CA1196680A - Vehicle propulsion motor control apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A DC series motor control apparatus is operative with a voltage source and includes respective thyristor switch devices to provide power and brake operation of that motor as selected by a conduction control circuit, with a commutation circuit being connected to each one of the thyristor switch devices when desired to terminate the conduction of each thyristor switch device that is made conducting by the conduction control circuit.

Description

1 50,032 VEHICLE PROPULSION MOTOR CONTROL APPARATUS

CROSS-REFE~ENCE TO ~ELATED ~PPLIC~TIONS
The present application is related to U.S.
Patent No. 4,284,930 of T. C. Matty and entitled "Motor Control Apparatus and Method" and is related to U.S.
Patent 4~471,277 to J. H. Franz, Jr. and is entitled "Vehicle Propulsion Motor Control Apparatus", which are assigned to the same assignee as the present application.
BACKGP.OUND O~ THE I~v~NlLON
It is known in the prior art to control the speed of a vehicl~ propulsion direc~ current series motor by a chopper apparatus including a ~hyristor switch device in series with the motor, as sho~n in U.S. Patents 3,769,566 and 4,284,930. Speed control of the motor is provided by varying the width of voltage pulses supplied to the motor such that the resulting average power supplied to the motor establishes the operational speed thereof. A cGmmutation circuit including a charge capa-citor has been used to provide a biased voltage across a conducting thyristor device for cummutating ~he conduction of that thyristor device. A propulsion motor is operative in a motorin~ mode when the passenger vehicle is being propelled or accelerated along a track and in a brake mode when the vehicle is being stopped or decelerated.

3~ ~

2 50,032 As described in a published article in the "Westinghouse Engineer" for March, 1973 at pp. 34-41, the average voltage applied to the motor armature is con-trolled by adjusting the ratio of chopper OFF time to the chopper ON time with the resulting average motor armature current determining the motor torque for moving the ve-hicle along the track.
In the motoring or power mode of operation the motors of a vehicle are connected in relation to a direct current voltage source such that the armature current is supplied through a chopper when the chopper is ON and through the motors to ground. When the chopper is turned OFF the energy stored in the motor reactor and the induct-ance of the motor field maintains current flow in the motor circuit through a freewheeling diode. With the chopper ON the motor curren~ increases and with the chop-per OFF the current is forced into the power supply through the freewheeling diode by the motor reactor.
SUMMARY OF THE INVENTION
The armature of at least one series DC vehicle propulsion motor is energized by a chopper to regulate the current of that motor. The armature is connected in a bridge circuit with thyristor switch devices to select-ively provide each of forward and reverse operations for each o power and brake operations of the motor, with selective operation of thyristor co~nutation apparatus for all of the thyristor switch devices to enable the required motor current switching characteristics to be provided between these respective operations.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 shows a prior art DC motor control apparatus as described in U.S. Patent No. 4 284 930;
Figure 2 shows a prior art bridge circuit ar-rangement for a DC series motor;
Figure 3 shows a bridge control circuit arrange-ment for a DC motor in accordance with the present inven-tion;

