METHOD AND SYSTEM CONFIGURED FOR DETERMINING THE STATOR RESISTOR OF AN ELECTRIC MOTOR

Abstract

Methods and systems for determining the stator resistance value of an electric motor are provided. The systems can include the electric motor, comprising a stator and a rotor; a sensor system configured to generate sensor data indicating detected electric motor operating conditions, including current, phase angle, motor speed, stator temperature, and rotor temperature; and a controller operationally coupled to the sensor system and the electric motor.The controller is configured to: determine an initial stator resistance value based on a stator reference temperature and either estimated data or sensor data received from the sensor system; determine a stator temperature coefficient based on the sensor data and a non-linear stator resistance-ratio curve; and determine the stator resistance value based on the initial stator resistance value and the stator temperature coefficient.

Description

INTRODUCTION

[0001] The technical field generally relates to electric motor operation and, more particularly, to systems and methods for determining the stator resistance of a 3-phase alternating current (AC) motor, e.g., a vehicle propulsion system.

[0002] The document US 2017 / 0 126 166 A1 discloses an electrical machine arrangement with an electrical machine comprising a stator and a rotor.

[0003] Electric vehicles use control systems to manage performance, efficiency, and the overall driving experience. The control systems use a combination of sensor inputs, algorithms, and mathematical models that provide several parameters for vehicle operation. One such parameter is stator resistance. A stator is a stationary electric motor component, and its resistance refers to how much the stator opposes the flow of an electric current. Control systems can use stator resistance to regulate the current flowing through the motor windings. By adjusting the current flow, the control systems can control the motor's torque output and acceleration characteristics. Accurate knowledge of stator resistance allows control systems to achieve consistent performance under various operating conditions.

[0004] Therefore, it is an object of the invention to provide a system and a method capable of accurately determining the stator resistance of an electric motor during its operation.

[0005] The problem is solved by the features of the independent claims.

[0006] Furthermore, other desirable features and characteristics of the present invention will become apparent from the following detailed description and the dependent claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background. SUMMARY

[0007] A method for use with an electric motor is provided. In one example, the method, with one or more processors, comprises: determining an initial stator resistance value based on a stator reference temperature and either estimated data or sensor data indicative of sensed conditions of an electric motor, including a current, a phase angle, a motor speed, a stator temperature of the electric motor, and a rotor temperature of the electric motor; determining a stator temperature coefficient based on the sensor data and a nonlinear stator resistance ratio curve; and determining the stator resistance value based on the initial stator resistance value and the stator temperature coefficient.

[0008] In various examples, the stator reference temperature of the method is determined with the one or more processors by: receiving stator design resistance values ​​of the electric motor; determining at least two stator resistance values ​​for at least two different stator reference temperatures; determining stator temperature coefficients for each of the at least two different reference temperatures; determining calculated stator resistance values ​​for each of the at least two different reference temperatures based on the at least two resistance values ​​and the temperature coefficient values; determining error values ​​between the design resistance values ​​and the calculated resistance values ​​at each of the at least two different reference temperatures; determining which of the at least two different reference temperatures has the lowest error value;and setting the one of the at least two different reference temperatures with the lowest error value as the stator reference temperature;

[0009] In various examples, the temperature coefficient values ​​of the method are defined by nonlinear resistance ratio curves.

[0010] In various examples, the initial stator resistance value is determined based on the sensor data and the stator reference temperature.

[0011] In various examples, the method's nonlinear stator resistance ratio curve is based on the stator reference temperature.

[0012] In various examples, the electric motor of the method is a vehicle propulsion system component, wherein the stator resistance value is determined during operation of the propulsion system.

[0013] In various examples, the electric motor of the process is a 3-phase AC motor.

[0014] In various examples, the method includes adjusting an operating parameter of the electric motor based on the stator resistance value.

