GB1587464A - Transit vehicle chopper control apparatus and method - Google Patents

Description

(54) TRANSIT VEHICLE CHOPPER CONTROL APPARATUS AND METHOD (71) We, WESTINGHOUSE ELEC TRIC CORPORATION of Westinghouse Building, Gateway Center, Pitsburgh, Pennsylvania, United States of America, a company organised and existing under the laws of the Commonwealth of Pennsylvania, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention generally relates to the application of thyristor chopper apparatus for determining the propulsion power and electric brake operations of a transit vehicle having series propulsion motors, and more particularly to control apparatus including a microprocessor that is programmed for the desired control of such thyristor chopper apparatus.

Series propulsion motors supplied with direct current power have been known to be used for a transit vehicle with a thyristor chopper, such as disclosed in U.S. Patent 3,530,503 of H.C. Appelo et al, for controlling the acceleration and speed of the vehicle by turning the propulsion motor current ON and OFF in a predetermined pattern. The thyristor chopper can provide either regenerative braking or dynamic braking when braking is desired.

In an article entitled "Automatic Train Control Concepts Are Implemented By Modern Equipment", published in the Westinghouse Engineer for September 1972 at pages 145 to 151, and in an article entitled "Propulsion Control For Passenger Trains Provides High Speed Service" published in the Westinghouse Engineer for September 1970 at pages 143 to 149, there is described the operation of the P signal for controlling all powered vehicles in a train to contribute the same amount of propulsion of braking effort.

In an article entitled "Alternative Systems For Rapid Transit Propulsion and Electrical Braking", published in the Westinghouse Engineer for March, 1973, at pages 34-41, there is described a thyristor chopper control system for propulsion and electrical braking of transit vehicles. The thyristor chopper provides a propulsion system that is superior in smoothness and ease of maintaining a given speed, which latter feature provides the desired automatic train control. Moreover the thyristor system makes regenerative braking practical because the response is fast enough to continuously match regenerated voltage to line voltage, and that matching prevents transients in braking current and torque due to sudden transients in line voltage.The reduction in power consumption that results from regenerative braking can be significant; also, another advantage is in relation to minimizing heat input to tunnels otherwise caused by lack of dynamic braking.

The use of presently available microprocessor devices, such as for example the commercially available "Intel 8080" family of devices, is described in a published article entitled "Microprocessors - Designers New Gain Freedom as Options Multiply" in Electronics Magazine for April 15, 1976 at page 78 and in a published article entitled "Is There A High-Level Language In Your Microcomputer's Future?" in EDN Magazine for May 20, 1976 at page 62.

Reference is made to copending U.K.

application 30009/77 (Serial No. 1587462) entitled "Transit vehicle motor effort control apparatus and method" and to copending U.K. application 30013/77 (Serial No.

1587463) entitled "Transit vehicle electrical brake control apparatus and method." The present invention provides a control apparatus using a programmed microprocessor for the control of thyristor chopper apparatus.

The invention generally resides in a microprocessor control apparatus connected to a chopper operative with a power supply and having an ON operation and an OFF operation, said chopper being operative to control the energization of an electric traction motor, the apparatus comprising: means for providing a first pulse signal and a second pulse signal having a predetermined relationship with said first pulse signal, means responsive to the provision of said first pulse signal for determining the ON operation of said chopper, and means responsive to the provision of said second pulse signal for determining the continued operation of said chopper with said power supply.

In a preferred embodiment a programmed microprocessor apparatus establishes a boost signal, for controlling the operation of a transit vehicle electric motor chopper apparatus, every cycle of the program operation including an ON control pulse positioned within the boost signal.

The chopper operation monitors the provision of the boost signal to determine the proper operation of the programmed microprocessor apparatus and to maintain the operation of the chopper motor control apparatus.

A programmed microprocessor apparatus establishes at least one limit for each of a vehicle speed signal for controlling the operation of the braking resistors to determine the motor electric braking effort in the brake mode and the chopper phase angle signal for controlling the field shunt operation of the motor to determine the motor tractive effort in the power mode for more than one program cycle.

For a more detailed understanding of the invention, reference may be had to the following description of a preferred embodiment to be studied in conjunction with the accompanying drawing in which: Figure 1 is a functional showing of the present control apparatus in relation to the input signals and the output signal operative with the control apparatus; Figure 2 illustrates the input signal operations and the output signal operations of the present control apparatus; Figures 3A and 3B illustrate schematically the provided interface of the present control apparatus; Figure 4 illustrates the coding of a program listing which can be applied to the invention Figure 5 shows the prior art response of a propulsion motor control apparatus to a P signal;; Figure 6 shows the time relationships of the boost pulse, the ON signal within the boost pulse and the clock pulse; and Figure 7 shows in greater detail the time relationships of the boost pulse and the ON signal within the boost pulse; Figure 8 shows a well known operational characteristic curve for a typical series propulsion motor operative with a train vehicle and the present control apparatus; Figure 9 illustrates the speed signal determination in accordance with the present invention; Figure 10 illustrates the relationship of requested current as a function of speed provided by the present invention; Figure 11 illustrates the provided electrical brake fade out in relation to the operation of the mechanical brake; and Figure 12 illustrates the phase angle sensing operation provided by the present invention.

In Figure 1 there is shown a functional illustration of a preferred embodiment of the present control apparatus in relation to the input signals and the output signals operative therewith, and including a CPU microprocessor 94 operative with a PROM programmable memory 96 and a scratch pad RAM random access memory 98 used for intermediate storage. An application program is stored in the programmable memory 96. The microprocessor 94 can be a commercially available unit e.g. INTEL 8080, the random access memory 98 can be an INTEL 8101, and the programmable memory 96 can be INTEL 1702 programmable read only memory, said items being currently available in the open market. There are four illustrated categories of input and output signals relative to the processor controlled operation of a transit vehicle.

