APPARATUS FOR CONTROLLING ELECTRIC CAR

Abstract: An apparatus for controlling electric car equipped with at least two induction motors (4a-4d) for driving the electric car. The individual motors are connected with variable-voltage variable-frequency inverters (3a-3d) combined with tacho-generators (5a-5d), respectively, to constitute a plurality of drive control units ( A-D ). And the inverters (3a-3d) of the drive control units ( A-D ) are all controlled by an integral controller (1). This apparatus for controlling a car includes torque reduction control means for reducing the torque of a predetermined one of the induction motors (4a-4d) by a predetermined value from the command value of the corresponding drive control unit. Frequencies of the inverters of the remaining drive control units are controlled based on the frequency of rotational speed obtained from the tacho-generator of the above drive control unit.

Description: The present invention relates to an electric car/locomotive controller for use in an electric car/locomotive according to the preamble of claim 1. Such a controller is known from JP-A-55-127806. More particularly, the invention relates to a general controller of an electric car/locomotive for general control of a plurality of units which are formed by combining variable voltage variable frequency inverter and induction motors in one-to-one correspondence. Recently, as requests for high output of a motor and a maintenance-free motor have become strong, there is a tendency that electric cars/locomotives using, as a motor for powering, an induction motor driven by a variable voltage variable frequency inverter are put into practical use. In an electric car/locomotive, the improvement of readhesion characteristic is a ceaseless proposition, and to this end, it is necessary to detect the real running speed of an electric car/locomotive. Accordingly, in a conventional control apparatus for example as disclosed in JP-A-55-127806, the rotating speed of a trailer wheel of an electric car/locomotive (a wheel to which no motor for driving the electric car/locomotive is connected) is detected and readhesion control is performed on the basis of the detected rotating speed as a reference representing the real running speed of the electric car/locomotive. Specifically, the output frequency (inverter frequency) of a variable voltage variable frequency inverter is controlled on the basis of the rotating speed of the trailer wheel so as to prevent the inverter frequency from rising or falling uncontrollably even in the case of occurrence of slide, so that the shunt motor characteristic (the characteristic that the generated torque decreases as the rotating speed rises) of the induction motor per se can function effectively to thereby obtain a sufficient improvement in readhesion performance. In the prior art, a trailer wheel and the means of detecting the rotating speed of the trailer wheel are required for detection of the real running speed of the electric car/locomotive. Accordingly, the prior art has a problem in that not only increase in cost is inevitable but trailer wheels must be provided because an electric car/locomotive having no trailer wheel cannot be used. An object of the present invention is to provide an electric car/locomotive controller in which the real running speed of the electric car/locomotive can be detected easily and securely without provision of any trailer wheel and any means of detecting the rotating speed thereof; and variable voltage variable frequency inverters can be controlled on the basis of the detected real running speed so as to prevent the inverter frequency from rising or falling uncontrollably to thereby attain a sufficient readhesion performance against the occurrence of slide. This object is solved in accordance with the features of independent claim 1. Dependent claims are directed on preferred embodiments of the invention. According to an aspect of the present invention, induction motors for powering the electric car/locomotive are combined with corresponding variable voltage variable frequency inverters in pairs so as to form driving control units, and a torque reduction control means is provided for reducing the instructed torque value of the induction motor of a preset one of the driving control units from the instructed torque value given to every driving control unit by a predetermined rate to thereby control the output frequencies of the variable voltage variable frequency inverters of the remaining driving control units on the basis of the rotating speed frequency obtained by the preset driving control unit in which the torque is reduced by the torque reduction control means. The control means acts to reduce the torque of the induction motor of a specific driving control unit to be smaller than the torque of the induction motors of the remaining driving control units. As a result, the occurrence of slide in the driving wheel connected to the induction motor of the specific driving control unit is substantially perfectly prevented. Accordingly, the rotating speed frequency obtained from the specific driving control unit can be used as a value sufficiently corresponding