Battery power system with alternating current self-heating mode

Abstract

A battery power system with an alternating current self-heating mode is disclosed. A battery power system includes an inverter connected to a battery pack and a direct current (DC) voltage bus, first and second electrical switches, and a battery controller. The first switch is connected between the inverter and the battery pack and is open during an alternating current (AC) self-heating mode of the battery pack. The mode includes generating, via an inverter, an AC waveform that passes through the battery pack at a controlled amplitude. A second switch connected to the inverter and the first switch is closed during the self-heating mode. The controller, in response to a calibrated entry criterion, opens the first switch, closes the second switch, and controls a conduction state of on / off of the power switch to self-heat the battery pack using the AC waveform. The entry criterion includes a required charging of the battery pack when the temperature of the battery pack is below a calibrated temperature limit.

Description

Technical Field

[0001] The present disclosure relates to circuit topologies and computer-based methods for heating electrochemical batteries. More specifically, aspects of the present disclosure relate to automatic self-heating of batteries without a fluid thermal management system or external heating equipment. Background Art

[0002] The battery power systems of advanced hybrid electric vehicles and all-electric vehicles draw electrical power from a high-energy traction battery pack. The discharge and charging modes of the constituent electrochemical cells of the battery pack generate heat. Therefore, battery power systems based on motor vehicles use a thermal management system, typically by circulating a coolant through and around the battery pack to help heat or cool the battery pack and associated power electronics. In cold ambient conditions, such as winter or cold weather operations, the battery pack can be warmed up by the thermal management system before the charging operation is initiated. However, the battery power system may lack a resident thermal management system, in which case heating of the battery pack will typically be achieved by wrapping the battery pack in a resistive heating blanket or heating the surrounding ambient environment. Summary of the invention

[0003] Disclosed herein are circuit topologies and associated control methods for enabling self-heating of battery packs, particularly battery packs characterized by the absence of a resident thermal management system, external heating blanket, or external heating. For example, boats, recreational vehicles (RVs), and other systems may use lower cost lithium iron phosphate (LFP) batteries that typically do not permit charging operations to proceed while the battery temperature is maintained below a predetermined temperature limit. While such batteries may be heated using a heating blanket or by warming the surrounding ambient environment as noted above, such alternative heating techniques tend to be relatively slow and energy inefficient. Therefore, the present self-heating solution based on an alternating current (AC) waveform is intended to enable faster and more energy efficient self-heating of a battery pack in preparation for battery charging.

[0004] In an exemplary embodiment, the battery power system includes a direct current (DC) voltage bus, a battery pack, an inverter connected to the DC voltage bus, a first electrical switch and a second electrical switch, and an electronic battery controller. The first electrical switch ("first switch") is connected between the inverter and the battery pack and is configured to be open during the AC self-heating mode of the battery pack. The performance of the AC self-heating mode includes generating an AC waveform through the battery pack with a controlled amplitude via the inverter. The second electrical switch connected to the inverter and the first electrical switch is configured to be closed during the AC self-heating mode.

[0005] The battery controller in this embodiment communicates with the power switch of the inverter and also communicates with the first electrical switch and the second electrical switch. In response to the calibrated entry criteria, the battery controller opens the first electrical switch, closes the second electrical switch, and controls the conduction state of the power switch ON / OFF. In this way, the battery controller uses the AC waveform from the inverter to self-heat the battery pack to a predetermined temperature limit. The entry criteria can include the required charging of the battery pack when the temperature of the battery pack is below the temperature limit, such as below the threshold of 32-35°F noted above or another temperature suitable for the application.

[0006] The battery controller in one or more embodiments is configured to measure an open circuit voltage (OCV) of the battery pack, compare the OCV of the battery pack to a predetermined OCV to determine whether the battery pack requires charging, and enter an AC self-heating mode when the battery pack requires charging.

[0007] Six of the power switches are configured as upper switches connected to a positive voltage rail of the DC voltage bus. Six of the power switches are configured as lower switches connected to a negative voltage rail of the DC voltage bus. During the AC self-heating mode, the battery controller closes only one of the upper switches and only one of the lower switches.

[0008] An inverter according to one aspect of the present disclosure includes: a transformer having a primary winding and a secondary winding; and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack. The current output node of the second switch can be connected to the current input node of the first switch so that the second switch is arranged in series with the first switch. In such an embodiment, the AC waveform is generated partially through the secondary winding, for example using a capacitor.