The digital input signals are supplied through digital input 100 from the transit vehicle and include the slip slide signal SLIP, the thyristor temperature sensor thermal overload signal THOUL, the effective value of the line filter capacitor as indicated by the fuse counter signal FUSE, the power circuit condition indication signal LCOC, the power and brake feedback signal BFEED, the field shunt feedback signal FS, the brake status signal BRKI and the clock signal 218HZ. The analog input signals are supplied through analog input 102 and include the first propulsion motor leg current I1, the second propulsion motor leg current I2, the line current IL, the line voltage LV, the primary power request or brake request control signal P, the air pressure in the vehicle support bag members providing load weighed current request signal IRW, the analog phase signal IP and the vehicle actual speed signal S1.The digital output signals are supplied through digital output 104 to the controlled transit vehicle and include the line switch control signal LS, the power brake mode control signal P/B, the field shunt control signal FS, the first braking resistor control B1, the second braking resistor control signal BC2, the third braking resistor control signal BC3, the zero ohm field shunt control signal BDC, the 10 kilometer per hour signal 10 KPH, the 25 kilometer per hour signal 25 KPH, the phase zero control signal P),,-the timing control signal BOOST, the ON suppress control signal SUPP and the zero speed signal ZS.The analog output current request signal I+ is supplied through analog output 106 going to an analog phase controller 108 operative to supply the control signal ON to fire the chopper thyristor T1, the control signal OFF to fire the commutating chopper thyristor T3, the control signal T5 for the T5 thyristor in the propulsion motor control chopper apparatus and the analog phase indication signal IP going to analog input 102. The time period associated with turning the chopper ON and OFF is at a constant frequency of 218 Hz, that defines the clock time interval for the program cycle and for checking the process operation.

During each of the 218 time intervals per second, the program cycle operates through the application program. It was necessary in the prior art for some of the input signals to be filtered to slow down the effects of noise transients and the like, but the microprocessor now samples the input signals 218 times every second, so if desired each signal can be checked during each program cycle and, if the signal stays the same as it was before the proper response can be provided. By sampling all the input signals every program cycle and by addressing every output signal every program cycle, if noise transients are received, their effect can be minimized or eliminated. In relation to output signals, a correct output can be given 5 milliseconds later, which is faster than the power response time of the propulsion motor.In relation to input signals, digital filtering by comparison with old data can eliminate transient effects.

The train control system operative with each vehicle provides a P signal which selects a desired propulsion effort and this signal, as will be described in relation to Figure 5, goes from 0 to 100 milliamps and establishes how much propulsion power or braking effort is desired by a particular train vehicle. The P signal is decoded to determine the proper motor current to generate the proper effort. In addition, there is a confirming signal, called the BRKI signal which determines when propulsion power and when braking effort is applied. The purpose of the BRKI signal is to control the power switching at the correct time to avoid one car braking while another car is in propulsion. Contact closures in the power circuitry are detected to establish that the power contacts have been made up properly and to Yeaåjust the settings in the logic.For instance, in field shunt operation, the amount of motor current is adjusted to keep from getting an undesired physical jerk of the vehicle. A failsafe reading of the P signal level is made such that, should the P signal be lost, the train control automatically goes into a brake mode. The present propulsion control apparatus determines which switches to close and when to close them to modify the power circuit properly. A dynamic brake feedback signal is sent to the mechanical brake control for providing the blending of mechanical brake necessary to maintain the deceleration level required by the P signal. The P signal is in reality a vehicle acceleration or deceleration request.

The propulsion control apparatus provides output pulses to the main power thyristors to tell them when to turn ON and when to turn OFF. When a command signal is sensed, for example, if the vehicle is in propulsion or power mode and the command signal desires the vehicle to brake, the control apparatus senses any difference between the desired motor current and the actual motor current and ramps down the actual current as required. When the current gets down to a desired level, the control apparatus opens all the propulsion switches and reconnects for a brake operation, then ramps the motor current back up again to the level established by the desired brake operation.

In Figure 2 there is illustrated the input signal operations and the output signal operations of the present control apparatus, including the microprocessor 94 operative with its random access memory 98 and its programmable memory 96. The analog input signals are supplied through the analog input 102, through the multiplexer 120 and analog-to-digital converter 122 and input port 124 of the microprocessor 94 operative with a data bus 126 and the address bus 128.

The address bus 128 abnd data bus 126 are operative through an output port 130 to control the multiplexer 120 and the analogto-digital converter 122. The digital input signals are supplied through the digital input 100 operating through buffer 132 with the input port 136 operative with the data bus 126 and the address bus 128. The digital output signals are supplied through digital output 104 including output ports 140 and 142 and respective isolation circuits 144 and 146 with drivers 148 and 150 in relation to the data bus 126 and the address bus 128.

The analog output 106 is operative through output ports 152 and 154 through a buffer 156 and a digital-to-analog converter 158 with the analog phase controller 108.

The central processor 94 addresses a particular input port or output port or memory location and then transmits data to, or receives data from, that location on the data bus 126. For example, the central processor 94 can address an input port, such as input port 124 for the analog-to-digital converter 122 and the multiplexer 120. First it presents data to output 130 to tell the multiplexer 120 which analog circuit input signal is desired with some sort of buffering, such as a differential amplifier or a low pass filter. When the particular input is addressed, the analog-to-digital converter 122 cycles converting that data. The digital feedback signals from the digital feedback 100 come in and can be read whenever desired.

A monitor or display panel 192 can be provided to indicate the state of operation of the central processor 94. The output port 153 is operative through digital-to-analog converter and buffer amplifier 194 with the provided test point 190 and is operative with display 192. The manual switches 196 are operative with input port 137 as shown.

