Back electromotive force management for electric vehicles

Abstract

An electric vehicle battery control system includes: a first electric motor configured to propel a vehicle in a drive mode in response to a drive current; a second electric motor operable to generate a back electromotive force voltage in a failure mode; a battery having an open battery discharge voltage for generating a drive current for coupling to the first electric motor; and a vehicle controller for limiting the driving current in response to a difference between the back electromotive force voltage and the open battery discharge voltage being less than a threshold voltage difference.

Description

Technical Field

[0001] The present disclosure generally relates to controlling vehicle systems in response to predictions of excess back EMF from an electric motor, and more particularly to methods and apparatus for voltage management through torque determination to prevent damage caused by back EMF from a faulty permanent magnet motor on a multi-motor vehicle. Background Art

[0002] Electric motors are used in electric vehicles (EVs) to convert electrical energy from batteries into mechanical energy to turn the wheels. Typically, two main types of electric motors are used in EVs: induction motors and permanent magnet synchronous motors (PMSMs). Induction motors are the most common type of electric motors used in EVs. They are relatively simple and cheap to manufacture. Induction motors are also very efficient, and they can provide high torque output. PMSMs are more expensive than induction motors, but they are also more efficient and provide better performance. PMSMs are often used in high-performance EVs, such as sports cars and racing cars. Modern EVs typically have two electric motors, one for each axle, but some EVs may have a single motor located under the hood, or four motors, one for each wheel.

[0003] While the need to protect vehicle operation during damaging or destructive operating conditions is clear, it is desirable that any vehicle protection algorithm be optimally used to provide maximum protection to the vehicle while continuing to provide service to the driver. It is desirable to overcome the above-described problems in order to provide systems and methods for vehicle system protection and for continued vehicle operation of vehicle propulsion and driver assistance systems. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. Summary of the invention

[0004] Disclosed herein are vehicle control methods and systems and related electrical systems for supplying motor systems, methods for manufacturing such systems, and methods for operating such systems, as well as motor vehicles and other equipment, such as aircraft, ships, wind turbines, and other EVs equipped with onboard propulsion systems. By way of example and not limitation, various embodiments of systems for mitigating vehicle hardware damage due to back EMP generated from an electric drive motor in regenerative mode are presented.

[0005] In a first non-limiting embodiment, a propulsion system includes: a first electric motor configured to propel a vehicle in a drive mode in response to a drive current; a second electric motor operable to generate a back EMF voltage in a fault mode; a battery having an open circuit battery discharge voltage for generating the drive current for coupling to the first electric motor; and a vehicle controller for limiting the drive current in response to a difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

[0006] According to another aspect of the present disclosure, the battery forms part of a rechargeable energy storage system.

[0007] According to another aspect of the present disclosure, a vehicle speed sensor is used to determine vehicle speed, and wherein the threshold voltage difference is determined in response to the vehicle speed and a predicted motor torque and a predicted motor power of the second electric motor at the vehicle speed and a predicted back EMF voltage of the second electric motor in a fault mode.

[0008] According to another aspect of the present disclosure, a battery charge level sensor is used to determine a battery charge level, and wherein a threshold voltage difference is determined in response to the battery charge level and a motor output voltage.

[0009] According to another aspect of the present disclosure, a processor is configured to calculate a predicted motor torque and a predicted motor power for a first electric motor, and wherein the drive current is further limited in response to a discharge voltage limit of a back EMF voltage.

[0010] According to another aspect of the present disclosure, the vehicle controller is further configured to apply a mechanical brake to the first electric motor in response to a difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

[0011] According to another aspect of the present disclosure, the vehicle controller is further configured to reduce the vehicle speed in response to a difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

[0012] According to another aspect of the present disclosure, the vehicle controller is further configured to short-circuit at least three phases of the second electric motor in response to a difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

[0013] According to another aspect of the present disclosure, a fuel cell is included, and wherein the vehicle controller is further configured to activate the fuel cell in response to a difference between a back electromotive force voltage and an open circuit battery discharge voltage being less than a threshold voltage difference, wherein the fuel cell is configured to generate an auxiliary voltage to boost the open circuit battery discharge voltage, thereby increasing the difference between the back electromotive force voltage and the open circuit battery discharge.

[0014] According to another aspect of the present disclosure, the vehicle controller is further configured to detect an undesirable condition of the second electric motor, and to limit the vehicle speed in response to the detection of the undesirable condition of the second electric motor.

[0015] According to another aspect of the present disclosure, a method of controlling a rechargeable energy storage propulsion system includes: calculating a back EMF voltage from an electric motor; determining a vehicle speed; determining a battery output voltage; and limiting at least one of torque and power to a drive unit and the vehicle speed in response to a difference between the back EMF voltage and the battery output voltage being less than a threshold difference.

[0016] According to another aspect of the present disclosure, at least one of torque and power to the drive unit is determined in response to a difference between the back EMF voltage and the battery output voltage being less than a threshold difference.

[0017] According to another aspect of the present disclosure, the back EMF voltage is limited by reducing the speed of the host vehicle.

[0018] According to another aspect of the present disclosure, the back EMF voltage is limited by causing a short circuit of at least three coils of the electric motor.

[0019] According to another aspect of the present disclosure, wherein the threshold difference is determined in response to a difference between a predicted back EMF voltage determined in response to a vehicle speed and a battery output voltage.

[0020] According to another aspect of the present disclosure, the back EMF voltage is estimated in response to vehicle speed and at least one of a stator temperature and a rotor temperature of the electric motor.

[0021] According to another aspect of the present disclosure, the back EMF voltage is calculated in response to the electric motor being in a fault state and the drive motor being in a drive state.

[0022] According to another aspect of the present disclosure, an alternative power source and control are also included, which artificially increases the open circuit battery discharge voltage via the alternative power source to provide additional voltage drop margin between the open circuit battery discharge voltage and the back electromotive force voltage to provide additional torque and power for traction in the drive motor in a driving state.