[0009] The battery pack in one or more implementations may be configured as a lithium iron phosphate or lithium iron phosphate (LFP) battery.

[0010] A DC load may be connected to the inverter, in which case the battery controller may simultaneously power the DC load in AC self-heating mode.

[0011] A vehicle is also disclosed herein. In various representative and non-limiting embodiments, the vehicle is a recreational vehicle or a watercraft.

[0012] An embodiment of a vehicle includes a vehicle body and a battery power system connected thereto. The battery power system includes a DC voltage bus, a battery pack (e.g., an LFP battery), and an inverter connected to the DC voltage bus and having a plurality of solid-state power switches. The battery power system also includes a first switch connected between the inverter and the battery pack, wherein the first switch is configured to open during an AC self-heating mode of the battery pack. As noted above, the AC self-heating mode includes generating an AC waveform that passes through the battery pack with a controlled amplitude. A second switch connected to the inverter and the first switch is closed during the AC self-heating mode.

[0013] As part of this embodiment, the battery controller communicates with the power switch and the first and second switches. The battery controller is configured to open the first switch, close the second switch, and control the on / off conduction state of the power switch in response to a calibrated entry criterion to thereby self-heat the battery pack to a predetermined temperature using an AC waveform. The entry criterion may include a required charge of the battery pack when a battery temperature of the battery pack is below a calibrated temperature limit.

[0014] The battery controller may measure the OCV of the battery pack and then compare the OCV to a predetermined OCV to determine the required charge.

[0015] The DC voltage bus has a positive voltage rail and a negative voltage rail. Six of the power switches are upper switches connected to the positive voltage rail. Six of the power switches are lower switches connected to the negative voltage rail. The battery controller is configured to close only one of the upper switches and only one of the lower switches during the AC self-heating mode.

[0016] The inverter may include a transformer having a primary winding and a secondary winding, and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack.

[0017] In one possible configuration, the current output node of the second switch is connected to the current input node of the first switch, so that the second switch is connected in series with the first switch. In such an embodiment, the AC current is generated in part by the secondary winding. Alternatively, the AC current is generated in part using a capacitor.

[0018] Also disclosed herein is a method for performing an AC self-heating mode of a battery pack in a battery power system having a direct current (DC) bus. The method may include, in response to a calibrated entry criterion: opening a first switch, closing a second electrical switch, and controlling the on / off conduction state of a solid-state power switch of an inverter via a battery controller. The first switch is connected between the inverter and the battery pack. The second switch is connected to the inverter and the first switch. The method in this embodiment may also include generating an AC waveform through the battery pack with a controlled amplitude through the second switch and a set of power switches with an open conduction state, so as to thereby self-heat the battery pack to a predetermined temperature. The entry criteria may include the required charging of the battery pack when the battery temperature of the battery pack is below a calibrated temperature limit.

[0019] According to one aspect of the present invention, a battery power system comprises:

[0020] Direct current (DC) voltage bus;

[0021] A battery pack having a battery temperature;

[0022] an inverter connected to the DC voltage bus and including a plurality of solid-state power switches operable to output an alternating current (AC) waveform;

[0023] a first electrical switch connected between the inverter and the battery pack, the first electrical switch being configured to open during an AC self-heating mode of the battery pack;

[0024] a second electrical switch connected to the inverter and the first electrical switch and configured to close during an AC self-heating mode of the battery pack; and

[0025] A battery controller in communication with the power switch, the first electrical switch, and the second electrical switch, wherein the battery controller is configured to selectively open the first electrical switch, close the second electrical switch, and control the on / off conduction state of each of the power switches before charging the battery pack, and thereby heat the battery pack via an AC waveform when the battery temperature is below a calibrated temperature limit.

[0026] A battery power system as described above, wherein the battery controller is configured to measure an open circuit voltage (OCV) of the battery pack as a measured OCV, compare the measured OCV with a predetermined OCV to determine whether the battery pack requires charging, and enter an AC self-heating mode when the battery pack requires charging.

[0027] A battery power system as described above, wherein the DC voltage bus has a positive voltage rail and a negative voltage rail, six of the power switches are configured as upper switches connected to the positive voltage rail, six of the power switches are configured as lower switches connected to the negative voltage rail, and the battery controller is configured to close only one of the upper switches and only one of the lower switches during the AC self-heating mode.

