Patent Application
20250162460
The present disclosure relates to heating of a battery pack in an electrical system having multiple alternating current (AC)-powered rotary electric machines, and to computer-based control methodologies for heating such a battery pack.
Advanced hybrid-electric and full-electric motor vehicles may include multiple rotary electric machines, with such machines configured as electric propulsion or traction motors and a traction battery pack. For instance, different drive axles or road wheels of a motor vehicle may be driven by a corresponding traction motor. In such a powertrain configuration, the various traction motors are energized by the controlled discharge of the traction battery pack. When the traction motors are configured as AC machines, one or more inverter circuits are disposed between the traction battery pack and the traction motors. High-speed switching operation of internal power switches of the power switches inverts a direct current (DC) voltage from the traction battery pack to form an AC waveform suitable for energizing phase windings of the traction motors. The energized traction motors are thus able to power a driven load, including one or more road wheels in a representative automotive application.
Motor vehicles and other electrical systems having the above-noted traction battery pack are frequently idle when parked for extended periods. This may occur in cold ambient conditions, which in turn lowers the battery's temperature. For optimal charging efficiency and prolonged battery life, the traction battery pack is typically warmed to a threshold charging temperature prior to commencing offboard charging. However, the motor vehicle or other host electrical system may lack a resident fluidic thermal management system (TMS), or the available heating response of an onboard TMS may be suboptimal for a given charging scenario and/or prevailing weather conditions.
Disclosed herein are electric circuit topologies and related computer-based control methodologies for selectively heating an electrochemical battery pack of an electrical system having two or more rotary electric machines, each of which is powered by a respective motor drive circuit. The electrical system is exemplified herein as a hybrid electric or battery electric motor vehicle solely for illustrative consistency. The motor vehicle includes two or more such electric machines each constructed and operating as an alternating current (AC) traction motor. The traction motors are configured to generate torque for powering one or more road wheels of the motor vehicle. However, other mobile or stationary electrical systems having multiple electric machines may similarly benefit from the present teachings, and therefore the present disclosure is not limited to vehicular applications.
A multi-motor electrical system in accordance with an aspect of the disclosure includes a battery pack, a plurality of inverter circuits, a plurality of electric motors, and an electronic controller. The electric motors are connected to the battery pack via a corresponding one of the inverter circuits. The electronic controller is in communication with the inverter circuits. In response to predetermined entry conditions, e.g., a temperature of the battery pack and/or an ambient temperature being less than a minimum charging temperature, the electronic control monitors respective motor temperatures of the electric motors, e.g., as reported or measured values, and selectively inject respective direct-axis (d-axis) currents into the electric motors. This occurs via manipulation of a corresponding d-axis voltage command thereto, as appreciated in the art. The electronic controller also generates an AC battery current via the electric motors using the d-axis currents.
As part of this embodiment, the electronic controller heats the battery pack using the AC battery current. This action occurs until a battery temperature of the battery pack reaches a predetermined battery temperature limit, and includes coordinating the d-axis currents such that the respective motor temperatures do not exceed a predetermined motor temperature limit of the electric motors.
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.
For purposes of this Detailed Description, unless specifically disclaimed: the singular includes the plural and vice versa; the words “and” and “or” shall be both conjunctive and disjunctive; the words “any” and “all” shall both mean “any and all”; and the words “including,” “containing,” “comprising,” “having,” and the like, shall each mean “including without limitation.” Moreover, words of approximation, such as “about,” “almost,” “substantially,” “generally,” “approximately,” and the like, may each be used herein to denote “at, near, or nearly at,” or “within 0-5% of,” or “within acceptable manufacturing tolerances,” or any logical combination thereof, for example. Lastly, directional adjectives and adverbs, such as fore, aft, inboard, outboard, starboard, port, vertical, horizontal, upward, downward, front, back, left, right, etc., may be with respect to a motor vehicle, such as a forward driving direction of a motor vehicle when the vehicle is operatively oriented on a horizontal driving surface.
