Power system

A power system includes a power source, a first electric machine drivingly connected to the power source, a second electric machine drivingly connected to the power source, and power-system controls. The power-system controls may include a bidirectional power regulator operable to cause the first electric machine to operate as an electric motor and also operable to cause and regulate generation of electricity by the first electric machine. Additionally, the power-system controls may include a unidirectional power regulator operable to cause and regulate generation of electricity by the second electric machine.

TECHNICAL FIELD

The present disclosure relates to power systems and, more particularly, to power systems having one or more electric machines.

BACKGROUND

Many power systems include an electric machine drivingly connected to a power source, such as an internal combustion engine. Such power systems often have controls that are operable to cause the electric machine to generate electricity when the power source is driving the electric machine. Using an electric machine to convert power produced by a power source into electricity enables using power from the power source to operate other electric machines. In some circumstances, it may be desirable to operate the electric machine of such a power system as an electric motor rather than an electric generator. Unfortunately, the controls of many such power systems are not capable of operating the electric machine as an electric motor.

U.S. Pat. No. 6,622,804 to Schmitz et al. (“the '804 patent”) shows a power system having an electric machine drivingly connected to an engine and controls operable to cause the electric machine to operate as an electric generator and also operable to cause the electric machine to operate as an electric motor. The power system disclosed by the '804 patent is a series type hybrid electric power system for a vehicle. The power system's controls include an electronic control unit and a power converter. The power converter is connected between the electric machine and a battery array. The electronic control unit and the power converter of the '804 patent also start the engine by operating the electric machine as an electric motor driving the engine. Subsequently, the electronic control unit and the power converter cause the electric machine to generate electricity using power from the engine.

Although the power system of the '804 patent includes controls operable to cause the electric machine to operate as an electric generator and also operable to cause the electric machine to operate as an electric motor, certain disadvantages persist. For example, employing a single power converter to regulate electric current flowing into and out of the electric machine may entail compromises. Various factors may make it desirable to transmit electricity at significantly higher rates when the electric machine is operating as an electric generator than when the electric machine is operating as an electric motor. Additionally, the power converter's power capacity for regulating the flow of electricity when the electric machine is operating as an electric motor may be the same as the power converter's power capacity for regulating the flow of electricity when the electric machine is operating as an electric generator. Accordingly, the power converter may have more power capacity than necessary for transmitting power to the electric machine when it is operating as an electric motor and/or less power capacity than desired for transmitting power from the electric machine when it is operating as an electric generator.

As a result, the overall component cost of the power system of the '804 patent may be undesirably high and/or the power system may have compromised capacity for generation of electricity. Power converters that are operable to regulate both generation of electricity by an electric machine and consumption of electricity by an electric machine operating as an electric motor are generally more expensive per unit of capacity than power converters that are only operable to regulate generation of electricity. Accordingly, configuring the power converter of the '804 patent with power capacity that is higher than necessary for operation of the electric machine as an electric motor in order to provide the desired capacity for generation of electricity may make the power converter undesirably expensive. Conversely, configuring the power converter with power capacity substantially equal to the capacity necessary for operating the electric machine as an electric motor may undesirably limit the capacity to regulate generation of electricity by the power system.

The power system of the present disclosure solves one or more of the problems set forth above.

SUMMARY OF THE INVENTION

One disclosed embodiment relates to a power system having a power source, a first electric machine drivingly connected to the power source, a second electric machine drivingly connected to the power source, and power-system controls. The power-system controls may include a bidirectional power regulator operable to cause the first electric machine to operate as an electric motor and also operable to cause and regulate generation of electricity by the first electric machine. Additionally, the power-system controls may include a unidirectional power regulator operable to cause and regulate generation of electricity by the second electric machine.

