Startup railway vehicles with asynchronous traction motors

Gabriel Popa 1, Sorin Arsene2, Mihai Mihailescu3 lUniversity Politehnica of Bucharest, 2University Politehnica of Bucharest, 3Fujitsu Romania

1 gabi2I popa@yahoo.com, 2sorinarsene@gmaiLcom, 3m ihai. m ihai lescu@opensys.ro

Abstract- The traction motors, in order for the vehicle to operate at the start up regime. The analysis of the control parameters was accomplished considering the case of a 6400 kW locomotive with four asynchronous tri-phase traction motors.

I. INTRODUCTION

The railway operators are influenced by many elements in the economic efficiency analysis of the railway companies. One of the most important elements is to respect the travel time (even to travel faster). The travel-time is the main reference system, especially when they are related to the fuel or electric energy consumption. The traction optimization involves the respect of the time-travel and a low level of fuel or electric energy consumption related to the volume of the transported passengers or cargo. This may be achieved by means of a strict control of the traction force and of the travel speed which should be optimized in respect to the maximal efficiency characteristic, using as much of the vehicles power as possible.

II. THE START UP REGIME

During the start up the speed varies from zero to the value which corresponds to the constant power traction characteristic. This regime is characterized by an accelerated movement of the vehicle and the equation of motion has the form:

dv (t) = <p . (r(v(t» - revet)) + ri) (1) dt

where: <I> is the acceleration; f(v(t)) is the traction force; revet)) is the resistant force; vet) is the running speed; ft<:v(t)) is the braking force; rj(t) is the force caused by the railway slope.

At start up the running speed is a variable function of time or space. This function depends on the necessary time to reach the constant power regime and on the variation of the acceleration. Even if the railway slope is constant the acceleration changes its value. The first reason is that it depends on the variation of the traction force of the locomotive and the second is that it depends on the resistant force, which is a function of speed.

978-1-4673-1372-8/12/$31.00 ©2012 IEEE

The actual tendencies of perfectioning the railway transport are in regard to the increase of the running speed and the passengers comfort. In order to obtain a higher speed it should be achieved a higher acceleration while the comfort is in inverse proportion with the square of the acceleration. Therefore, to simultaneously fulfill these demands a modem solution became necessary. This solution should shorten the start up time, especially for the passenger trains frequently stopping and it should improve the travel conditions diminishing the shock transmitted to the passengers. These conditions are fulfilled if the start up acceleration is constant and it has its maximum value.

For vehicles powered by three phase induction motors with slip rings, the speed is controlled by the number of pole pairs and by the frequency of the supply voltage. The intensity of the traction force is given by the value of the supply voltage. The current is constant and it should not overheat the motor.

The start up regime is related to the values of Fa, Po, V, U, I, f, s and Ku.

The necessary traction force is imposed by the demand of a stabilized functioning regime. For the start up the following choices should be considered: Fa = constant or dv/dt =

constant. In the period of the start up the speed varies 0 < V < Va, while the frequency, between fp < f < fa, where fp is the start up frequency and the point a is the beginning of the nominal functioning regime.

The choice a = dV/dt = constant may not be applied for railway vehicles for the following reasons: the total train weight Gt and the railway slope may not be foreseen for any part of the line. More than that, the traction force may surpass the adherence limit and the motor wheels may slip. This choice may be applied only for the towing of passenger trains where the adherent mass of the vehicle isn't of much importance.

The value of the main vehicle regime frequency should be the main motors frequency.

The analysis of the control parameters was accomplished considering the case of a 6300 kW locomotive with 4 asynchronous traction motors with slip rings. The maximum running speed is 240 km/h and the main speed is 144 km/h. The traction characteristic of the engine is presented in Fig. 1.

III. THE START UP REGIME

We shall study the start up regime in the case of a traction force which is held constant till the main regime is reached. The over-demand coefficient T is also constant.

For the main regime, the critical slip Sk is given by the real solution of the function, fig. 2.

where:

S4 _ b. 3 2 F (s1 ) = a· sk + c, S + d· s - e, n ( k k Ie

1\ \ 1\ \

\ 1\ " " F(V) 2 ·j()S

(2)

I 240

S = sk . (T - �) , (3)

For the main regime we obtain Sial = 0,12, s,,=0,04, f,,=74,787 Hz and for the entire domain of values the solutions are plotted in Fig. 3.

