GB2145592A

GB2145592A - Motor control apparatus

Info

Publication number: GB2145592A
Application number: GB08419360A
Authority: GB
Inventors: Henry Joseph Wesling
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1983-08-26
Filing date: 1984-07-30
Publication date: 1985-03-27
Also published as: CA1260057A; GB8419360D0; GB2145592B; JPS6070995A

Abstract

A motor control apparatus for a motor (43) having a chopper (40) for regulating the motor current and a filter capacitor (56) is provided with a programmed microprocessor (104) for controlling the operation of the chopper in accordance with a comparison of a sensed voltage change (102) across the filter capacitor with an allowed voltage change determined in relation to the motor current (106). The capacitor bank (56) smooths out voltage changes caused by the chopper (40). If the effective capacitance is reduced (e.g. by an open fuse 76,78), voltage ripple may increase to a point at which generated EMI might interfere with other systems. Ripple is thus detected (102) and compared with an allowed figure that depends on the motor current (106). If necessary the chopper (40) is then controlled to reduce the motor current, or is turned off. <IMAGE>

Description

SPECIFICATION Motor Control Apparatus The invention relates in general to a motor control apparatus, and more specifically to thyristor controlled chopper apparatus for controlling the current in vehicle propulsion motors.

It is known in the prior art to employ thyristor switch devices in a chopper apparatus to control the current supplied to transit vehicle propulsion motors. The use of an electrolytic capacitor coupled with a power supply line of chopper control apparatus for a vehicle propulsion motor is known in the prior art to suppress transient energy voltages by storing the energy within the capacitor.

It is known that the ripple voltage or voltage changes across the filter capacitor of a chopper control apparatus for a vehicle propulsion motor, which voltage changes result from the ON and OFF operations of the chopper apparatus should not become excessive to conflict with the track signaling. Transient propulsion motor control system filter capacitor typically includes a plurality of capacitors as disclosed in U.K. Letters Patent 2,036,467 which capacitors are arranged in several columns of fuse protected series connected multiple capacitors.It is known to provide a fuse counter apparatus sensing the voltage on each column of such capacitors to determine when one or more capacitor column fuses are open to such that the chopper should then be controlled to reduce the motor current to avoid ripple voltage interference with the adjacent vehicle controlling track signal circuit operations.

The control of vehicle speed has been determined in the prior art through speed command signals supplied to respective signal blocks into which the roadway track of the vehicle is divided such as disclosed in U.K. Letters Patent 1,199,353.

The chief object of the present invention is to provide a motor control apparatus which detects and corrects the ripple voltage fluctuations to an allowed limit.

With this object in view, the invention resides in a motor control apparatus for a motor operative with a power supply connected across a filter capacitor, to energize the motor in electrical series with a chopper for regulating the motor current in accordance with a motor effort request signal, the combination of: first means for determining the voltage across the filter capacitor, means for determining the motor current, means for determining the change in the voltage across the filter capacitor connected to said first voltage means, means for establishing an allowed voltage change across the filter capacitor in relation to said motor current, and means responsive to the allowed voltage change for controlling the operation of the chopper.

The invention will become more readily apparent from the following exemplary description, taken in connection with the accompanying drawings, in which: Figure 1 schematically shows a prior art track circuit signaling system operative with a transit vehicle; Figure 2 shows a prior art transit vehicle operated with the third rail of a power supply; Figure 3 schematically shows a prior art propulsion motor current regulating chopper apparatus including a filter capacitor; Figure 4 shows a plurality of capacitors in a typical prior art filter capacitor; Figure 5 shows a prior art ripple voltage control apparatus operative in response to the number of fuses that is open; Figure 6 shows the propulsion motor ripple voltage control apparatus including a programmed microprocessor in accordance with the present invention;; Figure 7 shows a flow chart to illustrate the control program operative with the microprocessor shown in Figure 6; Figure 8 shows the ripple voltage sensing apparatus of Figure 6; Figure 9 illustrates the comparison of the sensed ripple voltage with the calculated allowed ripple voltage; Figure 10 shows the operation of the chopper as a function of the sensed level of ripple voltage.

