An output torque prediction method and system for an electric drive system

Abstract

The application provides an output torque prediction method of an electric drive system, comprising the following steps: calculating a stator generated heat prediction value and a stator predicted temperature based on copper loss power and iron loss power of a motor; calculating a transient loss and an IGBT predicted temperature based on a duty cycle, a real-time current and a switching loss of an IGBT module; calculating a predicted speed and a predicted bus voltage based on a current speed and a speed in the last n seconds before the current time, and obtaining a predicted external characteristic torque by table lookup; obtaining a first predicted torque based on the stator predicted temperature, obtaining a second predicted torque based on the IGBT predicted temperature, and taking the minimum value in the first predicted torque, the second predicted torque and the predicted external characteristic torque as a predicted output torque. After the above technical scheme is adopted, the future output torque can be accurately calculated in combination with various influencing factors.

Description

Technical Field

[0001] This invention relates to the field of hybrid vehicles, and more particularly to a method and system for predicting the output torque of an electric drive system. Background Technology

[0002] In pure electric or hybrid vehicles, the electric drive system mainly consists of a drive motor, a motor controller, and a high-voltage battery. Depending on the vehicle's topology, the electric drive system can also work in conjunction with a traditional engine system. As a core component, the motor controller controls the motor's output torque based on external commands and its own current state. Considering the needs of the overall vehicle control strategy and the safety protection requirements of the motor controller itself, the maximum torque that the electric drive system can output within a certain future timeframe is predicted to determine whether to further increase the torque command value of the motor controller in the overall vehicle control strategy.

[0003] In the existing technology, the prediction of output torque is based on the current temperature and operating parameters of the drive module. That is, the predicted temperature of the drive module is calculated, and the predicted torque of the motor is calculated based on the predicted temperature. However, there are many factors that affect torque, and the torque value predicted by the drive module alone has a large deviation from the actual value.

[0004] Therefore, a new method for predicting output torque is needed, which can accurately calculate future output torque by combining multiple influencing factors. Summary of the Invention

[0005] To overcome the above-mentioned technical defects, the present invention aims to provide a method for predicting the output torque of an electric drive system, comprising the following steps:

[0006] Based on the copper and iron power losses of the motor, the predicted value of the stator heat generated by the motor during the interval from the current time to the target time is calculated. Based on the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the winding, and the current stator temperature, the predicted stator temperature after the interval is calculated.

[0007] Based on the duty cycle, real-time current, and switching losses of the IGBT module, the transient losses of the IGBT module during the interval from the current time to the target time are calculated. Based on the transient losses, the thermal resistance of the electric drive system, and the current IGBT temperature, the predicted temperature of the IGBT after the interval is calculated.

[0008] Based on the motor's current speed and its speed n seconds before the current time, calculate the predicted speed of the motor within the interval from the current time to the target time. Based on the motor's current bus voltage and its current bus voltage n seconds before the current time, calculate the predicted bus voltage of the motor within the interval from the current time to the target time. And based on the predicted speed and predicted bus voltage, look up the table to obtain the predicted external characteristic torque.

[0009] The motor derating factor is calculated based on the stator predicted temperature, the first temperature threshold for derating initiation, and the second temperature threshold for derating to zero. The motor derating factor is then multiplied by the motor's maximum torque to obtain the first predicted torque. The IGBT derating factor is calculated based on the IGBT predicted temperature, and the IGBT derating factor is then multiplied by the motor's maximum torque to obtain the second predicted torque. The minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque is taken as the predicted output torque.

[0010] Preferably, the step of calculating the predicted value of the stator heat generated by the motor during the interval from the current time to the target time based on the copper loss power and iron loss power of the motor, and calculating the predicted stator temperature after the interval based on the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the windings, and the current stator temperature includes:

[0011] The copper loss power consumption is calculated based on the following formula: P Cu =I 2 ·R, where P Cu Where I is the copper loss power consumption, I is the bus current, and R is the bus resistance;

[0012] The iron loss power consumption is calculated based on the following formula: P Fe =P h +P c +P e , where P Fe For iron loss power consumption, P h For hysteresis loss, P c For classic eddy current losses, P e Abnormal eddy current loss is calculated using the following formulas: hysteresis loss, classical eddy current loss, and abnormal eddy current loss.

[0013] Where k h Here, f is the magneto-induced loss coefficient, and B is the motor frequency. p k is the amplitude of magnetic flux density. c k is the classical eddy current loss coefficient. e This is the abnormal eddy current loss coefficient;

[0014] The predicted value of stator heat generation is calculated based on the following formula: Q = K cool ·(P Cu +P Fe )·Δt, where Q is the predicted value of stator generated heat, K cool Δt is the correction factor, and Δt is the interval duration.