Referring to the drawings, wherein like reference numerals correspond to like or similar components throughout the several Figures, a multi-motor electrical system 10 is illustrated in
One or more of the road wheels 14 may be powered by respective first and second traction motors 16A and 16B of the multi-motor electrical system 10 in such a construction, i.e., with generated motor output torques TO,A and TO,B ultimately being delivered to one or more drive axles and/or road wheels 14 of the motor vehicle 12. A traction battery pack 18 of the multi-motor electrical system 10 may be constructed from an application-suitable group of electrochemical battery cells (not shown), e.g., lithium-ion or lithium-polymer battery cells of a pouch, can, or prismatic type, to output a direct current (DC) voltage (VDC). The traction battery pack 18 as contemplated herein is selectively heated by an alternating current (AC) battery current 22. The AC battery current 22 for its part is generated by direct-axis (d-axis) voltage control of the first and second traction motors 16A and 16B as set forth below, and the resulting injection of a d-axis current as appreciated in the art. Additionally, AC heating of the traction battery pack 18 (and optionally the first and second traction motors 16A and 16B in some embodiments) may be assisted by a coordinated fluidic heat exchange between interconnected cooling loops CL-A, CL-B, and CL-BAT as described below. Thus, heating of the traction battery pack 18 may continue even after AC heating is completed.
In the simplified circuit topology of
As appreciated in the art, the inverter circuits 24A and 24B contain therein various solid-state power switches, e.g., insulated-gate bipolar transistors (IGBTs), metal-oxide-semiconductor field-effect transistors (MOSFETs), or other switchable semiconductor-based components. High-speed switching control of the inverter circuits 24A and 24B, typically via pulse-width modulation (PWM), thus converts a DC voltage from the traction battery pack 18 to an AC voltage suitable for energizing individual phase windings of the first and second traction motors 16A and 16B. Using PWM, operation of the inverter circuits 24A and 24B ultimately controls an output state of the first and second traction motors 16A and 16B when generating the output torque TO,A and/or TO,B during electric or hybrid electric propulsion modes of the motor vehicle 12.
HIGH-FREQUENCY AC HEATING: Selective AC-based internal heating of the traction battery pack 18 (“self-heating”) as contemplated herein requires the selective application to the traction battery pack 18 of the high-frequency AC battery current 22. The term “high frequency” as used herein may be about 200 hertz (Hz) to 1 kHz or more in a possible implementation. In the illustrated
Performance of the d-axis injections for the purpose of heating the traction battery pack 18 without overheating the first and second traction motors 16A and 16B involves the selective use of an oscillating d-axis voltage command to the first and second traction motors 16A and 16B. This occurs in conjunction with a quadrature-axis (q-axis) voltage command of zero. As a result of d-axis and q-axis voltage command manipulation on the d-axis and q-axis, a d-axis current is injected into the control architecture of the first and second traction motors 16A and 16B to cause the AC current waveforms 22A and 22B. As noted above, the AC current waveforms 22A and 22B ultimately combine to form the resulting AC battery current 22, which is then applied across electrode terminals of the traction battery pack 18. This oscillating current thus heats the traction battery pack 18, albeit at the expense of heating the first and second traction motors 16A and 16B. Coordination of d-axis current injections of the first and second traction motors 16A and 16B is thus performed by the electronic controller 50 as described below.
Charging of the traction battery pack 18 of
Within the scope of the present disclosure, the electronic controller 50 includes one or more processors 52 and memory 54. Each processor 52 is configured to receive or self-generate input signals (CCI). The input signals (CCI) may include the measured battery temperature (TBAT) as communicated by the temperature sensor 18S, a mode signal indicative of a present operating mode of the multi-motor electrical system 10, e.g., the speed, transmission state, and on/off state of the motor vehicle 12, and possibly other input values. In response to receipt of the input signals (CCI), the electronic controller 50 is configured to execute the present strategy as one or more algorithms or instruction sets, with the electronic controller 50 ultimately transmitting output signals (CCO) to the inverter circuits 24A and 24B of
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.