The P signal goes through the multiplexer 120 to request a particular vehicle operation. The control processor 94 senses the various currents, the various voltages and the vehicle speed. It takes digital feedback signals through buffers to know what is going on in the power circuit in relation to currents and voltages. The control processor 94 provides output command signals to the power circuit. Command signals go on the data bus and output ports function as latches so the control processor 94 can proceed to do other things while each latch remembers what is on the data bus at a given address.

The control processor 94 outputs a signal to close whatever power switches are desired and also outputs a requested motor current.

The requested current is decoded in a digital-to-analog converter. The analog motor control circuit, in response to this current request, senses the actual motor current and the commutating capacitor voltage, and if everything is satisfactory, the motor control circuit appropriately fires the drivers for the chopper apparatus.

In relation to effort versus motor current, at up to about 100 amps, a typical series propulsion motor as shown by Figure 5 provides little practical effort, and above 100 amps the characteristic looks more or less like a straight line. As speed increases, there is wind resistance, so the effective effort available is actually less in power, and in braking, the reverse is true. When power is requested, motor current comes up to the P signal requested level at a jerk limited rate. The vehicle increases its speed because of the effort supplied. The phase increases with speed, and when the phase approaches almost 100%, the full field operation is completed and the field shunt is used to weaken the motor field, and this provides a transient response problem; a very fast controller is required, such that it can properly control the phase on the thyristors.

In actual practice, propulsion power is easier to control because in power a particular phase angle sets a percentage of line volts on the motor, and this will give a particular amount of motor current, such that if the phase is set at 50who, a particular amount of current is provided in power operation for a given speed. During braking, this same relationship is not true since brake operation is more unstable. If the phase is held at a desired place in power operation, the motor current is stable; if a particular phase setting is held in brake operation, the motor may go to overload or to zero.If it is desired to initiate brake operation, the control apparatus has to command brake which ramps down the motor current on a jerk limit, then opens up the power switches and reconnects the power switches for brake operation; thereafter, the control apparatus goes into brake operation and ramps up the motor current to give the torque necessary to get the desired brake effort. The motor may be generating a considerable voltage that goes back into the supply line so a resistor is put into the circuit to dissipate the excess voltage. As the vehicle comes down in speed, the motor counter EMF drops and the chopper can no longer sustain the motor current, so switches are operated to change the resistors to maintain the desired motor current.If the line voltage exceeds a particular value to indicate that the line is not receptive and won't accept the generated current, the motor current is reduced; if no dynamic braking resistor is used, with dynamic resistors in the circuit, and if the line voltage becomes excessive, the motor current is shunted into the dynamic braking resistor.

In Figures 3A and 3B there is schematically illustrated the provided interface of the present chopper logic control apparatus.

The digital input 100 is shown in Figure 3B operative through the buffers 132 with the input port 136. The analog input 102 is shown in Figure 3A operative through multiplexer 120 and the analog to digital converter 122 with the input port 124 of the microprocessor. The output port 130 is operative with the register 131 to control the multiplexer 120 and the analog to digital converter 122. The output port 152 is shown in Figure 3A operative with the digital to analog converter 158 and the analog phase controller 108; the output port 106 is shown in Figures 3A and 3B operative through buffer amplifiers 156 with the drivers 109, 111 and 113 for controlling the respective thyristors T1, T2 and T5. The output port 142 is shown in Figure 3B operative with the isolation amplifiers 146. The output port 140 is shown in Figure 3B operative with the isolation amplifiers 144.The output port 153 is shown in Figure 3B operative with isolation amplifiers 194 and test point 190 and operative with display 192.

The pump circuit 151 operates to verify the proper working of the present control apparatus including the microprocessor 94 before the line switch is picked up and the desired propulsion motor control operation takes place. A dummy boost signal is initially put out at program line 16 to enable the line switch to be picked up, and during the main program operation if something goes wrong the boost signal disappears and the line switch drops out. The Y carrier shown in Figure 4 has added to it the boost bit, and then time is called to wait as shown by the code sheet; the Y carrier indicates whether the OFF suppress or the ON suppress is called for.

The load weighed current request signal is put out by amplifier 153. Then the buffer 155 leads to the phase controller amplifier 157, which takes the current request signal from buffer 155 and the motor current signals I1 and 12 from lines 159 and 161. The output of controller amplifier 157 is the requested OFF pulse position or the phase angle IP. The output of the amplifier 157 is compared by comparator 163 with the timing ramp from amplifier 165 which is reset by the computer each 218 hertz. The comparator 163 establishes when phase angle signal IP has exceeded the timing ramp, and this would determine at the output of comparator 163 where the OFF pulse is positioned. The logic block 167 determines whether or not the OFF pulse position output of comparator 163 is actually used.

For example, if comparator 169 determines there is too much current in the system, the OFF pulse will be fired and might inhibit or suppress the ON pulse in logic block 171 which is operative with the ON pulse. The boost pulse comes from the computer and goes into the logic block 167 on line 173, and will fire an OFF pulse on the leading edge if comparator 169 has not already fired a pulse and suppress any further action out of the control system. The logic block 167 includes a flip-flop operative such that if an OFF pulse is fired once during a given program cycle, a second OFF pulse is not fired during that same program cycle. The power up restart circuit 175 suppresses pulses until the control system has time to operate properly.

