Peak power limiter system for excavator

• US 4,358,719 A
• Filed: 07/18/1980
• Issued: 11/09/1982
• Est. Priority Date: 07/18/1980
• Status: Expired due to Term

• Current Assignee: Bucyrus International Incorporated (Caterpillar Incorporated)
• Original Assignee: Bucyrus-Erie Company (Caterpillar Incorporated)
• Inventors: Mains, Donald M., Currier, Richard G.
• Primary Examiner(s): Weldon, Ulysses
• Application Number:
  US06/170,183
• Time in Patent Office: 844 Days
• Field of Search: 414/692, 254/327, 254/393, 180/8 D, 310/74, 318/140, 318/150, 318/161, 318/34, 318/49, 318/50
• US Class Current: 318/161
• CPC Class Codes: B60L 50/30 using propulsion power stored mechanically, e.g. in fly-wheels
• CPC Class Codes: B60L 9/16 using ac induction motors
• CPC Class Codes: H02J 3/30 using dynamo-electric machines coupled to flywheels
• CPC Class Codes: Y02E 60/16 Mechanical energy storage, e.g. flywheels or pressurised fluids
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/70 Energy storage systems for electromobility, e.g. batteries

Abstract

A motor drive system for a mining shovel includes three a.c. motors which are driven by associated inverter circuits that receive power from a common d.c. bus. The d.c. bus connects to the a.c. power lines through a rectifier circuit and large variations in power occur during various portions of the digging cycle. To limit the peak power demanded during a digging cycle a peak power limiter system comprised of a fourth inverter driven a.c. motor is attached to the d.c. bus. This a.c. motor drives a flywheel which is operated to store energy during periods of low power demand and which is operated to regenerate stored energy to the d.c. bus when power demanded from the a.c. power lines exceeds a preset amount.

Claims

1. In a drive system for a mining machine having a plurality of electric drives which drive the various mining machine motions and which draw electric power from a common bus that is coupled to a power line through a rectifier circuit, the improvement therein comprising a peak power limiter system which includes:

a flywheel mounted on the mining machine;

an electric motor coupled to the flywheel and to the common bus, the electric motor being operable to convert electrical energy received from the common bus to mechanical energy which is stored in the flywheel and being operable to convert mechanical energy which is stored in the flywheel to electrical energy which is delivered to the common bus;

means for sensing the power required by the mining machine from the common bus and generating an electrical signal which is proportional thereto; and

a motor control circuit connected to receive the electrical signal and in response thereto operate the electric motor to convert electrical energy to stored mechanical energy when the required mining machine power drops below a preselected level, and being operable when the required mining machine power exceeds a preselected level to cause the electric motor to deliver stored mechanical energy as electrical energy to the common bus and to thereby reduce the peak power required by the mining machine during each digging cycle.

2. The improvement as recited in claim 1 in which the electric motor is an a.c. induction motor and the motor control circuit is responsive to the electrical signal from the power sensing means to alter the speed of the electric motor.

3. The improvement as recited in claim 2 in which the motor control circuit includes an inverter which connects between the electric motor and the common bus and the inverter alters the speed of the electric motor by varying the frequency of the electrical power applied to the motor.

4. In a drive system for a mining machine having a hoist motor, a crowd motor and a swing motor, the combination comprising:

a rectifier circuit having inputs connected through lines to a source of a.c. power and an output terminal at which d.c. power is produced;

a d.c. bus connected to said rectifier output terminal;

a set of inverters, each having an input connected to said d.c. bus, each having an output connected to one of said motors and each being operable in response to signals from an associated inverter control circuit to deliver power to its attached motor from said d.c. bus and to regenerate power to said d.c. bus from its attached motor; and

a peak power limiter system which includes;

(a) a flywheel mounted to the mining machine,

(b) A flywheel motor coupled to rotate the flywheel when electrical power is supplied to the flywheel motor and to regenerate electrical power when the flywheel rotates the flywheel motor,

(c) a flywheel inverter having an input connected to said d.c. bus and an output connected to the flywheel motor, the flywheel inverter being responsive to signals from an associated flywheel inverter control circuit to deliver electrical power to the flywheel motor from said d.c. bus and to regenerate power to said d.c. bus from the flywheel motor, and

(d) power sensing means for generating a power signal to said flywheel inverter control circuit which is indicative of the total electrical power being delivered to the mining machine by said a.c. power source,

wherein the flywheel inverter control circuit operates the flywheel inverter and flywheel motor to deliver power to the flywheel when the total electrical power supplied to the mining machine drops below a preselected level and to deliver power to the d.c. bus from the flywheel when the total electrical power supplied to the mining machine exceeds a preselected level.