International Journal of Advanced Research in Engineering and Technology (IJARET) Volume 11, Issue 11, November 2020, pp. 82-90, Article ID: IJARET_11_11_008 Available online at http://iaeme.com/Home/issue/IJARET?Volume=11&Issue=11 ISSN Print: 0976-6480 and ISSN Online: 0976-6499 DOI: 10.34218/IJARET.11.11.2020.008

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PERMANENT TRACTION DRIVE SYSTEM FOR SUB- URBAN SERVICES IN INDIA

Dr. C. Nagamani Associate Professor, Dept. of Electrical and Electronics Engineering, Anurag University, Hyderabad, India.

Dr. T. Anil Kumar Professor and HOD, Dept. of Electrical and Electronics Engineering, Anurag University, Hyderabad, India

Dr. G. Venu Madhav Professor, Dept. of Electrical and Electronics Engineering, Anurag University, Hyderabad, India

ABSTRACT The Sub-Urban Services are the Backbone of Transportation System in Metro Cities of India. The riders expect comfortable journey from their Home to Workplace and vice versa. The Sub-Urban services are made up of Electrical Multiple Units which are driven by Squirrel Cage Induction Motors of lower Wattage. The Squirrel Cage Induction Motors work on low Power Factor, are noisy, prone to Vibrations and more bulky as compared to a Permanent Magnet Synchronous Motor of the same Power ratings. Also Gate Turn-off Thyristors are currently used for the Converter System which is less efficient as compared to an Insulated Gate Bi-Polar Transistor Drive. The Drive System with Insulated Gate Bi-Polar Transistor as switches for Rectifier-Inverter System driving Permanent Magnet Synchronous Motors as Traction Motors is proposed and simulated in this Paper Keywords: Efficiency, Electrical Multiple Units, Permanent Magnet Synchronous Motor, Power factor, Squirrel Cage , Traction Motors Cite this Article: C. Nagamani, T. Anil Kumar and G. Venu Madhav, Permanent Magnet Synchronous Motor Traction Drive System for Sub-Urban Services in India, International Journal of Advanced Research in Engineering and Technology, 11(11), 2020, pp. 82-90. http://iaeme.com/Home/issue/IJARET?Volume=11&Issue=11

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1. INTRODUCTION The Sub-Urban Services provide economical and round-the-Clock transportation to people living in Metro Cities in India. The Sub-Urban services of Mumbai, Kolkata and Chennai are best examples of this. The Electrified Sub-Urban service in India is called the Electrical Multiple Unit. It Consists of Power cum Passenger Cars and Passenger Cars of two Classes namely the Second Class and First Class. There can be different arrangements of the formation of the Electrical Multiple Units. It can consist of two power cars on both end and two passenger Cars in between. It can also consist of three or four Power Cars and six or more Passenger Cars. Essentially, a Power cum Passenger Car consists of a Driver Unit and Machine Unit in the front and Passenger section in the rear of the Car. Usually, when the rake is made up of more than 4 Passenger Cars, there will be additional Power Cars in between the formation. The noise and the Vibrations generated in these Power Cars cause considerable discomfort to the riders. The Passengers riding the Mumbai Suburban have often complained about the ride being not smooth and prone to jerking especially during Braking [1]. Hence, there is a Research going on to design a Gear-less or Direct Drive to improve the Efficiency of operation and also to reduce the discomfort caused by Vibrations by Indian Railways. It is worth mentioning here that a comfortable jerk-free, vibration-free, noise-free riding experience has been reported by Consumers in the Suburban system of Japan for which Toshiba has provided with the Power Cars consisting of a Direct Drive Technology using Permanent Magnet Synchronous Motors [3]. An attempt is being made in this Paper to suggest a new Design for Drive System of the EMUs with Permanent Magnet Synchronous Motor, which can be cost effective and also give a comfortable travelling experience to the Daily Commuters of Sub-Urban Systems in India.