[0028] The battery power system as described above, wherein the inverter includes: a transformer having a primary winding and a secondary winding; and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack.

[0029] A battery power system as described above, wherein the current output node of the second electrical switch is connected to the current input node of the first electrical switch so that the second electrical switch is arranged in series with the first electrical switch, and wherein the AC waveform is generated in part by the secondary winding.

[0030] As previously described with respect to a battery power system, wherein the AC waveform is generated in part using capacitors.

[0031] As in the aforementioned battery power system, the battery pack is a lithium iron phosphate (LFP) battery.

[0032] The battery power system as described above further comprises:

[0033] A DC load is connected to the inverter, wherein the battery controller is configured to simultaneously power the DC load in the case of the AC self-heating mode.

[0034] According to another aspect of the present invention, a carrier includes:

[0035] The vehicle body; and

[0036] A battery power system connected to the vehicle body and comprising:

[0037] Direct current (DC) voltage bus;

[0038] Battery pack;

[0039] an inverter connected to the DC voltage bus and having a plurality of solid-state power switches;

[0040] a first electrical switch connected between the inverter and the battery pack, the first electrical switch being configured to open during an alternating current (AC) self-heating mode of the battery pack, wherein the AC self-heating mode includes generating an AC waveform with a controlled amplitude through the battery pack;

[0041] a second electrical switch connected to the inverter and the first electrical switch and configured to close during the AC self-heating mode; and

[0042] A battery controller in communication with the power switch, the first electrical switch, and the second electrical switch, wherein the battery controller is configured to open the first electrical switch, close the second electrical switch, and control the on / off conduction state of the power switch in response to calibrated entry criteria to thereby self-heat the battery pack to a predetermined temperature using an AC waveform, wherein the entry criteria includes a required charging of the battery pack when a battery temperature of the battery pack is below a calibrated temperature limit.

[0043] The vehicle as described above, wherein the vehicle is a recreational vehicle.

[0044] A vehicle as described above, wherein the vehicle is a ship.

[0045] A vehicle as described above, wherein the battery controller is configured to measure an open circuit voltage (OCV) of the battery pack as the measured OCV, and compare the measured OCV to a predetermined OCV to determine the required charge.

[0046] A load as described above, wherein the DC voltage bus has a positive voltage rail and a negative voltage rail, six of the power switches are upper switches connected to the positive voltage rail, six of the power switches are lower switches connected to the negative voltage rail, and the battery controller is configured to close only one of the upper switches and only one of the lower switches during the AC self-heating mode.

[0047] In the vehicle as mentioned above, the inverter comprises: a transformer having a primary winding and a secondary winding; and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack.

[0048] A vehicle as previously described, wherein a current output node of the second electrical switch is connected to a current input node of the first electrical switch such that the second electrical switch is connected in series with the first electrical switch, and wherein the AC current is generated in part by the secondary winding.

[0049] A vehicle as previously described, wherein the AC current is generated in part using capacitors.

[0050] As in the aforementioned vehicle, the battery pack is a lithium iron phosphate (LFP) battery.

[0051] According to yet another aspect of the present invention, a method for performing an alternating current (AC) self-heating mode of a battery pack in a battery power system having a direct current (DC) voltage bus, the method comprising:

[0052] In response to a calibrated entry criterion, opening a first electrical switch, closing a second electrical switch, and controlling an on / off conduction state of a solid-state power switch of an inverter via a battery controller, wherein the first electrical switch is connected between the inverter and a battery pack, and wherein the second electrical switch is connected to the inverter and the first electrical switch; and

[0053] generating an AC waveform through the battery pack with a controlled amplitude through the battery pack via the second electrical switch and the set of power switches having an open conduction state to thereby self-heat the battery pack to a predetermined temperature, wherein the entry criteria include a required charge of the battery pack when a cell temperature of the battery pack is below a calibrated temperature limit, wherein:

[0054] The DC voltage bus has a positive voltage rail and a negative voltage rail;

[0055] Six of the power switches are upper switches connected to the positive voltage rail;

[0056] Six of the power switches are lower switches connected to the negative voltage rail; and

[0057] The set of power switches having an open conduction state includes only one upper switch of the upper switches and only one lower switch of the lower switches.

[0058] The method as above further comprises:

[0059] measuring an open circuit voltage (OCV) of the battery pack as measured OCV; and

[0060] The measured OCV is compared to a predetermined OCV limit to determine the required charge.

