3kV SCR controller for Transnet DC series traction motor

Electrical Design 5Final report

AbstractThis report is about the electrical design project: Design a DC Series Motor Chopper Controller for 3kV Transnet Electric Locomotives.It includes theory on DC series motor, steady state and dynamic analysis, SCR Thyristor, Chopper circuits and their design considerations. The Troge Chopper circuits were implemented on 6E1 Traction motor and simulated on Matlab Simulink. The behaviour of the motor was observed when current controller and speed controller were implemented and was observed when no controllers were implemented. The circuits were also made to operate as regenerative choppers. Simulation results are presented and the performance and the efficiency of the system are discussed. Lastly at the end of this report there is a detailed time schedule of this design project showing the time allocated for each task of the project.

Declaration

I here declare that the contents of this report are my own original an unassisted work, except where specific mention is made to the contrary in the form of a numbered reference.Authors full name: Sureshan NaidooAuthors student number: 209503235 Date: 16 May 2013

ContentsAbstract1Declaration2List of Figures4List of Symbols51. Introduction72. Design Specification83. Feasibility Study93.1 Transnet 6E1 Traction Motors93.1.1 The Resistor Controlled 6E1 Train DC Power Circuit113.1.2 DC Resistance Control123.1.3 Camshaft123.1.4 Notching Relay123.1.5 Motor Resistance Control and Protection133.1.6 The Chopper Controlled 6E1 Train DC Power Circuit133.2 Basics of DC Series motor143.3 DC chopper153.3.1 Control Strategies [3]163.3.2 Thyristor Chopper circuit173.3.3 Troge Chopper173.4 Regenerative braking183.5 Control loops194. Design Calculations204.1 DC series motor204.2 Trge chopper215. Simulations and results235.1 Troge Chopper235.2 Regeneration285.3 The Troge Chopper Circuit with control loops305.3.1 Speed controller305.3.2 Current controller315.3.2 Torque load system316. Efficiency of the DC Chopper circuit337. Conclusion33References33Appendix I: Time Plan34Appendix 2: Results34Speed controller34Current controller36Appendix 3: Thyristor data sheet39

List of FiguresFigure 1: Block diagram8Figure 2 : Stripped loco and 6E1 Traction motor [1]10Figure 3: The winding process [1]10Figure 4 : Armature and fully assembled 6E1 Traction motor [1]10Figure 5: Back to Back test facility and 6E1 motor on a bogie [1]11Figure 6: The DC Power Circuit for 6E1 Loco [1]11Figure 7: Resistor control and protection circuit [1]13Figure 8: The DC Chopper Controller Power Circuit [1]13Figure 9: DC series motor equivalent circuit [2]14Figure 10: Chopper circuit (a), current and voltage waveforms (b) [3]15Figure 11: Semiconductor chopper controlled DC motor [3]17Figure 12: Basic Troge chopper circuit [4]17Figure 13: Voltage and current waveforms for Troge chopper [4]18Figure 14: Regenerative braking of a series DC motor by chopper control19Figure 15: PI Current and Speed Loops [6]19Figure 16: The Troge chopper simulated on matlab23Figure 17: The voltage waveforms across the diode, capacitor, SCR1 and SCR224Figure 18: The current waveforms across the diode, capacitor, SCR1 and SCR224Figure 19: Pulse Generator response at 30% pulse ratio25Figure 20: The Speed (rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s) at 30% Duty cycle and T = 0.0033s25Figure 21: The Speed (rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s) at 50% Duty cycle and T = 0.0033s26Figure 22: The Speed(rad/s), Armature(A) and Electromagnetic torque(N.m) vs. Time (s) at 70% Duty cycle and T = 0.0033s27Figure 23: The Regeneration circuit simulated on matlab28Figure 24: The Speed (Rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s)29Figure 25: The Simulation Circuit with Both Speed and Current Controllers for the Troge chopper30Figure 26: Speed controller30Figure 27: Current controller31Figure 28: Torque load system31Figure 29: The Speed (Rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s)32Figure 30: Transfer function35Figure 31 :Step function before tuning35Figure 32: Matlab Graphs used for tuning35Figure 33 : Matlab graphs used for tuning36Figure 34 : Current transfer function36Figure 35 : Step function before tuning37Figure 36: Matlab graphs used for tuning37Figure 37: Matlab graphs used for tuning38

