CA1130482A - Mine hoist drive - Google Patents
Mine hoist driveInfo
- Publication number
- CA1130482A CA1130482A CA325,421A CA325421A CA1130482A CA 1130482 A CA1130482 A CA 1130482A CA 325421 A CA325421 A CA 325421A CA 1130482 A CA1130482 A CA 1130482A
- Authority
- CA
- Canada
- Prior art keywords
- converter
- hoist
- speed
- drive
- inversion
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B66—HOISTING; LIFTING; HAULING
- B66B—ELEVATORS; ESCALATORS OR MOVING WALKWAYS
- B66B1/00—Control systems of elevators in general
- B66B1/24—Control systems with regulation, i.e. with retroactive action, for influencing travelling speed, acceleration, or deceleration
- B66B1/28—Control systems with regulation, i.e. with retroactive action, for influencing travelling speed, acceleration, or deceleration electrical
- B66B1/30—Control systems with regulation, i.e. with retroactive action, for influencing travelling speed, acceleration, or deceleration electrical effective on driving gear, e.g. acting on power electronics, on inverter or rectifier controlled motor
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
- H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
- H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/145—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means
- H02M7/155—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only
- H02M7/162—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration
- H02M7/1623—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit
- H02M7/1626—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a thyratron or thyristor type requiring extinguishing means using semiconductor devices only in a bridge configuration with control circuit with automatic control of the output voltage or current
-
- 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
- H02P7/24—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 discharge tubes or semiconductor devices
- H02P7/28—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 discharge tubes or semiconductor devices using semiconductor devices
- H02P7/281—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 discharge tubes or semiconductor devices using semiconductor devices the DC motor being operated in four quadrants
- H02P7/2815—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 discharge tubes or semiconductor devices using semiconductor devices the DC motor being operated in four quadrants whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Automation & Control Theory (AREA)
- Control Of Ac Motors In General (AREA)
Abstract
Case 2609 MINE HOIST DRIVE
ABSTRACT OF THE DISCLOSURE
A friction-type mine hoist drive has at least one d.c. motor to drive the hoist. Two six pulse converters are connected in series to provide d.c.
power for the motor. A free-wheeling diode is connec-ted across the output of one converter. A control uses a first one of the converters (without the free-wheeling diode) to provide power for the hoist for the first 50% of the speed range and then phases on the second of the converters to add power from 50%
to substantially 100% speed. While there is no kvar reduction in the first converter the kvar demand is less than 50% of conventional back to back converter, and the free-wheeling diode across the second converter reduces kvar demand and reduces ripple when the second converter is operating. There is little requirement for fourth quadrant operation because deceleration is normally taken care of by gravity. However the possibility of fourth quadrant operation may be handled in several ways. First, a load value is determined for a particular hoist representing the dividing point between inversion being required and not required when decelerating from full speed. By measuring speed and current when the hoist begins operation, the actual load is determined and the actual load compared with the predetermined load value.
If inversion might be required when decelerating from full speed, the hoist can be limited to half speed by locking out the second converter and operating with the first converter. As one alternative the first converter can handle the requirement for inversion by operating in the fourth quadrant when required. As another alternative, a switch can be provided in series with the free-wheeling diode to remove it from continued.........
Case 2609 ABSTRACT OF THE DISCLOSURE (continued) the circuit to make both the first and second converters available for fourth quadrant operation.
ABSTRACT OF THE DISCLOSURE
A friction-type mine hoist drive has at least one d.c. motor to drive the hoist. Two six pulse converters are connected in series to provide d.c.
power for the motor. A free-wheeling diode is connec-ted across the output of one converter. A control uses a first one of the converters (without the free-wheeling diode) to provide power for the hoist for the first 50% of the speed range and then phases on the second of the converters to add power from 50%
to substantially 100% speed. While there is no kvar reduction in the first converter the kvar demand is less than 50% of conventional back to back converter, and the free-wheeling diode across the second converter reduces kvar demand and reduces ripple when the second converter is operating. There is little requirement for fourth quadrant operation because deceleration is normally taken care of by gravity. However the possibility of fourth quadrant operation may be handled in several ways. First, a load value is determined for a particular hoist representing the dividing point between inversion being required and not required when decelerating from full speed. By measuring speed and current when the hoist begins operation, the actual load is determined and the actual load compared with the predetermined load value.
If inversion might be required when decelerating from full speed, the hoist can be limited to half speed by locking out the second converter and operating with the first converter. As one alternative the first converter can handle the requirement for inversion by operating in the fourth quadrant when required. As another alternative, a switch can be provided in series with the free-wheeling diode to remove it from continued.........
Case 2609 ABSTRACT OF THE DISCLOSURE (continued) the circuit to make both the first and second converters available for fourth quadrant operation.
Description
11~048;~
1 Case 2609 MINE HOIST DRIVE
This invention relates to a mine hoist drive, and in particular it relates to a system which supplies d.c. power to the motors of a mine hoist and the related controls for the mine hoist.
A mine hoist normally has large d.c. motors which receive power from a polyphase a.c. source through a converter system. There are a variety of converter systems known for converting power from a polyphase a.c. source, for example a three phase a.c.
source, into a suitable d.c. supply for motors. These systems include simple arrangements of diode rectifiers to more complex arrangements of silicon controlled rectifiers (SCR) with additional circuitry to control power factor. One such power conversion system is described in Canadian patent application Serial No.
291 811 in the name of Herbert W. Weiss, filed November 25, 1977. One of the arrangements described therein has two six pulse bridges connected in series to the load. Each bridge has a wye arranged secondary of a transformer to provide the a.c. power to the bridge, and each wye secondary has a neutral. Controlled rectifiers are connected from each winding to the output and from each neutral to the output. With this arrangement it is possible to operate over a range of loads. For example, one six pulse bridge may be used for lower speeds and the other six pulse bridge may be brought into operation as required by higher speeds.
