FI66507B - DRIV- OCH REGLERINGSSYSTEM FOER GENOM EN LIKRIKTARE MATAD LIKSTROEMSMOTOR - Google Patents

Description

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Fat «n«> · och ragtstantyralMn Amekan uthgd och utUkiifton puMcarad 29.06.84 (32) (33) (31) Pyy4 «** x« owHmot Bumprtorttt 31-12.75 Canada (CA) 242842 (71) Canadian General Electric Company Limited, 214 King St. W., Toronto,

Ontario, Canada (CA) (72) Ronald Clare Trussler, Peterborough, Ontario, Canada (CA) (74) Leitzinger Oy (54) Rectifier-fed DC motor drive and control system - Oriv- och regleringssystem för genom en likriktare matad 1ikströmsmotor

In DC motor operating systems in which a DC motor is supplied by a DC generator, lowering the output voltage of the generator in order to decelerate the motor tends to cause a change in the direction of the anchor current, which results in feedback to the generator. In electric operating systems with an alternator and using thyristor control to supply direct current to the motor, it is also possible to provide feedback when desired to brake the motor (regenerative and * "- ,, rutus). However, in electric operating systems where the alternator is operated by uncontrolled rectifiers current to the DC motor, there can be no feedback to the generator because the current cannot be reversed through the rectifiers.There are problems in the design of such systems especially when the motor needs to be slowed down quickly or reversed, as in propulsion drive systems.

When the power delivered by the power supply to the motor is reduced, the motor tends to act as a generator and if the energy absorbed by the motor load is so small that the power generated by the decelerating motor cannot be consumed by the circuit's natural resistance, it is necessary to connect a power consuming device. In most propulsion 2 66507 systems, the decelerating engine has considerable kinetic energy and it is necessary to absorb or consume the stored energy to stop the engine. In addition, it is often necessary, especially in propulsion operation, to develop a counter-torque to change the direction of rotational movement of the motor. In a DC motor, the torque is generated by the interaction of the fields caused by the anchor current and the excitation current of the motor. The anchor current cannot be easily reversed in a system supplied by a rectifier, and in this situation the excitation current of the motor must be reversed to produce a counter-electric motor force. Changing the direction of the magnetizing current causes other problems.

When the DC motor is running normally, it develops a counter-electric motor force (smv) and only smv resists the electric motor force applied to the motor. A change in the direction of the motor excitation current changes the direction of the counter-smv. In a rectifier-supplied motor system in which the motor decelerates and the kinetic energy of the motor and the load connected to it maintains the rotation of the motor, a change in the direction of the motor excitation current results in a counter-smv acting in the same direction as the rectifier output. This can cause the anchor current to be too high. It is necessary to limit or adjust this anchor current while generating as much counter-electromotive force as is practically possible to stop the motor or reverse its direction as quickly as possible.

Systems are known which are intended to assist in the braking of a rectifier-supplied DC motor, but the systems are not entirely satisfactory, especially if a change in direction of use is desired.

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Fund. // //

In a known system using a rectifier-supplied DC motor to drive a vehicle, the vehicle has a resistance circuit and as soon as braking begins, the traction motors are connected so that all the electrical power generated by the motors is consumed or absorbed in the resistance circuit.

It is also known from diesel electric locomotives to change the dynamic braking by changing the excitation current of the motor. In one such arrangement, the motor excitation circuit is directly connected to the generator output and the excitation of the generator is varied to maintain its output control and thus to control the motor excitation field and braking efficiency.

Neither of these known systems involves a change of direction following the stopping of the engine and does not provide control that allows a rapid change of direction of the engine.

The object of the present invention is to provide a rectifier-supplied DC motor drive which achieves enhanced braking and, if desired, a rapid change in the direction of rotation of the motor.

This object is achieved on the basis of the features of the invention set out in the appended claims.

The invention is described in more detail below with reference to the accompanying drawings, in which:

Figure 1 shows a considerably simplified block diagram, illustrating the operation of a control system according to the invention.

Figure 2 shows a block diagram according to an embodiment of the invention.