List of Symbols

Symbol Description Units R resistance I Current A N Speed rpm W Speed rad/s Efficiency Kp Proportional gain Ki Integral gain V Voltage V F Frequency Hz P Active Power kW T Period s t Time s D Duty Cycle K Motor constant

1. IntroductionA number of Industrial applications take power from DC rather than from AC Voltage sources. The Transnet Electric Locomotives, Subway Cars, Forklift Trucks, and Mine haulers are but a few examples. The majority of them on the dc traction systems are driven by series motors. The series motors have a high starting torque and they drive big loads. Their speed control is achieved mostly by a variable resistance in series with the armature and the field. The resistors are varied in steps and this speed control is known as cam controller.In case of 6E1 Traction Motors for Transnet Locos, there are 18 steps to vary resistance in order to reach maximum speed. However, armature voltage control is also being used more and more for speed control of series motors. In order to satisfy the requirements of the speed control, the DC voltage must be adjusted with the speed of the motor. The cam controller has many known disadvantages i.e. to run for a long time with resistance in circuit is not economical friendly because of the energy loss involved, the need for the resistors with high thermal rating to handle the power involved, complicated regenerative braking and starting losses.The solid state equivalent of cam controller is a DC/DC chopper. Choppers provide smooth acceleration control, high efficiency and fast dynamic response. They can be used in regenerative braking of dc motors to return energy back to into the supply and that feature results in energy savings for transportation systems with frequent stops. The problem of this project is to design a chopper controller for dc series motor. To do that I will do the following: Feasibility study, modelling of DC series motor for drive system, Chopper controller design, implement motor ratings and parameters, Matlab simulation, results and analysis.

2. Design SpecificationDesign a DC Series Motor Chopper Controller for 3kV Transnet Electric Locomotives. Control loops (Protection)

ControllerDC series motor3kV DC supply

Regenerative braking

Figure 1: Block diagram

Do a detailed Study of the DC Series Motors, their steady state and dynamic properties, DC Chopper operation, different topologies of chopper circuits. Select a dc chopper circuit to be applied on 6e1 traction motor Simulate the start-up characteristics of a dc series motor Simulate the chopper circuits and implement 6e1 traction motor ratings Include regenerative braking Include Current Controller Include speed Controller

3. Feasibility StudyBefore any design aspect can be analysed, it is important to understand the basic theory behind the operation of different components or sections of a given design project. This project required background knowledge of 6E1 DC Series machines, DC Choppers and their elements such as Thyristors, Diodes etc. and Matlab3.1 Transnet 6E1 Traction Motors Transnet Rail Engineering (TRE) is the division of Transnet that deals with the manufacture and repairs of locomotives. There are different types of traction motors used in different kinds of electric locomotives i.e. Class 6E1, 8E, 10E, 10E1, 10E2and 18E.[1]For the purpose of this design project class 6E1 is chosen. Following are pictures showing Traction Motors and the sub components comprising their assembly which are fully refurbished, remanufactured or upgraded and tested for conformance to technical specifications. Prior to delivery, the motor's output performance is load tested in the "back to back" test facility. The back to back test facility is a means of proving that after the motor has been repaired, it conforms to the original or upgraded design specification by putting the motors through a full-load test. The motor is then reassembled to the bogie. Each bogie has two motors back to back and there are two bogies in a loco which means that a loco is made up of 4 dc series motors. [1]6E1 Motor Specification [1] Motor type: 6E1 Motors per loco=4 Series field mmf = 100% Armature motor voltage =1450V Series motor current = 415A Speed = 664rpm Power = 565KW Series field resistance =0.15 Armature resistance =0.2 Overspeed = 3000rpm Interpoles= 0.016 Torque =78kNm Mutual inductance = 1.5 mH Field inductance = 25mH Armature inductance = 30mH Total inertia = 10 kg.m^2 Viscous friction coefficient = 1.07*10-6 N.m.s

Following is a stripped locomotive and a stator for dismantled 6e1 dc series motors

Figure 2 : Stripped loco and 6E1 Traction motor [1]Following is armature rewinding process

Figure 3: The winding process [1]Following is the rewound armature and the fully assembled 6e1 dc series motor

Figure 4 : Armature and fully assembled 6E1 Traction motor [1]

Following is the test facility which is a means of proving that after the motor has been repaired, it conforms to the original or upgraded design specification by putting the motors through a full-load test and two back to back traction motors on a bogie.

