractiveeffort to move the train from stationaryposition. In this process it overcomes the train air resistance,air drag, gradient& provides the desired acceleration tomovethe train not only onstraight track but also on curvedtrack.TheStatePowerUtilities,supply powerat220/132/110/66 kV Extra High Voltage (EHV) at each tractionsubstation which is owned, installed, operated and maintainedby the Railways.AC voltage from the 25 kV catenary supply is reduced to therequired voltage of the single phase rectifier. The properlyfiltered output of rectifier becomes the input to the inverter. Athree phase inverter provides this high frequency controlledinput to the motor. Depending upon the control schemeadopted, the firing pattern of three-phase inverter isestablished and the desired inverter output is achieved. Thedesired high frequency output of inverter is then fed to threephase induction motor to get required value of torque andspeed.With nanotechnology in place & cut throat competition,designs for traction drive have to be built with optimal cost.To achieve that model based design techniques are preferred tocreate implementable product specifications. Simulation toolshelp to optimally design the system & engineer can bebenefitted by integration of simulation with the design processto reduce design time and cost. This is a great tool forindustries to first design & then validates the test results [1, 2].IJERTV3IS051344www.ijert.orgFig. 1: Electric Traction Drive with Catenary Supply940

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 5, May - 2014III. MODEL DEVELOPMENT PROCESSThe Simulink based PWM inverter model has been used forthe paper contains fault simulations blocks where varioustypes of three–phase inverter faults can be simulated, transientconditions of current and torque has been displayed underNormal and Inverter Fault Conditions. Its performance isstudied under PWM mode and Six Step Mode.PWM inverter-fed induction motor drives are being used inlarge numbers throughout a wide variety of industrial andtraction applications. Both voltage & frequency are varied byPWM inverter. As input voltage given to a PWM invertershould be constant and not variable, therefore an uncontrolledrectifier can be used so input power factor is much better ascompared to scheme with a square wave inverter.1. Simulation Model BlocksThe modelling of the rectifier system has been carried out byusing universal bridge to provide a perfect DC signal. Therectifier model has been developed by making use ofMATLAB/Power System Block (PSB) software. The rectifiedDC voltage is fed to a PWM inverter [4].Fig. 2: Internal details of ' Inverter Block'“Fig. 3”, shows the details of the „Power Circuit Block‟, inwhich there are six switches taken, whose threshold inputs arethe gating pulses previously received. 0.5 Vdc and zero arethe upper and lower signal inputs for the three top levelswitches and -0.5Vdc and zero are the upper and lower signalinputs for the three bottom level switches.IJERTIn AC Propulsion system, 25 kV single phase line voltages isfed to a transformer, whose secondary winding is connected tosingle-phase diode rectifier with a DC link capacitor whichproduces a DC output. The DC voltage is then passed to theinverter, which provides the controlled three phase supply tothe traction motors. This forms the source for the two voltagesource inverters that supply power to six AC motors. Themodels of the all individual systems are integrated in to oneconnected system for simulation purpose.In traction locomotive, there are two inverters and eachinverter feed, three induction motors which drive the axles andwheels through the gear boxes. The present work does amathematical modeling of the inverter system including faultcondition. The conditions of current imbalance & brakingtorque developed to estimate the induction machine maximumtransient torque in the event of inverter fault [5].Fig. 3: Internal details of ' Power Circuit2. Inverter Model DescriptionThe inverter model is realized by generating voltage outputs ofthe inverter by algebraic calculations based on „ON‟ or „OFF‟state of the pulses. At OFF state, switches are modeled asideal open-circuits. The models consist of several blocks andeach block is a combination of subsystems of smaller blocks.In the „Inverter block‟sine wave modulating signal and thecarrier waveform are given to the modulator block, whichcompares the two waveforms and according to the sine PWMprinciple, generates thetwelve gate pulses.There are totaltwelve pulses, six for each inverter. The gating pulses aregiven to the „Power Circuit Block‟ as shown in “Fig. 2”, where0.5 Vdc and -0.5 Vdc signals are also given. The outputs of thepower circuit block are the required to be fed as three phasevoltages for all the six motors.IJERTV3IS051344Fig. 4: Rectifier two inverter model with six motors3. Inverter Fed Induction Motor Model DescriptionRectifier - DC Link -Two inverter model with six motors is asshown in “Fig. 4”,. The Rectifier - DC Link - inverter fedmachine model shown in “Fig. 5”.www.ijert.org941

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 5, May - 2014Figure 5: Rectifier inverter fed machine modelIV. OPERATION OF INVERTER MODEL1. Inverter model with fault simulation capabilityIJERTThe inverter model has been built with the fault simulationcapability to model the faults as shown in “Fig. 6”. The blockis a switch of SIMULINK, which has three inputs and oneoutput. The first input here is an array, whose value is dependsupon the type of fault that has to be simulated.Fig. 6: Inverter model with fault simulation blocki)Six- Step Mode: The torque, speed, stator current and outputvoltage waveforms obtained for 6-step (square wave) mode ofoperation with rectifier are shown in “Fig. 7”.Fig. 7: Torque, Speed Current and Inverter Voltages for Six Step Operationwith fault at 0.4 sec.ii)PWM Mode: The PMW mode of operation of the inverterwas obtained using sinusoidal pulse width modulation. TheIJERTV3IS051344www.ijert.org942

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 5, May - 2014torque, speed, stator current and output voltage waveforms forPWM operation with rectifier are shown in “Fig. 8.”operation with rectified input supply to inverter at six-stepmode with rectifier are shown in “Fig. 9a, b, c, & d”.Fig. 9 a: Torque profile of motor in six step mode under normal operationIJERTFig. 9 b: Speed of motor in RPM in six step mode under normal operationFig. 9 c: Stator current of phase in six step mode under normal operationFig. 9 d: Inverter voltages for six step operation under normal operationFig. 8: Torque, Speed, Stator Current and Inverter Voltages PMW operan.2.Inverter operation under normal conditionii) PWM Mode : The torque, Speed and voltages developed byan induction machine drive during normal operation withrectified dc supply to inverter at PWM Mode with rectifier areshown in “Fig. 10 a, b, & c”.i) Six- Step Mode : The torque, Speed, currents and voltagesdeveloped by an induction machine drive during normalIJERTV3IS051344www.ijert.org943

International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 3 Issue 5, May - 2014seconds. The simulated wave form of electromagnetic torqueshows that the torque produced by the motor has transients butdampens out quickly to settle to an equilibrium point and thusfollow the changes in load torque.IJERTFig. 10 a: Torque profile of motor in PWM mode under normal operationFig. 10 b: Speed of motor in RPM in PWM mode under normal operationFig. 11: Torque and speed profile of motor under normal condition in PWMmode with rectifier (Load disturbance)Fig. 10 c: Inverter voltages for PWM operation under normal operationV. CONCLUSIONThe rectifier, inverter and induction machine model in PWMmode was subjected to sudden variation in load [6]. Thetorque, speed responses after the machine settled atsynchronous speed are obtained as shown in “Fig. 11”. Theinitial torque is zero under these conditions. A load torque 450Nm is applied at t 2.25 seconds and removed at t 4.25IJERTV3IS051344The inverter model has been studied with rectifier outputvoltage. The simulation has further been carried put under twomodes; PWM mode & Six Step Mode. The simulation for allthese conditions has been carried for both normal & faultcondition for electric traction drive under loaded conditions.www.ijert.org944