Patent Publication Number: US-2023150386-A1

Title: Current regulation overcharge protection for vehicle battery systems

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Application No. 63/279,201, filed on Nov. 15, 2021. The disclose of the above-identified application is hereby incorporated by reference in its entirety. 
    
    
     FIELD 
     The present application generally relates to vehicle battery systems and, more particularly, to techniques for current regulation overcharge protection for vehicle battery systems. 
     BACKGROUND 
     Vehicles typically include one or more low voltage batteries (e.g., 12 volt (V) lead-acid batteries) for cranking/starting an internal combustion engine and/or for powering low voltage vehicle accessory components. These batteries are typically recharged via current generated by an engine-driven alternator or DC-DC converter. In the event of abnormally high recharging currents while the batteries have a low state of charge (SOC), the batteries could be overcharged and “swell,” which could potentially shorten the life of the batteries. 
     Conventional overcharge protection techniques include electrical and mechanical systems that retroactively disable recharging based on battery voltage monitoring. These techniques utilize a voltage charging setpoint that is only based on battery temperature. Battery temperature, however, changes over time based on other factors such as charging current and ambient temperature. Accordingly, while such conventional battery overcharge protection techniques do work for their intended purpose, there exists an opportunity for improvement in the relevant art. 
     SUMMARY 
     According to one example aspect of the invention, an overcharge protection system for a battery system of an electrified vehicle is presented. In one exemplary implementation, the overcharge protection system comprises an intelligent battery sensor (IBS) configured to generate an IBS current signal indicative a measured current at the battery system and a controller in communication with the IBS via a controller area network communication (CAN-C) bus and configured to determine whether the IBS current signal is available based on an awake/asleep status of the CAN-C bus, when the IBS current signal is unavailable because the CAN-C bus status is asleep, monitor an output current of an auxiliary power module (APM) configured to control a direct current (DC)-to-DC (DC-DC) converter, based on a comparison of the monitored APM output current and a first predefined maximum current threshold, selectively request the CAN-C bus to transition to the awake status and obtain the IBS current signal from the IBS, determine whether the IBS current signal is valid based on a comparison of the IBS current signal to a set of expected values, and based on the determined validity of the IBS current signal, the measured battery system current, and the CAN-C bus status, adjust a charging voltage set point for the APM for the battery system to be battery current-based, battery temperature-based, or a predetermined constant value. 
     In some implementations, when the IBS current signal is invalid and the request to transition the CAN-C bus to the awake status was generated, the controller is configured to adjust the charging voltage set point to the predetermined constant value. In some implementations, when the IBS current signal is invalid and the request to transition the CAN-C bus to the awake status was not generated, the controller is configured to perform battery temperature-based adjusting of the charging voltage set point. In some implementations, the controller is further configured to cancel the request to transition the CAN-C bus to the awake status for energy saving purposes. 
     In some implementations, when the IBS current signal is valid and its value is higher than a second predefined maximum threshold, the controller is configured to perform battery current-based adjusting of the charging voltage set point to ensure the charging current does not exceed the second predefined maximum threshold until at least a next key cycle. In some implementations, when the IBS current signal is valid and its value is lower than the predefined maximum threshold, the controller is configured to perform temperature-based adjusting of the charging voltage set point. In some implementations, the controller is further configured to cancel the request to transition the CAN-C bus to the awake status for energy saving purposes. 
     In some implementations, the controller is further configured to perform the battery current-based control of the charging voltage set point for the APM for the battery system using a gain adjustable integrator with an integral anti-windup. In some implementations, the gain adjustable integrator with the integral anti-windup comprises (i) applying a low-pass filter to the IBS current signal to remove high-frequency noise and (ii) applying a rate limiter to and constraining the charging voltage set point to avoid steady-state error in step input tracking. 