[0015] A system for use with an electric motor is provided. In one example, the system includes an electric motor comprising: a stator and a rotor; a sensor system including one or more sensors configured to generate sensor data indicative of sensed electric motor operating conditions including a current, a phase angle, a motor speed, a stator temperature, and a rotor temperature; and a controller operatively coupled to the sensor system and the electric motor.The controller is configured by one or more processors to: determine an initial stator resistance value based on a stator reference temperature and either estimated data or sensor data received from the sensor system; determine a stator temperature coefficient based on the sensor data and a nonlinear stator resistance ratio curve; and determine a stator resistance value based on the initial stator resistance value and the stator temperature coefficient.

[0016] In various examples, the stator reference temperature used by the system controller is a first of a plurality of reference temperatures, wherein each of the plurality of reference temperatures is used to determine corresponding calculated stator resistance values, wherein error values ​​between the calculated resistance values ​​and corresponding stator design resistance values ​​at the plurality of reference temperatures are determined, wherein the first of the plurality of reference temperatures has the lowest error value. In various examples, the calculated resistance values ​​are based on a plurality of resistance values ​​at each of the plurality of reference temperatures and on temperature coefficients at each of the plurality of reference temperatures, wherein the temperature coefficient values ​​are defined by nonlinear resistance ratio curves.

[0017] In various examples, the initial stator resistance value is determined by the system controller based on the sensor data and the stator reference temperature.

[0018] In various examples, the nonlinear stator resistance ratio curve used by the system controller is based on the stator reference temperature.

[0019] In various examples, the electric motor of the system is a vehicle propulsion system component, wherein the stator resistance value is determined during operation of the propulsion system.

[0020] In various examples, the system's electric motor is a 3-phase AC motor.

[0021] In various examples, the system controller is configured, through the one or more processors, to adjust an operating parameter of the electric motor based on the stator resistance value.

[0022] A vehicle is provided that, in one example, includes an electric motor comprising: a stator and a rotor; a sensor system including one or more sensors configured to generate sensor data indicative of sensed electric motor operating conditions including a current, a phase angle, a motor speed, a stator temperature, and a rotor temperature; and a controller operatively coupled to the sensor system and the electric motor.The controller is configured by one or more processors to: determine an initial stator resistance value based on a stator reference temperature and either estimated data or sensor data received from the sensor system; determine a stator temperature coefficient based on the sensor data and a nonlinear stator resistance ratio curve; determine a stator resistance value based on the initial stator resistance value and the stator temperature coefficient; and adjust an operating parameter of the electric motor based on the stator resistance value.

[0023] In various examples, the stator reference temperature used by the vehicle controller is a first of a plurality of reference temperatures, wherein each of the plurality of reference temperatures is used to determine corresponding calculated stator resistance values, wherein error values ​​between the calculated resistance values ​​and corresponding stator design resistance values ​​at the plurality of reference temperatures are determined, the first of the plurality of reference temperatures having the lowest error value, wherein the initial stator resistance value is determined based on the sensor data and the stator reference temperature.

[0024] In various examples, the nonlinear stator resistance ratio curve used by the vehicle controller is based on the stator reference temperature.

[0025] In various examples, the vehicle's electric motor is a vehicle propulsion system component, wherein the stator resistance value is determined during operation of the propulsion system. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The exemplary embodiments are described below in conjunction with the following drawing figures, wherein like reference numerals indicate like elements; Fig. 1 is a functional block diagram of a vehicle including an engine control system configured to operate in combination with an electric motor of the vehicle, according to one embodiment; Fig. 2 is a system and data flow diagram for the engine control system and the electric motor according to an embodiment of the vehicle of Fig. 1; Fig. 3 is a flowchart of a method for determining stator resistance for an electric motor according to one embodiment; Fig. 4 is a graph illustrating resistance values ​​versus motor speed for an exemplary electric motor according to one embodiment at various reference temperatures; and Fig. 5 is a graph illustrating resistance ratios versus motor speed for an exemplary electric motor according to an embodiment at a reference temperature. DETAILED DESCRIPTION

[0027] The following detailed description is merely exemplary in nature. As used herein, the term module refers to any hardware, software, firmware, electronic control component, processing logic, and / or processor device, individually or in any combination, including, without limitation, an application-specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) with memory executing one or more software or firmware programs, a combinational logic circuit, and / or other suitable components that provide the described functionality.