to the real running speed of the electric car/locomotive. Accordingly, the real running speed of the electric car/locomotive necessary for controlling readhesion can be detected easily and securely without use of any trailer wheel and without use of any means of detecting the rotating speed thereof. Fig. 1 is a block diagram showing a controller of an electric car/locomotive according to an embodiment of the present invention. A controller of an electric car/locomotive according to the present invention will be described hereunder with reference to an embodiment illustrated in the drawing. Fig. 1 shows an embodiment in which the present invention is applied to an electric car/locomotive having four axes of driving wheels, and, therefore, having four driving control units constituted by induction motors for powering and variable voltage variable frequency inveters in pairs. In Fig. 1, the reference characters A, B, C and D represent four driving control units. The reference numeral 1 designates a general controller; 2a, 2b, 2c and 2d designate voltage current controllers respectively; 3a, 3b, 3c and 3d designate variable voltage variable frequency inverters respectively; 4a, 4b, 4c and 4d designate induction motors for powering respectively, connected to the driving wheels; and 5a, 5b, 5c and 5d designate rotating speed detectors respectively. Accordingly, each of the driving control units A to D includes one of the variable voltage variable frequency inverters 3a, 3b, 3c and 3d and one of the induction motors 4a, 4b, 4c and 4d in pairs and further includes one of the voltage current controllers 2a, 2b, 2c and 2d and one of the rotating speed detectors 5a, 5b, 5c and 5d in pairs. The functions of the respective parts will be described hereunder before description of the function of the general controller 1. The voltage current controllers 2a to 2d control the variable voltage variable frequency inverters 3a to 3d on the basis of the torque instructions given by the general controller 1, to thereby set the output frequencies and voltages thereof to values corresponding to the torque instructions, respectively. The variable voltage variable frequency inverters 3a to 3d convert electric power supplied from the catenary wire into three-phase AC electric power of a predetermined frequency and a predetermined voltage and supply the three-phase AC electric power to the induction motors 4a to 4d to act to move the electric car/locomotive. The rotating speed detectors 5a to 5d are respectively connected to rotary shafts of the induction motors 4a to 4d to act to detect the rotating speed thereof. More in detail, the output frequency (inverter frequency) from each of the variable voltage variable frequency inverters 3a to 3d is controlled by corresponding voltage current controllers 2a to 2d, to be a frequency obtained by adding a slip frequency determined on the basis of the instructed torque value to the frequency of an output signal from any one of the rotating speed detectors 5a to 5d (at the time of powering of the electric car/locomotive) or by subtracting the slip frequency from the frequency of an output signal from any one of the rotating speed detectors 5a to 5d (at the time of braking of the electric car/locomotive). The output voltage from each of the variable voltage variable frequency inverters is controlled, by the corresponding voltage current controllers, to be substantially proportional to the inverter frequency (constant control of frequency/voltage ratio) unless the output voltage reaches the maximum value limited by the rated voltage of each of the induction motors 4a to 4d. Further, each of the voltage current controllers 2a to 2d monitors the rate of change of the output frequency (or the voltage representing the frequency) from corresponding one of the rotating speed detectors 5a to 5d in the corresponding driving control unit. When the rate of change of the output frequency (or the voltage) exceeds a reference change rate determined in advance, each of the voltage current controllers 2a to 2d makes a decision that slide has occurred in the driving wheel connected to the induction motor of the driving control unit. As a result, the voltage current controller supplies a slide detection signal to the general controller 1 and then receives the torque instruction from the general controller 1 and further receives a selection signal to select one rotating speed detector (which needs fetching of the output signal) from the rotating speed detectors 5a to 5d as a reference used for control of the inverter frequency. On the other hand, the general controller 1 calculates the torque instructions by arithmetic operation according to electric car/locomotive accelerating/decelerating instructions or the like supplied by a main controller (not shown) and supplies the torque instructions to the voltage current controllers 2a to 2d of the driving control units A to D. Further, the general controller 1 monitors the slide detection signals supplied from the voltage current controllers 2a to 2d of the driving control units, so that when the frequency of occurrence of slide exceeds a preset threshold value, the general controller 1 