Timer for battery charge balancing system

Abstract

Battery system comprising: a traction battery supplying a high-voltage range; a traction battery controller powered by a low-voltage range separate from the high-voltage range and configured to deactivate cell balancing of the traction battery after a main timer has expired; and a backup controller powered by and within the high voltage range, implementing a backup timer including logic circuitry separate from the processor, and configured to disable cell balancing upon expiration of the backup timer.

Description

TECHNICAL FIELD

[0001] This application generally concerns energy management for hybrid vehicles. GENERAL STATE OF THE ART

[0002] Many batteries, such as a battery pack, have an operating voltage that is greater than the voltage of an individual cell of the battery. For example, the voltage of a traction battery pack for a hybrid electric vehicle may be 200-300 volts DC, while the voltage of an individual battery cell may be 1-4 volts DC. The 1-4 volt range for an individual battery cell is usually related to the battery cell technology. For example, a nickel-metal hydride (NiMH) battery cell typically has a cell voltage of approximately 1.2 volts, and a lithium-ion (Li-ion) battery cell typically has a cell voltage of approximately 3.6 volts. A traction battery of a hybrid electric vehicle provides power for vehicle propulsion and accessories.To meet voltage and current requirements, the traction battery typically consists of multiple battery cells connected in a combination of series and parallel. During vehicle operation, the traction battery can be charged or discharged based on operating conditions, including battery state of charge (SOC), internal combustion engine (ICE) operation, driver demand, and regenerative braking. The state of charge of individual battery cells within a battery pack can be uneven due to many factors, including manufacturing variations, cell age, cell temperature, or cell technology. Battery cell balancing can be used to equalize the state of charge of individual battery cells within the battery pack and improve battery pack operation. SUMMARY

[0003] A battery system includes a traction battery, a traction battery controller, and a backup controller. The traction battery supplies a high-voltage compartment. The traction battery controller may be supplied by a low-voltage compartment separate from the high-voltage compartment. The traction battery may be configured to deactivate cell balancing of the traction battery after a main timer expires. The backup controller may be supplied by and within the high-voltage compartment. The backup controller implements a backup timer that includes logic circuitry separate from the processor and is configured to deactivate cell balancing after the backup timer expires.

[0004] A battery system includes a traction battery, a traction battery controller, and a backup timer. The traction battery may source a high-voltage range. The traction battery controller may be galvanically isolated from the high-voltage range and configured to prevent cell balancing of the traction battery after a timeout period. The backup timer may be powered by and within the high-voltage range, may include an oscillator and digital logic, and may be configured to prevent cell balancing of the traction battery after a backup period longer than the timeout period.

[0005] A traction battery includes battery cells, cell balancing circuitry, and a backup timer. The battery cells generate a high-voltage range. The cell balancing circuitry may be configured to be deactivated by a galvanically isolated controller after a timeout period. The backup timer, powered by and within the high-voltage range, may include an oscillator and digital logic and may be configured to deactivate cell balancing of the traction battery after a backup period longer than the timeout period. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is an exemplary representation of a hybrid vehicle illustrating the common powertrain and energy storage components. Fig. 2 is an exemplary illustration of a battery pack controlled by a battery energy control module. Fig. 3 is an exemplary schematic diagram illustrating a timer for a charge balancing circuit. DETAILED DESCRIPTION

[0006] Embodiments of the present disclosure are described herein. It should be understood, however, that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or reduced to show details of particular components. Accordingly, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching those skilled in the art to variously employ the embodiments.It will be appreciated by those of ordinary skill in the art that various features illustrated and described with reference to any of the figures may be combined with features illustrated in one or more other figures to produce embodiments not explicitly illustrated or described. The illustrated combinations of features provide representative embodiments for typical applications. However, various combinations and modifications of the features consistent with the teachings of this disclosure may be desirable for particular applications or implementations.

[0007] The embodiments of the present disclosure generally provide a variety of circuits or other electrical devices. All references to the circuits and other electrical devices, and the functionality provided by all, are not intended to be limited to including only what is illustrated and described herein. While specific labels may be assigned to various circuits or other electrical devices disclosed, such labels are not intended to limit the scope of operation for the circuits or other electrical devices. Such circuits and other electrical devices may be combined and / or separated from one another in any manner based on the particular type of electrical implementation desired.It will be appreciated that any circuit or other electrical device disclosed herein may include any number of microprocessors, integrated circuits, memory devices (e.g., FLASH, random access memory (RAM), read-only memory (ROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or other suitable variations thereof), and software that cooperate with one another to perform the operation(s) disclosed herein. In addition, any one or more of the electrical devices may be configured to execute a computer program embodied in a non-transitory computer-readable medium programmed to perform any number of the disclosed functions.