     According to another example aspect of the invention, an overcharge protection method for a battery system of an electrified vehicle is presented. In one exemplary implementation, the overcharge protection method comprises receiving, by a controller and from an intelligent battery sensor (IBS) via a controller area network communication (CAN-C) bus, an IBS current signal indicative a measured current at the battery system, determining, by the controller whether the IBS current signal is available based on an awake/asleep status of the CAN-C bus, monitoring, by the controller, an output current of an auxiliary power module (APM) when the IBS current signal is unavailable because the CAN-C bus status is asleep, wherein the APM is configured to control a direct current (DC)-to-DC (DC-DC) converter, selectively requesting, by the controller, the CAN-C bus to transition to the awake status based on a comparison of the monitored APM output current and a first predefined maximum current threshold and thereby obtain the IBS current signal from the IBS, determining, by the controller, whether the IBS current signal is valid based on a comparison of the IBS current signal to a set of expected values, and adjusting, by the controller, a charging voltage set point for the APM for the battery system to be battery current-based, battery temperature-based, or a predetermined constant value, based on the determined validity of the IBS current signal, the measured battery system current, and the CAN-C bus status. 
     In some implementations, the method further comprises adjusting, by the controller, the charging voltage set point to the predetermined constant value when the IBS current signal is invalid and the request to transition the CAN-C bus to the awake status was generated. In some implementations, the method further comprises performing, by the controller, battery temperature-based adjusting of the charging voltage set point when the IBS current signal is invalid and the request to transition the CAN-C bus to the awake status was not generated. In some implementations, the method further comprises canceling, by the controller, the request to transition the CAN-C bus to the awake status for energy saving purposes. 
     In some implementations, performing, by the controller, battery current-based adjusting of the charging voltage set point when the IBS current signal is valid and its value is higher than a second predefined maximum threshold to thereby ensure the charging current does not exceed the second predefined maximum threshold until at least a next key cycle. In some implementations, the method further comprises performing, by the controller, temperature-based adjusting of the charging voltage set point when the IBS current signal is valid and its value is lower than the predefined maximum threshold. In some implementations, the method further comprises canceling, by the controller, the request to transition the CAN-C bus to the awake status for energy saving purposes. 
     In some implementations, the method further comprises performing, by the controller, the battery current-based control of the charging voltage set point for the APM for the battery system using a gain adjustable integrator with an integral anti-windup. In some implementations, the gain adjustable integrator with the integral anti-windup comprises (i) applying a low-pass filter to the IBS current signal to remove high-frequency noise and (ii) applying a rate limiter to and constraining the charging voltage set point to avoid steady-state error in step input tracking. 
     Further areas of applicability of the teachings of the present application will become apparent from the detailed description, claims and the drawings provided hereinafter, wherein like reference numerals refer to like features throughout the several views of the drawings. It should be understood that the detailed description, including disclosed embodiments and drawings referenced therein, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the present disclosure, its application or uses. Thus, variations that do not depart from the gist of the present application are intended to be within the scope of the present application. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a functional block diagram of an electrified vehicle having an example electrical system according to the principles of the present application; 
         FIG.  2    is a functional block diagram of a portion of an example electrical system of an electrified vehicle according to the principles of the present application; 
         FIG.  3    is a flow diagram of an example battery overcharge protection control method according to the principles of the present application; and 
         FIG.  4    is a functional block diagram of an example control architecture configured for battery overcharge protection according to the principles of the present application. 
     
    
    
     DESCRIPTION 
     As previously discussed, conventional battery overcharge protection techniques utilize devices such as electrical overcharge protection devices and mechanical overcharge protection devices. The electrical overcharge protection devices continuously sense the voltage of a battery cell, and the sensor is connected to one of the cells in the battery module. When the battery cell is overcharged and the voltage of the battery cell exceeds a certain voltage, the electrical overcharge protection device opens the switch of a main relay by interrupting the supply of voltage applied to the actuation coil of the main relay, hereby the electrical connection between the battery module and the charging power source or load is disconnected. The mechanical overcharge protection devices, on the other hand, continuously monitor if a battery cell is abnormally swelling, and the monitor is connected to one of the cells in a battery module. 
