CA1050103A - Electrical control in a generator rectifier fed motor system - Google Patents
Electrical control in a generator rectifier fed motor systemInfo
- Publication number
- CA1050103A CA1050103A CA242,842A CA242842A CA1050103A CA 1050103 A CA1050103 A CA 1050103A CA 242842 A CA242842 A CA 242842A CA 1050103 A CA1050103 A CA 1050103A
- Authority
- CA
- Canada
- Prior art keywords
- motor
- current
- signal
- control
- armature
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
- H02P7/06—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
- H02P7/18—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power
- H02P7/34—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using Ward-Leonard arrangements
- H02P7/347—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using Ward-Leonard arrangements in which only the generator field is controlled
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
- H02P7/03—Arrangements for regulating or controlling the speed or torque of electric DC motors for controlling the direction of rotation of DC motors
- H02P7/05—Arrangements for regulating or controlling the speed or torque of electric DC motors for controlling the direction of rotation of DC motors by means of electronic switching
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Direct Current Motors (AREA)
- Control Of Eletrric Generators (AREA)
- Stopping Of Electric Motors (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A control system for controlling a drive system which has an alternating current generator driven by a prime mover, a rectifier and a direct current motor powered by the rectified output of the generator, has a main control which provides a reference signal for the generator field and a reference signal for the motor field. An energy absorbing device is arranged to be switched into and out of the motor armature circuit. The speed of the motor is sensed to determine deceleration and to determine maximum counter electromotive force (emf) based on speed and maximum motor field. If the maximum counter emf will exceed a predetermined level, the energy absorbing device is the decelerating motor and to avoid excessive current caused by reversal of the motor field when the drive is being stopped or reversed. The control system also includes circuitry which senses armature current, compares it with an armature current reference signal and provides a current control signal. This current-control signal is normally directed to control armature current via the generator field winding. This circuitry also senses a reversal of counter emf and the motor field less than maximum to switch the current control signal from the generator field and direct it to the motor field since during regeneration only the motor field can control the armature current by controll-ing the motor counter emf. When maximum motor field current is achieved the current control signal is switched back to control current in the generator field winding because at this point the counter emf cannot develop full armature current even with maximum motor field. Thus the control system provides for deceleration and permits a controlled maximum torque for reversal without excessive armature current.
A control system for controlling a drive system which has an alternating current generator driven by a prime mover, a rectifier and a direct current motor powered by the rectified output of the generator, has a main control which provides a reference signal for the generator field and a reference signal for the motor field. An energy absorbing device is arranged to be switched into and out of the motor armature circuit. The speed of the motor is sensed to determine deceleration and to determine maximum counter electromotive force (emf) based on speed and maximum motor field. If the maximum counter emf will exceed a predetermined level, the energy absorbing device is the decelerating motor and to avoid excessive current caused by reversal of the motor field when the drive is being stopped or reversed. The control system also includes circuitry which senses armature current, compares it with an armature current reference signal and provides a current control signal. This current-control signal is normally directed to control armature current via the generator field winding. This circuitry also senses a reversal of counter emf and the motor field less than maximum to switch the current control signal from the generator field and direct it to the motor field since during regeneration only the motor field can control the armature current by controll-ing the motor counter emf. When maximum motor field current is achieved the current control signal is switched back to control current in the generator field winding because at this point the counter emf cannot develop full armature current even with maximum motor field. Thus the control system provides for deceleration and permits a controlled maximum torque for reversal without excessive armature current.
Description
Case 2407 50~L~3 This invention relates to a control system, and in particular it rel~tes to a control system for controlling a rectifier fed direct current motor drive system.
In electric drive systems having a direct current motor supplied by a direct current generator, reduction of the generator output in order to slow the motor will tend to cause a reversal of armature current which will provide regeneration back to the generator. In electric drive systems having an alternating current generator and using a thyristor arrangement to provide direct current for a motor, it is also possible to arrange for regeneration when it is desired to decelerate the motor. However, in electric drive systems where an alternating current generator or generators are used with non-controlled rectifiers to provide power to a direct current motor drive, there can be no regeneration back to the generators because current cannot be reversed through the rectifiers. There are problems in the design of such a system, particularly where the motor must be slowed quickly or reversed such as in a propulsion drive system.
When a power source feeding a motor i5 reduced the motor tends to act as a generator and, unless the motor load energy is so low that ~he power generated by the decelerating motor can be absorbed by the natural resistance of the loop, it is neces~ary to introduce into the loop a power ab~orbing device. In most propul~ion drive systems a decelerating motor will have considerable inertia and it is necessary to absorb or dispose of the ~tored energy in order to stop the motor. In addition, it is frequently necessary, particularly in a propulsion drive, to develop a counter torque in order to reverse the rotation of the motor. In a direct current motor, torque is produced by interaction of the fields caused by armature current and motor field current. The armakure current cannot I
,' ~
Case 2407 l~SO103 conveniently be reversed in a rectifier fed system and in this situation the motor field current must be reversed to develop a counter tor~ue. ~he reversal of the fie~d current will introduce another problem.
When a direct current motor is running normally it develops a counter electromotive force (emf) and the counter emf opposes the em~ applied to the motor. Reversing the motor field current will reverse the direction of the counter emf.
In a rectifier fed motor system where the motor i5 decelerating and the inertia of the motor and its connected load maintain rotation of the motor, a reversal of the motor field will result in a counter emf which acts in the same direction as the rectifier output~ This may cause armature currents which are unacceptably large. It is necessary to limit or control these armature currents while providing as much reverse torque as practical to stop or reverse the motor as quickly as possible.
