Method for controlling current in a load

One embodiment relates to a control system. The control system includes a controller configured to drive a load based on a set-point of the load. The controller is also configured to measure a load characteristic of the load and compute an average load characteristic. The controller 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. Other systems and methods are also disclosed.

FIELD OF THE INVENTION

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.

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

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.

DETAILED DESCRIPTION OF THE INVENTION

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.

FIG. 1shows one embodiment for a compensated hysteretic control system100comprising a controller102configured to measure a load characteristic of a load (not shown) at an input106thereof, and further configured to drive the load based on a set-point of the load. The control system100further comprises a correction circuit104configured to compute an average load characteristic, and to determine a corrected set-point based on the computed average. The controller is also configured to drive the load when operably coupled to an output108thereof in response to the corrected set-point.

In one embodiment, the compensated hysteretic control system100comprises a hysteretic controller102that 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 input106thereof, 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 system100of the embodiment also has a correction circuit104that can compute an average load characteristic using the measured load characteristic110over an integer number of cycles (in other embodiments, load switching cycles, or the cycles of another signal time base source).

The correction circuit104of the present embodiment is configured to determine a corrected set-point112from 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 output108thereof in response to the second or corrected set-point112determined by the correction circuit104, and optionally, to provide an on/off status indication114of the drive output108.

FIGS. 2A and 2Billustrate embodiments of the compensated hysteretic control system ofFIG. 1used for driving a load in accordance with the present invention.

FIG. 2A, for example, illustrates one embodiment of a compensated hysteretic control system200similar to that ofFIG. 1. Control system200comprises a hysteretic controller102, a correction circuit104, and several external drive and load components201including a shunt resistor204and a load206, which are driven by complementary drive transistors210and212driven from differential drive outputs108a,108bof controller102. The external drive and load components201receive supply power between supply voltage Vbat202and ground voltage Vgnd203. The control system200of the embodiment can manage, in one embodiment, a current that is delivered to the load206(in other embodiments, a solenoid, a motor, a light, or an inductive load) by selectively increasing or decreasing the current to properly drive the load, such that the current is maintained by driving (in one embodiment switching) the load between a preset upper limit and lower limit, sometimes called hysteretic switching, accomplished within a hysteretic band as will be discussed further in association withFIG. 3infra. The frequency of this load switching may be determined by the particular load characteristics, the supply voltage used, and the hysteretic band chosen.

In the illustrated embodiment ofFIG. 2A, the controller102has a pair of differential inputs106a,106bwhich sense a voltage drop across the shunt resistor204proportional to the load current thru load206. A Hall Effect sensor may also be used at the input106, wherein a magnetic field is associated with the current in the load206, and a voltage proportional to the magnetic field may be provided as the load characteristic input. Thus, as the current through the shunt resistor204or Hall Effect sensor, for example, increases, the shunt resistor or sensor voltage typically increases proportionally. Similarly, as the current through the sensor decreases, the sensor voltage typically decreases proportionally, although other conventions could also be used.

After the shunt resistor204provides the sensed voltage, the sensed voltage travels to the pair of differential inputs106a,106bof the controller102, one embodiment of which is now discussed in more detail.

Differential amplifier116senses the differential voltage at106a,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 at117to an analog to digital converter ADC118, which are well known in the art. ADC118provides a digital measurement110of the load current, or another such load characteristic to a digital comparator120in the controller102and to an averaging functional block130in the correction circuit104.

Where a desired set-point of the load characteristic is compared to the measured load characteristic in an analog comparator, in the embodiment ofFIG. 2A, the digital comparator receives a corrected set-point112that provides an accurate representation of a measured average of the load characteristic. Accordingly, the averaging block130receives the measured load characteristic110(in one embodiment, a load current), over a known time interval, or a number of cycles of a signal source used as a time base such as the load switching cycles or a dither signal, for example, and computes the average load characteristic130bmeasured over this time interval. A synchronous serial peripheral interface SPI132or another such interface may be used to supply an initial set-point of the load characteristic (in one embodiment an initial current setting)132ato a current setting functional block134and a correction block140, and a hysteretic band value132bsupplied to a hysteresis functional block136.

The correction block140compares or computes the difference between the computed average load characteristic130band the initial set-point132ato obtain a correction error141. The correction error141is then summed in a digital summer functional block142in one embodiment with a digital representation of the initial set-point135provided by the current setting block134and a hysteretic band value137from hysteresis block136used to determine whether to add or subtract the hysteretic band value132bsupplied by SPI132, based upon the on/off status114indicated by logic block122.

The summation (or other suitable operation in other embodiments) within the digital summer142results in a corrected set-point112from the correction circuit104to the digital comparator120of the controller102. Digital comparator120then compares the corrected set-point112with the measured load characteristic110to provide a drive command signal121to logic block122. Logic block122then issues a drive signal to output driver124to drive or switch the external drive transistors210and212, and also issues the on/off status114to hysteresis block136to 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 circuit104, the synchronous serial peripheral interface SPI132or 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 circuit104, the digital summer functional block142may comprise a digital adder or subtractor, or another such processor function capable of summing or mixing the initial set-point135, the hysteretic band value137, the error correction value141, and optionally the amplitude component139of the dither signal, to supply a corrected set-point112.

In one embodiment of the controller102, the output121(in one embodiment a digital word result) of the comparator120is provided to the logic block122to provide a logical drive signal123to a gate driver or an output driver124and an on/off status114to the hysteresis block136. This logical drive signal123may, for example, be delayed or be related to the comparator output signal121by some other state-machine included in the logical block in one embodiment. The logical drive signal123is then passed to the gate driver or output driver140, which may amplify or otherwise condition the signal to provide the drive signal on108band the inverted drive signal on108ato a first field effect transistor FET210and a second field effect transistor FET212, respectively.