Figure 5: Back to Back test facility and 6E1 motor on a bogie [1]3.1.1 The Resistor Controlled 6E1 Train DC Power Circuit

Figure 6: The DC Power Circuit for 6E1 Loco [1]The above figure shows the power flow within a bogie of a loco. Two circuits connected in parallel to the 3kV DC supply are required for the loco. Each loco has two bogies which in turn has two series motors connected in series making the four total number of DC Series motors. Each Motor has four 11 resistors mounted in non-corrosive sheet steel housing. This means that the total resistance for the resistance controller for each motor is 44 [1]

3.1.2 DC Resistance ControlAs the DC motor starts to turn, the interaction of the magnetic fields inside it causes it to generate a voltage internally. This "back voltage" opposes the applied voltage and the current that flows is governed by the difference between the two. So, as the motor speeds up the internally generated voltage rises, the effective voltage falls, less current is forced through the motor and thus the torque falls. The motor naturally stops accelerating when the drag of the train matches the torque produced by the motors. To continue accelerating the train, resistors are switched out in steps, each step increasing the effective voltage and thus the current and torque for a little bit longer until the motor catches up. This can be heard and felt in older DC trains as a series of clunks under the floor, each accompanied by a jerk of acceleration as the torque suddenly increases in response to the new surge of current. When no resistor is left in the circuit, the full line voltage is applied directly to the motor. The train's speed remains constant at the point where the torque of the motor, governed by the effective voltage, equals the drag - sometimes referred to as balancing speed. If the train starts to climb a grade, the speed reduces because drag is greater than torque. But the reduction in speed causes the back voltage to decline and thus the effective voltage rises - until the current forced through the motor produces enough torque to match the new drag. [1]3.1.3 CamshaftMost DC electric traction power circuits use a camshaft to open or close the contactors controlling the resistances of the traction motor power circuit. The camshaft is driven by an electric motor or pneumatic cylinder. The cams on the shaft are arranged to ensure that the contactors open and close in the correct sequence. It is controlled by commands from the driver's cab and regulated by the fall of current in the motor circuit as each section of resistance is cut out in steps. The sound of this camshaft stepping can be heard under many older (pre electronics) trains as they accelerate. [1]3.1.4 Notching RelayA DC motor power circuit relay which detects the rise and fall of current in the circuit and inhibits the operation of the resistance contactors during the acceleration sequence of automatically controlled motors. The relay operates a contactor stepping circuit so that, during acceleration of the motor, when the current falls, the relay detects the fall and calls for the next step of resistance to be switched out of the circuit. [1]3.1.5 Motor Resistance Control and Protection

Figure 7: Resistor control and protection circuit [1]

The above circuit tries to explain what has been discussed above. The DC motors are controlled by a "notching relay" set into the power circuit. But there are other relays provided for motor protection. Sharp spikes of current will quickly damage a DC motor so protective equipment is provided in the form of an "overload relay", which detects excessive current in the circuit and, when it occurs, switches off the power to avoid damage to the motors. Power is switched off by means of Line Breakers, one or two heavy-duty switches similar to circuit breakers which are remotely controlled. They would normally be opened or closed by the action of the driver's controller but they can also be opened automatically by the action of the overload relay. [1]3.1.6 The Chopper Controlled 6E1 Train DC Power Circuit

Figure 8: The DC Chopper Controller Power Circuit [1]The objective of the project is to design a DC chopper for 3kV DC Electric Locomotives. The circuit above is a flow diagram of the system to be studied, designed, simulated and implemented [1]3.2 Basics of DC Series motor