controls previously preselected one of the driving control units A to D. When, for example, the driving control unit A is previously selected, the general controller 1 controls the driving control unit A so that the instructed torque value given to the driving control unit A just before this point of time is reduced by a predetermined value. After the control to reduce the instructed torque value is performed, the general controller 1 further supplies the selection signal to the voltage current controllers 2a to 2d of the respective driving control units to make an instruction to control the inverter frequency by using the signal outputted from the rotating speed detector in the driving control unit now subjected to the reduction of the instructed value, for example, the rotating speed detector 5a in the driving control unit A. Accordingly, while an electric car/locomotive having a plurality of driving wheels is running, one of the driving wheels can be necessarily subjected to read-hesion control by reducing the torque thereof even in the case where the driving wheel is in the slide state. Accordingly, the signal obtained from the rotating speed detector of the induction motor connected to the driving wheel, for example, the signal obtained from the rotating speed detector 5a of the induction motor 4a, accurately becomes a signal corresponding to the real running speed of the electric car/locomotive at this point of time. Accordingly, in this embodiment, the real running speed of the electric car/locomotive can be always faithfully detected without use of any trailer wheel and without use of any speed detector as connected to such a trailer wheel. Further, in this embodiment, the inverter frequencies of the remaining driving control units, that is, the driving control units B to D in this case, are controlled on the basis of the running speed signal obtained from the driving wheel securely subjected to readhesion control by reducing the torque thereof by a predetermined value in the aforementioned manner. Accordingly, the inverter frequencies of the variable voltage variable frequency inverters 3b to 3d in these driving control units are securely prevented from rising uncontrollably. As a result, the shunt motor characteristic of the induction motor per se can function effectively, so that excellent readhesion characteristic can be provided. In this embodiment of the present invention, on the basis of the consideration that it is preferable that the quantity of reduction of the torque is minimized, the driving control unit requiring reduction of the instructed torque value is selected as follows. Although this selection must be modified correspondingly to the structure of the electric car/locomotive, a unit which is so large in axle weight as to attain a relatively good rail level condition to thereby prevent the occurrence of slide, the rearmost driving control unit in the direction of the running of the electric car/locomotive is generally selected. The quantity of reduction of the instructed torque value for the previously selected driving control units A to D, for example, the quantity of reduction of the instructed torque value for the driving control unit A, will be described hereunder. On the whole of the electric car/locomotive, the tractive force or braking force is low when the frequency of occurrence of slide is high. Accordingly, it can be considered that partial reduction of torque has no large influence as long as readhesion characteristic can be improved. Assuming now that the total torque quantity Tτ of the electric car/locomotive is 100% in the case where the electric car/locomotive has four driving control units A to D as described above, then the torque quantity of one driving control unit is 25%. When the torque quantity of one driving control unit is halved, that is, when the torque quantity of some driving control unit is reduced to 12.5%, the total torque quantity Tτ' of the electric car/locomotive is reduced to 87.5% as represented by the following expression. Tτ' = 100 - 12.5 = 87.5% In the case where the electric car/locomotive has six driving control units, the torque quantity of one driving control unit is about 16.6% and the reduction of the total torque quantity Tτ' obtained in the same manner as described above is smaller as follows. Tτ' = 100 - 8.3 = 91.7% On the contrary, in the condition that the frequency of occurrence of slide is high, it is known that the torque is reduced by 10% at the least, as shown in Fig. 8 in "HITACHI Review", Vol. 61, No. 5, 1979-5, P. 32. Therefore, according to the present invention, a sufficient improvement of readhesion characteristic can be attained without increase of torque reduction. Although the above description has been made for the assumption that the torque of one driving control unit is halved, the occurrence of slide can be prevented sufficiently in practical use even in the case where the rate of torque reduction is smaller than the aforementioned rate. Accordingly, in practical use, not only the rate of torque reduction can become smaller but readhesion characteristic can be improved securely. Although the above description has been made for the case that