[0028] Here, embodiments of the present disclosure may be described in terms of functional and / or logical block components and various processing steps. It should be appreciated that such block components may be implemented by any number of hardware, software, and / or firmware components configured to perform the specified functions. For example, an embodiment of the present disclosure may employ various integrated circuit components, e.g., memory elements, digital signal processing elements, logic elements, lookup tables, or the like, capable of performing a variety of functions under the control of one or more microprocessors or other control devices.In addition, those skilled in the art will understand that embodiments of the present disclosure may be practiced in connection with any number of systems and that the systems described herein are merely exemplary embodiments of the present disclosure.

[0029] For brevity, conventional techniques related to signal processing, data transmission, signaling, control, and other functional aspects of the systems (and the individual operating components of the systems) need not be described in detail here. Furthermore, the interconnections shown in the various figures included herein are intended to represent examples of functional relationships and / or physical couplings between the various elements. It should be appreciated that many alternative or additional functional relationships or physical connections may be present in an embodiment of the present disclosure.

[0030] Systems and methods described herein promote efficient operation of an electric motor, such as a 3-phase alternating current (3-phase AC) motor. In particular, the systems and methods provide for accurate determination of stator resistance during operation of the electric motor. The systems and methods account for a nonlinear relationship of stator resistance at various operating speeds of the electric motor by determining, in certain embodiments, a reference temperature that has a low error relative to other possible reference temperatures. The systems and methods can promote efficient determination of stator resistance with relatively low processing power.

[0031] Fig. 1 illustrates a vehicle 10 according to an exemplary embodiment. In certain embodiments, the vehicle 10 comprises an automobile. The vehicle 10 includes an engine control system 100 having a database of one or more reference temperatures accessible by the engine control system 100 for calculating or looking up a stator resistance of an electric motor 21 of the vehicle 10. The one or more reference temperatures are determined using the methods disclosed herein.

[0032] In various embodiments, the vehicle 10 may be one of a number of different types of automobiles such as a sedan, a station wagon, a truck, or an off-road vehicle (SUV), and in certain embodiments may be two-wheel drive (2WD) (i.e., rear-wheel drive or front-wheel drive), four-wheel drive (4WD), or all-wheel drive (AWD), and / or various other types of vehicles or mobile platforms.

[0033] As in Fig. 1, the vehicle 10 generally includes a chassis 12, a body 14, front wheels 16, and rear wheels 18. The body 14 is disposed on the chassis 12 and substantially encloses components of the vehicle 10. The body 14 and the chassis 12 may together form a frame. The wheels 16-18 are each rotationally coupled to the chassis 12 near a respective corner of the body 14.

[0034] The vehicle 10 further includes a propulsion system 20, a transmission system 22, a steering system 24, a sensor system 28, an actuator system 30, at least one data storage device 32, at least one controller 34, and a connection (e.g., via a wireless communication system) to a remote system 36. The propulsion system 20 includes an electric motor 21, such as a 3-phase AC motor. The transmission system 22 is configured to transfer power from the propulsion system 20 to the wheels 16-18 according to selectable speed ratios. According to various embodiments, the transmission system 22 may include a stepped-ratio automatic transmission, a continuously variable transmission, or another suitable transmission. The steering system 24 influences a position of the wheels 16-18.While illustrated as including a steering wheel for illustrative purposes, in some embodiments contemplated within the scope of the present disclosure, the steering system 24 may not include a steering wheel.

[0035] The sensor system 28 includes one or more sensing devices 40a-40n that sense observable conditions of the external environment, the internal environment, and / or a status or condition of a corresponding component of the vehicle 10 and provide such a condition and / or status to other systems of the vehicle 10, such as the controller 34. It should be understood that the vehicle 10 may include any number of the sensing devices 40a-40n. The sensing devices 40a-40n may include, but are not limited to, current sensors, voltage sensors, temperature sensors, engine speed sensors, position sensors, etc.

[0036] The actuator system 30 includes one or more actuator devices 42a-42n that control one or more vehicle features such as, but not limited to, the propulsion system 20, the transmission system 22, and / or the steering system 24.