[0015] Preferably, the step of calculating the predicted value of the stator heat generated by the motor during the interval from the current time to the target time based on the copper loss power and iron loss power of the motor, and calculating the predicted stator temperature after the interval based on the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the windings, and the current stator temperature, further includes:

[0016] The stator temperature rise is calculated based on the following formula: Where ΔT str For stator temperature rise, A is the heat transfer area of ​​the winding, λ is the thermal conductivity, and σ is the heat transfer thickness of the stator winding.

[0017] The stator predicted temperature is calculated based on the following formula: T str_pre =T str +ΔT str T str_pre For predicting the stator temperature, T str This is the current stator temperature.

[0018] Preferably, the step of calculating the predicted value of the stator heat generated by the motor during the interval from the current time to the target time based on the copper loss power and iron loss power of the motor, and calculating the predicted stator temperature after the interval based on the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the windings, and the current stator temperature, further includes:

[0019] The first predicted torque is calculated based on the stator predicted temperature, and then compared with the current torque.

[0020] When the first predicted torque is greater than or equal to the current torque, output the first predicted torque;

[0021] When the first predicted torque is less than the current torque, the bus current is replaced by the maximum available current, and the above steps are iterated until the first predicted torque is greater than or equal to the current torque for output.

[0022] Preferably, the step of calculating the transient losses of the IGBT module within the interval from the current time to the target time based on the duty cycle, real-time current, and switching losses of the IGBT module, and calculating the predicted IGBT temperature after the interval based on the transient losses, the thermal resistance of the electric drive system, and the current IGBT temperature includes:

[0023] The conduction loss of the IGBT module is calculated based on the following formula: P con_IGBT =duty·[i(t)·V CE0 +i(t) 2 ·r CE ], where P con_IGBT Here, is the conduction loss, duty is the duty cycle, i(t) is the real-time current, and V is the voltage. CE0 For the voltage of the IGBT module, r CEThe impedance of the IGBT module;

[0024] The switching loss of the IGBT module is calculated based on the following formula: P sw_IGBT =f sw ·E on+off(i(t)) , where P sw_IGBT For switching losses, f sw E is the switching frequency. on+off(i(t)) For the turn-on and turn-off losses of the IGBT module;

[0025] The transient loss of the IGBT module is calculated based on the following formula: P IGBT =P con_IGBT +P sw_IGBT , where P IGBT Transient loss;

[0026] The junction temperature rise of the IGBT module is calculated based on the following formula: ΔT IGBT =P IGBT *Δt*R c , where ΔT IGBT R represents the nodal temperature rise, Δt is the time interval, and R is the temperature rise at the node. c Thermal resistance of the electric drive system;

[0027] The predicted IGBT temperature is calculated based on the following formula: T IGBT_pre =T IGBT +ΔT IGBT T IGBT_pre For IGBT temperature prediction, T IGBT This represents the current IGBT temperature.

[0028] Preferably, the step of calculating the transient losses of the IGBT module from the current time to the target time based on the duty cycle, real-time current, and switching losses of the IGBT module, and calculating the predicted IGBT temperature after the time interval based on the transient losses, the thermal resistance of the electric drive system, and the current IGBT temperature, further includes:

[0029] The second predicted torque is calculated based on the IGBT predicted temperature, and then compared with the current torque.

[0030] When the second predicted torque is greater than or equal to the current torque, output the second predicted torque;

[0031] When the second predicted torque is less than the current torque, the second predicted torque replaces the current torque to calculate the duty cycle and real-time current under the second predicted torque, and the duty cycle, real-time current and the above steps are iterated until the second predicted torque is greater than or equal to the current torque for output.

[0032] Preferably, the steps of calculating the predicted motor speed within the interval from the current time to the target time based on the motor's current speed and its speed n seconds before the current time, calculating the predicted motor bus voltage within the interval from the current time to the target time based on the motor's current bus voltage and its current bus voltage n seconds before the current time, and obtaining the predicted external characteristic torque by looking up a table based on the predicted speed and predicted bus voltage include:

[0033] The predicted rotational speed is calculated based on the following formula: Where Spd(t+N*T) is the predicted rotational speed, Spd(t) is the current rotational speed, T is the unit time, and N is the number of units of time such that n=N*T;

[0034] The predicted bus voltage is calculated based on the following formula: Where U(t+N*T) is the predicted bus voltage, and U(t) is the current bus voltage;

[0035] The predicted external characteristic torque is obtained by looking up a table based on the predicted rotational speed and predicted bus voltage.

[0036] Preferably, the step of calculating the motor derating factor based on the stator predicted temperature, the first temperature threshold for derating initiation, and the second temperature threshold for derating to zero, and multiplying the motor derating factor by the maximum torque of the motor to obtain the first predicted torque, calculating the IGBT derating factor based on the IGBT predicted temperature, and multiplying the IGBT derating factor by the maximum torque of the motor to obtain the second predicted torque, and taking the minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque includes:

[0037] The motor derating factor is calculated by subtracting the predicted stator temperature from the current stator temperature and dividing by the difference between the first temperature threshold and the second temperature threshold. The motor derating factor is then multiplied by the maximum torque of the motor to obtain the first predicted torque.