     When the battery cell is overcharged and the internal pressure thereof increases, the battery cell swells and causes the mechanical overcharge protection device to open the switch of a main relay by opening a closed circuit that includes the actuation coil of the main relay, whereby the electrical connection between the battery module and the charging power source or load is disconnected. As previously discussed, these techniques utilize a voltage charging setpoint that is only based on battery temperature. Battery temperature, however, changes over time based on other factors such as charging current and ambient temperature. Furthermore, another drawback is that the power source disconnection will cause system failure for vehicles. For example, the 12 volt (V) battery is the power source of the low voltage systems such as controllers, fans, pumps, valves, accessory devices, etc. Disconnection of the power source from an auxiliary power module (APM) will eventually deplete the 12V battery and cause the low voltage system losing functionalities. Yet another drawback is that the mechanism takes reaction when the battery is already overcharged and swelling. The remedial reaction can stop further damage of the battery, but it cannot prevent the overcharge from happening. 
     Accordingly, improved battery overcharge protection techniques for electrified vehicles are presented. These techniques improve the conventional charging control method by avoiding abnormal high current overcharging the 12V lead-acid batteries. These techniques operate with the low voltage (e.g., 12V) battery control system of electrified vehicles (e.g., battery electric vehicles, or BEVs, and hybrid electric vehicles, or HEVs), which typically includes an HCP (Hybrid Control Processor), an APM, an IBS (Intelligent Battery Sensor), a BCM (Body Control Module), a 12V lead-acid battery, and a high voltage battery pack. This overcharge protection or prevention includes three primary aspects: (1) immediate detection of high charging current even when the battery current signal is invalid; (2) smartly adjusts the charging voltage set point for the APM (i.e., for a respective direct current (DC)-to-DC (DC-DC) converter) for the battery system by switching the control laws according to different conditions of charging current, battery temperature, and the validity of sensor signals; and (3) achieving accurate current control and avoiding noise interference against the system. This third (3) aspect could include, for example, using a gain adjustable integrator with an integral anti-windup, which may have been previously used in current tracking but has never been used in battery overcharge protection. 
     Referring now to  FIG.  1   , a functional block diagram of an electrified vehicle  100  having an example electrical system  104  according to the principles of the present application is illustrated. The electrified vehicle  100  generally comprises an electrified powertrain  108  configured to generate and transfer drive torque to a driveline  112  for vehicle propulsion. The electrified powertrain  108  could include one or more electric motors  116  and an optional internal combustion engine  120 . 
     The electrical system  104  is configured to power the electrified powertrain  108  (specifically, the electric motor(s)  116 ) and generally comprises a high voltage battery system  124  and a low voltage battery system  128  (e.g., a 12V lead-acid battery). A controller  132  (e.g., an HCP) controls operation of the electrified powertrain  104  and a driver interface  136  is configured to receive driver input (e.g., a driver torque request) and output information to the driver. The electrical system  104  also includes other non-illustrated components as previously discussed above and that will now be described in greater detail, including an overcharge protection system according to the principles of the present application. 
     Referring now to  FIG.  2   , a functional block diagram of a portion  200  of the example electrical system  104  of an electrified vehicle  100  according to the principles of the present application is illustrated. An HCP  204  processes the control logic based on the input signals such as current, voltage, temperature, etc., and outputs the charging voltage set point to the APM  208 . It will be appreciated that the HCP  204  could be the controller  132  as illustrated in  FIG.  1    and otherwise described herein. The connection between the HCP  204  and the APM is via CAN-ePT bus  212 . The APM controls a DC/DC buck converter  216 , which can be separate or integrated therein. 
     The DC/DC buck converter  216  converts the high voltage power of battery  124  to low voltage power for charging the low voltage battery  128 . The APM  208  receives command signals and desired charging voltage set point from the HCP  204 . The APM also has its own sensors to monitor the output current, voltage, power, etc., and the sensed signals are sent back to the HCP  204 . The IBS  220  also senses the current, voltage, and temperature signals of the low voltage battery  128 . The sensed signals are sent to a BCM  224  through a LIN (Local Interconnect Network) bus  228 . The BCM  224  bypasses the IBS signals to the HCP  204 . The connection between the HCP  204  and the BCM  224  is via a controller area network communication (CAN-C) bus  232 . 