Briefly, the disclosure reveals a motor control apparatus which relates the measured actual ripple voltage of a chopper propulsion motor control, filter capacitor banks with an allowed ripple voltage, determined in accordance with a measured motor current, to establish if any of the capacitors banks have opened or degraded. A microprocessor controls the chopper to operate at a level determined by the comparative amount of actual ripple voltage on the filter capacitors.

In Figure 1 there is provided a schematic showing of a signaling system operative with two roadway track rails 10 and 12. A vehicle 14 is provided to move along the track. A signal transmitter 16 operating at frequency F1 is connected to energize an antenna 18 such that there is induced within the rails 10 and 12 a signal at frequency F1. When the vehicle 14 is positioned as shown in Figure 1, a signal receiver 22 is operative with the antenna 20 to receive the track signal at frequency F1. The receiver 22 receives the signal F1 at a high magnitude when the vehicle 14 is not positioned between the location of the antenna 18 and the antenna 20. The receiving antenna 20 is coupled to a short circuiting bar or conductor 24 which is electrically connected between the rails 10 and 12 at the location of the receiving antenna 20.A similar short circuit bar or conductor 26 is electrically connected between the rails 10 and 12 at the location of the antenna 18. The antenna 18 operates to introduce a local signal at frequency F1 into the rails 10 and 12. The receiving antenna 20 is operative to sense the track signal at frequency F1 which is flowing in the short circuit conductor 24 between the rails 10 and 12.When the vehicle 14 moves in a direction to pass the location of the short circuit conductor 24 and more specifically when the front wheels 27 of the vehicle 14 passes the location of the short circuiting conductor 24, the front wheels 27 provide a short circuit connection between the rails 10 and 12 such that a substantially smaller portion of the track signal at frequency F1 flows through the conductor 24 and at this time the receiving antenna 20 senses a substantially lower value of the track signal at frequency F1 to indicate to the receiver 22 that the vehicle 14 is now located between the position of the transmitting antenna 18 and the position of the receiving antenna 20.The track signal at frequency at F1 is coded to provide a speed command for the vehicle 14, when the vehicle 14 is located between the position of the short circuiting conductor 24 and the short circuiting conductor 26.

In Figure 2 there is shown the vehicle 14 of a rapid transit system which is supplied direct current power from a power supply source such as a third rail 32. The vehicle includes propulsion motors and motor current control apparatus 34.

In Figure 3 there is shown a well known propulsion motor current control chopper apparatus 40 connected in the motoring mode. The chopper 40 feeds current to two propulsion motors 42 and 44 of the vehicle 14. A thyristor firing control 48 provides an OFF pulse to turn ON the turn off thyristor T2 such that the commutating capacitor CC charges to the same level as the line voltage. The commutating capacitor CC would charge to twice line voltage due to its combination with the smoothing reactor L2 if it were not for the free wheeling diode FWD. When the voltage on the commutating capacitor CC reaches the line voltage level, current through the capacitor CC and the thyristor T2 goes to zero and the thyristor T2 turns OFF. An ON pulse is now provided by the firing control 48 which turns ON the thyristor T1 and the reversing loop thyristor T3.The motors are thus connected directly to the supply voltage causing the motor current to build up. Also the voltage of the capacitor CC begins to decay as current flows through the thyristor T3 a reversing loop reactor L3 and the thyristor Ti. The thyristor T3 turns OFF when this current has reached zero and the voltage on capacitor CC has reversed completely. Current now flows in the load only and the circuit is ready for turning OFF. Turn OFF is accomplished by the firing control 48 turning the thyristor T2 ON. The load current now flows through the thyristor T2 and the capacitor CC. After a short delay due to the reactor L2 the thyristor T1 turns OFF and the diode D4 conducts helping speed the charging of the capacitor CC.The reactor L4 limits the rate of rise of current in the diode D4 and the diode D4 stops conducting before the capacitor CC charges to the line voltage. When the capacitor CC has charged to the line voltage, the free wheeling diode FWD conducts current and the thyristor T2 turns OFF leaving the circuit ready for another ON pulse and the start of another cycle. The current from the third rail 50 goes through the line fuse 52 and the line filter reactor 54to the chopper apparatus 22. The line filter capacitor 56 is connected in parallel with the chopper apparatus 22.