The circuit 177 is a monostable to assure that only a pulse is output, and circuit amplifier 111 drives the OFF pulse going to the gate pulse amplifier for thyristor T2. In power mode the FET switch 179 is closed to provide the desired motor characteristics compensation signal, and in brake mode this switch is opened to provide a faster controller operation. The amplifier 181 checks the phase controller 157 to see if the signal IP is all the way up against the bottom stop to indicate too much current, and if so, the circuit 171 suppresses the ON pulses; this is used when starting up in power to skip ON pulses. The ON pulses are suppressed by the power up circuit 183. The ON pulses use the monostable 185 and the driver 109 as in the operation for the OFF pulses. The safety enable signal or pump circuit 151 will stop the firing of an ON pulse if repetitive boost signals are not provided.The FET switch 187 energizes the line switch output, such that if there is no activity on boost signal line 173, then the pump circuit 151 will cause FET switch 187 to keep the line switch dropped. The T5 signal comes from the computer to fire the T5 thyristor, and monostable 189 drives the driver circuit 191 going outside to the gated pulse amplifier for the T5 thyristor. The phase controller 108 includes the operational amplifier 157, with its attendant compensation for power and brake operations. The computer can force the controller 108 from output port 3-0 to zero for startup. The pumping circuit 151 checks the activity of the computer by looking at the boost line 173 for snubbing the provision of ON pulses and thereby controls the line switch.If the line switch is out, the propulsion and brake control system cannot operate the chopper apparatus, so if something is wrong, it is important to snub the ON pulses quickly, because the line switch takes time to drop out; for this reason an effort is made to stop the ON pulses when some control apparatus malfunction occurs and is sensed by the boost signals no longer being provided.

Figure 4 illustrates a code sheet that can be used to develop a program listing for the control apparatus. As shown in Figure 4 and in reference to Figure 2, output port 1 (shown in Figure 2 as 153) was used for a test mode, output port 3 (shown in Figure 2 as 154) was used for analog manipulation, output port 4 (shown in Figure 2 as 152) was used for analog command signal output, output port 5 (shown in Figure 2 as 142) and output port 6 (shown in Figure 2 divided into four bits each for 140 and 130) were used for digital command signal outputs, input port 4 (shown in Figure 2 as 136) was used for digital input data, input port 5 (shown in Figure 2 as 124) was used for analog input data and input port 6 (shown in Figure 2 as 137) was used for test purposes in relation to manual input switches.

In Figure 5 there is illustrated the wellknown response of the propulsion motor control apparatus to the P signal 30. When the P signal 30 is below a value of about 60 milliamps, the control apparatus operates in the brake mode and for a P signal above this value of 60 milliamps, the control apparatus operates in the power mode.

The boost pulse signal is developed within mode 4 of the program, which is operative during every cycle of the program operation. The start of the boost pulse as shown in Figure 6 is provided at program line 27. The position of the ON signal within the boost pulse is provided by program line 28, and the current request is provided at output four going to the digital to analog converter 158 and the analog phase controller 108 shown in Figure 2. The P signal determines the current request I+ to the analog phase controller for establishing the ratio of ON to OFF operation of the chopper. The end of the boost pulse is provided by the program line 29.

If for some reason the program operation were to fail, the boost signal would not be provided. The pump circuit 151 shown in Figure 3A must sense the provision of the successive boost signals, with one boost signal being provided for each cycle of the program operation, before the pump circuit 151 maintains an adequate output to enable the power supply line switch closed and not shut down the motor operation. The boost signal provides a protection time band during which an OFF pulse cannot be provided, which protection time band is selected in relation to the known operational speed of the microprocessor such that an OFF pulse cannot occur within a time period of 350 microseconds before the ON pulse and within a time period of 350 microseconds after the ON pulse as illustrated in Figure 7.The guard protection time band is provided to the analog system operation, since the boost is used to release the OFF pulse. The OFF pulse can be defeated during the boost signal interval, and the ON pulse can be suppressed by the SUPPRESS signal from the digital output 104 if desired for some reason. An OFF pulse is allowed only outside of the boost signal, and the position of the boost signal protects the ON pulse in this regard, and thus the man chopper circuit.

By sensing the occurrence of the boost signal by the pump circuit 151, the pump circuit 151 will not maintain its output adequately to keep the supply line switch closed if the boost signal does not continue to occur in a regular and successive manner.

At program line 27, the output three provides the boost signal to the buffer 156 and the analog phase controller 108 as shown in Figure 2. The microprocessor operates in a time sequential manner, so the command of program line 27 requires a known amount of time, which is 350 microseconds before the command of program line 28 is executed, and another 350 microseconds is then required before the command df program line 29 is executed. This provides the boost signal and the ON pulse positioned relationship shown in Figure 7.

The Y carrier information determines the ON pulse as shown by the code sheet of Figure 4. The inherent microprocessor operational time is utilized for the purpose of locating the ON pulse within the protection time band of the boost signal.

To provide the desired control system response characteristic in relation to a bandwidth consideration, the high speed analog phase controller is provided and controlled by providing the boost signal to protect the ON pulse and prevent an OFF pulse for a determined time period before and after the ON pulse and locating the ON pulse in a desired position, and then monitoring the continued and proper provision of the boost signal to maintain the operation of the chopper and subsequent motor control apparatus as determined by keeping the power supply line switch closed. The pump circuit 151 must be responsive to a sensitive signal to assure continued and proper operation and integrity of the program with the microprocessor. If the pump circuit 151 senses any failure in this regard, it will shut down the motor control system.An effort was made to select one of the most critical signals used by the program for this purpose, such as in relation to the location in the program where the boost signal is provided, and the program always goes through mode 4 during each program cycle of operation. In addition, the current request IR is provided during this same block of the program. Therefore the program operation must pass through the mode 4 block in order to keep the motor control system operational.

