Method of optimizing system efficiency of a battery powered electric motor

Abstract

This paper discloses a method for controlling a motor to optimize the system efficiency of a motor that can operate in pulse mode and continuous mode. The method includes receiving a requested torque for the motor, calculating a pulse system efficiency, calculating a continuous system efficiency, and operating the motor in pulse mode when the pulse system efficiency is higher than the continuous system efficiency. The pulse system efficiency is calculated to deliver the requested torque from the motor in multiple torque pulses greater than the requested torque. The continuous system efficiency is calculated to deliver the requested torque from the motor in continuous torque. The system efficiency may be based at least in part on battery efficiency and motor efficiency.

Description

Technical Field

[0001] This disclosure relates to methods for optimizing the system efficiency of battery-powered electric motors, and more specifically to methods for optimizing the system efficiency of battery-powered pulse electric motors. Background Technology

[0002] As is well known, electric motors can efficiently provide continuous torque to driven equipment. The torque delivery of an electric motor is typically continuous, without the pulsations associated with an internal combustion engine. Generally, electric motors have their optimal efficiency point in the low-to-medium torque range relative to their maximum torque. For example, the maximum efficiency of an electric motor can be in the range of 30% to 80% of its maximum torque.

[0003] When a motor provides continuous torque within a low range of its maximum torque (e.g., below 20% of its maximum torque), its efficiency is typically low. It has been found that by applying pulses to the motor at its optimal efficiency point to reduce the motor's duty cycle, the target torque can be provided with higher motor efficiency within this low range compared to providing continuous torque from the motor. Applying pulses to the motor at its optimal efficiency point involves delivering pulses at a modulated frequency.

[0004] Although applying pulses to the motor at a modulated frequency may result in higher motor efficiency compared to continuous torque delivery, applying pulses to the motor reduces the battery efficiency of the battery system that powers the motor. Summary of the Invention

[0005] The system efficiency of the pulse motor needs to be optimized so that improving motor efficiency does not reduce overall system efficiency due to decreased battery efficiency.

[0006] This disclosure generally relates to systems and methods for optimizing system efficiency by: calculating the pulsed system efficiency for a requested pulsed power request; comparing the pulsed system efficiency with the continuous system efficiency; and switching the motor to pulsed mode when the pulsed system efficiency is higher than the continuous system efficiency. The pulsed system efficiency and the continuous system efficiency can be calculated by multiplying the battery efficiency and the motor efficiency under the conditions of pulsed motor mode and continuous motor mode.

[0007] In embodiments of this disclosure, a method for controlling an electric motor includes receiving a requested torque for the motor, calculating a pulsed system efficiency, calculating a continuous system efficiency, and operating the motor in a pulsed mode when the pulsed system efficiency is higher than the continuous system efficiency. The pulsed system efficiency is calculated to deliver the requested torque from the motor in pulsed mode. The continuous system efficiency is calculated to deliver the requested torque from the motor in continuous mode.

[0008] In an embodiment, calculating the pulse system efficiency may include determining the pulse battery efficiency based at least in part on the battery's heat dissipation losses. Calculating the pulse system efficiency may also include determining the pulse battery efficiency based at least in part on battery temperature, pulse current, battery terminal voltage, or battery internal resistance.

[0009] In another embodiment of this disclosure, a non-transitory computer-readable medium stores instructions that, when executed by a controller, cause the controller to calculate pulse system efficiency, calculate continuous system efficiency, and operate the motor in pulse mode when the pulse system efficiency is higher than the continuous system efficiency. The controller calculates the pulse system efficiency by determining the system efficiency for delivering the requested torque from the motor in pulse mode. The controller calculates the continuous system efficiency by determining the system efficiency for delivering the requested torque from the motor in continuous mode.

[0010] In another embodiment of this disclosure, a controller for operating an electric motor to rotate a driven component includes a processor and a memory including a program for causing the processor to calculate the pulse system efficiency for delivering a requested torque from the electric motor in pulse mode, calculate the continuous system efficiency for delivering the requested torque from the electric motor in continuous mode, and operate the electric motor in pulse mode when the pulse system efficiency is higher than the continuous system efficiency.

