Patent Application
20080169798
The present invention relates generally to control methods and systems, and more specifically to a compensated hysteretic control system for controlling an average load characteristic associated with a load.
In many facets of today's rapidly changing economy, successful businesses must deliver quality products and maximize value to their customers to survive. Even in the high-tech electronic controls arena, this simple reality still holds true.
Two ways in which control systems suppliers deliver value is by providing more accurate control solutions and by providing faster controllers. Accordingly, there is a need in the electronics industry to deliver a control system that can drive a load faster and more accurately.
The following presents a simplified summary of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention, and is neither intended to identify key or critical elements of the invention nor to delineate the scope of the invention. Rather, the purpose of the summary is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.
In one embodiment, a control system measures and compensates a current for driving a load. The control system includes a controller configured to measure a load characteristic of a load at an input thereof, to drive the load based on a set-point of the load, and to compute an average load characteristic. The controller of the control system is further configured to determine a corrected set-point based on the computed average, and to drive the load in response to the corrected set-point to a desired load characteristic value.
The following description and annexed drawings set forth in detail certain illustrative aspects and implementations of the invention. These are indicative of but a few of the various ways in which the principles of the invention may be employed.
The present invention will now be described with respect to the accompanying drawings in which like numbered elements represent like parts. The figures and the accompanying description of the figures are provided for illustrative purposes and do not limit the scope of the claims in any way.
In one embodiment, the compensated hysteretic control system 100 comprises a hysteretic controller 102 that is configured to digitally measure a load characteristic (in other embodiments, a load current, a voltage, a magnetic field, a light energy, and a power) of a load (in other embodiments, a solenoid, a motor, a light, an inductive load) at an input 106 thereof, and further can drive the load based on a set-point (in other embodiments, a load current set-point, a voltage set-point, a magnetic field set-point, a light energy set-point, and a power set-point) of the load. The control system 100 of the embodiment also has a correction circuit 104 that can compute an average load characteristic using the measured load characteristic 110 over an integer number of cycles (in other embodiments, load switching cycles, or the cycles of another signal time base source).
The correction circuit 104 of the present embodiment is configured to determine a corrected set-point 112 from the computed average, by comparing (in other embodiments, comparing or computing the difference between two values) the average load characteristic to a first set point (in other embodiments, a predetermined, initial set-point, user supplied setting, programmed setting), and summing the result of this comparison with the initial set-point and a hysteretic band value (in other embodiments, peak, or peak-to-peak band of allowed variation of the load characteristic values). The controller then drives the load when operably coupled to an output 108 thereof in response to the second or corrected set-point 112 determined by the correction circuit 104, and optionally, to provide an on/off status indication 114 of the drive output 108.
In the illustrated embodiment of
After the shunt resistor 204 provides the sensed voltage, the sensed voltage travels to the pair of differential inputs 106a, 106b of the controller 102, one embodiment of which is now discussed in more detail.
Differential amplifier 116 senses the differential voltage at 106a, 106b, for example, or another such load characteristic (in other embodiments, a load current, a voltage, a magnetic field, a light energy, and a power) indicative of the load, which is communicated at 117 to an analog to digital converter ADC 118, which are well known in the art. ADC 118 provides a digital measurement 110 of the load current, or another such load characteristic to a digital comparator 120 in the controller 102 and to an averaging functional block 130 in the correction circuit 104.
Where a desired set-point of the load characteristic is compared to the measured load characteristic in an analog comparator, in the embodiment of
The correction block 140 compares or computes the difference between the computed average load characteristic 130b and the initial set-point 132a to obtain a correction error 141. The correction error 141 is then summed in a digital summer functional block 142 in one embodiment with a digital representation of the initial set-point 135 provided by the current setting block 134 and a hysteretic band value 137 from hysteresis block 136 used to determine whether to add or subtract the hysteretic band value 132b supplied by SPI 132, based upon the on/off status 114 indicated by logic block 122.
The summation (or other suitable operation in other embodiments) within the digital summer 142 results in a corrected set-point 112 from the correction circuit 104 to the digital comparator 120 of the controller 102. Digital comparator 120 then compares the corrected set-point 112 with the measured load characteristic 110 to provide a drive command signal 121 to logic block 122. Logic block 122 then issues a drive signal to output driver 124 to drive or switch the external drive transistors 210 and 212, and also issues the on/off status 114 to hysteresis block 136 to indicate whether the load is being driven in a direction that will increase or decrease the load characteristic. Thus the present embodiment of the invention may be used to regulate the average load characteristic of a load, for example, a load current of a solenoid.
In one embodiment of the correction circuit 104, the synchronous serial peripheral interface SPI 132 or another such interface may be used to supply the initial settings for the required load characteristic set-points (in one embodiment, a 500 mA load current), the hysteretic band value (in one embodiment ±10 mA load current), the dither amplitude (in one embodiment 150 mA P-P), the dither frequency (in one embodiment 175 Hz), or the number of dither cycles to average over (in one embodiment 4 dither cycles), for example.
In an embodiment of the correction circuit 104, the digital summer functional block 142 may comprise a digital adder or subtractor, or another such processor function capable of summing or mixing the initial set-point 135, the hysteretic band value 137, the error correction value 141, and optionally the amplitude component 139 of the dither signal, to supply a corrected set-point 112.
In one embodiment of the controller 102, the output 121 (in one embodiment a digital word result) of the comparator 120 is provided to the logic block 122 to provide a logical drive signal 123 to a gate driver or an output driver 124 and an on/off status 114 to the hysteresis block 136. This logical drive signal 123 may, for example, be delayed or be related to the comparator output signal 121 by some other state-machine included in the logical block in one embodiment. The logical drive signal 123 is then passed to the gate driver or output driver 140, which may amplify or otherwise condition the signal to provide the drive signal on 108b and the inverted drive signal on 108a to a first field effect transistor FET 210 and a second field effect transistor FET 212, respectively.