3 50,032 Figure 4 shows a modification of the bridge circuit arrangement for a DC series motor in accordance with the present invention;
Fiqure 5 shows the commutation control signal and thyristor switch conduction relationships of the present invention; and Figure 6 shows the motor current characteristics for the motor operation provided in accordance with the prior art motor control apparatus; and Figure 7 shows the motor current characteriskics for the motor operation provided in accordance with the present motor control apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In Figure 1 there is shown a prior art direct current motor control apparatus as described in U.~.
Patent No. 4,284,930, including a motor armature current reversing circuit arrangement, and operative for deter-mining the average current supplied ~rom a direct current voltage source 10 to a direct current motor armature load 12, and including a series main thyristor switch device 14 that repetitively operates in an ON condition and an OFF
condition to chop and regulate the voltage applied to the motor armature load 12. The control of this voltage is determined by changing the ON operation time in relation to the OFF operation time of the conduction by the main thyristor 14 for controlling the speed of the motor 12.
To reduce the speed of the motor armature 12 the armature voltage is decreased and to increase the motor armature speed the armature voltage is increased. The voltage source 10 for a typical traction motor application can be a relatively constant direct current voltage source, such as 600 volts from a central power station. As is well known to persons skilled in this art, the main thyristor switch 14 is gated by a conventional conduction control apparatus 16 in response to a P signal effort re~uest input 17 to turn ON and become conductive and is subse-quently commutated b~ the commutation thyristor 19 in ~ 50,032 conjunction with capacitor 21 to turn OFF and become non-conductive as required to provide a desired averaye voltage across th~ motor armature 12 to determine the motor speed. Each time the main thyristor switch 14 conducts, the volta~e across the motor armature 12 and the motor reactor 18 rises to the voltaye of the voltage source 10. Each time the main thyristor 14 blocks, the voltage across the motor armature 12 and the motor reactor 18 falls to zero, such that the motor 12 responds to the average motor voltaye. If the main thyristor switch 14 remains conductive for a longer time period, this raises the average motor voltage and if the main thyristor switch 14 remains blocked for a longer time period, this lowers the average motor voltage. The motor current increases each time the thyristor switch 14 becomes conductive and then decreases each time the main thyristor switch 14 blocks. The average motor current is proportional to the torque of the motor 12. The freewheeling diode 20 allows the motor current to continue due to the inductance of the motor circuit after the main thyristor switch 14 blocks and becomes non-conductive.
A power thyristor switch 22 is made conductive when it is desired for the motor circuit to operate in the power mode for thP propulsion of the vehicle coupled to the motor armature 12. A power diode 24 and a motor field winding 26 are connected iR the power mode circuit includ-ing the power thyristor switch 22, the return conductor 28, the voltage source 10 and the main thyristor switch 14. A brake thyristor switch 30 is made conductive when it is desired for the motor circuit to become operative in the brake mode. When dynamic braking operation is de-sired, one or more of the braking resistors 32, 34 and 36 are included in the brake circuit including the brake diode 38. A well~known commutation circuit ~0 is opera-tive to terminate the conduction of the power thyristorswitch 22 when it is desired for the motor clrcuit to operate in the brake mode with the brake current flowing 5 50,032 through the motor armature 12. A chanye in khe operation of the motor armature 12 between forward an~ reverse as may be desired in each of the power mode and the brake mode is provided by the well-known mechanical reverser switch arrangement 42, with each of the switches 44 and 46 being changed to the other positions for this purpose.
The brake mode with the main thyris-tor switch 14 not conducting provides current flow through a circuit including the voltage source 10, the freewheel.ing diode 10 20, the motor reactor 18, the motor field 26, the brake thyristor 30, the motor armature 12 and any of the resis-tors 32, 34 and 36 that are not short circuited and through the brake diode 38 to regenerate power into the voltage.source 10.
In reference to the motor control circuit shown in Fiyure 1, when the desired vehicle operation requires chanying from the power mode with the power thyristor 22 conducting to the brake mode with the brake thyristor 30 conducting, the brake thyristor 30 can be made conducting before the power thyristor 22 is made non-conducting such that both the power thyristor 22 and the brake thyristor 30 are conducting at the same time to establish a desired current path from the voltage source 10 and through the conduction control main thyristor 14, the motor reactor 25 18, the field winding 26, the brake thyristor 30, the power thyristor 22 and the ground return conductor 28 back to the voltage source 10 to provide a predet~rmined and controlled current path through the motor reactor 18 and the motor field 26.
To provide the desired control of the motor for particularly low vehicle operating speeds, a forced commu-tation circuit 40 is provided for the power thyristor 22.
When both the brake thyristor 30 and the power thyristor 22 are made onducting during the transition from power mode to brake mode of operation, the commutation circuit 40 is operated when desired to stop the conduction of the power thyristor 2~. The resulting current flow through (3 6 50,032 the inductance of the motor reactor 18 and the field winding 26 will now continue to flow as brake current through the motor armature 12 to provide in effect a very rapid changeover from the power mode to the brake mode of operation. Because of the provision of the commutation circuit 40, brake mode operation is available down to very low vehicle speeds with assured brake current build-up at much lower speeds and lower motor circuit currents than could be provided with previous control apparatus. In addition, the main thyristor 14 can determine the desired magnitude of this current in field 26 before the power thyristor 22 is commutated to establish at least the initial brake effort provided by the motor 12.
In Figure 2 there is shown a prior art motor control bridge circuit ap~aratus, as disclosed in the above-referenced p~tent app~ ca7~on, for a DC motor that provides forward and reverse operation of the motor. The chopper portion 50 of the controi apparatus includes the main thyristor switch device 14 operative with the voltage source 10. A forced commutation thyristor 19 and a commu-tàtion capacitor 21 are operative to terminate the conduc-tion of the main thyristor ~4. The chopper regulates the voltage applied to the motor circuit including armature 12, the motor reactor 18 and the motor field 26. The motor control circuit includes the control thyristor 70, the control thyristor 72, the forward power thyristor 74 and the reverse power thyristor 76 connected in a bridge arrangement with the motor armature 12. A forward brake diode 78 and a reverse brake diode 80 are connected from respective sides of the armature 12, through the brake resistors 32, 34 and 36 to the connec-tion 82 with the voltage source 10 and the main thyristor 14. A conven-tional and well known conduction control apparatus 16 is provided to fire the respecti.ve thyristor switches as required to provide the desired operation of the motor control apparatus. Forward power operation of the motor armature 12 is provided wlth the forward control thyristor ~,3~3~ ~ ~
7 50,032 70 and the forward power thyristor 74 made conductiny by the conduction control apparatus 16. Reverse power opera-tion of the motor arma-ture 12 is provided with the reverse control thyristor 72 and the reverse power thyristor 76 made conducting by the conduction control apparatus 16.
Forward brake operation of the motor armature 12 is pro-vided with the control thyristor 72 made conducting by the conduction control apparatus 16 and the forward brake diode 78 conducting this current through the brake resist-ors 32, 34 and 36 to the circuit connection 82. Reverse brake operation of the motor armature 12 is provided with the contro]. thyristor 70 made conducting by the conduction control apparatus 16 and the reverse brake diode 80 con-ducting this current through the brake resistors 32, 34 and 36 to the circuit connection 82.
In brake operation, regeneration of current to the voltage source 10 is provided when the main thyristor 14 turns OFF. For example~ in the forward brake mode with dynamic braking and the ~ain thyristor 14 turned ON, the brake current conducts from the armature 12, through the diode 78 and the brake resistors 32, 34 and 36, through the main thyristor 14, the motor reactor 18, the motor field 26 and the control thyristor 72. With the main thyristor 14 turned OFF, the brake current conducts from the motor armature 12 through the diode 78 and the brake resistors 32, 34 and 36 through the voltage source 10, the freewheeling diode 20, the motor reactor 18, the motor field 26, and the control thyristor 72. The ~iodes 78 and 80 prevent current from the voltage source 10 feeding back into the brake motor circuit. The reverse brake mode is operative with the control thyristor 70 conducti.ng in conjunction with the diode 80.
In Figure 3 there is shown the bridge control circuit arrangement for a DC motor haviny an armature 12 in accordance with the present invention and including a commutation circuit for each of the thyristor switches 70, '72, 74 and 76. A well-known conduction control apparatus ~'~¢3~