[0037] The data storage device 32 stores data for use in controlling the vehicle 10 and / or its systems and components. As can 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. The data storage device 32 may be any suitable type of data storage device, including a variety of different types of random access memory and / or other storage devices. In an exemplary embodiment, the data storage device 32 comprises a program product from which a computer-readable storage device can receive a program embodying one or more embodiments of one or more processes of the present disclosure, such as the steps of the process further described below in connection with Fig. 3. In a further embodiment, the program product can be directly stored in and / or accessed through the storage device and / or one or more data carriers and / or other storage devices.

[0038] The controller 34 includes at least one processor 44, a communications bus 45, and a computer-readable storage device or storage medium 46. The processor 44 performs the computation and control functions of the controller 34. The processor 44 may be any custom-manufactured or off-the-shelf processor, a central processing unit (CPU), a graphics processing unit (GPU), an auxiliary processor among multiple processors associated with the controller 34, a semiconductor-based microprocessor (in the form of a microchip or chipset), a macroprocessor, any combination thereof, or, in general, any device for executing instructions. The computer-readable storage device or storage medium 46 may include, for example, volatile and non-volatile memory in read-only memory (ROM), random access memory (RAM), and retained memory (RAM).KAM is a persistent or non-volatile memory that can be used to store various operating variables while the processor 44 is powered off. The computer-readable storage device or medium 46 can be implemented using any of a number of known storage devices such as PROMs (programmable read-only memories), EPROMs (electrical PROMs), EEPROMs (electrically erasable PROMs), flash memory, or other electrical, magnetic, optical, or combination storage devices capable of storing data, some of which represents executable instructions used by the controller 34 in controlling the vehicle 10. The bus 45 is used to transfer programs, data, status information, and other information or signals between the various components of the vehicle 10.Bus 45 may be any suitable physical or logical means for interconnecting computer systems and components. This includes, but is not limited to, direct hard-wired connections and fiber optic, infrared, and wireless bus technologies.

[0039] The instructions may include one or more separate programs, each comprising an ordered list of executable instructions for implementing logical functions. When executed by the processor 44, the instructions receive and process signals from the sensor system 28, perform logic, calculations, methods, and / or algorithms, and generate data based on the logic, calculations, methods, and / or algorithms. Although Fig. 1 only one controller 34 is shown, embodiments of the vehicle 10 may include any number of controllers 34 that communicate via any suitable communication medium or combination of communication media and that cooperate to process the sensor signals, perform logic, calculations, methods and / or algorithms, and generate data.

[0040] As can be appreciated, the controller 34 may differ in other ways from the embodiment shown in Fig. 1. For example, the controller 34 may be coupled to or otherwise utilize one or more remote computer systems and / or other control systems, e.g., as part of one or more of the vehicle devices and vehicle systems identified above. It is recognized that while this exemplary embodiment is described in the context of a fully functional computer system, those skilled in the art will recognize that the mechanisms of the present disclosure may be distributed as a program product, using one or more types of non-transitory computer-readable signal-bearing media, such as a non-transitory computer-readable medium carrying the program and including computer instructions stored therein to cause a computer processor (such as processor 44) to perform and execute the program, to store the program and its instructions, and to facilitate its distribution.Such a program product may take a variety of forms, and the present disclosure applies equally regardless of the particular type of computer-readable signal-bearing medium used to carry out the distribution. Examples of signal-bearing media include writable media such as floppy disks, hard disks, memory cards, and optical discs, and transmission media such as digital and analog communication links. It is recognized that cloud-based storage and / or other techniques may also be used in certain embodiments. It is also recognized that the computer system of the controller 34 may differ in other ways from the embodiment shown in FIG. Fig. 1, for example, in that the computer system of the controller 34 may be coupled to or otherwise utilize one or more remote computer systems and / or other control systems.

[0041] The remote system 36 may be any suitable computing system or electronic device configured to determine reference temperatures and temperature coefficients for a stator of the electric motor 21 of the vehicle 10, generate data including the reference temperatures and temperature coefficients, and send relevant data to the data storage device 32 and / or the controller 34.

