Method for compensating alternator regulation to control remote battery voltage utilizing adaptive variable

Abstract

A method for compensating for alternator to battery voltage drop in charging systems lacking external remote sensing capabilities and utilizing serial communications. A controller utilizes an adaptive variable for determining an alternator output voltage setpoint that compensates for battery cable voltage losses, and adjusting the setpoint to achieve substantially constant battery voltage of the entire range of alternator loads.

Claims

1. A method for regulating the output voltage setpoint (V.sub.CONTROL,ADAPT) of an alternator, comprising the steps of: establishing a first voltage setpoint of the alternator corresponding to a first alternator load level (V.sub.Set0) and an initial value (V.sub.100,INIT) for a second voltage setpoint of the alternator corresponding to a second alternator load level (V.sub.100) greater than the first load level; serially communicating information identifying the voltage level of a battery (V.sub.BAT,ADAPT) charged by the alternator through a battery cable continually to a controller; using the controller to incrementally increase the second voltage setpoint (V.sub.100) from its initial value (V.sub.100,INIT) until a desired relationship is reached between the battery voltage (V.sub.BAT,ADAPT) and the first voltage setpoint (V.sub.Set0), and to then define an end value (V.sub.100,END) for the second voltage setpoint (V.sub.100); using the controller to determine an adaptive variable (R.sub.ADAPT) based on the first voltage setpoint (V.sub.Set0) and the defined end value (V.sub.100,END) for the second voltage setpoint (V.sub.100), and to determine, utilizing the adaptive variable (R.sub.ADAPT), offsetting levels of the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) that compensate for battery cable voltage losses estimated to occur over a range of alternator load levels between the first and second alternator load levels; and continually regulating the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) to an offsetting level that compensates for the respective battery cable voltage drop between the alternator and the battery and maintain the battery voltage (V.sub.BAT,ADAPT) at a substantially constant level.

2. The method of claim 1, wherein the determined offsetting levels of the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) linearly increase with alternator load level.

3. The method of claim 1, wherein the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) is continually regulated to maintain the battery voltage (V.sub.BAT,ADAPT) at a value substantially equivalent to the first voltage setpoint (V.sub.Set0).

4. The method of claim 1, further comprising using the controller to determine, utilizing the adaptive variable (R.sub.ADAPT), offsetting levels of the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) that compensate for battery cable voltage losses estimated to occur at alternator load levels greater than the second alternator load level.

5. The method of claim 1, wherein the alternator is one of a plurality of parallel-connected alternators included in a parallel alternator system, wherein each alternator is connected to a voltage bus intermediate the alternator and the battery, and wherein the voltage bus is part of the battery cable through which the battery is charged by the alternator.

6. The method of claim 5, wherein the controller is a system controller, and further comprising regulating the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) of each alternator with an alternator controller in communication with the system controller.

7. The method of claim 6, wherein at least one of the first voltage setpoint (V.sub.Set0) and the initial value (V.sub.100,INIT) for the second voltage setpoint is established by the system controller.

8. The method of claim 6, wherein the system controller is a vehicle ECU.

9. The method of claim 1, wherein the established first voltage setpoint (V.sub.Set0) is serially communicated to the controller.

10. The method of claim 1, wherein information identifying the voltage level of a battery (V.sub.BAT,ADAPT) is serially communicated to the controller from a vehicle ECU.

11. The method of claim 1, wherein the controller is a digital alternator controller dedicated to controlling the operation of the alternator.

12. The method claim 11, wherein the alternator controller comprises a voltage regulator and/or rectifier of the alternator.

13. The method of claim 11, wherein the second alternator load level is a recognized 100% alternator load level.

14. The method of claim 1, wherein the first alternator load level is a substantially unloaded state of the alternator.

15. The method of claim 1, wherein the incremental voltage increases to the second voltage setpoint (V.sub.100) are made at a rate substantially corresponding to the rate at which information identifying the voltage level of a battery (V.sub.BAT,ADAPT) is serially communicated.

16. The method of claim 1, wherein the desired relationship between the battery voltage (V.sub.BAT,ADAPT) and the first voltage setpoint (V.sub.Set0) is substantially equivalence therebetween.

