Motor field weakening control method and system, storage medium and program product

Abstract

The invention relates to the technical field of motor control, and discloses a motor field weakening control method and system, a storage medium and a program product, and the method comprises the following steps: when bus undervoltage occurs in the operation process of a motor, if an instruction value of a D-axis current is not equal to an expected field weakening current output by a field weakening voltage closed loop, entering a next step; performing range limitation on the difference value between the instruction value of the D-axis current and the expected flux weakening current to obtain a range-limited difference value; multiplying the limited difference value by a Q-axis current derating coefficient, and then multiplying by a symbol coefficient to obtain a Q-axis derating current; and calculating a final output Q-axis current instruction value, wherein the calculation formula is as follows: the final output Q-axis current instruction value = Q-axis derated current + the original Q-axis current instruction value. The problem that in the prior art, effective flux weakening cannot be achieved when the motor operates in a medium-high-speed flux weakening area is solved.

Description

Technical Field

[0001] This invention relates to the field of motor control technology, specifically to a motor field weakening control method, system, storage medium, and program product. Background Technology

[0002] When the power supply system of the motor controller is depleted (such as when the battery is depleted), the bus voltage will be pulled down. If the motor continues to output high power at this time, the operating conditions will be further deteriorated, causing the bus voltage to be pulled down below the minimum supply voltage required by the chip. This will seriously affect the normal operation of the chip and the motor control system, and may even cause damage to the devices. In this case, power derating control is required.

[0003] The essence of power derating is to limit the current output. Limiting the total phase current output of the motor is one of the commonly used derating strategies. However, in a motor vector control system, if the total current is excessively limited, it will indirectly limit the field weakening current Id. If the motor is operating at high speed and there is an undervoltage at the power supply end, the insufficient field weakening current will lead to control voltage saturation and motor runaway.

[0004] In existing technologies, the current circle (total phase current output by the motor) is limited proportionally according to the bus voltage drop, thereby indirectly limiting the power at the controller input and alleviating the voltage drop problem caused by power supply failure.

[0005] Size of the current circle In conventional motor vector control algorithms, to ensure the field weakening depth, Is and Id are typically used to limit the output of Iq, and the control topology is as follows: Figure 1 As shown: in: Is: Current circle (total current magnitude) Iq: Q-axis current Id: D-axis current SpeedRef: Speed ​​command SpeedFbd: Actual rotational speed PI: Proportional-Integral Controller Udc: Bus voltage IdRef_out: Final D-axis current command IqRef_out: Final Q-axis current command like Figure 1 As shown, by proportionally limiting the size of the current circle Is based on voltage drop conditions, the sizes of Id and Iq are indirectly limited, thereby achieving the limiting function.

[0006] defect: When the motor is running in the medium-to-high speed field weakening zone, the D-axis field weakening current will account for most of the total current. If the current is limited due to derating, there is a chance that the D-axis current that is normally used for field weakening will be limited, which will cause the system to be unable to effectively weaken the field, resulting in control voltage saturation, PI controller saturation failure, and motor runaway. Summary of the Invention

[0007] To overcome the shortcomings of the prior art, the present invention provides a motor field weakening control method, system, storage medium and program product, which solves the problem that the prior art cannot effectively weaken the field when the motor is running in the medium and high speed field weakening zone.

[0008] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: A method for field weakening control of a motor includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current is not equal to the expected field weakening current output by the field weakening voltage closed loop, proceed to the next step. The range of the difference between the commanded value of the D-axis current and the desired field weakening current is limited to obtain the range-limited difference. Multiply the difference after the limit by the Q-axis current derating factor, and then multiply by the sign factor to obtain the Q-axis derating current; The final output Q-axis current command value is calculated using the following formula: Final output Q-axis current command value = Q-axis derating current + original Q-axis current command value.

[0009] The beneficial effects of this invention are: By employing a novel method, it is ensured that when the motor is running at high speed and undervoltage occurs, the field weakening control will not saturate and run away, regardless of how the total current Is is limited. The algorithm is simple and reliable, achieving the desired effect without increasing hardware costs.

[0010] Based on the above technical solution, the present invention can be further improved as follows.

[0011] As a preferred technical solution, the command value of the D-axis current is obtained based on the current circle after derating.