1~3048Z:
Case 2609 This arrangement also provides for power factor control and for fourth quadrant operation.
A mine hoist has characteristic requirements for power and control that are perhaps somewhat different from the requirements of other electrical apparatus. A friction type mine hoist may have, or example, d.c. motors of a size in the range of 2000 to 10 000 horsepower (HP). Because of the large motor size there may be heavy kilovolt-ampere reactive (kvar) demands, particularly as the hoist accelerates while lifting a heavy load, and it is desirable to reduce or control this kvar demand. It is also desirable to reduce ripple voltage. On the other hand, there is only a minor requirement to have the converters perform as inverters (i.e. to operate in the fourth quadrant) because when the hoist is raising a load and decelerates, the deceleration is usually taken care of by the force of gravity. When the hoist is decelerating from a non-lifting operation there is little regeneration.
It is therefore one of the features of the present invention to provide a mine hoist drive which determines whether regeneration would be required under certain conditions and, if regeneration would be required, to either avoid the conditions or arrange for limited regeneration.
It is also a feature of the invention to provide a simple and rugged mine hoist drive which requires no neutral connection and no tertiary windings in the transformers and requires no SCRs in the bypass circuit and hence has simpler firing arrangements.
It is also a feature of the invention to provide a contactor switching arrangement for removing the bypass diodes from the circuit under certain conditions and thereby provide full torque, full speed regeneration if required.
1~3~)4flZ
3 Case 2609 The mine hoist of this invention preferably uses two six pulse thyristor converters. The first converter uses a wye connected secondary with no neutral connection required, and the second converter uses a delta connected secondary. The outputs of the converters are connected in series to drive one or more d.c. motors in a mine hoist. A diode is connected across the output of the second converter. This diode arrangement is known in the art and is referred to as a free-wheeling diode. It functions to improve the power factor, i.e. to reduce the kvar demand, as well as to reduce ripple voltage.
When the mine hoist is started and is acceler-ating, only the first converter is used. The first converter provides the driving power up to 50 percent speed; then the second converter is sequentially phased on. Thus, as the hoist is accelerating from zero to 50% speed, the second converter is locked out and the current flows through the shunting diode. The kvar demand is therefore half what it would be if both converters were used. Similarly the harmonics and the ripple voltages are one half. In other words, while there is no reduction in kvar demand for the first converter, the total kvar demand is limited to one half. As the second converter is phased on at 50%
speed (there is some overlap provided in the 50%
region), the free-wheeling diode functions to reduce the kvar demand of that converter. Thus the overall kvar demand is reduced without introducing the complexities associated with the firing of controlled by-pass thyristors and/or more complex transformers.
In a slightly more complex form of the invention, a free-wheeling diode is used across the output of the first converter also. This further reduces the kvar demand.
In a majority of operations of a mine hoist, the hoist will be loaded when the skip is being raised 1~3048Z
Case 2609 and will have no load or little load when it is being lowered. When a mine hoist is raising a heavy load and it dece~erates, the force of gravity will normally provide satisfactory deceleration without requiring regeneration by the converters, as was previously mentioned. When the hoist is raising lighter loads and it decelerates from full speed, the converters may be required to provide regeneration. While different hoist designs will have different requirements, it has been found that for many hoists decelerating from a full speed raising operation, regeneration may be required when the load is less than about half.
This load may readily be determined and may be referred to as the critical regeneration load. Thus, when a lifting or raising operation is started, the control may determine the hoist load from inputs representing the motor field strength, the speed, and the current drawn, and this may be compared to a value representing the critical regeneration load. If the actual load is less than the critical regeneration load, then regeneration will be required when decelerating from full speed. In one form of the invention, when a raising operation is started, the control determines if the load is less than the critical regeneration load, and if so then the hoist is inhibited from exceeding half speed so that full torque regeneration may be carried out on the first converter. This may be done, for example, by locking out the second converter and running on the first converter only.
In another form of the invention, when it is determined regeneration might be required when decelerating from full speed, the control is placed in readiness to phase on converter one to operate in the fourth quadrant when appropriate. Because there is a free-wheeling diode across the output of the second 1~3048;~
Case 2609 converter it will not operate in the f~urth quadrant.
However, the requirements for regeneration in a mine hoist and particularly in a friction mine hoist are relatively small and one converter will normally be able to take care of regeneration at reduced motor field and full speed.
In yet another form of the invention, a switch or contactor is placed in series with the free-wheeling diode across the second converter to remove the diode from the circuit when regeneration is required. In a similar manner, if there is a free-wheeling diode used across the output of the first converter also, then a second switch or contactor is used in series with that diode to switch it out of the circuit when regeneration is required. As there is only an infrequent requirement for operating in a regenerating mode or fourth quadrant mode, the contactors operate infrequently and wear is not a problem.
In the description of the invention, it will be described with reference to a friction mine hoist, but it is also applicable to drum type hoists, particularly in shallower shafts where regeneration requirements are minimal.
In accordance with the invention in a basic form there is provided a drive for a mine hoist having a load-carrying skip, comprising at least one d.c.
motor for driving said hoist to raise and lower said skip, a first and a second thyristor converter connected in series to provide power for said motor, a diode connected across the output of said second converter, control means responsive to a control command signal for controlling said first converter during operation of the hoist between 0 and approxi-mately 50~ speed while inhibiting operation of the second converter, and for controlling said second converter during operation of the hoist above i~3048Z
Case 2609 approximately 50~ speed while maintaining operation of the first converter at its normal full voltage, and said control means including means for determining the degree of inversion required during normal deceleration.
The invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 is a schematic diagram showing a power conversion system connected to mine hoist motors and showing a control system in block form, in accordance with one form of the invention, Figure 2 is a diagram of output voltage and motor speed plotted against kvar, useful in describing the invention, and Figure 3 is an alternate arrangement of part of the Figure 1 circuitry, in accordance with another variation or form of the invention.
Referring to Figure 1, a source of a.c. power is shown at 10 as a source of three phase power and is connected to the primary windings 11 and 12 of trans~ormers 14 and 15. The transformers 14 and 15 could, of course, be replaced by a single transformer with two secondary windings. As shown, the secondary winding 16 of transformer 14 is wye connected and the secondary winding 17 of transformer 15 is delta connected. Each phase of the wye connected secondary 16 of transformer 14 is connected to an output by controlled rectifiers 18A - 18F to form a six pulse converter. No neutral connection is required. The output is represented by conductors 20 and 21. Each one of the controlled rectifiers 18A - 18F has a gate electrode and each gate electrode is connected to control 22 which provides gating or triggering pulses as is known in the art. For simplicity only one of the gate electrodes is shown connected to control 22 and that is the gate electrode of controlled rectifier 18A connected by conductor 23 to control 22. Large 11;3048Z
7 Case 2609 arrow 24 represents the conduetors connected to the gate electrodes of controlled rectifiers 18B - 18F.
The six pulse converter which comprises transformer 14, controlled rectifiers 18A - 18F, and with a d.c. output on conductors 20 and 21, is designated generally as A. Six pulse converters such as the converter A are known in the art, and one is described generally for example in connection with Figure 1 of Canadian Patent Application Serial No.
301 105 - Young, filed April 13, 1978, or a more basic description may be found in "Direct Current Transmission", Volume I, E.W. Kimbark, published by Wiley - Interscience 1971, chapter 2.
The controlled rectifiers employed in this invention may be of any suitable type but are preferably of the class known as thyristors, the most common of which is the silicon controlled rectifier or SCR.
In a generally similar manner the secondary winding 17 of transformer 15 is connected to controlled rectifiers 18G - 18L arranged as a six pulse converter having its d.c. output on conductors 25 and 26. Each of the controlled rectifiers 18G - 18L has a gate electrode connected to control 22 which provides an appropriate gating or triggering pulse. For simplieity, as before, only the controlled rectifier 18J is shown with its gate electrode conneeted to control 22 via conductor 27. Large arrow 28 represents the conductors connected to the gate electrodes of the other controlled rectifiers.
The six pulse converter which comprises transformer 15, controlled rectifiers 18G - 18L, and having a d.c. output on conductors 25 and 26 is designated generally as converter B and is known in the art.
A free-wheeling diode 30 is connected between conductors 25 and 26. The diode 30, of course, may represent several diodes in practice. As was previously 8 Case 2609 mentioned, the use of free-wheeling diodes is known.
The two six pulse converters A and B are connected in series with two d.c. motors 31 and 32.
That is, conductor 21 is connected to one input of motor 31, conductor 20 is connected to one input of motor 32, conductor 26 is connected to the other input of motor 32, and conductor 25 is connected through a circuit breaker 33 and an air core ripple reactor 34 to the other input of motor 31. The ripple reactor is for reducing excessive ripple and, depending on the particular system, may not be required.
It will, of course, be apparent that a single motor could be used for the mine hoist drive rather than two motors as shown.
There are four operating feedback signals to control 22 and a command signal input. Motors 31 and 32 are coupled by a shaft 35 and a speed or RPM sensor 36 is connected to shaft 35. Sensor 36 provides a signal via conductor 37 to control 22 and this signal represents speed feedback. A current sensor 38 is coupled to an armature current carrying conductor to sense current and to provide on conductor 40 a feedback signal representing current. Two voltage sensors l9A
and l9B are connected across the outputs of converters A and B respectively. The sensors provide signals, representing respective voltages at the outputs of converters A and B, on conductors 29A and 29B
respectively. Control 22 also receives a command signal at input 41 which requires a certain hoist operation. Control 22 also controls the fields to motors 31 and 32 as indicated at 39, 39A and 39B for example by reversing them as required during slowdown.
A signal is available which represents field strength.
Very briefly, the operation of the drive is controlled from input 41. The command signal at input 41 requires a certain hoist operation. Starting from rest, control 22 provides gating pulses to the 1~L304f~Z
Case 2609 six pulse converter A which will accordingly provide the required output to power electric motors 31 and 32.
As more power is required the gating is adjusted until converter A approaches its rated output. As the two converters are equal in rating and capacity, one converter alone provides half the output to power the motors and this will result in the motors running at half speed. As was previously mentioned, while converter A is providing power to operate the hoist between 0 and 50% speed, the operation of converter B is inhibited. It should be noted that while 5th and 7th harmonics may be present causing line harmonic currents, these occur at less than half the rated output for the drive. Also the kvar demand is less than half that for a conventional drive of the same rating, and the motor ripple voltage is similarly reduced.
As the output of converter A approaches its rated output, the signal representing output voltage of converter A is received by control 22 via conductor 29A. Control 22 uses this signal to phase on converter B, that is, control 22 compares the voltage signal with a reference selected to provide the desired overlap.
When the voltage signal equals the reference, control 22 begins to phase on the six pulse converter B. As converter A reaches its rated output is continues to provide that output and control passes to converter B.
Now the free-wheeling diode 30 comes into operation to reduce kvar demand and ripple. The output of converter B
increases until full speed is reached. In this manner at 100% rated speed, converter A is fully on, and speed control is by adjusting converter B.