[0008] Rechargeable batteries, such as battery packs, typically consist of multiple cells connected in parallel to form a cell group and multiple cell groups connected in series to form the battery pack. Battery packs are widely used as a power source for common electronic devices, including electrified vehicles, consumer and household electronics, industrial devices, and medical devices. Multiple cell groups connected in series allow the use of a low-voltage power cell to power a high-voltage battery. As an example, a battery pack designed to produce approximately 300 volts at the battery terminals may include 84 cell groups, with each cell group connected in series to form a string of cell groups.Each cell group may comprise 3 individual cells connected in parallel; the individual cells may have a nominal cell voltage of approximately 3.5-3.6 volts. In this example, any small change in voltage in the individual battery cell is multiplied by the number of cells in series, namely 84 in this example. Variations in manufacturing tolerances or operating conditions may create a small difference between individual cells or cell groups, which may increase with each charge or discharge cycle. To optimize battery operation, the use of cell balancing to equalize the charge on all of the cells in the series chain can be used to extend battery life.Typically, battery cell balancing systems include electrical components, including metal-oxide-semiconductor field-effect transistors (MOSFETs), bipolar transistors (BJTs), diodes, capacitors, resistors, and other semiconductor devices. The electrical components of the cell balancing system are typically designed to operate at voltages that are a fraction of the battery pack voltage. To prevent the application of a voltage greater than a component's maximum operating value, some balancing components are separated (e.g., isolated) from the battery pack voltages. This isolation can be galvanic isolation, implemented using an optocoupler or a transformer.Furthermore, many active cell balancing systems utilize a controller coupled to multiple cell balancing components, where the cell balancing components may be isolated from the controller, the vehicle's traction battery power system, and chassis ground. The cell typically includes a positive terminal and a negative terminal. The terminals are connected either directly or indirectly to electrodes, such as an anode and / or a cathode.

[0009] Charge balancing is important for both a battery's state of charge and its operating life. As noted above, many low-voltage cells or groups of cells are often connected in series, either directly or indirectly, to create a battery terminal voltage. A peculiarity of this configuration is that all of the battery's current flows through each of the cells or groups of cells during both charging and discharging. However, a cell or multiple cells can often have a cell voltage that differs due to history, manufacturing tolerances, or environmental conditions. As the cell discharges, that cell increases a pack resistance that is applied to a charger coupled to the pack.This increase in resistance reduces the power delivered to each cell, typically resulting in the other cells not receiving sufficient charge or in a slower charging rate for the other cells. If the charging system is configured and capable of increasing the overall charging voltage to compensate for the resistance, the weaker cell will begin to heat up and degrade further. A weaker cell contains less charge, so the other cells must be compensated to equalize their charge with the lower-charge cell.

[0010] Essentially, each battery cell acts as an integrator. Small changes in the capacity of any cell in the system can cause significant changes in how the system performs. If a few cells or groups of cells in the pack have lower voltages, current can be diverted from a few of the batteries. Battery life depends heavily on the charge / discharge pattern, and better cell voltage regulation extends the life of the system. One solution is to charge in parallel and discharge in series. In larger power systems, such as an electric car or a hybrid vehicle, maintaining a uniform charge in individual battery cells or groups of battery cells is desirable.

[0011] The two main methods for balancing battery cell charge in a group of battery cells are passive balancing and active balancing. Passive balancing involves reducing a battery cell's state of charge by converting the energy into thermal energy or heat. A slight overcharge of a battery cell can be detrimental to its lifetime, and the excess charge is released as thermal energy via an external circuit connected in parallel with each cell. The external circuit is typically a resistor and may include a semiconductor switch, such as a MOSFET or BJT, to connect and disconnect the resistor from the battery cell. Passive cell balancing can be used with many battery technologies and topologies.Passive balancing is commonly used in newer advanced battery systems, such as lithium-ion type batteries.