Thus, the control system 100 in one embodiment measures and adjusts a load characteristic of a load 206, for example, a load current between an upper limit and a lower limit to efficiently and accurately drive the load, wherein the output driver 124, in one embodiment, may be a single ended or a differential driver capable of driving one or more external or internal drive transistors, for example.
The dither block 138 receives the base dither frequency or period, in one embodiment, which it then suitably modifies to facilitate providing the time base signal at 131a and the amplitude component 139. In one embodiment, the dither block 138 provides a periodic wave that is a triangular wave of approximately 150 to 200 Hz that corresponds to the frequency at which the load oscillates about an initial set-point. For example, in one embodiment where the load 206 includes a solenoid, the dither block 138 provides a periodic wave that is superimposed on the average current to move the solenoid armature back and forth to avoid static friction (stiction).
In addition, the dither signal 419 having a dither amplitude 139 and a dither frequency or dither period 422, may be provided in the dither settings 132c supplied by serial interface SPI 132. The dither generator 138 may be used to provide a substantially continuous motion to the load (in other embodiments, the core or armature of a solenoid or a motor) when operably coupled thereto, and provides a time base source for the average block 130 via 131a for computing the average load characteristic 130b over an integer number of dither cycle periods 422. The amplitude component 139 of the dither signal is summed (or otherwise accounted for) in the embodiment of
In one embodiment, the control system 100 can provide an average current upon which a periodic wave is superimposed and wherein the periodic wave has a frequency that is associated with a load switching frequency at which the load is driven, for example, at a frequency of about 2-10 Khz, depending upon the load characteristics, the supply voltage, and the hysteresis band value chosen for the system.
In addition to or in substitution of one or more of the illustrated components, the illustrated hysteretic control system and other systems of the invention include suitable circuitry, state machines, firmware, software, logic, etc. to perform the various methods and functions illustrated and described herein, including but not limited to the methods described below. While the methods illustrated herein are illustrated and described as a series of acts or events, it will be appreciated that the present invention is not limited by the illustrated ordering of such acts or events. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein, in accordance with the invention. In addition, not all illustrated steps may be required to implement a methodology in accordance with the present invention. Furthermore, the methods according to the present invention may be implemented in association with the operation of systems which are illustrated and described herein (in other embodiments, circuit 100 of
Referring now to
At 520, an average load characteristic 130b is computed using the load characteristic measurement. In one embodiment, the averaging may be done by an average functional block 130 within the correction circuit 104, measured and averaged over a period of time, for example, a number of switch cycles or dither cycles, or another known time interval.
At 530, a corrected set-point 112 is determined based on the average load characteristic computation 130b. In one embodiment, a set-point of 500 mA is selected for a solenoid to operate at, and the set-point is compensated by the averaging 130 and correction 140 functions to provide a corrected set-point 112 that compensates for the load characteristics and dynamic variabilities of the system so as to provide a more accurate average current 130b.
At 540, the load 206 is driven in response to the corrected set-point 112. In one embodiment, the load 206 is driven by an output driver 124, for example, comprising a drive signal and a complementary drive signal.
In a further embodiment of method 500, and as illustrated at 511 in
In another embodiment of step 530 of method 500, the corrected set-point 112 may be derived, as shown in
Although the invention has been illustrated and described with respect to one or more implementations, alterations and/or modifications may be made to the illustrated examples without departing from the spirit and scope of the appended claims.
For example, in one embodiment, the load could be a solenoid. Further such a solenoid could be employed in an automotive system, such as an automatic transmission. In other embodiments, the load could be any other loads that a user desires to drive at an average load characteristic and frequency.
Further, although in the illustrated embodiment, the first and second drive transistor devices are n-type metal-oxide semiconductor field effect transistors (MOSFETs), p-type MOSFETS could also be used including other types of switching devices (in other embodiments, transistors, bipolar junction transistors (BJTs), vacuum tubes, relays, etc.).
In another embodiment, one of the first and second drive transistors may be a diode, for example FET 212 of
In addition, although various embodiments may indicate that a current delivered to the load could be increased if one voltage exceeds another, the conventions used herein could also be reversed. Thus, one will understand that increases or decreases in voltage or other variables could be transposed or otherwise rearranged in various embodiments.
Further, in various embodiments, portions of the control system 100 may be integrated into an integrated circuit, although in other embodiments the control system may be comprised of discrete devices. In one embodiment, the first and second devices or external drive components may be integrated into a single IC with the controller 102 and/or the correction circuit 104. The load characteristic sensor, for example, may be integrated into the same IC as the controller, or may be integrated into the same package as the controller, or may be integrated onto the same PCB board, or may be otherwise associated with the control system; depending on the implementation.
In particular regard to the various functions performed by the above described components or structures (blocks, units, engines, assemblies, devices, circuits, systems, etc.), the terms (including a reference to a “means”) used to describe such components are intended to correspond, unless otherwise indicated, to any component or structure which performs the specified function of the described component (or another functionally equivalent embodiment), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary implementations of the invention. In addition, while a particular feature of the invention may have been disclosed with respect to only one of several implementations, such feature may be combined with one or more other features of the other implementations as may be desired and advantageous for any given or particular application. Furthermore, to the extent that the terms “including”, “includes”, “having”, “has”, “with”, or variants thereof are used in either the detailed description and the claims, such terms are intended to be inclusive in a manner similar to the term “comprising”. In addition, to the extent that the terms “number”, “plurality”, “series”, or variants thereof are used in the detailed description or claims, such terms are to include any number including, but not limited to: positive integers, negative integers, zero, and other values.