[0011] Furthermore, where consistent, any embodiment or aspect described herein may be used in combination with any or all other embodiments or aspects described herein. Attached Figure Description

[0012] The various aspects of this disclosure are described below with reference to the accompanying drawings, which are incorporated in and form a part of this specification, in which:

[0013] Figure 1 This is a schematic diagram of an ideal voltage source model;

[0014] Figure 2 It is a schematic diagram of an ideal voltage source model that includes the state of charge;

[0015] Figure 3 This is a schematic diagram of the Rint model;

[0016] Figure 4 This is a diagram illustrating the first pulse control mode provided in this disclosure;

[0017] Figure 5 This is a diagram illustrating the second pulse control mode provided in this disclosure;

[0018] Figure 6 This is a graph of system efficiency as a function of battery efficiency, provided according to embodiments of this disclosure;

[0019] Figure 7 This is a flowchart illustrating a method for optimizing the system efficiency of a pulse motor according to embodiments of this disclosure; and

[0020] Figure 8 This is a schematic diagram of a system provided according to an embodiment of the present disclosure. Detailed Implementation

[0021] This disclosure will now be described more fully with reference to exemplary embodiments and the accompanying drawings, in which the same reference numerals denote the same or corresponding elements in each of several views. The description of these exemplary embodiments makes this disclosure exhaustive and complete, and will fully convey the scope of this disclosure to those skilled in the art at the time of invention. Features from one embodiment or aspect may be combined with features from any other embodiment or aspect in any suitable combination. For example, any single or collective feature of a method aspect or embodiment may be applicable to an apparatus, product, or component aspect or embodiment, and vice versa. This disclosure may be implemented in many different forms and should not be construed as limited to the embodiments set forth below; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. As used in the specification and appended claims, unless the context clearly indicates otherwise, the singular forms “a,” “an,” “the,” etc., include plural references. Furthermore, while quantitative measurements, numerical values, geometric relationships, etc., may be referenced herein, any one or more of them (if not all) may be absolute or approximate to account for acceptable variations that may occur, such as variations due to manufacturing or engineering tolerances, unless otherwise stated.

[0022] To improve the efficiency of an electric motor in its low torque range, pulses can be applied to the motor to reduce its duty cycle, thereby providing the target or required torque as an average torque delivered over a period of time by applying the pulses to the motor at its optimal efficiency point, or as torque delivered at a modulated frequency. This pulse to the motor can have a pulse width modulation (PWM) waveform for torque delivery. The duty cycle is selected to provide a low target torque to the driven device while applying the pulses to the motor at its optimal efficiency point. The modulation frequency can be selected to meet noise, vibration, and harshness (NVH) requirements, and / or to reduce or minimize transition losses between the motor's off and on states. In some embodiments, the modulation frequency is selected based on the torsional vibration of the driven device. For example, the motor can be pulsed with an efficient torque of 200 Nm and a 20% duty cycle to provide a target average torque of 40 Nm to the driven device. Depending on the NVH characteristics of the driven device, a 200 Nm pulse can be delivered at a modulation frequency of 30 Hz. In an exemplary electric motor, under certain operating conditions, applying pulses to the motor to reduce the duty cycle to deliver the target torque has shown that its motor efficiency is 9% higher than that of a motor that delivers the required torque by continuous torque delivery.

[0023] As mentioned above, applying pulses to a motor below its optimal efficiency point to deliver a target torque has been shown to improve motor efficiency. However, applying pulses to a motor can also affect the efficiency of the battery system that supplies energy to the motor. For example, when a motor is pulsed to improve its efficiency, losses in the battery system may increase, and therefore battery efficiency may decrease due to the pulsed energy delivery from the motor. This battery efficiency loss may be less than, offset, or greater than any motor efficiency gain; therefore, even if a motor efficiency gain is achieved, the system efficiency of both the battery system and the motor may decrease due to the pulsed energy delivery. As detailed below, a method for preventing system efficiency losses due to pulses applied to the motor is disclosed. As used herein, the term "system efficiency" refers to the efficiency of the entire power delivery system, including at least the motor efficiency of the motor and the battery efficiency of the battery system that supplies energy to the motor.

[0024] One way to quantify battery system efficiency is to determine the heat dissipation of the battery system. The heat dissipation of a battery system can be a function of the internal resistance of the battery system and the current flowing through it. Heat dissipation can also be affected by the battery system's terminal voltage. For example, when a decrease in terminal voltage causes an increase in overpotential, the current will increase to provide the same power output. Therefore, heat dissipation will also increase when the terminal voltage decreases. As used herein, the term battery system can refer to a battery having a single cell or multiple cells. The properties of a battery system can refer to the entire battery system or the individual cells within it.

