Patent Application
20140265569
The present disclosure generally relates to variable speed gensets, and more particularly, to systems for controlling an electric machine of a genset during transient conditions.
Electric machines, such as induction machines, switched reluctance machines, and other comparable types of electric machines, are commonly used in the industry to convert electrical energy into rotational torque or rotational torque into electrical energy for any one of a variety of different applications including machine tools, traction motors, industrial work machines, stationary drive machines, mobile work vehicles, hybrid electric vehicles, and the like. Electric machines are commonly employed in association with a primary power source, such as an internal combustion engine or any other comparable prime mover, to provide a combined genset which serves to generate electrical and/or mechanical energy.
As shown by example in
In a generating mode of operation, the primary power source 12 may mechanically rotate the rotor of the electric machine 14 to cause electromagnetic interactions between the rotor and the stator of the electric machine 14 and to generate electrical energy which may be stored or employed by one or more connected loads 24. Moreover, in typical variable speed gensets 10, the operating speed of the primary power source 12 is varied according to the demands of the loads 24, as shown for example in
One area of improvement associated with traditional variable speed gensets 10 pertains to the manner of operating the genset 10 during transient or step load conditions while engine speeds are relatively low. During such conditions, the power output by a genset 10 at low engine speeds may be insufficient on its own to maintain desirable operation of each connected load 24. Accordingly, traditional gensets 10 typically employ a secondary energy storage device, such as the ultracapacitor 26 of
However, adding a separate and secondary energy storage device such as an ultracapacitor introduces substantial increases in costs and weight to the overall variable speed genset and associated machine or work tool. The additional weight can further translate into increased fuel consumption and decreased efficiency. Moreover, incorporating secondary energy storage devices takes up additional space on the associated vehicle, machine or tool which can be better suited for other use. The present disclosure is directed at addressing one or more of the deficiencies set forth above.
In one aspect of the present disclosure, a variable speed genset system is provided. The variable speed genset system may include a primary power source, an electric machine, an energy storage device for starting the primary power source, and a boost converter. The electric machine may be mechanically coupled to the primary power source and electrically coupled to one or more loads through a common bus. The boost converter may be in electrical communication with each of at least the common bus and the energy storage device, and configured to selectively communicate power from the energy storage device to the common bus if a bus voltage of the common bus falls to a predetermined lower limit.
In another aspect of the disclosure, a transient assist system for a variable speed genset having a primary power source, an electric machine, a common bus and an energy storage device. The transient assist system may include a boost converter having an input and an output, a first interface electrically coupling the input of the boost converter to the energy storage device, and a second interface electrically coupling the output of the boost converter to the common bus. The second interface may be configured to electrically communicate the output voltage to the common bus when the bus voltage falls to a predetermined lower limit.
In yet another aspect of the disclosure, a variable speed genset system is provided. The variable speed genset system may include a primary power source, an electric machine mechanically coupled to the primary power source, a rectifier circuit electrically coupled to the electric machine, an inverter circuit electrically coupled to the rectifier circuit and forming a common bus therewith, a starter battery for starting the primary power source, and a high boost ratio boost converter electrically disposed between the starter battery and the common bus. The high boost ratio converter may be configured to boost an input voltage received from the starter battery to an output voltage to the common bus which substantially approximates a bus voltage of the common bus.
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.
The primary power source 102 may include an internal combustion engine or any other comparable prime mover suitable for outputting mechanical energy, such as rotational torque at an output shaft thereof. The electric machine 104 may employ an induction machine, a switched reluctance machine, or any other suitable electric motor or generator commonly used in the art. For example, the electric machine 104 may include a rotor that electromagnetically interacts with and is rotatably disposed within a stator such that electrical input at the stator generates mechanical or rotational output at the rotor, as in a motoring mode of operation, or alternately, mechanical or rotational input at the rotor generates electrical energy at an output of the stator, as in a generating mode of operation. Moreover, the rotor of the electric machine 104 may be mechanically coupled to the output of the primary power source 102 and the stator may be electrically coupled to the common bus 110 through the rectifier circuit 106.