2. THE EXISTING POWER CIRCUIT Each Power Car has Four Powered Axles driven by four Traction Motors which are primarily SCIM now-a-days. Each SCIM is rated at 295 kW with a rating of 2200 V. In the Power Car of EMUs, the overhead supply of 1500 V DC or 25 kV AC is connected to the traction system through a common single pantograph. The Power Circuit of the EMUs is designed in such a way that it can work with either 25 kV, 50 Hz supply or 1500 V DC supply. When the OHE supply is AC, the HVCC take the position on AC side. On closing the vacuum circuit breaker (VCB), 25 kV AC is fed to main traction transformer which in turn will step down the voltage to 1473 Volts and feed to Medium Voltage Change over switch (MVCC). A separate surge arrestor ACSA is provided to arrest the surges at primary winding of main traction transformer. When the OHE supply is DC, the HVCC takes the position on DC side. On closing the DC Circuit Breaker, 1500 V DC is fed to Medium voltage change over switch (MVCC). A separate surge arrestor DCSA is provided between HVCC and DCCB to arrest surges developed while working on DC mode. RLC (Resistor, Inductor and Capacitor) DC line filter is provided to dampen various harmonics developed while working in DC mode. The MVCC also has two positions. When OHE supply is AC, MVCC connects the single phase 1473 volts AC supply to Line converter. The GTO Line Converter is common for both the OHE supplies which can be either 25 KV AC or 1500 V DC supply. The line converter receives the input supply from Medium Voltage Change over Contactor which is either 1473 volts single phase AC supply received from secondary of traction transformer or 1500 V DC supply received from DCCB. The Line Converter coverts it to stabilized 2200 volts DC supply and feeds mainly to following three Components:

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3-Phase Traction Inverter: The GTO Traction Inverter inverts the 2200 volts DC Power to 3- phase Variable Voltage Variable Frequency and feeds 4 nos. Of traction motors connected in parallel. Three phase Squirrel cage Induction Motors are used as traction motors. Diverting : The diverting chopper functions whenever the DC link voltage exceeds above preset voltage. The diverting chopper also helps in providing dynamic brakes when the train is in regenerative braking mode and the OHE turns non receptive. Such dynamic brakes are in function for a short duration till the change over takes from regenerative braking to electro pneumatic braking. Down Chopper: It converts the 2200 volts DC to 530 volts DC and feeds to following three equipments: 20 kVA dedicated inverter for Main Compressor Motor: 20 kVA Inverter converts 530 volts DC to 3-phase 415 volts AC. 50 kVA Inverter: 50 kVA Inverter inverts 530 volts DC to 3-phase 415 volts AC, and feeds auxiliary transformer. The Auxiliary Transformer has two secondary windings which supply 415 volts 3-phase AC to Auxiliary Machines and 220 Volts 3-phase AC to Lights and Fans in coaches. The load of lights and fans are on single phase of 140 volts evenly distributed across each phase and neutral. 7 kW Battery Charger: The 7 kW battery chargers convert 530 volts DC to 110 volts DC for charging batteries and feeding control supply [2]. A Schematic of the Existing Power Circuit of EMUs in India is shown in Fig. 1.

Figure 1 Schematic of Existing Power Circuit for Electrical Multiple Units in India

3. DRAWBACKS AND RECOMMENDED IMPROVEMENTS OF THE EXISTING SYSTEM The major Drawbacks reported by the Passengers riding the Suburban Systems in India are jerks during Braking and Noise produced by the Power Car Units. The noise observed in the modern AC/DC EMUs was about 68dB. Though this is considerable reduction with the introduction of pneumatic suspension and Squirrel Cage Induction Motors in place of DC Series Motors as Traction Motors [1], it is still a cause for concern. Theses jerks and the noise can be further reduced by using a Direct Drive without the Gear Mechanism. The Permanent Magnet Synchronous Motors are ideally suited for Direct Drives and hence a three-phase PMSM can be used as the Traction Motor.

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The Existing Power Circuit has been designed for the EMUs to work on both 25 kV, 1-ph, 50 Hz AC and 1500 V DC. As all the existing Electrified Routes of Indian Railways have been changed to 25 kV, 1-ph, 50 Hz AC Traction Supply System, the use of Chopper in the Existing Circuit becomes obsolete. A Fully Controlled Rectifier would be better suited for operations on AC Supply as compared to a Chopper. Hence, a Fully Controlled Full Wave Rectifier with Insulated Gate Bi-polar Transistor as the Switching Device is being suggested in this Paper. Lastly in place of the Gate Turn-Off Thyristor based PWM Inverter, Insulated Gate Bi- polar Transistor based PWM Inverter is suggested in this Paper as the IGBTs have better thermal Stability, Over-load Capacity to with stand sudden High due to Pantograph Bounce or mis-fire of Inverter, less on-state conduction losses and less bulky Snubber Circuits as compared to a GTO.

