Hybrid vehicle energy balance control system for CO2 reduction

1 . A hybrid electric vehicle (HEV), comprising:

an internal combustion engine;

an electric traction motor;

a belt starter generator (BSG) unit configured to start the internal combustion engine;

a low voltage battery system including a low voltage battery electrically coupled to the BSG unit;

a high voltage battery system including a high voltage traction battery configured to power the electric traction motor;

a DC/DC converter configured to convert high voltage from the high voltage battery system into low voltage to charge the low voltage battery and support low voltage loads; and

a powertrain control system for reducing CO2 emissions of the HEV, including a controller configured to control an output voltage setpoint of the DC/DC converter and the BSG unit,

wherein the controller is configured to selectively increase or decrease the output voltage setpoints of the DC/DC converter and/or the BSG unit to reduce high voltage battery power consumption to thereby avoid or delay turning on the internal combustion engine thereby reducing CO2 emissions, and

wherein the controller is programmed to maintain a state of charge (SOC) of the low voltage battery within a predefined range to reduce CO2 emissions, including:

monitoring the low voltage battery SOC to determine an increase or decrease in the SOC;

increasing the output voltage setpoints for the DC/DC converter and/or the BSG unit when the low voltage battery SOC is increasing within the predefined range to thereby charge the low voltage battery; and

decreasing the output voltage setpoint of the DC/DC converter and/or the BSG unit when the low voltage battery SOC is decreasing within the predefined range to thereby discharge the low voltage battery.

2 . The HEV of claim 1 , wherein the powertrain control system further includes:

an auxiliary power module (APM) in signal communication with the controller and configured to control the output voltage setpoint of the DC/DC converter; and

a motor control processor (MCP) in signal communication with the controller and configured to control the output voltage setpoint of the BSG unit.

3 . The HEV of claim 2 , wherein the powertrain control system further includes:

a sensor system configured to monitor a temperature and state of charge (SOC) of the low voltage battery; and

a body control module (BCM) in signal communication with the sensor system and the controller.

4 . The HEV of claim 1 , wherein the low voltage battery predefined range is between approximately 80% SOC and approximately 90% SOC.

5 . The HEV of claim 4 , wherein the controller is further programmed to periodically fully recharge the low voltage battery to approximately 100% SOC, after the expiration of a predefined time period, to maintain full capacity of the low voltage battery.

6 . The HEV of claim 1 , wherein the controller is programmed to adjust the output voltage setpoint of the DC/DC converter based on a condition of the high voltage traction battery, including:

monitoring the high voltage traction battery to determine if a power usage thereof is greater than a predetermined threshold; and

decreasing the output voltage setpoint of the DC/DC converter when the power usage is greater than the predetermined threshold, to thereby conserve high voltage traction battery energy.

7 . The HEV of claim 1 , wherein the controller is programmed to adjust the output voltage setpoint of the DC/DC converter based on a performance of the DC/DC converter, including:

monitoring the DC/DC converter for a derating or saturation condition; and

decreasing the output voltage setpoint of the DC/DC converter when the DC/DC converter has the derating or saturation condition.

8 . The HEV of claim 1 , wherein the controller is programmed to adjust the output voltage setpoints of the DC/DC converter and/or BSG unit to meet high-performance, increased power requests, including:

monitoring low voltage devices powered by the low voltage battery system for high-performance, increased power requests; and

increasing the output voltage setpoints of the DC/DC converter and/or BSG unit to meet the high-performance, increased power requests.

9 . The HEV of claim 1 , wherein the controller is programmed to increase the output voltage setpoint and a corresponding voltage ramping rate of the DC/DC converter for transition from an EV mode to a hybrid mode of the HEV, including:

determining the HEV is operating in the EV mode where the engine is off; and

increasing the output voltage setpoint and corresponding voltage ramping rate of the DC/DC converter to provide sufficient power for an engine start when transitioning to the hybrid mode.