[0038] The IGBT derating factor is calculated by subtracting the predicted IGBT temperature from the current IGBT temperature and dividing by the difference between the first and second temperature thresholds. The second predicted torque is then obtained by multiplying the IGBT derating factor by the maximum torque of the motor.

[0039] The minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque is taken as the predicted output torque.

[0040] The predicted output torque is iterated to the calculation of the stator predicted temperature and IGBT predicted temperature.

[0041] This invention also discloses an output torque prediction system for an electric drive system, comprising: a predicted torque calculation module, a motor temperature prediction module, an IGBT temperature prediction module, and a voltage / speed temperature prediction module, wherein...

[0042] The motor temperature prediction module includes a motor heat calculation unit, a motor temperature calculation unit, and a motor derating factor calculation unit.

[0043] The IGBT temperature prediction module includes an IGBT loss calculation unit, an IGBT temperature calculation unit, and an IGBT derating factor calculation unit.

[0044] The motor heat calculation unit calculates the predicted value of the stator heat generated by the motor within the interval from the current time to the target time based on the copper loss power and iron loss power of the motor. The motor temperature calculation unit calculates the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the winding, and the predicted stator temperature after the current stator temperature calculation interval.

[0045] The IGBT loss calculation unit calculates the transient loss of the IGBT module from the current time to the target time based on the duty cycle, real-time current, and switching loss of the IGBT module. The IGBT temperature calculation unit calculates the predicted IGBT temperature based on the transient loss, the thermal resistance of the electric drive system, and the current IGBT temperature calculation interval.

[0046] The voltage / speed and temperature prediction module calculates the predicted speed of the motor from the current time to the target time based on the motor's current speed and the speed n seconds before the current time. It also calculates the predicted bus voltage of the motor from the current time to the target time based on the motor's current bus voltage and the current bus voltage n seconds before the current time. Finally, it looks up the predicted external characteristic torque based on the predicted speed and predicted bus voltage.

[0047] The motor derating factor calculation unit calculates the motor derating factor based on the stator predicted temperature, the first temperature threshold for derating to start, and the second temperature threshold for derating to zero. The motor derating factor is then multiplied by the maximum torque of the motor to obtain the first predicted torque. The IGBT derating factor calculation unit calculates the IGBT derating factor based on the IGBT predicted temperature. The IGBT derating factor is then multiplied by the maximum torque of the motor to obtain the second predicted torque. The predicted torque calculation module takes the minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque.

[0048] Compared with existing technologies, the above technical solution has the following advantages:

[0049] 1. The predicted output torque will be iterated repeatedly to get closer to the actual output torque at future moments;

[0050] 2. By combining multiple influencing factors to predict output torque, the prediction results are more accurate. Attached Figure Description

[0051] Figure 1A flowchart illustrating the output torque prediction method for an electric drive system in a preferred embodiment of the present invention. Detailed Implementation

[0052] The advantages of the present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments.

[0053] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0054] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The singular forms “a,” “the,” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any and all possible combinations of one or more of the associated listed items.

[0055] It should be understood that although the terms first, second, third, etc., may be used in this disclosure to describe various information, such information should not be limited to these terms. These terms are used only to distinguish information of the same type from one another. For example, without departing from the scope of this disclosure, first information may also be referred to as second information, and similarly, second information may also be referred to as first information. Depending on the context, the word "if" as used herein may be interpreted as "when," "when," or "in response to determination."

[0056] In the description of this invention, it should be understood that the terms "longitudinal", "lateral", "up", "down", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0057] In the description of this invention, unless otherwise specified and limited, it should be noted that the terms "installation", "connection" and "linking" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two components. They can be direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0058] In the following description, suffixes such as "module," "part," or "unit" used to denote elements are used only for the convenience of the description of the invention and have no specific meaning in themselves. Therefore, "module" and "part" can be used interchangeably.

[0059] See Figure 1 To illustrate the flowchart of the output torque prediction method for an electric drive system in a preferred embodiment of the present invention, the output torque prediction method includes the following steps:

[0060] S100: Based on the copper loss power and iron loss power of the motor, calculate the predicted value of the stator heat generated by the motor during the interval from the current time to the target time, and calculate the predicted stator temperature after the interval based on the predicted value of the stator heat generated, the thermal conductivity of the stator, the heat transfer area of ​​the winding and the current stator temperature.

[0061] Output torque is primarily affected by temperature factors, specifically the IGBT module temperature, motor temperature, and coolant temperature. To protect the hardware from damage, the electronic control software is configured to reduce the external characteristic torque when these temperatures reach certain values, thereby lowering the temperature of related components in the electric drive system. Therefore, based on the influence of temperature factors, temperature changes are predicted, and subsequently, torque changes are predicted. Specifically, based on the copper and iron losses that affect motor temperature, the predicted value of the stator heat generated by the motor is calculated over the interval from the current moment to the target moment (e.g., 20 seconds later). Then, based on the predicted stator heat generated, the stator's thermal conductivity, the winding heat transfer area, and the current stator temperature, the predicted future stator temperature is calculated after the interval, considering both the generated and dissipated heat.