In the past there have been developed systems which aid in the braking of rectifier fed direct current motors, buk the systems have not been completely satisfactory particularly where reversal of the drive must be considered.
In one prior art system using a rectifier fed direct current motor in a vehicle drive system, a resistance grid is carried in the vehicle and as soon as braking action is initiated the traction motors are connected to the grid so that any electrical power generated by the motor is dissipated or absorbed in the resistance grid.
It is also known in a diesel-electric locomotive to 6~ 6 vary the dynamic ~ g b~ changing the motor field excitation.
In one such arrangement the motor field is directly connected to the generator output and the excitation to the generator varied to control the output and thus control the motor field and the braking effort.
Case 2407 l~S01~3 Neither of these prior art arrangements are concerned with a reversal following the stopping of the motor and do not describe a control which will permit rapid motor reversal.
It is a feature of the present invention to provide a control system for a rec~ifier fed direct current motor drive which achieves improved deceleration and when required rapid reversal of the motor drive.
According to the present invention there is provided a control system for controlling a drive system having an alternating current genera~or, rectifier means for rectifying the output of said generator and a direct current motor supplied by tha rectified output of said generator, said generator and said motor each having a field winding, ~aid control system comprising an energy absoxbing device for connection in the armature circuit of said motor to absorb energy from said motor when said motor is being decelerated, sensor means for sensing the speed of said motor and providing a speed signal representing the ~ensed speed, circuit means connected to said sensor means and including a counter emf determination control, said counter emf determination control receiving said speed signal and determining a computed counter emf using said speed signal and a maximum motor field current and being responsive to said computed counter emf exceed.ing a predetermined level of counter em~ to connect 3aid energy absorb~ng. device into said armature circuit.
Also according to the invention in another form there is provided in the control ~ystem a generator field current control means and a motor ~ield current control means each being responsive to a control signal to control the current in the re~pective field winding, means providing an armature current reference signal and a motor field reference signal representing respectively a desired armature current and a Case 2407 desired motor field current, sensor means for sensing a~mature current in said motor armature and providing an armature current signal representing the sensed current, first and second comparing means, said irst compa.ring means receiving said armature current reference signal and said armature current signal and providing an armature current control signal related to a comparison of the received signals, switching means for receiving said armature current control signal and having a first position where said armature current control signal i5 directed ~o said generator field current control means to control current in said generator field winding tending to cause in armature current in accordan~e with s aid armature currant reference ~ignal, and a second position where said arm-ature current control signal i9 directed to said ~econd comparing mean~, ~aid second comparing means receiving said motor field reference signal and with said switching means in said second position said armature current control signal for comparing the received signals and providing a motor field control signal based on the compari~on, said motor field control signal being applied to said motor field current control means providing a controlled value of armature current permitting maximum deceleration with said switching means in said second position, ~aid switching means normally being in said first position and responsive to a reversal of direction of motor field current with said motor field current below maximum to switch to said second position and responsive to said motor ~ield current reading maximum ~ return to said first position.
1~e invention will be described with reference to the accompanying drawings, in which:
Figure 1 is a block diagram in greatly 3implified form, useful in explaining the operation of the control system of the invention, and Case 2407 1~5~1~3 Figure 2 is a block diagram showing one form of the invention.
m e control system as shown in greatly simplified form in Figure 1 will be described first, together with its operation, and then a description will be given of the control system of Figure 2 which is a more complete block diagram. The control system is particularly useful on a ship, such as an ice-breaker for example, where rapid reversal of the drive is often re~uired.
However, the control system of the invention may be used on any drive system which requires braking and reversal, and which may in addition have several generator rectifiers supplying a motor.
Referring to Figure 1, block 10 represents a system control having an input 11~ The input 11 sets the output requirements of the drive and may be a control for actuation by an operator. Input 11 may require the motor to provide a certain steady speed, or it may require braking or reversal.
The system control lQ provides two reference signals.
One reference is on conductor 12 and the other is on conductor 14. The conductor 12 is connected to circuitry represented by block 27 as will be described hereinafter. The conductor 14 is connected to a motor field current control represented by block 16. The two reference signals on conductors 12 and 14 represent levels of generator voltage and motor field current respectively, required by system control 10.
The drive portion of the system includes an alternating current generator 17, driven by a prime mover ~not shown) such as a diesel engine, a rectifier system 18 and a direct current motor 20. The generator 17, rectifier 18 and motor 20 are connected in the usual manner so the generator 17 provides alternating current, rectified by rectifier 18, to drive motor 20. An energy absorbing device 21 is included in a series arrangement in the circuit of the drive system and it may Case 2407 ~050103 be switched into and out of the circuit by a switching control 22a and switch 22.