17. A method for regulating the output voltage setpoint of an alternator, comprising the steps of: establishing a first output voltage setpoint corresponding to a 0% alternator load level (V.sub.Set0) and an initial value (V.sub.100,INIT) for a second output voltage setpoint corresponding to a 100% alternator load level (V.sub.100); serially communicating information regarding the voltage level of a battery (V.sub.BAT,ADAPT) charged by the alternator through a battery cable continually to a controller; using the controller to incrementally increase the second output voltage setpoint level (V.sub.100) from its initial value (V.sub.100,INIT) until the serially communicated battery voltage level (V.sub.BAT,ADAPT) is substantially equal to the first output voltage setpoint level (V.sub.Set0), and to then define an end value (V.sub.100,END) for the second output voltage setpoint level (V.sub.100); using the alternator controller to determine an adaptive variable (R.sub.ADAPT) based on the first output voltage setpoint level (V.sub.Set0) and the defined end value (V.sub.100,END) for the second output voltage setpoint level (V.sub.100), and to determine the offsetting level of alternator output voltage setpoint (V.sub.CONTROL,ADAPT) that compensates for the battery cable voltage drop relative to the first output voltage setpoint level (V.sub.Set0) at a respective alternator load level in a range between the 0% and 100% alternator load levels; and regulating the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) to its offsetting level to maintain the battery voltage (V.sub.BAT,ADAPT) at a substantially constant value equivalent to the first output voltage setpoint level (V.sub.Set0).

18. The method of claim 17, wherein the offsetting levels of the alternator output voltage setpoint (V.sub.CONTROL,ADAPT) increase linearly with alternator load above the 0% alternator load level.

19. The method of claim 17, wherein the alternator is one of a plurality of parallel-connected alternators included in a parallel alternator system, wherein each alternator is connected to a voltage bus intermediate the alternator and the battery, and wherein the voltage bus is part of the battery cable through which the battery is charged by the alternator.

20. The method of claim 17, wherein the incremental voltage increases to the second output voltage setpoint level (V.sub.100) are made at a rate substantially corresponding to the rate at which information identifying the voltage level of a battery (V.sub.BAT,ADAPT) is serially communicated.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-mentioned aspects and other characteristics and advantages of a method and/or system according to the present disclosure will become more apparent and will be better understood by reference to the following description of exemplary embodiments taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a graph showing the voltage delivered to the battery (V.sub.BAT), between 0% and 100% alternator load (or rotor field duty cycle), of three different 24-volt battery charging systems respectively associated with battery voltages V.sub.BAT,COMP and V.sub.BAT,UNCOMP according to the prior art, and V.sub.BAT,ADAPT according to the present disclosure;

(3) FIG. 2 is a graph showing the alternator output voltage setpoints at the alternator's B+ terminal (V.sub.CONTROL), between 0% and 100% alternator load (or rotor field duty cycle), of the three battery charging systems indicated in FIG. 1, which are respectively associated with V.sub.CONTROL,COMP and V.sub.CONTROL,UNCOMP according to the prior art, and V.sub.CONTROL,ADAPT according to the present disclosure;

(4) FIG. 3 is a schematic showing information transmitted, partially through a serial communication network such as a vehicle CAN, according to a first battery charging system or method embodiment according to the present disclosure; and

(5) FIG. 4 is a schematic showing information transmitted, partially through a serial communication network such as a vehicle CAN, according to an alternative, second battery charging system or method embodiment according to the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENT(S)

(6) The embodiments of the present invention described below are not intended to be exhaustive or to limit the invention to the precise forms disclosed in the following detailed description. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the present invention.

(7) FIG. 1 is a graph showing the voltage delivered to the battery (V.sub.BAT), between 0% and 100% alternator load (or rotor field duty cycle), of three different 24-volt battery charging systems respectively associated with battery voltages V.sub.BAT,COMP and V.sub.BAT,UNCOMP described above, and V.sub.BAT,ADAPT described below

(8) The prior battery charging system corresponding to the constant battery voltage indicated by line 20 of FIG. 1 (V.sub.BAT,COMP) has external remote sensing capabilities that offset or compensate for the battery cable voltage losses between the alternator B+ terminal and the battery. Such a system provides the actual battery voltage level as an analog signal to the alternator regulator via a remote sensing wire.

(9) The prior battery charging system corresponding to the linearly varying battery voltage indicated by line 30 of FIG. 1 (V.sub.BAT,UNCOMP) altogether lacks compensation for a cable voltage drop between the alternator B+ terminal and the battery. As is typical of such a system, in the present example the alternator includes internal voltage sensing and control capabilities through which the alternator output voltage setpoint V.sub.CONTROL,UNCOMP at the B+ terminal is held constant at a prescribed V.sub.Set0 level over the entire alternator load range.

(10) A battery charging system corresponding to the constant battery voltage indicated by line 40 of FIG. 1 (V.sub.BAT,ADAPT) employs a method according to the present disclosure. This method and system utilize serial communications and an adaptive variable to offset or compensate for the battery cable voltage losses between the alternator B+ terminal and the battery, and in the present example substantially matches the charging performance of the above mentioned system having external remote sensing capabilities, which yields curve V.sub.BAT,COMP. In FIG. 1 line 40 (V.sub.BAT,ADAPT) substantially coincides with line 20 (V.sub.BAT,COMP).