[0062] S200: Based on the duty cycle, real-time current, and switching losses of the IGBT module, calculate the transient losses of the IGBT module within the interval from the current time to the target time, and calculate the predicted temperature of the IGBT after the interval based on the transient losses, the thermal resistance of the electric drive system, and the current IGBT temperature.

[0063] The output torque is affected by the IGBT's temperature. Therefore, in this step, based on the IGBT module's duty cycle, real-time current, and switching losses, the transient losses of the IGBT module over the interval from the current time to the target time are calculated. More specifically, the transient losses can be expressed as power. Then, based on the transient losses, the thermal resistance of the electric drive system, and the current IGBT temperature, the predicted IGBT temperature after the interval is calculated. This predicted IGBT temperature represents the possible temperature of the IGBT module after the interval.

[0064] S300: Based on the current speed of the motor and the speed n seconds before the current time, calculate the predicted speed of the motor within the interval from the current time to the target time. Based on the current bus voltage of the motor and the current bus voltage n seconds before the current time, calculate the predicted bus voltage of the motor within the interval from the current time to the target time. And obtain the predicted external characteristic torque by looking up the table based on the predicted speed and the predicted bus voltage.

[0065] Understandably, after the motor reaches its inflection point speed, the external characteristic torque decreases. On the bus voltage side, the lower the bus voltage, the earlier the inflection point speed, and the lower the external characteristic torque after the inflection point speed. Therefore, it is necessary to predict the motor speed and bus voltage at future moments. Specifically, based on the motor's current speed and the speed n seconds prior to the current moment, the variation pattern of the speed within the previous n seconds is calculated and superimposed on the future to calculate the predicted motor speed within the interval from the current moment to the target moment. On the other hand, based on the motor's current bus voltage and the current bus voltage n seconds prior to the current moment, the variation pattern of the bus voltage within the previous n seconds is calculated and superimposed on the future to calculate the predicted bus voltage within the interval from the current moment to the target moment. Based on the predicted speed and predicted bus voltage, the predicted external characteristic torque is obtained by looking up a table. This table is a pre-existing expression of the speed, bus voltage, and external characteristic torque curves within the motor controller. By looking up the curves or the table, the torque change affected by the motor speed and bus voltage can be obtained.

[0066] S400: Calculate the motor derating factor based on the stator predicted temperature, the first temperature threshold for derating to start, and the second temperature threshold for derating to zero (the first and second temperature thresholds are values ​​fixed in advance according to the motor characteristics). Multiply the motor derating factor by the maximum torque of the motor to obtain the first predicted torque. Calculate the IGBT derating factor based on the IGBT predicted temperature. Multiply the IGBT derating factor by the maximum torque of the motor to obtain the second predicted torque. Take the minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque.

[0067] The first and second predicted torques are calculated separately at the stator predicted temperature and the IGBT predicted temperature. During the calculation, the relationship between motor temperature and torque change, and the relationship between IGBT module temperature and torque change (usually linearly) are considered. Specifically, the motor derating factor and the IGBT derating factor are calculated separately. These represent the torque that may change under the relationship between the first temperature threshold corresponding to maximum torque and the stator predicted temperature and IGBT module temperature. Finally, the minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque is taken as the predicted output torque. This takes into account all factors that can affect torque in the future. For safety reasons, the smallest of the three is chosen to provide current or speed adjustments in advance for possible increases in torque.

[0068] In a preferred embodiment, step S100 includes:

[0069] S110: Based on the following formula and Joule's law, calculate the copper loss power consumption: P Cu =I 2 ·R, where P Cu The copper loss power consumption is where I is the bus current and R is the bus resistance. The copper loss power consumption represents the heat that may be generated in the copper part of the motor stator.

[0070] S120: Calculate iron loss power consumption based on the following formula: P Fe =P h +P c +P e , where P Fe For iron loss power consumption, P h For hysteresis loss (the energy consumed by a ferromagnetic material or similar object during repeated magnetization due to hysteresis), P c For classic eddy current losses, P e Abnormal eddy current loss (eddy current loss refers to the energy loss caused by eddy currents when a current conductor moves in a non-uniform magnetic field or is in a time-varying magnetic field), where hysteresis loss, classical eddy current loss, and abnormal eddy current loss are calculated respectively according to the following formulas:

[0071] Where k h Here, f is the magneto-induced loss coefficient, and B is the motor frequency. p k is the amplitude of magnetic flux density. c k is the classical eddy current loss coefficient. e The superscripts above represent the abnormal eddy current loss coefficients, indicating f and B respectively. p to the power of;

[0072] S130: Calculate the predicted stator heat generation value based on the following formula: Q = K cool ·(P Cu +P Fe )·Δt, where Q is the predicted value of stator generated heat, K cool The parameters are: coolant temperature and flow rate correction factors, and Δt is the interval duration. All of these parameters can be obtained from the motor manufacturer.