Another embodiment relates to a method of operating a power system having a power source and one or more electric machines drivingly connected to the power source. The method may include selectively operating a bidirectional power regulator to cause one or more of the electric machines to operate as an electric motor. The method may also include selectively operating the bidirectional power regulator to cause and regulate generation of electricity by one or more of the electric machines. Additionally, the method may include selectively operating a unidirectional power regulator to cause and regulate generation of electricity by one or more of the electric machines.

A further embodiment relates to a power system having a power source, an electric machine drivingly connected to the power source, and power-system controls. The power-system controls may include a bidirectional power regulator operable to cause the electric machine to operate as an electric motor and also operable to cause and regulate generation of electricity by the electric machine. Additionally, the power-system controls may include a unidirectional power regulator operable to cause and regulate generation of electricity by the electric machine.

DETAILED DESCRIPTION

FIG. 1illustrates one embodiment of a machine10having a power system12according to the present disclosure. Machine10may be a mobile machine having one or more propulsion devices14in addition to power system12.

Power system12may include a power source16, an electric machine18, an electric machine19, an electric machine20, an electrical power-transfer network25, one or more energy sources and/or sinks, and power-system controls22. Power source16may be any type of device configured to produce power, including, but not limited to, a diesel engine, a gasoline engine, a gaseous fuel-driven engine, and a gas turbine engine.

Each electric machine18,19,20may be any type of machine configured to operate as an electric motor and/or an electric generator. Electric machines18,19,20may each include a rotor24,26,28disposed adjacent a stator winding30,32,34. Rotors24,26may be drivingly connected to power source16. Each stator winding30,32,34may be either a single-phase stator winding or a multiple-phase stator winding, such as a three-phase stator winding. In some embodiments, electric machine18may be a wound-rotor synchronous type electric machine, an induction-type electric machine, a switched-reluctance type electric machine, a permanent-magnet type electric machine, or a direct current type electric machine. Additionally, in some embodiments, electric machine19may be a wound-rotor synchronous type electric machine, a permanent-magnet type electric machine, or a direct current type electric machine.

Electrical power-transfer network25may be any type of system configured to transfer electricity between electrical components of power system12. Electrical power-transfer network25may include various types of electricity-conducting components, including, but not limited to, wires and switching devices.

The one or more energy sources and/or sinks of power system12may include an electrical storage device27and a braking resistor and chopper29. Electrical storage device27may be electrically connected to electrical power-transfer network25by a power regulator57. Electrical storage device27may be any type of device configured to receive electric current from electrical power-transfer network25and store at least some of the energy of the electric current for later use in supplying electric current to one or more devices of power system12. For example, electrical storage device27may be a battery or a capacitor. Braking resistor and chopper29may be electrically connected to electrical power-transfer network25. Braking resistor and chopper29may include one or more components with electrical resistance (not shown) and one or more components (not shown) operable to regulate the flow of electricity between electrical power-transfer network25and the one or more components with electrical resistance. Thus, braking resistor and chopper29may be operable to dissipate electricity from electrical power-transfer network25at a controllable rate.

Power-system controls22may include power regulators52,54,56,57, controllers58,59,60,61,62,63and an operator interface66. Each power regulator52,54,56may be connected between a stator winding30,32,34of an electric machine18,19,20and electrical power-transfer network25. Each power regulator52,54,56may be operable to regulate one or more aspects of operation of the electric machine18,19,20and power transfer between that electric machine18,19,20and electrical power-transfer network25. Each power regulator52,54,56may be operable to regulate the rate of power transfer between the stator winding30,32,34it is connected to and electrical power-transfer network25. Additionally, in some embodiments, one or more of power regulators52,54,56may be operable to regulate one or more timing aspects of electric current flowing to/from a stator winding30,32,34or electric current in electrical power-transfer network25. For example, a power regulator52,54,56may be operable to control the phase and/or frequency of alternating current flowing to/from a stator winding30,32,34. Furthermore, in some embodiments, a power regulator52,54,56may be operable to convert power between two different forms, such as alternating current and direct current, as the power flows between a stator winding30,32,34and electrical power-transfer network25.