[0012] Active balancing is the active movement of electrical charge from one cell to another. Active balancing is applicable to most battery technologies and topologies. Active cell balancing can transfer energy from an individual cell to the battery pack as a whole, from the battery pack as a whole to an individual cell, or from an individual cell to another individual cell. Generally, energy is transferred from a cell with a high state of charge to a cell with a low state of charge. Similarly, electrical charge can be transferred to battery cells with a low state of charge.

[0013] Within a battery system, such as a battery energy control module (BECM), there is a need to equalize the state of charge of one or more cells in a battery pack. To minimize energy consumption that drains the vehicle's low-voltage (12 V) battery, a controller such as a BECM determines any need for equalization and then shuts itself down or enters a sleep state. Typically, cell monitoring ICs are powered separately from the high-voltage battery and can therefore remain independently powered to equalize based on equalization needs over a predetermined period of time. At the end of the predetermined time interval, the BECM can turn off cell equalization (e.g., via a microcontroller wake-up signal) and reevaluate any need for further cell equalization.If more cell balancing is needed, cell balancing can be re-enabled and the predetermined time interval can be reset.

[0014] A wake-up time interval can be implemented by a timer control circuit, such as a real-time clock module (RTC) or another timer (e.g., an integrated circuit (IC)) used to manage this function. If the main timer fails to wake up the cell balancing controller, the balancing loads would not be turned off, resulting in an over-discharge condition on the cells being balanced. If this discharge causes one or more cells to discharge below a certain limit determined by the controller, the battery pack would log error codes and become dead and unusable. A single timer (e.g., the main timer) used to terminate balancing does not meet the standard (e.g., ASL "C" or "D" system), and a backup / alternate timer may be required to ensure that balancing is disabled and shut down.

[0015] A common way to implement a secondary equalization deactivation or wake-up timer function is with an analog resistor / capacitor (RC) circuit or a current source / capacitor circuit, where the current source is used instead of the resistance of an RC circuit. If the desired timeout is very long, such as 30 minutes, the values ​​of the resistors and capacitors of an RC circuit can become very large. At large values, fluctuations in resistance and capacitance can occur, and these fluctuations can be influenced by external factors. Thus, as the resistance increases, these external factors can have an amplified effect.

[0016] Another detrimental aspect is the capacitance required to generate a long timeout. A large capacitance may require the use of an aluminum electrolytic capacitor, which can exhibit a relatively large leakage current and values ​​that vary considerably. Finally, the long timeout is achieved by small currents interacting with these components, where leakage and temperature changes typically lead to large errors. In practice, the use of only analog circuitry is difficult to achieve, as variations in tolerances are magnified by the small currents, and the available component selection may require the use of materials with low reliability.

[0017] Here, an oscillator driving a long counter chain of flip-flops (FF) divides the oscillator rate downwards to a very slow rate. By using a flip-flop chain divided by a large number (e.g., 2 24 times or 16777216), the oscillator rate can be a value that does not interfere with other electrical systems. Typically, a main timer and a backup timer are used as a redundant system so that the battery power is not depleted. For example, an RC oscillator set to 9.3 kHz and divided by 2 24 divided (using the output after the 24th flip-flop), an approximately 30-minute period, an approximately 30-minute interval, or an approximately 30-minute timeout. For example, it may be more desirable to use an output after the 19th flip-flop (so that one can have a 2 19 or 524288 division / timeout) instead of the 2 24, since the oscillator can be at a more favorable frequency. By using a chain that has 2 19 times, the oscillator may have a favorable frequency that can easily generate the required delay. While many oscillator rates and divisor combinations are applicable for this application, the 2 19 Divisor rate provides a timeout required by the backup timer. Using the 2 19 Divisors with an oscillator set to 300 Hz produces a suitable backup timer interval, but is still slow enough to produce minimal EMC effects / problems, and after dividing by 2 19 the output is 29 minutes. In another example, a 32 kHz clock crystal in combination with a 26-stage frequency divider (with a 2 26or 67108864 counter overrun) may be used to generate a timeout of approximately 35 minutes. The backup timer may use digital logic, such as a dedicated multi-stage (e.g., n-stage frequency divider) frequency divider, a programmable logic device (PLD), a programmable array logic (PAL), a generic array logic (GAL), a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or other integrated circuit that can be used to generate the timeout. In another embodiment, the backup timer may be a separate logic circuit from the processor, such that it is not implemented by a microprocessor or microcontroller.Because a microprocessor or microcontroller executes instructions stored in memory during operation, the logic circuitry separate from the processor does not execute instructions stored in memory. Similar to the use of a 32 kHz crystal, a different crystal or resonator can be used. The timer can use integrated logic blocks, such as flip-flops or inverters. Taking it further, the entire oscillator and counter chain can be found in a single IC (e.g., a 24-stage frequency divider), and in yet another embodiment, the backup timer can be implemented by a microcontroller.

