NZ198584A

NZ198584A - Multiple shunt motor control in electric vehicle

Info

Publication number: NZ198584A
Application number: NZ198584A
Authority: NZ
Inventors: Y Ueda
Original assignee: Mitsubishi Electric Corp
Priority date: 1980-10-15
Filing date: 1981-10-08
Publication date: 1985-08-16
Also published as: JPS5768605A; KR830007318A; WO1982001350A1; KR870000654B1; ZA817055B; AR226755A1; MX151654A

Description

<div class="application article clearfix" id="description"> 1 98584 Priority Dataf s): . 'r? '5? I P."? Complete Specification Filed: & I Class .Publioation Date. It §,^9, $85.. P.O. Journal No: .... A \\ NEW ZEALAND PATENTS ACT, 1953 No.: Date: COMPLETE SPECIFICATION "CONTROL APPARATUS OF AC ELECTRIC CAR AND CONTROL METHOD" WWe, MITSUBISHI DENKI KABUSHIKI KAISHA, a Japanese company, of 2-3, Marunouchi 2-chome, Chiyoda-ku, Tokyo, Japan hereby declare the invention for which "I / we pray that a patent may be granted to-me-/us, and the method by which it is to be performed, to be particularly described in and by the following statement: - - 1 - 198584 BACKGROUND OF THE INVENTION: FIELD OF THE INVENTION: The present invention relates to a control apparatus of AC electric car having a DC motor driven by a rectification of an AC power source and a control method. DESCRIPTION OF THE PRIOR ART: A DC series motor is usually used as a traction motor in an AC electric car as well as a DC electric car. However, sometimes a DC shunt motor is used because of the following reason: (1) A speed characteristic is flat in comparison with that of a DC series motor whereby a readhesion characteristic between wheels and rails is superior. (2) A field winding circuit is separated from an armature circuit whereby it can be easily controlled and a continuous control of a field current is easily attained. (3) A switching of a main circuit in a switching to a power running or a braking is remarkably simple in the case of a rheostatic braking and a regenerative braking. On the other hand, one of the disadvantages of the use of the shunt motor is as follows. When a plurality of motors are connected to one power device such as rectification device as an electric car, the revolution per second is different depending upon difference of characteristics of motors and difference of diameters of wheels whereby the currents passed through the armatures of the motors are not balanced. 198584 In such unbalanced current, torques of the motors are unbalanced and moreover, the motor passing the larger current is heated to higher temperature to cause overheating. In a special case, a large transversal current is passed between the motors. In order to overcome the disadvantages, the following improvements have been usually considered. (1) The field currents of the motors are independently controlled for each motor. (2) Each rectifying device for controlling the armature current is connected for each motor to independently control the motors. (3) A combination of (1) and (2). Figure 1 shows one embodiment of the conventional system wherein two motors are controlled. In a practical electric car, 4 or more of motors are usually controlled. In Figure 1, the reference (1) designates a pantograph for collecting an AC power source through an electric power supply line; (2) designates a primary winding of a transformer; (3) - (8) respectively designate secondary windings of the transformer connected to the armature circuit of the motors; (9), (10) respectively designate third windings of the transformer connected to the field winding circuit of the motors; (11) - (16) respectively designate rectification devices for controlling armature currents of the motors; (17), (18) respectively field rectification devices for controlling the field winding current of the motors; (19), (20) respectively designate smoothing reactors for smoothing pulse current obtained by full-wave rectification by the rectifiers; (21), (22) respectively designate armatures of the motors; (23), (24) respectively designate field windings of the traction motors and the first traction motor (25) and the second traction motor (26) are respectively formed by a pair of t 985 84 (21), (23) and a pair of (22), (24). The references (27), (28) respectively designate current detectors. In a practical electric car, a filter device is connected to a breaker, however, it is not shown in Figure 1. As shown in Figure 1, the armature circuits and the field circuits of the first traction motor (25) and the second traction motor (26) are electrically, independently controlled. The operation of the circuits of the first traction motor will be illustrated. A high voltage applied through the pantograph (1) to the primary winding (2) of the transformer is reduced to a predetermined voltage by the transformer to apply the voltage to the secondary windings (3) - (5). In the secondary windings (3) - (5), each of rectification devices (11) (13) (in Figure 1, hybrid bridge formed by a thyristor and a diode) is connected to attain full-wave rectification of an AC current. The current is converted into the smooth current by the smoothing reactor (19) and is fed to the armature (21) of the first traction motor (25). A phase control of the rectification device is performed to coincide the armature current to the current reference (current limit) given by a current limit setter. The rectification devices (11) - (13) are sequentially actuated and controlled depending upon control signals corresponding to speeds and