[0012] The beneficial effects of adopting the above-mentioned preferred technical solution are: The command value of the D-axis current is obtained from the current circle.

[0013] As a preferred technical solution, when the D-axis current before derating is greater than the total phase current, the commanded value of the D-axis current is equal to the D-axis current before derating; when the D-axis current before derating is less than the total phase current, the commanded value of the D-axis current is equal to the current circle after derating.

[0014] The beneficial effects of adopting the above-mentioned preferred technical solution are: Obtain the command value of the D-axis current when the D-axis current before derating is greater than or less than the total phase current.

[0015] As a preferred technical solution, when undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating limit based on the voltage drop.

[0016] The beneficial effects of adopting the above-mentioned preferred technical solution are: The power derating module obtains the current circle after derating based on the voltage drop.

[0017] As a preferred technical solution, when undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating based on the voltage drop, including the following steps: The speed request signal and the actual speed signal are closed-loop subtracted, and then the unprocessed Q-axis current command is obtained through the PI regulator. After being limited by the current circle, the limited Q-axis current request is obtained. The limited Q-axis current request and the actual Q-axis current signal are closed-loop subtracted, and then the Q-axis output voltage is obtained after passing through the PI regulator. The difference between the D-axis current feedforward command and the field weakening current closed loop is used to obtain the unrestricted D-axis command current. Then, the current is restricted by the current circle to obtain the restricted D-axis current. The difference between the restricted D-axis current and the actual D-axis current signal closed loop is used to obtain the D-axis output voltage after passing through the PI regulator. The phase voltage is obtained by performing Euclidean norm calculation on the Q-axis output voltage and D-axis output voltage. The phase voltage is then compared with the actual bus voltage in a closed loop. The result is then passed through a PI regulator and the D-axis current PI output limiter in the field weakening loop to obtain the desired field weakening current output by the field weakening voltage closed loop. Based on the desired field weakening current output from the field weakening voltage closed loop, the actual bus voltage is input to the power derating module for linear lookup to obtain the current circle after derating limitation.

[0018] The beneficial effects of adopting the above-mentioned preferred technical solution are: This facilitates the realization of the current circle after obtaining the derating limit.

[0019] As a preferred technical solution, when the range of the difference between the commanded value of the D-axis current and the desired field weakening current is limited, the range of the difference after the range limitation is [0, Q-axis current derating value].

[0020] This ensures that the difference between the commanded value of the D-axis current and the desired field weakening current is kept within a reasonable range.

[0021] As a preferred technical solution, if the actual feedback speed is positive, the value of the sign coefficient is -1; if the actual feedback speed is negative, the value of the sign coefficient is 1.

[0022] The beneficial effects of adopting the above-mentioned preferred technical solution are: This facilitates current control that is opposite to the actual feedback speed.

[0023] A motor field weakening control system includes a processor, a memory, and a computer program stored in the memory. When the computer program is executed by the processor, it implements the steps of the motor field weakening control method.

[0024] A storage medium internally storing a computer program, which, when executed, implements the steps of the aforementioned motor field weakening control method.

[0025] A program product includes a computer program that, when executed, implements the steps of the described motor field weakening control method. Attached Figure Description

[0026] Figure 1 This is a control topology diagram of the existing technology; Figure 2 This is the control topology diagram of the present invention; Figure 3 for Figure 2 One of the magnified views of a section; Figure 4 for Figure 2 The second enlarged view of a section; Figure 5 for Figure 2 The third enlarged view of a section; Figure 6 for Figure 2 The fourth enlarged view of a part. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0028] The principles and features of the present invention are described below. The embodiments given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0029] Example 1 like Figures 1 to 6 As shown, a field weakening control method for a motor includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current is not equal to the expected field weakening current output by the field weakening voltage closed loop, proceed to the next step. The range of the difference between the commanded value of the D-axis current and the desired field weakening current is limited to obtain the range-limited difference. Multiply the difference after the limit by the Q-axis current derating factor, and then multiply by the sign factor to obtain the Q-axis derating current; The final output Q-axis current command value is calculated using the following formula: Final output Q-axis current command value = Q-axis derating current + original Q-axis current command value.

