Methods and apparatus for battery cell management

Abstract

A battery cell management system configured for use with a battery pack is provided and comprises a plurality of battery cells connected to a primary winding of a transformer, an auxiliary battery, and a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

Description

METHODS AND APPARATUS FOR BATTERY CELL MANAGEMENTBACKGROUND1. Field of the Disclosure

[0001] Embodiments of the present disclosure generally relate to power systems and, for example, to methods and apparatus for battery cell management.2. Description of the Related Art

[0002] Conventional storage systems comprise one or more batteries that can be coupled to one or more microinverters. For example, the one or more batteries can comprise one or more lithium ferrophosphate (LFP) batteries. While the LFP batteries are suitable fortheir intended purposes, overtime voltage variances can lead to safety issues near the LFP battery end points. Additionally, over time capacity erosion can lead to reduced LFP battery capacity, and capacity erosion variations can lead to shortened lifetime of the entire battery pack in which the LFP battery can be installed. With respect to capacity erosion, which is a function of many factors (e.g., C-rate, temperature, etc.) and is proportional to Coulomb or Ampere-hour (Ah) throughput, the more the throughput, the greater the erosion of capacity. Additionally, weak cells of the battery pack tend to erode faster than strong cells of the battery pack.

[0003] Conventional methods and apparatus can use passive cell balancing (or dissipative) or active cell balancing (or non-dissipative) for cell management to reduce the effects of voltage variances and / or capacity erosion. Such methods, however, are limited in at least one of providing safety, maximizing battery pack capacity, and maximizing battery pack life. For example, during dormant periods of a battery pack (e.g., during storage of the battery pack), the conventional methods are not configured to provide cell management, as the controllers that are configured to perform cell management are not provided with power.

[0004] Therefore, the inventors have provided herein improved methods and apparatus methods and apparatus for battery cell management.SUMMARY

[0005] In accordance with some aspects of the present disclosure, there is provided a battery cell management system configured for use with a battery pack.The battery cell management system comprises a plurality of battery cells connected to a primary winding of a transformer, an auxiliary battery, and a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

[0006] In accordance with some aspects of the present disclosure, there is provided a method for controlling a battery cell management system configured for use with a battery pack. The method comprises periodically determining a state-of- charge of a plurality of battery cells connected to a primary winding of a transformer and based on a determined state-of-charge of the plurality of battery cells, providing power from an auxiliary battery to a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

[0007] In accordance with some aspects of the present disclosure, there is provided a non-transitory computer readable storage medium having instructions stored thereon that when executed by a process perform a method for controlling a battery cell management system configured for use with a battery pack. The method comprises periodically determining a state-of-charge of a plurality of battery cells connected to a primary winding of a transformer and based on a determined state-of- charge of the plurality of battery cells, providing power from an auxiliary battery to a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

[0008] Various advantages, aspects, and novel features of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.BRIEF DESCRIPTION OF THE DRAWINGS

[0009] So that the manner in which the above recited features of the present disclosure can be understood in detail, a more particular description of the disclosure, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only a typical embodiment of this disclosure and are therefore not to be considered limiting of its scope, for the disclosure may admit to other equally effective embodiments.

[0010] Figure 1 is a block diagram of a system for power conversion, in accordance with at least some embodiments of the present disclosure;

[0011] Figure 2 is a block diagram of an AC battery system, in accordance with at least some embodiments of the present disclosure;

[0012] Figure 3 is a schematic diagram of an apparatus configured for use with the AC battery system of Figure 2, in accordance with at least some embodiments of the present disclosure; and

[0013] Figure 4 is a flowchart of a method for controlling a battery cell management system configured for use with a battery pack, in accordance with at least some embodiments of the present disclosure.DETAILED DESCRIPTION

[0014] In accordance with the present disclosure, provided herein are improved methods and apparatus for battery cell management. For example, a battery cell management system can be configured for use with a battery pack and comprises a plurality of battery cells connected to a primary winding of a transformer and an auxiliary battery comprising one or more battery cells. A DC to DC converter comprises an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system, which can be especially useful, for example, when the battery pack is in a dormant state. The methods and apparatus described provide an intelligent, cost effective wayof managing battery cells of a battery pack, e.g., when the battery pack is in a dormant state.