First, the control system according to the block diagram of Fig. 1 and its operation will be described. The steering system is particularly useful on ships, such as icebreakers, which often require a rapid change of direction. However, the control system according to the invention is suitable for use in any drive system which requires braking and rerouting and which may additionally have several generator rectifiers supplying the motor.

In Figure 1, block 10 shows a system controller having an input 11. The input 11 sets the output requirements for the drive and may be a control for use by the operator. Input 11 may give a constant speed to the motor or may cause braking or a change of direction.

The system controller 10 provides two reference signals. The second reference is in conductor 12 and the second reference is in conductor 14. Conductor 12 is connected to the circuit shown as block 27, which will be described below. Conductor 14 is connected to the motor excitation current control shown in block 16. These two reference signals in conductors 4 66507 12 and 14 represent the levels of generator voltage and motor excitation current required by system control 10.

The drive side of the system includes an alternator 17 driven by a power engine (not shown), such as a diesel engine, a rectifier 18 and a DC motor 20. The generator 17, rectifier 18 and motor 20 are connected in a conventional manner so that the generator 17 generates alternating current rectified 18 The power consuming device 21 is connected in series to the operating system circuit and can be switched on and off by the switch controller 22a and the switch 22.

In Figure 1, four parameters are felt. The anchor current is measured and the signal representing it is in line 23. The motor speed is measured and the signal representing it is in line 24 and the signal representing the motor excitation current is in line 25. The motor anchor voltage is measured and the measurement result is in line 29. The signals representing the measured parameters are applied to two circuits. One of them is shown as a block 26 to which the speed signal of the line 24 is applied and the output of which controls the switch controller 22a to drive the switch 22 to connect the energy consuming device 21 to and from the motor anchor circuit. The control signal is also obtained via line 11A. The second circuit is shown as a block 27 to which the signals of the conductors 12, 23, 25 and 29 are conducted and the output of which controls the operation of the switch controller 28a to control the switch 28, in addition to which a control signal is applied to the switch 28. This control signal is coupled by a switch 28 so that it either enters the conductor 30 and becomes conducted to the generator magnetizing current controller 15 or is applied to the conductor 31 and fed to the motor excitation current controller 16.

The circuit of block 26 responds to the speed and direction of rotation of the motor and its effect can be called primary control for simplicity. It can be seen that a change in the direction of the motor excitation current causes a change in the direction of the counter-electromotive force and a counter-electromotive force that changes its direction causes the anchor current to be in the discharge direction of the rectifier.

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The control circuit block 26 receives a signal representing the motor speed and a reference signal 11A representing the control 11. If the signal representing the control means that a stop or reversal is desired (by comparing the reference signal with the actual speed signal), then the circuit determines whether the energy absorbing device 21 should be connected to the anchor circuit. This is the first step in the control decision. The counter-torque required to decelerate the motor is a quantity determined by the motor anchor current and the motor excitation flux. The excitation flux of the motor is substantially proportional to the excitation current. The excitation current of the motor must not exceed a value determined by the permissible counter-electromotive force of the motor, which can be generated without exceeding the permissible anchor current. The counter-electric motor force is proportional to the quantity determined by the motor speed and the motor excitation flux. Thus, at a given allowable anchor current, the motor excitation flux (approximately proportional to the motor excitation current) may be higher at low motor speeds and thus may generate a higher counter torque than at high motor speeds. At high motor speeds, the magnetization current must be reduced to avoid counter-electromotive force that would cause excessive anchor current. Therefore, if the motor speed is above a certain limit, the energy consuming device 21 must be connected to the anchor circuit in order to allow the motor excitation flux and thus the counter-electric motor force of the motor to increase without exceeding the allowable anchor current.

Thus, if the control circuit block 26 detects that stopping or reversing is desired and that the motor speed is above a certain limit, then a signal is applied to the switch controller 22 which causes the switch 22 to operate to connect the energy absorbing device 21 to the anchor circuit. This method of control can be called control through the determination of counter torque and counter-electromotive force.