Power regulator52may be a bidirectional power regulator operable to regulate power transmission in both directions between stator winding30and electrical power-transfer network25. In such embodiments, power regulator52may be operable to cause and regulate generation of electricity in stator winding30and also operable to regulate current supply to stator winding30in such a manner to cause electric machine18to operate as an electric motor. In embodiments where power regulator52is a bidirectional power regulator, power regulator52may include SCRs (sillicon controller rectifiers), GTOs (gate turn-offs), and/or IGBTs (insulated gate bipolar transistors). In some embodiments, power regulator56may also be a bidirectional power regulator operable to regulate power transfer in both directions between stator winding34and electrical power-transfer network25.

In contrast to power regulators52,56, power regulator54may be a unidirectional power regulator operable to regulate power transfer in only one direction between stator winding30and electrical power-transfer network25. For example, power regulator54may be operable to cause and regulate generation of electricity in stator winding32by electric machine19, but not operable to regulate power transmission to electric machine19in a manner to cause it to operate as an electric motor. In some embodiments where power regulator54is a unidirectional power regulator, power regulator54may include diode rectifiers and/or simple SCRs.

Power regulator57may be operable to regulate one or more aspects of power transfer between electrical power-transfer network25and electrical storage device27. For example, power regulator57may be operable to regulate the rate and direction of electricity transfer between electrical power-transfer network25and electrical storage device27. Additionally, power regulator57may be operable to regulate any other aspect of power transfer between electrical power-transfer network25and electrical storage device27.

Operator interface66may include any types of components configured to transmit operator inputs to other components of machine10. For example, operator interface66may include an accelerator pedal68and a brake pedal70for receiving acceleration and braking requests from an operator, and operator interface66may include various other components for transmitting these and other requests to other components of power system12.

Each controller58-63may be any type of information processor configured to control one or more aspects of the operation of power system12. Each controller58-63may include one or more processors (not shown) and memory devices (not shown). Controllers58-63may be operatively connected to one another so that they may share information. Controller58may also be operatively connected to power source16and configured to control one or more aspects of the operation of power source16, such as operation of a fuel-metering system (not shown). Controller58may be a dedicated controller for controlling power source16, or controller58may be operable to monitor and/or control one more other components of machine10. Each controller59,60,61,62may be operatively connected to and configured to control power regulators52,54,56,57. Controllers59-62may be dedicated controllers for controlling the operation of power regulators52,54,56,57, respectively, or one or more of controllers59-62may be configured to monitor and/or control one or more other components of machine10. Controller63may be operatively connected to braking resistor and chopper29and configured to control one or more aspects of the operation thereof. For example, controller63may be operable to control the one or more components of braking resistor and chopper29that regulate transfer of electricity between electrical power-transfer network25and braking resistor and chopper29.

Each of controllers58-63may be operatively connected to various components configured to provide them with information for use in controlling power source16, power regulator52, power regulator54, power regulator56, power regulator57, and braking resistor and chopper29, respectively. For example, power-system controls22may include information channels80-89configured to provide controllers59-63with information relating to electrical activity in electrical power-transfer network25. Additionally, power-system controls22may include information channels90-92configured to provide controllers59-61with information relating to electrical activity in stator windings30,32,34and/or the electrical connections between stator windings30,32,34and power regulators52,54,56. Power-system controls22may also include information channels93,94configured to provide controller62with information relating to the electrical activity in electrical storage device27and the electrical connections between electrical storage device27and power regulator57. Controller63may receive information relating to electrical activity in braking resistor and chopper29through the operative connection between controller63and braking resistor and chopper29. Additionally, controllers59-63may all be operatively connected to operator interface66so as to receive information relating to operator requests. Furthermore, each of controllers58-63may be operatively connected to various other sensors, controllers, and/or other sources of information not shown inFIG. 1.

