Patent Application
20240429481
The present disclosure relates to circuit topologies and computer-based methods for heating an electrochemical battery pack. More specifically, aspects of the disclosure relate to the automated self-heating of a battery pack in the absence of a fluidic thermal management system or external heating device.
Battery electric systems of advanced hybrid-electric and full-electric vehicles draw electrical power from a high-energy traction battery pack. Discharging and charging modes of constituent electrochemical cells of the battery pack generates heat. Motor vehicle-based battery electric systems therefore use a thermal management system to help heat or cool the battery pack and related power electronics, typically by circulating coolant through and around the battery pack. Under cold ambient conditions, e.g., winter or cold weather operation, the battery pack may be warmed by the thermal management system before commencing charging operations. However, a battery electric system could lack a resident thermal management system, in which case heating of the battery pack would typically be accomplished by wrapping the battery pack in a resistive heating blanket or heating the surrounding ambient environment.
Disclosed herein are circuit topologies and related control methods for self-heating a battery pack, in particular one that is characterized by an absence of a resident thermal management system, external heating blanket, or ambient heating. For example, boats, recreational vehicles (RVs), and other systems may use lower-cost lithium ferrophosphate (LFP) batteries that do not ordinarily permit charging operations to proceed when the battery temperature remains below a predetermined temperature limit. While such batteries could 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. The present alternating current (AC) waveform-based self-heating solution is therefore intended to realize faster and more energy-efficient self-heating of the battery pack in preparation for battery charging.
In an exemplary embodiment, a battery electric system includes a direct current (DC) voltage bus, a battery pack, an inverter connected to the DC voltage bus, first and second electrical switches, and an electronic battery controller. The first electrical switch (“first switch”) is connected between the inverter and the battery pack, and is configured to open during an AC self-heating mode of the battery pack. Performance of the AC self-heating mode includes generating, via the inverter, an AC waveform through the battery pack at a controlled amplitude. The second electrical switch, which is connected to the inverter and the first electrical switch, is configured to close during the AC self-heating mode.
The battery controller in this embodiment is in communication with power switches of the inverter, and also with the first and second electrical switches. In response to calibrated entry criteria, the battery controller opens the first electrical switch, closes the second electrical switch, and controls ON/OFF conducting states of the power switches. In this manner, the battery controller self-heats the battery pack to a predetermined temperature limit using the AC waveform from the inverter. The entry criteria could include required charging of the battery pack while a temperature of the battery pack is less than the temperature limit, for example 32-35° F. threshold noted above or another application-suitable temperature.
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 the AC self-heating mode when the battery pack requires charging.
Six of the power switches are configured as upper switches connected to the positive voltage rail of the DC voltage bus. Six of the power switches are configured as lower switches connected to the negative voltage rail of the DC voltage bus. The battery controller closes only one of the upper switches and only one of the lower switches during the AC self-heating mode.
The inverter in accordance with an aspect of the disclosure includes a transformer having primary and secondary windings, and a capacitor connected in parallel with the battery pack between the secondary winding and the battery pack. A current output node of the second switch may be connected to a current input node of the first switch, such that the second switch is arranged in series with the first switch. In such an embodiment, the AC waveform is generated in part through the secondary winding, e.g., using the capacitor.
The battery pack in one or more implementations may be constructed as a lithium-iron phosphate or lithium ferrophosphate (LFP) battery.
A DC load may be connected to the inverter, in which case the battery controller may power the DC load concurrently with the AC self-heating mode.
A vehicle is also disclosed herein. The vehicle is a recreational vehicle or a boat in different representative and non-limiting embodiments.
An embodiment of the vehicle includes a vehicle body and a battery electric system connected thereto. The battery electric 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 electric system also includes a first switch connected between the inverter and the battery pack, with the first switch being 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 through the battery pack at a controlled amplitude. A second switch, which is connected to the inverter and the first switch, closes during the AC self-heating mode.
As part of this embodiment, a battery controller is in communication with the power switches and the first and second switches. The battery controller is configured, in response to calibrated entry criteria, to open the first switch, close the second switch, and control ON/OFF conducting states of the power switches to thereby self-heat the battery pack to a predetermined temperature using the AC waveform. The entry criteria may include a required charging of the battery pack while a battery temperature of the battery pack is less than a calibrated temperature limit.
The battery controller may measure an OCV of the battery pack and then compare the OCV to a predetermined OCV to determine the required charging.
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.
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.
A current output node of the second switch is connected to a current input node of the first switch in a possible construction, such that the second switch is in series with the first switch. In such an embodiment, the AC current is generated in part through the secondary winding. Alternatively, the AC current is generated in part using the capacitor.
Also disclosed herein is a method for performing AC self-heating mode of a battery pack in a battery electric system having a direct current (DC) bus. The method may include, in response to calibrated entry criteria: opening a first switch, closing a second electrical switch, and controlling ON/OFF conducting states of solid-state power switches 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 at a controlled amplitude through the second switch and a set of the power switches having an OFF conducting state to thereby self-heat the battery pack to a predetermined temperature. The entry criteria may include a required charging of the battery pack while a battery temperature of the battery pack is less than a calibrated temperature limit.
The above features and advantages, and other features and advantages, of the present teachings are readily apparent from the following detailed description of some of the best modes and other embodiments for carrying out the present teachings, as defined in the appended claims, when taken in connection with the accompanying drawings.
The present disclosure may be modified or embodied in alternative forms, with representative embodiments shown in the drawings and described in detail below. Inventive aspects of the present disclosure are not limited to the disclosed embodiments. Rather, the present disclosure is intended to cover alternatives falling within the scope of the disclosure as defined by the appended claims.