Figure 9: DC series motor equivalent circuit [2]DC series motor, with its own characteristics of high starting torque which makes it suitable for high inertia as well as traction systems which has a nonlinear dynamical model. As its name indicates, the field circuit is connected in series with the armature and therefore the armature and field currents are the same. The equivalent circuit of a DC series motor is as follows. [2]Therefore, with the additional relation that = the differential equations are:

The dynamic equations are:

3.3 DC chopperA chopper is a high speed on" or off semiconductor switch. It connects source to load and load and disconnect the load from source at a fast speed. In this manner, a chopped load voltage as shown in the figure below is obtained from a constant dc supply of magnitude Vs. For the sake of highlighting the principle of chopper operation, the circuitry used for controlling the on, off periods is not shown. During the period Ton, chopper is on and load voltage is equal to source voltage Vs. During the period Toff, chopper is off, load voltage is zero. In this manner, a chopped dc voltage is produced at the load terminals. [3]

Figure 10: Chopper circuit (a), current and voltage waveforms (b) [3]Average Voltage, Vo = (Ton/ (Ton+Toff))*Vs = (Ton/T)*Vs =Vs Ton=on-time. Toff=off-time. T=Ton+Toff = Chopping period. =Ton/Toff.Thus the voltage can be controlled by varying duty cycle . Vo = f* Ton* Vs f=1/T=chopping frequency.

3.3.1 Control Strategies [3]The average value of output voltage Vo can be controlled through duty cycle by opening and closing the semiconductor switch periodically. The various control strategies for varying duty cycle are as following: 1. Time ratio Control (TRC) Time ratio Control (TRC) in this control scheme, time ratio Ton/T (duty ratio) is varied. This is realized by two different ways called Constant Frequency System and Variable Frequency System as described below:a) CONSTANT FREQUENCY SYSTEMIn this scheme, on-time is varied but chopping frequency f is kept constant. Variation of Ton means adjustment of pulse width, as such this scheme is also called pulse-width-modulation scheme.b) VARIABLE FREQUENCY SYSTEMIn this technique, the chopping frequency f is varied and either (i) on-time Ton is kept constant or (ii) off-time Toff is kept constant. This method of controlling duty ratio is also called Frequency-modulation scheme.2. Current-Limit Control.In this control strategy, the on and off of chopper circuit is decided by the previous set value of load current. The two set values are maximum load current and minimum load current. When the load current reaches the upper limit, chopper is switched off. When the load current falls below lower limit, the chopper is switched on. Switching frequency of chopper can be controlled by setting maximum and minimum level of current. Current limit control involves feedback loop, the trigger circuit for the chopper is therefore more complex. PWM technique is the commonly chosen control strategy for the power control in chopper circuit.For the purpose of this design Time ratio control will be used because we are using thyristors as switches.

3.3.2 Thyristor Chopper circuitThyristors can be used in various combinations but whatever the choice the overall problem is either the voltage adjustment of the supply to the armature or the field winding. A matching thyristor unit can be placed between the supply and the motor. The thyristor chopper circuit will be used in this case because of the high dc supply which will use constant frequency pulse width modulation. The chopping frequency used will be 300Hz. [3]

Figure 11: Semiconductor chopper controlled DC motor [3]3.3.3 Troge Chopper

Figure 12: Basic Troge chopper circuit [4]The two SCRs used above give a higher degree of control and flexibility. One is used to turn on and other to turn off. SCR2 is triggered first, capacitor C charges to positive on the SCR1 side through the motor from applied voltage Vb. SCR1 is triggered, load current flows through the capacitor voltage reverses polarity through SCR1, L and D1. On retrigger of SCR2, load current id diverted away through SCR2 and C, SCR1 commutes. Capacitor C recharges to original polarity. The above model uses a pulse generator to fire the gate of the thyristor. SCR1 is fired directly from the pulse generator and SCR2 is fired from the pulse generator through a not gate. [4]

Figure 13: Voltage and current waveforms for Troge chopper [4]