It is common practice to designate the rated output of a converter as the output which will provide continuous running power to the load it is intended to drive. As explained hereinafter with reference to Figure 2, the converter may have a capacity in excess of this, for example to provide a higher output voltage for "- .,~
11304~3Z
Case 2609 unusual temporary conditions and as a safety factor, however its rated output is designated as that which will provide rated running of its load. In this case, converter A will drive the hoist motors between 0 and approximately 50% speed, while converter A plus converter B at rated output will drive the hoist motors to 100% spe~ed.
Slowdown from a lifting operation is made by phasing back converter B and then phasing back converter A in a manner substantially the reverse of accelerating.
As was previously mentioned, with a loaded skip the force of gravity usually takes care of deceleration without any need for the converters to operate as inverters. When slowing down or decelerating a skip that is empty or partially loaded, there may be a requirement for fourth quadrant operation but it is usually a relatively small requirement and can be handled by converter A alone with the motor(s) operating at less than half field down to half speed. Because of the diode 30, the converter B
cannot operate in the fourth quadrant. Control 22 also provides protection for converter A during inverting operation. Control 22 receives a signal on conductor 29A
representing voltage at the output of converter A. When this voltage signal indicates, during inversion, that the voltage across the inverter A is approaching the allowable maximum voltage, it reduces the motor field which in turn lowers the voltage to keep it below the allowable inversion voltage level.
In another form of the invention the problem of inversion is handled by first determining, during acceleration and running of the hoist, if inversion is likely to be required during slowdown. Sensors 36 and 38 monitor RPM and current and control 22 receives signals representing these values. Control 22 also provides a signal representing motor field strength. From these signals torque can be determined and a signal derived that will representative 113~4~Z
Case 2609 10a of the load in the skip. As the slowdown or deceleration in a mine hoist is a controlled process, it is possible to determine in advance the amount of regenerative torque that will be needed. Thus, while the hoist is accelerating, the load is determined and the control compares this with the predetermined value for critical regeneration load, i.e. the load that will require inversion when decelerating. If inversion will not be required, nothing further need be done. If heavy inversion will be required during deceleration, the control 22 can be preset to lock out converter B and the mine hoist will operate at half speed. In other words, the hoist is limited to approximately 50%
speed or less when heavy inversion would be required, for example when full rated torque would be required during deceleration. In fact, for deceleration where more than 50~ of available torque is required, the hoist speed is limited to less than about 50~.
The slowdown from half speed, can be handled by operating converter A in the fourth quadrant.
Alternately, the hoist is permitted to operate to 100% speed when not more than 50~ torque would be required during deceleration. On the other hand, if heavy inversion is required from top speed, the free-wheeling diode 30 can be switched out of the circuit as shown in Figure 3.
Referring now to Figure 3, there is shown a 113~)~8;~
Case 2609 modified converter B' which is similar to converter ~
of Figure 1 except it has a switch or contactor 42 that is actuated by control 22. When control 22 determines from the mine hoist load that heavy inversion may be required when decelerating from full speed, when the deceleration or slowdown is started control 22 opens switch 42 removing diode 30 from the circuit so that converter B' can operate in the fourth quadrant. This makes converter A and B' available for fourth quadrant operation. The wear on switch 42 will not be excessive as it will not be required to operate each time the hoist slows down, but only if the load is such that heavy inversion is required.
It will be apparent that converter A could be provided with a free-wheeling diode across its output to improve the power factor, i.e. to reduce kvar demand, and reduce ripple, provided that a switch similar to switch 42 is incorporated. This would enable converter A to operate in the fourth quadrant when required.
Referring now to Figure 2, there is shown a plot of speed (in percent full speed) and output voltage (in percent of rated output voltage) against kvar demand (as a percent). In the plot or graph of Figure 3, full speed has been shown at 80~ output voltage. It is customary to provide some voltage reserve at full speed, and while 80% voltage is an arbitrary selection for full speed operation it is fairly typical and suitable for illustrating the invention. The curves or paths are approximate and intended for comparison purposes. If the mine hoist drive were operating as a standard unidirectional or back-to-back converter, that is with no diode 30 and both converters A and Bphased forward together as the hoist is accelerated, then the drive will accelerate along the outer part of the circle, i.e. by the path 113~4~1~
Case 2609 represented by 0 - 50 - 51 - 52. If converter A is phased on first and permitted to approach its full capacity before converter B is phased on, with diode 30 conducting, then it will first follow the path 0 - 53 - 54 which represents converter A, and then add 54- 55 - 56 - 57 which represents converter B. It will be seen that there is a considerable reduction in kvar demand as shown by cross hatching and this is obtained without special transformers and with conventional simple SCR gating. If a second free-wheeling diode is used across the output of converter A, the path during acceleration would be 0 - 60 - 61 -62 - 55 - 56 - 57.
Also shown in Figure 2 is the path which represents operation in accordance with the arrangement of the aforementioned Canadian patent application Serial No. 291 811. This path is shown by broken line 0 - 63 - 64 - 65 - 66 - 67 - 68. This path represents the greatest reduction in kvar demand but requires transformers with neutral connections, controlled rectifiers in the neutral circuits, and more complex gating arrangements. The different forms of the invention described herein are suitable for a mine hoist drive which has certain requirements. The kvar demand is reduced to a level suitable for mine operation with simple means, the control and gating is simple, and the possibility of operation in the fourth quadrant is first determined and either avoided by changing hoist operation or otherwise provided for with simple controls.
1 Case 2609 MINE HOIST DRIVE
This invention relates to a mine hoist drive, and in particular it relates to a system which supplies d.c. power to the motors of a mine hoist and the related controls for the mine hoist.
A mine hoist normally has large d.c. motors which receive power from a polyphase a.c. source through a converter system. There are a variety of converter systems known for converting power from a polyphase a.c. source, for example a three phase a.c.
source, into a suitable d.c. supply for motors. These systems include simple arrangements of diode rectifiers to more complex arrangements of silicon controlled rectifiers (SCR) with additional circuitry to control power factor. One such power conversion system is described in Canadian patent application Serial No.