8 50,032 16 provides the gate signals to select the conductive operation of the desired thyristor switches such as the thyristor switches 70 and 74 for the forward power opera-tion, the thyristor switch 72 for the forward brake opera-tion through the diode 78, the thyristor switches 72 and76 for the reverse power operation and the thyristor switch 70 for reverse brake operation through the dïode 80. The commutation circuit 100 is connected across the control thyristor switch 70 for terminatlng conductivity 10 of the thyristor switch 70 when desired. The commutation circuit 102 is connected across the control thyristor 72 for terminating the conductivity of the thyristor switch 72 when desired. The commutation circuit 104 is connected across the thyristor switch 74 for terminating the con-ductivity of the forward power thyristor switch '74 whendesired. The commutation circuit 106 is connected across the reverse power thyristor switch 76 for terminating the conductivity of the thyristor switch 76 when desired.
Each of the commutation circuits 100, 102, 104 and 106 can include a commutation thyristor switch and a charge capa-citor, such as the thyristor switch 19 and the capacitor 21 shown in Figure 1.
In Figure 4 there is shown a single commutation circuit 110 connected across the bridge circuit 112 with the positive terminal 114 of the commutation circuit 110 being connected to the ground conductor 28 and the nega-tive terminal 116 of the commutation circuit 110 bPing connected to the conductor 118 leading from the common connection 120 of the brake diodes 78 and 80 to the con-nection 122 with the first brake resistor 32. A current control diode 124 is connected from the connection 126 with the bridge circuit 112 and the negative terminal of the commutation circuit 110 to assure that desired commu-tation turn OFF of all four thyristor devices 70, 72, 74 and 76 in relation to any stray current flow in the bridge circuit 112 that may be caused by the reactance of arma-ture 12.