voltages. On the other hand, the field current is simultaneously controlled by the field rectification device (17) depending upon the armature current. Thus, the revolution per second of the first traction motor (25) as the speed of the electric car can be controlled from the starting to high speed in broad regions. As described, the first traction motor (25) and the second traction motor (26) are electrically independent in both of the armature circuits and the field circuits whereby they can be easily controlled as desired regardless of the difference of the I 98584 characteristics of the motors (25), (26) and the difference of the diameters of wheels. However, as shown in Figure 1, the numbers of the secondary windings and the rectification devices are increased to be a large size apparatus and the costs are uneconomic ally high. Such 5 disadvantages are further severely caused in the case of the multi-division of the secondary winding of the transformer for reducing induction trouble in the adjacent telephone line etc. caused by higher harmonic components in the current of the electric power supply line as the primary winding of the transformer in the phase control of the rectification device. 10 SUMMARY OF THE INVENTION: The present invention is to provide a control apparatus of an AC electric car which comprises a first rectification device of a conduction controllable bridge circuit connected to a first AC power source; a DC terminal of said first rectification device being connected I® to a terminal of one of first and second traction motors; second and third rectification devices connected respectively to each of second and third AC power sources as each conduction controllable bridge circuit; DC terminals of said second and third rectification devices being connected to the other terminals of said first and second traction motors; and 20 the other DC terminal of said second and third rectification devices being connected to the other DC terminal of said first rectification device whereby currents passing through said traction motors are independently controlled and a control method thereof. In accordance with the present invention, a gate control 25 circuit of the common side of the rectification devices can be simplified since only on-off control is given and the number of the rectification - 5 - 1 98584 devices having phase control function can be the same as the number of the traction motors. The number of the elements such as thyristors and diodes of the common side of the rectification devices is depending upon the rated current and the current fed. In the conventional system, the number of the elements should be at least number of the circuits of the traction motor, however, the number of the elements can be remarkably reduced by the common connection in the present invention. Moreover, the number of the secondary windings of the transformer can be decreased in the present invention. In accordance with the present invention, the rectification devices and the transformer can be compact and light weight and low cost. The effects are remarkable. BRIEF DESCRIPTION OF THE DRAWINGS: Figure 1 is a main circuit diagram of the conventional control apparatus of an AC electric car; Figure 2 is a circuit diagram of one embodiment of the control apparatus of the present invention; Figure 3 is a timing diagram for the operation of the control apparatus shown in Figure 2; Figure 4 is a control block diagram to Figure 2; Figures 5 and 6 respectively graphs showing relations of motor currents and speeds; and Figure 7 is a block diagram of one embodiment of the control method of the present invention. 1 98584 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS: Referring to Figure 2, one embodiment of the present invention will be illustrated. The structure of the embodiment which is remarkably different from the conventional structure is as follows: Among the plural steps of rectification devices (11) - (14) which are connected in series, the rectification devices (11), (14) are connected in parallel corresponding to the two traction motors (25), (26) and the other rectification devices are commonly used. One terminal of the motors (25), (26) are commonly connected and further connected to the DC terminal of the common rectification device (13). The other terminals of the motors (25), (26) are respectively connected to the DC terminals of the rectification devices (11), (14) and the other DC terminals of the rectification devices (11), (14) are connected to the DC terminals of the common rectification device (12). The field control circuit can be the same as that of the conventional structure. Referring to Figure 2, the operation will be illustrated. The AC voltage applied to the secondary winding (3) of the transformer is controlled by the phase control of the thyristor of the rectification device (11) so as to control the armature current of the first traction motor (25) to the predetermined current limit. At the same time, the armature current of the second traction motor (26) is separately controlled by the phase control of the thyristor of the rectification device (14). Both DC terminals of the rectification devices (11), (14) are connected. The other terminals are separated for each of the motors (25), (26) whereby the armature currents of the first traction motor (25) and the second traction motor (26) are independently controlled. The field current is separately controlled depending upon each of the armature 198584 