[0015] Figure 1 is a block diagram of a system 100 (energy management system) for power conversion using one or more embodiments of the present disclosure. This diagram only portrays one variation of the myriad of possible system configurations and devices that may utilize the present disclosure.

[0016] The system 100 is a microgrid that can operate in both an islanded state and in a grid-connected state (i.e., when connected to another power grid (such as one or more other microgrids and / or a commercial power grid). The system 100 comprises a plurality of power converters 102-1 , 102-2, ... ,102-N, 102-N+1 , and 102- N+M collectively referred to as power converters 102 (which also may be called power conditioners); a plurality of DC power sources 104-1 , 104-2, ... ,104-N, collectively referred to as power sources 104 (e.g., resources); a plurality of energy storage devices / delivery devices 120-1 , 120-2, ....120-M collectively referred to as energy storage / delivery devices 120; a system controller 106; a plurality of BMlls 190-1 , 190- 2, ... ,190-M (battery management units) collectively referred to as BMlls 190; a system controller 106; a bus 108; a load center 110; and an HD 140 (island interconnect device) (which may also be referred to as a microgrid interconnect device (MID)). In some embodiments, such as the embodiments described herein, the energy storage / delivery devices are rechargeable batteries (e.g., multi-C-rate collection of AC batteries) which may be referred to as batteries 120, although in other embodiments the energy storage / delivery devices may be any other suitable device for storing energy and providing the stored energy. Generally, each of the batteries 120 comprises a plurality cells that are coupled in series, e.g., two or more cells in series to form a battery 120.

[0017] Each power converter 102-1 , 102-2....102-N is coupled to a DC power source 104-1 , 104-2... ,104-N, respectively, in a one-to-one correspondence, although in some other embodiments multiple DC power sources may be coupled to one or more of the power converters 102. The power converters 102-N+1 , 102-N+2... 102- N+M are respectively coupled to plurality of energy storage devices / delivery devices 120-1 , 120-2... 120-M via BMUs 190-1 , 190-2.. ,190-M to form AC batteries 180-1 , 180-2. ,.180-M, respectively. Each of the power converters 102-1 , 102-2. ,.102-N+Mcomprises a corresponding controller 114-1 , 114-2...114-N+M (collectively referred to as the inverter controllers 114) for controlling operation of the power converters 102- 1 , 102-2. ,.102-N+M.

[0018] In some embodiments, such as the embodiment described below, the DC power sources 104 are DC power sources and the power converters 102 are bidirectional inverters such that the power converters 102-1 ...102-N convert DC power from the DC power sources 104 to grid-compliant AC power that is coupled to the bus 108, and the power converters 102-N+1. ,.102-N+M convert (during energy storage device discharge) DC power from the batteries 120 to grid-compliant AC power that is coupled to the bus 108 and also convert (during energy storage device charging) AC power from the bus 108 to DC output that is stored in the batteries 120 for subsequent use. The DC power sources 104 may be any suitable DC source, such as an output from a previous power conversion stage, a battery, a renewable energy source (e.g., a solar panel or photovoltaic (PV) module, a wind turbine, a hydroelectric system, or similar renewable energy source), or the like, for providing DC power. In other embodiments the power converters 102 may be other types of converters (such as DC-DC converters), and the bus 108 is a DC power bus.