[0023] According to another aspect of the present disclosure, a rechargeable energy storage system control system includes: a first electric motor configured to propel a vehicle in response to a first drive current; a second electric motor configured to propel the vehicle in response to a second drive current and operable to generate a back electromotive force voltage during a fault state; a battery for storing charge to generate the first drive current and the second drive current, wherein the battery has an open circuit battery discharge voltage; and a controller including a processor configured to limit the first drive current in response to a difference between the open circuit battery discharge voltage and the back electromotive force voltage being less than a threshold difference.

[0024] According to another aspect of the present disclosure, the controller is further configured to limit the vehicle speed in response to the second electric motor being in a fault state, and to limit at least one of the determined minimum torque and the determined minimum power available to the first electric motor unit in response to a difference between the back EMF voltage and the battery output voltage being less than a threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Exemplary embodiments will be described below with reference to the following drawings, wherein like numerals designate like elements, and wherein:

[0026] Figure 1 illustrates a control system associated with a vehicle according to various embodiments;

[0027] Figure 2A and Figure 2B is a diagram depicting a cross-sectional view of an exemplary electric machine from two different perspectives according to various embodiments;

[0028] Figure 3 illustrates an exemplary EV propulsion system for use with back EMF management for an electric vehicle in accordance with various embodiments;

[0029] Figure 4 shows a graph illustrating operating voltage with back EMF control across vehicle speeds according to various embodiments;

[0030] Figure 5 A flow chart illustrating a method for controlling an exemplary EV propulsion system for use with back EMF management for an electric vehicle is shown in accordance with various embodiments; and

[0031] Figure 6 A flow chart illustrating another method for controlling an exemplary EV propulsion system for use with back-EMF management for an electric vehicle is shown in accordance with various embodiments. DETAILED DESCRIPTION

[0032] The following detailed description is merely exemplary in nature and is not intended to limit application and use. In addition, it is not intended to be bound by any express or implied theory presented in the aforementioned technical field, background technology, invention content or the following detailed description. As used herein, the term "module" refers to any hardware, software, firmware, electronic control component, processing logic and / or processor device (alone or in any combination), including but not limited to: application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), electronic circuits, processors (shared, dedicated or groups) and memories that execute one or more software or firmware programs, combinational logic circuits and / or other suitable components that provide the described functions.

[0033] Embodiments of the present disclosure may be described herein in terms of functions and / or logic block components and various processing steps. It should be understood that such block components may be implemented by any number of hardware, software and / or firmware components configured to perform a specified function. For example, embodiments of the present disclosure may employ various integrated circuit components, such as memory elements, digital signal processing elements, logic elements, lookup tables, etc., which may perform various functions under the control of one or more microprocessors or other control devices. In addition, those skilled in the art will appreciate that embodiments of the present disclosure may be practiced in conjunction with any number of systems, and the systems described herein are only exemplary embodiments of the present disclosure.

[0034] For the sake of brevity, conventional techniques related to other functional aspects of signal processing, data transmission, signaling, control, machine learning, image analysis, and systems (and the various operating components of the systems) may not be described in detail herein. In addition, the connecting lines shown in the various drawings included herein are intended to represent example functional relationships and / or physical couplings between various elements. It should be noted that many alternative or additional functional relationships or physical connections may exist in embodiments of the present disclosure.

[0035] refer to Figure 1 According to various embodiments, the control system 100 is associated with a vehicle 10 (also referred to herein as a "host vehicle"). Generally, the control system (or simply "system") 100 provides control of various actions of the vehicle 10 (e.g., torque control) established by reinforcement learning (RL) that is or can be stored in a DNN-type model that controls operations in response to data from vehicle inputs, for example, as described below in conjunction with FIG. Figure 4 Further described in more detail.

[0036] In various exemplary embodiments, the system 100 provides a process that allows DNN to be used in an ACC behavior prediction model for algorithms controlling torque and speed in the embedded controller software of the host vehicle 10 using the system 100. The system 100 enables learning of driver preferences for following distances for different vehicles, such as a target vehicle, and categorizes the driver's preferences based on driving scenarios (e.g., traffic signs, stop-and-go traffic, city driving, etc.). The system 100 builds a knowledge base for target vehicles that follows performance preferences using a Q matrix by leveraging online and historical driver and environment information.

[0037] like Figure 1 As depicted, vehicle 10 generally includes a chassis 12, a body 14, front wheels 16, and rear wheels 18. Body 14 is disposed on chassis 12 and substantially surrounds components of vehicle 10. Body 14 and chassis 12 may together form a frame. Wheels 16-18 are each rotationally coupled to chassis 12 near respective corners of body 14. In various embodiments, wheels 16, 18 comprise a wheel assembly that also includes respectively associated tires.

[0038] In various embodiments, the vehicle 10 is autonomous or semi-autonomous, and the control system 100 and / or its components are incorporated into the vehicle 10. The vehicle 10 is, for example, a vehicle that is automatically controlled to transport passengers from one location to another. The vehicle 10 is depicted as a passenger car in the illustrated embodiment, but it should be understood that any other means of transportation may also be used, including motorcycles, trucks, sport utility vehicles (SUVs), recreational vehicles (RVs), boats, aircraft, etc.

[0039] As shown, the vehicle 10 generally includes a propulsion system 20, a transmission system 22, a steering system 24, a braking system 26, a canister purge system 31, one or more user input devices 27, a sensor system 28, an actuator system 30, at least one data storage device 32, at least one controller 34, and a communication system 36. In various embodiments, the propulsion system 20 may include an internal combustion engine, an electric machine such as a traction motor, and / or a fuel cell propulsion system. The transmission system 22 is configured to transmit power from the propulsion system 20 to the wheels 16 and 18 according to a selectable speed ratio. According to various embodiments, the transmission system 22 may include a step-ratio automatic transmission, a continuously-variable transmission, or other suitable transmission.