3.4 Regenerative braking In the absence of chopper control, a series motor cannot undergo regenerative braking. Therefore chopper control is essential for the regenerative braking of a series DC motor. It essentially uses a step up chopper with the motor forming the low voltage side and the source the high voltage side. In regenerative braking, the series motor works as a self-excited DC generator. It requires the field to be reverse with respect to the armature, compared to their connection the motoring operation. A filter is connected between the source and the chopper in order to reduce fluctuations in the source current and voltage. [5]

Figure 14: Regenerative braking of a series DC motor by chopper controlA dc chopper circuit in a regenerative braking is shown in the figure above. When the main thyristor T1, and reversing thyristor T3 are fired, the machine current increases exponentially due to short-circuiting the machine terminals, and simultaneously the charge on the commutation capacitor C is reversed through the resonant circuit formed by the reversing thyristor T3 and reversing choke L1. Firing thyristor T2 causes a reverse loop current through the main thyristor and reduces the forward current below the holding current; and the main thyristor is switched off. Once the main thyristor switches off, the commutation capacitor discharges and recharges through the machine at a rate determined by the machine current. When the commutation capacitor is recharged to the filter capacitor voltage, the diode D1 is forward biased and the machine regenerates to the supply.3.5 Control loops

Figure 15: PI Current and Speed Loops [6]When the machine is made to run from zero speed to a high speed then motor has to go to specified speed. But due to electromechanical time constant motor will take some time to speed up. But the speed controller used for controlling speed acts very fast. Speed feedback is zero initially. So this will result in full controller output and hence converter will give maximum voltage. So a very large current flow at starting time because back Emf is zero at that time which sometime exceeds the motor maximum current limit and can damage the motor windings. Hence there is a need to control current in motor armature. To solve the above problem we can employ a current controller which will take care of motor rated current limit. The applied voltage Va will now not dependent on the speed error only but also on the current error. We should ensure that Va is applied in such a way that machine during positive and negative torque, does not draw more than the rated current. So, an inner current loop hence current controller is required. [6]4. Design Calculations4.1 DC series motor From 6e1 Traction motor specification: Armature motor voltage Eb = 1450 V Armature resistance Ra = 0.2 Field resistance Rf = 0.15 Armature Current Ia = Field Current If = 415A Rated speed N = 664 rpm Field inductance = 25 mH Mutual inductance = 1.5 mH Armature inductance = 30mH Power = 565kwV = + + = 1450 + (415) (0.2) + (415) (0.15) = 1595.25 V

P = Tw 565 = T (664*)T = 8125.53 N.m

4.2 Trge chopper

i. Capacitor C

Tq= 250s . . . obtained from the datasheet [Appendix]

Peak voltage = 1.5VB = 2392.88V

ii. SCR1

For SCR1 is chosen to be 500 . . . obtained from the datasheet [Appendix]

Vrev = 2VB = 3190.5VVfor = 2VB = 3190.5V

iii. SCR2

= 1000 . . . obtained from the datasheet [Appendix]Vrev = 2VB = 3190.5VVfor = 2VB = 3190.5V

iv. 2.4) Diode D

i.

ii.

iii. Vrev = 2VB = 3190.5Vv. 2.5) Min ON time

5. Simulations and results5.1 Troge ChopperThe simulation model was used to verify the theoretical results of the Troge chopper. A pulse generator was used to fire the gate of the thyristor. SCR T1 was fired directly from a pulse generator. And SCR T2 was fired from the pulse generator through a not gate. The aim of that was to fire a different SCR at a different time. The results of the simulation were obtained for different pulse ratios. They were taken at 30%, 50% and 70% pulse ratios.

Figure 16: The Troge chopper simulated on matlab

Figure 17: The voltage waveforms across the diode, capacitor, SCR1 and SCR2

Figure 18: The current waveforms across the diode, capacitor, SCR1 and SCR2These above waveforms are used to verify the voltage and current calculations of the troge chopper with regards to the voltage and current across the capacitor, diode, SCR1 and SCR2.

Figure 19: Pulse Generator response at 30% pulse ratioThe above graph is the waveform to show that the pulse generator which is set to a chopping frequency of 300 Hz and a period of 0.0033s. The duty cycles were taken at 30%, 50% and 70%.