[0018] The front end of this device can contain all the necessary inverters and buffers to build an oscillator from a simple resistor / capacitor (RC) network, a crystal, or a resonator. It may be useful to use a differential amplifier or other unbuffered or "raw" inverter to support oscillation (e.g., a crystal). Furthermore, the logic device can simply accept a clock signal from another source, such as another IC. The oscillator output is then fed into the flip-flop divider chain, where it is subsequently divided. For example, consider a 24-stage frequency divider IC, which typically includes outputs from stages 18 to 24, so several options can be considered. It may also be advantageous to integrate an external reset pin into the logic IC, allowing control of the start time for the timeout interval.Additionally, the reset can be used to cancel the timeout interval, such as when the main duration from the main controller shuts down the equalization or a vehicle start occurs.

[0019] Fig. 1 shows a typical plug-in hybrid-electric vehicle (PHEV) with a powertrain or powerplant that includes the major components that generate power and deliver power to the road surface for propulsion. A typical plug-in hybrid-electric vehicle 12 may include one or more electric machines 14 mechanically connected to a hybrid transmission 16. The electric machines 14 may be capable of operating as a motor or generator. Furthermore, the hybrid transmission 16 is mechanically connected to an internal combustion engine 18, also referred to as an ICE or motor. The hybrid transmission 16 is also mechanically connected to a driveshaft 20, which is mechanically connected to the wheels 22. The electric machines 14 may provide propulsion and deceleration capability when the internal combustion engine 18 is turned on or off.The electric machines 14 also function as generators and can provide fuel efficiency benefits by recovering energy that would normally be lost as heat in a friction braking system. The electric machines 14 can also reduce vehicle emissions by enabling the engine 18 to operate at more efficient speeds and, under certain conditions, enabling the hybrid electric vehicle 12 to operate in electric mode with the engine 18 off. A powertrain has losses, which can include transmission losses, motor losses, electrical conversion losses, electric machine losses, electrical component losses, and road losses. These losses can be attributed to several aspects, including fluid viscosity, electrical impedance, vehicle rolling resistance, ambient temperature, component temperature, and duration of operation.

[0020] A traction battery or battery pack 24 stores energy that can be used by the electric machines 14. A vehicle battery pack 24 typically provides a high-voltage direct current output. The traction battery 24 is electrically connected to one or more power electronics modules 26. One or more contactors 42 can isolate the traction battery 24 from other components when opened and connect the traction battery 24 to other components when closed. The power electronics module 26 is also electrically connected to the electric machines 14 and provides the capability to transfer power bidirectionally between the traction battery 24 and the electric machines 14. For example, a typical traction battery 24 may provide a direct current voltage, while the electric machines 14 may operate on three-phase alternating current.The power electronics module 26 can convert the DC voltage into a three-phase AC voltage for use by the electric machines 14. In a regeneration mode, the power electronics module 26 can convert the three-phase AC power from the electric machines 14, which function as generators, into the DC voltage compatible with the traction battery 24. The description herein applies equally to a pure electric vehicle. In a pure electric vehicle, the hybrid transmission 16 can be a gear box connected to an electric machine 14, and the internal combustion engine 18 may not be present.

