US 3870939 A
Speed control system method for a traction motor in which speed setting signals are compared with the actual speed of the vehicle to provide a signal for selecting a value of the derivative of the setting acceleration, this derivative being integrated by an integrator taking the constraints relative to the integral into account, and the resultant setting acceleration serving to control the motor.
Claims available in
Description (OCR text may contain errors)
United States Patent 1 [1 1 Robert METHOD FOR CONTROLLING ACCELERATION AND DECELERATION OF A TRACTION MOTOR  Inventor: Michel Robert, Gif sur Yvette,
France  Assignee: Engins Matra, Yvelines, France  Filed: June 22, 1972  Appl. No.: 265,161
 Foreign Application Priority Data 3,350,612 10/1967 Hansen et al. 187/29 X Mar. 11, 1975 3,523,232 8/1970 Hall et al. 187/29 X Primary Examiner-T. E. Lynch Attorney, Agent, or Firm-Kinzer, Plyer, Dorn & McEachran  ABSTRACT Speed control system method for a traction motor in which speed setting signals are compared with the actual speed of the vehicle to provide a signal for selecting a value of the derivative of the setting acceleration, this derivative being integrated by an integrator taking the constraints relative to the integral into account, and the resultant setting acceleration serving to control the motor.
8 Claims, 9 Drawing Figures PATENTEDHAR] 1191's SHEET 1 BF 4 PATEHTEDWIRI 1 I015 SHEET I UF 4 FIG.6A
I I l I I l I I I I l I I l I l I I I I I l I I l l I I I I I L I METHOD FOR CONTROLLING ACCELERATION ANDZDECELERATION OF A TRACTION MOTOR Y The present invention relates to a speed control system and method for a traction motor in particular for vehicles moving along their own track, with an automatic pilot, such as, for example, vehicles of a subway train or the like.
The automatic piloting of such vehicles causes a certain number of problems. Thus the acceleration or deceleration and derivatives of acceleration to which the vehicle or vehicles of a train are subjected, may not exceed certain physiologically acceptable values without causing passengers discomfort or other troubles.
Thus it is commonly agreed that the acceleration or the deceleration may not exceed a value of 1.3 m/sec and that the normal derivative of the acceleration may not exceed a value of 0.6m/sec.
The motor control systems, known at present, do not make it possible to take such values, called constraints, into account. i
The object of the present invention is to provide a speed control system and method for a traction motor of a vehicle, enabling, with the aid of speed settings transmitted continuously or intermittently, a continuous motor control signal to be obtained taking into account the constraints imposed on the acceleration and the derivatives of the acceleration.
It is also the object of the invention to construct a control system and device enabling the setting speed to be obtained in minimum time, while respecting the said constraints, the motor thus controlled being possibly already under speed control.
To this end the present invention relates to a speed control system and method for a traction motor comprising the following steps:
the actual speed (V of the vehicle is determined,
this actual speed is compared with the speed settings (V a selector signal is provided by said comparison,
a certain number of values (+a, 0, a) of the derivative of the setting acceleration is fixed and one of these values is chosen in accordance with said selector signal,
the constraints relative to the integral (l-L, L') are fixed and the derivative of the setting acceleration is integrated (l/p) taking into account the constraints and obtaining the setting acceleration ('ye) giving the control acceleration ('yc),
the motor is controlled with the setting acceleration thus obtained (70).
The present invention will be described in greater detail with the aid of two modes of construction of a control system, illustrated schematically by way of example in the accompanying drawings in which:
FIG. 1 is a diagram showing the units of a first mode of construction of a control system,
FIG. 2 represents the acceleration diagram obtained as a result of constraints imposed on the derivative of the acceleration,
FIGS. 3A, 3B, 3C represent the geometric shapes of the servo response of the control system as a function of time,
FIG. 4 is the distance-speed diagram of a vehicle which is under control between two stations,
FIG. 5 is a diagram showing the units of a second mode of construction of a control system according to the invention,
FIG. 6A represents a control system for a discontinuous setting speed,
FIG. 68 represents a control system for an all or nothing speed setting control signal.
As shown in FIG. 1, the control system is intended to drive a vehicle 1 at speed, powered by a motor 2, c0ntrolled by an amplifier 3. The control system receives speed settings V in a discontinuous manner and must obtain a continuous motor control signal, respecting the acceleration and the derivative of the acceleration constraints.
The constraints relative to the derivative of the acceleration i are the following:
The derivative of the acceleration can assume only three values: +a, 0 a; a is the maximum permitted value for the comfort of the passengers. This is one example of the utilization of the controlled vehicle. These constraints could be different in the case where a vehicle is transporting fragile or other objects.
