APPARATUS FOR CONTROLLING ELECTRIC VEHICLE USING INDUCTION MOTOR

Abstract: A main circuit of an electric vehicle using an induction motor is constituted by an invertor (2) for producing three phase AC power having a variable frequency and a variable voltage and a three-phase induction motor (31, 32) supplied with the AC power by the invertor. The rotational speed of the induction motor is detected and a slip frequency signal is added (in power running) or subtracted (in regenerating runn­ ing) to or from the rotational speed to control the output frequ­ ency of the invertor. On the other hand, the output voltage of the invertor is controlled to be in proportion to the output frequency thereof. The output voltage of the invertor is limited in accordance with notch positions of a master controller (6) of the electric vehicle so as to be provided with a voltage notch stopping characteristic of the conventional electric vehicle. A constant speed notch for producing a constant speed running command is additionally provided in the master controller, and in response to the constant speed running command, the speed command for constant speed running is selected to be a value equal to or a value higher by a predetermined value than an actual speed of the electric vehicle at that time. When the speed of the electric vehicle approaches the speed com­ mand for constant speed running, the slip frequency is redu­ ced to realize the constant speed running.

Description: BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to an improvement of an apparatus for controlling an electric vehicle using an induction motor, and particularly relates to an apparatus for controlling an electric vehicle in constant speed operation. DESCRIPTION OF THE PRIOR ART As to constant speed running of an electric vehicle using an induction motor, Japanese Patent Unexamined Publication No. 48-12418 discloses a control apparatus for an electromobile for running on a road. That is, the control apparatus is arranged such that a slip frequency is determined by a function generator so that the slip frequency changes linearly in proportion to a deviation of an actual speed of an induction motor from a required speed with positive and negative limitations. Being not different from the general ones, the other control systems are arranged to control the output voltage of an invertor in response to a frequency command applied to the invertor. Further, Japanese Patent Unexamined Publication No. 54-22607 discloses a control apparatus for a railway electric vehicle in which the output frequency of an invertor is controlled in response to various speed commands which are set correspondingly to respective notch commands, for example, such that 10 km/h, 30 km/h, 60 km/h, and 100 km/h are set respectively correspondingly to the first, the second, the third, and the fourth notches. The magazine "Science of Electric Vehicle" Vol. 38, No. 2, 1985, pages 15 through 24, particularly page 20, discloses constant speed control which is attained by reducing the slip frequency when the speed of an electric vehicle approaches a limit speed. A similar control apparatus is further disclosed in DE-A-30 08 279. Here, the limit speed is determined by a frequency signal which is set to a specific fixed value by the driver of the vehicle. A detailed description of the principles of controlling a three-phase motor of a railway vehicle is further given in EP-A-0 059 924. In those control methods, however, there are disadvantages that the two former ones are much different in handling of operation of the railway electric vehicle from the conventional one and that the latter one is insufficient in freedom in the constant speed running. SUMMARY OF THE INVENTION An object of the present invention is to provide a control apparatus for controlling an electric vehicle using an induction motor, in which constant speed running can be performed at a desired speed thereby maintaining the handling of operation by a driver like in the conventional electric vehicle. This object is solved by the invention characterized in claim 1. Such an arrangement makes it possible to perform constant speed running at a desired speed while maintaining the handling of operation which is not much different from that in the conventional electric vehicle. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a block diagram of an embodiment of the control apparatus for controlling an electric vehicle using an induction motor according to the present invention; Fig. 2 is a diagram showing a command characteristic of tractive force versus speed deviations, and Figs. 3A and 3B are diagrams showing speed characteristics in transition into constant speed running. DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring to the drawings, a preferred embodiment according to the present invention will be described in detail hereunder. In Fig. 1, the DC power taken into an invertor 2 from a DC contact wire 1 is converted into an AC power of a variable voltage and a variable frequency and the AC power is supplied to induction motors 31 and 32. In order to obtain a frequency signal f r corresponding to an actual vehicle speed, there are provided pulse generators 41 and 42 connected to the respective induction motors 31 and 32 so as to produce pulses corresponding to the actual rotational speed of the respective induction motors 31 and 32, and an N/f converter 5 for converting the number N of the pulses produced from each of the pulse generators 41 and 42 into a frequency signal f r . A master controller 6 is provided with an off notch position, a first and a second notch position for power running, and a further notch position for constant speed running. First, at the first or second notch for power running, a predetermined slip frequency