[0019] The power converters 102 are coupled to the system controller 106 via the bus 108 (which also may be referred to as an AC line or a grid). The system controller 106 generally comprises a CPU coupled to each of support circuits and a memory that comprises a system control module for controlling some operational aspects of the system 100 and / or monitoring the system 100 (e.g., issuing certain command and control instructions to one or more of the power converters 102, collecting data related to the performance of the power converters 102, and the like). The system controller 106 is capable of communicating with the power converters 102 by wireless and / or wired communication (e.g., power line communication) for providing certain operative control and / or monitoring of the power converters 102.

[0020] In some embodiments, the system controller 106 may be a gateway that receives data (e.g., performance data) from the power converters 102 and communicates (e.g., via the Internet) the data and / or other information to a remote device or system, such as a master controller (not shown). Additionally or alternatively, the gateway may receive information from a remote device or system(not shown) and may communicate the information to the power converters 102 and / or use the information to generate control commands that are issued to the power converters 102.

[0021] The power converters 102 are coupled to the load center 110 via the bus 108, and the load center 110 is coupled to the power grid via the HD 140. When coupled to the power grid (e.g., a commercial grid or a larger microgrid) via the 11 D 140, the system 100 may be referred to as grid-connected; when disconnected from the power grid via the II D 140, the system 100 may be referred to as islanded. The II D 140 determines when to disconnect from / connect to the power grid (e.g., the IID 140 may detect a grid fluctuation, disturbance, outage or the like) and performs the disconnection / connection. Once disconnected from the power grid, the system 100 can continue to generate power as an intentional island, without imposing safety risks on any line workers that may be working on the grid, using the droop control techniques described herein. The IID 140 comprises a disconnect component (e.g., a disconnect relay) for physically disconnecting / connecting the system 100 from / to the power grid. In some embodiments, the HD 140 may additionally comprise an autoformer for coupling the system 100 to a split-phase load that may have a misbalance in it with some neutral current. In certain embodiments, the system controller 106 comprises the HD 140 or a portion of the HD 140.

[0022] The power converters 102 convert the DC power from the DC power sources 104 and discharge the batteries 120 to grid-compliant AC power and couple the generated output power to the load center 110 via the bus 108. The power is then distributed to one or more loads (for example to one or more appliances) and / or to the power grid (when connected to the power grid). Additionally or alternatively, the generated energy may be stored for later use, for example using batteries, heated water, hydro pumping, HsO-to-hydrogen conversion, or the like. Generally, the system 100 is coupled to the commercial power grid, although in some embodiments the system 100 is completely separate from the commercial grid and operates as an independent microgrid.

[0023] In some embodiments, the AC power generated by the power converters 102 is single-phase AC power. In other embodiments, the power converters 102 generate three-phase AC power.

[0024] A storage system configured for use with an energy management system, such as the Enphase® Energy System, is described herein. For example, Figure 2 is a block diagram of an AC battery system 200 (e.g., a storage system) in accordance with one or more embodiments of the present disclosure.

[0025] The AC battery system 200 comprises a BMU 190 coupled to a battery (e.g., the battery 120) and one or more inverters (e.g., the power converters 102). In at least some embodiments, the battery 120 can comprise a plurality of cells (not shown) and the power converters 102 can comprise four embedded converters (e.g., four embedded microinverters). In at least some embodiments, the battery 120 can be the IQ Battery 3 (or the IQ Battery 10) and the microinverters can be the IQ8X-BAT microinverters, both available from Enphase®. A pair of metal-oxide-se mi conductor field-effect transistors (MOSFETs) switches - switches 228 and 230 - are coupled in series between a first terminal 240 of the battery 120 and a first terminal of the inverter 144 such the body diode cathode terminal of the switch 228 is coupled to the first terminal 240 of the battery 120 and the body diode cathode terminal of the switch 230 is coupled to the first terminal 244 of the power converter 102. The gate terminals of the switches 228 and 230 are coupled to the BMU 190.

[0026] A second terminal 242 of the battery 120 is coupled to a second terminal 246 of the power converter 102 via a current measurement module 226 which measures the current flowing between the battery 120 and the power converter 102.