The analog phase controller can respond to an OFF pulse anywhere between the falling edge of one boost signal and the leading edge of the next succeeding boost signal, and this establishes the ON/OFF ratio of the chopper since the microprocessor puts out the ON pulse shown as O in Figure 1 and it puts out the boost pulse. The phase controller cannot fire the OFF pulse before the falling edge and cannot fire after the leading edge of the boost pulse, so the boost pulse in effect determines a dead band. The boost pulse is in the order of 700 microseconds long and the time cycle of the boost pulses is in the order of 4600 microseconds as determined by the clock pulse rate, so the OFF period is substantially larger than the boost pulse period. The analog phase controller can fire the OFF pulse anywhere during the total time cycle other than during the boost pulse. The ON pulse is timed by the microprocessor to be approximately in the middle of the boost pulse, with about 350 microseconds within the boost pulse before the ON pulse occurs and about 350 microseconds within the boost pulse after the ON pulse occurs, as shown in Figure 7. This time relationship is required to allow the thyristor circuit of the chopper to complete the last received command signal; for example, after an OFF pulse is given to the thyristor T2 then this time period of about 350 microseconds is required before an ON pulse can be given to thyristor T1 to permit the chopper circuitry to reset properly for this operation.If the OFF pulse is not specifically suppressed before the leading edge of the next boost pulse, then an OFF pulse is fired by the phase controller, and after the leading edge of the boost pulse at about 350 microse conds an ON pulse is fired, if allowed.

Normally, this ON pulse is allowed, but the ON pulse can be suppressed independently as well as the OFF pulse can be suppressed if desired. But in normal operation, the leading edge of the boost would be followed after about 350 microseconds by the ON pulse, and after another about 350 microse conds the falling edge of the boost pulse and the phase controller would then establish the desired ON/OFF time ratio by appropriately firing the OFF pulse in accordance with the current request signal I+. The pump circuit 151 responds to the boost pulse to allow any ON pulses to be fired and the line switch to close. This assures that the microprocessor is operating validly.If the microprocessor is operating properly, it will provide the boost signals to keep pumping the safety enable circuit, and if the microprocessor outputs the ON pulse every 1/218 second, the pump circuit 151 allows firing the ON pulse and will allow pick up of the line switch. If for some reason the microprocessor discontinues providing the boost signals, the safety enable circuit 151 will stop pumping and will shut down the chopper and the motor control operation. A repetitive input boost pulse to the pump circuit 151 is required at substantially the rate of one every 1/218 second to continue the enable output from the pump circuit.

The digital output provides the boost pulse to the analog phase controller. The clock initiates each program cycle and at the beginning of each cycle provides the leading edge of the boost, then the microprocessor counts for 350 microseconds and provides the ON pulse and then counts for 350 microseconds and provides the trailing edge of the boost pulse. After the boost interval, the program goes through its desired operations before the next boost pulse.

The pump circuit 151 verifies the proper working of the microprocessor before the line switch is picked up and the propulsion motor control functions take place. A dummy boost signal is initially put out to enable the line switch to be picked up, and during the main program operation if something goes wrong the boost signal disappears and the line switch drops out. The Y carrier has added to it the boost signal bit, and then time is called to wait as shown by the code sheet in Figure 4; the Y carrier indicates whether either one or both of the OFF suppress or the ON suppress are called for.

In Figure 8 there is shown a motor characteristic for a well-known series Westinghouse traction motor of Type 1463 operative through a 5.58 to 1 gear ratio with 30 inch vehicle wheels.

SPEED SIGNAL HYSTERESIS The values of the brake resistors are selected for inherent stability of the system operation during brake mode. In reference to Figure 8 for a given supply line voltage as seen by the vehicle motor, realizing that Figure 8 relates to one motor and for two motors connected in series an 800 volts supply line would provide in the order of 400 volts across each motor, when the chopper is switched off the circuit should cause a motor current decrease in brake mode of operation. When the chopper is switched ON, the motor current should increase.For an 800 volts power supply line, about 400 volts is applied across each motor, and if a well-known load line is applied to Figure 8, the slope of that line would be a function of the resistance of the motor circuit with the motor considered to be a generator in the brake mode, the motor circuit includes a resistance and the voltage across the motor is determined by the speed of the motor and the requested motor current. On an average basis of the chopper operation, the voltage generated by the motor minus the motor circuit resistance IR drop must be equal to the supply line voltage. If the generated voltage minus the IR drop exceeds the supply line voltage, then a larger current will result and a lesser current will result if the opposite is true.The motor is operating as a generator, so the more current requested from the motor causes the motor voltage to go higher, since more current will cause more volts to be generated. In effect the generator is operating as a negative impedance device, and to assure stability of the circuit the positive resistance added to the circuit has to be greater than the negative resistance of the generator. Thusly, this limits the requested brake current available to avoid having the generated voltage exceed the line voltage and bring about an unstable system operation. In an effort to obtain the desired brake current magnitude, resistors are inserted into the circuit to provide a different slope to the load line in relation to the vehicle speed. When the chopper is OFF, the line voltage plus the IR drop should be greater than the generated motor voltage.When the chopper is ON, it more-or-less shorts the supply line and the applied supply line voltage goes down to near zero volts and a net positive voltage results. A chopper adjusts the time spent OFF at the higher applied supply line voltage compared to the time spent ON at the lower applied near zero supply line voltage, so the average voltage intercepts the speed characteristic curve at the desired motor current for the desired brake effort operation. As the vehicle slows down, the chopper has to be ON more to mantain this brake motor current until the chopper is ON full time and with no other action then the current would begin to decrease. The motor circuit resistance value can now be changed at some point as a function of vehicle speed, to change the slope of the load line and this permits the chopper to operate at a lower speed.Thus, the brake resistors are inserted into the motor circuit for the upper speed operation of the motor, and when the motor speed gets below a determined value the resistors are switched out of the circuit to improve the control range of the chopper circuit. The resistors have to dissipate a considerable amount of energy as heat loss in the regenerative brake mode and this should be minimized by changing the resistance as soon as practicable in relation to a reasonable number of brake resistors and switches and the time required to do this. In a typical installation for instance, at about 70 MPH the first resistor is changed, at about 60 MPH another resistor is changed, and at about 40 MPH the resistor is switched out.