Thus, the control system100in one embodiment measures and adjusts a load characteristic of a load206, for example, a load current between an upper limit and a lower limit to efficiently and accurately drive the load, wherein the output driver124, 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.

FIG. 2B, illustrates another embodiment of a control system220, having a compensated hysteretic control system100, comprising a controller102and a correction circuit104, and external load and drive components201. Control system220is similar to control system200ofFIG. 2A, and as such need not be completely described again for the sake of brevity. In this embodiment, correction circuit104further comprises a dither generator138that provides a dither signal based upon amplitude and frequency settings132csupplied by SPI132. The dither generator138provides 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 block130via131afor computing the average load characteristic130bover an integer number of dither cycles. The amplitude component139of the dither signal is also summed (or otherwise accounted for) in the present embodiment ofFIG. 2Bin summer block142with the initial set-point135, the hysteretic band value137, and the error correction value141, to supply a corrected set-point112, which is further based on the dither signal amplitude and period settings132c.

The dither block138receives the base dither frequency or period, in one embodiment, which it then suitably modifies to facilitate providing the time base signal at131aand the amplitude component139. In one embodiment, the dither block138provides 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 load206includes a solenoid, the dither block138provides a periodic wave that is superimposed on the average current to move the solenoid armature back and forth to avoid static friction (stiction).

FIG. 3illustrates an output waveform300of the control system embodiment200ofFIG. 2Awhile driving the load206. The load characteristic, or load current, for example is maintained at an average load current IAVG310, by driving (in one embodiment, switching) the load206between preset upper limit IMAX312and lower limit IMIN314, which define a hysteretic band316. The hysteretic band316may be programmed along with other initial settings, for example, within the serial interface SPI132. The frequency or period318of this load switching is generally determined by the particular load characteristics, the supply voltage used, and the hysteretic band316chosen.

FIG. 4illustrates an output waveform400of the control system embodiment220ofFIG. 2Bhaving a dither signal419, and driving the load206. The load characteristic, or load current, for example is maintained at an average load current IAVG410, by driving (in one embodiment, switching) the load206between preset upper limit IMAX412and lower limit IMIN414, which define a hysteretic band416. The hysteretic band416may be programmed along with other initial settings, for example, within the SPI132. The frequency or period418of this load switching is generally determined by the particular load characteristics, the supply voltage used, and the hysteretic band416chosen.

In addition, the dither signal419having a dither amplitude139and a dither frequency or dither period422, may be provided in the dither settings132csupplied by serial interface SPI132. The dither generator138may 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 block130via131afor computing the average load characteristic130bover an integer number of dither cycle periods422. The amplitude component139of the dither signal is summed (or otherwise accounted for) in the embodiment ofFIG. 2Bin summer block142with the initial set-point135, the hysteretic band value137, and the error correction value141, to supply a corrected set-point112, which is further based on the dither signal amplitude139and period settings132c. FromFIG. 2B, it may be observed that the output waveform400essentially comprises the dither signal419as an AC signal riding on, or summed with the hysteretic load switching signal or output waveform300ofFIG. 3without dither.

In one embodiment, the control system100can 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, circuit100ofFIGS. 1,2A, and2B) as well as in association with other systems not illustrated, wherein all such implementations are contemplated as falling within the scope of the present invention and the appended claims.

Referring now toFIGS. 5-7, one can see one or more embodiments of a method500in accordance with aspects of the present invention in the context of the control systems ofFIGS. 1,2A, and2B. In the method500, a load characteristic (in other embodiments, a load current, a voltage, a magnetic field, a light energy, or a power) associated with a load206(in other embodiments, a solenoid, a motor, a light, or an inductive load) driven at a set-point is measured and provided at510. In one embodiment, this measurement110may be performed digitally using an analog to digital converter118to supply a digital word representation110of the load characteristic in order to better facilitate computations of the load characteristic measurements, for example, using software based averaging and other such math function programs.

At520, an average load characteristic130bis computed using the load characteristic measurement. In one embodiment, the averaging may be done by an average functional block130within the correction circuit104, measured and averaged over a period of time, for example, a number of switch cycles or dither cycles, or another known time interval.

At530, a corrected set-point112is determined based on the average load characteristic computation130b. 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 averaging130and correction140functions to provide a corrected set-point112that compensates for the load characteristics and dynamic variabilities of the system so as to provide a more accurate average current130b.

At540, the load206is driven in response to the corrected set-point112. In one embodiment, the load206is driven by an output driver124, for example, comprising a drive signal and a complementary drive signal.

In a further embodiment of method500, and as illustrated at511inFIG. 6, after the load measurement of step510, a dither signal419is generated at512to provide motion to the load206when operably coupled to the control system100. Thereafter, at514, an average load characteristic is computed using the load characteristic measurement110over an integer number of dither cycles131a, and the method proceeds to step520.

In another embodiment of step530of method500, the corrected set-point112may be derived, as shown inFIG. 7, by comparing or computing the difference result of the average load characteristic130band the initial set-point132aat step532, and then summing the difference result141with the set-point135and the hysteretic band value137at step534.

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 FET212ofFIGS. 2A and 2B, wherein only FET210switches the load206. In another exemplary embodiment of the present invention, the locations of the shunt204and load206may be reversed. In still another embodiment, the FETs210and212ofFIGS. 2A and 2Bmay be located at the high side of the load, attached to the power supply Vbat202rather than to the ground Vgnd203. Numerous other such variations are also possible within the spirit and scope of the invention, and as such are anticipated.

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 system100may 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 controller102and/or the correction circuit104. 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.