Automotive voltage compensation system and method

1. Field of the Invention

The invention relates to automotive power systems and methods of controlling the same.

2. Discussion

In some vehicles, e.g., alternatively powered vehicles, a DC/DC power converter may be packaged in an interior of the vehicle. Such packaging may increase the length of a cable connecting the DC/DC power converter to a battery. This additional length may increase electrical resistance associated with the cable and increase the voltage drop across the cable. As a result, the battery and any electrical loads, may operate at a voltage lower than if the battery were packaged in the vicinity of the DC/DC power converter.

Embodiments of the invention may take the form of a power system for an automotive vehicle. The power system includes a power source for presenting a voltage and providing a current based on the presented voltage, a power storage unit configured to receive at least a portion of the provided current, and an electrical load having a variable demand for current and configured to receive at least a portion of the provided current. The power system also includes a control system for setting the presented voltage based on a temperature associated with the power storage unit and the provided current.

Embodiments of the invention may take the form of a power system for an alternatively powered vehicle. The power system includes a power converter having an output voltage and configured to provide current based on the output voltage, a battery configured to receive at least a portion of the provided current, and an electrical load having a variable demand for current and configured to receive at least a portion of the provided current. The power system also includes one or more controllers configured to set the output voltage based on a temperature associated with the battery and the provided current.

Embodiments of the invention may take the form of a method for setting an output voltage of a power source for an automotive vehicle. The method includes determining a desired charge voltage for a power storage unit, determining an offset voltage based on a current, and setting the output voltage of the power source based on the desired charge and offset voltages.

While exemplary embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the claims. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention.

FIG. 1 is a schematic diagram of an example automotive power system.

FIG. 2 is a schematic diagram of another example automotive power system.

FIG. 3 is a schematic diagram of example control logic for an automotive power system.

FIG. 4 is a schematic diagram of another example control logic for an automotive power system.

FIG. 5 is a schematic diagram of yet another example control logic for an automotive power system.

FIG. 6 is an example graphical representation of charge voltage versus battery temperature.

FIG. 7 is a flow chart of a control strategy for setting an output voltage of a power source.

Embodiments of the invention employ voltage compensation to regulate a voltage output of a power source. For example, because the length of a battery cable is fixed for a given vehicle configuration, cable resistance may be calibrated into the power source. Additionally, the current output of the power source may be monitored or inferred. These parameters may be used to regulate the voltage output. As such, the power source may have an output that takes into account losses associated with the battery cable. Such an output may ensure, for example, proper charging of the battery.

FIG. 1 is a schematic diagram of power system 10 for vehicle 12 . Heavy lines between elements indicate the flow of power, e.g., electrical power. Light lines between elements indicate the flow of information, e.g., communications. High voltage battery 14 provides high voltage power to DC/DC power converter 16 , e.g., bi-directional buck/boost converter. DC/DC power converter 16 converts this high voltage power to low voltage. As a result, DC/DC power converter outputs a voltage, e.g., V o .

Power distribution box 18 , e.g., electrical hub, distributes the current required, e.g., I o , to support low voltage battery 20 , air conditioning system 22 , audio system 24 , lighting system, 26 , and other electrical loads 28 . This current may vary over time as occupants of vehicle 12 may selectively operate loads, 22 , 24 , 26 , 28 and low voltage battery 20 may selectively be charged. Power distribution box 18 pulls the required current, e.g., I o , from DC/DC power converter 16 based on V o .

In the embodiment of FIG. 1 , an electrical cable, having a resistance R cable , electrically connects DC/DC power converter 16 and power distribution box 18 . As such, as current travels along this cable, the voltage drops due to losses, e.g., V loss =I o ×R cable . The resulting voltage at power distribution box 18 , e.g., V avail , is the voltage available, for example, to charge low voltage battery 20 .

Temperature sensor 30 senses a temperature, e.g., T batt , in the vicinity of low voltage battery 20 , e.g., under hood temperature, battery temperature, etc. Powertrain control module 32 reads T batt and determines a charge voltage, e.g., V charge , for low voltage battery 120 based on T batt . Powertrain control module communicates, e.g., broadcasts, V charge to DC/DC power converter 16 . As discussed below, DC/DC power converter 16 sets V o based on V charge and I o .