10 . A method of operating a powertrain control system to reduce CO2 emissions of a hybrid electric vehicle (HEV) having an internal combustion engine, an electric traction motor, a belt starter generator (BSG) unit, a low voltage battery, a high voltage traction battery, and a DC/DC converter, the method comprising:

selectively increasing or decreasing an output voltage setpoint voltage of the DC/DC converter and/or the BSG unit to reduce high voltage battery power consumption to thereby avoid or delay turning on the internal combustion engine to reduce CO2 emissions; and

maintaining a state of charge (SOC) of the low voltage battery within a predefined range to reduce CO2 emissions, including:

monitoring the low voltage battery SOC to determine an increase or decrease in the SOC;

increasing the output voltage setpoints for the DC/DC converter and/or the BSG unit when the low voltage battery SOC is increasing within the predefined range to thereby charge the low voltage battery; and

decreasing the output voltage setpoint of the DC/DC converter and/or the BSG unit when the low voltage battery SOC is decreasing within the predefined range to thereby discharge the low voltage battery.

11 . The method of claim 10 , wherein the low voltage battery predefined range is between approximately 80% SOC and approximately 90% SOC.

12 . The method of claim 11 , further comprising periodically fully recharging the low voltage battery to approximately 100% SOC, after the expiration of a predefined time period, to maintain full capacity of the low voltage battery.

13 . The method of claim 10 , further comprising adjusting the output voltage setpoint of the DC/DC converter based on a condition of the high voltage traction battery, including:

monitoring the high voltage traction battery to determine if a power usage thereof is greater than a predetermined threshold; and

decreasing the output voltage setpoint of the DC/DC converter when the power usage is greater than the predetermined threshold, to thereby conserve high voltage traction battery energy.

14 . The method of claim 10 , further comprising adjusting the output voltage setpoint of the DC/DC converter based on a performance of the DC/DC converter, including:

monitoring the DC/DC converter for a derating or saturation condition; and

decreasing the output voltage setpoint of the DC/DC converter when the DC/DC converter has the derating or saturation condition.

15 . The method of claim 10 , further comprising adjusting the output voltage setpoints of the DC/DC converter and/or BSG unit to meet high-performance, increased power requests, including:

monitoring low voltage devices powered by the low voltage battery system for high-performance, increased power requests; and

increasing the output voltage setpoints of the DC/DC converter and/or BSG unit to meet the high-performance, increased power requests.

16 . The method of claim 10 , further comprising increasing the output voltage setpoint and a corresponding voltage ramping rate of the DC/DC converter for transition from an EV mode to a hybrid mode of the HEV, including:

determining the HEV is operating in the EV mode where the engine is off; and

increasing the output voltage setpoint and corresponding voltage ramping rate of the DC/DC converter to provide sufficient power for an engine start when transitioning to the hybrid mode.

17 . The method of claim 10 , further comprising:

(i) maintaining a state of charge (SOC) of the low voltage battery within a predefined range to reduce CO2 emissions, including:

monitoring the low voltage battery SOC to determine an increase or decrease in the SOC;

increasing the output voltage setpoints for the DC/DC converter and/or the BSG unit when the low voltage battery SOC is increasing within the predefined range to thereby charge the low voltage battery; and

decreasing the output voltage setpoint of the DC/DC converter and/or the BSG unit when the low voltage battery SOC is decreasing within the predefined range to thereby discharge the low voltage battery;

(ii) periodically fully recharging the low voltage battery;

(iii) adjusting the output voltage setpoint of the DC/DC converter based on a condition of the high voltage traction battery, including:

monitoring the high voltage traction battery to determine if a power usage thereof is greater than a predetermined threshold; and

decreasing the output voltage setpoint of the DC/DC converter when the power usage is greater than the predetermined threshold, to thereby conserve high voltage traction battery energy;

(iv) adjusting the output voltage setpoint of the DC/DC converter based on a performance of the DC/DC converter, including:

monitoring the DC/DC converter for a derating or saturation condition; and

decreasing the output voltage setpoint of the DC/DC converter when the DC/DC converter has the derating or saturation condition;

(v) adjusting the output voltage setpoints of the DC/DC converter and/or BSG unit to meet high-performance, increased power requests, including:

monitoring low voltage devices powered by the low voltage battery system for high-performance, increased power requests; and

increasing the output voltage setpoints of the DC/DC converter and/or BSG unit to meet the high-performance, increased power requests; and

(vi) increasing the output voltage setpoint and a corresponding voltage ramping rate of the DC/DC converter for transition from an EV mode to a hybrid mode of the HEV, including:

determining the HEV is operating in the EV mode where the engine is off; and

increasing the output voltage setpoint and corresponding voltage ramping rate of the DC/DC converter to provide sufficient power for an engine start when transitioning to the hybrid mode.