In Figure 1 there are four parameters sensed. Armature current is sensed and a signal representing armature current i~
on conductor 23. Motor speed or rpm is sen~ed and a motor speed signal i5 provided on conductor 24, and a signal representing the motor field is on conductor 25. Motor armature voltage i~
sensed and appears on conductor 29. m ere are two circuits which receive the signals representing the sensed parameters. One of these is rspresented by block 26 which receives the ~ignal from conductor 24 and provides an output which controls switch control 22a to operate switch 22 to switch the energy absorbing device 21 into and out of the motor armature circuit. The other is represented by block 27 which receives the signals from conductors 12, 23, 25 and 29 and provides an output which control~ the operation of a switch control 28a to control switch ~8, and also provides a control signal to switch 28. The control signal i9 switched by switch 28 so that it either appears on conductor 30 and is applied to a generator field control 15 or it appears on conductor 3I and is applied to motor field control 16~
The circuitry of block 26 is re~ponsive to motor speed and direction and makes what may be referred to for convenience as a first decision. It will be recalled that a reversal of the motor fie}d current will reverse the counter emf, and that because the reversed counter emf will then be in the same direction as conduction through the rectifier there could be exces~ive armature current. The circuitry of block 26 receives a signal representing motor speed and, if there i9 a reversal of the motor field current, it derives a value for maximum possible counter emf (based on rpm and max permissible field current) and if this value exceeds a predetermined value, then a signal is applied to switch control 22a which operates switch 22 to switch Case 2407 ~IL05~103 energy absorbing device 21 into the armature circuit. This may be referred to as a counter emf determination control. In this case, the circuitry of block 26 will sense actual reversal of the motor shaft rotation and apply a signal to control 22a to switch 22 to switch energy absorbing device 21 out of the armature circuit.
It will be apparent that more than one energy absorbing device 21 could be switched into or out of the armature circuit depending on circumstances, or in other words, a variable energy absorbing load can be placed in the armature circuit in accordance with signals from the circuitry o~ s~itch control 22a.
It should be noted that the energy absorbing load is not switched into the armature circuit in response to ev~ry degree of deceleration, but only when the deceleration is such that the motor counter emf will exceed a predetermined limit.
The circuitry of block 27 is responsive mainly to two parameters to provide a control decision. One is counter emf in the motor (i.e. motor armature voltage) and the o~her is the motor field current. These two parameters may be derived in a number o~ ways and the simplified diagram of Figure 1 shows a signal input representing motor armature voltage on conductor 29 and a signal input representing field current on conductor 25.
The parameters may be determined from other signals. The circuitry of block 27 makes what may be re~erred to as a second decision.
The circuitry o~ block 27 normally receives a reference signal on conductor 12 from system control 10, and a signal representing armature current on conductor 23. These signals correspond to a desired armature current and an actual armature current. The difference or error signal resulting from a comparision of the two signals is provided on conductor Case 2407 ~ L05i0103 30 to control the generator field and thereby control armature current as is well known in the art. Also in normal operation, the motor field control 16 receives a control signal on conductor 14 from system control 10 and this will control the motor field.
However, when certain conditions exist, block 27 makes a second decision as referred to previously and redirects the control signals. When the circuitry of block 27 determlnes there has been a reversal of the counter emf and the motor field is below its maximum permissible level, then switch 28 is activated by switch control 28a and the control signal which is normally on conductor 30 is switched to conductor 31.
The signal on conductor 31 representing an armature circuit control is applied over conductor 31 to oo~b~ with the signal on conductor 14 from system control 10 to determine the motor field. The ~ignal representing armature current control remains on conductor 31 until maximum motor field current is reached. At this point the counter emf cannot increase further and therefore cannot maintain full armature current. Thus, when maximum motor field current is reached, the circuitry of block 27 actuates switch control 28a causing switch 28 to restore normal operation. The generator voltage can now be increased in the normal manner to provide maximum armature current as re~uired.
It will be seen that a maximum torque is available for stopping or reversing the motor. The control system permits modification of the control of the torque to meet various needs.
Referring now to Figure 2, there i5 shown a block diagram which represents in more detail one form of the invention.
The generator 17, rectifier 18, energy absorbing device 21, switch 22 with switch control 22a, motor 20, and generator and motor field control 15 and 16 have the same designation numbers for convenience.
In Figure 2 an input 11 is provided on a system Case 2407 ~5~03 control and decision circuitry 33 to enable required operational values to be achieved. System control and decision circuitry provides the necessary output reference signals as well be described. A motor speed sensor 34 detects or senses motor speed and direction and is connected by a conductor 39 to the system control and decision circuitry 33 to provide another input.
The system control and decision circuitry 33 provides output signals on conductors 35 - 38. The signal on conductor 35 represents a desired generator output voltage. The signal on conductor 36 represents the "second decisi.on" signal referred to in connection with Figure 1. The signal on conductor 37 represents the "first decision" signal referred to in connection with Figure 1. The signal on conductor 38 represents a desired motor field current.
A voltage sensor 40 detects motor volta~e and provides a signal representing motor voltage on conductor 41. Conductors 35 and 41, carr~ing signals respectively representing desired voltage and sensed voltage, are connected to a device 42 which provides an output signal which is a function of the difference of the two voltage signals. This difference signal or "error"
signal is applied to voltage control and current reference 43.
An output signal is provided from voltage control and current reference 43 which is related to its input signal but which may have maximum or minimum values (for example, it may have a maximum limit to avoid an excessive rectifier output current) and this is applied as one signal to device 44, This is a current reference signal. A current sensor 45 senses armature current and provides on conductor 46 a signal representing armature current. Conductor 46 is connected to device 44 to provide the armature current signal to device 44. Device 44 pro-vides an output which is a function of the difference of the cur~
rent reference signal and the actual armature current signal. The Case 2407 ~OSOiO3 difference signal or error signal from device 44 i5 applied to armature current regulator 47. The current error signal is intended in normal operation to alter the generator field to change the armature current in such a manner that the armature current signal on conductor 46 will approach the current reference signal from current reference 43~ The armature current regulator 47 then acts to control the armature curren~ to the desired level. The control signal from armature current regulator 47 is applied to a control and routing amplifier 48 which routes the control signal over either conductor 50 to generator field regulator 15 or conductor 51 to device 52. In other words, the control and routing amplifier 48 i9 responsive to a signal on conductor 36 (the "second decision" signal) to switch the control signal to conductor 50 or 51. When the control signal is on conductor 50 it actuates generator field control 15 to regulate the generator field thereby controlling armature current.
