Patent Application
20100085676
The present invention generally relates to pulse width modulation (PWM) control and, more particularly, to a nested PWM control scheme for components, such as solenoid valves, which are used to control pressurized air flow to a machine, such as a turbine engine starter.
An air turbine starter, as is generally known, may be used to rotate an aircraft gas turbine engine spool. Typically, this is done during a starting sequence of the gas turbine engine. However, an air turbine starter may additionally be used to rotate gas turbine engines during aircraft ground operations for various other reasons. Aircraft gas turbine engines may at times be motored (e.g., rotated without burn fuel flow) while the aircraft is on the ground.
No matter the specific reason for using the air turbine starter to rotate a gas turbine engine, most air turbine starters include a turbine wheel that is rotationally mounted within a housing assembly. The turbine wheel includes an output shaft and, in some instances may additionally include a gear train mechanically coupled between the turbine wheel and the output shaft. The output shaft is mechanically coupled to a spool (e.g., the high pressure spool) of a gas turbine engine through an accessory gearbox mounted to the engine's exterior. To motor the gas turbine engine, pressurized air is supplied to an inlet of the air turbine starter via a valve, such as a solenoid-operated valve. The pressurized air flows past the turbine wheel, causing it to rotate and drive the gas turbine engine.
At times, it may be desirable to control the speed of the gas turbine engine while it is being motored via the air turbine starter. For example, if the gas turbine engine is motored while experiencing, or shortly after experiencing, large internal temperature gradients, speed control may be needed to prevent the turbine blade tips from striking the case. However, controlling air turbine starter speed, and thus gas turbine engine speed, may not be effectually accomplished via, for example, the solenoid-operated valve.
Hence, there is a need for a control scheme that may be used to effectually implement speed control of a machine, such as an air turbine starter for a gas turbine engine, that is powered by pressurized air via a control valve. The present invention addresses at least this need.
In one embodiment, and by way of example only, a circuit includes a first PWM driver, a duty cycle compensator, and a second PWM driver. The first PWM driver is adapted to receive duty cycle commands and is operable to generate a first PWM driver signal having a duty cycle that varies based on the duty cycle commands. The duty cycle compensator is coupled to receive the first PWM driver signal and a sensor signal representative of a value of a sensed physical parameter. The duty cycle compensator is operable to supply compensated duty cycle commands based on the duty cycle of the first PWM driver signal and the value of the sensed physical parameter. The second PWM driver is coupled to receive the compensated duty cycle commands and is operable to generate a hybrid PWM driver signal having a duty cycle that varies based on the compensated duty cycle commands.
In another exemplary embodiment, a solenoid valve control circuit includes a first PWM driver, a duty cycle compensator, a solenoid PWM driver, and a solenoid valve. The first PWM driver is adapted to receive duty cycle commands and is operable to generate a first PWM driver signal having a duty cycle that varies based on the duty cycle commands. The duty cycle compensator is coupled to receive the first PWM driver signal and a sensor signal representative of a value of a sensed physical parameter. The duty cycle compensator is operable to supply compensated duty cycle commands based on the duty cycle of the first PWM driver signal and the value of the sensed physical parameter. The solenoid PWM driver is coupled to receive the compensated duty cycle commands and is operable to generate a solenoid PWM driver signal having a duty cycle that varies based on the compensated duty cycle commands. The solenoid valve is coupled to receive the solenoid PWM driver signal and is operable, in response thereto, to move between a closed position and an open position at the duty cycle of the solenoid PWM driver signal.