[0030] The beneficial effects of this invention are: By employing a novel method, it is ensured that when the motor is running at high speed and undervoltage occurs, the field weakening control will not saturate and run away, regardless of how the total current Is is limited. The algorithm is simple and reliable, achieving the desired effect without increasing hardware costs.

[0031] Based on the above technical solution, the present invention can be further improved as follows.

[0032] As a preferred technical solution, the command value of the D-axis current is obtained based on the current circle after derating.

[0033] The beneficial effects of adopting the above-mentioned preferred technical solution are: The command value of the D-axis current is obtained from the current circle.

[0034] As a preferred technical solution, when the D-axis current before derating is greater than the total phase current, the commanded value of the D-axis current is equal to the D-axis current before derating; when the D-axis current before derating is less than the total phase current, the commanded value of the D-axis current is equal to the current circle after derating.

[0035] The beneficial effects of adopting the above-mentioned preferred technical solution are: Obtain the command value of the D-axis current when the D-axis current before derating is greater than or less than the total phase current.

[0036] As a preferred technical solution, when undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating limit based on the voltage drop.

[0037] The beneficial effects of adopting the above-mentioned preferred technical solution are: The power derating module obtains the current circle after derating based on the voltage drop.

[0038] As a preferred technical solution, when undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating based on the voltage drop, including the following steps: The speed request signal and the actual speed signal are closed-loop subtracted, and then the unprocessed Q-axis current command is obtained through the PI regulator. After being limited by the current circle, the limited Q-axis current request is obtained. The limited Q-axis current request and the actual Q-axis current signal are closed-loop subtracted, and then the Q-axis output voltage is obtained after passing through the PI regulator. The difference between the D-axis current feedforward command and the field weakening current closed loop is used to obtain the unrestricted D-axis command current. Then, the current is restricted by the current circle to obtain the restricted D-axis current. The difference between the restricted D-axis current and the actual D-axis current signal closed loop is used to obtain the D-axis output voltage after passing through the PI regulator. The phase voltage is obtained by performing Euclidean norm calculation on the Q-axis output voltage and D-axis output voltage. The phase voltage is then compared with the actual bus voltage in a closed loop. The result is then passed through a PI regulator and the D-axis current PI output limiter in the field weakening loop to obtain the desired field weakening current output by the field weakening voltage closed loop. Based on the desired field weakening current output from the field weakening voltage closed loop, the actual bus voltage is input to the power derating module for linear lookup to obtain the current circle after derating limitation.

[0039] The beneficial effects of adopting the above-mentioned preferred technical solution are: This facilitates the realization of the current circle after obtaining the derating limit.

[0040] As a preferred technical solution, when the range of the difference between the commanded value of the D-axis current and the desired field weakening current is limited, the range of the difference after the range limitation is [0, Q-axis current derating value].

[0041] This ensures that the difference between the commanded value of the D-axis current and the desired field weakening current is kept within a reasonable range.

[0042] As a preferred technical solution, if the actual feedback speed is positive, the value of the sign coefficient is -1; if the actual feedback speed is negative, the value of the sign coefficient is 1.

[0043] The beneficial effects of adopting the above-mentioned preferred technical solution are: This facilitates current control that is opposite to the actual feedback speed.

[0044] A motor field weakening control system includes a processor, a memory, and a computer program stored in the memory. When the computer program is executed by the processor, it implements the steps of the motor field weakening control method.

[0045] A storage medium internally storing a computer program, which, when executed, implements the steps of the aforementioned motor field weakening control method.

[0046] A program product includes a computer program that, when executed, implements the steps of the described motor field weakening control method.

[0047] The present invention has the following technical effects: (1) By using a new method, it is ensured that when the motor is running at high speed and undervoltage occurs, no matter how the total current Is is limited, the field weakening control will not saturate and run out of control. (2) The algorithm is simple and reliable, and achieves the desired effect without increasing hardware costs.

[0048] As described above, the present invention can be implemented well.

[0049] Example 2 like Figures 1 to 6 As shown, based on Example 1, this example provides a more detailed implementation method.

[0050] When the motor is running at high speed, dynamic derating causes the D-axis field weakening current to be limited, which leads to control voltage saturation and motor runaway. This invention is a solution to this problem.

[0051] This invention provides a performance improvement method for high-speed weak magnetic undervoltage conditions, which solves the problem of transient voltage saturation while limiting current.