Referring to the drawings, wherein like reference numerals correspond to like or similar components throughout the several Figures, a battery electric system 10 is illustrated in
As appreciated by those skilled in the art, the inverter 18 includes a plurality of solid-state power switches 180, which are shown in detail as power switches Q1, Q2, . . . , Q12 in the non-limiting embodiments of
The DC voltage bus 14 shown in
To that end, the main battery switch S1, acting herein as a first electrical switch of the battery electric system 10, is connected between the inverter 18 and the battery pack 12. The main battery switch S1 is configured to open in response to control signals (CCO) from the battery controller 50 during AC self-heating modes. During this mode, with the active components of the battery electric system 10 illustrated in
Still referring to
In response to 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 conducting states of the power switches 180 of the inverter 18 to thereby self-heat the battery pack 12 to at least a predetermined temperature limit using the resulting AC waveform, e.g., the AC waveform 25 of
Within the scope of the present disclosure, the battery controller 50 illustrated schematically in
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) (ASIC), Field-Programmable Gate Array (FPGA), electronic circuit(s), central processing unit(s), e.g., 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.). Non-transitory components of the memory 54 are those which are 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 circuitry and other components that can be accessed by the processor(s) 52 to provide the described functionality.
Input/output circuit(s) and devices include analog/digital converters and related devices that monitor inputs from sensors, with such inputs monitored at a preset sampling frequency or in response to a triggering event. Software, firmware, programs, instructions, control routines, code, algorithms, and similar terms mean controller-executable instruction sets including calibrations and look-up tables. Each controller executes control routine(s) to provide desired functions. Routines may be executed at regular intervals, for example about 50-100 microsecond (ms) intervals during ongoing operation. Alternatively, routines may be executed in response to occurrence of a triggering event.
Referring now to
The illustrated circuit also includes a transformer (TR) 30 providing galvanic isolation as appreciated in the art, with first and second capacitors C1 and C2 arranged in parallel with each other within the inverter 18. Other depicted circuit elements include an inductor (L) disposed on the positive voltage rail 14+, with the battery pack 12 shown in parallel with the second capacitor C2. A switching circuit 35 is formed by the above-noted first and second electrical switches S1 and S1a.
In the embodiment of
Referring now to
In this arrangement, the AC current waveform 25 of
Referring briefly to
Mathematically, the present approach may be understood using a target root mean square (RMS) current. This value may be calculated based on a target temperature rise as follows:
Using nominal example values solely for illustration, a representative arrangement of 100 amp-hour (Ah) battery cells with a nominal voltage of 12.8V, and a total of 400 Ah and 5.12 kWh, and assuming a 3 kW embodiment of the inverter 18, the battery pack 12 would see a maximum heating current (RMS) of 300 A, with a cell current (Icell, RMS) of 75 A. Assuming the resistance per cell (Rcell) is 8 mΩ, the per-cell heating power would be 45 W, with a total heating power of 720 W. Now, assuming a cell level of 250 kWh/kg, the total cell mass (mbattery) is 20.5 kg. With a specific heat capacity (Cp,battery) of 1130 J/kgK for an exemplary LFP embodiment of the battery pack 12, the above formulation results in a temperature rise of 1.86° C./minute. As most commercially-available inverters are rates for 2 kW or more and 300 A (RMS), such a rate would be more than sufficient to provide the necessary heating power in an efficient and uniform manner when self-heating the battery pack 12 in accordance with the disclosure. As an additional benefit, the present method does not affect connected DC loads. AC loads are temporarily affected, however, due to the use of the power switches 180 of
Referring now to
The method 100 commences at block B102 in response to calibrated entry criteria. For example, the method 100 could proceed at regular timer-based intervals or in response to a user-initiated input. The battery controller 50 of
Block B104 of
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. The method 100 proceeds to block B126 when charging is not required, with the method 100 otherwise proceeding to block B108.
At block B108, the battery controller 50 next determines, in response to charging being required, whether Charge Sources A, B, or C are presently available. If so, the method 100 proceeds to block B110, with the method 100 otherwise proceeding to block B126.
Block B110 of the method 100 shown in
Block B112 includes comparing the measured battery temperature from block B110 to a calibrated temperature limit (TLim) below which charging of the battery pack 12 is not permitted. In a non-limiting implementation, the calibrated temperature limit could be about 32-35° F. In other embodiments, the calibrated temperature limit could be variable, for instance set at different temperatures depending on ambient conditions, or user-selectable above a particular manufacturer limit. The method 100 proceeds to block B114 when the measured battery temperature is less than the calibrated temperature limit, and to block B122 in the alternative when the measured battery temperature equals or exceeds such a calibrated temperature limit.
Still referring to
At block B116, the battery controller 50 once again measures the battery temperature (TBat) as noted above in block B110, thereafter proceeding to block B118.
Block B118, which is analogous to block B112 as described above, includes comparing the measured temperature to the calibrated temperature limit (TLIM). Blocks B116 and B118 continue in a loop until the measured temperature equals or exceeds the calibrated temperature limit, or until a predetermined time limit is reached. The method 100 then proceeds to block B120.
At block B120 of
At block B122, the battery controller 50 may connect the battery electric system 10 of
Block B124 includes commencing charging of the battery pack 12 using the connected Charge Source A, B, or C from block B120. The method 100 then proceeds to block B126.
The battery controller 50 when performing the method 100 of
The absence of a thermal management system in turn requires slower, less efficient ambient heating or the use of heating blankets. The present solutions instead take advantage of available hardware of an onboard inverter/charger, exemplified herein as the inverter 18 of
The detailed description and the drawings or figures are supportive and descriptive of the present teachings, but the scope of the present teachings is defined solely by the claims. While some of the best modes and other embodiments for carrying out the present teachings have been described in detail, various alternative designs and embodiments exist for practicing the present teachings defined in the appended claims.