[0073] Furthermore, step S100 also includes:

[0074] S140: Calculate the stator temperature rise based on the following formula: Where ΔT strThe stator temperature rise is given by A, where A is the heat transfer area of ​​the winding, λ is the thermal conductivity, and σ is the heat transfer thickness of the stator winding. Based on the metal structure of each motor, the temperature change of the stator under the heat generated above is calculated.

[0075] S150: The final stator predicted temperature is calculated based on the following formula: T str_pre =T str +ΔT str T str_pre For predicting the stator temperature, T str This is the current stator temperature.

[0076] In a preferred embodiment, the calculation of the stator predicted temperature also includes a closed-loop iterative process. Specifically, step S100 further includes:

[0077] S160: Calculate the first predicted torque based on the stator predicted temperature, and compare the first predicted torque with the current torque;

[0078] S170: When the first predicted torque is greater than or equal to the current torque, output the first predicted torque, indicating that more torque will be needed in the future, and prepare in advance for increasing the corresponding torque change.

[0079] S170': When the first predicted torque is less than the current torque, the maximum available current replaces the bus current, and the above steps are iterated until the calculation of motor losses is fed back into the calculation of closed-loop heat correction, that is, the P value in the calculation process is continuously updated. Cu The torque output continues until the first predicted torque is greater than or equal to the current torque. In other words, when the first predicted torque is less than the current torque, it means that no additional torque is needed in the future, i.e., no preparation is needed for increasing torque.

[0080] In one optional embodiment, step S200 includes:

[0081] S210: Calculate the conduction loss of the IGBT module based on the following formula: P con_IGBT =duty·[i(t)·V CE0 +i(t) 2 ·r CE ], where P con_IGBT Here, is the conduction loss, duty is the duty cycle, i(t) is the real-time current, and V is the voltage. CE0 For the voltage of the IGBT module, r CE Given the impedance of the IGBT module, the heat power generated by the IGBT module when it is turned on can be calculated using the above formula.

[0082] S220: Calculate the switching loss of the IGBT module based on the following formula: P sw_IGBT =f sw ·E on+off(i(t)), where P sw_IGBT For switching losses, f sw E is the switching frequency. on+off(i(t)) The turn-on and turn-off losses of the IGBT module represent the losses incurred during the instantaneous switching between turn-on and turn-off.

[0083] S230: Calculate the transient loss of the IGBT module based on the following formula: P IGBT =P con_IGBT +P sw_IGBT , where P IGBT Transient loss;

[0084] S240: Calculate the junction temperature rise of the IGBT module based on the following formula: ΔT IGBT =P IGBT *Δt*R c , where ΔT IGBT R represents the nodal temperature rise, Δt is the time interval, and R is the temperature rise at the node. c Thermal resistance of the electric drive system;

[0085] S250: Calculate the IGBT predicted temperature based on the following formula: T IGBT_pre =T IGBT +ΔT IGBT T IGBT_pre For IGBT temperature prediction, T IGBT This represents the current IGBT temperature.

[0086] Furthermore, the calculation of the IGBT predicted temperature also involves a closed-loop iterative process, and step S200 further includes:

[0087] S260: Calculate the second predicted torque based on the IGBT predicted temperature, and compare the second predicted torque with the current torque;

[0088] S270: When the second predicted torque is greater than or equal to the current torque, output the second predicted torque;

[0089] S270': When the second predicted torque is less than the current torque, the second predicted torque replaces the current torque to calculate the duty cycle and real-time current under the second predicted torque, and the above steps are iterated until this is fed back into the calculation of IGBT losses, thus correcting the heat calculation in a closed loop. That is, the duty cycle and real-time current in the calculation process are continuously updated until the second predicted torque is greater than or equal to the current torque for output. In other words, when the second predicted torque is less than the current torque, it means that no increase in torque is needed in the future, i.e., no preparation is needed for increasing torque.

[0090] On the other hand, step S300 includes:

[0091] S310: Predicted rotational speed is calculated based on the following formula: Where Spd(t+N*T) is the predicted rotational speed, Spd(t) is the current rotational speed, T is the unit time, and N is the number of unit times such that n = N*T. It can be understood that in the above calculation formula, T is the unit time, for example, it could be 1 second or 2 seconds, and 5*T represents the rotational speed in the past 5 or 10 seconds. The calculation can reveal the change in rotational speed per second over the past 5 or 10 seconds, and further, it can be used to predict the rotational speed at any future time.