4. FEATURES OF PMSM FOR TRACTION There are many features of Permanent Magnet Synchronous Motors that make it suitable for use as Traction Motors in Sub-Urban Services. The first and foremost feature is that the PMSM are more efficient in operation as compared to SCIM. Efficiency of 97% has been reported in Sub-Urban services in Japan [3]. The second feature is that the PMSM have reduced noise and vibrations during operation. This is a feature that is not found in Inverter fed SCIM. Thirdly, the PMSM weigh lesser as compared to a SCIM for similar Power ratings, for example a PMSM rated at 205 kW may weigh up to 565 kg whereas a SCIM rated at 165 kW may weigh 690 kg. When it comes to ventilation of Traction Motors, the PMSMs are now manufactured with self-ventilation there by reducing the need for separate Blower Motors and this has given PMSM an enhanced performance of 20% as compared to the SCIM. The noise in PMSM is reduced by about 12 dB as compared to a SCIM thus giving a quieter Motor. The Permanent are also of good quality thus eliminating the need for frequent maintenance. The PMSM also gives high reliability in operation. The Inverter driven PMSMs are smarter in operation with microprocessor control of the Drive system. Also another advantage of the PMSM is that the existing SCIMs can be replaced easily without much of retention for re-wiring and re-connections. The Interior Permanent Magnets Synchronous Motors with Distributed Windings are suitable for high Power Applications like Traction Drive Systems [4], [7], [8]. The high Torque/Volume ratio of PMSM makes it ideally suited for Traction Drives [5], [6]. Hence, a Drive System with PMSM as Traction Motors for Sub-Urban Systems driven by IGBT Rectifier-Inverter System is proposed in this Paper.

5. SIMULATION AND RESULTS The proposed circuit of Traction Drive System for Electric Multiple Units is described in this section. 5.1 Description of the Circuit: The circuit is broken up into three parts for analysis namely (a) Rectifier (b) DC Link (c) Inverter. The proposed circuit diagram is shown in Fig. 2. 5.1.1 Rectifier Circuit: Two 4-Pulse Bridges are connected in parallel to form one unit of Traction Rectifier. The input to the Rectifier is 2500 V, 50 Hz AC supply fed from the secondary Winding of the Traction Transformer which is a high impedance Transformer with a primary Voltage of 25 kV, AC at 50 Hz frequency. In this proposed circuit two secondary tapings are taken out with each supplying 2500 V to the Traction Rectifier. The output of the Rectifier is fed to the DC Link.

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5.1.2 DC Link: The Traction Rectifier output is connected to the DC Link. The DC Link consists of a Capacitor Bank of 815μF and 11.41 mF connected in parallel to filter out the Harmonics in the DC Voltage. A Diode is connected in the DC Link to ensure unidirectional current. The output of the DC Link is connected to the Traction Inverter. The details of the Circuit of Rectifier - DC Link Sub-system are shown in Fig. 3 5.1.3 Traction Inverter: The Traction inverter is a 6-Pulse Bridge Inverter circuit which is capable of generating Sine waves displaced by a phase difference of 120˚. The Pulses are delivered by means of a PWM generator. The output of the Traction Inverter is fed to the Traction Motors. The system is designed in such a way that, a Traction Inverter will supply Power to Two Traction Motors. There will be two 3-ph Inverters in a Power Car to drive the four Permanent Magnet Synchronous Motors. A pair of PMSM will be connected in parallel to be powered by an Inverter. The details of the Circuit for Inverter Sub-system are shown in Fig. 4.The circuit diagram shown in Fig. 2 is simulated using MATLAB Simulink.