FIG. 2 is a schematic diagram of power system 110 for vehicle 112 . Elements differing by factors of 100 have similar, although not necessarily identical, descriptions. Engine 134 provides mechanical power to alternator 136 . Alternator 136 converts this mechanical power to electrical power. As a result, alternator 136 outputs a voltage, e.g., V o .

Power distribution box 118 distributes the current required, e.g., I, to support loads 128 . This current may vary over time as occupants of vehicle 112 may selectively operate loads 128 . Power distribution box 118 pulls the required current, e.g., I, from alternator 136 .

In the embodiment of FIG. 2 , an electrical cable, having a resistance R cable , electrically connects alternator 136 with low voltage battery 120 . As such, as current, e.g., I o , travels along this cable, the voltage drops due to losses, e.g., I o ×R cable . The resulting voltage at low voltage battery 120 , e.g., V avail , is the voltage available, for example, to charge low voltage battery 120 .

Controller 138 , e.g., microprocessor, reads the temperature from temperature sensor 130 , e.g., T batt , and communicates it, e.g., responds to requests for information, to alternator 136 . Alternator 136 reads the current, e.g., I o , from current sensor 140 , e.g., hall sensor, shunt, etc. As discussed below, alternator 136 sets V o based on T batt and I o .

FIG. 3 is a schematic diagram of control logic 42 . At control block 44 , power in, P in , e.g., power from high voltage battery 14 ( FIG. 1 ), is divided by V o yielding I o . At control block 46 , I o is multiplied by R cable yielding V loss . At 48 , V loss is summed with V charge yielding V o . In the embodiment of FIG. 3 , control logic 42 is implemented by DC/DC power converter 16 ( FIG. 1 ). In alternative embodiments, control logic 42 may be implemented by one or more controllers collectively configured to execute the strategies discussed herein. Some or all of these controllers, for example, may be integrated with other components, e.g., DC/DC power converter 16 .

FIG. 4 is a schematic diagram of control logic 142 . At control block 146 , I o is multiplied by R cable yielding V loss . At 148 , V loss is summed with V charge yielding V o . In the embodiment of FIG. 4 , control logic 142 of FIG. 4 is implemented by alternator 136 ( FIG. 2 ). In alternative embodiments, control logic 142 may be implemented by one or more controllers collectively configured to execute the strategies discussed herein. Some or all of these controllers, for example, may be integrated with other components, e.g., alternator 136 , controller 138 , etc.

FIG. 5 is a schematic diagram of control logic 242 . At control block 244 , power in, P in , is divided by V o yielding I o . At control block 246 , I o is multiplied by R cable yielding V loss . At control block 250 , a look up table is inspected to determine V charge based on T batt . At 248 , V loss is summed with V charge yielding V o . As discussed above, control logic 242 may be implemented by one or more controllers collectively configured to execute the strategies discussed herein. For example, control block 250 may be implemented by powertrain control module 32 ( FIG. 1 ), DC/DC power converter 16 ( FIG. 1 ), or controller 138 ( FIG. 2 ).

FIG. 6 is an example graphical representation of charge voltage versus battery temperature. For lower battery temperatures, e.g., temperatures below 30 degrees F., a higher charge voltage, e.g., 16 volts, may be used to charge low voltage battery 20 ( FIG. 1 ). As battery temperatures increase, however, a lower charge voltage may be used, e.g., 15.5 volts, etc. Charge voltages that are too high or too low, for a given battery temperature, may adversely affect battery performance and life. The graphical representation of FIG. 6 may be implemented, for example, as the look up table in control block 250 ( FIG. 5 ).

FIG. 7 is a flow chart of a control strategy for setting an output voltage of a power source. At 52 , a battery temperature is determined. At 54 , a charge voltage is determined. At 56 , an output current is determined. At 58 , an offset voltage is determined. At 60 , the charge and offset voltages are summed. At 62 , the output voltage is set equal to the sum of the charge and offset voltages.

While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.