The speed signal sensing operation for this purpose requires a stable speed signal to determine the switching of these brake resistors, and further it is not desired to switch these resistors into and then back out of the motor circuit as a result of noise signal effects and the like. The whole motor circuit would be significantly disturbed by such a practice. For each resistor change that is made, the motor is generating so many volts, the supply line is providing so many volts and a sudden resistor change creates a delta voltage condition in the motor circuit, and to reestablish the desired circuit operation level the chopper phase angle is changed. The chopper operates to determine the net voltage across the motor circuit, including inductance. The current rate of change is determined by the voltage across that inductance.

The measured vehicle actual speed S1 varies as required by the desired transit vehicle performance. The internal program speed S shown in Figure 6 as curves 160 and 162 is made to follow the measured actual speed S1 shown by curve 164. The program speed S shown by curve 160 follows in the up direction of the actual speed and the program speed S shown by curve 164 follows in the down direction of the actual speed.

When the actual speed S1 shown by curve 164 and on line 166 is increasing, the program speed S shown by curve 160 is at a predetermined difference such as 1 KPH less; and when the actual speed S1 shown by curve 164 and on line 166 is decreasing, the program speed S shown by curve 162 is at a predetermined difference such as 1 KPH greater. This results in the program speed S following behind the actual speed by the 1 KPH difference until the actual speed S1 reverses and begins to decrease, at which time the program speed S would stay at the same value until the actual speed S1 decreased to 1 KPH below the program speed, and the program speed S would then follow at 1 KPH above the actual speed.If, for some reasn, a noise perturbation of the speed vehicle actual reading taken from a tachometer operative with a wheel axle should occur, this might otherwise needlessly trip the switch contactors in the brake resistor circuits, and a considerable number of other speed related decisions are made in the course of the program operation. If the actual speed S1 is greater than the program speed S plus three units (about 1 KPH) then the program speed S is incremented by one, and if the program speed S is greater than the actual speed S1 plus three then the program speed S is decremented by one, which provides in effect a two KPH speed signal hysteresis band.It was known in the prior art to provide a hysteresis effect for each speed signal decision operational amplifier, but not to involve many functions of the same speed variable and put the hysteresis on the speed variable before making the many desired functional decisions.

Because there are a number of decisions that are made throughout the whole program in response to vehicle speed, by providing this hysteresis effect, the general problem of oscillating decisions in relation to sensed speed is avoided. Every time a decision level in speed is reached, the speed has to be determined by this provided hysteresis band before the control action responds for the rest of the program operation.

The internal artificial parameter S is established in relation to S1 the currently read actual speed, so the parameter inside the program is related to the actual speed. If the actual speed S1 is greater than S + 3, such that the new value of speed or the currently read value of speed is greater by a magnitude of 3 more than the program speed S, then the program speed S is incremented by 1 once every program cycle. First, this operation gives a bulk hysteresis on all decisions made on measured actual speed and secondly it acts as a filter because the internal speed S is changed only one incre ment per program cycle. If there is any noise in the measured speed, the program speed S will only change by a small amount once per cycle.A hysteresis condition is put on measured speed by requiring that the new measured actual speed changed by an amount greater than 3 units, and then only allows a one unit change to the speed S seen by the program.

Since the program speed moves faster than the vehicle speed S only noise is filtered out, and the actual speed is not affected.

ELECTRIC BRAKE EFFORT FADE OUT The brake fade out occurs after all the brake resistors are out of the motor circuit, and the thyristor chopper is full ON, and the speed is going down such that current can no longer be maintained. The purpose is to adapt the faster electrical brake effort char acteristic to the known slower mechanical brake effort characteristic. It is desired to slow the electrical fade so that together with the mechanical brakes no jerk is noticed in the net brake effort. This permits the slower mechanical brake effort to keep up with the drop off of the electrical brake effort. The minimum circuit resistance is known and the operating characteristics of the chopper apparatus is known. There is a motor current point of minimum voltage for the chopper at maximum ON time. The brake effort request determines the motor current.

If the speed goes down beyond this current point, the motor current cannot be sus tained and electrical brake effort control will be lost. The mechanical brake must satisfy the jerk limit rate of change of deceleration or how fast the mechanical brakes can be applied, and is is known to require a certain time period to apply the mechanical brakes from zero to maximum levels of operation. Knowing the accelerat ing rate of the vehicle, the time for a change in speed determines the speed value at which the computed electric brake fade out should start, and the program line 85 states this vehicle speed is in the range of 60 hexadecimal to 10 hexadecimal.A speed range of 0 to 100 KPH may be represented for instance by a binary relationship of 0 to 256, and 60 hexadecimal represents 37 percent or 37 KPH and 10 hexadecimal represents 4 percent or 4 KPH. If the requested current PO is greater than twice the value of speed minus 20 hexadecimal, then PO is set equal to the latter. In Figure 10 the speed versus requested current re lationship is shown to illustrate how the value of PO falls offs as a function of speed reduction until the speed reaches a value of 11 hexadecimal in program line 88 where PO is set at a fixed value.

The provided taper allows the mechanical brakes to build up in effort to compensate for the reduction in the electric brake effort.

In Figure 11 curve 194 shows the provided electrical brake fade out and curve 196 shows the friction mechanical brake effort build-up, and the sum of these two curves 194 and 196 is the desired constant value curve of resulting net brake effort 198.

Without the here provided controlled electric brake fade out, the curve 190 illustrates the uncontrolled electric brake fade out that would otherwise result.