~hen the control slgnal is on conductor 51 there has been a reversal of the counter emf in motor 20 but the motor field is below its maximum level. The control signal is applied to device 52 where it is added to the motor field reference on conductor 38. The resulting signal is applied via a reference limiter 53 to regulate the motor field thereby controlling armature current.
Reference limiter 53 prevents the motor field from exceeding a permissible level. mis gives maximum braking effect and the energy i5 absorbed by energy absorbing device 21.
At some point in the deceleration the motor speed will decrease to a level where its counter emf cannot develop full armature current even when the motor field current is at its maximum. As the maximum field is reached the control and decision circuitry 33 provides the signal on conductor 36 which routes the currenk control back to conductor 50 restoring normal operation. It should be noked that this can take place before - Case 2407 there is actual reversal of the motor. With the motor field at a maximum the generator field will increase according to the control signal from armature current regulator 47 until maximum armature current is achieved. The motor torque is now maximum and will provide maximum braking and acceleration in the opposite direction.
~ he operation of switch control 22a and switch 22 to switch energy absorbing device 21 into and out of the armature circuit is the same as was described in connection with Figure 1.
It is believed that the operation of the Figure 2 form of the invention should be clear. The control system operates to achieve a greater dynamic braking and a rapid reversal of a dr,ive motor.
In electric drive systems having a direct current motor supplied by a direct current generator, reduction of the generator output in order to slow the motor will tend to cause a reversal of armature current which will provide regeneration back to the generator. In electric drive systems having an alternating current generator and using a thyristor arrangement to provide direct current for a motor, it is also possible to arrange for regeneration when it is desired to decelerate the motor. However, in electric drive systems where an alternating current generator or generators are used with non-controlled rectifiers to provide power to a direct current motor drive, there can be no regeneration back to the generators because current cannot be reversed through the rectifiers. There are problems in the design of such a system, particularly where the motor must be slowed quickly or reversed such as in a propulsion drive system.
When a power source feeding a motor i5 reduced the motor tends to act as a generator and, unless the motor load energy is so low that ~he power generated by the decelerating motor can be absorbed by the natural resistance of the loop, it is neces~ary to introduce into the loop a power ab~orbing device. In most propul~ion drive systems a decelerating motor will have considerable inertia and it is necessary to absorb or dispose of the ~tored energy in order to stop the motor. In addition, it is frequently necessary, particularly in a propulsion drive, to develop a counter torque in order to reverse the rotation of the motor. In a direct current motor, torque is produced by interaction of the fields caused by armature current and motor field current. The armakure current cannot I
,' ~
Case 2407 l~SO103 conveniently be reversed in a rectifier fed system and in this situation the motor field current must be reversed to develop a counter tor~ue. ~he reversal of the fie~d current will introduce another problem.
When a direct current motor is running normally it develops a counter electromotive force (emf) and the counter emf opposes the em~ applied to the motor. Reversing the motor field current will reverse the direction of the counter emf.
In a rectifier fed motor system where the motor i5 decelerating and the inertia of the motor and its connected load maintain rotation of the motor, a reversal of the motor field will result in a counter emf which acts in the same direction as the rectifier output~ This may cause armature currents which are unacceptably large. It is necessary to limit or control these armature currents while providing as much reverse torque as practical to stop or reverse the motor as quickly as possible.
In the past there have been developed systems which aid in the braking of rectifier fed direct current motors, buk the systems have not been completely satisfactory particularly where reversal of the drive must be considered.
In one prior art system using a rectifier fed direct current motor in a vehicle drive system, a resistance grid is carried in the vehicle and as soon as braking action is initiated the traction motors are connected to the grid so that any electrical power generated by the motor is dissipated or absorbed in the resistance grid.
It is also known in a diesel-electric locomotive to 6~ 6 vary the dynamic ~ g b~ changing the motor field excitation.
In one such arrangement the motor field is directly connected to the generator output and the excitation to the generator varied to control the output and thus control the motor field and the braking effort.
Case 2407 l~S01~3 Neither of these prior art arrangements are concerned with a reversal following the stopping of the motor and do not describe a control which will permit rapid motor reversal.
It is a feature of the present invention to provide a control system for a rec~ifier fed direct current motor drive which achieves improved deceleration and when required rapid reversal of the motor drive.
According to the present invention there is provided a control system for controlling a drive system having an alternating current genera~or, rectifier means for rectifying the output of said generator and a direct current motor supplied by tha rectified output of said generator, said generator and said motor each having a field winding, ~aid control system comprising an energy absoxbing device for connection in the armature circuit of said motor to absorb energy from said motor when said motor is being decelerated, sensor means for sensing the speed of said motor and providing a speed signal representing the ~ensed speed, circuit means connected to said sensor means and including a counter emf determination control, said counter emf determination control receiving said speed signal and determining a computed counter emf using said speed signal and a maximum motor field current and being responsive to said computed counter emf exceed.ing a predetermined level of counter em~ to connect 3aid energy absorb~ng. device into said armature circuit.