Each propulsion device14may be any type of component configured to receive power from power system12and propel machine10by transferring that power to the environment surrounding machine10. For example, as is shown inFIG. 1, propulsion devices14may be track units. Alternatively, propulsion devices14may be wheels, other types of devices configured to transmit power to the ground, propellers, or other types of devices configured to move fluid to propel machine10. AsFIG. 1shows, propulsion devices14may be drivingly connected to rotor28of electric machine20.

FIG. 2shows machine10with a second embodiment of power system12. The embodiment shown inFIG. 2is generally the same as the embodiment shown inFIG. 1, except that stator winding32is part of electric machine18, and power system12does not include electric machine19. In this embodiment, stator windings30,32may be in separate stators, asFIG. 2shows, or stator windings30,32may be incorporated into a common stator. As with the embodiment illustrated inFIG. 1, power regulator52may be a bidirectional power regulator operable to cause and regulate generation of electricity in stator winding30and also operable to regulate power transfer to stator winding30in a manner to cause electric machine18to operate as an electric motor. Additionally, power regulator54may be a unidirectional power regulator operable to cause and regulate generation of electricity in stator winding32, but not operable to regulate power transfer to stator winding32in a manner to cause or contribute to electric machine18operating as an electric motor.

FIG. 3shows machine10with another embodiment of power system12. This embodiment may be the same as the embodiment shown inFIG. 2, except that power regulator52and power regulator54are both connected to stator winding30, and stator winding32is omitted. As in the embodiments shown inFIGS. 1 and 2, power regulator52may be a bidirectional power regulator and power regulator54may be a unidirectional power regulator. Additionally, in the embodiment shown inFIG. 3, power-system controls22may include provisions (not shown) for selectively disconnecting power regulator54from stator winding30. Such provisions may include, for example, SCRs or mechanical switching devices. Such provisions may be used to disconnect power regulator54from stator winding30when power regulator52is regulating power transfer to stator winding30in a manner to cause electric machine18to operate as an electric motor, which may prevent the electricity delivered to stator winding30from circulating between power regulator52and power regulator54.

Additionally, the embodiment shown inFIG. 3may have provisions for ensuring that power is properly distributed between power regulator52and power regulator54when power regulators52and54are both regulating generation of electricity in stator winding30. For example, the connections between stator winding30and power regulators52,54may be configured with impedances such that power is distributed between power regulators52,54in proportion to their respective power capacities. Alternatively, stator winding30may be wound in such a manner to ensure such a distribution of power transfer to power regulators52,54. In addition, controlling features in controllers59,60may ensure that power is properly proportioned between power regulators52,54when regulating generation of electricity by stator winding30.

Power-system controls22are not limited to the configurations shown inFIGS. 1-3. For example, in place of bidirectional power regulator52, power-system controls22may include multiple bidirectional power regulators. Similarly, in place of unidirectional power regulator54, power-system controls22may include multiple unidirectional power regulators. Additionally, power-system controls22may include one or more other controllers in addition to controllers58-63, and/or power-system controls22may omit one or more of controllers58-63. In some embodiments, one controller may be operatively connected to and configured to control the operation of two or more of power source16, power regulator52, power regulator54, power regulator56, power regulator57, and braking resistor and chopper29. Furthermore, power-system controls22may include various other types of logic systems, such as hard-wired electric logic circuits. Moreover, in some embodiments, power regulator56may be a unidirectional power regulator, rather than a bidirectional power regulator.

Additionally, the general configurations of power system12and machine10are not limited to those shown inFIGS. 1-3. For example, power source16, electric machine18, electric machine19, electric machine20, and propulsion devices14may be connected in different manners. Power system12may include various additional power-transfer components, such as additional gears, shafts, pulleys, belts, chains, friction couplers, and/or viscous couplers connected between power source16and one or both of electric machines18,19. Some of these power-transfer components may be operable to selectively disconnect power source16from one or both of electric machines18,19. Similarly, power system12may include various additional power-transfer components connected between electric machine20and propulsion devices14. Additionally, power system12may include additional electric machines drivingly connected to propulsion devices14. In some embodiments, power system12may include one or more dedicated electric machines for each propulsion device14. Furthermore, machine10may include fewer or more propulsion devices14thanFIGS. 1-3show. Additionally, in some embodiments, machine10may omit propulsion devices14.