[0021] In addition to providing propulsion power, the traction battery 24 can provide power to other vehicle electrical systems. A typical system may include a DC / DC converter module 28 that converts the high-voltage DC output of the traction battery 24 into a low-voltage DC supply compatible with other vehicle loads. Other high-voltage loads 46, such as compressors and electric heaters, may be directly connected to the high voltage without the use of a DC / DC converter module 28. The low-voltage systems may be electrically connected to an auxiliary battery 30 (e.g., a 12 V battery). Here, the high-voltage range refers to a number of components and modules that are substantially operated and powered by the terminal voltage of the traction battery 24.The high-voltage section includes the traction battery 24, the switch 42, the power conversion module 32, the power electronics module 26, the electric machine(s) 14, the DC / DC converter module 28, and the electrical loads 46. The high-voltage section does not include the auxiliary battery 30 and loads powered by the auxiliary battery 30. It should be noted that some modules can operate in both the high-voltage and low-voltage sections (operated and powered by the auxiliary battery 30), but the circuits and systems within these modules are separate. For example, the DC / DC converter module 28 is coupled between the high-voltage section and the auxiliary battery 30, but the DC / DC converter 28 separates the low-voltage section from the high-voltage section.The isolation is achieved by modulating IGBTs and using an inductive element of the DC / DC converter 28, so that the energy potential is essentially maintained on each side of the DC / DC converter 28. In many vehicles, the high-voltage loads within the high-voltage compartment are isolated from the low-voltage loads within the low-voltage compartment, so that modules in each compartment communicate via optocouplers, transformers, wireless transceivers, or other techniques for communication across isolation.

[0022] In some vehicles, the auxiliary battery 30 and the low-voltage section are galvanically isolated from the high-voltage section, with no DC / DC converter 28 present, but instead the low-voltage section is powered by an alternator coupled to the engine 18, and the electric machine(s) 14 are powered by the traction battery 24. In this type of system, modules can communicate via optocouplers, transformers, wireless transceivers, or other techniques for communicating across isolation.

[0023] The vehicle 12 may be an electric vehicle or a plug-in hybrid vehicle in which the traction battery 24 may be charged by an external power source 36. The external power source 36 may be a connection to an electrical outlet that receives power from an electric utility. The external power source 36 may be electrically connected to an electric vehicle supply equipment (EVSE) 38. The EVSE 38 may provide circuitry and controls to regulate and manage the transfer of energy between the power source 36 and the vehicle 12. The external power source 36 may provide electrical power to the EVSE 38 as direct current or alternating current. The EVSE 38 may include a charging connector 40 for plugging into a charging port 34 of the vehicle 12.The charging port 34 may be any type of port configured to transfer power from the EVSE 38 to the vehicle 12. The charging port 34 may be electrically connected to a charging station or an on-board power conversion module 32. The power conversion module 32 may condition the power supplied by the EVSE 38 to provide the proper voltage and current levels to the traction battery 24. The power conversion module 32 may interface with the EVSE 38 to coordinate the delivery of power to the vehicle 12. The EVSE connector 40 may have pins that mate with corresponding recesses of the charging port 34. Alternatively, various components described as being electrically connected may transfer power using wireless inductive coupling.

[0024] One or more wheel brakes 44 may be provided to decelerate the vehicle 12 and prevent movement of the vehicle 12. The wheel brakes 44 may be hydraulically actuated, electrically actuated, or a combination thereof. The wheel brakes 44 may be part of a braking system 50. The braking system 50 may include other components for operating the wheel brakes 44. For simplicity, the figure depicts a single connection between the braking system 50 and one of the wheel brakes 44. A connection between the braking system 50 and the other wheel brakes 44 is implied. The braking system 50 may include a controller for monitoring and coordinating the braking system 50. The braking system 50 may monitor the braking components and control the wheel brakes 44 to decelerate the vehicle. The braking system 50 may respond to driver commands and may also operate autonomously to implement features such as stability control.The control of the braking system 50 may implement a method for applying a requested braking force when requested by another control or sub-function.

[0025] One or more electrical loads 46 or additional electrical loads may be connected to the high-voltage bus. The electrical loads 46 may have an associated controller that operates and controls the electrical loads 46, if appropriate. Examples of additional electrical loads or electrical loads 46 include a battery cooling fan, an electric air conditioning unit, a battery cooler, an electric heater, a cooling pump, a cooling fan, a windshield defroster unit, an electric power steering system, an AC inverter, and an engine water pump.

[0026] The various components discussed may have one or more associated controllers to control and monitor the operation of the components. The controllers may communicate via a serial bus (e.g., a Controller Area Network (CAN), Ethernet, Flexray) or via separate conductors. A system controller 48 may be present to coordinate the operation of the various components.