The constraints relative to the derivative of the acceleration 7 are given in table 1 below;
( -$=+qif 636,
3 0 if e e +e a if e56 In this table, the variable e on which 1? depends is obtained by comparing the speed setting V and the actual speed V as will be explained later.
To avoid oscillation at the level of O, a limit 6, is-
chosen which is not zero but rather small when the motor speed is steady. Thus e, is fixed at about 0.5 percent on the speed scale V From the values of 3 indicated above. the various segments are integrated, which gives the acceleration indicated in the table 2 as follows:
w m v A coefficient K l0 is chosen so that the actual acceleration ys is close to the acceleration ye.
The control system receives the setting speed signal V It also receives the actual speed signal V obtained on the vehicle. A comparison of these two speeds in the comparator 4 results in a certain signal V V As this signal does not take into account the phase advance, the signal V is used and modified in the device 5 and multiplied by K, in the multiplier 6 for transmission to the comparator 7.
This comparator 7 provides an output signal P is the LAPLACE, operator. 7
The signal eis transmitted to the setting value selector device 8 which outputs one of the three values of -7 given in table 1. This derivative of the acceleration is integrated in the integrator 9. Parallelto this integrator 9 is a limitator device 10, fixing the maximum values, (L) andminimum values (-L) of the setting acceleration yeQThis limitator device operates, for example, by total feed-back when the signal provided by the integrator 9 exceeds the value L or is less than the value L. Thelimitator 10 also makes it possible to make a digital control device by means of which the output of the integrator 9 is compared with two value limits, which, when they have been reached, eliminates the integrator. The signal ye is transmitted to the comparator 11 which compares it with the actual acceleration ys obtained from the actual speed V The output signal of this comparator 11 is multiplied by K in the multiplier 12. This gives the control acceleration 70 sent to the amplifier 3. This latter controls the motor 2 driving the vehicle 1.
By appropriate choice of the various control elements and in particular by fixing K 10, the control system is freed from the considerable variations to which the mass transported by the vehicle is subjected. Thus, between one station and the other, the vehicle can be full'or empty. The actual speed of the vehicle, signal Vs, is determined in the known way. To obtain the actual acceleration 'ys of the vehicle, from the actual speed, the actual speed signal is differentiated within the used frequency band (O-l hz).
The geometric representation of the servo response is shown in FIGS. 3A, 3B and 3C which show the speeds and accelerations as a function of time.
By rearranging the formula 4, the following formula is obtained:
In the present case,
I T -01 s and K, 1.1 s 7 By putting V* [1 (7+ K,)P/1+rP]V the curve in FIG. 3A is obtained.
Since the value limits of e are given, the three possible values of represented in FIG. 3B are obtained. The value 7s represented in FIG. 3C is obtained by integration. This servo response. is extremely rapid. Taking this into account, it is necessary only to modify the setting speed V to modify the speed of the controlled vehicle. Applying this control system to a vehicle which moves on a line between various stations,a distancespeed diagram is obtained as shown in FIG. 4. In this diagram the speed setting V is represented by a broken line. The diagram illustrates in particular the slowing down of the vehicle which, starting from the station A at zero speed, accelerates to reach a speed corresponding to the setting V The vehicle moves at that speed and then gradually slows down after receiving, at points a, b, c, the settings V V V,- to come finally to a stop at the station B. It is seen from this diagram that a continuous speed is obtained as a result of a discontinuous speed setting.
A second mode of construction of a control system according to the invention is shown inFIG. 5; In this case the control of a motor is concerned whose speed is already under control. This arrangement is very close to that of the mode of construction shown in FIG. I and, for the sake of simplifying the description, the same references have been used for similar units.
The control system applies to a vehicle 1 driven by a motor 2- whose speed is already under control. The motor 2 receives a speed control signal V which takes into consideration the actual speed V and the constraints related to the acceleration and to the derivative of the acceleration. To this effect, the phase of the actual speed V is advanced by device 13'. The output signal is transmitted to the comparator 4 which also receives the signal corresponding to the speed setting V The output signal e provides one of the values of the derivative of the acceleration 3, in the device 8. This derivative of the acceleration f is integrated at 9, the value of the integral being limited at 10. This gives the setting acceleration ye which is transmitted to the comparator 14. This comparator 14 also receives a signal coming from the positive part of the speed difference modifier device 17, itself receiving a speed difference signal coming from the comparator 16. The positive part function of device 17 is such that for a positive input its output is equal to the input; for a negative input its output is zero. The two inputs to the comparator 16 are the actual speed V and the control speed V The comparator 14 provides a signal which is transformed at 15, providing the control speed V As stated above, in the second mode of construction of the control system according to the invention, the control variable is no longer a couple, as in the first case, but a speed. The servo response is similar to that obtained with the first mode of construction and the fields of application are the same.