'-... \ \ r---r--I� l\ � F a(v) Fig. 3 The function Fn( sn) for all the speed values

-"'- "\

'" � �V)\s.j()s

-

2) )0 7) [00 12:;. [)O [7) 200 22) 2:;.0

[kmlh] Fig. 1 The traction characteristics of the engine

0.05

-0.0

-0.5

Fig. 2 Function Fn( sk) plot

Taking into account the relation:

0.4

.. 239.5 ..

0.5

For the startup regime between ° and 144 km/h the control parameters variation is represented in the figures 4 - 10.

�

c1376x 1 03"

U(Va)

1500

1000

500

o 0

-- ---

(

---

/ V"

---

V

---

/ ---bni4� /

W � M W 100 lW 1� 1M V d(V a) c144" [km/h]

Fig. 4 The variation of the tension in the start up regime

150 0

100 0

[V] 500

-- ---

(

---

V

---

V

---

/

---

./ �

- - - r� l� V 478

] 0 20 30 40 50 60 70 80

fano�Va) [Hz]

Fig. 5. The relation between tension and frequency

601--��--_+----�--�--�----+----1

i \ fanom(Va) 40 �----++-'\:-+---+-----t---+----+--�

i \, [Hz]

[Hz]

20 1--�

,

�--_+--���-----t----+----+----1

: --r--_ o 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

sa tYa) Fig. 6. The relation between slip and frequency

80

60

20

00

- o :�-:\ 1

---- ---- ---- 747R7 ----

1

� 1 1 1 1 1 1 1

0.2

� r--r--OA 0.6

ska(Va) 0.8

Fig 7. The relation between frequency and critical slip

150

100

50

-- --- --

/� ) ( 0 10

V 20

--- -----V�7;7 /'

V /

30 40 )0 f anom (v a)

[Hz]

60

Fig 8. The relation between running speed and frequency

150 ,---,--,------,------,------,---��

50 I----"------t-----"':--t------+------+------I

0.2 OA 0.6 S ka (V a) 0.8

Fig 9. The relation between running sped and critical slip

150 L144" --ov---o:r 1

1 100

1 \ 1 1

:c 1 E 1

--- --- -------- 44 ----

\ V d (V a) 1 �-- 1 1

50 "'-1 1 1 ............. 1 r--1 --1 -.5" o

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

LO.04" S a (V a) LO.332"

Fig 10. The relation between running speed and slip

In order to realize the optimal train regime, it's important to relate the electrical and mechanical parameters of the train, respectively the running speed and the acceleration. For the case we study, considering a train mass of 389 tones, the startup acceleration is presented in Fig. 11, 12 and 13.

0.33

0.32

0.31

0.3

029 � "'0.28

Q,2i

026

0,25

0.24

0.33

0.32

0.31

0.3

f O.29

0,28

0,27

0,26

0.25

-� r-+-� -. �

� "-"' �

"

10 30 40 fanom[Hz]

60

Fig. II. The relation between train acceleration and frequency

f.'" � -

v /

4 , 0.05 0.1 0.15 0.2 0." 0.3

Fig. 12. The relation between train acceleration and slip

70

...

0.35

03 3

03 2

03 1

3

0.29

029

0.27

0.26

0.25

0.24

V 1

� -.

01 0,2

� I+"" �

03 04 05 06 ,k.

07 08 09

Fig. 13. The relation between train acceleration and frequency

11

If s and Sk decline while the frequency increases, hence the running speed increases, it follows that the rigidity of the vehicle characteristics also increases all at once with the speed.

For different values of the startup frequency there are two ways to control the locomotive by frequency and by tension:

The constant values of the tuning coefficient Ku=U/f are held only when the speed values are in the domain 0 - Va. Tn this case, for all the control values the traction forces are constant while the powers and the tensions have a linear variation. Fig. 14.

The values of the tuning coefficient will remain constant until the constant power characteristic is reached. In this case, the traction forces obtained will be constant even for speeds which are higher then Va. Fig. 15

Fo,Po U, f al

.... ----- Po

��-+-------Umax f

. ..,_...,...:;....� ___ Umin

\,...I;C-:�::""�F-----po min

o � V Fig 14. The relation between the main functioning characteristics and the

running speed

If we take into account the fact that for the frequency f < �, and mostly at low frequencies the influence of the resistance Rl on the torque cannot be anymore neglected in comparison

to the sum of the dispersion withstanding (the maximal torque of the motor, respectively the traction force of the vehicle, decreases while the frequency increases).

Fo,Po U,f ....-_____ b3

U

bl

o Va Vb V Fig 15. The relation between the main functioning characteristics and the

running speed

In order to realize a rigorous control and a constant traction force during the entire start up period, at low frequencies it is necessary to take into account the correction due to the tension.