[0061] The method as above further comprises:

[0062] The DC load is simultaneously powered via the inverter while the AC self-heating mode is executed.

[0063] The above features and advantages and other features and advantages of the present teachings as defined in the appended claims are apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings when considered in connection with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 A battery power system is illustrated having a battery pack that is self-heated via an alternating current (AC) waveform and the inverter-based control method described herein.

[0065] Figure 1A The diagram shows that when AC self-heating of the battery pack is in progress, Figure 1The battery is the active part of the power system.

[0066] Figure 2 is a time graph of battery current during AC self-heating mode, wherein battery current in amperes is plotted on the vertical axis and time in seconds is plotted on the horizontal axis.

[0067] Figure 3 and Figure 4 yes Figure 1 and Figure 2 A representative circuit topology of an inverter and a battery pack is shown in FIG.

[0068] Figure 5A , Figure 5B , Figure 5C and Figure 5D ] are representative primary voltage, transformer primary current, transformer secondary current, and battery current waveforms resulting from operation of the AC self-heating method of the present disclosure.

[0069] Figure 6 is a flow chart illustrating an embodiment of the AC self-heating method described herein.

[0070] The present disclosure may be modified or embodied in alternative forms, wherein representative embodiments are shown in the accompanying drawings and are described in detail below. The innovative aspects of the present disclosure are not limited to the disclosed embodiments. On the contrary, the present disclosure is intended to cover alternatives falling within the scope of the disclosure defined by the appended claims. DETAILED DESCRIPTION

[0071] Referring to the drawings, wherein like reference numerals correspond to the same or similar components throughout the several views, Figure 1 The battery power system 10 illustrated in the figure is configured to perform alternating current (AC)-based self-heating of the associated battery pack 12, as explained herein. The battery power system 10 that can be used on a boat 10A or another watercraft, a recreational vehicle 10B, or another vehicle having a body 11 in one or more embodiments includes a battery pack 12, which is in turn connected to the body 11 or positioned relative to the body 11. As shown, the battery pack 12 is connected to a direct current (DC) bus 14 via a main battery switch S1, a main fuse 15, and a shunt resistor (R-Shunt) 16. The battery power system 10 also includes an inverter 18, such as a power inverter / charging module, which is in turn connected to the DC voltage bus 14. The inverter 18 is connectable to an off-board alternating current (AC) charging station 20A via a switch S2, which is also referred to as a charging source A hereinafter.

[0072] As will be appreciated by those skilled in the art, the inverter 18 includes a plurality of solid-state power switches 180. Figure 3 and Figure 4 In a non-limiting embodiment, power switches Q1, Q2, ..., Q 12 When charging the battery pack 12 via the AC charging station 20A, the various on / off conduction states of the various power switches 180 performed by the resident battery controller (C) 50 are used to output a DC voltage to the DC voltage bus 14. The same power switches 180 are used as described below with reference to Figure 6 The described exemplary embodiment of the method 100 for performing AC self-heating of the battery pack 12 is controlled via the battery controller 50 during an AC self-heating mode of the battery pack 12 .

[0073] Figure 1 The DC voltage bus 14 shown in FIG. 1 can be connected to several other DC devices, including but not necessarily limited to a DC load 22, a DC-DC charger 20B, and a solar charger 20C, where the latter two devices act as charging sources B and C, respectively. Thus, the battery pack 12 can be recharged via charging sources A, B, or C as needed based on availability. For example, if Figure 1 If the battery power system 10 is to be used as part of a vessel 10A while at sea, then charging source A will generally be unavailable, but solar charging may remain available via charging source C. However, when the temperature of the battery pack 12 remains below a specified lower temperature limit, such as approximately 32-35° F. in some implementations, the battery controller 50 may not permit charging via Figure 1 The various charging sources A, B and C are used to charge the battery pack 12. In this case, the battery controller 50 performs the embodiment Figure 6 The method 100 is provided to initiate the above-noted AC self-heating of the battery pack 12 , wherein the process occurs via switching control of the inverter 18 , as explained in detail below.