Additionally, power system12may have different combinations of electrical components connected to electrical power-transfer system12than shown inFIGS. 1-3. For example, power system12may omit electrical storage device27and/or braking resistor and chopper29, in which case power system12may also omit the associated components of power-system controls12. Also, in addition to the electrical components shown inFIGS. 1 and 2, power system12and machine10may include various other electrical components connected to electrical power-transfer network25.

INDUSTRIAL APPLICABILITY

Machine10and power system12may have application wherever power is required for performing one or more tasks. Operation of machine10and power system12will be described herein below.

Under some circumstances, power-system controls22may operate power system12to generate electricity with electric machine18and/or electric machine19. Controller58may cause power source16to produce power and drive rotor24and, in the embodiment shown inFIG. 1, rotor26. Simultaneously, controllers59,60and power regulators52,54may cause and regulate generation of electricity in one or both of stator windings30,32while transferring the generated electricity to electrical power-transfer network25. Using information from the various sources of information they are connected to, controllers58,59,60may adjust the power output of power source16and the rate of electricity generation in stator windings30,32as necessary to meet varying power needs and other objectives. When electrical power needs are high, controllers59,60may operate both power regulator52and power regulator54to cause and regulate generation of electricity. In this manner, controllers59,60may effect generation of electricity at rates as high as the aggregate power capacity of power regulators52,54or the power capacity of power source16, whichever is lower.

The generated electricity may be received by various devices for various purposes. For example, under some circumstances, some of the generated electricity may be received by electrical storage device27and stored for later use by other devices connected to electrical power-transfer network25. Additionally, under some circumstances, such as in response to an acceleration request from an operator, controller61may cause power regulator56to supply electricity from electrical power-transfer network25to stator winding34to cause electric machine20to operate as an electric motor and propel machine10.

Once machine10is in motion, if an operator makes a braking request with brake pedal70, power-system controls22may operate power system12to electrically brake machine10. In order to electrically brake machine10, controller61and power regulator56may cause electric machine20to generate electricity using kinetic energy transferred from machine10, through propulsion devices14, to rotor28.

Power-system controls22may coordinate use of electricity generated through such electrical braking of machine10. Various electrical loads (not shown), such as lights, a radio, and/or other electrical devices, may draw some of the electricity from electrical power-transfer network25. If such other electrical loads do not consume all of the electric power generated by electrical braking and electrical storage device27is not at its full charge capacity, controller62may cause power regulator57to transfer power to electrical storage device27. Controller62and power regulator57may limit the rate at which electricity is transferred to electrical storage device27to prevent charging electrical storage device27at an undesirably high rate.

If the above-described activities do not consume all of the electrical power generated by electrical braking, controller59may cause power regulator52to regulate current supply to stator winding30in such a manner to cause electric machine18to operate as an electric motor. Simultaneously, controller58may suppress power production of power source16, such as by suppressing fuel delivery to power source16, so that power source16absorbs power produced by electric machine18operating as an electric motor. Under such circumstances, operating electric machine18as an electric motor to drive power source16may dissipate electricity. Operating electric machine18to dissipate electricity by driving power source16may enable electrical braking at an increased rate or for an increased period without overcharging electrical storage device27. Additionally, using electricity to drive power source16under such circumstances may allow reducing fuel consumption by power source16.

During electrical braking of machine10, if it is necessary to dissipate electricity by driving power source16with electric machine18, controller59and power regulator52may adjust the flow of electricity to electric machine18as necessary to ensure that all electric power generated by electrical braking is consumed. However, controller59and power regulator52may only do so up to the capacity of power source16and electric machine18to dissipate electricity. The capacity of power source16and electric machine18to dissipate electricity may be determined by the capacity of power source16to absorb power from electric machine18and the efficiency of electric machine18.