291 811 in the name of Herbert W. Weiss, filed November 25, 1977. One of the arrangements described therein has two six pulse bridges connected in series to the load. Each bridge has a wye arranged secondary of a transformer to provide the a.c. power to the bridge, and each wye secondary has a neutral. Controlled rectifiers are connected from each winding to the output and from each neutral to the output. With this arrangement it is possible to operate over a range of loads. For example, one six pulse bridge may be used for lower speeds and the other six pulse bridge may be brought into operation as required by higher speeds.
1~3048Z:
Case 2609 This arrangement also provides for power factor control and for fourth quadrant operation.
A mine hoist has characteristic requirements for power and control that are perhaps somewhat different from the requirements of other electrical apparatus. A friction type mine hoist may have, or example, d.c. motors of a size in the range of 2000 to 10 000 horsepower (HP). Because of the large motor size there may be heavy kilovolt-ampere reactive (kvar) demands, particularly as the hoist accelerates while lifting a heavy load, and it is desirable to reduce or control this kvar demand. It is also desirable to reduce ripple voltage. On the other hand, there is only a minor requirement to have the converters perform as inverters (i.e. to operate in the fourth quadrant) because when the hoist is raising a load and decelerates, the deceleration is usually taken care of by the force of gravity. When the hoist is decelerating from a non-lifting operation there is little regeneration.
It is therefore one of the features of the present invention to provide a mine hoist drive which determines whether regeneration would be required under certain conditions and, if regeneration would be required, to either avoid the conditions or arrange for limited regeneration.
It is also a feature of the invention to provide a simple and rugged mine hoist drive which requires no neutral connection and no tertiary windings in the transformers and requires no SCRs in the bypass circuit and hence has simpler firing arrangements.
It is also a feature of the invention to provide a contactor switching arrangement for removing the bypass diodes from the circuit under certain conditions and thereby provide full torque, full speed regeneration if required.
1~3~)4flZ
3 Case 2609 The mine hoist of this invention preferably uses two six pulse thyristor converters. The first converter uses a wye connected secondary with no neutral connection required, and the second converter uses a delta connected secondary. The outputs of the converters are connected in series to drive one or more d.c. motors in a mine hoist. A diode is connected across the output of the second converter. This diode arrangement is known in the art and is referred to as a free-wheeling diode. It functions to improve the power factor, i.e. to reduce the kvar demand, as well as to reduce ripple voltage.
When the mine hoist is started and is acceler-ating, only the first converter is used. The first converter provides the driving power up to 50 percent speed; then the second converter is sequentially phased on. Thus, as the hoist is accelerating from zero to 50% speed, the second converter is locked out and the current flows through the shunting diode. The kvar demand is therefore half what it would be if both converters were used. Similarly the harmonics and the ripple voltages are one half. In other words, while there is no reduction in kvar demand for the first converter, the total kvar demand is limited to one half. As the second converter is phased on at 50%
speed (there is some overlap provided in the 50%
region), the free-wheeling diode functions to reduce the kvar demand of that converter. Thus the overall kvar demand is reduced without introducing the complexities associated with the firing of controlled by-pass thyristors and/or more complex transformers.
In a slightly more complex form of the invention, a free-wheeling diode is used across the output of the first converter also. This further reduces the kvar demand.
In a majority of operations of a mine hoist, the hoist will be loaded when the skip is being raised 1~3048Z
Case 2609 and will have no load or little load when it is being lowered. When a mine hoist is raising a heavy load and it dece~erates, the force of gravity will normally provide satisfactory deceleration without requiring regeneration by the converters, as was previously mentioned. When the hoist is raising lighter loads and it decelerates from full speed, the converters may be required to provide regeneration. While different hoist designs will have different requirements, it has been found that for many hoists decelerating from a full speed raising operation, regeneration may be required when the load is less than about half.
This load may readily be determined and may be referred to as the critical regeneration load. Thus, when a lifting or raising operation is started, the control may determine the hoist load from inputs representing the motor field strength, the speed, and the current drawn, and this may be compared to a value representing the critical regeneration load. If the actual load is less than the critical regeneration load, then regeneration will be required when decelerating from full speed. In one form of the invention, when a raising operation is started, the control determines if the load is less than the critical regeneration load, and if so then the hoist is inhibited from exceeding half speed so that full torque regeneration may be carried out on the first converter. This may be done, for example, by locking out the second converter and running on the first converter only.
In another form of the invention, when it is determined regeneration might be required when decelerating from full speed, the control is placed in readiness to phase on converter one to operate in the fourth quadrant when appropriate. Because there is a free-wheeling diode across the output of the second 1~3048;~
Case 2609 converter it will not operate in the f~urth quadrant.
However, the requirements for regeneration in a mine hoist and particularly in a friction mine hoist are relatively small and one converter will normally be able to take care of regeneration at reduced motor field and full speed.
In yet another form of the invention, a switch or contactor is placed in series with the free-wheeling diode across the second converter to remove the diode from the circuit when regeneration is required. In a similar manner, if there is a free-wheeling diode used across the output of the first converter also, then a second switch or contactor is used in series with that diode to switch it out of the circuit when regeneration is required. As there is only an infrequent requirement for operating in a regenerating mode or fourth quadrant mode, the contactors operate infrequently and wear is not a problem.
In the description of the invention, it will be described with reference to a friction mine hoist, but it is also applicable to drum type hoists, particularly in shallower shafts where regeneration requirements are minimal.