[0074] To this end, a main battery switch S1 serving as the first electrical switch of the battery power system 10 is connected between the inverter 18 and the battery pack 12. The main battery switch S1 is configured to respond to a control signal (CC) from the battery controller 50 during the AC self-heating mode. O ) and open circuit. During this mode, the Figure 1A The active components of the battery power system 10 are shown in FIG. 1 and other components are shown in phantom or removed for simplicity and clarity of illustration. The battery controller 50 operates the inverter 18 to output an AC current waveform with a controlled amplitude through the battery pack 12, such as Figure 2 As shown in the representative AC waveform 25 of FIG. Figure 3 and Figure 4 As depicted, the second electrical switch S1 a , which may be housed within the inverter 18 , is connected to the first electrical switch S1 , wherein the second electrical switch S1 a is configured to be closed during the AC self-heating mode as contemplated herein.

[0075] Still refer to Figure 1 , the battery controller 50 communicates with the power switch 180, the first electrical switch S1 and the second electrical switch S1a, and various other switches S2, S3, S4, S5, and S6 as shown. The switches S2-S6, where switch S3 is a DC load switch for connecting and disconnecting the DC load 22 and switch S4 is an AC load switch for connecting and disconnecting the AC load 122, are positioned between the DC voltage bus 14 and various AC and DC devices, namely, the DC load 22, the AC load 122, the DC-DC charger 20B, and the solar charger 20C.

[0076] In response to the calibrated entry criteria, the battery controller 50 is configured to open the first electrical switch S1, close the second electrical switch S1a, and control the above-noted on / off conduction state of the power switch 180 of the inverter 18 to thereby use the resulting AC waveform (e.g. Figure 2 The AC waveform 25 of FIG. 25) self-heats the battery pack 12 to at least a predetermined temperature limit. Entry criteria as contemplated herein may include a determination by the battery controller 50 that the battery pack 12 requires charging, such as via an open circuit voltage (OCV) measurement described below, while the temperature of the battery pack 12 is maintained below a calibrated temperature limit.

[0077] In the scope of this disclosure, Figure 1 The battery controller 50 schematically illustrated in FIG. 1 includes a battery controller configured to receive or generate an input signal (CC I ) of one or more processors (P) 52. In response to an input signal (CC I ), the battery controller 50 executes one or more algorithms Figure 6 Method 100. Computer readable code or instructions for implementing such method 100 may be stored in the memory (M) 54 of the controller 50, including tangible, non-transitory computer-readable storage media, such as magnetic or optical media, CD-ROM and / or solid-state / semiconductor memory (e.g., various types of RAM or ROM).

[0078] The term "controller" and related terms, such as control module, module, control, control unit, processor and similar terms, refer to one or various combinations of: application specific integrated circuit(s) (ASICs), field programmable gate arrays (FPGAs), electronic circuit(s), central processing unit(s), such as microprocessor(s), and associated non-transitory memory component(s) in the form of memory and storage devices (read-only, programmable read-only, random access, hard drive, etc.). The non-transitory components of memory 54 are those components capable of storing machine-readable instructions in the form of one or more software or firmware programs or routines, combinational logic circuit(s), input / output circuit(s) and devices, signal conditioning and buffer circuits, and other components that can be accessed by processor(s) 52 to provide the described functionality.

[0079] (One or more) input / output circuits and devices include analog / digital converters and related devices that monitor inputs from sensors, where such inputs are monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, codes, algorithms and similar terms mean a set of instructions executable by a controller, including calibration and lookup tables. Each controller executes (one or more) control routines to provide the desired functionality. Routines can be executed at regular intervals, such as at intervals of approximately 50-100 microseconds (ms) during ongoing operation. Alternatively, routines can be executed in response to the occurrence of a triggering event.

[0080] Now refer to Figure 3 , suitable for implementing the AC self-heating solution described in this article Figure 1 An embodiment of the battery power system 10 is shown in a more detailed view of the inverter 18 . Figure 1 The power switch 180, which may be embodied as an IGBT as shown or alternatively as a MOSFET, a thyristor, etc., is connected to the above-described Figure 1 The positive voltage rail 14 of the DC voltage bus 14 + and negative voltage rail 14 - . is connected to the positive voltage rail 14 + The power switch 180 is referred to herein and in the art as the "upper switch" and is connected to the negative voltage rail 14 - The power switch 180 is referred to as the "lower switch". Figure 3 In the illustrated inverter 18, the upper switches include switches Q1, Q2, Q5, Q6, Q9, and Q 10 The lower switches in this embodiment include the remaining switches Q3, Q4, Q7, Q8, Q 11and Q 12 .