Figure 20: The Speed (rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s) at 30% Duty cycle and T = 0.0033sThe above graph which the duty cycle was set to 30% in the pulse generator and a speed of 190 rad/s. after 5 seconds a step was input at the load torque of the motor and the speed reduced to 100rad/s.

Figure 21: The Speed (rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s) at 50% Duty cycle and T = 0.0033sThe above graph which the duty cycle was set to 50% in the pulse generator and a speed of 300 rad/s. after 5 seconds a step was input at the load torque of the motor and the speed reduced to 180rad/s.

Figure 22: The Speed (rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s) at 70% Duty cycle and T = 0.0033sThe above graph which the duty cycle was set to 70% in the pulse generator and a speed of 530 rad/s. after 5 seconds a step was input at the load torque of the motor and the speed reduced to 300rad/s.DiscussionThe troge chopper was implemented on the dc series motor for speed control and from the results above it can be clearly seen that as the pulse modulation is being changed hence the speed and armature current is increasing and decreasing in accordance with the pulse modulation and speed control has been established. The specifications of the dc series motor on matlab can be found under the design specifications above.

5.2 RegenerationTo configure a regenerative chopper an SCR is connected and is in the opposite direction of the other two SCRs as seen in the figure below. For the circuit to regenerate, the armature voltage and armature current must have opposite polarities, applied Torque TL must be bigger than the generated Torque Te and the speed must be negative. The operation of the circuit is as detailed in section 3.4

Figure 23: The Regeneration circuit simulated on matlab

Figure 24: The Speed (Rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s)DiscussionThe above simulated results show negative armature current, negative speed and TL > Te. The results conform to the requirement for regenerative chopper.5.3 The Troge Chopper Circuit with control loops

Figure 25: The Simulation Circuit with Both Speed and Current Controllers for the Troge chopper5.3.1 Speed controller

Figure 26: Speed controllerThe speed controller designed in Matlab Simulink is shown in Figure 26 above. The inputs to the controller are the speed reference (in rpm) and the rotor speed of the motor. The rotor speed is subtracted from reference speed to produce an error. This error is then converted to per unit value by dividing the error value by the rated speed (base speed). This value is then the input to the PI controller and the output from the PI controller is the armature current reference (in per unit) which is used by the current controller in order to obtain the electromagnetic torque needed to reach the desired speed. The speed ramp is used to define the acceleration and deceleration of the speed in order to avoid sudden reference changes that could cause armature over-current and destabilize the system5.3.2 Current controller

Figure 27: Current controllerThe current controller designed in Matlab Simulink is shown in Figure 27. The controller inputs are the current reference (in per unit) from the speed controller and the armature current flowing through the motor. The armature current is first converted to a per unit value by dividing it by the rated current (base current) and it is then subtracted from the current reference to produce an error which is the input to the PI controller. The arccosine function is used to linearize the control system. 5.3.2 Torque load system

Figure 28: Torque load systemFigure 28 below shows the subsystem of TL block which is the feedback loop for the torque load. The input is the rotor speed (rad/sec) of the motor which is squared and then multiplied by the output of block sign. The block sign is used to keep the sign (positive or negative) of the speed input after the speed has been squared.