currents of the motors. The controlled phase angle of the thyristors gain depending upon the increase of the speed of the motor to reach the full conduction state, whereby the rectification device (12) connected in series in the common side, is actuated to give the full conduction state. At the same time, the controlled phase angles of the rectification device (11) and the rectification device (14) are rapidly decreased to give zero of the output voltage in the DC side thereof. At this moment, the output voltages of the secondary windings (3), (6) of the transformer are the same as the output voltage of the secondary winding (4) whereby the voltage applied to both terminals of the motors (25), (26) is not substantially changed. Then, the phase controls of the thyristors of the rectification device (11) and the rectification device (14) are performed to control the armature current of the first traction motor (25) and the secondary traction motor (26) to the current limit. Then, the controlled phase angles of the thyristors gain depending upon the increase of the speed to reach the full, conduction state, whereby the common rectification device (13) is actuated to give the full conduction state. At the same time, the. states of thyristors of the rectification devices (11), (14) are decreased to perform the phase control as the aforementioned phase control. In Figure 3, the output voltages of the rectification devices (11) - (14) and the terminal voltages of the motors in the operation steps are shown. In the case shown in Figure 3, the terminal voltage of the first traction motor (25) is higher than the voltage of the second traction motor (26) at the same time point. That is, the controlled phase angle of the thyristor a-^ is smaller than in Figure 3. Figure 4 is a block diagram of an embodiment of the control program for performing the control described above. In the figure, the reference numeral (29) designates a master controller for outputting 198584 a control signal, (30) designates a rectification device selecting circuit, (31) designates a rectification-device-bridge switching circuit, (32) designates a gate circuit of the common rectification devices (only one step is shown in the figure), (33) designates a synchronous power source circuit, (34) designates a current limit pattern generating circuit, (35), (36) respectively designate comparators for comparing the armature currents of the traction motors (25), (26) with the current limit, (37), (38) respectively designate phase detectors for determining the phase angle of a thyristor of the rectification device depending upon the output of the comparator, (39) designates a gate circuit of the rectification device (11), and (40) designates a current feeding rate detector for detecting the phase angle of each thyristor of the rectification devices (11), (14). The other reference numerals designate parts the same as those in Figure 2. A control block diagram for controlling the field current is not shown in the figure. In Figure 4, when a control signal is given from the master controller (29) to the rectification device selecting circuit (30), one of the rectification devices (11) - (14) is actuated depending upon the control signal, especially the sequence of actuation of the common rectification devices (12), (13) being determined. The output of the selecting circuit (30) is applied to the comparators (35), (36) and the bridge switching circuit (31). Description will be made concerning the first traction motor (25). When the output of the rectification device selecting circuit (30) is applied to the comparator (35), the output of the current limit pattern generator (34) is compared with the output of the current detector (27) of the motor and the output corresponding to the difference of both the outputs is applied to the phase detector (37) which detects the phase 198584 angle of the thyristor, thus the rectification device (11) is actuated through the gate circuit (39). The constant current controlling is performed in such a loop so that the armature current of the first traction motor (25) is in coincident with the current limit. The output 5 of the phase detector (37) is also input to the current feeding rate detector (41), where the phase angle for the thyristor is monitored and is output when the maximum current feeding rate, that is, the controlled phase angle (a in Figure 3) is zero or below a predetermined value and the output is applied to the rectification-device-bridge switching circuit 10 (31). The second traction motor (26) is also controlled by the same loop. Both the current feeding rates of the rectification devices (11), (14) become the largest, the output from the bridge switching circuit (31) is applied through the gate circuit (32) to the thyristor of the common rectification device (13) as an actuation signal. At the same time, decrease signals are given to the phase detectors (37), (38) to rapidly decrease the output of the rectification devices (11), (14). The synchronous power source circuit (33) is provided to perform the switching and the phase control of the rectification device bridge in synthronism with the AC voltage, i.e. the voltage of the electric power supply line. The output from the power source circuit is fed to the bridge switching circuit (31) and the phase detectors (37), (38). Figure 5 shows the change of currents of the rectification device bridges when the controlling described above is performed. In the figure, the current characteristic of the first traction motor (25) is indicated by solid lines and that of the 25 second traction motor (26) is indicated by broken lines. As it is clear from the figure as well as Figure 3, the change of the controlled phase angle of the thyristor, i.e. the current feeding rate for the first traction motor (25) is ahead that for the second traction motor (26). 