INTRODUCTION

The present disclosure generally relates to propulsion systems of vehicles, and more particularly relates to an energy storage system with multiple battery modules for improving the performance of motor vehicles.

Automotive manufacturers are continuously investigating battery modules for propulsion systems of motor vehicles. Below freezing temperatures can drain power from a conventional battery, which can in turn lead to difficulty with starting an internal combustion engine, restrict regenerative braking, decrease vehicle cruise range, and slow charging of the battery. To avoid these adverse effects on vehicle performance, manufacturers can replace the comparably smaller conventional battery with a larger and more powerful battery. However, the larger battery can be significantly more expensive than the smaller conventional battery.

Thus, while existing propulsion systems of electric vehicles achieve their intended purpose, there is a need for a new and improved energy storage system for a vehicle propulsion system that address these issues.

SUMMARY

According to several aspects of the present disclosure, an energy storage system (ESS) for a propulsion system of a motor vehicle includes a first battery electrically coupled to a first voltage bus, a second battery electrically coupled to a second voltage bus, and a bidirectional DC/DC power converter (“converter”) electrically coupled to the voltage buses. The ESS further includes a starter electrically coupled to the first voltage bus and mechanically coupled to an engine for cranking the engine during a cranking event. The ESS further includes a controller electrically coupled to the converter and the batteries. The ESS further includes a memory, which is electrically coupled to the controller and stores computer code for execution by the controller. The computer code is configured to operate the converter in a boost mode to transfer power from the second voltage bus to the first voltage bus, in response to the controller determining that: a power capability of the first battery is below a power demand on the first voltage bus; a state of charge of the first battery is below a minimum state of charge threshold associated with the first battery; or a temperature of the first battery is below a minimum temperature threshold associated with the first battery.

In one aspect, the computer code is configured to operate the converter in a buck mode to transfer power from the first voltage bus to the second voltage bus, in response to the controller determining that the engine has started.

In another aspect, the ESS further includes a motor-generator unit (“MGU”) for generating power during a battery regeneration event. The computer code is configured to set the converter to a standby mode to transfer power from the MGU to the first battery, in response to the controller determining that: a torque of the MGU is below zero; the power demand on the first voltage bus is above the power generated by the MGU; and at least one of: the state of charge of the first battery is below the minimum state of charge threshold associated with the first battery; and the temperature of the first battery is below the minimum temperature threshold associated with the first battery.

In another aspect, the computer code is configured to operate the converter in the buck mode to transfer a portion of the power generated by the MGU from the first voltage bus to the second voltage bus, in response to the controller determining that: the power demand on the first voltage bus is below the power generated by the MGU; and a state of charge of the second battery is below a minimum state of charge threshold associated with the second battery.

In another aspect, the computer code is configured to set a DC/DC output voltage of the converter to a maximum level, in response to the controller determining that the energy of the first battery is above an energy storage limit associated with the first battery.

In another aspect, the computer code is configured to set the DC/DC output voltage of the converter based on a regulated voltage control command (“RVC command”), in response to the controller determining that the energy of the first battery is below the energy storage limit.

In another aspect, the computer code is configured to operate the converter in the boost mode to provide torque assist by transferring power from the second voltage bus to the first voltage bus, in response to the controller determining that: the state of charge of the second battery is above the minimum state of charge threshold associated with the second battery; and the power demand on the MGU is above the power capability of the first battery.

In another aspect, the first battery is a 48-Volt battery, and the second battery is a 12-Volt battery.

According to several aspects of the present disclosure, a method is provided for operating an energy storage system (ESS) of a propulsion system for a motor vehicle. The ESS includes a first battery electrically coupled to a first voltage bus, a second battery electrically coupled to a second voltage bus, a bidirectional DC/DC power converter (“converter”), a starter, a motor-generator unit (“MGU”), a controller, and a memory storing computer code. The method includes the controller comparing a power capability of the first battery to a power demand on the first voltage bus during an engine crank event. The controller further compares a state of charge of the first battery to a minimum state of charge threshold associated with the first battery. The controller further compares a temperature of the first battery to a minimum temperature threshold associated with the first battery. The converter is operated in a boost mode to transfer power from the second voltage bus to the first voltage bus, in response to the controller determining that at least one of: the power capability of the first battery is below the power demand on the first voltage bus during the engine crank event; the state of charge of the first battery is below the minimum state of charge threshold associated with the first battery; and the temperature of the first battery is below the minimum temperature threshold associated with the first battery.

In one aspect, the converter is operated in a buck mode to transfer power from the first voltage bus to the second voltage bus, in response to the controller determining that the engine has started.