In Figure 4 there is shown a typical prior art line filter capacitor arrangement 56 for the example of the third rail power supply 32 being 600 volts direct current, there can be provided in each column as many capacitors as required, for example,three series connected 300 volts rated capacitor 64,66 and 68 in each parallel branch or column of the line filter capacitor to give a 900 volts rated capacitor column. The motor apparatus 43 is shown connected in parallel with the line filter capacitor 56 and having the chopper 40 connected to control the current through the motor apparatus 43.

As shown in Figure 5 a chopper controlled transit vehicle propulsion motor system utilizes a bank of input filter capacitors 56 to smooth out the voltage change effects of the on/off operation of the chopper 40.

If the effective capacitance of the filter capacitor bank 56 is reduced the chopper 40 might cause too much of a change in the loading on the power supply voltage 32 as the chopper 40 goes from OFF to ON to OFF again. The reduced capacitance of the filter capacitor 56 will then result in greater voltage ripple, which can cause excessive EMI generation which might interfere with other systems such as the track signal speed command system. Each of the capacitor branches or columns 72,74 and so forth is connected through a fuse 76,78 and so forth with the last fuse shown as 80. For each fuse that is open and not conductive the effective capacitance of the filter capacitor 56 is reduced. The ripple voltage control apparatus shown in Figure 5 is responsive to the number of fuses that is open.The voltage across each column of capacitors is applied across a different input resistor, such as input resistor 82 for column 72, of an operational amplifier 84 such that the output voltage of the operational amplifier 84 is proportional to the sum of the individual capacitor column voltages. For each fuse 76,78 and so forth that is open for some reason, such as a fault condition of the track system or the like, this output voltage 86 is reduced. A comparator 88 makes a comparison of the summed output voltage 86 with a desired reference voltage 90, and when the summed output voltage 86 goes below this reference voltage 90 the propulsion motor control 92 is caused to reduce the operation of the chopper 40. The propulsion motor control 92 can include a programmed microprocessor such as disclosed in U.K.Letters Patent 1,587,462 with the operation of the chopper 40 being reduced by reducing the retard effort parameter RE described in the above U.K. patent, as desired in response to the summed output voltage 86 going below the reference voltage 90.

In Figure 6 there is shown the ripple voltage control apparatus of the present invention including the line filter capacitor bank 56 connected to be energized by a third rail power supply 32. A voltage sensor 100 is connected to sense the AC portion, such as the voltage change from 700 volts to 800 volts, across the capacitor bank and which is supplied to a ripple voltage sensing apparatus 102 to provide an output to the microprocessor 104 that is proportional to the voltage change, for example 0 to 100 volts ripple.A current sensor 106 senses the current of the motor 43 and supplies this to the microprocessor 104, which includes a program for establishing an allowed ripple voltage in accordance with the relationship that the allowed ripple voltage at the present motor current equals the known allowed ripple voltage at a predetermined maximum current times the present actual motor current divided by the predetermined maximum current, or (ripple voltage at max. current)x(motor current) allowed ripple voltage= (1) max. current The microprocessor 104 then control the operation of the chopper 40 to reduce the motor current in relation to increases in the sensed ripple voltage across the filter capacitor bank 56 above the allowed ripple voltage.

If desired an alarm 106 can be energized to indicate to the vehicle operator that the capacitor filter bank ripple voltage is above the desired allowed ripple voltage.