We must also mention that a rigorous design of the traction motor and a suitable control solution allow to obtain a traction force which shall be very close to the adherence limit. This will contribute to the substantial improvement of the traction performances, especially when a train is running up a ramp with a large inclination, Fig. 16. At low frequencies this aim will not be achieved without a correction of the tension.

TV. THE ASYNCHRONOUS TRACTION MOTOR MODEL

We have determined the necessary values of the control parameters in the precedent paragraph and we will now analyze the behavior of the considered actuating system when it produces the locomotive traction force. In order to achieve this we considered the three phase induction motor model of the damped rotary vector as in Fig. 15 .

(4)

.' 3L . .' 3L o = R 212 + (L 2 + � )(p - Jill 2 )1 2 + � (p - jill 2 )i 1 (7)

, jS. i 2 = e 12 (8)

numitor

i1

Integrator

Sine Wave B Scope

Fig 15. The correction coefficient of the tension.

We analyze the control by tension and frequency considering the tensions given by:

For the tension control we took into account the correction and for the correction factor the values presented in Fig.16. As one can see, this assumption is essential for frequency values between 0-5 Hz.

]5

]0

r(f p) 5

"----2

f p [Hz]

I

4

Fig 16. The correction coefficient of the tension.

5

The answer of the control system at start up is presented in Fig.17. and Fig.18., and at nominal regime is presented in Fig.19.

,15YIO�

� F . 1,1

2'1� 1.5'10'

1'10'

5 '104

-----

/ J

I 115761� ------------ ------V

0.5 1.5 � �.o �

]sec] Fig. 17. The traction force of the locomotive at start up for a frequency value

ofO,7 Hz

�1.6 4i:lO�

� F. I,i

,-234�

21e? I lSlO" T

/ lie?

5'104

/ /

) 0.5

,Q di.O [sec]

I 15761e?

15

Fig 18. The traction force of the locomotive at start up for a frequency value ofl Hz

,2 04Al& VHY

210'

18·10' 1.5760'

� F .. 1&10' 1,1

0 14'10'

12·10'

110' 110' 0 0.5 1.5 ,Q 9,0 2

[sec] Fig. 19. The traction force of the locomotive at the end of the start up for a

frequency value of 74,787 Hz and a speed value of 144 km/h

U sing the asynchronous motor model and the control parameters analysis model which was formerly described, we obtain the traction force through a rigorously control system for to values of the towed masses Fig.20.

F�V ) Rt.38$Y)

� Rt.20�Y) F1 (V ) F�V )

\

0 0 50 100

I I

14�

150 VJV )

[km/h]

�4

200 250

Fig. 20. The traction force of the locomotive for two values of the towed masses

V. CONCLUSIONS

The analysis model developed in this paper for the transitory processes of the three phase induction motors at start up led us to the following conclusions regarding its potential use:

1. The study allows the analysis of the traction motor stability at start up and it allows corrections for the electric parameters of the electric motors to make the suitable for the railway traction.

2. The selection of the optimum control system and the proper motor design enables the use of the motor at the adherence limit which contributes to the substantial improvement of the vehicle performances especially when it circulates on ramps.

3. The determination of optimal criteria for the control system and for the traction motors adjustment.

4. The control by means of tension is the optimal solution through the rigorous control of the asynchronous motor frequency and tension of the stator.

5. In the case of control through frequency and tension the systems construction is simple and the reliability is very good.

6. The analysis of the transitory regimes of the motor is very important for the tuning of electric parameters and of the maximal values of the oscillating electromagnetic torque.

7. The optimal control of the tuning parameters allows the optimization of the fuel and energy consumption together with the running speed and time travel.

VI. CONCLUSIONS INDEX OF TERMS

• K" - the tuning coefficient; • U - voltage (Un - the nominal voltage; U, - stator phase

voltage); • I - current; • RJ - the stator withstanding; • R] - the rotor withstanding; • L,,2 - the spread inductance for stator (I) and rotor (2); • L", - the mutual inductance; • cpu. t2 - total magneticfieldfrom stator and rotor; • f-frequency (j;, - the nominalfrequency) : • f(f) - relative frequency • s - the slip; • Sk - the critical slip;

• i, - gear ratio; • PI - number of pole pairs; • D - the wheel diameter; • T- the overload coefficient: • V - velocity: • Fa - the vehicle's traction force; • 10 -the vehicle's relative traction force; • If! - train specific acceleration; • p - Laplace operator (p�d/dt); • P a - the vehicle's power;

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