Patent Application
20130134912
The present disclosure relates generally to electric motors, and more particularly, to systems and methods of controlling the transition of switched reluctance motors between different modes of operation.
With the growing interest in energy conservation, increasingly more industrial work machines are supplied with electric drive assemblies for driving the work machine and operating its various tools or functions. Ongoing developments in electric drives have made it possible for electrically driven work machines to effectively match or surpass the performance of purely mechanically driven work machines while requiring significantly less fuel and overall energy. As electric drive assemblies become increasingly more commonplace with respect to industrial work machines, and the like, the demands for more efficient generators and techniques for controlling same have also increased.
A generator or an electric motor of an electric drive machine is typically used to convert mechanical power received from a primary power source, such as a combustion engine, into electrical power for performing one or more operations of the work machine. Additionally, an electric motor may be used to convert electrical power stored within a common bus or storage device into mechanical power. Among the various types of electric motors available for use with an electric drive assembly, switched reluctance (SR) motors have received great interest for being robust, cost-effective, and overall, more efficient. While currently existing systems and methods for controlling SR generators provide adequate control, there is still room for improvement.
Typical control schemes for SR motors may involve operating the motor in one of two general operating modes, for example, current regulation and single pulse modes of operation. Current regulation modes are directed toward lower speed tasks requiring more torque output from a driven machine, while single pulse modes are directed toward higher speed tasks requiring more power output. Throughout the use of the machine, the motor is continuously switched between such different modes of operation, and each transition can be very unsmooth. This is mainly because current transitions are executed at transition speeds that are dictated by fixed speed transition limits which remain constant regardless of torque loading conditions. Such unsmooth and unnatural transitions between operating modes in such machines can amount to a substantial loss of machine power and torque utilization over time, and thus, a significant loss in the overall efficiency of the machine.
Accordingly, there is a need to improve the overall efficiency and functionality of an electric drive assembly. Moreover, there is a need to improve machine power and torque utilization across the transition speed region and provide a more natural transition between different modes of operating a switched reluctance motor. Furthermore, there is a need to take into consideration both the load torque and the observed speed of a switched reluctance motor upon making transitions between different operating modes.
In one aspect of the present disclosure, a method of controlling a motor is provided. The method may monitor a plurality of operational characteristics of the motor, determine an optimum transition speed of the motor based on the operational characteristics, and engage a transition of the motor between a current regulation mode of operation and a single pulse mode of operation at the optimum transition speed.
In a refinement, the motor may be a switched reluctance motor configured to generate constant torque while operating in the current regulation mode, and generate constant power while operating in the single pulse mode.
In another refinement, the operational characteristics may include data pertaining to at least an actual speed of the motor and a load torque of the motor.
In another refinement, the optimum transition speed may be computed using a predefined function of at least an actual speed of the motor and a load torque of the motor.
In another refinement, the optimum transition speed may be determined using a predefined transition control map configured to output the optimum transition speed based on an actual speed of the motor and a load torque of the motor.
In a related refinement, the transition control map may be preprogrammed with a lookup table having a plurality of optimum transition speed values corresponding to different actual speed and load torque values.
In yet another refinement, the transition may be engaged when motor current reaches a unique single peak value point.
In a related refinement, the motor current may reach the single peak value point when a voltage applied to the motor substantially equates a sum of a back electromotive force (EMF) voltage and a resistive voltage drop at a current reference level for a particular load torque.
In another aspect of the present disclosure, a method of controlling a transition of a switched reluctance motor between current regulation operation and single pulse operation is provided. The method may monitor an actual speed of the motor, monitor a load torque of the motor, determine an optimum transition speed of the motor based on a predefined transition control map, and engage the transition when motor current reaches a unique single peak value point. The transition control map may be configured to output the optimum transition speed based on the actual speed and the load torque of the motor.
In a refinement, the motor may be configured to generate constant torque while operating in the current regulation mode, and generate constant power while operating in the single pulse mode.
In another refinement, the optimum transition speed may be computed using a predefined function of at least the actual speed and the load torque of the motor.
In another refinement, the optimum transition speed may be determined using a predefined transition control map configured to output the optimum transition speed based on the actual speed and the load torque of the motor.
In a related refinement, the transition control map may be preprogrammed with a lookup table having a plurality of optimum transition speed values corresponding to different actual speed and load torque values.
In yet another refinement, the motor current may reach the single peak value point when a voltage applied to the motor substantially equates a sum of a back EMF voltage and a resistive voltage drop at a current reference level for a particular load torque.
In yet another aspect of the present disclosure, a transition control system for a motor is provided. The transition control system may include a control circuit operatively coupled to at least one or more phases of a stator of the motor, and a controller in communication with each of the motor and the control circuit. The controller may be configured to monitor an actual speed and a load torque of the motor, determine an optimum transition speed of the motor based on the actual speed and the load torque, and enable the control circuit to engage a transition of the motor between a current regulation mode of operation and a single pulse mode of operation at the optimum transition speed.