Figure 29: The Speed (Rad/s), Armature (A) and Electromagnetic torque (N.m) vs. Time (s)DiscussionThe initial speed reference is set to 0 rpm, the armature current and the electromagnetic torque is also zero. At t = 0.05s the speed reference is set to 1100 rpm. This causes the armature current and electromagnetic torque to rise and reach a steady value of 600 A and 550 Nm respectively. The speed also rises and reaches the reference speed 1100 rpm.At t = 5s the speed reference is then set to 1900 rpm. The motor begins to decelerate and this causes the armature current and electromagnetic torque to decrease and reach a steady value of 450 A and 300 Nm respectively. t =10s the speed reference is then set to 1100 rpm. This causes the armature current and electromagnetic torque to rise and reach a steady value of 600 A and 550 Nm respectively. The speed also rises and reaches the reference speed 1100 rpm.The graphs of the speed, armature current and electromagnetic toque are shown above the purpose of the control loops is basically used as a protection device for the motor we can compare the graphs before the control loops in figures 20, 21 and 22 it can be seen that when the motor starts up there is a lot of current drawn which can be seen by the rising and settling of the graphs which could damage the motor due to overcurrent. Therefore control loops are important to reduce this over current as it can be seen in the graphs above that the graphs does not have a sudden rise and drop of current due to the control loop. 6. Efficiency of the DC Chopper circuit The efficiency is defined as output power Pout over input power Pin. Pin = V x I = 1595.25 *415 = 662.03kW. Pout = Torque x Speed = 500 * 1100 = 550 kW Therefore Efficiency of the Chopper = 550kW/662.03kW * 100% = 83.07 %.7. ConclusionThis report concludes the work that was done for the design project: Design a 3kV SCR controller for Transnet DC series traction motor . The work that was covered in this design project included information on the 6E1 DC series Transnet motor, thyristor ratings, Dc choppers, simulation results for the DC chopper and regenerative braking and optimization of control loops. The voltage and current rating of the thyristor was calculated so that an appropriate thyristor could be chosen. The troge chopper was simulated and the calculations of the SCR, diode and capacitor were verified by simulation results and speed control can be seen at different duty cycles. The regenerative circuit was simulated and produced graphs that determined that regenerative braking was taking place. The speed controller and current controller were added to the simulation circuit. The circuit had then been successfully simulated and from the graphs obtained. To optimize the performance of the drive the control loops were tuned using Sisotool. The simulation was done again with the optimized controllers and a noticeable difference could be seen from the results obtain. It took a much quicker time to reach the steady state value of the reference speed. The aim of the project to design a motor controller for Transnet dc series motor with regenerative braking included and this has been successfully achieved and all design specifications had been adhered. It was also a requirement that the protection be implemented to protect semiconducting devices and the motor from getting damaged during fault conditions. The fast fuses can be used for protection but must be designed in accordance with the armature current rating of the motor and must be installed in series with armature of the motor.References1. Transnet Rail Engineering, ERS Workshop Bayhead Durban.2. Dr. Zainal Salam, UTMJB. Power Electronics and Drives. [Online] 2003. [Cited: July 12, 2011.] encon.fke.utm.my/courses/see_5433/dc_m.pdf.3. Bimbhra, P.S., Power Electronics. New Delhi, Khanna Publishers, 2006.4. SCR forced commutation.pdf, Power Electronics 3 practical handout, Prof. E.J Odendal, 20095. M D Singh, K B Khanchandani. Power Electronics. s.l. : McGraw-Hill, 20076. Hughes, A. Electric Motor and Drives, Third Edition. 2006Appendix I: Time Plan

Appendix 2: ResultsSpeed controllerThe voltage (Va) to rotor speed () closed loop transfer function was transferred to Sisotool in order to tune and ultimately obtain the optimum proportional gain (Kp) and integral gain (Ki) resulting to the three important characteristics mentioned above. Figure 30 below show the root locus and the corresponding bode plot for the plant and the speed controller. The speed step response graph in Figure 32 was designed to have a small overshoot and fast settling time. It can be seen from the graph that the speed response of the plant has been optimized having a minimum The corresponding proportional gain (Kp) and integral gain (Ki) values for the optimized speed controller are Kp= 3.8294 x 10-3Ki= 0.95736

Figure 30: Transfer function

Figure 31 : Step function before tuning

Figure 32: Matlab Graphs used for tuning

Figure 33 : Matlab graphs used for tuningCurrent controllerSimilarly the voltage (Va) to armature current (Ia) closed loop transfer function was transferred to Sisotool in order to tune and ultimately obtain the optimum proportional gain (Kp) and integral gain (Ki). Figure 36 below show the root locus method and the corresponding bode plot for the plant and the current controller. The current step response graph is shown in Figure 36 below. From the graph it can be see that the step response has almost no overshoot and a quick rise time and settling time of approximately 0.04seconds. The corresponding proportional gain (Kp) and integral gain (Ki) values for the optimized current controller are:Kp= 24Ki= 1344

Figure 34 : Current transfer function

Figure 35 : Step function before tuning

Figure 36: Matlab graphs used for tuning

Figure 37: Matlab graphs used for tuning

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