15 20 - 10 - 1 98584 Accordingly, after the current feeding rate for the first traction motor (25) reaches the maximum, the current decreases depending upon the increase of speed. During this time, the phase control of the second traction motor (26) is continuously performed and the first and second traction motors (25), (26) are switched, at the same time, to the common rectification device after the current feeding rate for the second traction motor reaches the maximum. That is, the current of the first traction motor (25) is changed through the points (g) *■©-*- (§)-*-(e)->-(F)-*- © and the current of the second traction motor (26) is changed through the points ® -»-(§)-»-(g) in Figure 5. However, the difference can be practically neglected because the variations of the currents ((c)-^® and ©"*"©) at the switching are minor. It can be considered to employ a control method in which one side of the common rectification device is switched, e.g. the switching is performed when the current feeding rate for the first traction motor (25) reaches the maximum. Figure 6 shows the change of current in this control method. Selection of these control methods depends upon the characteristic difference of the motors and the impedance of AC power source including a transformer. In the embodiment of the present invention, two traction motors are used and the secondary winding of the transformer is divided into three parts; however, a case of increased number of the motors and different number of divided parts, even devided into unequal winding parts, is applicable. Furthermore, it is clear that the same effect can be obtained when the rectification devices connected respectively to each motor are connected to the upstream (the positive side with regard to the power source) of the common rectification device. In the embodiment, a hybrid bridge consisting of thyristors and diodes is used as a rectification device; however, a thyristor bridge to which regenerative braking is applicable can be also used. - 11 - 198584 In the embodiment described above, two motor having the same current limit are used. It is possible to use motors having different current limit values because the rectification devices connected in parallel can be separately controlled. With this structure, a shaft load shifting compensation control which is often used in an electric locomotive can be easily applied. Figure 7 is a block diagram of this control system which is the same as that of Figure 4 except it having a plurality of current limit pattern generators (34a), (34b). The current of the traction motors (25), (26) are respectively controlled by the rectification device (11), (14) which are respectively connected to the traction motors (25), (26) so as to be in coincident with each current limit pattern of the motors and when the thyristors reach the maximum current feeding rate, the motors are switched to the common recfitication device. If free rotation of a wheel occurs, the current in a motor for the wheel is reduced to reduce a force given to the wheel thereby preventing the free rotation to attain readhesion between the wheel and the rail. The description was made concerning a case having only a constant current controlling function. Thus, addition of a constant voltage controlling function is remarkably effective. The description was made concerning an application to a DC shunt motor. Thus, the same effect can be obtained in case of DC series motor. The present invention can be applied to a control device and a control method for a DC electric car such as a DC electric locomotive whic.i rectifys AC power to drive the DC traction motor. - 12 - </div>

Claims

<div class="application article clearfix printTableText" id="claims"> WHAT WE CLAIM IS:

1. A control apparatus of an AC electric car which comprises first and second DC motors each having an armature actuated by separate excitation field control, a first armature terminal of each of said motors being connected in common; a first rectification device formed by a conduction controllable bridge circuit connected to a first AC power source, one DC terminal of said first rectification device being connected to said commonly connected terminals of said armatures; and second and third rectification devices, each formed by conduction controllable bridge circuits connected respectively to each of second and third AC power sources, one DC terminal of each of said second and third rectification devices being respectively connected to a second armature terminal of each motor and the second DC terminal of said second and third rectification devices being connected to the second DC terminal of said first rectification device.

2. A control apparatus of an AC electric car according to Claim 1 wherein said first rectification device is formed by connecting a plurality of conduction controllable bridge circuit rectification devices in series.

3. A control apparatus of an AC electric car substantially as hereinbefore described with reference to the accompanying drawings. Mij B^-HisfTheir Authorised Agents, A. J- PARK & SON Per -13- </div>