In Figure 7 there is shown a flow chart to illustrate the control program operative with the microprocessor 104 shown in Figure 6 which program is called VRPL. At block 110, the ripple voltage is measured by the sensor 100 across the filter capacitor bank 56. At block 112 the current of the motor 43 is measured by the sensor 106. At block 114 a determination of the allowed ripple voltage is made in accordance with the above relationship (1). At block 116 a check is made to see if the measured ripple voltage is greater than the allowed ripple voltage. If not, the program returns to the beginning and again makes the measurement of the measured ripple voltage at block 110. If yes, at block 118 the chopper 40 is turned off or its operation reduced as desired in accordance with the magnitude of the measured ripple voltage in relation to the allowed ripple voltage.The program shown in Figure 7 cycles through the operation of steps illustrated on a continuous basis, or if desired, this can be a routine called by a main program controlling the general operation of the propulsion motor 43 as shown in above referenced patent U.K. Patent 1,587,462 and the program shown in Figure 7 is then called each program cycle to determine if the measured ripple voltage is above an allowed maximum value such as 68 volts at a maximum current of 1500 amperes for a well-known Westinghouse type 1462 propulsion motor.

The program shown in Figure 7 controls the operation of the chopper 40 in accordance with the measured ripple voltage related to the allowed ripple voltage which depends upon the amount of motor current. In this way missing capacitor columns as well as degraded capacitance of the filter capacitor 56 can be detected at a lower motor current and before the ripple voltage becomes large enough to create a vehicle signalling interference problem. The formula to establish the allowed ripple voltage provides a proportional relationship between the present motor current and the known maximum motor current, such that an excessive ripple voltage can be determined even at a lower present motor current, for example at 100 amperes.This motor control apparatus permits restricting the chopper operation whenever a defective filter capacitor condition is determined and before the maximum motor current with its associated and undesired ripple voltage is reached.

At the maximum motor current that is known and desired for the particular motor 43 shown in Figure 6 there is established a maximum ripple voltage that will be allowed, and then in accordance with the present motor current the above relationship (1) is utilized to establish the amount of filter capacitance required in the filter bank 56. A present ripple voltage greater than this allowed value will signal that some of the effective capacitance of the filter capacitor 56 is lost either through degrading or a loss of the capacitors resulting from one or more open fuses, and this will cause the chopper 40 either to shut OFF or to reduce its operational performance because the presently allowed ripple voltage is proportional to the present motor current, and by using the above equation (1) there is established the presently allowed ripple voltage for any present motor current.

The control program shown in Figure 7 operates to detect both an open fuse condition which causes the actual ripple voltage across the filter capacitor bank 56 to increase as well as does a decreased capacitance condition of the filter capacitor bank 56 resulting from a degrading of individual capacitors within the filter capacitor bank.

The ripple voltage sensing or detector apparatus shown in Figure 8 operates to measure the actual ripple voltage across the filter capacitor bank 56. The AC or voltage change part of the voltage across the filter capacitor bank 56 is what is considered to be the ripple voltage. As the motor 43 is energized by the chopper 40 the motor current sensed by the current sensor 106 builds up to a maximum level established by the motor effort request signal 108 to the microprocessor 104. There is an allowed maximum ripple voltage related to the desired maximum current level, and the allowed present ripple voltage is established by above equation (1) in relation to that maximum current and allowed maximum ripple voltage.

As the motor current builds up, the control program shown in Figure 7 determines if the measured present actual ripple voltage is greater than the present allowed ripple voltage. If not the motor current is allowed to build up as required by the motor effort request or P signal 108. In this way if some of the capacitor column fuses 76 or 78 are open or if the individual capacitors are degraded to reduce the effective capacitance of the filter capacitor bank 56 the control program shown in Figure 7 will detect this reduced capacitance and permit the requested motor current or reduce the actual motor current as required to keep the actual ripple voltage from becoming greater than the presently allowed ripple voltage.