[0042] With reference to Fig. 2 and with continued reference to Fig. 1 shows a system and data flow diagram of elements of the engine control system 100 according to various embodiments. As can be appreciated, various embodiments of the engine control system 100 according to the present disclosure may include any number of modules embedded within the controller 34, which may be combined and / or further subdivided to implement systems and methods described herein in a similar manner. Furthermore, inputs to the engine control system 100 may be received from other control modules (not shown) associated with the vehicle 10 and / or determined or modeled by other sub-modules (not shown) within the controller 34. Furthermore, the inputs may also be subjected to preprocessing such as subsampling, noise reduction, normalization, feature extraction, missing data reduction, and the like.According to various embodiments, the motor control system 100 includes a motor control module 210, an initial stator resistance module 212, a temperature coefficient module 214, and a stator resistance module 216.

[0043] According to various embodiments, the initial stator resistance module 212 receives as input various sensor data indicative of the current 220, the phase angle 222, and the motor speed 224 generated by the sensor system 28. The initial stator resistance module 212 determines an initial stator resistance at a preprogrammed reference temperature. According to some embodiments, the initial stator resistance module 212 determines an initial stator resistance using the sensor data. According to some embodiments, the initial stator resistance module 212 determines an initial stator resistance using calculated and / or estimated values, e.g., the current, the phase angle, and / or the motor speed.The initial stator resistance value module 212 generates the initial stator resistance data 225 indicating the determined initial stator resistance value.

[0044] According to various embodiments, the temperature coefficient module 214 receives as input sensor data indicative of the stator temperature 226, the rotor temperature 228, and the motor speed 224, generated by the sensor system 28. The temperature coefficient module 214 determines a temperature coefficient value based on the sensor data and a preprogrammed nonlinear resistance ratio curve. The temperature coefficient module 214 generates temperature coefficient data 230 indicative of the determined temperature coefficient value.

[0045] According to various embodiments, the stator resistance module 216 receives as input the initial stator resistance data 225 generated by the initial stator resistance module 212 and the temperature coefficient data 230 generated by the temperature coefficient module 214. The stator resistance module 216 determines a stator resistance value based on the initial stator resistance data 225 and the temperature coefficient data 230. According to some embodiments, the stator resistance module 216 determines the stator resistance value by multiplying the initial stator resistance value and the temperature coefficient value. The stator resistance module 216 generates stator resistance data 232 indicative of the determined stator resistance.

[0046] According to various embodiments, the motor control module 210 receives as input the stator resistance data 232 generated by the stator resistance module 216. The motor control module 210 may adjust one or more operating parameters of the electric motor 21 based on the stator resistance value of the stator resistance data 232. According to various embodiments, the motor control module 210 may use the stator resistance value and / or the motor position 240 and / or the current 238 and / or the direct current (DC) voltage 236 and / or a torque command 234 to adjust one or more parameters, such as, but not limited to, current control, reference current generation, modulation index calculation, observer, state filter, and online calculation related to the motor state at given speeds.

[0047] With reference to Fig. 3 and with continued reference to the Fig. 1-2, a flowchart provides, according to exemplary embodiments, a method 300 for determining a reference temperature and a nonlinear resistance ratio curve that may be uploaded and stored by the engine control system 100 (e.g., by the initial stator resistance module 212 and the temperature coefficient module 214, respectively). As can be appreciated from the disclosure, the order of operation within the method 300 is not limited to the sequential execution described in Fig. 3, but may be performed in one or more different orders as applied and in accordance with the present disclosure. According to various embodiments, certain steps of method 300 may be performed by one or more processors not associated with a vehicle (e.g., remote system 36), and certain steps of method 300 may be performed by one or more processors associated with vehicle 10 (e.g., processor(s) 44).

[0048] In one example, method 300 may begin at 310. As will become apparent from the following description, one or more steps of method 300 may be performed one or more times during method 300. Therefore, various steps may be described as being performed in one or more iterations. At 312, method 300 may include receiving a stator design resistance value (R D ) of the electric motor 21. According to some embodiments, the design resistance value (R D ) provided by the manufacturer of the electric motor 21.