[0040] Braking system 26 is configured to provide braking torque to wheels 16 and 18. In various embodiments, braking system 26 may include friction brakes, brake-by-wire brakes, a regenerative braking system such as an electric motor, and / or other suitable braking systems.

[0041] The steering system 24 affects the positioning of the wheels 16 and / or 18. Although depicted as including a steering wheel for illustrative purposes, in certain embodiments contemplated within the scope of the present disclosure, the steering system 24 may not include a steering wheel.

[0042] The controller 34 includes at least one processor 44 (and neural network) and a computer-readable storage device or medium 46. As described above, in various embodiments, the controller 34 (e.g., its processor 44) provides data related to the expected future path of the vehicle 10, including expected future steering instructions, to the steering control system 84 in advance for controlling steering for a limited period of time in the event that communication with the steering control system 84 becomes unavailable. In addition, in various embodiments, the controller 34 communicates with the steering control system 84 via the communication system 36 (e.g., via a communication bus and / or a transmitter ( Figure 1 (not depicted)) provides communication to the steering control system 84.

[0043] In various embodiments, the controller 34 includes at least one processor 44 and a computer readable storage device or medium 46. The processor 44 can be any custom or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), a secondary processor of several processors associated with the controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), any combination thereof, or any device generally used to execute instructions. For example, the computer readable storage device or medium 46 can include volatile and non-volatile storage in read-only memory (ROM), random access memory (RAM), and keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store multiple neural networks and various operating variables when the processor 44 loses power. The computer readable storage device or medium 46 may be implemented using any of several known memory devices such as a PROM (programmable read-only memory), an EPROM (electrical PROM), an EEPROM (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combination memory device capable of storing data, some of which represents executable instructions used by the controller 34 to control the vehicle 10.

[0044] The instructions may include one or more separate programs, each of which includes an ordered list of executable instructions for implementing logical functions. The instructions, when executed by the processor 44, receive and process signals from the sensor system 28, execute logic, calculations, methods and / or algorithms for automatically controlling components of the vehicle 10, and generate control signals to the actuator system 30 based on the logic, calculations, methods and / or algorithms to automatically control components of the vehicle 10. Although in Figure 1 Only one controller 34 is shown, but embodiments of the vehicle 10 may include any number of controllers 34 that communicate via any suitable communication medium or combination of communication mediums and collaborate to process sensor signals, execute logic, calculations, methods and / or algorithms, and generate control signals to automatically control features of the vehicle 10.

[0045] like Figure 1 As shown, in addition to the above-mentioned steering system 24 and controller 34, the vehicle 10 generally includes a chassis 12, a body 14, front wheels 16 and rear wheels 18. The body 14 is arranged on the chassis 12 and substantially surrounds the components of the vehicle 10. The body 14 and the chassis 12 can together form a frame. The wheels 16-18 are each rotationally coupled to the chassis 12 near a corresponding corner of the body 14. In various embodiments, the wheels 16, 18 include a wheel assembly, which also includes a tire associated with each.

[0046] In various embodiments, the vehicle 10 is an autonomous vehicle, and the control system 100 and / or its components are incorporated into the vehicle 10. The vehicle 10 is, for example, a vehicle that is automatically controlled to transport passengers from one location to another. The vehicle 10 is depicted as a passenger car in the illustrated embodiment, but it should be understood that any other means of transportation may also be used, including motorcycles, trucks, sport utility vehicles (SUVs), recreational vehicles (RVs), boats, aircraft, etc.

[0047] The controller 34 comprises a vehicle controller that operates based on the output of the neural network 33 model. In an exemplary embodiment, a feed-forward operation may be applied to an adjustment factor that is a continuous output of the neural network 33 model to generate a control action for a desired torque or other similar action (e.g., in the case of a continuous neural network 33 model, a continuous APC / SPARKS prediction value is the output).

[0048] In various embodiments, the one or more user input devices receive input from one or more passengers of the vehicle 10 (and the driver 11). In various embodiments, the input includes a desired travel destination for the vehicle 10. In certain embodiments, the one or more input devices 27 include an interactive touch screen in the vehicle 10. In certain embodiments, the one or more input devices 27 include a speaker for receiving audio information from the passenger. In certain other embodiments, the one or more input devices 27 may include one or more other types of devices and / or user devices (e.g., smart phones and / or other electronic devices) that may be coupled to the passenger.

[0049] The sensor system 28 includes one or more sensors 40a-40n that sense observable conditions of the external environment and / or the internal environment of the vehicle 10. The sensors 40a-40n include, but are not limited to, radar, lidar, global positioning system, optical camera, thermal imager, ultrasonic sensor, inertial measurement unit, and / or other sensors.

[0050] The actuator system 30 includes one or more actuators 42a-42n that control one or more vehicle features such as, but not limited to, the canister purge system 31, the air intake system 38, the propulsion system 20, the transmission system 22, the steering system 24, and the braking system 26. In various embodiments, the vehicle 10 may also include Figure 1 Not shown are interior and / or exterior vehicle features, such as various doors, trunk, and cabin features, such as air, music, lighting, touch screen display components (such as those used in conjunction with a navigation system), etc.

[0051] The data storage device 32 stores data for automatically controlling the vehicle 10, including the storage of data of the DNN established by RL for predicting the driver's behavior for vehicle control. In various embodiments, the data storage device 32 stores the machine learning model of the DNN and other data models established by RL. The model established by RL can replace the DNN behavior prediction model or the model established by RL (see Figure 2, DNN prediction model or RL prediction model). In an exemplary embodiment, the DNN does not require separate training, instead, the DNN behavior prediction model (i.e., DNN prediction model) is implemented using a set of learning functions. In various embodiments, the neural network (i.e., DNN behavior prediction model) can be established by RL or trained by a remote system through a supervised learning method, and communicated or supplied in the vehicle 10 (wirelessly and / or wiredly) and stored in the data storage device 32. The DNN behavior prediction model can also be trained via supervised or unsupervised learning based on input vehicle data of the main vehicle operation and / or sensory data about the main vehicle operating environment.