The energy absorbing device 21 is normally disconnected (bypassed) by the switch 22 before the actual change of direction, e.g. at a low speed close to zero speed, where the excitation current of the motor is at its maximum allowable value and the anchor current is below its allowable value. However, if the 6 66507 energy absorbing device is not disconnected from the circuit before the change of direction, it is arranged so that it becomes disconnected when the direction of rotation changes.

It is clear that several energy consuming devices 21 could also be connected to and from the anchor circuit depending on the conditions, or i.e. a variable energy consumption load could be connected to the anchor circuit depending on the signals of the switch controller 22A circuit.

It should be noted that the energy consuming load does not engage the anchor circuit as a result of any braking, but only when the motor speed is such that the motor counter-torque is insufficient to stop the motor.

The circuit of block 27 responds primarily to two parameters to perform control. One is the counter-electric motor force of the motor (i.e. the anchor voltage of the motor) and the other is the excitation current of the motor. These two parameters can be obtained in several different ways, and the simplified diagram of Figure 1 shows the input of the motor anchor voltage signal in conductor 29 and the input of the excitation current signal in conductor 25. The parameters can be measured or derived from other signals. The operation of the circuit of block 27 ^ can be called secondary control.

A reference signal from the system controller 10 and a signal representing the anchor current are normally applied to the circuit of block 27 by conductor 12 and conductor 23. These signals correspond to the desired anchor current and the actual anchor current. The difference, i.e. the error signal resulting from the comparison of the two signals, is conducted by conductor 30 to control the excitation current of the generator and thus to control the anchor current, as is known. In normal operation, the motor excitation current controller 16 also receives a control signal via a conductor 14 from the system controller 10, and this controls the motor excitation current.

However, under certain conditions, block 27 performs secondary control, as mentioned above, and redirects the control signals. When the circuit of block 27 detects a change in the direction of the counterelectric force 66507 and the excitation current of the motor is below its maximum allowable value, the switch controller 28a operates the switch 28 and the control signal normally on the conductor 30 is connected to the conductor 31. The signal on the conductor 31 to a signal in conductor 14 from controller 10 to determine the excitation current of the motor.

The signal representing the anchor current control remains in the conductor 31 until the maximum motor excitation current is reached. At this point, the counter-electromotive force can no longer increase and therefore cannot maintain full anchor current. Thus, when the maximum motor excitation current is reached, the circuit of block 27 controls the switch controller 28a, which causes the switch 28 to return to normal operation. The generator voltage can now be increased in the normal way to provide the maximum anchor current required.

It can be seen that the maximum torque is available to stop the engine and change direction. The control system makes it possible to make variations in the torque control to meet different needs.

Reference is now made to Figure 2, which shows a block diagram of an embodiment of the invention. The generator 17, the rectifier 18, the energy polishing device 21, the switch 22 with its switch controllers 22a, the motor 20 and the generator and motor excitation current regulators 15 and 16 have the same reference numerals as in Fig. 1. I

In Figure 2, the system controller and control circuit 33 have an input 11 to achieve the required operating values. The controller and control circuit of system j provide the necessary output reference signals,! as presented as ice skins. Engine tachometer 34 measures! the speed and direction of rotation of the motor and is connected by a wire 39 to the system controller and the control circuit 33 to its second input. The system controller and control circuit 33 provide output signals to leads 35 to 38. The signal at lead 35 represents the desired generator output voltage. The signal in conductor 36 represents the "secondary control" signal mentioned in connection with Figure 1. The signal in conductor 37 represents the "primary control" signal mentioned in connection with Figure 1. The signal on conductor 38 represents the desired motor excitation current.

j i 66507 The voltage sensor 40 measures the motor voltage and provides a signal to the conductor 41 corresponding to the motor voltage. Conductors 35 and 41 having signals corresponding to the desired voltage and the measured voltage, respectively, are connected to a device 42 which provides an output signal which is a function of the difference between the voltage signals.