The speed control system of the invention is suited in particular to the control of traction motors, pulling vehicles, enabling automatic piloting to be effected on site, such as a subway network or similar.
In the description above, consideration is given to effecting control by means of discontinuous speed settings. However, control by all or nothing speed signals can equally be envisaged.
These two control modes are represented schematically in FIGS. 6A and 6B. The feature of the first mode of control is to ensure a modulation of the speed amplitude while the second mode of control enables durable control to be ensured. The two types of control can be super-imposed when, for example, it is desired to effect speed corrections.
In comparing the FIGS. 6A and 6B, it is seen that in the first case (FIG. 6A) the actual speed signal V of the vehicle becomes equal to the setting speed signal V a certain time. On the other hand, in the case of the all or nothing control FIG. 6B, the input signal (positivea negative, in the present case) is a signal of large amplitude. The amplitude of the signal is of little importance. The control system thus follows the path of the continuous lines without attaining the input signal.
In FIG. 68 there is a first positive signal. At a a negative signal is sent and the servo curve inverts itself up to the moment B where the device again receives a positive signal which redresses the curve.
It is obvious that the invention is not limited to the examples of its application hereinabove described and illustrated and that if necessary, other modes and other forms of application can be used without departing from the scope of the invention.
What is claimed is:
l. The method of controlling a traction motor, in the operation of a railroad train, rapid tansit train, or like vehicle, comprising the following steps:
A. sensing the actual speed of the vehicle to develop an actual speed signal V,;
B. developing a speed setting signal V,,;
C. modifying the actual speed signal to advance the phase thereof, thus developing a modified actual speed signal;
D. additively comparing the signals from steps B and C to develop a selector signal 6;
E. differentiating the selector signal 6 within the constraint limits +a, 0, a to develop a derivative of setting acceleration signal 3 having values as follows:
: +a A a 1 wherein a, is of a predetermined amplitude;
F. integrating the derivative of setting acceleration signal in accordance with l/p and within acceleration constraint limits +L and L to develop a setting acceleration signal ye;
G. additively comparing the setting acceleration signal ye with an actual acceleration signal to develop an initial control signal 'yc;
H. and effectively applying the initial control signal to the traction motor to control motor operation.
2. The method according to claim I in which the speed setting signal V is discontinuous.
3. The method according to claim 1 in which the speed setting signal V is continuous.
4. The method according to claim 1 in which the speed setting signal V is a step signal varying between two fixed values.
5. The method according to claim 1 in which the traction motor is subject to an additional speed setting control, and including the following additional steps:
I. integrating the initial control signal yc in accordance with l/p to develop a control speed signal V which is applied to the traction motor;
J. and additively combining the control speed signal V with the actual speed signal V and the positive part of the resulting signal constitutes the actual acceleration signal employed in step G.
6. The method according to claim 1, including the following additional step:
B. additively comparing the signals V and V to develop a speed difference signal;
and in which that speed difference signal is employed as the speed setting signal in step D.
7. A speed control system for controlling a a traction motor in a railroad train, rapid transit train, or like vehicle, comprising:
sensing means for sensing the actual speed of the vehicle to develop an actual speed signal V first additive comparator means for comparing the actual speed signal V with a speed setting signal V received from an external source to develop a selector signal 6;
differentiating and limiting means for differentiating the selector signal 6 to generate a derivative of setting acceleration signal within predetermined limits;
first integrating means for integrating the signal 3 in accordance with l/p to generate a setting acceleration signal ye;
limiting feedback means, coupled to the first integrating means, for limiting the amplitude of the setting acceleration signal ye within limits +L and L;
second additive comparator means for comparing the limited setting acceleration signal ye with an actual acceleration signal ys for the vehicle to generate an initial control signal yc;
second integrating means for integrating the initial control signal yc to develop a speed control signal c;
and means for applying the speed control signal V to the traction motor.
8. A speed control system according to claim 7 in which the differentiating and limiting means is constructed to operate within the constraint limits +a, 0, and a, so that the signal 3'? varies as follows:
a if e s e, where e, is a predetermined amplitude.