pattern f SP1 and a motor current command I MP1 are generated by an f S pattern generator 7 and an I M pattern generator 8 respectively. At the notch position for power running, change-over switches 9 and 10 are respectively put in such states as shown in Fig. 1. Accordingly, the slip frequency command f SP1 is applied to an adder 11 as it is. On the other hand, an actual motor current I M is detected by a current detector 12 and compared with a motor current command I MP by a comparator/amplifier 13. The comparator/amplifier 13 generates an f S correction signal for correcting a slip frequency command f SP when the actual motor current I M is deviated from the motor current command I MP , the correction signal f S being applied to another input of the adder 11. The output of the adder 11, which is a slip frequency signal f S , is applied to an adder 14. The adder 14 adds or subtracts the slip frequency signal f S to or from the above-mentioned signal f r corresponding to the vehicle speed (which may be a rotor speed of the motor) in power running or in regeneration. The output f INV of the adder 14 is applied to a PWM modulating unit 15 as a frequency command for the invertor. The invertor frequency command f INV is applied also to a V/f converter 16 for generating a control voltage V C1 so as to make the ratio (V/f) of the voltage V to the frequency f constant. At the first or second notch for power running, a maximum modulation ratio limit voltage generator 17 generates a maximum modulation ratio limit V C2 settled for every notch as shown in the drawing. A lower rank preference circuit 18 selects one of the control voltage V C1 and the maximum modulation ratio limit V C2 which is lower in rank than the other and applies the selected voltage of a lower rank to the PWM modulating unit 15 as an invertor-output voltage command V C . The PWM modulating unit 15 controls the operation frequency and degree of modulation of the invertor 2 on the basis of the invertor frequency command f INV and the invertor-output voltage command V C . Now, in the I M pattern generator 8, the output I MP1 is maintained constant at the second power running notch, but given such a limitation as shown in the drawing in the first power running notch as the invertor frequency command f INV is increased. This is because if only the control voltage V C would be suppressed to the maximum modulation ratio limit V C2 in the first power running notch while leaving the slip frequency f S as it is in a large value, the limitation for the voltage would be released so that large torque might be suddenly generated when the second power running notch is tuned on next. Accordingly, also the slip frequency f S is reduced by the f S correction signal of the current control system. In this embodiment, there are provided only two notches, the first and the second ones, for power running, and at the second notch, a voltage corresponding to the maximum output voltage of the invertor is produced from the maximum modulation ratio limit generator 17 as illustrated by the reference characters V Cmax in the drawing, with no factual voltage limitation. This is because it is considered that more than two power running notches are not necessary since also a constant speed running command described later is used. Of the foregoing control systems, the control system for controlling the control voltage V C on the basis of V/s = constant may be substituted by such a control system as follows. That is, the control voltage V C1 to be applied to the low rank preference circuit 18 is obtained in accordance with the output of the comparator/amplifier 13 for amplifying the deviation of the current feedback value I M from the current command I MP . This is because in the frequency control system on the basis of f INV = f r ± f S , I M becomes nearly constant if V/f is made constant, while V/f becomes nearly constant if I M is made constant, and therefore it is possible to use any one of the two control systems based on the two foregoing relations under the conditions that V/f and IM are made constant respectively. The foregoing control in power running and in regeneration is carried out in the same manner as the well-known control of the electric vehicle using an induction motor, for example, as shown in the notching curve in page 20 of the above-mentioned "Science of Electric Vehicle". Here, if the master controller 6 is turned onto the constant speed running notch position, a constant speed command line 19 responds to a constant speed command to change the respective contact positions of the change-over switches 9 and 10 into positions in contrast to those shown in the drawing. The constant speed command is applied also to a target speed setter 20 so that the signal f r corresponding to the vehicle speed at that time (which may be the rotational speed of the motor) is latched and made to be a speed command signal f p thereafter. On the other hand, if there exists a signal representing the fact that the immediately preceding notch is the second one for power running when the constant speed command is applied, the setting is made such that Speed command signal f p = (Latched signal f r corresponding to vehicle speed) + (Signal corresponding to 5 km/h) A comparator/amplifier 21 compares the speed command signal f p with the vehicle speed corresponding signal f r and generates a second slip frequency signal f SP2 and a second current command signal I MP2 with respect to the deviation f of the signal f r from the speed command signal f p as shown in Fig. 2. These second command signals f SP2 and I MP2 are passed through the change-over switches 9 and 10 respectively so as to be used as a new slip frequency command f SP and a new motor current command I MP respectively. Accordingly, if the