[0052] Brief description of the plan: When using the current circle limit derating strategy, if field weakening voltage saturation occurs due to current limit, the difference between the current before and after the D-axis limit can be multiplied by the calibration coefficient, and then the sign of the rotation speed can be reversed to compensate for the Q-axis command. This achieves the effect of reducing the Q-axis command when the D-axis cannot increase the field weakening depth.

[0053] Detailed plan: Control topology diagram as follows Figure 2 As shown: Figure 2 The parameters are defined as follows: SpeedRef: Speed ​​command SpeedFdb: Actual feedback speed Iq: Unrestricted Q-axis current Id: Unrestricted D-axis current IdFdFwd: D-axis current feedforward Is: The current circle (total phase current) limited by looking up the table based on the bus voltage. Iq_Limit: The Q-axis current after being limited. Id_Limit: The D-axis current after being limited. IqRef_out: Derating-compensated Q-axis current IqFdb: Actual Q-axis feedback current IdFdb: Actual feedback current of the D-axis Udc: Bus voltage Uq: Q-axis voltage Ud: D-axis voltage Id_PI_Limit: Limiting the D-axis current output of the field weakening loop (PI output). Id_Dy_Limit: Total D-axis current output limit Iq_Cmp_Limit: Preset limit for Q-axis current derating; the limit range here is [0, IqCompMax]. IqCompMax: Q-axis current derating value, maximum limit value during intermediate processes. IdFluxWeaken: The field weakening D-axis current output by the field weakening loop. DegCoef: Q-axis current derating factor IqDeg: Q-axis current derating value ΔId: The difference between Id_Limit and IdFluxWeaken ΔIdLimit: The value after pre-limiting Sign: The sign coefficient (+1 or -1) after negating the actual rotational speed. Figure 2 The structure outside the dashed box is a conventional motor control loop topology, which will be briefly described below: 1. Q-axis branch: After the speed request SpeedRef signal is input, it is looped with the actual speed signal. After passing through the PI regulator, the unprocessed Q-axis current command Iq is obtained. Then it is limited by the current circle Is to obtain the limited Q-axis current request IqRef_out. It is looped with the actual Q-axis current IqFdb signal. After passing through the PI regulator, the Q-axis output voltage Uq is obtained.

[0054] 2. D-axis branch: After the D-axis current feedforward command IdFdFwd is input, a field-weakening current IdFluxWeaken is added to obtain the unlimited D-axis command current Id. After being limited by the current circle, the limited current Id_Limit is obtained. Id_Limit serves as both the input to the current circle limiting command Iq and the command for the D-axis current, forming a closed loop with the actual D-axis current IdFdb signal. After passing through a PI regulator, the D-axis output voltage Ud is obtained.

[0055] 3. Weakening branch: The voltages Ud and Uq output by the D / Q axes can be used to calculate the phase voltage Us. Then, the difference between the phase voltage Us and the actual bus voltage Udc / sqrt(3) is calculated in a closed loop. After passing through the PI regulator and then through the limiting Id_PI_Limit, the closed-loop regulation obtained by the D-axis weakening current request command IdFluxWeaken is used for subsequent loop control.

[0056] 4. Derating branch: The bus voltage Udc is used as input to the power derating module for linear lookup. Based on the real-time voltage Udc, the current circle limit value Is is obtained for subsequent loop control.

[0057] The steps involved in this plan are explained below: (1) When undervoltage occurs on the busbar during motor operation, Figure 2 The power derating module in the middle will obtain the derating limit current circle Is based on the voltage drop.

[0058] (2) Based on the current circle Is, the command value of the D-axis current can be obtained: when Id>-Is, the output D-axis command Id_Limit=Id; when Id<-Is, the output D-axis command Id_Limit=-Is.

[0059] (3) This scheme discusses the situation where the bus voltage drops transiently, and the D-axis command cannot continue to increase negatively to increase the field weakening depth due to the limitation of Is. At this time, due to voltage saturation, the field weakening voltage closed loop will continue to work, and the expected field weakening current IdFluxWeaken output by the loop will continue to increase negatively. At this time, Id_Limit≠IdFluxWeaken.