This difference signal or error signal is input to a unit 43 having a voltage controller and a current reference. The output signal from the voltage control and current reference unit 43 is proportional to its input signal, but may have maximum or minimum values (e.g., it may have a maximum limit to prevent excessive rectifier output current) and is applied as a single signal to device 44. This is the current reference signal. The current measuring member 45 measures the anchor current and provides a signal to the conductor 46 representing the anchor current. Conductor 46 is connected to device 44 to conduct an anchor current signal to device 44. Device 44 provides an output signal that is a function of the difference between the current reference signal and the actual anchor current signal. The differential signal or error signal from device 44 is applied to the anchor current controller 47. The current differential signal is normally used to change the excitation current of the generator to change the anchor current so that the anchor current signal on line 46 approaches the current reference signal at current The control signal from the anchor current regulator 47 is applied to a control and direction amplifier 48 which directs the control signal either by conductor 50 to the generator magnetic current regulator 15 or by conductor 51 to device 52. That is. adjustments, the directional amplifier 48 responds to a signal in the conductor 36 ("secondary control" signal) to apply a control signal to the conductor 50 or 51. When the control signal is in the conductor 50, it acts on the generator excitation current controller 15 to adjust the generator excitation current and thus control the anchor current. When the control signal is in the conductor 51, there has been a change in the direction of the counter-electric motor force in the motor 20, but the excitation current of the motor is below its maximum value. The control signal is applied to the reference 52 of the devices 52, where it is summed to a reference of the motor excitation current in the conductor 38. The resulting signal is passed through a reference limiter 53 to adjust the motor excitation current and thus to control the anchor current. The reference limiter 53 prevents the motor excitation current from exceeding the allowable limit. This gives maximum braking power and the energy is absorbed by the energy consuming device 21.

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At some point during braking, the rotational speed of the motor slows to a level where its counter-electric motor force cannot generate a full anchor current even when the motor excitation current is at its maximum. Since the maximum excitation current has been reached, the system controller and the control circuit 33 provide a signal to the conductor 36 which directs the current control back to the conductor 50 to restore normal operation.

It should be noted that this can occur before the actual change of direction of the motor occurs. When the excitation current of the motor is at its maximum, the excitation current of the generator increases according to the control signal received from the anchor current regulator 47 until the maximum anchor current is reached. The engine torque is now at its maximum and causes maximum braking and acceleration in the \ stepped direction.

The operation of the switch controller 22a and the switch 22 for connecting the energy consuming device 21 to and from the anchor circuit is similar to that shown in connection with Figure 1.

The purpose of the control system is to achieve greater dynamic braking and rapid reversal of the drive motor.

Claims (3)

A drive and control system for a direct current motor supplied via a rectifier, to which is an alternator (17), a rectifier (18) for rectifying the generator output and a direct current motor (20), which is measured with the generator's rectified output, both the generator and the motor are separately magnetized, and the system includes an energy consumption device (21) which can be coupled to the motor's anchor circuit to consume the motor's energy when the motor is braked; and a means for measuring the rotation speed of the motor, for delivering a speed signal (24, 39) representing the engine speed characterized by a control circuit (26, 33), which comprises a control executable by determining the counter-electromotive force and receiving the speed signal ( 24, 39) from said measuring circuit and determining the calculated counter-electromotive force using the speed signal and the maximum allowable magnetizing current of the motor and reacting, where the calculated counter-electromotive force exceeds a predetermined value of the countercurrent energy applied under the electric motor force 21) into the anchor circuit. Drive and control system according to claim 1, characterized in that said control circuit (26, 33) responds to the monitoring of the counter-electromotive force, as it determines a smaller value for the counter-electromotive force than the predetermined value of the counter-electromotive force. , to disconnect the energy-consuming device (21) from the anchor circuit, and the control circuit also responds to a directional change of the motor shaft's rotational motion, thereby ensuring that the energy-consuming device is coupled from the anchor circuit. The drive and control system according to claim 2, further comprising: a generator (15) for the magnetizing current and a control (16) for the magnetizing current, both of which respond to the control signal for controlling the magnetization current in the magnetizing windings; means (33) for