[0027] A traction battery 24 can be constructed from a variety of chemical formulations. Typical battery pack chemistries can be lead-acid, nickel-metal hydride (NiMH), or lithium-ion. Fig. 2 shows a typical traction battery pack 24 in a series configuration of N battery cells 72. However, other battery packs 24 may consist of any number of individual battery cells connected in series or parallel, or a combination thereof. A battery management system may include one or more controllers, such as a battery energy control module (BECM) 76, that monitors and controls the performance of the traction battery 24. The BECM 76 may include sensors and circuitry to monitor several battery pack level characteristics, such as pack current 78, pack voltage 80, and pack temperature 82. The BECM 76 may include non-volatile memory so that data may be stored when the BECM 76 is in a powered-off state. Stored data may be available at the next ignition cycle.

[0028] In addition to the pack level characteristics, there may be level characteristics of the battery cells that are measured and monitored. For example, the terminal voltage, current, and temperature of each cell 72 may be measured. The battery management system may use a sensor module 74 to measure the characteristics of the battery cells. Depending on their capabilities, the sensor modules 74 may include sensors and circuitry to measure the characteristics of one or more of the battery cells 72. The battery management system may measure up to N cSensor modules 74, such as a battery monitoring integrated circuit (BMIC) module, may be used to measure the characteristics of all battery cells 72. Each of the sensor modules 74 may transmit the measured values ​​to the BECM 76 for further processing and coordination. The sensor module 74 may transmit signals in analog or digital form to the BECM 76. In some embodiments, the functionality of the sensor module 74 may be integrated internally into the BECM 76. That is, the sensor module hardware may be integrated into the BECM 76 as part of the circuitry, and the BECM 76 may handle the processing of raw signals.

[0029] The BECM 76 may include circuitry for interfacing with the one or more contactors 42. The positive and negative terminals of the traction battery 24 may be protected by the contactors 42.

[0030] The battery pack state of charge (SOC) indicates how much charge remains in the battery cells 72 or the battery pack 24. The battery pack SOC may be output to inform the driver, similar to a fuel gauge, how much charge remains in the battery pack 24. The battery pack SOC may also be used to control the operation of an electric or hybrid electric vehicle 12. Calculating the battery pack SOC may be accomplished by a variety of methods. One possible method for calculating the battery SOC is to perform an integration of the battery pack current over time. This is well known in the art as ampere-hour integration.

[0031] The BECM 76 can have power available at all times. The BECM 76 can include a wake-up timer so that a wake-up can be scheduled at any time. The wake-up timer can wake the BECM 76 so that predetermined functions can be performed. The BECM 76 can include non-volatile memory so that data can be saved when the BECM 76 is turned off or loses power. The non-volatile memory can include electrically erasable programmable read-only memory (EEPROM) or non-volatile random access memory (NVRAM). The non-volatile memory can include a microcontroller's FLASH memory.

[0032] When the vehicle is operating, actively modifying how the battery's SOC is managed can yield greater fuel efficiency, longer operation in EV mode (electric propulsion), or both. The vehicle controller must make these modifications at both high SOC and low SOC. At low SOC, the controller can review recent operating data and decide to increase the SOC via opportunistic engine charging (opportunistic means doing this when the engine is already running). This is done to provide longer operation in EV mode when the engine is off. Conversely, at high SOC, the controller can review recent operating data and other data (location, temperature, etc.) to decide to reduce the SOC via EV mode propulsion, reduced engine output, or additional electrical loads.This is done to provide higher battery capacity to maximize energy capture during an anticipated regenerative braking event, such as high-speed deceleration or downhill driving.

[0033] Fig.3 is an exemplary schematic diagram illustrating a timer for a charge balancing circuit 300. A timer logic circuit 302 may use an oscillator, such as a crystal, a resonator, or resistor / capacitor (RC), to generate a reference clock. In this illustration, resistor 304, capacitor 306, and resistor 308 form the RC feedback oscillator circuit. Although this illustration shows an RC oscillator, the circuit 300 may use a crystal, a crystal oscillator, a resonator, or other clock generator. The first resistor 304 is coupled between a first input and both the capacitor 306 and the feedback resistor 308.The other lead of capacitor 306 is coupled to a first output, which is a buffered version of the input, and to a second input. The second output is an inverted output of the second input. Feedback resistor 308 and capacitor 306 set the clock rate. Once the oscillations start, the oscillations propagate through a series of flip-flops (e.g., latches) to reduce the switching rate by a factor of 2. For example, 2. n, where n is the number of flip-flops in the counter chain. Furthermore, the circuit may include a first control input 310 and a second control input 312. The first control input 310 may be an enable input and the second input 312 may be a reset input. After propagation through the flip-flops of the logic circuit 302, one or more outputs (314) may be used to provide a signal based on the time rate. Here, an 18th output 314A switches on at a 2 18 time base. Similarly, a 19th output 314B switches at 2 19 to, a 20th output 314C switches at 2 21 a 22nd output 314D switches at 2 22 a 23rd output 314E switches at 2 23 a 24th output 314F switches at 2 24 and a 25th output 314G switches at 2 25The logic circuit 302 uses a chain of 24 flip-flops to generate the time base, but the flip-flop chain can be longer or shorter depending on the battery chemistry and system design.