[0027] The BMU 190 is coupled to the current measurement module 226 for receiving information on the measured current, and also receives an input 224 from the battery 120 indicating the battery cell voltage and temperature. The BMU 190 is coupled to the gate terminals of each of the switches 228 and 230 for driving the switch 228 to control battery discharge and driving the switch 230 to control battery charge as described herein. The BMU 190 is also coupled across the first terminal 244 and the second terminal 246 for providing an inverter bias control voltage (which may also be referred to as a bias control voltage) to the inverter 102 as described further below.

[0028] The configuration of the body diodes of the switches 228 and 230 allows current to be blocked in one direction but not the other depending on state of each of the switches 228 and 230. When the switch 228 is active (i.e., on) while the switch230 is inactive (i.e. , off), battery discharge is enabled to allow current to flow from the battery 120 to the power converter 102 through the body diode of the switch 230. When the switch 228 is inactive while the switch 230 is active, battery charge is enabled to allow current flow from the power converter 102 to the battery 120 through the body diode of the switch 228. When both switches 228 and 230 are active, the system is in a normal mode where the battery 120 can be charged or discharged.

[0029] The BMU 190 comprises support circuits 204 and a memory 206 (e.g., non- transitory computer readable storage medium), each coupled to a CPU 202 (central processing unit). The CPU 202 may comprise one or more processors, microprocessors, microcontrollers and combinations thereof configured to execute non-transient software instructions to perform various tasks in accordance with embodiments of the present disclosure. The CPU 202 may additionally or alternatively include one or more application specific integrated circuits (ASICs). In some embodiments, the CPU 202 may be a microcontroller comprising internal memory for storing controller firmware that, when executed, provides the controller functionality described herein. The BMU 190 may be implemented using a general purpose computer that, when executing particular software, becomes a specific purpose computer for performing various embodiments of the present disclosure.

[0030] The support circuits 204 are well known circuits used to promote functionality of the CPU 202. Such circuits include, but are not limited to, a cache, power supplies, clock circuits, buses, input / output (l / O) circuits, and the like. The BMU 190 may be implemented using a general purpose computer that, when executing particular software, becomes a specific purpose computer for performing various embodiments of the present disclosure. In one or more embodiments, the CPU 202 may be a microcontroller comprising internal memory for storing controller firmware that, when executed, provides the controller functionality described herein.

[0031] The memory 206 may comprise random access memory, read only memory, removable disk memory, flash memory, and various combinations of these types of memory. The memory 206 is sometimes referred to as main memory and may, in part, be used as cache memory or buffer memory. The memory 206 generally stores the OS 208 (operating system), if necessary, of the inverter controller 114 that can be supported by the CPU capabilities. In some embodiments, the OS 208 maybe one of a number of commercially available operating systems such as, but not limited to, LINUX, Real-Time Operating System (RTOS), and the like.

[0032] The memory 206 stores non-transient processor-executable instructions and / or data that may be executed by and / or used by the CPU 202 to perform, for example, one or more methods for discharge protection, as described in greater detail below. These processor-executable instructions may comprise firmware, software, and the like, or some combination thereof. The memory 206 stores various forms of application software, such as an acquisition system module 210, a switch control module 212, a control system module 214, and an inverter bias control module 216. The memory 206 additionally stores a database 218 for storing data related to the operation of the BMU 190 and / or the present disclosure, such as one or more thresholds, equations, formulas, curves, and / or algorithms for the control techniques described herein. In various embodiments, one or more of the acquisition system module 210, the switch control module 212, the control system module 214, the inverter bias control module 216, and the database 218, or portions thereof, are implemented in software, firmware, hardware, or a combination thereof.

[0033] The acquisition system module 210 obtains the cell voltage and temperature information from the battery 120 via the input 224, obtains the current measurements provided by the current measurement module 226, and provides the cell voltage, cell temperature, and measured current information to the control system module 214 for use as described herein.