[0052] The data storage device 32 is not limited to control data, as other data may also be stored in the data storage device 32. For example, route information may also be stored within the data storage device 32 - that is, a collection of road segments (geographically associated with one or more of the defined maps) that together define a route that a user may take to travel from a starting location (e.g., the user's current location) to a target location. As will be appreciated, the data storage device 32 may be part of the controller 34, separate from the controller 34, or part of the controller 34 and part of a separate system.

[0053] The controller 34 implements the logic model established by RL or for the DNN based on the DNN behavior model that has been trained with a set of values, and the controller 34 includes at least one processor 44 and a computer-readable storage device or medium 46. The processor 44 can be any customized or commercially available processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor in several processors associated with the controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), any combination thereof, or any device generally used to execute instructions. For example, the computer-readable storage device or medium 46 may include volatile and non-volatile storage in a read-only memory (ROM), a random access memory (RAM), and a keep-alive memory (KAM). KAM is a persistent or non-volatile memory that can be used to store various operating variables when the processor 44 loses power. The computer readable storage device or medium 46 may be implemented using any of several known memory devices such as a PROM (programmable read-only memory), an EPROM (electrical PROM), an EEPROM (electrically erasable PROM), flash memory, or any other electrical, magnetic, optical, or combination memory device capable of storing data, some of which represents executable instructions used by the controller 34 to control the vehicle 10.

[0054] The instructions may include one or more separate programs, each of which includes an ordered list of executable instructions for implementing logical functions. The instructions, when executed by the processor 44, receive and process signals from the sensor system 28, execute logic, calculations, methods and / or algorithms for automatically controlling components of the vehicle 10, and generate control signals to the actuator system 30 based on the logic, calculations, methods and / or algorithms to automatically control components of the vehicle 10. Although in Figure 1 Only one controller 34 is shown, but embodiments of the vehicle 10 may include any number of controllers 34 that communicate via any suitable communication medium or combination of communication mediums and collaborate to process sensor signals, execute logic, calculations, methods and / or algorithms, and generate control signals to automatically control features of the vehicle 10.

[0055] The communication system 36 is configured to wirelessly communicate information to and from other entities 48, such as, but not limited to, other vehicles ("V2V" communications), infrastructure ("V2I" communications), remote transportation systems, and / or user equipment (described in more detail with respect to FIG. 2 ). In an exemplary embodiment, the communication system 36 is a wireless communication system configured to communicate via a wireless local area network (WLAN) using the IEEE 802.11 standard or by using cellular data communications. However, additional or alternative communication methods, such as dedicated short-range communications (DSRC) channels, are also considered within the scope of the present disclosure. A DSRC channel refers to a one-way or two-way short-range to medium-range wireless communication channel designed specifically for automotive use and a corresponding set of protocols and standards.

[0056] In various embodiments, the communication system 36 is used for communication between the controllers 34, including data related to the expected future path of the vehicle 10, including expected future steering instructions. Additionally, in various embodiments, the communication system 36 can facilitate communication between the steering control system 84 and / or more other systems and / or devices.

[0057] In certain embodiments, the communication system 36 is also configured for communication between the sensor system 28, the input device 27, the actuator system 30, one or more controllers (e.g., the controller 34), and / or more other systems and / or devices. For example, the communication system 36 may include any combination of a controller area network (CAN) bus and / or direct wiring between the sensor system 28, the actuator system 30, one or more controllers 34, and / or one or more other systems and / or devices. In various embodiments, the communication system 36 may include one or more transceivers for communicating with one or more devices and / or systems of the vehicle 10, devices of passengers, and / or one or more sources of remote information (e.g., GPS data, traffic information, weather information, etc.).

[0058] Figure 2A and Figure 2B2 is a diagram depicting a cross-sectional view of an exemplary motor 200 from two different perspectives. The exemplary motor 200 includes a housing 202 surrounding the exemplary motor 200 and a stator stack 204 within the housing 202. The exemplary stator stack 204 includes a plurality of windings 206 around the inner circumference of the stator stack 204. Enclosed within the exemplary stator stack 204 is a rotor stack 208. The exemplary rotor stack 208 includes a plurality of magnets 210 and a rotor hub 212. The exemplary rotor stack 208 is configured to rotate within the stator stack 204 using a bearing set 214. The exemplary stator stack 204 and the exemplary rotor stack 208 are enclosed within the housing 202 by an end cap 216. The exemplary motor 200 also includes a resolver 218 for measuring the rotation angle of the rotor stack 208.

[0059] Now turn to Figure 3 , an exemplary EV propulsion system 300 for use with back EMF management for an electric vehicle according to various embodiments is shown. The exemplary EV propulsion system 300 may include a motor controller 310, a power converter 340, a first drive motor 320, a second drive motor 330, a battery 350, a vehicle controller 370, and a sensor 360.

[0060] The vehicle controller 370 is configured to convert the desired trajectory or motion path of the vehicle into control commands for the actuators (such as steering wheels, throttles, and brakes) of the vehicle. The vehicle controller 370 considers the current state and environment of the vehicle to determine the best way to achieve the desired trajectory. The vehicle controller 370 may include longitudinal control and lateral control. Longitudinal control is responsible for controlling the speed and acceleration of the vehicle, while lateral control is responsible for controlling the steering angle and direction of travel of the vehicle. The vehicle controller 370 may use various sensors 360 to collect information about the vehicle state and environment. These sensors include cameras, radars, laser radars, and ultrasonic sensors. The vehicle controller 370 may use this sensor information to create a model of the vehicle's surroundings and predict the future behavior of the vehicle. Once the vehicle controller 370 has a model of the vehicle and its surroundings, it may use this model to determine the best way to achieve the desired motion path. The vehicle controller 370 will consider factors such as vehicle speed, road conditions, the presence of other vehicles and pedestrians, and traffic regulations. The vehicle controller 370 then issues control commands to the motor controller 310 and other lateral and longitudinal controllers to control the vehicle along the desired motion path.