[0034] The processes, methods, or algorithms disclosed herein may be implementable by / deliverable to a processing device, controller, or computer, which may include any pre-existing programmable electronic control unit or dedicated electronic control unit. Similarly, the processes, methods, or algorithms may be stored as data and instructions executable by a controller or computer in many forms, including, but not limited to, information permanently stored on non-writable storage media, such as read-only devices, and information modifiably stored on writable storage media, such as floppy disks, magnetic tapes, compact discs, random access memory devices, and other magnetic and optical media. The processes, methods, and algorithms may further be implemented in a software-executable object.Alternatively, the processes, methods, or algorithms may be implemented in whole or in part using suitable hardware components, such as application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), state machines, controllers, or other hardware components or devices, or a combination of hardware, software, and firmware components.

[0035] Although exemplary embodiments are described above, these embodiments are not intended to describe all possible forms encompassed by the claims. Instead, 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 disclosure. As described above, the features of various embodiments may be combined to form further embodiments of the invention that may not be explicitly described or illustrated.While various embodiments may be described as advantageous or preferred over other prior art embodiments or implementations with respect to one or more desired characteristics, one of ordinary skill in the art will recognize that one or more features or characteristics may be compromised to achieve the desired overall system attributes, depending on the particular application and implementation. These attributes include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, maintainability, weight, manufacturability, ease of assembly, etc. Therefore, embodiments described as less desirable than other prior art embodiments or implementations with respect to one or more characteristics are not outside the scope of the disclosure and may be desirable for certain applications.

Claims

[1] Battery system comprising: a traction battery supplying a high-voltage range; a traction battery controller powered by a low-voltage range separate from the high-voltage range and configured to deactivate cell balancing of the traction battery after a main timer has expired; and a backup controller powered by and within the high voltage range, implementing a backup timer including logic circuitry separate from the processor, and configured to disable cell balancing upon expiration of the backup timer. [2] The battery system of claim 1, wherein the logic circuit separate from the processor includes a chain of flip-flops. [3] The battery system of claim 1, wherein the logic circuit separate from the processor is an n-stage frequency divider where n is greater than 20. [4] The battery system of claim 1, wherein the logic circuit separate from the processor is a digital timer. [5] The battery system of claim 1, wherein the backup timer further includes an oscillator. [6] The battery system of claim 5, wherein the oscillator includes a quartz or a resonator. [7] The battery system of claim 5, wherein the oscillator is coupled to a differential input operational amplifier of the logic circuit separate from the processor. [8] The battery system of claim 5, wherein the oscillator oscillates at a rate less than 1 MHz. [9] The battery system of claim 5, wherein the oscillator is a 32 kHz crystal. [10] Battery system comprising: a traction battery that sources a high voltage range; a traction battery controller galvanically isolated from the high-voltage region and configured to prevent cell balancing of the traction battery after a timeout period; and a backup timer powered by and within the high voltage range, including an oscillator and digital logic and configured to prevent cell balancing of the traction battery after a backup duration longer than the timeout duration. [11] The battery system of claim 10, wherein the digital logic includes a chain of flip-flops. [12] The battery system of claim 10, wherein the oscillator includes a quartz crystal or a resonator. [13] The battery system of claim 10, wherein the oscillator is coupled to a differential input operational amplifier of the digital logic. [14] The battery system of claim 10, wherein the digital logic is an n-stage frequency divider where n is greater than 20. [15] The battery system of claim 10, wherein the digital logic is a microcontroller, a programmable logic device (PLD), a field programmable gate array (FPGA), a programmable array logic (PAL), or a generic array logic (GAL).

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