     Referring now to  FIG.  3   , a flow diagram of an example battery overcharge protection method  300  according to the principles of the present application is illustrated. While the components of the electrified vehicle  100  and its example electrical system  104 / 200  are specifically referenced, it will be appreciated that this method  300  could be applicable to any suitable electrified vehicle electrical system. At  304 , the controller  132  determines the APM measured/monitored current is greater than a first maximum threshold (TH MAX1 ). When true, the method  300  proceeds to  308 . Otherwise, the method  300  returns to  304 . At  308 , the controller  132  enables the CAN-C network to transition to the awake status and holds the CAN-C network at this control status. At  312 , the controller  132  determines whether the IBS current signal is valid. This could include, for example, verifying that there are no malfunctions of the IBS  220  or its related components and that the IBS current signal is within a range of expected values. When true, the method  300  proceeds to  316 . Otherwise, the method  300  proceeds to  328 . 
     At  316 , the controller  132  determines whether the IBS current signal is larger than the second maximum threshold TH MAX2 , which could be less than the first maximum threshold TH MAX1 . When true, current-based control is performed at  320  by using a current-based set point for the voltage set point for the APM and DC-DC converter control and the CAN-C status is held awake. The method  300  then ends or returns to  304 . When false, temperature-based control is performed at  324  using a temperature-based setpoint for the voltage set point for the APM and DC-DC converter and the method  300  ends or returns to  304 . The CAN-C awake request could also be canceled to save power/energy. At  328 , the controller  132  checks the previous CAN-C wake-up request. When verified, constant value control is performed at  332  using a constant value for the voltage set point for the APM and DC-DC converter and the method  300  ends or returns to  304 . Otherwise, at  336 , temperature-based control is performed using a temperature-based setpoint for the voltage set point for the APM and DC-DC converter and the method  300  ends or returns to  304 . The CAN-C awake request could also be canceled to save power/energy. 
     Referring now to  FIG.  4   , an example current control architecture  400  (also referred to as “current controller  400 ”) according to the principles of the present application is illustrated. The current controller  400  is one part of the current regulation overcharge protection. A similar current control architecture may have been previously used in constant current charging controls (i.e., fast charging control/tracking), but they have not been used in an overcharge protection method as proposed herein. When used in an overcharge protection method, the current controller  400  regulates the charging current to prevent the current from exceeding the predefined maximum threshold. Despite the differences in application, the control law design of the current regulation overcharge protection is also different from previously known methods, which normally use PID (Proportional-Integral-Derivative) or PI (Proportional-Integral) controller, while the current regulation overcharge protection of the present application uses the gain adjustable integrator with an integral anti-windup method as described in greater detail below 
     The idea behind this design is that, based on the system dynamics modeling and analysis, conventional low voltage charging systems suffer from two primary flaws: (1) high-pass characteristics and (2) zero-system type. The high pass characteristics amplifies high frequency noise. The zero-system type, on the other hand, causes the steady-state error for tracking a step input. To optimize the control system, the current controller  400  is designed by using a gain adjustable integrator with an integral anti-windup (box  420 ), so as to achieve the goals of accurate current control and anti-noise interference. The IBS current  408  is filtrated by a low pass filter  412 . The target current  404  subtracts at  412  the filtrated current to obtain the input of the current controller  400 . The calculated result of the current controller will go through a rate limiter  424  to prevent the rapid change of the output value. This output value  428  is constrained in a proper range set by the system, and will be sent to the APM as the charging voltage set point. 
     It will be appreciated that the term “controller” as used herein refers to any suitable control device or set of multiple control devices that is/are configured to perform at least a portion of the techniques of the present application. Non-limiting examples include an application-specific integrated circuit (ASIC), one or more processors and a non-transitory memory having instructions stored thereon that, when executed by the one or more processors, cause the controller to perform a set of operations corresponding to at least a portion of the techniques of the present application. The one or more processors could be either a single processor or two or more processors operating in a parallel or distributed architecture. 
     It should also be understood that the mixing and matching of features, elements, methodologies and/or functions between various examples may be expressly contemplated herein so that one skilled in the art would appreciate from the present teachings that features, elements and/or functions of one example may be incorporated into another example as appropriate, unless described otherwise above.