[0049] At 314, method 300 may include determining and storing a reference temperature (T x ). During a first iteration of step 314, the reference temperature (T x ) may be a first reference temperature (e.g., 20°C). During such a first iteration, the first reference temperature may be set to a first value of 316 (e.g., Tx=1 ) can be set. In subsequent iterations of steps 314 and 316, the reference temperature (T x ) a subsequent reference temperature (e.g. 50 °C, 90 °C, 150 °C, etc.) and a subsequent value (e.g. T x=2, 3,4, ...n ) can be set.

[0050] At 318, method 300 may include determining a stator resistance value (R s ) at the stator reference temperature (T x ) depending on the current (Iss), the phase angle (I beta ) and the engine speed (S M ) at the reference temperature (T x ) with one or more processors. For example, Fig. 4 the stator resistance values ​​(R s ; y-axis 420) of an exemplary electric motor in relation to the motor speed (M s ; x-axis 410) at reference temperatures of 20°C (reference 430), 50°C (reference 432), 90°C (reference 434) and 150°C (reference 436). As shown, the resistance values ​​(R s) with increasing engine speed (M s ) increase non-linearly and vary between the reference temperatures (T x ). The resistance values ​​(R s ) are shown per unit (PU), which can refer to different units such as ohms.

[0051] In 320, the method 300 may include determining a temperature coefficient (T coeff ), ie a non-linear stator resistance ratio curve for the reference temperature (T x ) with the one or more processors. For example, Fig. 5 a representation of the resistance ratios (y-axis 520) for the stator of the exemplary electric motor in relation to the motor speed (M s ; x-axis 510) using a reference temperature (T x ) of 50°C. The data correspond to 20°C / 50°C (reference 530), 90°C / 50°C (reference 532) and 150°C / 50°C (reference 534).

[0052] At 322, method 300 may include determining a reconstructed or calculated stator resistance value (R S_calc ) for the reference temperature (T x ) based on the resistance value (R s ) and the temperature coefficient value (T coeff ) include.

[0053] At 324, method 300 may include determining an error value between the design resistance value (Ro) and the calculated resistance value (R S_calc ) with the one or more processors.

[0054] At 326, method 300 may include updating the reference temperature to a subsequent reference temperature and setting the reference value to a subsequent value at 328. Method 300 may then include repeating steps 318 through 324 for the subsequent reference temperature. This process may be repeated for all reference temperatures (e.g., T x+1 , T x,2,... T x,n ) be repeated.

[0055] Once the previously described steps 318 to 328 are completed for all reference temperatures, the method 300 proceeds to 330, wherein the one or more processors determine one of the reference temperatures (T x ) which has the lowest error value, which will be referred to below as the final reference temperature (T final ) is called.

[0056] According to various embodiments, the final reference temperature (T final ) in the data storage device 32 on the vehicle side (e.g., for the vehicle 10) to determine the stator resistance during operation of an electric vehicle. According to various embodiments, the method 300 may include determining the resistance value (R s ) at the final reference temperature (T final ) and in 334 determining the temperature coefficient (T coeff ) at the final reference temperature (T final). Steps 332 and 334 may be performed during operation of the electric vehicle. According to various embodiments, steps 332 and 334 may be performed by one or more processors of the vehicle (e.g., processor(s) 44).

[0057] The systems and methods disclosed herein offer several advantages over certain existing systems and methods. For example, various existing systems and methods may be less accurate in determining the stator resistance of an electric motor during its operation relative to the systems and methods herein. The systems and methods, taking into account the nonlinear relationship of stator resistance at various operating speeds of the electric motor, promote the accuracy of this determination by, in some embodiments, determining a reference temperature that has a small error relative to other possible reference temperatures. In contrast, certain known systems rely on linear algorithms for calculating and / or estimating the resistance with temperature compensation, such as in Equation 1 below: Rs(T)=Rs(25°C)×Rs(AC)×(1+α×(T−25°C)) where R s(T) is the stator DC resistance at T, R s (25 °C) is the stator resistance at 25 °C, AC is the alternating current coefficient (AC coefficient), α is the material-dependent temperature coefficient, and T is the temperature. Such linear methods can lead to a significant error (e.g., greater than 10%), especially with increasing motor speed.