[0034] The switch control module 212 drives the switches 228 and 230 as determined by the control system module 214. The control system module 214 provides various battery management functions, including protection functions (e.g., overcurrent (OC) protection, overtemperature (OT) protection, and hardware fault protection), metrology functions (e.g., averaging measured battery cell voltage and battery current over, for example, 100 ms to reject 50 and 60 Hz ripple), state of charge (SoC) analysis (e.g., coulomb gauge 250 for determining current flow and utilizing the current flow in estimating the battery SoC; synchronizing estimated SOC values to battery voltages (such as setting SoC to an upper bound, such as 100%, at maximum battery voltage; setting SoC to a lower bound, such as 0%, at a minimum battery voltage); turning off SoC if the power converter 102 never drives the battery120 to these limits; and the like), cell balancing (e.g., autonomously balancing the charge across all cells of a battery to be equal, which may be done at the end of charge, at the end of discharge, or in some embodiments both at the end of charge and the end of discharge). By establishing upper and lower estimated SoC bounds based on battery end of charge and end of discharge, respectively, and tracking the current flow and cell voltage (i.e., battery voltage) between these events, the BMU 190 determines the estimated SoC.

[0035] Continuing with reference to Figure 2, the inverter controller 1 14 comprises support circuits 254 and a memory 256, each coupled to a CPU 252 (central processing unit). The CPU 252 may comprise one or more processors, microprocessors, microcontrollers and combinations thereof configured to execute non-transient software instructions to perform various tasks in accordance with embodiments of the present disclosure. The CPU 252 may additionally or alternatively include one or more application specific integrated circuits (ASICs). In some embodiments, the CPU 252 may be a microcontroller comprising internal memory for storing controller firmware that, when executed, provides the controller functionality herein. The inverter controller 114 may be implemented using a general purpose computer that, when executing particular software, becomes a specific purpose computer for performing various embodiments of the present disclosure.

[0036] The support circuits 254 are well known circuits used to promote functionality of the CPU 252. Such circuits include, but are not limited to, a cache, power supplies, clock circuits, buses, input / output (I / O) circuits, and the like. The inverter controller 114 may be implemented using a general purpose computer that, when executing particular software, becomes a specific purpose computer for performing various embodiments of the present disclosure. In one or more embodiments, the CPU 252 may be a microcontroller comprising internal memory for storing controller firmware that, when executed, provides the controller functionality described herein.

[0037] The memory 256 may comprise random access memory, read only memory, removable disk memory, flash memory, and various combinations of these types of memory. The memory 256 is sometimes referred to as main memory and may, in part, be used as cache memory or buffer memory. The memory 256 generallystores the OS 258 (operating system), if necessary, of the inverter controller 114 that can be supported by the CPU capabilities. In some embodiments, the OS 258 may be one of a number of commercially available operating systems such as, but not limited to, LINUX, Real-Time Operating System (RTOS), and the like.

[0038] The memory 256 stores non-transient processor-executable instructions and / or data that may be executed by and / or used by the CPU 252. These processorexecutable instructions may comprise firmware, software, and the like, or some combination thereof. The memory 256 stores various forms of application software, such as a power conversion control module 270 for controlling the bidirectional power conversion, and a battery management control module 272.

[0039] Figure 3 is a schematic diagram of an apparatus 300 (e.g., a battery cell management system) configured for use with the AC battery system of Figure 2, and Figure 4 is flowchart of a method 400 for controlling a battery cell management system configured for use with a battery pack, in accordance with at least some embodiments of the present disclosure. For example, the control system module 214 of the BMU 190 is configured to perform balancing of the individual battery cells of the batteries 120 using one or more cell balancing techniques, e.g., passive (or dissipative) cell balancing methods (e.g., a passive battery cell management system) and / or active (or non-dissipative) cell balancing methods (e.g., an active battery cell management system.