9 50,032 In E.icJure 5 th~re is shown the operational relationship between the provided thyristor switch con-duction gating control siynals and the commutakion circuit control si~nals for controlling a DC propulsion motor circuit as shown in Figure 4 in accordance with the pres-ent invention. At time T1 the thyristor switches 70 and 74 are shown conducting the current through the motor armature in the forward power mod~ as regulated by the main thyristor ~witch 14 and as shown by the curves 130 and 132. At time T2, ln preparation for going from the forward po~er mode to the forward brake mode of operation, the thyristor 72 is gated ON as shown by curve 134, and this is provided to assure a known and desired energiza-ion of the motor field 26 in the event the previouslS current flow through the motor field 26 was too low. The commutation pulse 136 is provided at time T3 for terminat-ing the conduction of all thyristor switches 70, 72, 74 and 76. During the commutation pulse 136, the gating ON
of the thyristor switches 70 and 74 terminates, but the gating ON of the thyristor switch 72 continues, such that at the end of the commutation pulse 136, the thyristor switch 72 continues to conduct with the thyristor switches 74 and 76 no longer conducting and the motor operation changes into the forward ~rake mode of opera-tion. A
desired forcing function is determined by the desired current level already flowing in the motor reactor 18 and motor field 26, since if the main chopper 14 had been OFE
prior to the changeover to forward brake, there might otherwise have been too little flux in the motor field 26 and a problem could have been presented by the changeover to forward brake operation without the conduction of thyristor 72 for the time period T2 to T3. Since the main chopper 14 is functioning as a motor current source lt can be used in this manner to control the current of motor field 26 up to a predetermined level before the turn OFF
of the forward power ~hyristor 74 to force the current flsw through the diode 78 and the brake resistor circuit.