Also according to the invention in another form there is provided in the control ~ystem a generator field current control means and a motor ~ield current control means each being responsive to a control signal to control the current in the re~pective field winding, means providing an armature current reference signal and a motor field reference signal representing respectively a desired armature current and a Case 2407 desired motor field current, sensor means for sensing a~mature current in said motor armature and providing an armature current signal representing the sensed current, first and second comparing means, said irst compa.ring means receiving said armature current reference signal and said armature current signal and providing an armature current control signal related to a comparison of the received signals, switching means for receiving said armature current control signal and having a first position where said armature current control signal i5 directed ~o said generator field current control means to control current in said generator field winding tending to cause in armature current in accordan~e with s aid armature currant reference ~ignal, and a second position where said arm-ature current control signal i9 directed to said ~econd comparing mean~, ~aid second comparing means receiving said motor field reference signal and with said switching means in said second position said armature current control signal for comparing the received signals and providing a motor field control signal based on the compari~on, said motor field control signal being applied to said motor field current control means providing a controlled value of armature current permitting maximum deceleration with said switching means in said second position, ~aid switching means normally being in said first position and responsive to a reversal of direction of motor field current with said motor field current below maximum to switch to said second position and responsive to said motor ~ield current reading maximum ~ return to said first position.
1~e invention will be described with reference to the accompanying drawings, in which:
Figure 1 is a block diagram in greatly 3implified form, useful in explaining the operation of the control system of the invention, and Case 2407 1~5~1~3 Figure 2 is a block diagram showing one form of the invention.
m e control system as shown in greatly simplified form in Figure 1 will be described first, together with its operation, and then a description will be given of the control system of Figure 2 which is a more complete block diagram. The control system is particularly useful on a ship, such as an ice-breaker for example, where rapid reversal of the drive is often re~uired.
However, the control system of the invention may be used on any drive system which requires braking and reversal, and which may in addition have several generator rectifiers supplying a motor.
Referring to Figure 1, block 10 represents a system control having an input 11~ The input 11 sets the output requirements of the drive and may be a control for actuation by an operator. Input 11 may require the motor to provide a certain steady speed, or it may require braking or reversal.
The system control lQ provides two reference signals.
One reference is on conductor 12 and the other is on conductor 14. The conductor 12 is connected to circuitry represented by block 27 as will be described hereinafter. The conductor 14 is connected to a motor field current control represented by block 16. The two reference signals on conductors 12 and 14 represent levels of generator voltage and motor field current respectively, required by system control 10.
The drive portion of the system includes an alternating current generator 17, driven by a prime mover ~not shown) such as a diesel engine, a rectifier system 18 and a direct current motor 20. The generator 17, rectifier 18 and motor 20 are connected in the usual manner so the generator 17 provides alternating current, rectified by rectifier 18, to drive motor 20. An energy absorbing device 21 is included in a series arrangement in the circuit of the drive system and it may Case 2407 ~050103 be switched into and out of the circuit by a switching control 22a and switch 22.
In Figure 1 there are four parameters sensed. Armature current is sensed and a signal representing armature current i~
on conductor 23. Motor speed or rpm is sen~ed and a motor speed signal i5 provided on conductor 24, and a signal representing the motor field is on conductor 25. Motor armature voltage i~
sensed and appears on conductor 29. m ere are two circuits which receive the signals representing the sensed parameters. One of these is rspresented by block 26 which receives the ~ignal from conductor 24 and provides an output which controls switch control 22a to operate switch 22 to switch the energy absorbing device 21 into and out of the motor armature circuit. The other is represented by block 27 which receives the signals from conductors 12, 23, 25 and 29 and provides an output which control~ the operation of a switch control 28a to control switch ~8, and also provides a control signal to switch 28. The control signal i9 switched by switch 28 so that it either appears on conductor 30 and is applied to a generator field control 15 or it appears on conductor 3I and is applied to motor field control 16~
The circuitry of block 26 is re~ponsive to motor speed and direction and makes what may be referred to for convenience as a first decision. It will be recalled that a reversal of the motor fie}d current will reverse the counter emf, and that because the reversed counter emf will then be in the same direction as conduction through the rectifier there could be exces~ive armature current. The circuitry of block 26 receives a signal representing motor speed and, if there i9 a reversal of the motor field current, it derives a value for maximum possible counter emf (based on rpm and max permissible field current) and if this value exceeds a predetermined value, then a signal is applied to switch control 22a which operates switch 22 to switch Case 2407 ~IL05~103 energy absorbing device 21 into the armature circuit. This may be referred to as a counter emf determination control. In this case, the circuitry of block 26 will sense actual reversal of the motor shaft rotation and apply a signal to control 22a to switch 22 to switch energy absorbing device 21 out of the armature circuit.
It will be apparent that more than one energy absorbing device 21 could be switched into or out of the armature circuit depending on circumstances, or in other words, a variable energy absorbing load can be placed in the armature circuit in accordance with signals from the circuitry o~ s~itch control 22a.
It should be noted that the energy absorbing load is not switched into the armature circuit in response to ev~ry degree of deceleration, but only when the deceleration is such that the motor counter emf will exceed a predetermined limit.
The circuitry of block 27 is responsive mainly to two parameters to provide a control decision. One is counter emf in the motor (i.e. motor armature voltage) and the o~her is the motor field current. These two parameters may be derived in a number o~ ways and the simplified diagram of Figure 1 shows a signal input representing motor armature voltage on conductor 29 and a signal input representing field current on conductor 25.
The parameters may be determined from other signals. The circuitry of block 27 makes what may be re~erred to as a second decision.