[0060] (4) When the operating condition in (3) occurs, it indicates that due to the total current limitation, the system can no longer further reduce Id to weaken the magnetism under the undervoltage condition. At this time, it is necessary to increase the Q-axis current value in the opposite direction. On the one hand, this reduces the motor speed to reduce the influence of back EMF; on the other hand, when the direction of Q-axis current is opposite to the speed, the system enters the power generation condition, which helps to exit the voltage saturation condition. Therefore, when ΔId is not equal to 0, it indicates that the system has a voltage saturation condition when Id is limited. At this time, the range of ΔId should be limited to keep it between 0 and IqCompMax.

[0061] (5) Multiply the limited ΔIdLimit by the Q-axis current derating factor DegCoef. Then multiply by the sign of the inverse speed. More specifically, take the sign of the actual feedback speed to get +1 (positive speed sign) or -1 (negative speed sign), then multiply by -1 to get the sign of the opposite speed. (Example: When the actual feedback speed is -1000 rpm, take the sign of the actual feedback speed and the variable is -1, then multiply by the gain -1 to get Sign = -1 * -1 = 1).

[0062] (6) Finally, the derating current IqDeg of the Q axis is obtained and superimposed on the original Q axis command Iq_Limit to obtain the final output Q axis current command IqRef_out.

[0063] The present invention has the following technical effects: (1) By using a new method, it is ensured that when the motor is running at high speed and undervoltage occurs, no matter how the total current Is is limited, the field weakening control will not saturate and run out of control. (2) The algorithm is simple and reliable, and achieves the desired effect without increasing hardware costs.

[0064] As described above, the present invention can be implemented well.

[0065] Example 3 like Figures 1 to 6 As shown, based on Embodiment 1, the present invention also provides a motor field weakening control system.

[0066] A motor field weakening control system includes a processor, a memory, and a computer program stored in the memory. When the computer program is executed by the processor, it implements the steps of the motor field weakening control method.

[0067] A method for field weakening control of a motor includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current Id_Limit ≠ the expected field weakening current IdFluxWeaken output by the field weakening voltage closed loop, then proceed to the next step. The difference ΔId between Id_Limit and IdFluxWeaken is range-limited to obtain the range-limited difference ΔIdLimit; Multiply the limited ΔIdLimit by the Q-axis current derating factor DegCoef, and then multiply by the sign factor Sign to obtain the Q-axis derating current IqDeg; The final output Q-axis current command value IqRef_out is calculated using the formula: IqRef_out = IqDeg + Iq_Limit; where Iq_Limit represents the original Q-axis current command value.

[0068] The beneficial effects of this invention are: By employing a novel method, it is ensured that when the motor is running at high speed and undervoltage occurs, the field weakening control will not saturate and run away, regardless of how the total current Is is limited. The algorithm is simple and reliable, achieving the desired effect without increasing hardware costs.

[0069] Example 4 like Figures 1 to 6 As shown, based on Embodiment 1, the present invention also provides a storage medium that stores a computer program internally, which, when executed, implements the steps of the motor field weakening control method described above.

[0070] A method for field weakening control of a motor includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current Id_Limit ≠ the expected field weakening current IdFluxWeaken output by the field weakening voltage closed loop, then proceed to the next step. The difference ΔId between Id_Limit and IdFluxWeaken is range-limited to obtain the range-limited difference ΔIdLimit; Multiply the limited ΔIdLimit by the Q-axis current derating factor DegCoef, and then multiply by the sign factor Sign to obtain the Q-axis derating current IqDeg; The final output Q-axis current command value IqRef_out is calculated using the formula: IqRef_out = IqDeg + Iq_Limit; where Iq_Limit represents the original Q-axis current command value.

[0071] The beneficial effects of this invention are: By employing a novel method, it is ensured that when the motor is running at high speed and undervoltage occurs, the field weakening control will not saturate and run away, regardless of how the total current Is is limited. The algorithm is simple and reliable, achieving the desired effect without increasing hardware costs.

[0072] Example 5 like Figures 1 to 6 As shown, based on Embodiment 1, the present invention also provides a program product.

[0073] A program product includes a computer program, wherein when the computer program is executed, the steps of a motor field weakening control method are described.