[0061] The battery 350 stores electrical energy that provides power to the first drive motor 320, the second drive motor 330, and other EV systems. The battery 350 is rechargeable and is typically composed of hundreds or even thousands of individual battery cells. EV batteries are different from starting, lighting, and ignition (SLI) batteries because they are typically lithium-ion batteries designed for high power-to-weight ratios and energy density. Smaller, lighter batteries are desirable because they reduce the weight of the vehicle and thus improve its performance. Individual battery cells are connected in series and in parallel to achieve the desired voltage and capacity. The units are typically arranged in modules, which are then packaged together in a battery pack installed in the vehicle.

[0062] The most common type of EV battery is the lithium-ion (Li-ion) battery. Li-ion batteries have a high energy density, meaning they can store a large amount of energy in a relatively small and lightweight package. They also have a low self-discharge rate, meaning they can retain their charge for a long time when not in use. Other types of batteries sometimes used in EVs include nickel metal hydride (NiMH) batteries, lead-acid batteries, solid-state batteries, lithium-sulfur batteries, and aluminum-ion batteries. NiMH batteries have a lower energy density than Li-ion batteries, but they are cheaper. Lead-acid batteries have the lowest energy density of all three types of batteries, but they are also the cheapest. Solid-state batteries use a solid electrolyte instead of a liquid electrolyte. This makes them safer and more energy dense than traditional lithium-ion batteries. Lithium-sulfur batteries have a higher energy density than lithium-ion batteries, but they are still under development. Aluminum-ion batteries are cheaper than lithium-ion batteries, but they have a lower energy density.

[0063] The battery 350 first provides electrical energy to the power converter 340. The power converter 340 is configured to convert direct current (DC) electricity from the battery 350 into alternating current (AC) electricity to provide power to the first drive motor 320 and the second drive motor 330. The power converter 340 uses a plurality of electronic switches (such as MOSFETs) to switch current on and off at different frequencies and durations to convert DC power into AC power. The power converter 340 may also include a battery management system (BMS) to monitor and manage the battery 350 to ensure safe and efficient operation by tracking the charge state, temperature, and other parameters of the battery 350.

[0064] In certain exemplary embodiments, the motor controller 310 can be configured to control the current from the power converter 340 to the first drive motor 320 and the second drive motor 330. This allows the motor controller 310 to control the speed and torque of the drive motors 320 and 330. In certain exemplary embodiments, the motor controller 310 can use field-oriented control (FOC) to accurately control the torque and speed of the motor. FOC is a control algorithm that uses feedback from motor positioning and current sensors to calculate the optimal voltage and frequency applied to the motor windings. This results in a smoother, more efficient and more responsive motor. As electric vehicle technology continues to develop, more advanced and complex motor controllers may appear and may be used to control electric motors 320, 330 and / or power converters 340.

[0065] In certain exemplary embodiments, the motor controller 310 and the power converter 340 may also control the drive motors 320, 330 to generate electricity to charge the vehicle battery 350. For example, when the driver releases the accelerator or depresses the brake pedal, the drive motors 320, 330 may be placed in a regenerative mode to act as a generator to convert the kinetic energy of the vehicle back into electrical energy known as back electromotive force (EMF). Back EMF is a voltage generated by a rotating coil within the electric motor 320, 330 that is opposite to the voltage applied to the motor 320, 330. Back EMF is caused by electromagnetic induction. When a coil moves through a magnetic field, a current is induced in the coil. The direction of the current is determined by Lenz's law, which states that the induced current will always flow in the opposite direction to the change in magnetic flux. In the electric motors 320, 330, the rotating coil moves through a magnetic field created by a permanent magnet or an electromagnet. This induces a voltage in the coil, which is the back EMF. When the electric motor 320, 330 is not rotating, the back EMF is zero. As the electric motor 320, 330 begins to rotate, the back EMF increases. As the electric motor 320, 330 rotates faster, the back EMF increases further.

[0066] Back EMF is an important concept in the design and operation of electric motors. It is responsible for several important effects, including reducing current consumption, reducing power consumption, and enabling regenerative braking. Regenerative braking systems utilize back EMF to generate electrical energy to recharge the vehicle battery 350 and provide power to the vehicle power system. In a regenerative braking system, the kinetic energy of moving the vehicle is converted into back EMF and stored in the battery 350 using the electric motors 320, 330 as generators. The motor controller 310 can control the power converter 340 to convert the energy generated by the back EMF from AC to DC to store the generated electricity back in the battery 350.

[0067] When one or more of the drive motors 320, 330 supply a back EMF exceeding a threshold voltage to the power converter 340 and the high voltage DC bus, problems may arise. For example, continuing to drive with disabled drive motors 320, 330 on a multi-motor vehicle including both wheel hub motors and drive unit motors may generate a back EMF having a voltage level exceeding the threshold difference more than the voltage level of the battery 350. This excess voltage may cause damage to the battery 350 and the power converter 340. In certain exemplary embodiments, a vehicle having disabled drive motors 320, 330 capable of generating a back EMF exceeding the threshold difference is disabled by the vehicle controller 370 to avoid this potential damage. However, by controlling the system voltage response limits to below these levels, danger can be prevented and vehicle availability can be extended. If the system voltage response limits cannot be met or cannot be controlled to below these levels, the motor controller 310 or the vehicle controller 370 can use mechanical braking to reduce speed and prevent danger. Supervisory control can observe the battery, motor, brake system limits, and vehicle load estimators to intervene if open-loop control does not meet the target voltage response quickly enough to prevent a hazard.