the torque quantity of one driving control unit is reduced but the torque quantities of the remaining driving control units are not specially controlled and are left as the original torque quantities, the invention can be applied as an embodiment thereof to the case that the torque quantities of the residual driving control units may be controlled so as to be increased correspondingly to the reduction of the torque quantity of one driving control unit to keep the total torque quantity of the electric car/locomotive constant, that is, to keep the total tractive force of the electric car/locomotive constant. This is because the inverter frequency can be prevented from rising uncontrollably to thereby attain a sufficient improvement of readhesion characteristic on the basis of the shunt motor characteristic of the induction motor. Accordingly, in this embodiment, not only the real running speed of the electric car/locomotive can be securely detected substantially without lowering of performance of the electric car/locomotive, but readhesion characteristic can be improved sufficiently. In a real electric car/locomotive, one specific driving wheel of all driving wheels, such as the driving wheel located in the head in the direction of running of the electric car/locomotive, has a tendency that slide occurs particularly frequently. The occurrence of slide can be predicted to some degree. In such a case, the instructed torque value given to the driving control unit corresponding to the driving wheel located in the head may be initially reduced by the aforementioned predetermined value in advance regardless of the detection of occurrence of slide, or in addition to that, the instructed torque values of the other driving control units may be increased by a value corresponding to the reduction of the torque quantity. In the embodiment of the present invention using such a measure, the general controller can be simplified in structure to attain reduction in cost. As described above, the real running speed of the electric car/locomotive can be securely detected without provision of any trailer wheel and any rotating speed detector connected to the trailer wheel. Accordingly, the number of parts can be reduced. Further, the inverters of the driving control units can be controlled on the basis of the thus detected real running speed, so that the inverter frequency can be prevented from raising or falling uncontrollably. Accordingly, the shunt motor characteristic of the induction motor can function effectively to thereby obtain excellent readhesion characteristic easily.

Claims: An electric car/locomotive controller for use in an electric car/locomotive of the system in which there are provided at least two induction motors (4a-d) for powering said electric car/locomotive and in which said induction motors are combined with variable voltage variable frequency inverters (3a-3d) in one-to-one correspondence so as to form a plurality of driving control units (A, B, C, D) to thereby generally control the respective variable voltage variable frequency inverters of said driving control units, characterized in that the electric car/locomotive controller comprises a torque reduction control means (1, 2a-d) for reducing the instructed torque value of one of the induction motors belonging to a preselected one of said driving control units by a predetermined value, wherein the output frequencies of the variable voltage variable frequency inverters of the remaining driving control units are controlled on the basis of the rotating speed frequency obtained by said preselected driving control unit. A controller according to claim 1, characterized in further comprising a detection means (5a-d) for detecting the occurrence of slip or slide in a driving wheel, wherein said torque reduction control means fulfills its torque reduction control function when occurrence of slip or slide is detected by said detection means. A controller according to claim 1 or 2, characterized in further comprising a torque increase control means for increasing the instructed torque values of the induction motors of the driving control units other than said preselected driving control unit by a predetermined value, wherein the torque increase control function of said torque increase control means acts simultaneously when the torque reduction control function of said torque reduction control means acts. A controller according to claim 2, characterized in that the detection means judges occurrence of slip or slide in a driving wheel on the basis of the fact that the rate of change of the rotating speed frequency of the induction motor in each of the driving control units exceeds a reference value being set in advance. An electric car/locomotive controller according to claim 3, characterized in that the quantity of increase of torque obtained by said torque increase control means serves as a torque quantity necessary for cancelling the quantity of reduction of torque obtained by said torque reduction control means.

Inventors: OKAMATSU SHIGETOSHI, OKAMATSU, SHIGETOSHI
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1992
Main classification: B60L9
IPC codes: B60L3, B60L9, H02P5