(11) FIG. 2 correlates with FIG. 1, and is a graph showing the alternator output voltage setpoints (or internal voltage control points) at the alternator B+ terminal (i.e., V.sub.CONTROL), between 0% and 100% alternator load (or rotor field duty cycle), of the three above-mentioned battery charging systems respectively associated with V.sub.CONTROL,COMP and V.sub.CONTROL,UNCOMP discussed above, and V.sub.CONTROL,ADAPT discussed below.

(12) The prior battery charging system yielding curve V.sub.BAT,COMP of FIG. 1, yields the linearly varying control point voltages indicated by line 22 of FIG. 2 (V.sub.CONTROL,COMP). The prior battery charging system yielding curve V.sub.BAT,UNCOMP of FIG. 1, yields the constant, level control point voltage indicated by line 32 of FIG. 2 (V.sub.CONTROL,UNCOMP). The battery charging system yielding curve V.sub.BAT,ADAPT of FIG. 1, yields the linearly varying control point voltages indicated by line 42 of FIG. 2 (V.sub.CONTROL,ADAPT), which substantially coincides with line 22 (V.sub.CONTROL,COMP).

(13) A battery charging method or system utilizing serial communications according to the present disclosure may be readily accommodated in a CAN-equipped vehicle, and can match or exceed the performance of prior battery charging systems having external remote sensing capabilities by similarly providing a constant desired voltage level at the battery (see FIG. 1), and at relatively lower cost and wiring complexity. This is achieved by using a controller receivable of sensed battery voltage information that is serially communicated, to linearly scale alternator output voltage setpoint changes between 0% and 100% of alternator load (see FIG. 2), without requiring prior external remote sensing capabilities, relatively faster or more expensive serial communication networks, or assigning higher priority to serially communicated messages regarding battery voltage level information.

(14) Referring to FIG. 2, in an exemplary 24-volt battery charging system embodiment according to the present disclosure, V.sub.CONTROL,ADAPT at 100% alternator load is 28.5 volts (i.e., V.sub.Set0+0.2 volts). At less than the 100% alternator load, the alternator's output voltage setpoint, or internal control point voltage, V.sub.CONTROL,ADAPT linearly decays along line 42 towards the original V.sub.Set0 value at 0% alternator load (which is 28.3 volts in this example). Linear scaling of the change in voltage control point V.sub.CONTROL,ADAPT along line 42 to offset or compensate for battery cable voltage losses encountered over the range of alternator loads helps keep the voltage at the battery, V.sub.BAT,ADAPT substantially constant at the 28.3 volt, V.sub.Set0, level indicated by line 40 of FIG. 1, matching the performance of the example prior battery charging system having external remote sensing capabilities, which is indicated by the V.sub.BAT,COMP curve, line 20, of FIG. 1. Thus, a method or system according to the present disclosure beneficially provides charging system performance previously realized by a comparable battery charging system having external remote sensing capabilities, without the added expense and wiring complexity of actually providing remote sensing, and can be achieved utilizing serial communications capability and messaging priority levels already provided by a typical vehicle CAN.

(15) Serial communication between nodes of a vehicle CAN in a first embodiment battery charging system 44 according to the present disclosure is indicated in FIG. 3. As shown, the alternator regulator/controller 46 of the sole alternator, or of each of a plurality of parallel-connected alternators, as the case may be, is a node on the CAN, and receives a message providing the sensed, actual battery voltage, V.sub.BAT,ADAPT, which is continuously monitored and serially communicated over the CAN bus to the alternator regulator/controller 46.

(16) In conjunction with the communication flow shown FIG. 3, a first embodiment of a method according to the present disclosure proceeds by establishing V.sub.Set0, the desired output voltage setpoint for 0% alternator loading (and for 0% rotor field duty cycle). V.sub.Set0 can be established or prescribed either as a fixed, default value or an initialization value previously determined to represent the desired alternator output voltage setpoint. V.sub.Set0 is established by a vehicle electronics control unit (ECU), is serially communicated to the alternator regulator/controller 46, and is the battery voltage level desired to be held constant regardless of alternator load, as indicated by the V.sub.BAT,ADAPT voltage level at point 48 of FIG. 1, which in the present example is 28.3 volts. Referring to FIG. 2, in the present example the V.sub.CONTROL,ADAPT curve (line 42) desirably coincides with the V.sub.CONTROL,COMP curve (line 22).