The circuitry o~ block 27 normally receives a reference signal on conductor 12 from system control 10, and a signal representing armature current on conductor 23. These signals correspond to a desired armature current and an actual armature current. The difference or error signal resulting from a comparision of the two signals is provided on conductor Case 2407 ~ L05i0103 30 to control the generator field and thereby control armature current as is well known in the art. Also in normal operation, the motor field control 16 receives a control signal on conductor 14 from system control 10 and this will control the motor field.
However, when certain conditions exist, block 27 makes a second decision as referred to previously and redirects the control signals. When the circuitry of block 27 determlnes there has been a reversal of the counter emf and the motor field is below its maximum permissible level, then switch 28 is activated by switch control 28a and the control signal which is normally on conductor 30 is switched to conductor 31.
The signal on conductor 31 representing an armature circuit control is applied over conductor 31 to oo~b~ with the signal on conductor 14 from system control 10 to determine the motor field. The ~ignal representing armature current control remains on conductor 31 until maximum motor field current is reached. At this point the counter emf cannot increase further and therefore cannot maintain full armature current. Thus, when maximum motor field current is reached, the circuitry of block 27 actuates switch control 28a causing switch 28 to restore normal operation. The generator voltage can now be increased in the normal manner to provide maximum armature current as re~uired.
It will be seen that a maximum torque is available for stopping or reversing the motor. The control system permits modification of the control of the torque to meet various needs.
Referring now to Figure 2, there i5 shown a block diagram which represents in more detail one form of the invention.
The generator 17, rectifier 18, energy absorbing device 21, switch 22 with switch control 22a, motor 20, and generator and motor field control 15 and 16 have the same designation numbers for convenience.
In Figure 2 an input 11 is provided on a system Case 2407 ~5~03 control and decision circuitry 33 to enable required operational values to be achieved. System control and decision circuitry provides the necessary output reference signals as well be described. A motor speed sensor 34 detects or senses motor speed and direction and is connected by a conductor 39 to the system control and decision circuitry 33 to provide another input.
The system control and decision circuitry 33 provides output signals on conductors 35 - 38. The signal on conductor 35 represents a desired generator output voltage. The signal on conductor 36 represents the "second decisi.on" signal referred to in connection with Figure 1. The signal on conductor 37 represents the "first decision" signal referred to in connection with Figure 1. The signal on conductor 38 represents a desired motor field current.
A voltage sensor 40 detects motor volta~e and provides a signal representing motor voltage on conductor 41. Conductors 35 and 41, carr~ing signals respectively representing desired voltage and sensed voltage, are connected to a device 42 which provides an output signal which is a function of the difference of the two voltage signals. This difference signal or "error"
signal is applied to voltage control and current reference 43.
An output signal is provided from voltage control and current reference 43 which is related to its input signal but which may have maximum or minimum values (for example, it may have a maximum limit to avoid an excessive rectifier output current) and this is applied as one signal to device 44, This is a current reference signal. A current sensor 45 senses armature current and provides on conductor 46 a signal representing armature current. Conductor 46 is connected to device 44 to provide the armature current signal to device 44. Device 44 pro-vides an output which is a function of the difference of the cur~
rent reference signal and the actual armature current signal. The Case 2407 ~OSOiO3 difference signal or error signal from device 44 i5 applied to armature current regulator 47. The current error signal is intended in normal operation to alter the generator field to change the armature current in such a manner that the armature current signal on conductor 46 will approach the current reference signal from current reference 43~ The armature current regulator 47 then acts to control the armature curren~ to the desired level. The control signal from armature current regulator 47 is applied to a control and routing amplifier 48 which routes the control signal over either conductor 50 to generator field regulator 15 or conductor 51 to device 52. In other words, the control and routing amplifier 48 i9 responsive to a signal on conductor 36 (the "second decision" signal) to switch the control signal to conductor 50 or 51. When the control signal is on conductor 50 it actuates generator field control 15 to regulate the generator field thereby controlling armature current.
~hen the control slgnal is on conductor 51 there has been a reversal of the counter emf in motor 20 but the motor field is below its maximum level. The control signal is applied to device 52 where it is added to the motor field reference on conductor 38. The resulting signal is applied via a reference limiter 53 to regulate the motor field thereby controlling armature current.
Reference limiter 53 prevents the motor field from exceeding a permissible level. mis gives maximum braking effect and the energy i5 absorbed by energy absorbing device 21.
At some point in the deceleration the motor speed will decrease to a level where its counter emf cannot develop full armature current even when the motor field current is at its maximum. As the maximum field is reached the control and decision circuitry 33 provides the signal on conductor 36 which routes the currenk control back to conductor 50 restoring normal operation. It should be noked that this can take place before - Case 2407 there is actual reversal of the motor. With the motor field at a maximum the generator field will increase according to the control signal from armature current regulator 47 until maximum armature current is achieved. The motor torque is now maximum and will provide maximum braking and acceleration in the opposite direction.
~ he operation of switch control 22a and switch 22 to switch energy absorbing device 21 into and out of the armature circuit is the same as was described in connection with Figure 1.
It is believed that the operation of the Figure 2 form of the invention should be clear. The control system operates to achieve a greater dynamic braking and a rapid reversal of a dr,ive motor.