[0025] There are several models for estimating the heat dissipation loss of a battery system. Referring to Figure 1 , the ideal voltage source model (where v(t) = OCV) provides a starting point, but is clearly insufficient to fully model the heat dissipation loss of a battery system. For example, in the ideal voltage source model, the voltage is not a function of current, the voltage is not a function of past usage, and the voltage is constant. Therefore, a more accurate model is needed.

[0026] Now referring to Figure 2 , a second model for estimating the heat dissipation loss of a battery system can be an ideal voltage source model that includes the state of charge (SOC). In such a model, when the battery cell is fully charged, the state of charge z can be equal to 100%, and when the cell is fully discharged, the state of charge can be equal to 0%. The SOC can be modeled as follows:

[0027]

[0028]

[0029] where Q is the total capacity, i.e., the total charge removed when discharging from fully charged to fully discharged. It is known that battery cells are not perfectly efficient. For example, the energy efficiency of a battery cell is defined as the output energy divided by the input energy. For a battery cell, this energy efficiency can be approximately 95%. The energy loss may be the result of resistive heating during charging and discharging. In addition, during charging, due to unwanted side reactions occurring within the battery cell, the Coulomb efficiency is less than 1, which results in energy loss of the battery cell. However, during discharge of the battery cell, the Coulomb efficiency is typically equal to 1.

[0030] Referring to Figure 3 , a third model for estimating the heat dissipation loss of a battery system can be the "Rint" model shown as including a series resistance. The Rint model can be modeled as follows:

[0031] V(t) = OCV(z(t), T(t)) - i(t)R0

[0032] where, during charging, V(t) > OCV(z(t), T(t)), and during discharge, V(t) < OCV(z(t), T(t)). The power dissipated by R0 is dissipated as heat, i.e., representing the heat dissipation loss. Although this Rint model may be sufficient for simple electronic designs, it may be inaccurate if applied to advanced electronic devices and EV applications. For example, there may be a diffusion process within the battery cell, so when the cell is stationary, the voltage does not immediately return to OCV.

[0033] While more advanced models that take into account diffusion voltage and hysteresis (such as the Thevenin model or the Enhanced Self-Changing (ESC) cell model) may exist, the Rint model allows for in-depth understanding of how heat dissipation losses within a battery cell vary under continuous power delivery versus pulsed power delivery conditions. These and other models can be used when implementing the methods detailed in this paper.

[0034] Now refer to Figure 4 According to this disclosure, a first pulse control mode is provided. In the first pulse control mode, a pulse current I is provided. 脉冲 This allows the application of pulsed torque to the motor to deliver the target torque. The target torque is the average value of the pulsed torque over a certain period of time, or the product of the duty cycle of the pulsed torque and the pulsed torque value. The current delivered to the motor has an average current I. 脉冲 and root mean square current I rms The average current is the average current supplied to the motor over a certain period of time.

[0035] To calculate the heat loss during pulsed power delivery, the first step is to calculate the heat dissipated during continuous current delivery, commonly referred to as Q. 基线 Using the Rint model above, Q 基线 The following can be calculated:

[0036]

[0037] Then, turning to the first pulse control model, we can calculate the heat loss Q, where:

[0038]

[0039] Make:

[0040]

[0041] Therefore, the pulse width or duty cycle of the motor in pulse mode is proportional to the baseline heat dissipation loss of the battery system in continuous mode. For example, when the duty cycle is 33% or the pulse width is 1 / 3 of time T, n equals 3. When n equals 3, I 均值 For I 脉冲 One-third of that. Therefore, according to the Rint model, when the duty cycle of the pulse control mode is 33%, the heat dissipation loss of the battery system is three times that of the baseline heat dissipation loss of the battery system with constant power delivery. According to the Rint model, it is clear that as the duty cycle decreases, the efficiency of the battery system in the first pulse control mode also decreases.

[0042] Now refer to Figure 5According to this disclosure, a second pulse control mode is provided. In the second pulse control mode, a first pulse current I is provided. 脉冲A In order to apply pulses to the motor with pulsed torque and to receive a second pulse current I from the motor 脉冲B To deliver the target torque. This mode may result from applying pulses of high positive torque to the motor and regenerating or recapturing energy between the positive torque pulses. This mode causes I rms with I 均值 The difference is significant. The heat loss in the second mode is greater than Q. 基线 n times. In the example shown below, the heat loss in the second pulse control mode can be 10 times the baseline heat loss caused by constant current delivery to the motor.