During electrical braking, if electric machine18is operating at its full capacity to dissipate electricity by driving power source16and there remains a need to dissipate more electric power generated by electrical braking, controller63may cause braking resistor and chopper29to dissipate electricity. Under such circumstances, controller63may adjust the amount of electricity dissipated by braking resistor and chopper29as necessary to ensure that all electric power generated by electrical braking is dissipated, up to the power capacity of braking resistor and chopper29. If braking resistor and chopper29reaches its full power capacity, controller61and power regulator56may limit the amount of power generated by electric machine20to prevent damage to electrical components of power system12.

Coordination of power distribution between the various electrical devices of power system12is not limited to the examples provided herein above. For example, use of electricity generated by electrical braking may be prioritized in a different manner than discussed above. Additionally, use of electricity generated by electrical braking may be controlled according to various other types of control algorithms other than prioritization.

In addition to operating electric machine18as an electric motor to dissipate electricity during electrical braking, power-system controls22may also operate electric machine18as an electric motor under various other circumstances. For example, power-system controls22may operate electric machine18as an electric motor to drive power source16when starting power source16operating under its own power. Additionally, if other power loads are drivingly connected to power source16and/or electric machine18, power-system controls22may operate electric machine18as an electric motor to assist power source16in driving those other loads.

When causing operation of electric machine18as an electric motor, controller59may use inputs from its various sources of information to adjust operation of power regulator52as necessary to meet various objectives. For example, in some embodiments, when driving power source16with electric machine18during electrical braking, controller59may adjust the operation of power regulator52to maintain voltage in electrical power-transfer network25near a target level. Additionally, when causing electric machine18to drive power source16to enable power source16commencing operation under is own power, controller59may adjust the operation of power regulator18to cause electric machine18to drive power source16at a target speed.

The disclosed embodiments may provide a number of performance and cost benefits. Many factors may make it desirable for power system12to have a higher capacity for regulating generated electricity than would be necessary for regulating electricity for operating electric machine18as an electric motor. For example, power source16may be able to produce and transmit more power to electric machines18,19when they operate as electric generators than power source16can absorb from electric motor18when it operates as an electric motor. Additionally, in many applications, it may be desirable to construct the power regulators that regulate electricity generated by power source16with a power capacity substantially equal to that of the capacity to generate electricity with power source16. However, this power capacity may be greater than the power capacity necessary for regulating electricity used to drive power source16with electric machine18because of the inability of power source16to absorb as much power as it can produce.

The disclosed embodiments may allow separately tailoring the capacity of power system12to regulate electricity generated with power source16and the capacity of power system12to regulate electricity used to operate electric machine18as an electric motor. Bidirectional power regulator52may be constructed with capacity approximately equal to the desired capacity to regulate electricity used to operate electric machine18as an electric motor. Unidirectional power regulator54may be constructed such that the aggregate power capacity of bidirectional power regulator52and unidirectional power regulator54is equal to or greater than the desired capacity to regulate generation of electricity with power source16. For example, unidirectional power regulator54may be constructed such that this aggregate power capacity is equal to or greater than the capacity to generate electricity with power from power source16.

This approach may be a cost-effective way to provide power system12with the desired power-regulation capacities. Unidirectional power regulator54may be less expensive per unit of capacity than bidirectional power regulator52. Accordingly, limiting the capacity of bidirectional power regulator54to the capacity desired for operating electric machine18as an electric motor and employing unidirectional power regulator52to provide the balance of capacity desired for generating electricity may keep the cost of power system12low.

It will be apparent to those skilled in the art that various modifications and variations can be made in the power system and methods without departing from the scope of the disclosure. Other embodiments of the disclosed power system and methods will be apparent to those skilled in the art from consideration of the specification and practice of the power system and methods disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.