[0040] The passive (or dissipative) cell balancing methods use a cell balancing controller that is configured to remove energy from a battery cell (over-charged) by turning on a FET connected to the battery cell. In doing so, energy in the battery cell is dissipated in the form of heat through a resistor that is connected between the battery cell and the FET.

[0041] Likewise, the active (or non-dissipative) cell balancing methods use a cell balancing controller that is configured to remove energy from a battery cell (overcharged) by turning on a FET connected to the battery cell and causing energy to flow from that battery cell to a non-dissipative element such as and inductor or capacitor and then turning on another FET connected to another battery cell (under-charged) which allows the energy in the inductor or capacitor to be transferred to the receivingcell. In doing so, energy in the battery cell is moved from the overcharged battery cell to the under-charged battery cell.

[0042] Continuing with reference to Figure 3, the apparatus 300 can comprise one or more FETS 302 that are coupled to corresponding battery cells 301 (e.g., four battery cells). In at least some embodiments, depending on a control method, one or more FETs may be needed in an anti-series connection to block current in both directions when the FET is off or open. Alternatively, in at least some embodiments, a single FET can be used, e.g., when current can flow through the body diode even when the FET is off. In the illustrated embodiment, two FETS are shown. Each of the FETS 302 and corresponding battery cells 301 are coupled to a primary winding 303 (a respective primary winding, four primary windings are shown connected in series to each other) that are coupled to a secondary windings 305 (e.g., a common secondary winding) of a transformer 306. In operation, during discharging, the cell balancing controller (e.g., the control system module 214) turns on one or more of the FETS of the one or more battery cells that need to be discharged (e.g., remove excess energy), and the remaining FETS are kept open. This process transfers energy from the targeted battery cell and stores the energy in a core of the transformer 306. After a sufficient period of time, the closed FET is opened on the primary and the secondary FET(s) is closed allowing the energy in the transformer to flow into the load. Thus, the excess energy from the one or more battery cells is routed thru the controlled FET(S), to the primary winding 303, to the secondary winding 305, and to a corresponding load. Similarly, during charging, the cell balancing controller turns on a main FET 308, extracts energy from the charging source and stores that energy in the core of the transformer 306. After a period of time, the main FET 308 is opened and one or more of the FETS of the one or more battery cells that need to be charged are closed, while the remaining FETS are kept open. Additionally, during charging, a main FET 308 is turned on to allow energy from a power source (e.g., the DC power sources 104, another battery system, a portable energy system (PES), etc.) to be routed to the secondary winding 305, to the primary winding 303, thru the turned on FETS, and to the battery cells. In at least some embodiments, the active (or non- dissipative) cell balancing methods are configured such during a charging cycle, stronger cells 310 are charged differently than weaker cells 312 from the chargingsource since they have a larger capacity than the weaker cells 312. As noted above, improved methods and apparatus for battery cell management are described herein. For example, at 402, the method 400 can comprise periodically determining a state- of-charge of a plurality of battery cells connected to a primary winding of a transformer. Next, at 404, the method 400 can comprise based on a determined state-of-charge of the plurality of battery cells, providing power from an auxiliary battery to a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system. For example, an auxiliary battery 314 can comprise FETS 302 that are coupled across the transformer 306 (e.g., opposite the primary winding 303) and one or more battery cells. In the illustrated embodiment, the auxiliary battery 314 is shown comprising one battery cell 315, which can be configured similarly to the corresponding battery cells 301 . Unlike the corresponding battery cells 301 , however, the battery cell 315 is not configured to be connected to the secondary winding 305 of the transformer 306, i.e., the battery cell 315 is not configured to top up the strong battery cells as described above. In at least some embodiments, the battery cell 315 can be charged from the charging source (e.g., the DC power sources 104) or from one or more of the corresponding battery cells 301 in the battery pack.