[0068] In certain exemplary embodiments, a back EMF voltage for a given motor's voltage constant Ke across a temperature and speed range may first be calculated. This back EMP voltage across a temperature and speed range may be stored in a memory communicatively coupled to the motor controller 310. This calculated back EMF voltage may then be used as a limit on available battery power, further limiting the maximum voltage limit available to the power converter 340 to below the current battery voltage.

[0069] The available maximum voltage limit can then be used to generate a torque limit for operating the drive motor while still producing torque. By limiting the operating motor torque, the overall system voltage response is maintained below the calculated back EMF voltage. This limit reduces the likelihood of potential safety hazards and hardware damage. If the power converter 340 cannot control to these torque limits due to battery 350 or environmental conditions, the motor controller 310 can perform a mechanical torque reduction to ensure that the vehicle speed is reduced to the point where the default voltage response of the motor is sufficiently reduced to avoid potential damage or safety hazards.

[0070] The back EMF voltage point can be provided to the power converter 340 to establish a real-time control point to ensure that the gate command matches the desired gate state. Without this closed-loop design, the inverter gate may remain in a state that can cause a hazard at the system level. Throughout this operating state, the motor controller 310 and / or the vehicle controller 370 can execute a supervisory algorithm to observe the current motor temperature, battery current and voltage limits, and mechanical brake system limits. If the supervisory level leaves the target range for a given vehicle load for a period of time, the motor controller 310 can shut down the vehicle to prevent a hazard. If any key input to this control strategy is lost, the supervisory control can command a minimum operating state based on the vehicle speed that includes the lowest operating voltage point.

[0071] In certain exemplary embodiments, a drive motor alternative power source 380 may be used when the back EMF is greater than the current battery charge level by more than a threshold difference. An alternative power source 380 (such as a fuel cell, an alternative battery, a generator, etc.) may be used to increase the current battery charge level to reduce the difference between the current battery charge level and the back EMF voltage level. Such deployment of an alternative power source 380 may reduce the potential for dangerous high ampere currents to be coupled between the regenerative mode electric motors 320, 330 and the power converter 340.

[0072] Now turn to Figure 4 , a graph 400 illustrating operating voltage with back EMF control across vehicle speeds according to various embodiments is shown. Graph 400 illustrates an exemplary control region when the electric motor is in a regeneration mode. The current voltage level of the vehicle battery system is indicated on the vertical axis and the current vehicle speed is indicated on the horizontal axis. As the vehicle battery discharges while the vehicle is in use, the voltage indicated on the vertical axis will drop.

[0073] Graph 400 first illustrates line 435 indicating the maximum allowable rotor temperature for various back EMF voltages and vehicle speeds. In certain exemplary embodiments, the maximum allowable rotor temperature may be 90° C., where the 90° C. threshold is the maximum desired operating temperature to avoid potential system damage. Additionally, 430 indicates a maximum operating speed to which the vehicle is limited during regenerative braking due to a motor failure. In certain exemplary embodiments, the maximum operating speed may be 80 km / h. Such vehicle speed limits for control areas may be imposed to encourage vehicle maintenance.

[0074] A first permissible control region 410 is shown (where the vehicle may be in regeneration mode) and is limited below an expected maximum permissible rotor temperature 435 and a maximum operating speed 430. This first permissible control region 410 indicates a higher battery system charge level where the difference between the back EMF voltage level and the battery system voltage level will not be large enough to cause a potentially damaging high ampere current flow between the regeneration mode motor and the battery system. In certain exemplary embodiments, the first permissible control region 410 indicates the current permissible control region for a vehicle having one or more disabled electric motors.

[0075] A second allowed control region 420 is shown, where the battery charge level has been reduced to a level where the back EMF voltage level and the battery system voltage level can have a difference large enough to cause a high current between the regenerative mode motor and the battery system operating at high speed. A discharge region 425 is indicated, where the vehicle can be operated below the maximum allowed speed and at a battery charge level that may cause the rotor temperature to exceed the maximum allowed rotor temperature 435. In this discharge region 425, a three-phase short circuit can be commanded to the power converter and / or the vehicle motor. When the battery system voltage is lower than the back EMF voltage, the allowed control region 420 is indicated for vehicle operation using the regenerative mode motor mode, potentially causing thermal damage to the power converter. When the battery is at a battery charge level lower than the battery charge level allowed in the unregulated regenerative motor mode, the exemplary algorithm promotes operation of the vehicle at a lower speed. In certain exemplary embodiments, when the vehicle is in the discharge region 425, a second maximum speed level 432 can be achieved, which limits the vehicle to a second maximum speed lower than the initial maximum allowed speed, thereby preventing the vehicle from operating in the discharge region 425.

[0076] Now turn to Figure 5 , a method 500 for operating an exemplary EV propulsion system for use with back EMF management for an electric vehicle according to various embodiments is shown. The exemplary method 500 is first operable to monitor 515 that at least one of a plurality of electric motors is in a motor fault state. This motor fault state can be determined in response to one or more diagnostic trouble codes (DTCs) and fault flags. The motor fault can be detected at a power converter, a motor controller, a battery charger, etc., and the DTC and fault flag can be received via a controller area network (CAN) bus or other data bus. The motor fault state can indicate a faulty electric drive motor that rotates in response to friction between the tire and the road surface while one or more other drive motors are actively propelling the vehicle. If the motor is not in a motor fault state mode, the method 500 returns to detecting a faulty motor 515.

[0077] If it is determined 515 that one or more faulty motors are present, the method may next be operable to initiate 520 a back EMF monitoring algorithm. The back EMF monitoring algorithm may be initiated in response to detection of a faulty motor and / or initiation of an electric vehicle control and monitoring algorithm in response to the electric vehicle transitioning from a standby or off mode to a run mode. A run mode is a vehicle operating mode in which vehicle movement may be initiated.