[0092] S320: Calculate the predicted bus voltage based on the following formula: Where U(t+N*T) is the predicted bus voltage, and U(t) is the current bus voltage. It can be understood that in the above calculation formula, T is used as the unit of time, for example, 1 second or 2 seconds. 5*T represents the bus voltage over the past 5 or 10 seconds. The calculation can reveal the change per second of the bus voltage over the past 5 or 10 seconds, and further, it can be used to calculate the predicted bus voltage at any future time.

[0093] S330: The predicted external characteristic torque is obtained by looking up a table based on the predicted rotational speed and predicted bus voltage.

[0094] Additionally, step S400 includes:

[0095] S410: Subtract the predicted stator temperature from the current stator temperature and divide by the difference between the first temperature threshold and the second temperature threshold to calculate the motor derating factor, and multiply the motor derating factor by the maximum torque of the motor to obtain the first predicted torque.

[0096] Specifically, the first temperature threshold corresponds to the maximum motor temperature that the motor can withstand, for example, 150°C, and the second temperature threshold corresponds to the motor temperature at which the motor begins to be derated, for example, 170°C. The motor derating factor calculated by subtracting the predicted stator temperature from the current stator temperature and dividing by the difference between the first and second temperature thresholds represents the proportion of the predicted stator temperature to the stator's operating temperature range. Multiplying this by the maximum torque of the motor yields the first predicted torque.

[0097] S420: Subtract the predicted IGBT temperature from the current IGBT temperature and divide by the difference between the first temperature threshold and the second temperature threshold to calculate the IGBT derating factor, and multiply the IGBT derating factor by the maximum torque of the motor to obtain the second predicted torque.

[0098] Specifically, the first temperature threshold corresponds to the maximum motor temperature that the motor can withstand, such as 150°C, and the second temperature threshold corresponds to the motor temperature at which the motor begins to be derated, such as 170°C. The IGBT derating factor calculated by subtracting the IGBT predicted temperature from the current IGBT temperature and dividing by the difference between the first and second temperature thresholds represents the proportion of the IGBT predicted temperature to the operating temperature range of the IGBT module. This is then multiplied by the maximum torque of the motor to obtain the second predicted torque.

[0099] In steps S410 and S420 above, the minimum value of the derating factor calculated based on the stator predicted temperature / IGBT module predicted temperature is used to derating the torque to obtain the maximum usable torque after a certain period of time.

[0100] S430: The minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque is taken as the predicted output torque;

[0101] S440: Iterates the predicted output torque to the calculation of the stator predicted temperature and IGBT predicted temperature.

[0102] This invention also discloses an output torque prediction system for an electric drive system, comprising: a predicted torque calculation module, a motor temperature prediction module, an IGBT temperature prediction module, and a voltage / speed temperature prediction module. The motor temperature prediction module includes a motor heat calculation unit, a motor temperature calculation unit, and a motor derating factor calculation unit. The IGBT temperature prediction module includes an IGBT loss calculation unit, an IGBT temperature calculation unit, and an IGBT derating factor calculation unit. The motor heat calculation unit calculates the predicted stator heat generated by the motor within an interval from the current time to the target time based on the motor's copper and iron loss power. The motor temperature calculation unit calculates the predicted stator heat generated, the stator's thermal conductivity, the winding heat transfer area, and the predicted stator temperature after the current stator temperature calculation interval. The IGBT loss calculation unit calculates the transient losses of the IGBT module within an interval from the current time to the target time based on the IGBT module's duty cycle, real-time current, and switching losses. The IGBT temperature calculation unit calculates the transient losses based on the transient losses, the electric drive system... The IGBT predicted temperature is calculated based on the thermal resistance and current IGBT temperature over a specified interval. The voltage / speed temperature prediction module calculates the predicted motor speed from the current time to the target time based on the motor's current speed and the speed n seconds before the current time. It also calculates the predicted motor bus voltage from the current time to the target time based on the motor's current bus voltage and the current bus voltage n seconds before the current time. The predicted external characteristic torque is obtained by looking up a table based on the predicted speed and predicted bus voltage. The motor derating factor calculation unit calculates the motor derating factor based on the stator predicted temperature, the first temperature threshold for derating, and the second temperature threshold for derating to zero. The motor derating factor is multiplied by the motor's maximum torque to obtain the first predicted torque. The IGBT derating factor calculation unit calculates the IGBT derating factor based on the IGBT predicted temperature and multiplies the IGBT derating factor by the motor's maximum torque to obtain the second predicted torque. The predicted torque calculation module takes the minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque.