Figure 2 Proposed Circuit Diagram for Drive System with PMSM for EMUs

Figure 3 Rectifier - DC Link Sub-System

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Figure 4 Inverter - Traction Motor Sub-System 5.1.4 Traction Motors: Four Permanent Magnet Synchronous Motors of the ratings 300 kW, 1800 Volts, 1500 rpm are used for the Simulation in this proposed Circuit. Two Motors are connected in parallel to be driven by an Inverter. The proposed circuit was simulated using MATLAB Simulink Software for various Speeds. The results are discussed below. 5.2 Analysis of Results: The Speed-Time curve is taken as reference. The Sub-Urban services do not have the free running period but may have a short coasting period to save energy [9]. As the distance between any two stops is about a Kilometre or more, the EMUs have Acceleration period, Deceleration period and Braking only. The same concept is implemented in this simulation by means of a simple Embedded MATLAB Program wherein the program is written with Speed reduction commands, Acceleration Commands at different time intervals. The Braking is introduced by means of connecting the Braking Chopper by gating the IGBT used in Braking circuit. The output of the DC Link was observed to be a constant of 2200 V during the period of Acceleration of the Traction Motors. When the Braking Chopper was introduced, the DC Link Capacitor discharged increasing the DC Link Voltage to about 3000 V. The Voltage levels of the DC Link observed are shown in Fig. 5.

DC Link Voltage 4500

4000

3500

3000 t l o V 2500 n i

e g a

t 2000 l o V 1500

1000

500

0 0 2 4 6 8 10 12 14 16 18 20 Time in seconds

Figure 5 DC Link Output Voltage In line with the DC Link Voltage, the Traction Inverter Output Voltage was observed to be 2200 V, 3-ph AC at 50 Hz. The Inverter Voltages dropped to zero during the time period when the Inverter side Circuit Breaker was closed to initiate Braking mode of operation. The Traction Inverter was given pulsation by a simple PWM Generator. The principle of Control

http://iaeme.com/Home/journal/IJARET 87 [email protected] C. Nagamani, T. Anil Kumar and G. Venu Madhav was Variable Voltage Variable Frequency with constant V/f control for varying the Speed of the Traction Motors. It is also observed that the transients during the transition in Speed and during Braking are minimal and the System reached Steady state faster. The observed Inverter Output Waveforms are shown in Fig. 6.

Inverter Output Voltage

3000

2000

1000 s t l o V

n i 0 e g a t l o

V -1000

-2000

-3000

0 2 4 6 8 10 12 14 16 18 20 Time in seconds

Figure 6 Inverter Output Voltage The Traction Motors were initially accelerated up to time t = 2 seconds. The Motors reached their rated Speed of 1500 rpm. At time t = 2 seconds, the Speed required at the Wheel is specified as 80 Kmph which is converted to Motor Speed of about 750 rpm. After the deceleration period of 1 seconds, Braking is initiated at t = 3 seconds. The Motors are again accelerated from time t = 5 seconds. The process of deceleration and Braking again initiated at time t = 10 seconds with Motor Speed being brought down to 500 rpm. Again at time t = 14 seconds, the Traction Motors are accelerated. The Simulation was run for a time period of 20 seconds of the Simulation Time in MATLAB. The various instances of operation of the Traction Motors are recorded in Graph depicted in Fig. 7.

Traction Motors Speed 4000

3000

Acceleration 2000 Deceleration and Braking Deceleration and m p r

Braking

n 1000 i

d Accele- e

e ration p

S 0

-1000

-2000

0 2 4 6 8 10 12 14 16 18 20 Time in seconds

Figure 7 Traction Motors Speed Curve

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Motor Parameters Motor Type Three Phase Permanent Magnet Synchronous Motor Nominal Power 300 kW Voltage (line-line) 1800 V Frequency 50 Hz Rated Speed 1500 rpm No. Of poles 4 Resistance 3 Ω Stator Inductance 0.021435 Ω

6. EQUATIONS AND CALCULATIONS It is assumed that the EMU starts on a plane surface without Gradient and Curvature hence, the Tractive Effort required would be only Tractive Effort for Acceleration. Let us assume that the Electrical Multiple Unit has 12-Car formation with four Power Cars and eight Trailing Passenger Cars (most common formation of EMU on Indian Railways Suburban System). There are four Traction Motors per Power Car and hence, 16 Traction Motors in 12- Car Formation of Rake. Let us assume that the EMU has to be accelerated to 60Kmph in about 60 seconds.