The dynamic brake feedback signal to the mechanical brake system causes the mechanical brake to build up early and follow the controlled decrease of the dynamic electric brake system. The program line 86 operates to reduce the P signal current request as a function of speed, and this controls the generated brake current in the regenerating motors. A false motor current fade out is provided while the vehicle speed is adequate to maintain the motor current as desired.

FIELD SHUNT CONTROL Motor operation characteristic curves such as those shown in Figure 8, but related to tractive effort for full field operation and field shunt operation, are well known to persons skilled in this art. For a given motor current, the tractive effort of the motor with full field operation and for shunt field operation can be determined. In power more current is requested as the speed increases whereas in brake less current is requested as the speed is increased. When the field is shunted, this shifts the motor characteristics and if a given tractive effort is required to give the acceleration rate desired, as the speed increases for a given current the full field operation is suitable up to some speed.If it is desired to keep the same tractive effort level, it becomes necessary to shunt the field and increase the motor current to a new level corresponding to the shunt field operation. At this new current level, the desired tractive effort can be obtained up to a higher speed of motor operation. This additional speed is obtained by paralleling the motor fields into shunt operation, to provide one-half the motor armature current in each motor field. Once the 95% ON duty cycle of the chopper is reached, before the field shunt is changed, a predetermined time delay is provided by counting a number of clock pulses to avoid instability of field shunt change.When the field shunt is changed, this significantly changes the motor characteristics and the chopper has to adjust from the 95% ON duty cycle to a new phase angle of operation, such as in the order of 70% ON duty cycle of the chopper. It is desired to assure that the chopper operation is actually stable at the 95 o ON duty cycle and not an anomaly of noise perturbation to only momentarily bring the chopper to the 95% ON duty cycle level. The phase angle controller is very fast in operation and it is not desired to respond to a momentary high phase angle condition and change the field shunt before the chopper is at a steady-state 95% ON duty cycle of operation, and then have to unshunt the fields when the chopper returns to its stable operation below the 95% on duty cycle condition.This would require going from a parallel field connection back to a series field connection and this is objectionable in relation to the switches and the motor operation. Once the 95% ON duty cycle condition is maintained for the provided time period, the switches are operated to shunt the motor fields and this causes the chopper to phase back to about a 75% ON duty cycle. Therefore, the decision point has to be moved now from the previous 95% ON level to a lower value of about a 60% ON duty cycle level, so the motor fields do not unshunt by the expected phase back of the chopper operation. This provides a hysteresis conditioning of the response to the chopper phase angle, including a time element in the response, to improve and make more stable the motor field shunt control operation.

If the phase angle PH is greater than OE5 hexadecimal, then a timer TP is incremented by one per program cycle if the phase angle stays continuous. If TP becomes greater than 13 hexadecimal then TP is forced to have a maximum of 13 hexadecimal. If TP is greater than 10 hexadecimal, the field shunt switches are operated. The instant is sensed when the phase angle exceeds about 95% ON duty cycle, and the operation of time TP to increment by one for each program cycle provides a desired time characteristic for the phase angle to remain above this upper limit of about 95% ON duty cycle. This operation is shown in Figure 9 where the phase angle 191 has to remain above the provided upper limit 193 for a time period before the field shunt operation is effected. When the field shunt changes, then the phase angle of the chopper drops to about a 70% ON duty cycle.

The available dynamic range of the full field operation was about finished since with a full field the motor was generating a lot of back EMF which was equalizing the supply line voltage and this required the chopper to be ON most of the time. When some of the field is shunted, this weakens the magnetic field in the motor and reduces the back EMF, and to get more current at the same torque the chopper is phased back towards the OFF position to give more dynamic range again. If the phase angle goes below a minimum limit of about 60% ON duty cycle, then the timer TP is decremented by one for each program cycle. This recognizes when the phase angle is below a certain limit for a given number of program cycles, and when the time TP is less than 10 hexadecimal this opens the field shunt contactor.The input 4 is read to bring back the status of field shunt FS, to indicate whether or not the field shunt has actually closed because this is a non-time related thing; and is, whenever the request is made to close the field shunt, there is a time element involved in the mechanics, so it takes a certain amount of time for it to happen, and the microprocessor waits after the request is put out for the response that says the field shunt has actually closed; and when it is actually closed, an increment of current of 49 hexadecimal is added to the current request.

The present control apparatus, including the microprocessor, is more reliable; in terms of mean time between failures, there is improvement by a factor of 5 to 10 as compared to prior art analog control systems using hard wired digital logic circuitry.

In the event a prior art analog control system did fail, there was no provision for monitoring or sensing the proper and continued operation of the system, unlike as here provided by the pump circuit 151 responding to the boost signal.

WHAT WE CLAIM IS: 1. A microprocessor control apparatus connected to a chopper controlled transit vehicle motor for determining an ON operation and an OFF operation of said electric motor, the apparatus comprising: means including a programmed digital apparatus to provide a digital signal in response to a selected operating condition related to the operation of said transit vehicle, chopper and motor; means for sensing when said signal is greater than a predetermined limit and lasts longer than a known time period; and means operative with said sensing means to control the operation of said electric motor.

2. The control apparatus of claim 1, with said condition being the speed of said motor.

3. The control apparatus of claim 1, with said condition being the phase angle of said chopper for selecting the ratio of the ON operation to the OFF operation of said chopper.