[0103] It should be noted that the embodiments of the present invention have better implementability and are not intended to limit the present invention in any way. Any person skilled in the art may use the above-disclosed technical content to change or modify it into equivalent effective embodiments. However, any modifications or equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. An output torque prediction method of an electric drive system, characterized by, The method comprises the following steps: based on the copper loss power and the iron loss power of the motor, calculating a stator generated heat prediction value of the motor within an interval time from the current time to a target time, and based on the stator generated heat prediction value, the thermal conductivity coefficient of the stator, the winding heat transfer area and the current stator temperature, calculating a predicted stator temperature after the interval time; based on the duty ratio, the real-time current and the switching loss of the IGBT module, calculating a transient loss of the IGBT module within the interval time from the current time to the target time, and based on the transient loss, the thermal resistance of the electric drive system and the current IGBT temperature, calculating a predicted IGBT temperature after the interval time; based on the current speed of the motor and the speed of n seconds before the current time, calculating a predicted speed of the motor within the interval time from the current time to the target time, based on the current bus voltage of the motor and the current bus voltage of n seconds before the current time, calculating a predicted bus voltage of the motor within the interval time from the current time to the target time, and based on the predicted speed and the predicted bus voltage, obtaining a predicted external characteristic torque by table lookup; based on the predicted stator temperature, a first temperature threshold of de-rating start and a second temperature threshold of de-rating to zero, calculating a motor de-rating coefficient, and multiplying the motor de-rating coefficient by the maximum torque of the motor to obtain a first predicted torque, based on the predicted IGBT temperature, calculating an IGBT de-rating coefficient, and multiplying the IGBT de-rating coefficient by the maximum torque of the motor to obtain a second predicted torque, and taking the minimum value among the first predicted torque, the second predicted torque and the predicted external characteristic torque as a predicted output torque.

2. The output torque prediction method of claim 1, wherein The step of calculating a stator generated heat prediction value of the motor within an interval time from the current time to a target time based on the copper loss power and the iron loss power of the motor, and calculating a predicted stator temperature after the interval time based on the stator generated heat prediction value, the thermal conductivity coefficient of the stator, the winding heat transfer area and the current stator temperature comprises: The copper loss power consumption is calculated based on the following equation: wherein is the copper loss power consumption, is the bus current, is the bus resistance; The iron loss power consumption is calculated based on the following equation: wherein P is the iron loss power consumption, Ph is the hysteresis loss, Pc is the classical eddy current loss, Pe is the anomalous eddy current loss, wherein the hysteresis loss, the classical eddy current loss and the anomalous eddy current loss are calculated according to the following equations, respectively: , , wherein is the magnetic loss coefficient, is the motor frequency, is the magnetic flux density amplitude, is the classical eddy current loss coefficient, is the anomalous eddy current loss coefficient; The stator generated heat prediction value is calculated based on the following equation: wherein is the stator generated heat prediction value, is the correction coefficient, is the interval duration.

3. The output torque prediction method of claim 2, wherein, The step of calculating a stator generated heat prediction value of the motor within an interval time from the current time to a target time based on the copper loss power and the iron loss power of the motor, and calculating a predicted stator temperature after the interval time based on the stator generated heat prediction value, the thermal conductivity coefficient of the stator, the winding heat transfer area and the current stator temperature further comprises: The stator temperature rise is calculated based on the following equation: wherein is the stator temperature rise, is the winding heat transfer area, is the thermal conductivity, is the heat transfer thickness of the stator winding; The stator predicted temperature is calculated based on the following equation: wherein is the stator predicted temperature, is the current stator temperature.

4. The output torque prediction method of claim 3, wherein The step of calculating a stator generated heat prediction value of the motor within an interval time from the current time to a target time based on the copper loss power and the iron loss power of the motor, and calculating a predicted stator temperature after the interval time based on the stator generated heat prediction value, the thermal conductivity coefficient of the stator, the winding heat transfer area and the current stator temperature further comprises: S160: calculating a first predicted torque based on the predicted stator temperature, and comparing the first predicted torque with the current torque; S170: when the first predicted torque is greater than or equal to the current torque, outputting the first predicted torque; S170': when the first predicted torque is less than the current torque, replacing the bus current with the maximum available current, and iterating the steps of S160, S170 and S170' until the first predicted torque is greater than or equal to the current torque for output.

5. The output torque prediction method of claim 1, wherein, The step of calculating the transient loss of the IGBT module in the interval from the current time to the target time based on the duty cycle, real-time current, and switching loss of the IGBT module, and calculating the IGBT predicted temperature after the interval based on the transient loss, thermal resistance of the electric drive system, and current IGBT temperature comprises: The turn-on loss of the IGBT module is calculated based on the following formula: wherein is the turn-on loss, is the duty cycle, is the real-time current, is the voltage of the IGBT module, is the impedance of the IGBT module; The switching loss of the IGBT module is calculated based on the following formula: wherein is the switching loss, is the switching frequency, is the turn-on and turn-off loss of the IGBT module; The transient loss of the IGBT module is calculated based on the following formula: wherein is the transient loss; The junction temperature rise of the IGBT module is calculated based on the following formula: wherein is the junction temperature rise, is the interval duration, is the thermal resistance of the electric drive system; The IGBT predicted temperature is calculated based on the following equation: wherein is the IGBT predicted temperature, is the current IGBT temperature.