50,032 When it is desired to return from forward brake mode to forward power mode of operation, and particularly from high speed forward brake mode, it i~ desirec1 by operation of the conduction control apparatus 16 to gate ON the thyristor switches 70 and 74 at time T4, and pro-vide the commutation pulse 138 to all thyristor switches 70, 72, 74 and 76 from the commutation circuit llO. When the commutation pulse 138 terminates, khe thyristor switches 70 and 74 begin conducting as shown by curves 130 and 132. From high speed brake operation without the application of the commutation pulse 138 to all of thy-ristors 70, 72, 74 and 76, the motor brak current may not die down quickly enough for the desired changeover to the desired power operation. If the forward power control thyristors 70 and 74 are turned ON before the thyristor 72 turns OFF, this can result in an undesired excitatio~ of the field 25 without proper current control resistors.
To assure the desired changeover operation of the motor control circuit shown in Figure 4 from brake to power and from ~ower to brake at all motor speeds and at all practical current levels, the operation of the commu-tation circuit llO ~y the conduction control apparatus l6 in accordance with the present invention is desired, as illustrated in Figure 5.
When it is required to change either way between forward power operation and reverse power operation, for the comfort and safety of the passengers, it is desired that a tachometer lO9 be coupled with the motor armature 12 ~or sensing when the motor sp~ed is substantially zero and a current sensor lll be provided in the circuit of the motor armature 12 to sense when the armature current is substantially zero before the conduction control apparatus 16 provides such a changeover between forward power opera-tion and reverse power operation. For this purpose, a commutation pulse 140 can be applied at time T5 to all of the thyristors 70, 72, 74 and 76 to remove the current from the armature 12.

11 50,032 If r~verse power operation i.s ~esired, at time T6 gating pulses turn ON the thyristor switche.s 72 and 76 as shown by curves 134 and 135. At time T7, in prepara tion for going from the reverse power mode to the reverse brake mode, the thyristor 70 is gated ON as shown by curve 130. This provides energization of the motor field 26 regardless of the previous current flow through the motor field 26.
The commutation pulse 142 is provided at time T7 for terminating the conduction of all thyristor switches 70, 72 and 76. Duriny the provision of the commutation pulse 142, the gating ON of the thyris~or switches 72 and 76 terminates but the gating ON of the thyristor switch 70 continues such that at the end of the pulse 142 the thyris-tor switch 70 continues to conduct. The motor operationchanges into the reverse brake mode. When it is desired to return from the reverse brake mode to the reverse power mode, particularly from high speed reverse brake opera-tion, the thyristor switches 72 and 76 are gated ON and the commutation pulse 144 is provided to all thyristor switches from the circuit 110. When the pulse 144 ends, the thyristor switches 72 and 76 begin conducting as shown by the curves 134 and 135 in the reverse power mode. The vehicle motor control operation then can continue in accordance with this general illustration to estab3ish the desired direction of vehicle movement and the desired speed of that movement.
In Figure 6 there is shown the armature current versu~ time characteristic for the prior art motor circuit shown in Figure 1 and Figure 2 for particular low speed power and high speed brake operations. In lower speed power, as shown in Figure 1, with the main thyristor 14 turned OFF, the freewheeling diode 20, the motor reactor 18, the motor field 26 and the motor armature 12 are in a series circuit with not a substantial voltage drop across the motor armature 12. This causes the motor current to decrease very slowly after the thyristor switch 14 is 12 50,032 turned OFF and as shown in Figure 6 at low speed operation and in the power mode. The brake thyristor switch 30 as shown in Figure 1 has to see a zero current condition before it will turn OFF without a commutation operation such as provided for the power thyristor switch 22 by khe commutation circuit 40. Therefore, an undesired long period of time is required for the motor armature current to go to zero, for the Figure 1 circuit con~iguration, and thereby turn OFF the thyristor switch 30.
In brake operation the brake resistors 32, 34 and 36 as shown in Figure 1 may or may not be in the circuit. With the main thyristor 14 in the OFF condition, the brake current of the armature 12 is freewheeling into the voltage source 10. At high speed brake operation with the main thyristor 14 in the OFF condition, each of the output voltage of the voltage source 10, the voltage drop across the brake resistors, the motor armature back EMF
and the motor reactor voltage drop all determine how long the armature brake current continues to flow and how rapidly this current continues. When the output voltage of the voltage source 10 gets very low and even close to the back EMF voltage of the armature 12, which happens frequently in actual operation for the well-known third rail power supply operative with transit vehicles, this can result in substantially reduced voltage drops in the motor armature circuit and such a reduced voltage drop condition requires a substantially longer time delay to bring the armature brake current to zero.
The provision of commutation circuits for each of the thyristor switches as shown in Figures 3 and 4 provides an improved control of the motor operation in particularly high speed brake and low speed power condi-tions of operation. All of the thyristor switches pro-vided to select the power and brake operation o~ the propulsion motor for both forward and reverse direc-tion of operation are commutated at the same time and then the desired subse~uent conduction of one or more of these {,~