[0078] The exemplary method 500 is next operable to determine 525 a voltage gradient for the expected back EMF of the faulty electric motor. The voltage gradient corresponds to the predicted back EMF of a particular motor at multiple rotational speeds and multiple operating temperatures. The voltage gradient may be used to generate a lookup table, may be used to generate a threshold function, or may be stored in a memory, processor memory or algorithm, or other data storage medium accessible to a motor controller and / or power converter. In certain exemplary embodiments, the back EMF voltage gradient may be provided by a faulty inverter associated with the faulty motor. In certain exemplary embodiments, if the inverter is capable of communication, the back EMF may be provided to the supervisory control in real time by the inverter, or if communication with the inverter does not exist, the back EMF may be calculated by the supervisory control based on available information or a worst case calibration, for example, if the drive unit temperature is unknown, it may use the ambient temperature if it is -10C.

[0079] The method 500 is next configured to determine 530 an open circuit battery discharge voltage (OCV). The OCV and the detected vehicle speed may be used to estimate whether the difference between the OCV and the back EMF voltage gradient for the current vehicle speed may be less than the voltage corresponding to the minimum operating torque requirement. The voltage difference between the OCV and the back EMF voltage gradient may be used to provide 535 a torque and power determination to subsequently calculate the minimum acceleration capability for a given vehicle speed associated with the back EMF voltage curve or gradient. Additionally, the motor controller, vehicle controller, or power converter may detect or determine vehicle mass, motor speed, inverter high voltage DC bus voltage, battery high voltage DC charge level, bus voltage, PSA state, motor stator & rotor temperature, battery pack & cell UV and current limits, and / or mechanical brake system limits to estimate the potential DC voltage generated by the electric motor in a fault mode. For example, observations of motor temperature, battery current and voltage limits, and mechanical brake system limits relative to vehicle mass may be used to determine an estimated under load battery voltage. In response to the minimum acceleration requirement, the OCV, and the back EMF voltage gradient, the method 500 may next determine 540 a maximum allowable vehicle speed. In certain exemplary embodiments, the maximum vehicle speed may be established based on only the battery available power applied to ensure that there is sufficient available power to meet the minimum starting acceleration requirement. The method 500 may then limit the vehicle speed to a speed less than the maximum allowable vehicle speed using a vehicle controller, a throttle controller, or a brake controller. For example, the vehicle speed may be limited to 80 km / h or another reduced speed. The reduced speed may serve as a safety measure to limit the generation of back EMF by a faulty electric motor during operation of the vehicle. The limited vehicle speed may also serve as an inducement for vehicle motor repair.

[0080] The method 500 may detect the current vehicle speed and determine whether the current vehicle speed is greater than the maximum allowed vehicle speed. Alternatively, the method 500 may determine whether the estimated underload battery voltage or OCV minus the minimum operating torque voltage load at the current vehicle speed is less than the predicted back EMF voltage gradient at the current vehicle speed. If the current vehicle speed exceeds the maximum allowed vehicle speed 550, then supervisory remedial action control may be initiated 555. Supervisory remedial action control may include limiting the vehicle speed to a lower maximum vehicle speed, such as 40 km / h, and / or may command a three-phase short circuit for both the faulty motor and the motor providing traction. In certain exemplary embodiments, a supplemental power source (such as a fuel cell) may be used to temporarily increase the battery charge voltage level to temporarily artificially increase the voltage of the battery above the OCV to provide additional torque, power, and speed to determine margin availability. In addition, friction brakes or mechanical brakes may be engaged to reduce vehicle speed and reduce back EMF voltage levels.

[0081] Now turn to Figure 6 , another method 600 for operating an exemplary EV propulsion system for an electric vehicle for use with back EMF management according to various embodiments is shown. The exemplary method 600 is first operable to monitor 605 for an electric motor fault. A motor fault may be determined in response to excessive current draw, incorrect rotational speed, out-of-range operating temperature, or excessive vibration. In addition, a rotation sensor (such as a Hall sensor resolver, a reluctance sensor, or sensorless feedback) may be used to detect the positioning of the electric motor. If the rotation sensor signal does not correspond to the expected motor positioning, a motor fault may be assumed. A faulty electric motor may result in a back EMF generated by the motor and coupled to a vehicle battery, a vehicle power system, and the like. If this back EMF exceeds the output voltage of the vehicle battery, damage to the electric motor, battery, high voltage bus, or other vehicle systems may occur.

[0082] If a motor fault is detected, the method 600 may next be operable to initiate 610 a back EMF management algorithm. The back EMF management algorithm may be operable to limit the rotation of the faulty battery so that any back EMF generated by the battery is limited to a level below the OCV of the battery. The back EMF may be generated by the rotation of the rotor of the faulty motor. In certain exemplary embodiments, the anti-EMP management algorithm may be configured to redirect the under-voltage limit to a predicted back EMF voltage for the faulty motor at the current vehicle speed. This provides a narrower voltage subset of the rechargeable energy storage system (RESS) voltage range. The algorithm may direct open-loop and closed-loop hybrid operation control and undervoltage control in response to power and torque determinations based on protection against a commanded three-phase short circuit.

[0083] In response to initiating the algorithm, the method 600 is operable to calculate 615 a back EMF gradient for the faulty motor across the motor speed for the current motor temperature. The back EMF gradient is the expected back EMF generated for a specific motor rotational speed at a given temperature. As the rotational speed of the motor increases (corresponding to an increased vehicle speed), a higher voltage back EMF is generated. In certain exemplary embodiments, the back EMF may be a volt / rpm value that varies with the temperature of the motor. This back EMF gradient may be stored in a memory, a lookup table, or used to generate a back EMF prediction formula for use by the back EMF management algorithm. The back EMF gradient may also be coupled 630 to a monitoring device for use by the monitoring device to monitor 645 key parameters. In certain exemplary embodiments, the method 600 may determine 630 a back EMF voltage gradient corresponding to a torque voltage limit. When the back EMF voltage is predicted to exceed a battery undervoltage limit, the back EMF voltage gradient-torque voltage limit may replace the battery undervoltage limit at vehicle speed.