[0081] The illustrated circuit also includes a transformer (TR) 30 that provides galvanic isolation as is appreciated in the art, with the first capacitor C1 and the second capacitor C2 being arranged in parallel with each other within the inverter 18. Other depicted circuit elements include a first capacitor C1 disposed on the positive voltage rail 14 and a second capacitor C2 disposed on the positive voltage rail 14. + The inductor (L) on the battery pack 12 is shown in parallel with the second capacitor C2. The switch circuit 35 is formed by the first electrical switch S1 and the second electrical switch S1a indicated above.

[0082] exist Figure 3 In an embodiment, six of the power switches 180 are connected to the positive voltage rail 14 + The upper switch of the power switch 180 is connected to the negative voltage rail 14. - The battery controller 50 is configured to close only one of the upper switches, in this example switch Q, during the AC self-heating mode. 10 , and close only one of the lower switches, Q 12 That is, during the AC self-heating mode, switches Q1-Q9 and Q 11 The first switch S1 remains disconnected / opened, while the second switch S1a in this embodiment is turned on / closed. 10 and Q 12 The second capacitor C2 and the battery pack 12 and the cable inductance (L) in between are used as a quasi-resonant circuit to generate a Figure 2 The battery current (i BAT As shown, the primary current i p and the secondary current i s Flows through the respective primary and secondary windings of transformer 30 .

[0083] Now refer to Figure 4 , shows an alternative switch circuit 350 in which the first electrical switch S1 and the second electrical switch S1a are arranged in series. That is, with respect to the current flow from the power switch 180 of the inverter 18, the current output node N1 of the second electrical switch S1a is connected to the current input node N2 of the first electrical switch S1, so that the second electrical switch S1a is connected in series with the first electrical switch S1.

[0084] In this arrangement, Figure 2The AC current waveform 25 is generated in part by the secondary winding of the transformer 30. During the AC self-heating mode, the power switches Q1-Q8 are commanded to be disconnected, i.e., open circuited or non-conductive, by the battery controller 50. The first electrical switch S1 is turned on. The second electrical switch S1a is turned off. Therefore, the switches Q9-Q 11 Together with the secondary winding of transformer 30, it is used to generate Figure 2 The AC waveform of the battery current (i BAT ).

[0085] Brief reference Figure 5A , Figure 5B , Figure 5C and Figure 5D , as described above Figure 3 and Figure 4 The operation of the switching circuits 35 and 35 together with the PWM control of the various power switches 180 corresponds to several exemplary waveforms. For example, the primary voltage (V P ) is shown as Figure 5A The voltage trajectory 40 , for example, rises from V1 to just below V2 in a short amount of time. Figure 5B and Figure 5C 1 and 10 respectively illustrate the primary transformer current 42 (I P ) and the secondary transformer current 44 (I S ). Effective self-heating depends on Figure 5D The battery current trace 46 shows the oscillating current I BAT , oscillating current I BAT This reflects the desired current waveform 25 (see FIG. 1 ) in the battery pack 12 for increasing the temperature of the battery pack 12 from within the battery pack 12. Figure 2 ).

[0086] Mathematically, this method can be understood using a target root mean square (RMS) current. This value can be calculated based on the target temperature rise as follows:

[0087]

[0088] Using nominal example values ​​only for illustration, a representative arrangement of 100 ampere-hour (Ah) battery cells has a nominal voltage of 12.8V and totals 400Ah and 5.12kWh, and assuming a 3kW embodiment of the inverter 18, the battery pack 12 will see a maximum heating current (RMS) of 300A, with a cell current (I cell,RMS ). Assume that the resistance of each unit (R cell) is 8mΩ, the heating power of each unit will be 45W, with a total heating power of 720W. Now, assuming the unit level is 250kWh / kg, the total unit mass (m battery ) is 20.5 kg. At a specific heat capacity (C ) of 1130 J / kgK for an exemplary LFP embodiment of the battery pack 12 p,battery ), the above mathematical formula results in a temperature rise of 1.86°C / minute. Since most commercially available inverters are rated for 2kW or more and 300A (RMS), such ratings will be more than sufficient to provide the necessary heating power in an efficient and uniform manner when the battery pack 12 is self-heated according to the present disclosure. As an added benefit, the present method does not affect the connected DC load. However, due to the use of Figure 3 and Figure 4 The power switch 180 is used to drive the AC self-heating process, and the AC load is temporarily affected.