13 50,032 switches is provided, such as shown in Figure 5. This can be done with a conduction control apparatus 16 including a programmed microprocessor operative for respective cycles at a 218 Hz rate such as disclosed in U.S. Patent No.

4,282,466 of T. C. Makty, and such that one cycle of the conduction control apparatus 116 will commutate all of these thyristor switches and if desired the next cycle will provide gate pulses to fire only the selected thyris-tor switches that are to be conductive for the next de-sired operation of the motor circuit, such as shown in Figure 5.
In Figure 7, there is shown the brake current characteristic 160 that would take an undesired time delay period to go to zero without provided commutation of the brake thyristor. For the example of forward brake mode of operation, at time T10 the commtttation circuit 110 is operated to commutate the thyristor switch 72 and the brake current goes to zero. This allows the conduction con-trol apparatus 16 to gate ON the forward power mode thyristor switches 70 and 74, such tha~ the desired motor current builds up as shown by curve 162 in the forward power direction.

Claims (6)

CLAIMS:

1. In control apparatus for a motor including an armature and being operative with a voltage source for determining each of a power mode of operation and a brake mode of operation, the combination of first switch means connected to determine current flow in a first direction through said armature, second switch means connected to determine current flow in a second direction through said armature, commutation control means coupled with each of the first and second switch means and providing commutation control signals for terminating simultaneously the conductivity of said first and second switch means, and conduction control means coupled with each of the first and second switch means and coupled with the commutation control means for selecting one of the power mode or the brake mode of operation by providing a gate control signal to establish the conductivity of a predetermined one of the first and second switch means prior to providing said commutation control signals to the first and second switch means for terminating the conductivity of the first and second switch means and continuing said gate control signal to said one switch means after said commutation control signals are provided.

2. The motor control apparatus of claim 1, with the conduction control means selecting the power mode by establishing the conductivity of the first switch means in relation to terminating the conductivity of the second switch means and providing the brake mode by establishing the conductivity of the second switch means in relation to term-inating the conductivity of the first switch means.

3. The motor control apparatus of claim 1 for a motor including a field winding, with said conduction control means providing a predetermined energization of the field winding in prepara-tion for the brake mode of operation by establishing the conductivity of said one switch means prior to the conductivity termination of the first and second switch means.

4. The method of controlling a motor having an armature and being operative with a voltage source in one of a power mode and a brake mode, including the steps of determining the conductivity of first switch means to provide current flow through said armature in a first direction, determining the conductivity of a second switch means to provide current flow through said armature in a second direction, terminating at the same time the conductivity of said first and second switch means in relation to a desired changeover from one of said power and brake modes to the other of said power and brake modes, and initiating the conductivity of said first switch means at a predetermined time in relation to said conductivity termination and continuing said conductivity of the first switch means after said termination for providing said desired change-over.

5. The method of controlling a motor of claim 4, with said predetermined time being ahead of said conductivity termination when the desired changeover is from the power mode to the brake mode and being substan-tially simultaneous with said conductivity termination when the desired changeover is from the brake mode to the power mode.

6. The method of claim 4 for controlling a motor having a field winding, with said predetermined time being prior to said conductivity termination for providing a desired energiza-tion of said field winding when said changeover is from the power mode to the brake mode.