constant speed notch is turned on when the vehicle speed has been accelerated to a speed in the vicinity of a desired one, the vehicle speed is smoothly further raised by 5 km/h and then constant speed running is carried out so as to keep the raised speed while effecting power or regeneration running. If the constant speed notch is turned on from coasting at the off-notch or from the first power running notch, the vehicle speed corresponding signal f r is used as it is as the speed command f p thereafter, and the constant speed running is effected in the same manner as above. The change-over between the power running and regenerating running can be performed smoothly by providing a slight dead zone (corresponding to ± 5 km/h) in the characteristics of the comparator/amplifier 21 as shown by way of example in Fig. 2. Further, if the characteristics of the comparator/amplifier 21 are set so as to saturate at values corresponding to ± 5 km/h, it is possible to obtain a constant speed characteristic within a range of a constant speed command ± 5 km/h. Figs. 3A and 3B show examples of changes of the vehicle speed corresponding signal f r and the speed command f p , in the case where the constant speed notch is turned on from the second power running notch and in the case where the constant speed notch is turned on from the off-notch (for coasting), respectively, in the foregoing embodiment. As seen from Figs. 3A and 3B, if the constant speed notch is turned on in the midway of acceleration at the second power running notch, the constant speed command f p thereafter is made to be f p = (Vehicle speed corresponding signal f r1 at that time) + (Value corresponding to 5 km/h) so that the running can be smoothly shifted to the constant speed running without suddenly reducing the torque. Further, if the notch is changed over from the off-notch position (for coasting) to the constant speed notch position, the constant speed command f p thereafter is made to be f p = (Vehicle speed corresponding signal f r1 at that time) so that the running can be smoothly shifted from coasting to the constant speed running similarly to the above case. Although provided in the master controller in this embodiment, the operation means for generating a constant speed command may be provided separately from the master controller. Although selected to be only two, the number of the power running notches may be easily selected to be more than two. Further, it is easy to provide a modification in which the running mode is shifted to the constant speed running through such a procedure that constant speed running is commanded after designation of a speed command in the constant speed running by using a key board or the like, without determining the speed command for the constant speed running in accordance with a signal corresponding to an actual vehicle speed. According to the present invention, it is made possible to perform constant speed running at a desired speed while remaining the sense of handling notches in the conventional railway electric vehicle.

Claims: An apparatus for controlling an electric vehicle provided with an electric power converter (2) for supplying a variable voltage of variable frequency to an induction motor (31, 32), speed detecting means (41, 42) for producing an actual speed signal (fr) corresponding to the actual speed of said vehicle, frequency control means (11, 13, 14) for adding/subtracting a slip frequency command (fs, fsp, fsp1, fsp2) to/from said actual speed signal (fr) to control the frequency of said power converter (2), voltage control means (15, 16, 18) for controlling the voltage of said power converter (2) in proportion to the frequency control command (finv) of said frequency control means (11, 13, 14) or for controlling said voltage in accordance with a deviation of an actual motor current signal (IM) from a motor current command (IMP, IMP1, IMP2), characterized by operation means (6) for generating a constant speed command; means (20) for determining and generating a speed command signal (fp) on the basis of said actual speed signal (fr) in response to said constant speed command when said operation means (6) is operated; comparator means (21) for comparing said actual speed signal (fr) with said speed command signal (fp); and means (21) for generating a slip frequency command (fsp2) changing positively or negatively in accordance with the output signal of said comparator means (21). An apparatus for controlling an electric vehicle according to Claim 1, in which said speed command signal is said actual vehicle speed signal when said operation means (6) is operated in coasting. An apparatus for controlling an electric vehicle according to Claim 1 or 2, in which said speed command signal is made higher than said actual vehicle speed signal by a predetermined value when said operation means (6) is operated from a last one of notches for power running. An apparatus for controlling an electric vehicle according to any of Claims 1 to 3, in which said operation means (6) is constituted by said master controller and arranged to generate said constant speed command when said master controller is operated to put a lever thereof at a specific position. An apparatus for controlling an electric vehicle according to Claim 1, in which said slip frequency command generating means (21) is provided with comparator means (13) for comparing said actual motor current signal (IM) with said motor current command (IMP) to thereby adjust said slip frequency command (fsp) in accordance with the deviation of said actual motor current signal (IM) from said motor current command (IMP).

Inventors: MIZOBUCHI, TETSUYA, OZAWA, TSUTOMU
Applicants: HITACHI, LTD.
Application year: 1986
Main classification: B60L15
IPC codes: B60L15, H02P27, B60L9