GB2217532A

GB2217532A - Motor control system

Info

Publication number: GB2217532A
Application number: GB8809689A
Authority: GB
Inventors: Eric Anthony Lewis
Original assignee: General Electric Co PLC
Current assignee: General Electric Co PLC
Priority date: 1988-04-25
Filing date: 1988-04-25
Publication date: 1989-10-25
Anticipated expiration: 2008-04-25
Also published as: GB8809689D0; ZA892862B; GB2217532B

Abstract

A motor control system for controlling two drum winders (5, 6) for raising and lowering respective loads (1, 2) substantially in synchronism comprises two a.c. or d.c. motors (7, 8) for driving the respective drum winders. First and second converters (9, 10) supply the two motors, respectively, from a d.c. supply link (11, 12) which is common to the converters, each of the converters being capable of passing regenerative current fed to the d.c. supply by the other of those converters. A third converter (13) receives power from an a.c. supply (14) and thereby feeds d.c. power to the d.c. supply link. <IMAGE>

Description

Motor Control System This invention relates to a motor control system for a double drum winder such as is used in a mine shaft for simultaneously raising one cage and lowering another.

It has previously been proposed to provide a motor control system comprising two d.c. motors driving respective drums, the motors being interconnected so that regenerative power provided by the motor which is lowering its cage is used to supply at least part of the power requirement of motor which is raising its cage.

It is an object of the present invention to provide an improved motor control system.

According to the invention there is provided a motor control system for controlling two drum winders for raising and lowering respective loads substantially in synchronism, the system comprising first and second a.c. or d.c. motors for driving the respective drum winders; first and second converters for supplying the first and second motors, respectively, from a d.c. supply link which is common to said first and second converters, each of the first and second converters being capable of passing regenerative current fed to the d.c. supply by the other of those converters; and a third converter to receive power from an a.c. supply and thereby to feed d.c. power to the d.c. supply link.

A battery may be connected in parallel with the d.c. supply link to act as a reservoir.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawing, which is a block schematic diagram of a motor control system in accordance with the invention.

Referring to the drawing, two mine cages 1 and 2 carried by cables 3 and 4 are raised and lowered by winder drums 5 and 6, respectively. Each drum 5, 6 is mechanically coupled to the shaft of a respective 3-phase a.c. motor 7 and 8. Each motor is coupled to a respective inverter 9 or 10, each of which is coupled to a common d.c.

supply link comprising positive and negative lines 11 and 12. The d.c. supply link is connected to a rectifier circuit 13, which takes power from a 3-phase a.c. supply 14.

In operation of the circuit, the inverters 9 and 10 are controlled to provide the required phase sequence for each motor 7 and 8 for upward or downward winding of the respective cage, as the case may be. Sufficient power is taken from the d.c. link 11, 12 by each inverter to provide the requirements of its respective motor.

The motors are subjected to a very wide range of loading conditions. The maximum loading occurs as a loaded cage is accelerated from rest at the beginning of an upward journey and minimum loading occurs as a loaded cage is descending. In the latter case the motor tends to be driven by the weight of the descending load, and the motor therefore produces regenerative current. This is fed back into the d.c. supply link, and the inverters 9, 10 must be designed to pass this current. The regenerative power supplements the power taken from the a.c. supply 14, and the average power consumption from the a.c. supply is therefore reduced. The rectifier circuit 13 can therefore operate at a substantially constant output voltage, which results in high operating efficiency.Furthermore, the power factor of the load which the system constitutes across the a.c. supply can be maintained at a substantially constant high value.

Further advantages of the system are as follows. The system reduces harmonics and voltage disturbances on the a.c. supply. The system will operate with both induction and synchronous motors. All modes of operation required by electrically-coupled winder motors can be achieved by the present system. For example, a single motor can, if necessary, be operated at any time. If necessary, the voltage of the d.c. supply link described above (i.e. without an additional battery which is mentioned later) can be varied to vary the motor speed.

The input rectifier circuit 13 may be of any suitable kind, such as a thyrister bridge circuit. It may operate in, for example, 6 pulse, 12 pulse, 6/12 pulse sequence control, 24 pulse or 12/24 sequence control mode. The inverters 9 and 10 can be of any suitable kind, such as thyrister inverters but, as stated above, they must be able to pass regenerative current.

In an extension of the circuit described above, a battery 15 is connected in parallel with the d.c. supply link 11, 12. This battery will have a terminal voltage such that it will act as a reservoir, smoothing out variations in the motor power demands. The input rectifier circuit 13 can then operate at substantially constant voltage and current levels. This will help to minimise transients on the a.c. supply 14. The battery 15 will also act as a temporary power suply in the event of failure of the a.c. supply 14.

Furthermore, with the battery 15 connected, there may, at any instant be excess power available in the d.c. supply link 11, 12. Provided that the input circuit 13 is designed to incorporate an inverter function, the excess power can then be fed into the a.c. supply, so that peak power limit control is effected.

Although the above embodiment uses a.c. motors, it would alternatively be possible to drive d.c. motors from the d.c. supply link via suitable converters.

Depending upon the circuit conditions, the input converter 13 may be either a single-way operation device, or it may pass power in both directions, even in the absence of the battery 15.

Claims

1. A motor control system for controlling two drum winders for raising and lowering respective loads substantially in synchronism, the system comprising first and second a.c. or d.c. motors for driving the respective drum winders; first and second converters for supplying the first and second motors, respectively, from a d.c.

supply link which is common to said first and second converters, each of the first and second converters being capable of passing regenerative current fed to the d.c. supply by the other of those converters; and a third converter to receive power from an a.c.

supply and thereby to feed d.c. power to the d.c. supply link.

2. A system as claimed in Claim 1, comprising battery means connected in parallel with the d.c. supply link to act as a reservoir.

3. A system as claimed in Claim 2, wherein said third converter is adapted to feed excess power from the d.c. supply link into the a.c.supply.

4. A motor control system substantially as hereinbefore described with reference to the accompanying drawing.