[0084] The method 600 is next operable to determine 620 whether the available power for a given voltage point on the back EMF gradient exceeds the minimum required power. The minimum required power is the amount of power that needs to be supplied to one or more currently operating drive motors to maintain a minimum required operating torque. In certain exemplary embodiments, this minimum required operating torque may be the amount of torque required to maintain vehicle speed on a slope of a particular grade (such as a 3% grade) or to provide minimum acceleration for the vehicle on a flat slope. The available torque is determined in response to the difference between the current OCV and the predicted back EMF for the vehicle speed and the fault motor temperature. In response to the minimum operating torque demand, the minimum operating torque corresponds to an expected battery voltage drop such that at a particular speed, the underloaded battery voltage continues to exceed the back EMF gradient voltage.

[0085] Responsive to the available power for a given voltage point on the back EMF gradient, method 600 may next operate to determine if the available power is greater than a minimum required power for minimum vehicle performance.

[0086] In certain exemplary embodiments, if the available power is not greater than the minimum required power at 625, the method 600 determines at 635 whether there is an available alternative power source, such as a fuel cell, an auxiliary battery, or other voltage supply device. If no alternative power source is available, the method 600 returns to determining at 620 the available power for a given voltage point. If an alternative power source is available, the method 600 can activate at 650 the alternative power source to temporarily increase the OCV. This temporarily artificially raises the voltage of the battery above the OCV to provide additional torque, power, and speed to determine margin availability. A fuel cell or series generator can be used to provide additional voltage drop margin based on the back EMF voltage from the faulty motor, which in turn provides additional torque and power for traction in the inverter module and the motor.

[0087] The method 600 next determines 655 whether the combined power is greater than the minimum required power. If the combined power is not greater than the minimum required power, the method 600 returns to determining 620 the available power for a given voltage point. If the combined power is greater than the minimum required power, the method 600 next limits 640 the vehicle speed based on the predicted back EMF voltage point for the motor speed associated with the new and higher level of available power and available torque.

[0088] The method 600 next monitors 645 the key parameters of vehicle speed, bus voltage, motor temperature, battery voltage, and battery undervoltage limit. The method 600 checks these key parameters against predetermined thresholds. If none of the thresholds are exceeded, the method 600 returns to monitoring 645 the key parameters. If one or more of the thresholds are exceeded, the method 600 may take 665 additional protective measures. In certain exemplary embodiments, the protective measures may include engaging friction brakes or other regenerative braking motors, or initiating a three-phase short circuit on a faulty motor, one or more active drive motors, or all motors. Additionally, if one or more of the key parameters exceed a threshold, the method 600 may disable the vehicle.

[0089] Although at least one exemplary embodiment has been presented in the foregoing detailed description, it should be understood that there are a large number of variations. It should also be understood that one or more exemplary embodiments are merely examples and are not intended to limit the scope, applicability, or configuration of the present disclosure in any way. Specifically, the foregoing detailed description will provide a convenient roadmap for implementing one or more exemplary embodiments for those skilled in the art. It should be understood that various changes may be made to the functions and arrangements of the elements without departing from the scope of the present disclosure as set forth in the attached claims and their legal equivalents.

Claims

1. A power control system, comprising: a first electric motor configured to propel the vehicle in a drive mode in response to the drive current; a second electric motor operable to generate a back EMF voltage in a fault mode; a battery having an open circuit battery discharge voltage for generating the drive current for coupling to the first electric motor; as well as A vehicle controller is provided for limiting the drive current in response to a difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

2. The power control system of claim 1 , a vehicle speed sensor for determining vehicle speed, and wherein the threshold voltage difference is determined in response to the vehicle speed and a predicted motor torque and a predicted motor power of the second electric motor at the vehicle speed and a predicted back EMF voltage of the second electric motor in the fault mode.

3. The power control system of claim 1, a battery charge level sensor for determining a battery charge level, and wherein the threshold voltage difference is determined in response to the battery charge level and a motor output voltage.

4. The power control system of claim 1 , a processor to calculate a predicted motor torque and a predicted motor power for the first electric motor, and wherein the drive current is further limited in response to a discharge voltage limit of the back EMF voltage. 5 . The power control system of claim 1 , wherein the vehicle controller is further configured to apply a mechanical brake to the first electric motor in response to the difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference. 6 . The power control system of claim 1 , wherein the vehicle controller is further configured to reduce vehicle speed in response to the difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

7. The power control system of claim 1, wherein the vehicle controller is further configured to short circuit at least three phases of the second electric motor in response to the difference between the back EMF voltage and the open circuit battery discharge voltage being less than a threshold voltage difference.

8. The power control system of claim 1 , comprising a fuel cell, and wherein the vehicle controller is further configured to activate the fuel cell in response to a difference between the back EMF voltage and the open cell discharge voltage being less than a threshold voltage difference, wherein the fuel cell is configured to generate an auxiliary voltage to boost the open cell discharge voltage, thereby increasing the difference between the back EMF voltage and the open cell discharge.

9. The power control system of claim 1, wherein the vehicle controller is further configured to detect an undesirable condition of the second electric motor and to limit vehicle speed in response to detecting the undesirable condition of the second electric motor.

10. A method of controlling a rechargeable energy storage propulsion system, comprising: Calculate the back EMF voltage from the electric motor; Determine vehicle speed; Determine the battery output voltage; as well as At least one of torque and power to a drive unit and the vehicle speed are limited in response to a difference between the back EMF voltage and the battery output voltage being less than a threshold difference.

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