D-AXIS VOLTAGE COMMANDS: as appreciated in the art, d-axis and q-axis commands in a motor control context are used as adjustable setpoints or control “knobs” or “handles” that may be accessed by the electronic controller 50 when controlling flux and torque settings of the first and second traction motors 16A and 16B. In geometric terms, the d-axis and q-axis are single-phase representations of the flux contribution of separate sinusoidal phase quantities occurring at the same angular velocity. The d-axis for a given one of the first and second traction motors 16A and 16B is aligned/in-phase with the permanent magnet field of a rotor thereof (not shown), and is the particular axis by which flux is primarily produced. The d-axis current is manipulatable by the electronic controller 50 using d-axis voltage commands, as described below when performing the AC-based self-heating mode of the traction battery pack 18.
Torque production of the first and second traction motors 16A and 16B is produced primarily on its q-axis, which is typically aligned with the rotating field of a stator thereof (not shown), i.e., 90° out-of-phase with the magnetic field of the rotor. During the present self-heating mode, the q-axis voltage command is therefore set to zero to minimize torque generation and resulting movement of the motor vehicle 12. The q-axis command is used in motor control strategies to influence torque production. During the AC-based self-heating mode considered, however, the q-axis voltage command is purposefully set to zero and maintained there for the duration of the self-heating mode.
ZERO-SEQUENCE VOLTAGE COMMAND: a zero-sequence voltage command could be applied in one or more constructions of the first and second traction motors 16A and 16B to generate a balanced set of phase voltages. In a balanced three-phase system, for example, the individual phase voltages may be represented using complex numbers, with the zero-sequence voltage representing a voltage signal that is applied simultaneously to all three electrical phases, nominally the a, b, and c phases. Application of a balanced voltage signal causes a current to flow through stator windings of such a machine, which in turn produces a rotating magnetic field having a zero net magnetic field in every direction. Zero-sequence voltage commands, which do not contribute to mechanical torque production, may be selectively used herein to modify the magnetic field produced in the first and second traction motors 16A and 16B during the contemplated self-heating mode. That is, although a neutral connection point does not typically exist in an AC motor constructed for use in the multi-motor electrical system 10, unlike residential electrical systems, such a motor construction could be used in some embodiment. In such a case, the zero-sequence voltage command adds another control handle that could be leveraged for optimal performance of the self-heating mode.
Referring now to a time plot 30 of
As part of the present approach, the electronic controller 50 of
The motor temperature limit (TMAX) may be established as a static thermal limit, and thus recorded as a reference value in memory 54 of the electronic controller 50 shown in
When this occurs, the electronic controller 50 may commence AC heating of the traction battery pack 18 using d-axis voltage control of the second traction motor 16B. As the first traction motor 16A cools, the second traction motor 16B begins to heat up as it outputs the AC current waveform 22B of
By t2 in
As noted briefly above, the electronic controller 50 in one or more embodiments may be configured to heat the traction battery pack 18 by transferring heat through a plurality of interconnected cooling loops each configured to circulate coolant to a respective one of the first and second traction motors 16A and 16B and the traction battery pack 18. The electronic controller 50 may be configured to direct waste heat from the first and second traction motors 16A and 16B to the traction battery pack 18 via the interconnected cooling loops, in this case from the cooling loop CL-A and/or CL-B of
Instead of doing this, some of the waste heat from the first and/or second traction motors 16A and/or 16B may be transferred into the cooling loop CL-BAT, thereby heating the traction battery pack 18 with heated coolant even after the electronic controller 50 discontinues AC-based heating. Thus, termination of AC-based heating of the traction battery pack 18 of
Referring to
Viewing
The AC battery current (IBAT) (trace 46 of
Referring briefly to
To find this optimal phase angle, the electronic controller 50 of
Synchronization of AC Heating: AC-based heating of the traction battery pack 18 of
where n is the number of waveforms, i.e., the two AC current waveforms 22A and 22B in the two-motor embodiment of
and thus less AC heating than the synchronized case.