In yet another exemplary embodiment, a control system for controlling the speed of a machine includes a speed sensor, a pressure sensor, a valve, and a controller. The speed sensor is operable to sense the speed of the machine and supply a speed feedback signal representative thereof. The pressure sensor is operable to sense a pressure of a fluid that drives the machine and supply a pressure signal representative thereof. The valve is coupled to receive valve command signals having a duty cycle and is operable, in response thereto, to move between an open position and a closed position at the duty cycle of the valve command signals to thereby control fluid flow to the machine. The controller is coupled to receive a speed command, the speed feedback signal, and the pressure signal and is operable, in response thereto, to supply the valve command signals. The controller includes a comparator, a first PWM driver, a duty cycle compensator, and a valve PWM driver. The comparator is coupled to receive a speed command and the speed feedback signal and is operable, in response thereto, to supply duty cycle commands representative of a difference between the speed command and the speed feedback signal. The first PWM driver is coupled to receive the duty cycle commands and is operable to generate a first PWM driver signal having a duty cycle that varies based on the duty cycle commands. The duty cycle compensator is coupled to receive the first PWM driver signal and the pressure signal. The duty cycle compensator is operable to supply compensated duty cycle commands based on the duty cycle of the first PWM driver signal and the sensed pressure. The valve PWM driver is coupled to receive the compensated duty cycle commands and is operable to supply the valve command signals at a duty cycle that varies based on the compensated duty cycle commands.
Other desirable features and characteristics of the inventive control scheme will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.
The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:
The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background or the following detailed description. In this regard, although the control circuit is described in the context of a controller for an air turbine starter of a gas turbine engine to control the speed of the air turbine starter, and thus the gas turbine engine, it will be appreciated that it may be implemented in numerous and other environments and may be used to control the speed of numerous and varied fluid-powered machines.
Turning now to
The control valve 104 is disposed between, and is in fluid communication with, the non-illustrated pressurized air source and the air turbine starter 102. The control valve 104 is movable between a closed position and an open position. In the closed position, pressurized air does not flow through the control valve 104 to the air turbine starter 102. In the open position, however, pressurized air does flow through the control valve 104 to the air turbine starter 102. The control valve 104 is responsive to valve command signals it receives from the controller 106 to move between its open and closed positions. It will be appreciated that the control valve 104 may be implemented using any one of numerous types of controllable valves. In a particular preferred embodiment, however, the control valve 104 is a solenoid-operated, dual-position valve that includes a solenoid-piloted actuator 114 coupled to a valve element 116. The control valve 104 is configured such that when the solenoid-piloted actuator 114 is energized it moves the valve element 116 to the open position, and when the solenoid-piloted actuator 114 is de-energized it moves the valve element 116 to the closed position. As will now be described, the valve command signals supplied to the control valve 104 comprise pulses having a duty cycle. The control valve 104, in response to these valve command signals, thus moves between its open and closed positions at the duty cycle of the valve command signals to thereby control the flow of pressurized air to the air turbine starter 102.
The controller 106, as was just noted, supplies the valve command signals to the control valve 104. The controller 106 is configured to generate and supply the valve command signals in response to a plurality of input signals. As
Before proceeding further, it is noted that the pressure of the air that drives the air turbine starter 102 is merely exemplary of just one sensed physical parameter that may be used by the controller 106. For example, if needed or desired, one or more other pressures, one or more temperatures, one or more other speeds, one or more fluid viscosities, one or more chemical contents, just to name a few, could be sensed and supplied to the controller 106. No matter the particular physical parameter that is sensed and used by the controller 106, the controller 106 uses the sensor signal supplied from the suitable sensor in a manner that will be described below. Referring now to
The controller 106 includes a comparator 202, a first PWM driver 204, a duty cycle compensator 206, and a second PWM driver 208. The comparator 202 is coupled to receive the speed command from the non-illustrated source, and the speed feedback signal from the speed sensor 118. The comparator 202, upon receipt of these signals, supplies duty cycle commands representative of the difference between the speed command and the speed feedback signal (i.e., the speed error) to the first PWM driver 204.