When operating in a generating mode of operation, as diagrammatically demonstrated in the genset system 100 of
Furthermore, the variable speed genset system 100 may be configured to vary the operating speed of the primary power source 102 and the connected electric machine 104 according to any changes in the load demand. During transient conditions or in the presence of step loads, however, the combination of the primary power source 102 and the electric machine 104 may be unable on its own to immediately source adequate power to the changing loads 112 as desired. Accordingly, the variable speed genset 100 may further include a transient assist system 200 as shown in
As shown in
Still referring to the embodiment of
In addition, the output 206 and/or the second interface 210 of the transient assist system 200 may be electrically coupled relative to each of the output of the rectifier circuit 106 and the common bus 110 such that connected loads 112 are not negatively affected or impacted by any sudden deficiencies in the power output by the primary power source 102 and electric machine 104. Moreover, the transient assist system 200 may be disposed at the output of the rectifier circuit 106 and coupled directly to the common bus 110 such that the output voltage of the boost converter 202 is substantially isolated from the rectifier circuit 106. Furthermore, the second interface 210 may include an arrangement of one or more diodes that are coupled directly to the common bus 110 and configured to passively communicate any supplemental electrical power to the common bus 110 as needed, while preventing any substantial dissipation of the bus voltage in the common bus 110 through the boost converter 202.
In such a way, the transient assist system 200 may be passively but effectively implemented without the need of complex algorithms and/or additional hardware. In other modifications, the transient assist system 200 may be implemented as an actively engaging system within which one or more of the first and second interfaces 208, 210 of the transient assist system 200 may employ electronically engageable components, such as switches, gates, transistors, relays, or the like. However, such active systems would require additional control algorithms, hardware, and other considerations which may unnecessarily and undesirably add to the complexity and overall costs of implementation of the transient assist system 200 and the associated genset 100.
Furthermore, as implemented in
Referring now to
For example, connecting circuitry 208, 210 of a boost converter 202 that is configured to output a voltage, Vb,out, with a magnitude that is slightly less than the bus voltage, or the output voltage of the rectifier circuit 106, Vr,out, may be passively arranged to automatically supply power to the common bus 110 when the bus voltage falls to or below a predetermined lower limit, Vb,out. In other words, when the bus voltage is greater than the predetermined lower limit, Vr,out>Vb,out, the electric machine 104 may supply power to any loads 112 connected to the common bus 110, and when the bus voltage falls to or below the predetermined lower limit, Vr,out≦Vb,out, the transient assist system 200 may at least temporarily supply power to the connected loads 112 from the energy storage device 116 until the electric machine 104 regains nominal operating speeds and output power. The corresponding drop in voltage as perceived by the loads 112, approximately Vr,out−Vb,out, may be preconfigured to be minimal so as not to adversely affect functionality of any connected loads 112.
Still referring to the method 300 of
In general, the foregoing disclosure finds utility in various applications relating to the control of vehicles, machines and/or tools employing variable speed gensets. More specifically, the disclosed systems and methods may be used to provide more efficient control of electric machines typically used in association with electric or hybrid drive systems including machine tools, traction motors, industrial work machines, stationary drive machines, mobile work vehicles, hybrid electric vehicles, and the like.
In particular, the disclosed transient assist systems enable optimum control and performance of loads by automatically and immediately supplementing the common bus voltage in the presence of transient or step load conditions without requiring additional energy storage devices. Specifically, the present disclosure employs connections to a starter battery commonly found on traditional electric drive vehicles, machines and/or tools so as to eliminate the need for an additional energy source, such as an ultracapacitor, to supply power to the common bus during transient conditions.
In addition, the transient assist systems of the present disclosure may be implemented using relatively simple circuitry, such as an arrangement of one or more diodes, or the like, to effectively connect such pre-existing starter batteries to the common bus. By employing a passive configuration, the present disclosure further serves to eliminate the need for control algorithms, hardware, and other considerations which may unnecessarily and undesirably add to the complexity and overall costs of implementation of the transient assist system.
The transient assist systems disclosed herein also provide a basis upon which minor extensions and/or modifications can be made to further eliminate other pre-existing electric drive components and related hardware. For example, a bi-directional DC to DC converter may be used within the transient assist system to enable charging of the starter battery off of the bus voltage, and thus, eliminate the need for a traditional alternator. The transient assist system can also be used to effectively connect the starter battery to the electric machine and start the primary power source, and thus, eliminate the need for a traditional starter motor.
The present disclosure thus reduces complexity, costs, machine weight, and fuel consumption, while improving overall efficiency. The present disclosure further enables valuable space savings on the associated vehicle, machine and/or tool.
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.