A synchronization problem potentially arises due to the accuracy of oscillating crystals used by the electronic controller 50. A typical crystal is accurate to about ±100 parts per million, or about ±0.01%. Thus, for a representative 8 MHz oscillating crystal, the frequency will range from 7.9992-8.0008 MHz. In an exemplary case in which the injection frequency is 450 Hz, the frequency of the AC current waveforms 22A and 22B of
The electronic controller 50 may be configured to synchronize an injection frequency of the d-axis currents id-M1 and id-M2 using a predetermined synchronization strategy. Two exemplary synchronization strategies include: (1) a communication channel synchronization strategy, or (2) a phase-locked loop (PLL) synchronization strategy. Communication channel synchronization, i.e., option (1), may entail using controller area network (CAN) bus signals or other differential signals between different control processors to determine a difference between the frequencies, and to thereafter correct for the difference. This may occur every 5-10 s in the above-noted 11.11 s example, or at another desired frequency in other implementations. While relatively simple to implement, this option would be predicated on reliable high-speed network communication, and thus is not necessarily suitable or available in a given application. Option (2), i.e., PLL-based synchronization, will now be described with reference to
PLL-Based Synchronization: a variety of electrical values are depicted in
To solve this potential control issue, d-axis current injection of the second traction motor 16B may be interrupted for short intervals to allow the PLL logic to properly track the injection angle ϕM1 and injection frequency of the first traction motor 16A in case of small frequency or phase drift over time. The injection angle ϕM1 and frequency obtained during this short interval may be used for updating synchronism of AC injection in the second traction motor 16B at a fixed rate, e.g., every 5-10 s in a possible implementation, with the actual rate being dependent on how quickly the AC current waveforms 22A and 22B of
Also illustrated in
Asynchronous Operation of AC Heating: referring now to
Four examples are illustrated in
Each of the four examples uses a normalized amplitude (A) of 1. Example (1) is a single motor (n=1), with a representative AC current waveform 22A having a nominal injection frequency of 400 Hz. Such a signal when processed by an RMS calculation block 82 will output an RMS current of 0.7071 A.
Example (2) involves two motors, i.e., n=2, and thus representative AC current waveforms 22A and 22B, e.g., as shown in the simplified two-motor implementation of
Continuing with examples (3) and (4) for three-motor and four-motor embodiments in which n=3 and n=4, respectively, the RMS current increases to 1.229 A and 1.414 A. Thus, asynchronous operation will still result in AC heating of the traction battery pack 18 of
Referring now to
For instance, the method 100 may initiate onboard the motor vehicle 12 of
Block B104 (“INC id-M1”) includes increasing the pulsating d-axis current in the first motor generator 16A of
Block B106 (“INC id-M2”) is analogous to block B104, but performed for the second traction motor 16B. That is, block B106 includes increasing the pulsating d-axis current in the second motor generator 16B. This action is depicted in
At block B108 (“MOD ϕ-M2 (ϕ=ϕ+Δϕ)”) includes modifying the phase angle of the second traction motor 16B. The electronic controller 50 may increase the phase angle by Δ ϕ from subsequently described block B110, or may decrease the phase angle by Δ ϕ from subsequently described block B112. The method 100 then proceeds to block B109.
At block B109 (“Δ PB>0”) includes determining the change in output power (Δ PB) from the propulsion battery pack 18 of
Block B110 (“Δ ϕ=+Δ ϕ”) includes recording a delta phase angle value (4 ϕ) for current injection of the second traction motor 16B that increases the prior value by a set amount. For example, starting with a phase angle of 20°, the electronic controller 50 may increase this value by 5°, such that the increased delta phase angle value (+Δ ϕ) is +5°. The method 100 then returns to block B108 where the increased delta phase angle value (+Δ ϕ) is applied.
Block B112 (“Δ ϕ=−Δ ϕ”) is analogous to block B110, and includes recording a delta phase angle value (Δ ϕ) for current injection of the second traction motor 16B that decreases the prior value by a set amount. For example, starting with a phase angle of 20° in keeping with the example of block B110, the electronic controller 50 may decrease this value by 5°, such that the decreased delta phase angle value (−Δ ϕ) is −5°. The method 100 then returns to block B108 where the decreased delta phase angle value (−Δ ϕ) is applied as set forth above. Blocks B108-B112 thus collectively allow for maximum power point tracking to maximize AC heating of the traction battery pack 18.
The teachings set forth above with reference to
The AC-based battery heating process occurs without overheating the first and second traction motors 16A and 16B. Although optional, the use of supplemental cooling via the cooling loops CL-A, CL-B, and CL-BAT 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.