In accordance with the invention in a basic form there is provided a drive for a mine hoist having a load-carrying skip, comprising at least one d.c.
motor for driving said hoist to raise and lower said skip, a first and a second thyristor converter connected in series to provide power for said motor, a diode connected across the output of said second converter, control means responsive to a control command signal for controlling said first converter during operation of the hoist between 0 and approxi-mately 50~ speed while inhibiting operation of the second converter, and for controlling said second converter during operation of the hoist above i~3048Z
Case 2609 approximately 50~ speed while maintaining operation of the first converter at its normal full voltage, and said control means including means for determining the degree of inversion required during normal deceleration.
The invention will be described in more detail with reference to the accompanying drawings, in which Figure 1 is a schematic diagram showing a power conversion system connected to mine hoist motors and showing a control system in block form, in accordance with one form of the invention, Figure 2 is a diagram of output voltage and motor speed plotted against kvar, useful in describing the invention, and Figure 3 is an alternate arrangement of part of the Figure 1 circuitry, in accordance with another variation or form of the invention.
Referring to Figure 1, a source of a.c. power is shown at 10 as a source of three phase power and is connected to the primary windings 11 and 12 of trans~ormers 14 and 15. The transformers 14 and 15 could, of course, be replaced by a single transformer with two secondary windings. As shown, the secondary winding 16 of transformer 14 is wye connected and the secondary winding 17 of transformer 15 is delta connected. Each phase of the wye connected secondary 16 of transformer 14 is connected to an output by controlled rectifiers 18A - 18F to form a six pulse converter. No neutral connection is required. The output is represented by conductors 20 and 21. Each one of the controlled rectifiers 18A - 18F has a gate electrode and each gate electrode is connected to control 22 which provides gating or triggering pulses as is known in the art. For simplicity only one of the gate electrodes is shown connected to control 22 and that is the gate electrode of controlled rectifier 18A connected by conductor 23 to control 22. Large 11;3048Z
7 Case 2609 arrow 24 represents the conduetors connected to the gate electrodes of controlled rectifiers 18B - 18F.
The six pulse converter which comprises transformer 14, controlled rectifiers 18A - 18F, and with a d.c. output on conductors 20 and 21, is designated generally as A. Six pulse converters such as the converter A are known in the art, and one is described generally for example in connection with Figure 1 of Canadian Patent Application Serial No.
301 105 - Young, filed April 13, 1978, or a more basic description may be found in "Direct Current Transmission", Volume I, E.W. Kimbark, published by Wiley - Interscience 1971, chapter 2.
The controlled rectifiers employed in this invention may be of any suitable type but are preferably of the class known as thyristors, the most common of which is the silicon controlled rectifier or SCR.
In a generally similar manner the secondary winding 17 of transformer 15 is connected to controlled rectifiers 18G - 18L arranged as a six pulse converter having its d.c. output on conductors 25 and 26. Each of the controlled rectifiers 18G - 18L has a gate electrode connected to control 22 which provides an appropriate gating or triggering pulse. For simplieity, as before, only the controlled rectifier 18J is shown with its gate electrode conneeted to control 22 via conductor 27. Large arrow 28 represents the conductors connected to the gate electrodes of the other controlled rectifiers.
The six pulse converter which comprises transformer 15, controlled rectifiers 18G - 18L, and having a d.c. output on conductors 25 and 26 is designated generally as converter B and is known in the art.
A free-wheeling diode 30 is connected between conductors 25 and 26. The diode 30, of course, may represent several diodes in practice. As was previously 8 Case 2609 mentioned, the use of free-wheeling diodes is known.
The two six pulse converters A and B are connected in series with two d.c. motors 31 and 32.
That is, conductor 21 is connected to one input of motor 31, conductor 20 is connected to one input of motor 32, conductor 26 is connected to the other input of motor 32, and conductor 25 is connected through a circuit breaker 33 and an air core ripple reactor 34 to the other input of motor 31. The ripple reactor is for reducing excessive ripple and, depending on the particular system, may not be required.
It will, of course, be apparent that a single motor could be used for the mine hoist drive rather than two motors as shown.
There are four operating feedback signals to control 22 and a command signal input. Motors 31 and 32 are coupled by a shaft 35 and a speed or RPM sensor 36 is connected to shaft 35. Sensor 36 provides a signal via conductor 37 to control 22 and this signal represents speed feedback. A current sensor 38 is coupled to an armature current carrying conductor to sense current and to provide on conductor 40 a feedback signal representing current. Two voltage sensors l9A
and l9B are connected across the outputs of converters A and B respectively. The sensors provide signals, representing respective voltages at the outputs of converters A and B, on conductors 29A and 29B
respectively. Control 22 also receives a command signal at input 41 which requires a certain hoist operation. Control 22 also controls the fields to motors 31 and 32 as indicated at 39, 39A and 39B for example by reversing them as required during slowdown.
A signal is available which represents field strength.
Very briefly, the operation of the drive is controlled from input 41. The command signal at input 41 requires a certain hoist operation. Starting from rest, control 22 provides gating pulses to the 1~L304f~Z
Case 2609 six pulse converter A which will accordingly provide the required output to power electric motors 31 and 32.
As more power is required the gating is adjusted until converter A approaches its rated output. As the two converters are equal in rating and capacity, one converter alone provides half the output to power the motors and this will result in the motors running at half speed. As was previously mentioned, while converter A is providing power to operate the hoist between 0 and 50% speed, the operation of converter B is inhibited. It should be noted that while 5th and 7th harmonics may be present causing line harmonic currents, these occur at less than half the rated output for the drive. Also the kvar demand is less than half that for a conventional drive of the same rating, and the motor ripple voltage is similarly reduced.
As the output of converter A approaches its rated output, the signal representing output voltage of converter A is received by control 22 via conductor 29A. Control 22 uses this signal to phase on converter B, that is, control 22 compares the voltage signal with a reference selected to provide the desired overlap.