4. The control apparatus of claim 1, with said motor being operational in one of power and brake modes of operation and with said condition being speed; and said controlling means including changing means for changing an operational characteristic of

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. duty cycle to a new phase angle of operation, such as in the order of 70% ON duty cycle of the chopper. It is desired to assure that the chopper operation is actually stable at the 95 o ON duty cycle and not an anomaly of noise perturbation to only momentarily bring the chopper to the 95% ON duty cycle level. The phase angle controller is very fast in operation and it is not desired to respond to a momentary high phase angle condition and change the field shunt before the chopper is at a steady-state 95% ON duty cycle of operation, and then have to unshunt the fields when the chopper returns to its stable operation below the 95% on duty cycle condition.This would require going from a parallel field connection back to a series field connection and this is objectionable in relation to the switches and the motor operation. Once the 95% ON duty cycle condition is maintained for the provided time period, the switches are operated to shunt the motor fields and this causes the chopper to phase back to about a 75% ON duty cycle. Therefore, the decision point has to be moved now from the previous 95% ON level to a lower value of about a 60% ON duty cycle level, so the motor fields do not unshunt by the expected phase back of the chopper operation. This provides a hysteresis conditioning of the response to the chopper phase angle, including a time element in the response, to improve and make more stable the motor field shunt control operation. If the phase angle PH is greater than OE5 hexadecimal, then a timer TP is incremented by one per program cycle if the phase angle stays continuous. If TP becomes greater than 13 hexadecimal then TP is forced to have a maximum of 13 hexadecimal. If TP is greater than 10 hexadecimal, the field shunt switches are operated. The instant is sensed when the phase angle exceeds about 95% ON duty cycle, and the operation of time TP to increment by one for each program cycle provides a desired time characteristic for the phase angle to remain above this upper limit of about 95% ON duty cycle. This operation is shown in Figure 9 where the phase angle 191 has to remain above the provided upper limit 193 for a time period before the field shunt operation is effected. When the field shunt changes, then the phase angle of the chopper drops to about a 70% ON duty cycle. The available dynamic range of the full field operation was about finished since with a full field the motor was generating a lot of back EMF which was equalizing the supply line voltage and this required the chopper to be ON most of the time. When some of the field is shunted, this weakens the magnetic field in the motor and reduces the back EMF, and to get more current at the same torque the chopper is phased back towards the OFF position to give more dynamic range again. If the phase angle goes below a minimum limit of about 60% ON duty cycle, then the timer TP is decremented by one for each program cycle. This recognizes when the phase angle is below a certain limit for a given number of program cycles, and when the time TP is less than 10 hexadecimal this opens the field shunt contactor.The input 4 is read to bring back the status of field shunt FS, to indicate whether or not the field shunt has actually closed because this is a non-time related thing; and is, whenever the request is made to close the field shunt, there is a time element involved in the mechanics, so it takes a certain amount of time for it to happen, and the microprocessor waits after the request is put out for the response that says the field shunt has actually closed; and when it is actually closed, an increment of current of 49 hexadecimal is added to the current request. The present control apparatus, including the microprocessor, is more reliable; in terms of mean time between failures, there is improvement by a factor of 5 to 10 as compared to prior art analog control systems using hard wired digital logic circuitry. In the event a prior art analog control system did fail, there was no provision for monitoring or sensing the proper and continued operation of the system, unlike as here provided by the pump circuit 151 responding to the boost signal. WHAT WE CLAIM IS:

1. A microprocessor control apparatus connected to a chopper controlled transit vehicle motor for determining an ON operation and an OFF operation of said electric motor, the apparatus comprising: means including a programmed digital apparatus to provide a digital signal in response to a selected operating condition related to the operation of said transit vehicle, chopper and motor; means for sensing when said signal is greater than a predetermined limit and lasts longer than a known time period; and means operative with said sensing means to control the operation of said electric motor.

2. The control apparatus of claim 1, with said condition being the speed of said motor.

3. The control apparatus of claim 1, with said condition being the phase angle of said chopper for selecting the ratio of the ON operation to the OFF operation of said chopper.

4. The control apparatus of claim 1, with said motor being operational in one of power and brake modes of operation and with said condition being speed; and said controlling means including changing means for changing an operational characteristic of

said motor.

5. The control apparatus of claim 4, with said condition being the transit vehicle speed, and with said relationship including the difference between a first speed and a second speed in accordance with the operation of said transit vehicle.

6. The control apparatus of claim 4, with the motor operative in the brake mode and with said changing means including at least one brake resistor; said controlling means determining the operation of said brake resistor with said motor to control braking effort provided by said motor.

7. The control apparatus of claim 4, with the motor operative in the power mode and with said changing means including at least one field shunt member; said controlling means determining the operation of said field shunt member with said motor to control the tractive effort provided by said motor.

8. The control apparatus of claim 1, with said digital apparatus including clock means for providing clock pulse signals; and with said selecting means being operative to count the clock pulse signals to determine said time period.

9. A method of controlling an electric motor of a transit vehicle connected for operation with a chopper in one of power and brake modes, using a microprocessor, comprising the steps of: providing a signal in response to an operational condition of the motor, establishing when the signal satisfies a first predetermined relationship with a selected limit for longer than a first selected time period; and controlling a first operation of the motor when said signal satisfies said relationship for longer than said selected time period.

10. The method of claim 9, with said selected limit being in accordance with the speed of the transit vehicle and with said motor being operative in a brake mode; said step of controlling the operation, changing the brake effort provided by the motor.

11. The method of claim 9, with said selected limit being in accordance with a phase angle of the chopper and with said motor being operative in the power mode; said step of controlling the operation, changing the tractive effort provided by the motor.

12. The method of claim 9, with said selected limit being in accordance with a first phase angle of the chopper, the method including the steps of: estalishing an instant when the signal satisfies a second predetermined relationship with a second selected limit for longer than a selected second time period; and controlling a second operation of the motor when the signal satisfies said second relationship for longer than said second time period.

13. Microprocessor control apparatus for a chopper, the apparatus including a programmed digital apparatus, substantially as described with reference to and as illustrated in the accompanying drawings.

14. A method of controlling a transit vehicle motor which is connected for operation with a chopper substantially as described hereinbefore with reference to the accompanying drawings.