[0089] Now refer to Figure 6 , method 100 is described in terms of discrete logic blocks or code segments. Each logic block of method 100 can be stored as a computer-readable instruction in Figure 1 The memory 54 of the computer 20 is used for storing instructions, wherein such instructions are executed by the processor 52 to cause the controller 50 to perform the described functions.

[0090] In response to the calibrated entry criteria, the method 100 begins at block B 102. For example, the method 100 may be performed at regular timer-based intervals or in response to user-initiated input. Figure 1 The battery controller 50 closes the first electrical switch S1 at the beginning of the method 100 and then proceeds to block B104.

[0091] Figure 6 Block B104 of the method 100 includes determining whether charging of the battery pack 12 is required. This verification may be considered part of the entry criteria or a subsequent step. In a possible implementation, block B104 may include measuring the open circuit voltage (OCV) of the battery pack 12, i.e., the battery voltage when all loads on the battery pack 12 are completely disconnected. When the method 100 proceeds to block B106, the measured OCV is then stored in Figure 1 In the memory 54 of the battery controller 50.

[0092] At block B106, the battery controller 50 may compare the measured OCV from block B104 to a threshold OCV value to determine whether charging of the battery pack 12 is required. When charging is not required, the method 100 proceeds to block B126, otherwise the method 100 proceeds to block B108.

[0093] At block B108 , in response to charging being requested, the battery controller 50 next determines whether a charging source A, B, or C is currently available. If so, the method 100 proceeds to block B110 , otherwise the method 100 proceeds to block B126 .

[0094] Figure 6 Block B110 of the method 100 shown in FIG. 1 includes checking the battery temperature (T Bat As is appreciated in the art, block B110 may entail measuring the battery temperature using one or more temperature sensors (not shown) deployed on or within the battery pack 12, and then using the measured battery temperature as Figure 1 The input signal (CC I ) is reported to the battery controller 50. Thereafter, the method 100 proceeds to block B112.

[0095] Block B112 includes comparing the measured battery temperature from block B110 to a calibrated temperature limit (T Lim ) is compared to the calibrated temperature limit (T Lim ) when charging of the battery pack 12 is not permitted. In a non-limiting implementation, the calibrated temperature limit may be approximately 32-35°F. In other embodiments, the calibrated temperature limit may be variable, such as being set at different temperatures depending on ambient conditions, or user selectable above a specific manufacturer limit. When the measured battery temperature is below the calibrated temperature limit, the method 100 proceeds to block B114, and alternatively, when the measured battery temperature equals or exceeds such a calibrated temperature limit, the method 100 proceeds to block B122.

[0096] Still refer to Figure 6 , and continuing in the case of block B114, Figure 6 The method 100 is performed by Figure 1 The controller 50 then controls the various power switches 180 and Figure 3 and Figure 4 The on / off state of the first switch S1 and the second switch S1a is changed to start AC self-heating. Thereafter, the method 100 proceeds to block B116.

[0097] At block B116, the battery controller 50 again measures the battery temperature (T Bat ), after which proceed to block B118.

[0098] Block B118, similar to block B112 described above, includes comparing the measured temperature to a calibrated temperature limit (T LIM) is compared. Blocks B116 and B118 continue to loop until the measured temperature equals or exceeds the calibrated temperature limit, or until a predetermined time limit is reached. Method 100 then proceeds to block B120.

[0099] exist Figure 6 At block B120 , the battery controller 50 stops the AC self-heating of the battery pack 12 . Figure 3 and Figure 4 The affected power switches 180 of the inverter 18 shown in FIG. 1 are returned to their initial states, the first electrical switch S1 is closed, and the second electrical switch S1a is opened or closed depending on the embodiment. The method 100 then proceeds to block B122.

[0100] At block B122, the battery controller 50 may Figure 1 The battery power system 10 is connected to an available charging source A, B or C. The method 100 then proceeds to block B124.

[0101] Block B124 includes initiating charging of the battery pack 12 using the connected charging source A, B, or C from block B120. The method 100 then proceeds to block B126.

[0102] In execution Figure 6 When the method 100 is used, the battery controller 50 is thus Figure 1 The battery power system 10 illustrated in FIG. 1 provides a number of benefits to the user. Off-board charging of lithium-ion batteries is typically precluded when the batteries are too cold. While battery electric vehicles have integrated thermal management systems to regulate battery temperature and prepare on-board propulsion batteries for charging, as noted above, lower cost batteries typically used in electrical systems of RVs, boats, and other systems are often not so equipped.