In another aspect, the controller determines a battery regeneration event, in response to the controller determining that a torque of the MGU is below zero. The controller compares a power demand on the first voltage bus to a power generated by the MGU. The controller further compares the state of charge of the first battery to a minimum state of charge threshold associated with the first battery. The controller further compares the temperature of the first battery to a minimum temperature threshold associated with the first battery. The converter is operated in the stand-by mode to transfer all power from MGU to the first battery, in response to the controller determining that the power demand on the first voltage bus is above the power generated by the MGU and at least one of: the state of charge of the first battery is below the minimum state of charge threshold associated with the first battery; and the temperature of the first battery is below the minimum temperature threshold associated with the first battery.

In another aspect, the controller compares a state of charge of the second battery to a minimum state of charge threshold associated with the second battery. The converter is operated in the buck mode to transfer a portion of the power of the MGU from the first voltage bus to the second voltage bus, in response to the controller determining that: the power demand on the first voltage bus is below the power generated by the MGU; and the state of charge of the second battery is below the minimum state of charge threshold associated with the second battery.

In another aspect, the controller compares an energy of the first battery to an energy storage limit associated with the first battery. The controller sets a DC/DC output voltage of the converter to a maximum level, in response to the controller determining that the energy of the first battery is above the energy storage limit. The controller sets the DC/DC output voltage of the converter based on a regulated voltage control command, in response to the controller determining that the energy of the first battery is below the energy storage limit.

In another aspect, the controller compares the power demand on the MGU to the power capability of the first battery. The converter is operated in the boost mode to provide torque assist by transferring power from the second voltage bus to the first voltage bus and MGU, in response to the controller determining that: the state of charge of the second battery is above the minimum state of charge threshold associated with the second battery; and the power demand on the MGU is above the power capability of the first battery.

According to several aspects of the present disclosure, a method is provided for operating an energy storage system (ESS) of a propulsion system for a motor vehicle. The ESS includes a 48-Volt battery electrically coupled to a first voltage bus, a 12-Volt battery electrically coupled to a second voltage bus, a bidirectional DC/DC power converter (“converter”), a starter, a motor generator unit (“MGU”), a controller, and a memory storing computer code. The method includes the controller comparing a power capability of the 48-Volt battery to a power demand on the first voltage bus during an engine crank event. The controller further compares a state of charge of the 48-Volt battery to a minimum state of charge threshold associated with the 48-Volt battery. The controller further compares a temperature of the 48-Volt battery to a minimum temperature threshold associated with the 48-Volt battery. The converter is operated in a boost mode to transfer power from the second voltage bus to the first voltage bus, in response to the controller determining that at least one of: the power capability of the 48-Volt battery is below the power demand on the first voltage bus and starter during the engine crank event; the state of charge of the 48-Volt battery is below the minimum state of charge threshold associated with the 48-Volt battery; and the temperature of the 48-Volt battery is below the minimum temperature threshold associated with the 48-Volt battery.

In one aspect, the converter is operated in a buck mode to transfer power from the first voltage bus to the second voltage bus, in response to the controller determining that the engine has started.

In another aspect, the controller determines a battery regeneration event, in response to the controller determining that a torque of the MGU is below zero. The controller compares a power demand on the first voltage bus to a power generated by the MGU. The controller further compares the state of charge of the 48-Volt battery to a minimum state of charge threshold associated with the 48-Volt battery. The controller further compares the temperature of the 48-Volt battery to a minimum temperature threshold associated with the 48-Volt battery. The converter is operated in the stand-by mode to transfer all power generated by the MGU to the 48-Volt battery, in response to the controller determining that: the power demand on the first voltage bus is above the power generated by the MGU; and at least one of: the state of charge of the 48-Volt battery is below the minimum state of charge threshold associated with the 48-Volt battery; and the temperature of the 48-Volt battery is below the minimum temperature threshold associated with the 48-Volt battery.

In another aspect, the controller further compares a state of charge of the 12-Volt battery to a minimum state of charge threshold associated with the 12-Volt battery. The converter is operated in the buck mode to transfer a portion of the power generated by the MGU from the first voltage bus to the second voltage bus, in response to the controller determining that: the power demand on the first voltage bus is below the power generated by the MGU; and the state of charge of the 12-Volt battery is below the minimum state of charge threshold associated with the 12-Volt battery.

In another aspect, the controller compares an energy of the 48-Volt battery to an energy storage limit associated with the 48-Volt battery. The controller sets a DC/DC output voltage of the converter to a maximum level, in response to the controller determining that the 48-Volt battery is above the energy storage limit. The controller sets the DC/DC output voltage of the converter based on a regulated voltage control command, in response to the controller determining that the 48-Volt battery is below the energy storage limit.

In another aspect, the controller compares the power demand of the MGU to the power capability of the 48-Volt battery. The converter is operated in the boost mode to provide torque assist for transferring power from the second voltage bus to the first voltage bus, in response to the controller determining that: the state of charge of the 12-Volt battery is above the minimum state of charge threshold associated with the 12-Volt battery; and the power demand on the first voltage bus by the MGU is above the power capability of the 48-Volt battery.

Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