[0043] In at least some embodiments, the auxiliary battery 314 can be a component of the battery pack. Alternatively, the auxiliary battery 314 can be a separate component from the battery pack and can be configured to connect to the battery pack.

[0044] A DC to DC converter 316 comprises an input connected to an output of the auxiliary battery 314 and an output connected to a controller (e.g., the control system module 214) for providing power from the auxiliary battery 314 to the controller to drive the battery cell management system, especially when the battery pack is in a dormant state. For example, when the battery pack is being stored, the auxiliary battery 314 is configured to provide power, as needed to the DC to DC converter. The DC to DC converter can be, for example, a converter which uses very low power to power a battery management system that periodically (e.g., once per month) wakes up and evaluates the state of charge of each of the battery cells in the battery pack. Thus, ifany of the battery cells are significantly out of balance, the auxiliary battery cell and the DC to DC converter can provide power to one or more of the above-mentioned battery cell management systems to redistribute energy between the battery cells of the battery pack to re-stablish a balanced series of battery cells.

[0045] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

CLAIMS:

1. A battery cell management system configured for use with a battery pack, comprising: a plurality of battery cells connected to a primary winding of a transformer; an auxiliary battery comprising one or more battery cells; and a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

2. The battery cell management system of claim 1 , wherein the battery cell management system is at least one of a passive battery cell management system or an active battery cell management system.

3. The battery cell management system of claim 1 , wherein the auxiliary battery is charged from at least one of a charging source or from at least one of the plurality.

4. The battery cell management system of claim 1 , wherein to drive the battery cell management system, when the battery pack is in a dormant state.

5. The battery cell management system of claim 1 , wherein the auxiliary battery is not configured to be connected to a secondary winding of the transformer.

6. The battery cell management system as in any of claims 1 to 5, wherein the auxiliary battery comprises one battery cell.

7. A method for controlling a battery cell management system configured for use with a battery pack, comprising: periodically determining a state-of-charge of a plurality of battery cells connected to a primary winding of a transformer; andbased on a determined state-of-charge of the plurality of battery cells, providing power from an auxiliary battery, which comprises one or more battery cells, to a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system for providing power from the auxiliary battery to the controller to drive the battery cell management system.

8. The method of claim 7, wherein the battery cell management system is at least one of a passive battery cell management system or an active battery cell management system.

9. The method of claim 7, wherein the auxiliary battery is charged from at least one of a charging source or from at least one of the plurality.

10. The method of claim 7, wherein to drive the battery cell management system, when the battery pack is in a dormant state.

11. The method of claim 7, wherein the auxiliary battery is not configured to be connected to a secondary winding of the transformer.

12. The method as in any of claims 7 to 11 , wherein the auxiliary battery comprises one battery cell.

13. A non-transitory computer readable storage medium having instructions stored thereon that when executed by a process perform a method for controlling a battery cell management system configured for use with a battery pack, comprising: periodically determining a state-of-charge of a plurality of battery cells connected to a primary winding of a transformer; and based on a determined state-of-charge of the plurality of battery cells, providing power from an auxiliary battery, which comprises one or more battery cells, to a DC to DC converter comprising an input connected to an output of the auxiliary battery and an output connected to a controller of the battery cell management system forproviding power from the auxiliary battery to the controller to drive the battery cell management system.

14. The non-transitory computer readable storage medium of claim 13, wherein the battery cell management system is at least one of a passive battery cell management system or an active battery cell management system.

15. The non-transitory computer readable storage medium of claim 13, wherein the auxiliary battery is charged from at least one of a charging source or from at least one of the plurality.

16. The non-transitory computer readable storage medium of claim 13, wherein to drive the battery cell management system, when the battery pack is in a dormant state.

17. The non-transitory computer readable storage medium of claim 13, wherein the auxiliary battery is not configured to be connected to a secondary winding of the transformer.

18. The non-transitory computer readable storage medium as in any of claims 13 to 17, wherein the auxiliary battery comprises one battery cell.

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