[0103] The lack of a thermal management system in turn requires slower, less efficient external heating or the use of a heating blanket. Instead, the present solution utilizes the available hardware of an onboard inverter / charger, exemplified herein as Figure 1 The inverter 18 has an additional switch S1a to use a quasi-resonant circuit and Figure 2 The AC waveform 25 is used to quickly increase the battery temperature before off-board charging. After that, once the battery has been sufficiently warmed, charging is permitted. In view of the foregoing disclosure, those skilled in the art will easily appreciate these and other attendant benefits.

[0104] The detailed description and the accompanying drawings or each figure are support and description of the present teaching, but the scope of the present teaching is limited only by the claims. Although the best mode and some of other embodiments for carrying out the present teaching have been described in detail, there are various alternative designs and embodiments for practicing the present teaching defined in the appended claims.

Claims

1. A battery power system comprising: Direct current (DC) voltage bus; A battery pack having a battery temperature; an inverter connected to the DC voltage bus and including a plurality of solid-state power switches operable to output an alternating current (AC) waveform; a first electrical switch connected between the inverter and the battery pack, the first electrical switch being configured to open during an AC self-heating mode of the battery pack; a second electrical switch connected to the inverter and the first electrical switch and configured to close during an AC self-heating mode of the battery pack; as well as A battery controller in communication with the power switch, the first electrical switch, and the second electrical switch, wherein the battery controller is configured to selectively open the first electrical switch, close the second electrical switch, and control the on / off conduction state of each of the power switches before charging the battery pack, and thereby heat the battery pack via an AC waveform when the battery temperature is below a calibrated temperature limit.

2. The battery power system of claim 1 , wherein the battery controller is configured to measure an open circuit voltage (OCV) of the battery pack as the measured OCV, compare the measured OCV with a predetermined OCV to determine whether the battery pack requires charging, and enter an AC self-heating mode when the battery pack requires charging.

3. The battery power system of claim 1 , wherein the DC voltage bus has a positive voltage rail and a negative voltage rail, six of the power switches are configured as upper switches connected to the positive voltage rail, six of the power switches are configured as lower switches connected to the negative voltage rail, and the battery controller is configured to close only one of the upper switches and only one of the lower switches during the AC self-heating mode.

4. The battery power system of claim 1, wherein the inverter comprises: A transformer having a primary winding and a secondary winding; and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack.

5. The battery power system of claim 4, wherein a current output node of the second electrical switch is connected to a current input node of the first electrical switch such that the second electrical switch is arranged in series with the first electrical switch, and wherein the AC waveform is generated in part by the secondary winding.

6. The battery power system of claim 4, wherein the AC waveform is generated in part using a capacitor.

7. The battery power system of claim 1, wherein the battery pack is a lithium iron phosphate (LFP) battery.

8. The battery power system of claim 1, further comprising: A DC load is connected to the inverter, wherein the battery controller is configured to simultaneously power the DC load in the case of the AC self-heating mode.

9. A vehicle, comprising: Vehicle body; and A battery power system connected to the vehicle body and comprising: Direct current (DC) voltage bus; Battery pack; an inverter connected to the DC voltage bus and having a plurality of solid-state power switches; a first electrical switch connected between the inverter and the battery pack, the first electrical switch being configured to open during an alternating current (AC) self-heating mode of the battery pack, wherein the AC self-heating mode includes generating an AC waveform with a controlled amplitude through the battery pack; a second electrical switch connected to the inverter and the first electrical switch and configured to close during the AC self-heating mode; and A battery controller in communication with the power switch, the first electrical switch, and the second electrical switch, wherein the battery controller is configured to open the first electrical switch, close the second electrical switch, and control the on / off conduction state of the power switch in response to calibrated entry criteria to thereby self-heat the battery pack to a predetermined temperature using an AC waveform, wherein the entry criteria includes a required charging of the battery pack when a battery temperature of the battery pack is below a calibrated temperature limit.

10. The vehicle of claim 9 wherein the DC voltage bus has a positive voltage rail and a negative voltage rail, six of the power switches are upper switches connected to the positive voltage rail, six of the power switches are lower switches connected to the negative voltage rail, and the battery controller is configured to close only one of the upper switches and only one of the lower switches during the AC self-heating mode.

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