Claims (5)
1. A control system for controlling a drive system having an alternating current generator, rectifier means for rectifying the output of said generator and a direct current motor supplied by the rectified output of said generator, said generator and said motor each having a field winding, said control system comprising an energy absorbing device for connection in the armature circuit of said motor to absorb energy from said motor when said motor is being decelerated, sensor means for sensing the speed of said motor and providing a speed signal representing the sensed speed, circuit means connected to said sensor means and including a counter emf determination control, said counter emf determination control receiving said speed signal and determining a computed counter emf using said speed signal and a maximum motor field current and being responsive to said computed counter emf exceeding a predetermined level of counter emf to connect said energy absorbing device into said armature circuit.
2. A control system as defined in claim 1 in which said circuit means is responsive to said counter emf determination control determining a level of counter emf less than said predetermined level of counter emf to switch said energy absorbing device out of said armature circuit, said circuit means also being responsive to reversal of the motor shaft rotation to switch said energy absorbing device out of said armature circuit.
3. A control system as defined in claim 2 and further comprising a generator field current control means and a motor field current control means each being responsive to a control signal to control the current in the respective field winding,
3. A control system as defined in claim 2 and further comprising a generator field current control means and a motor field current control means each being responsive to a control signal to control the current in the respective field winding,
Claim 3 continued:
means providing an armature current reference signal and a motor field reference signal representing respectively a desired armature current and a desired motor field current, sensor means for sensing armature current in said motor armature and providing an armature current signal representing the sensed current, first and second comparing means, said first comparing means receiving said armature current reference signal and said armature current signal and providing an armature current control signal related to a compari-son of the received signals, switching means for receiving said armature current control signal and having a first position where said armature current control signal is directed to said generator field current control means to control current in said generator field winding tending to cause an armature current in accordance with said armature current reference signal, and a second position where said armature current control signal is directed to said sec-ond comparing means, said second comparing means receiving said motor field reference signal and with said switching means in said second position said armature current control signal for comparing the received signals and providing a motor field control signal based on the comparison, said motor field control signal being applied to said motor field current control means providing a controlled value of armature current permitting maximum deceleration with said switching means in said second position, said switching means normally being in said first position and responsive to a reversal of direction of motor field current with said motor field current below maximum to switch to said second position and responsive to said motor field current reaching maximum to return to said first position.
4. A control system for controlling a drive system having an alternating current generator, rectifier means for rectifying the output of said generator and a direct current motor supplied by the rectified output from said generator, said generator and said motor each having a field winding and a respective field current control means, said control system comprising decision circuitry means having input means for receiv-ing desired operation conditions for the drive system and provid-ing related first and second signals representing respectively a desired motor field and a desired armature current, first, second and third comparing means, a voltage sensor connected to said motor for providing a third signal representing sensed voltage, said first comparing means being connected to said decision circuitry means and to said voltage sensor for receiving said second and third signals, comparing said second and third signals, and providing as an output a fourth signal based on the comparison, a current sensor connected to the armature circuit of said motor for providing a fifth signal representing the sensed current, said second comparing means being connected to said first comparing means and to said current sensor for receiving said fourth and fifth signals, comparing said fourth and fifth signals, and providing as an output a sixth signal based on the comparison and being an armature current control signal, a speed sensor connected to said motor for providing a seventh signal representing motor speed and direction of rotation, said decision circuitry means being connected to said speed sensor to receive said seventh signal, said decision circuitry providing as an output an
means providing an armature current reference signal and a motor field reference signal representing respectively a desired armature current and a desired motor field current, sensor means for sensing armature current in said motor armature and providing an armature current signal representing the sensed current, first and second comparing means, said first comparing means receiving said armature current reference signal and said armature current signal and providing an armature current control signal related to a compari-son of the received signals, switching means for receiving said armature current control signal and having a first position where said armature current control signal is directed to said generator field current control means to control current in said generator field winding tending to cause an armature current in accordance with said armature current reference signal, and a second position where said armature current control signal is directed to said sec-ond comparing means, said second comparing means receiving said motor field reference signal and with said switching means in said second position said armature current control signal for comparing the received signals and providing a motor field control signal based on the comparison, said motor field control signal being applied to said motor field current control means providing a controlled value of armature current permitting maximum deceleration with said switching means in said second position, said switching means normally being in said first position and responsive to a reversal of direction of motor field current with said motor field current below maximum to switch to said second position and responsive to said motor field current reaching maximum to return to said first position.