6. The output torque prediction method of claim 5, wherein, The step of calculating the transient loss of the IGBT module in the interval from the current time to the target time based on the duty cycle, real-time current, and switching loss of the IGBT module, and calculating the IGBT predicted temperature after the interval based on the transient loss, thermal resistance of the electric drive system, and current IGBT temperature further comprises: S260: Calculate a second predicted torque based on the IGBT predicted temperature, and compare the second predicted torque with the current torque; S270: When the second predicted torque is greater than or equal to the current torque, output the second predicted torque; S270': When the second predicted torque is less than the current torque, replace the current torque with the second predicted torque to calculate the duty cycle and real-time current under the second predicted torque, and iterate the duty cycle, real-time current, and the above steps S260, S270, and S270' until the second predicted torque is greater than or equal to the current torque to output.

7. The output torque prediction method of claim 1, wherein, The step of calculating the predicted speed of the motor in the interval from the current time to the target time based on the current speed and the speed n seconds before the current time, calculating the predicted bus voltage of the motor in the interval from the current time to the target time based on the current bus voltage and the current bus voltage n seconds before the current time, and obtaining the predicted external characteristic torque by table lookup based on the predicted speed and the predicted bus voltage comprises: The predicted rotational speed is calculated based on the following equation: wherein is the predicted rotational speed, is the current rotational speed, is the unit of time, is the number of units of time such that ; The predicted bus voltage is calculated based on the following equation: wherein is the predicted bus voltage, is the current bus voltage; Obtaining the predicted external characteristic torque by table lookup based on the predicted speed and the predicted bus voltage.

8. The output torque prediction method of claim 1, wherein, The step of calculating the motor derating coefficient based on the stator predicted temperature, the first temperature threshold of the derating start, and the second temperature threshold of the derating to zero, multiplying the motor derating coefficient by the maximum torque of the motor to obtain the first predicted torque, calculating the IGBT derating coefficient based on the IGBT predicted temperature, multiplying the IGBT derating coefficient by the maximum torque of the motor to obtain the second predicted torque, and taking the minimum value of the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque comprises: Calculating the motor derating coefficient by subtracting the stator predicted temperature from the current stator temperature and dividing by the difference between the first temperature threshold and the second temperature threshold, and multiplying the motor derating coefficient by the maximum torque of the motor to obtain the first predicted torque; Calculating the IGBT derating coefficient by subtracting the IGBT predicted temperature from the current IGBT temperature and dividing by the difference between the first temperature threshold and the second temperature threshold, and multiplying the IGBT derating coefficient by the maximum torque of the motor to obtain the second predicted torque; Taking the minimum value of the first predicted torque, the second predicted torque, and the predicted external characteristic torque as the predicted output torque; Iterating the predicted output torque to the calculation of the stator predicted temperature and the IGBT predicted temperature.

9. An output torque prediction system of an electric drive system, characterized by, Comprise: The prediction torque calculation module, the motor temperature prediction module, the IGBT temperature prediction module, and the voltage / rotation speed temperature prediction module, wherein The motor temperature prediction module comprises a motor heat calculation unit, a motor temperature calculation unit, and a motor derating coefficient calculation unit. The IGBT temperature prediction module comprises an IGBT loss calculation unit, an IGBT temperature calculation unit, and an IGBT derating coefficient calculation unit. The motor heat calculation unit calculates a stator generated heat prediction value of the motor in an interval from a current time to a target time based on copper loss power and iron loss power of the motor, and the motor temperature calculation unit calculates a predicted stator temperature after the interval based on the stator generated heat prediction value, a thermal conductivity of the stator, a winding heat transfer area, and a current stator temperature. The IGBT loss calculation unit calculates a transient loss of the IGBT module in the interval from the current time to the target time based on a duty ratio, a real-time current, and a switching loss of the IGBT module, and the IGBT temperature calculation unit calculates a predicted IGBT temperature after the interval based on the transient loss, a thermal resistance of the electric drive system, and a current IGBT temperature. The voltage / rotation speed temperature prediction module calculates a predicted rotation speed of the motor in the interval from the current time to the target time based on a current rotation speed of the motor and a rotation speed n seconds before the current time, calculates a predicted bus voltage of the motor in the interval from the current time to the target time based on a current bus voltage of the motor and the current bus voltage n seconds before the current time, and obtains a predicted external characteristic torque by table lookup based on the predicted rotation speed and the predicted bus voltage. The motor derating coefficient calculation unit calculates a motor derating coefficient based on the predicted stator temperature, a first temperature threshold of a derating start, and a second temperature threshold of a derating to zero, and multiplies the motor derating coefficient by a maximum torque of the motor to obtain a first predicted torque, the IGBT derating coefficient calculation unit calculates an IGBT derating coefficient based on the predicted IGBT temperature, and multiplies the IGBT derating coefficient by the maximum torque of the motor to obtain a second predicted torque, and the prediction torque calculation module takes a minimum value among the first predicted torque, the second predicted torque, and the predicted external characteristic torque as a predicted output torque.

Images