[0043] Figure 6 The system efficiency is shown as a factor of the baseline battery efficiency for each of the continuous torque delivery or baseline, the first pulse control mode, and the second pulse control mode. Using the Rint model detailed above, there exists a crossover point where applying pulses to the motor improves the overall system efficiency compared to the baseline with continuous torque delivery. This shows that, to the left of the crossover point, the motor efficiency gain from pulsed torque delivery outweighs the decrease in battery efficiency, while on the other side of the crossover point, battery efficiency cancels out any potential motor efficiency gain. It is also shown that, to the right of the crossover point, the decrease in battery system efficiency outweighs the motor efficiency gain from the pulsed mode.

[0044] Now refer to Figure 7 This disclosure discloses a method for optimizing the system efficiency of a pulsed electric motor, commonly referred to as method 100. Method 100 is executed on a controller that signals the motor to deliver a target torque to the drive components.

[0045] Method 100 may include a controller for an electric motor that receives an input signal requesting a target torque from the electric motor (step 110). The controller may also receive motor speed from one or more sensors associated with the motor (step 115). In response to receiving the target torque from the electric motor, the controller generates a pulse control pattern (step 120). The generated pulse control pattern may be based at least in part on the motor speed. Alternatively or additionally, the generated pulse control pattern may be based at least in part on the operating conditions of the electric motor, including but not limited to vehicle speed or motor temperature. The controller may optimize the generated pulse control pattern to maximize the motor efficiency of the electric motor and determine the motor efficiency gain provided by the generated pulse control pattern compared to continuous torque delivery (step 130).

[0046] Before providing the generated pulse control pattern to the motor, the controller calculates the system efficiency of the generated pulse control pattern (step 160). To calculate the system efficiency, the controller needs at least the motor efficiency (step 130) and the battery efficiency (step 150). Therefore, the system efficiency depends at least in part on the motor efficiency and at least in part on the battery efficiency. The battery efficiency for the pulse power request is calculated using a battery model (step 140). The battery model can be any battery model, including but not limited to an ideal voltage source model, a SOC model, a Rint model, a Thevenin model, or an ESC model. The battery model can be based at least in part on the operating conditions of the battery or cell, including but not limited to the generated pulse pattern, cell current, cell terminal voltage, cell temperature, cell internal resistance, or pulse current. The battery model can include real-time operating condition inputs provided by one or more sensors. Based on these operating conditions, the battery efficiency is calculated using the battery model (step 150).

[0047] After calculating the battery efficiency and motor efficiency, the pulse system efficiency under the generated pulse pattern can be calculated (step 160). The controller compares the pulse system efficiency with the continuous or baseline system efficiency (step 170). The continuous system efficiency can be calculated by the controller based on the battery efficiency and motor efficiency for continuous torque delivery to the target torque (step 125). When the continuous system efficiency is higher than the pulse system efficiency, the controller operates the motor to deliver the target torque via continuous torque delivery (step 180). When the pulse system efficiency is higher than or equal to the continuous system efficiency, the controller operates the motor to deliver the target torque via the generated pulse pattern (step 190). The target torque delivery in step 180 or 190 continues until the controller requests and receives another target torque (step 110). For the requested new target torque, method 100 is repeated.

[0048] Now refer to Figure 8 An exemplary system is provided according to this disclosure. The system includes a controller 10, a motor 40, a battery system 45, and a driven component 50. The controller 10 includes a processor 20 and a memory 30. The memory 30 may include one or more programs stored in the memory 30 and executed on the processor 20. The controller 10 may be operatively coupled to the motor 40 and / or the battery system 45 such that the controller 10 operates the motor 40 and / or the battery system 45 based on instructions stored in the memory 30 and executed on the processor 20. The motor 40 may be operatively coupled to the driven component 50 such that the motor 40 operates to rotate the driven component 50. The controller 10 may perform any of the methods detailed herein to operate the motor 40 and / or the battery system 45.

[0049] While several embodiments of this disclosure have been shown in the accompanying drawings, they are not intended to limit the disclosure thereto, as the disclosure is intended to be as broad as permitted by the art, and the specification should be understood in the same manner. Any combination of the above embodiments is also contemplated, and such combinations are within the scope of the appended claims. Therefore, the foregoing description should not be construed as restrictive, but merely as illustrative of particular embodiments. Other modifications within the scope of the appended claims will be apparent to those skilled in the art.