4. A control system for controlling a drive system having an alternating current generator, rectifier means for rectifying the output of said generator and a direct current motor supplied by the rectified output from said generator, said generator and said motor each having a field winding and a respective field current control means, said control system comprising decision circuitry means having input means for receiv-ing desired operation conditions for the drive system and provid-ing related first and second signals representing respectively a desired motor field and a desired armature current, first, second and third comparing means, a voltage sensor connected to said motor for providing a third signal representing sensed voltage, said first comparing means being connected to said decision circuitry means and to said voltage sensor for receiving said second and third signals, comparing said second and third signals, and providing as an output a fourth signal based on the comparison, a current sensor connected to the armature circuit of said motor for providing a fifth signal representing the sensed current, said second comparing means being connected to said first comparing means and to said current sensor for receiving said fourth and fifth signals, comparing said fourth and fifth signals, and providing as an output a sixth signal based on the comparison and being an armature current control signal, a speed sensor connected to said motor for providing a seventh signal representing motor speed and direction of rotation, said decision circuitry means being connected to said speed sensor to receive said seventh signal, said decision circuitry providing as an output an
Claim 4 continued:
eighth signal having a first and a second condition and determining that the motor counter emf has reversed and that the current in said motor field winding is below a maximum permissi-ble current to provide said eighth signal in said second condition, a control and routing amplifiers connected to said second comparing means and to said decision circuitry means to receive said sixth and eight signals and having two outputs, said sixth signal being available at a first one of said outputs in response to said eighth signal being in said first condition and at said second one of said outputs in response to said eighth signal being on said second condition, said first output of said control and routing amplifies being connected to said field current control means of said generator to control the generator field and the armature current in accordance with said sixth signal when said eight signal is in said first condition, said second output of said control and routing amplifier being connected to said third comparing means to provide thereto said sixth signal when said eighth signal is in said second condition, said third comparing means being connected to said decision circuitry means to receive said first signal, comparing said first and sixth signals and to provide as an output a ninth signal based on the comparison, a limiting amplifier connected between said third comparing means and said motor field current control means to limit said ninth signal to a value which does not permit a field current in excess of a maximum value, said ninth signal being applied to said motor field current control means to control the operation of said motor, an energy absorbing device, switch means to connect said energy absorbing device into the armature circuit of said motor and to disconnect said energy absorbing device from said armature circuit, said decision circuitry means being connected to said switch means and determining a maximum possible counter emf based on motor speed and a maximum motor field current and being responsive to said determined maximum possible counter emf exceeding a predetermined level to provide a tenth signal to said switch means to connect said energy absorbing device into said armature circuit.
eighth signal having a first and a second condition and determining that the motor counter emf has reversed and that the current in said motor field winding is below a maximum permissi-ble current to provide said eighth signal in said second condition, a control and routing amplifiers connected to said second comparing means and to said decision circuitry means to receive said sixth and eight signals and having two outputs, said sixth signal being available at a first one of said outputs in response to said eighth signal being in said first condition and at said second one of said outputs in response to said eighth signal being on said second condition, said first output of said control and routing amplifies being connected to said field current control means of said generator to control the generator field and the armature current in accordance with said sixth signal when said eight signal is in said first condition, said second output of said control and routing amplifier being connected to said third comparing means to provide thereto said sixth signal when said eighth signal is in said second condition, said third comparing means being connected to said decision circuitry means to receive said first signal, comparing said first and sixth signals and to provide as an output a ninth signal based on the comparison, a limiting amplifier connected between said third comparing means and said motor field current control means to limit said ninth signal to a value which does not permit a field current in excess of a maximum value, said ninth signal being applied to said motor field current control means to control the operation of said motor, an energy absorbing device, switch means to connect said energy absorbing device into the armature circuit of said motor and to disconnect said energy absorbing device from said armature circuit, said decision circuitry means being connected to said switch means and determining a maximum possible counter emf based on motor speed and a maximum motor field current and being responsive to said determined maximum possible counter emf exceeding a predetermined level to provide a tenth signal to said switch means to connect said energy absorbing device into said armature circuit.
5. A control system as defined in claim 4 in which said decision circuitry means is responsive to said counter emf being less than the respective said predetermined level, and being responsive to reversal of said motor shaft rotation to alter said tenth signal to remove said energy absorbing device from said armature circuit.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,842A CA1050103A (en) | 1975-12-31 | 1975-12-31 | Electrical control in a generator rectifier fed motor system |
| JP15216176A JPS5285318A (en) | 1975-12-31 | 1976-12-20 | Drive system controller |
| DE19762658607 DE2658607A1 (en) | 1975-12-31 | 1976-12-23 | CONTROL SYSTEM |
| GB54155/76A GB1563936A (en) | 1975-12-31 | 1976-12-24 | Electrical motor control system |
| FI763701A FI66507C (en) | 1975-12-31 | 1976-12-27 | DRIV- OCH REGLERINGSSYSTEM FOER GENOM EN LIKRIKTARE MATAD LIKSTROEMSMOTOR |
| CH1641976A CH614323A5 (en) | 1975-12-31 | 1976-12-29 | Control system for a drive device, particularly for a vehicle drive device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA242,842A CA1050103A (en) | 1975-12-31 | 1975-12-31 | Electrical control in a generator rectifier fed motor system |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1050103A true CA1050103A (en) | 1979-03-06 |
Family
ID=4104878
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA242,842A Expired CA1050103A (en) | 1975-12-31 | 1975-12-31 | Electrical control in a generator rectifier fed motor system |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPS5285318A (en) |
| CA (1) | CA1050103A (en) |
| CH (1) | CH614323A5 (en) |
| DE (1) | DE2658607A1 (en) |
| FI (1) | FI66507C (en) |
| GB (1) | GB1563936A (en) |
-
1975
- 1975-12-31 CA CA242,842A patent/CA1050103A/en not_active Expired
-
1976
- 1976-12-20 JP JP15216176A patent/JPS5285318A/en active Pending
- 1976-12-23 DE DE19762658607 patent/DE2658607A1/en not_active Withdrawn
- 1976-12-24 GB GB54155/76A patent/GB1563936A/en not_active Expired
- 1976-12-27 FI FI763701A patent/FI66507C/en not_active IP Right Cessation
- 1976-12-29 CH CH1641976A patent/CH614323A5/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| FI763701A (en) | 1977-07-01 |
| FI66507C (en) | 1984-10-10 |
| GB1563936A (en) | 1980-04-02 |
| CH614323A5 (en) | 1979-11-15 |
| DE2658607A1 (en) | 1977-07-14 |
| JPS5285318A (en) | 1977-07-15 |
| FI66507B (en) | 1984-06-29 |
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