[0074] A method for field weakening control of a motor includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current Id_Limit ≠ the expected field weakening current IdFluxWeaken output by the field weakening voltage closed loop, then proceed to the next step. The difference ΔId between Id_Limit and IdFluxWeaken is range-limited to obtain the range-limited difference ΔIdLimit; Multiply the limited ΔIdLimit by the Q-axis current derating factor DegCoef, and then multiply by the sign factor Sign to obtain the Q-axis derating current IqDeg; The final output Q-axis current command value IqRef_out is calculated using the formula: IqRef_out = IqDeg + Iq_Limit; where Iq_Limit represents the original Q-axis current command value.

[0075] The beneficial effects of this invention are: By employing a novel method, it is ensured that when the motor is running at high speed and undervoltage occurs, the field weakening control will not saturate and run away, regardless of how the total current Is is limited. The algorithm is simple and reliable, achieving the desired effect without increasing hardware costs.

[0076] In the description of this invention, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0077] In the description of this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0078] In the description of this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0079] In the description of this invention, although embodiments of the invention have been shown and described herein, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this invention.

[0080] In the description of this invention, all features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method of field weakening control of an electric machine, characterized by, Includes the following steps: When a bus undervoltage occurs during motor operation, if the command value of the D-axis current is not equal to the expected field weakening current output by the field weakening voltage closed loop, proceed to the next step. The range of the difference between the commanded value of the D-axis current and the desired field weakening current is limited to obtain the range-limited difference. Multiply the difference after the limit by the Q-axis current derating factor, and then multiply by the sign factor to obtain the Q-axis derating current; The final output Q-axis current command value is calculated using the following formula: Final output Q-axis current command value = Q-axis derating current + original Q-axis current command value.

2. The method of claim 1, wherein, The command value of the D-axis current is obtained from the current circle after the derating limit.

3. The method of claim 2, wherein, When the D-axis current before derating is greater than the total phase current, the commanded value of the D-axis current is equal to the D-axis current before derating; when the D-axis current before derating is less than the total phase current, the commanded value of the D-axis current is equal to the current circle after derating.

4. The method of claim 1, wherein, When undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating limit based on the voltage drop.

5. The method of claim 4, wherein, When undervoltage occurs on the bus during motor operation, the power derating module obtains the current circle after derating limit based on the voltage drop, including the following steps: The speed request signal and the actual speed signal are closed-loop subtracted, and then the unprocessed Q-axis current command is obtained through the PI regulator. After being limited by the current circle, the limited Q-axis current request is obtained. The limited Q-axis current request and the actual Q-axis current signal are closed-loop subtracted, and then the Q-axis output voltage is obtained after passing through the PI regulator. The difference between the D-axis current feedforward command and the field weakening current closed loop is used to obtain the unrestricted D-axis command current. Then, the current is restricted by the current circle to obtain the restricted D-axis current. The difference between the restricted D-axis current and the actual D-axis current signal closed loop is used to obtain the D-axis output voltage after passing through the PI regulator. The phase voltage is obtained by performing Euclidean norm calculation on the Q-axis output voltage and D-axis output voltage. The phase voltage is then compared with the actual bus voltage in a closed loop. The result is then passed through a PI regulator and the D-axis current PI output limiter in the field weakening loop to obtain the desired field weakening current output by the field weakening voltage closed loop. Based on the desired field weakening current output from the field weakening voltage closed loop, the actual bus voltage is input to the power derating module for linear lookup to obtain the current circle after derating limitation.

6. The method of claim 1, wherein, When limiting the range of the difference between the commanded value of the D-axis current and the desired field weakening current, the range of the difference after the range limitation is [0, Q-axis current derating value].

7. The method of claim 1, wherein, If the actual feedback speed is positive, the sign coefficient is -1; if the actual feedback speed is negative, the sign coefficient is 1.

8. A system for field weakening control of an electric machine, characterized by The device includes a processor, a memory, and a computer program stored in the memory. When the computer program is executed by the processor, it implements the steps of the field weakening control method for a motor as described in any one of claims 1 to 7.

9. A storage medium, characterized by The device internally stores a computer program, which, when executed, implements the steps of the motor field weakening control method according to any one of claims 1 to 7.

10. A program product, characterized by It includes a computer program, which, when executed, implements the steps of the motor field weakening control method according to any one of claims 1 to 7.

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