Claims

[1] Procedure (300) which includes: Determining (318) an initial stator resistance value of an electric motor (21) by one or more processors (44) based on a stator reference temperature and either estimated data or sensor data indicating sensed conditions of the electric motor (21) including a current, a phase angle, a motor speed, a stator temperature of the electric motor (21), and a rotor temperature of the electric motor (21); Determining (320) a stator temperature coefficient by the one or more processors (44) based on the sensor data and a non-linear stator resistance ratio curve; and Determining (322) a stator resistance value by the one or more processors (44) based on the initial stator resistance value and the stator temperature coefficient. [2] The method (300) of claim 1, wherein the stator reference temperature is determined by: Receiving stator design resistance values ​​of the electric motor (21) with the one or more processors (44); determining at least two stator resistance values ​​for at least two different stator reference temperatures with the one or more processors (44); determining stator temperature coefficient values ​​for each of the at least two different reference temperatures with the one or more processors (44); determining calculated stator resistance values ​​for each of the at least two different reference temperatures based on the at least two resistance values ​​and the temperature coefficient values ​​with the one or more processors (44); determining error values ​​between the design resistance values ​​and the calculated resistance values ​​at each of the at least two different reference temperatures with the one or more processors (44); Determining which of the at least two different reference temperatures has the lowest error value with the one or more processors (44); and Setting one of the at least two different reference temperatures with the lowest error value as the stator reference temperature, where the temperature coefficient values ​​are defined by nonlinear resistance ratio curves. [3] The method (300) of claim 1, wherein the initial stator resistance value is determined based on the sensor data and the stator reference temperature, and wherein the non-linear stator resistance ratio curve is based on the stator reference temperature. [4] The method (300) of claim 1, wherein the electric motor (21) is a vehicle drive system component, wherein the stator resistance value is determined during operation of the drive system, and wherein the electric motor (21) is a 3-phase AC motor. [5] The method (300) of claim 1, further comprising adjusting (328) an operating parameter of the electric motor (21) based on the stator resistance value. [6] System (100) which includes: an electric motor (21) comprising a stator and a rotor; a sensor system (28) including one or more sensors (40) configured to generate sensor data indicative of sensed electric motor operating conditions including a current, a phase angle, a motor speed, a stator temperature, and a rotor temperature; and a controller (34) operatively coupled to the sensor system (28) and the electric motor (21), the controller (34) being configured, by one or more processors (44): determine an initial stator resistance value based on a stator reference temperature and either estimated sensor data or sensor data received from the sensor system (28); to determine a stator temperature coefficient based on the sensor data and a nonlinear stator resistance ratio curve; and to determine a stator resistance value based on the initial stator resistance value and the stator temperature coefficient. [7] The system (100) of claim 6, wherein the stator reference temperature is a first of a plurality of reference temperatures, each of the plurality of reference temperatures being used to determine corresponding calculated stator resistance values, wherein error values ​​between the calculated resistance values ​​and the corresponding stator design resistance values ​​are determined at the plurality of reference temperatures, the first of the plurality of reference temperatures having a lowest error value. [8] The system (100) of claim 7, wherein the calculated resistance values ​​are based on a plurality of resistance values ​​at each of the plurality of reference temperatures and on the temperature coefficient values ​​at each of the plurality of reference temperatures, the temperature coefficient values ​​being defined by non-linear resistance ratio curves. [9] The system (100) of claim 6, wherein the initial stator resistance value is determined based on the sensor data and the stator reference temperature, and wherein the non-linear stator resistance ratio curve is based on the stator reference temperature. [10] The system (100) of claim 6, wherein the electric motor (21) is a vehicle propulsion system component, wherein the stator resistance value is determined during operation of the propulsion system, wherein the electric motor (21) is a 3-phase AC motor, and wherein the controller (34) is configured, through the one or more processors (44), to adjust an operating parameter of the electric motor (21) based on the stator resistance value.

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