In a refinement, the motor may be a switched reluctance motor capable of operating in one of at least the current regulation mode and the single pulse mode. The current regulation mode may correspond to constant torque output and the single pulse mode may correspond to constant power output.
In another refinement, the optimum transition speed may be computed using a predefined function of at least an actual speed of the motor and a load torque of the motor.
In another refinement, the optimum transition speed may be determined using a predefined transition control map configured to output the optimum transition speed based on the actual speed and the load torque of the motor.
In a related refinement, the transition control map may be preprogrammed with a lookup table having a plurality of optimum transition speed values corresponding to different actual speed and load torque values.
In yet another refinement, the transition may be engaged when motor current reaches a unique single peak value point. The motor current may reach the single peak value point when a voltage applied to the motor substantially equates a sum of a back EMF voltage and a resistive voltage drop at a current reference level for a particular load torque.
Reference will now be made in detail to specific embodiments or features, examples of which are illustrated in the accompanying drawings. Generally, corresponding reference numbers will be used throughout the drawings to refer to the same or corresponding parts.
During a generating mode of operation, as the rotor 116 is rotated within the stator 118 by the engine 102, electrical current may be induced within the stator 118 and supplied to the control circuit 122. The control circuit 122 may in turn convert the electrical signals into an appropriate direct current (DC) voltage for distribution to the various electrical loads 114 of the machine 100. Additionally, the motor 110 may be enabled to cause rotation of the rotor 116 in response to electrical signals that are provided to the stator 118 from the common bus 120, for instance, during a motoring mode of operation. The common bus 120 may include a positive line 124 and a negative or ground line 126 across which a common DC bus voltage may be communicated to one or more loads 114 of the machine 100 coupled thereto. For instance, the control circuit 122 may provide a DC signal to be transmitted through the common bus 120 and to a rectifier circuit where the DC voltage may be converted into the appropriate alternating current (AC) signals for driving the one or more traction motors, or the like, for causing motion of the machine 100 via the traction device 106. The common bus 120 may also communicate the common DC voltage to other loads 114 of the machine 100, such as a hybrid system, electrically driven pumps, electrically driven fans, and the like.
Still referring to
By communicating with the motor 110 and the control circuit 122, the controller 130 may be configured to monitor and provide appropriate control over the operational state of the motor 110 and the associated electric drive 104. In applications employing an SR motor 110, for example, the controller 130 may be configured to determine the appropriate mode for operating the motor 110 based at least on the observed motor speed. More specifically, the controller 130 may monitor and compare the observed speed with one or more predefined speed thresholds to determine if the motor speed corresponds to a relatively low speed, a nominal or mid-range speed, a relatively high speed, or the like. If the observed speed is nominal or relatively low, the controller 130 may be configured to engage a current regulation mode of operating the motor 110. During the current regulation mode, the controller 130 may transmit gate signals configured to enable one or both of the switches 132 associated with each phase of the motor 110 in a pulsing or chopping manner so as to operate the motor 110 in a constant torque range of output. Alternatively, if the observed speed is relatively high, the controller 130 may be configured to engage a single pulse mode of operating the motor 110. During the single pulse mode, the controller 130 may transmit gate signals configured to continuously enable both of the switches 132 of the control circuit 122 associated with each phase of the motor 110 so as to operate the motor 110 in a constant power range of output.
Accordingly, based at least on the actual speed of the motor 110, the controller 130 of the transition control system 128 in
Referring now to
As shown in step 142-3 of the method 142 of
In step 142-4, the controller 130 may be configured to determine the optimum transition speed, or the speed most appropriate for enabling a smooth and natural transition of the motor 110 between current regulation and single pulse modes of operation. As illustrated in
In general, the foregoing disclosure finds utility in various industrial applications, such as the farming, construction and mining industries in providing smoother and more efficient control of motors typically used in association with work vehicles and/or machines, such as tractors, backhoe loaders, compactors, feller bunchers, forest machines, industrial loaders, skid steer loaders, wheel loaders, and the like. More specifically, the disclosed control systems and methods may be applied to electric drive assemblies and machines having switched reluctance motors or other comparable motors commonly used in the art. The systems and methods disclosed herein provide adaptive transition control of switched reluctance machines based on the actual speed and load torque. More specifically, a transition control map is provided to suggest the most appropriate speed at which to perform the transition between current regulation and single pulse modes of operation. By enabling more natural transitions between constant torque and constant power regions, the utilization of machine power and torque across the transition speed region as well as the overall efficiency of the machine are improved.
From the foregoing, it will be appreciated that while only certain embodiments have been set forth for the purposes of illustration, alternatives and modifications will be apparent from the above description to those skilled in the art. These and other alternatives are considered equivalents and within the spirit and scope of this disclosure and the appended claims.