The first PWM driver 204 is coupled to receive the duty cycle commands supplied from the comparator 202. The first PWM driver 204 is responsive to these duty cycle commands to generate a first PWM driver signal. The first PWM driver signal, as may be appreciated, comprises pulses having a duty cycle that varies based on the duty cycle commands supplied to the first PWM driver 204. In the depicted embodiment, if the speed error is relatively large, then the duty cycle commands will command the first PWM driver 204 to supply first PWM driver signals having relatively long duty cycles. As the speed error approaches zero, that is, as the sensed speed approaches commanded the speed, the duty cycle commands will command the first PWM driver 204 to supply first PWM driver signals having relatively shorter and shorter duty cycles. In any case, the first PWM driver signals are supplied to the duty cycle compensator 206.
The duty cycle compensator 206 is coupled to receive the first PWM driver signal. As
The lookup table 300, an exemplary embodiment of which is depicted in
It should be noted that the table 300 depicted in
The duty cycle compensator 206, based on the sensed pressure and the first PWM driver signal, indexes the lookup table 300 to supply appropriate compensated duty cycle commands to the second PWM driver 208. As an example, for relatively large speed errors, the first PWM driver signal will have a relatively large duty cycle, which means it will be in a logic-HIGH state (e.g., logical-1) for a greater percentage of time than it will be in a logic-LOW state (e.g., logical-0). Thus, depending upon the sensed pressure, the compensated duty cycle commands supplied by duty cycle compensator 206 will be a maximum duty cycle value for a greater percentage of time than a minimum duty cycle value. Again, the specific maximum and minimum duty cycle values will depend on the sensed pressure.
The second PWM driver 208, which may also be referred to as a solenoid PWM driver or a valve PWM driver, is coupled to receive the compensated duty cycle commands from the duty cycle compensator 206. The second PWM driver 208 is responsive to the compensated duty cycle commands to generate and supply the valve command signals to the control valve 104. The valve command signals also comprise pulses having a duty cycle that varies. The duty cycle of the valve command signals varies based on the compensated duty cycle commands supplied to the duty cycle compensator 206. From the previous description of the duty cycle compensator 206 it may thus be appreciated that the second PWM driver 208 will supply valve command signals having duty cycles that vary between predetermined minimum and maximum values (or interpolated values of these minimum and maximum values), thereby supplying what may be referred to herein as hybrid PWM signals to the control valve 104. An exemplary hybrid PWM signal 402 that may be generated and supplied by the second PWM driver 208 is depicted in
In addition to each of the major functional blocks described above, the controller 106 may include various other devices to enhance its operation. For example, and with reference once again to
The first and second quantizers 214, 216 are disposed just upstream of the first PWM driver 204 and the second PWM driver 208, respectively, and are operable to supply discrete values of the duty cycle commands and compensated duty cycle commands, respectively, that each receives. The discrete values that each supplies match allowable possibilities for the update rate of the controller 106. It will be appreciated that if the controller 106 is implemented as an analog device, rather than as a digital device, then the quantizers 214, 216 are not needed.
The filter 218, if included, is disposed between the pressure sensor 122 and the duty cycle compensator 206. In some cases, the sensor signal supplied from the pressure sensor 122 may undesirably include high frequency noise. The filter 218 is coupled to receive the sensor signal, and is operable to filter the high frequency noise from the sensor signal and supply a filtered sensor signal to the duty cycle compensator 206.
The override circuit 220, if included, is coupled between the duty cycle compensator 206 and the second PWM driver 208 and is operable to selectively modify the compensated duty cycle commands supplied to the second PWM driver 208. In the depicted embodiment, the override circuit 220 includes a summer 222 and a saturation block 224. The summer 222 is coupled to receive, from a signal source 226, an override signal, and is further coupled to receive the compensated duty cycle commands from the duty cycle compensator 206. The summer 222 mathematically sums these two signals and supplies a modified command signal to the saturation block 224. The saturation block 224 ensures that a duty cycle command of greater than 100% (e.g., ±1.0) is not exceeded, and supplies the command to the second PWM driver 208. It will be appreciated that the override signal may modify the compensated duty cycle commands so that the control valve 104 is commanded open or commanded closed. It will additionally be appreciated that the external source may be an external device or system, such as a non-illustrated override switch or other non-illustrated control device.
While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims.