When the voltage signal equals the reference, control 22 begins to phase on the six pulse converter B. As converter A reaches its rated output is continues to provide that output and control passes to converter B.
Now the free-wheeling diode 30 comes into operation to reduce kvar demand and ripple. The output of converter B
increases until full speed is reached. In this manner at 100% rated speed, converter A is fully on, and speed control is by adjusting converter B.
It is common practice to designate the rated output of a converter as the output which will provide continuous running power to the load it is intended to drive. As explained hereinafter with reference to Figure 2, the converter may have a capacity in excess of this, for example to provide a higher output voltage for "- .,~
11304~3Z
Case 2609 unusual temporary conditions and as a safety factor, however its rated output is designated as that which will provide rated running of its load. In this case, converter A will drive the hoist motors between 0 and approximately 50% speed, while converter A plus converter B at rated output will drive the hoist motors to 100% spe~ed.
Slowdown from a lifting operation is made by phasing back converter B and then phasing back converter A in a manner substantially the reverse of accelerating.
As was previously mentioned, with a loaded skip the force of gravity usually takes care of deceleration without any need for the converters to operate as inverters. When slowing down or decelerating a skip that is empty or partially loaded, there may be a requirement for fourth quadrant operation but it is usually a relatively small requirement and can be handled by converter A alone with the motor(s) operating at less than half field down to half speed. Because of the diode 30, the converter B
cannot operate in the fourth quadrant. Control 22 also provides protection for converter A during inverting operation. Control 22 receives a signal on conductor 29A
representing voltage at the output of converter A. When this voltage signal indicates, during inversion, that the voltage across the inverter A is approaching the allowable maximum voltage, it reduces the motor field which in turn lowers the voltage to keep it below the allowable inversion voltage level.
In another form of the invention the problem of inversion is handled by first determining, during acceleration and running of the hoist, if inversion is likely to be required during slowdown. Sensors 36 and 38 monitor RPM and current and control 22 receives signals representing these values. Control 22 also provides a signal representing motor field strength. From these signals torque can be determined and a signal derived that will representative 113~4~Z
Case 2609 10a of the load in the skip. As the slowdown or deceleration in a mine hoist is a controlled process, it is possible to determine in advance the amount of regenerative torque that will be needed. Thus, while the hoist is accelerating, the load is determined and the control compares this with the predetermined value for critical regeneration load, i.e. the load that will require inversion when decelerating. If inversion will not be required, nothing further need be done. If heavy inversion will be required during deceleration, the control 22 can be preset to lock out converter B and the mine hoist will operate at half speed. In other words, the hoist is limited to approximately 50%
speed or less when heavy inversion would be required, for example when full rated torque would be required during deceleration. In fact, for deceleration where more than 50~ of available torque is required, the hoist speed is limited to less than about 50~.
The slowdown from half speed, can be handled by operating converter A in the fourth quadrant.
Alternately, the hoist is permitted to operate to 100% speed when not more than 50~ torque would be required during deceleration. On the other hand, if heavy inversion is required from top speed, the free-wheeling diode 30 can be switched out of the circuit as shown in Figure 3.
Referring now to Figure 3, there is shown a 113~)~8;~
Case 2609 modified converter B' which is similar to converter ~
of Figure 1 except it has a switch or contactor 42 that is actuated by control 22. When control 22 determines from the mine hoist load that heavy inversion may be required when decelerating from full speed, when the deceleration or slowdown is started control 22 opens switch 42 removing diode 30 from the circuit so that converter B' can operate in the fourth quadrant. This makes converter A and B' available for fourth quadrant operation. The wear on switch 42 will not be excessive as it will not be required to operate each time the hoist slows down, but only if the load is such that heavy inversion is required.
It will be apparent that converter A could be provided with a free-wheeling diode across its output to improve the power factor, i.e. to reduce kvar demand, and reduce ripple, provided that a switch similar to switch 42 is incorporated. This would enable converter A to operate in the fourth quadrant when required.
Referring now to Figure 2, there is shown a plot of speed (in percent full speed) and output voltage (in percent of rated output voltage) against kvar demand (as a percent). In the plot or graph of Figure 3, full speed has been shown at 80~ output voltage. It is customary to provide some voltage reserve at full speed, and while 80% voltage is an arbitrary selection for full speed operation it is fairly typical and suitable for illustrating the invention. The curves or paths are approximate and intended for comparison purposes. If the mine hoist drive were operating as a standard unidirectional or back-to-back converter, that is with no diode 30 and both converters A and Bphased forward together as the hoist is accelerated, then the drive will accelerate along the outer part of the circle, i.e. by the path 113~4~1~
Case 2609 represented by 0 - 50 - 51 - 52. If converter A is phased on first and permitted to approach its full capacity before converter B is phased on, with diode 30 conducting, then it will first follow the path 0 - 53 - 54 which represents converter A, and then add 54- 55 - 56 - 57 which represents converter B. It will be seen that there is a considerable reduction in kvar demand as shown by cross hatching and this is obtained without special transformers and with conventional simple SCR gating. If a second free-wheeling diode is used across the output of converter A, the path during acceleration would be 0 - 60 - 61 -62 - 55 - 56 - 57.
Also shown in Figure 2 is the path which represents operation in accordance with the arrangement of the aforementioned Canadian patent application Serial No. 291 811. This path is shown by broken line 0 - 63 - 64 - 65 - 66 - 67 - 68. This path represents the greatest reduction in kvar demand but requires transformers with neutral connections, controlled rectifiers in the neutral circuits, and more complex gating arrangements. The different forms of the invention described herein are suitable for a mine hoist drive which has certain requirements. The kvar demand is reduced to a level suitable for mine operation with simple means, the control and gating is simple, and the possibility of operation in the fourth quadrant is first determined and either avoided by changing hoist operation or otherwise provided for with simple controls.