(a) Calculation of Tractive Effort: Weight of each Power Car = 60 tonnes

Weight of four Power Cars = Wl = 240 tonnes Weight of each Trailing Passenger Car = 33.6 tonnes

Weight of eight Trailing Passenger Car = Wt = 268.8 tonnes

Total Weight = W = ( Wl + Wt ) = 508.8 tonnes

Effective weight of Power Cars and Trailing Passenger Cars = We =   = 560 tonnes  Acceleration, α in Kmphps will be given as,      Tractive Effort for Acceleration ( Fa):   

Tractive Effort required for Acceleration = Fa =       

(b) Calculation of Power, Torque developed: Voltage per phase = 2000 V Current per phase = 100 A Power Factor = 0.95 (Assumed) Efficiency of the Machine = 97% (Assumed) Frequency = 50 Hz, No. Of Poles = 4, Diameter of the Wheel = 1092 mm Efficiency of the Gear = 0.9

Gear Ratio for EMU = Gr = 3.6 Power input to the PMSM =        =        Watts = 329090 Watts (per Motor) Power Output per Motor = 0.97 x 329090 = 319216 Watts   Speed of the PMSM = Ntm =  rpm =  = 1500 rpm   Torque developed per Machine =  Nm =  Nm = 2032 Nm

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Total Torque developed by 16 Traction Motors = Td = 32512 Nm      Tractive Effort Developed =    = = 193 kN      Speed of the EMU at Wheel =         = = 85.76 Kmph (at rated Speed of the  Traction Motor)  =  = 42.88 Kmph (During Deceleration) 7. CONCLUSIONS The Simulation of Permanent Magnet Synchronous Motor driven by 3-ph PWM Inverter with Insulated Gate Bi-polar Transistors as Switching Device was carried out. The Permanent Magnet Synchronous Motor was observed to have a quick transient response to variations in Speed and Braking Mode of Operations. As the Permanent Magnet Synchronous Motors have high Torque/Volume ratio, are self-ventilated, fully enclosed and have higher efficiency of operation, they can be adapted as Traction Motors for Electrical Multiple Units. For operating conditions like a dry tropical climate and polluted environment where in dust accumulation in Traction Motors are a serious problem, a fully enclosed Motor like the PMSM is ideally suited. As the noise and vibrations are considerably reduced in a PMSM, the ride in a Sub- Urban service would be very comfortable for the daily Commuters. As the EMUs are basically Passenger Cars, the Power output has to be constant with quick Acceleration and Deceleration which means they have to be lighter in Weight. Also as the present Power Cars can be easily re-configured to replace the existing Squirrel Cage Induction Motors with Permanent Magnet Synchronous Motors, it can be concluded that the Permanent Magnet Synchronous Motors Drive driven by Insulated Gate Bi-polar Transistor Converter System is ideally suited for Electrical Multiple Units in India.

REFERENCES [1] P.C. Sehgal, Teki Surrayya, “Innovative Strategic Management: The Case of Mumbai Suburban Railway System” , Vikalpa,Vol 36, No. 1, Jan-March 2011. [2] “A Course on 3-Phase Technology in Electric Traction Systems”, Indian Railways Institute of Electrical Engineers, Nasik, India. [3] Toshiba “Products Brochure on adjustable Speed Drives”, Toshiba Japan – 2014. [4] R. Krishnan “ Drives-Modelling, Analysis and Control” Prentice Hall, India. [5] Kondo Minoru “Application of Permanent Magnet Synchronous Motor to Driving Railway Vehicles”, Railway Technology Avalanche, No. 1, January 2003. [6] Jussi Puranen “Induction Motor versus Permanent Magnet Synchronous Motor in Motion Control Applications: A Comparative Study”, Thesis submitted to Lappeenranta University of Technology, Digipaino 2006. [7] Marek Franco, Jozef Ondrejicka, Jozef Kuchta “Development and Examination of Interior Permanent Magnet Synchronous Traction Motor” IEEE Proceedings 2012. [8] Hyung-Woo Lee, Chan-Bae Park, Byung-Song Lee “Performance comparison of the railway traction IPM motors between concentrated winding and distributed winding”, IEEE Proceedings 2012. [9] H. Partab "Modern Electric Traction", Pritam Surat Publications.

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