(17) Once the alternator is under load and producing current output, alternator regulator/controller 46 may determine that the received, serially communicated sensed value of V.sub.BAT,ADAPT (or its filtered average) is less than the established V.sub.Set0 value. Such a condition temporarily reflects the on-going operating condition of a comparable prior charging system lacking remote sensing capabilities, for V.sub.BAT,UNCOMP (line 30 of FIG. 1) is always less than V.sub.CONTROL,UNCOMP (line 32 of FIG. 2) other than at 0% alternator load. If such a determination is made, alternator regulator/controller 46 will then incrementally increase the alternator's internally sensed voltage control point V.sub.100, which is the alternator's output voltage setpoint at the B+ terminal at the recognized 100% alternator load, starting at its present, internally sensed initial value, V.sub.100,INIT.

(18) The incremental increases to the V.sub.100 setpoint are of a predefined amount, and can be small, e.g., as little as 0.01 to 0.1 volts, and may be made at a rate corresponding to the rate at which information identifying battery voltage level V.sub.BAT,ADAPT is serially communicated over the CAN bus. The voltage increments made to V.sub.100 continue until the serially communicated V.sub.BAT,ADAPT level (or its filtered average) reaches the level of V.sub.Set0, at which point an end value for V.sub.100, V.sub.100,END, is defined by adding the total of the increments to the internal output voltage setpoint to V.sub.Set0. A ratio, R.sub.ADAPT, the above-mentioned adaptive variable, is then established:
R.sub.ADAPT=(V.sub.100,ENDV.sub.Set0)/V.sub.Set0 (1)

(19) It is known by those having ordinary skill in the relevant art that the total electrical load on the alternator(s) as a percentage of the maximum charging system capacity, Alt.sub.LOAD%, can be represented by the rotor field coil excitation current(s), I.sub.ROTOR, and the speed of the alternator(s) in the system, N.sub.Alt. Thus:
Alt.sub.LOAD%=f(I.sub.ROTOR, N.sub.Alt) (2a)

(20) It is likewise known by those having ordinary skill in the relevant art that the total electrical load on the alternator(s) as a percentage of the maximum charging system capacity, Alt.sub.load%, can be alternatively represented by the rotor field duty cycle(s), F.sub.ROTOR, and the speed of the alternator(s) in the system, N.sub.Alt. Thus:
Alt.sub.LOAD%=f(F.sub.ROTOR, N.sub.Alt)(2b)

(21) The internal alternator control point V.sub.CONTROL,ADAPT at the alternator B+ terminal, between 0% and 100% percent alternator load (or rotor field duty cycle), which offsets or compensates for the battery cable voltage losses, can be estimated as:
V.sub.CONTROL,ADAPT=V.sub.Set0*(1+(Alt.sub.LOAD%*R.sub.ADAPT))(3)
The alternator controller's utilization of the adaptive variable, R.sub.ADAPT, facilitates a linear extrapolation in either direction along line 42 of FIG. 2 to increase or decrease the internal alternator control point voltage V.sub.CONTROL,ADAPT realized at the alternator B+ terminal. The method and system of the first embodiment thereby provides a constant voltage level V.sub.BAT,ADAPT at the battery, indicated at point 48 of FIG. 1, that is equivalent to the established V.sub.Set0 level. Referring to FIG. 2, in the present example the value of V.sub.CONTROL,ADAPT between 0% and 100% alternator load can thus be linearly regulated along line 42 between the established V.sub.Set0 value of 28.3 volts and a desired 28.5 volts at 100% alternator load to compensate for battery cable voltage losses. Alternator loads exceeding the recognized 100% level indicated in FIGS. 1 and 2 may be accommodated by further, commensurate increases in alternator output voltage setpoint along line 42, until the maximum alternator current output of the system is reached.

(22) A second, alternative embodiment of a method and charging system 44 according to the present disclosure provides serial communication between CAN nodes as indicated in FIG. 4. The second embodiment is substantially identical to the above-described first embodiment, except as follows:

(23) In the second embodiment, monitored battery voltage V.sub.BAT,ADAPT is serially communicated to the vehicle ECU, and V.sub.Set0 and V.sub.100INIT are established by and/or serially communicated from the vehicle ECU to the alternator regulator/controller 46.

(24) In the second embodiment, once the alternator is producing output, if the vehicle ECU determines that the sensed value of V.sub.BAT,ADAPT serially communicated to the ECU is less than the established value (e.g., a default value or serially communicated initialization value) of V.sub.Set0, then V.sub.100 is incrementally increased, starting from its established initial value, V.sub.100,INIT, by a predefined amount (e.g., 0.1 volt) until the sensed value of V.sub.BAT,ADAPT (or its filtered average), serially communicated to the ECU, reaches V.sub.Set0. In other respects, the first and second method and system embodiments are substantially identical functionally and structurally.

(25) While exemplary embodiments incorporating the principles of the present invention have been disclosed hereinabove, the present invention is not limited to the disclosed embodiments. Instead, this application is intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.