In Figure 8 there is shown the ripple voltage sensing apparatus 102 of Figure 6. A differential ripple voltage is applied, by the voltage divider 117 connected across the filter capacitor 56 and the differential amplifier 119 to output 0 to 10 volts corresponding to the 0 to 100 volts ripple voltage across the filter capacitor 56, to input 120. This voltage of 0 to 10 volts is applied to the operational amplifier 121 by the capacitor 122 and resistor 124 such that only the voltage change or AC portion of the voltage across the filter capacitor bank 56 is applied to the operational amplifier 120; which can be an MC3303 amplifier from Motorola Semiconductor Products, Inc. and currently available in the open market.The ground 126 is the main power ground 126 shown in Figure 6, such that the BLC plus voltage at terminal 128 above the filter capacitor 56 is relative to the BLC minus voltage at the terminal 130 below the filter capacitor 56. The resistors 132, 134 and 136 scale the actual ripple voltage such that if the measured ripple voltage at input 120 varies between 0 and 100 volts, the voltage at output 140 would be from 0 to 10 volts. The zener diode 142 clamps the output voltage from the operational amplifier 121 at 11 volts and there is about a 0.6 volt drop across the diode 142 such that the voltage at output 140 does not go above about 10 volts. If the ripple voltage at input 120 goes above 100 volts something is wrong in the operation of the motor control system and therefore the motor control system should be turned off.

In one actual embodiment of the ripple voltage sensing apparatus 102 that was built and operated, the following component values were used: C122 0.1,uF R122 4.22 K R124 196K Amplifier 121 MC3303 R132 196K D142 11 volt Zener D145 lN4148 C135 3.3 if R134 100 K R136 100 K R137 100 K Amplifier 139 MC3303 R143 10K C141 0.1 ,uF In Figure 9 there is illustrated the motor current control operation as determined by the allowed ripple voltage in relation to the measured ripple voltage in accordance with above equation (1), assuming the same motor effort request 108 and the same maximum current determined by that motor effort request 108.

The measured ripple voltage 150 is shown in Figure 9A to be less than the calculated allowed ripple voltage 152. In Figure 9B the measured ripple voltage 156 is greater than the allowed ripple voltage 152. In Figure 9C the measured ripple voltage 160 is additionally greater than the allowed ripple voltage 152.

In Figure 10 there is shown the operation of the chopper 40 in relation to the sensed level of ripple voltage across the filter capacitor bank 56. In Figure 1 OA, the output waveform 154 of the chopper 40 corresponds to the ripple voltage condition shown in Figure 9A. In Figure 1 OB, the output waveform 158 from the chopper 40 corresponds to the ripple voltage condition shown in Figure 9B. In Figure 1 0C, the output waveforms 162 of the chopper 40 corresponds to the ripple voltage condition of Figure 9C. At some difference magnitude of the sensed ripple voltage as compared to the allowed ripple voltage, the output waveform would be zero and the chopper 40 would be turned OFF.

Claims

1. A motor control apparatus for a motor operative with a power supply connected across a filter capacitor, to energize the motor in electrical series with a chopper for regulating the motor current in accordance with a motor effect request signal, the combination of: first means for determining the voltage across the filter capacitor, means for determining the motor current, means for determining the change in the voltage across the filter capacitor connected to said first voltage means, means for establishing an allowed voltage change across the filter capacitor in relation to said motor current, and means responsive to the allowed voltage change for controlling the operation of the chopper.

2. The motor control apparatus as claimed in claim 1, with the means for establishing an allowed voltage change being operative in accordance with a maximum current that is predetermined for the motor.

3. The motor control apparatus as claimed in claim 1 or 2, with the maximum motor current provided by the chopper being predetermined in relation to the known operating characteristics of the motor, said means for establishing an allowed voltage change being operative in accordance with the relationship (voltage change at maximum current)x(motor current) allowed voltage change= maximum current

4. The motor control apparatus as claimed in claim 1,2, or 3, with the allowed voltage change establishing means being operative to establish a presently allowed voltage change across the filter capacitor as a function of the present current of the motor and the allowed maximum voltage change in relation to the maximum current of that motor.