Claims

1. A method of controlling an electric motor, the method comprising: determining a pulsed system efficiency of the electric motor based at least in part on operating conditions of a battery system configured to provide energy to the electric motor to deliver a requested torque, the operating conditions of the battery system comprising a battery temperature, a pulsed current, a battery terminal voltage, or a battery internal resistance; and operating the electric motor in a pulsed mode when the pulsed system efficiency is higher than a continuous system efficiency. wherein the method further comprises: calculating the continuous system efficiency for delivering the requested torque from the electric motor in a continuous mode; and operating the electric motor in the continuous mode when the continuous system efficiency is higher than the pulsed system efficiency.

2. The method of claim 1, wherein, Determining the pulsed system efficiency comprises the pulsed system efficiency comprising a product of a pulsed motor efficiency and a pulsed battery system efficiency.

3. The method of claim 1, wherein, Determining the pulsed system efficiency comprises determining a pulsed battery efficiency based at least in part on a heat dissipation loss of the battery system.

4. The method of claim 1, wherein, Determining the pulsed system efficiency comprises determining a pulsed motor efficiency of the electric motor based at least in part on operating conditions of the electric motor.

5. The method of claim 4, wherein, Determining the pulsed motor efficiency comprises the operating conditions of the electric motor comprising a motor speed, a motor torque, a vehicle speed, or a motor temperature.

6. The method of claim 1, wherein, The method further comprises generating a pulsed waveform for delivering the requested torque from the electric motor in the pulsed mode.

7. The method of claim 6, wherein, Generating the pulsed waveform comprises applying a pulsed torque to the electric motor greater than the requested torque to deliver the requested torque.

8. The method of claim 6, wherein, Generating the pulsed waveform comprises regenerating energy between pulses of the electric motor.

9. A non-transitory computer readable storage medium having stored thereon instructions which, when executed by a controller, cause the controller to: determine a pulsed system efficiency of an electric motor based at least in part on operating conditions of a battery system configured to provide energy to the electric motor to deliver a requested torque, the operating conditions of the battery system comprising a battery temperature, a pulsed current, a battery terminal voltage, or a battery internal resistance; and operate the electric motor in a pulsed mode when the pulsed system efficiency is higher than a continuous system efficiency. wherein The instructions, when executed by the controller, further cause the controller to: calculate the continuous system efficiency for delivering the requested torque from the electric motor in a continuous mode; and operate the electric motor in the continuous mode when the continuous system efficiency is higher than the pulsed system efficiency.

10. The non-transitory computer-readable storage medium of claim 9, wherein, The controller determines the pulsed system efficiency by determining a pulsed battery efficiency based at least in part on a heat dissipation loss of the battery system.

11. The non-transitory computer-readable storage medium of claim 9, wherein, The controller calculates the pulsed system efficiency based at least in part on a pulsed motor efficiency.

12. A controller for operating an electric motor to rotate a driven component, the controller comprising: a processor; and a memory comprising a program that causes the processor to: determine a pulsed system efficiency of an electric motor based at least in part on operating conditions of a battery system configured to provide energy to the electric motor to deliver a requested torque, the operating conditions of the battery system comprising a battery temperature, a pulsed current, a battery terminal voltage, or a battery internal resistance; and operate the electric motor in a pulsed mode when the pulsed system efficiency is higher than a continuous system efficiency. The instructions, when executed by the controller, further cause the controller to: calculate the continuous system efficiency for delivering the requested torque from the electric motor in a continuous mode; and operate the electric motor in the continuous mode when the continuous system efficiency is higher than the pulsed system efficiency. wherein the program further causes the processor to perform the following operations: calculating a continuous system efficiency for delivering the requested torque from the electric motor in a continuous mode; and operating the electric motor in the continuous mode when the continuous system efficiency is higher than the pulsed system efficiency.

13. The controller of claim 12, wherein, Determining the pulsed system efficiency includes determining a pulsed battery efficiency based at least in part on a heat dissipation loss of the battery system.

14. The controller of claim 12, wherein, Calculating the pulsed system efficiency is based at least in part on a pulsed motor efficiency. Determining the pulsed system efficiency includes determining a pulsed battery efficiency based at least in part on a heat dissipation loss of the battery system.

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