Claims (11)
1. A drive for a mine hoist having a load-carrying skip, comprising at least one d.c. motor for driving said hoist to raise and lower said skip, a first and a second thyristor converter connected in series to provide power for said motor, a diode connected across the output of said second converter, control means responsive to a control command signal for controlling said first converter during operation of the hoist between 0 and approximately 50% speed while inhibiting operation of the second converter, and for controlling said second converter during operation of the hoist above approximately 50%
speed while maintaining operation of the first converter at its normal full voltage, and said control means including means for determining the degree of inversion required during normal deceleration.
speed while maintaining operation of the first converter at its normal full voltage, and said control means including means for determining the degree of inversion required during normal deceleration.
2. A drive as claimed in claim 1 in which said means for determining the degree of inversion comprises a speed sensor connected to said motor for providing a first signal representing hoist speed, a current sensor for detecting armature current and for providing a second signal representing current, means responsive to said first and second signals and to a signal representing motor field strength to provide a third signal representing the load carried by said skip, and comparing means comparing said third signal with a predetermined value representing the skip load at which inversion is required when decelerating, and providing a fourth signal representing the result of the comparison and indicative of the torque required Case 2609 for deceleration.
3. A drive as claimed in claim 2 in which, prior to said first converter reaching its full voltage output, said control means is responsive to said fourth signal to inhibit operation of said second converter and thereby limit hoist speed to approximately 50% or less when full rated torque of the system would be required during deceleration.
4. A drive as claimed in claim 2 in which, prior to said first converter reaching its full voltage output, said control means is responsive to said fourth signal to permit operation of said second converter and hoist operation to 100% speed when not more than 50% torque would be required during deceleration.
5. A drive as claimed in claim 3 or 4 and further comprising voltage sensors connected to the outputs of said first and second converters and responsive to the counter electromotive force generated by said motor to provide a fifth signal representing the total counter electromotive force, and said control means including means responsive to said fifth signal for limiting the field strength of said motor to limit the counter electromotive force and maintain it below the allowable safe inversion level for said first converter.
6. A drive as claimed in claim 2 and further comprising a first switch having an open and a closed position in series with said diode connected across the output of said second converter, said first switch being responsive to a signal from said control means when said fourth signal represents a condition where heavy inversion would be required if decelerating from full speed with full load, to operate said first switch to said open Case 2609 position whereby said second converter is able to operate in the fourth quadrant as well as in the first quadrant.
7. A drive as claimed in claim 6 and further comprising a diode and a second switch connected in series across the output of said first converter, said second switch having an open and a closed position and being responsive to said signal from said control means when said fourth signal represents a condition where inversion would be required if decelerating from full speed at full load with heavy inversion current, to operate said second switch to said open position whereby said first six pulse converter is able to operate in the fourth quadrant as well as in the first quadrant.
8. A drive for a friction mine hoist having a load carrying skip, comprising at least one d.c. motor for driving said hoist to raise and lower the skip, a first and a second six pulse thyristor converter having their outputs connected in series to provide power for said motor, a diode connected across the output of said second converter, a control means, first and second voltage sensors connected across the outputs of said first and second converters respectively, for providing to said control means first and second signals representing the voltages across said first and second converters respectively, said control means having an input for a command signal representing a required hoist operation, and responsive to said command signal for controlling said first converter during operation of said hoist between 0 and approximately 50% speed while inhibiting operation of said second converter, and for controlling said second converter during operation of said hoist Case 2609 above approximately 50% speed, said first and second signals indicating the point at which said second converter is phased on and off, and means for determining during acceleration of said hoist the degree of inversion required for deceleration with the particular load carried by said skip.
9. A drive as claimed in claim 8 in which said control means includes means for controlling motor field strength and in which said means for determining the degree of inversion required comprises a speed sensor for determining hoist speed, a current sensor for determining armature current, circuit means receiving signals from said speed sensor and said current sensor representing speed and current and receiving from said control means a signal representing field strength and deriving therefrom a value for hoist load, and comparing means receiving a signal from said circuit means representing said value for load and having a value for critical regeneration load, for comparing these to derive an indication of torque required for deceleration.
10. A drive as claimed in claim 9 in which said control means is responsive to said indication of torque required for deceleration exceeding 50% of the available torque to limit hoist speed to less than about 50%.
11. A drive as claimed in claim 9 in which said control means is responsive to said indication of Case 2609
11. A drive as claimed in claim 9 in which said control means is responsive to said indication of Case 2609
Claim 11 continued:
torque required for deceleration being less than 50%
of the available regenerative torque to permit hoist operation to 100% speed.
torque required for deceleration being less than 50%
of the available regenerative torque to permit hoist operation to 100% speed.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA325,421A CA1130482A (en) | 1979-04-12 | 1979-04-12 | Mine hoist drive |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA325,421A CA1130482A (en) | 1979-04-12 | 1979-04-12 | Mine hoist drive |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1130482A true CA1130482A (en) | 1982-08-24 |
Family
ID=4113967
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA325,421A Expired CA1130482A (en) | 1979-04-12 | 1979-04-12 | Mine hoist drive |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1130482A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006064279A1 (en) * | 2004-12-16 | 2006-06-22 | Converteam Ltd. | Matrix converters |
-
1979
- 1979-04-12 CA CA325,421A patent/CA1130482A/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2006064279A1 (en) * | 2004-12-16 | 2006-06-22 | Converteam Ltd. | Matrix converters |
| AU2005315333B2 (en) * | 2004-12-16 | 2010-06-24 | Converteam Uk Ltd | Matrix converters |
| US7944723B2 (en) | 2004-12-16 | 2011-05-17 | Converteam Uk Ltd | Matrix converters |
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