A method for protecting an electric machine from low temperatures

Abstract

The application provides a motor low-temperature protection method, which is implemented according to the following steps: step one, collecting an initial flux linkage value λ of a motor init and collecting a critical point of a motor entering a flux-weakening working condition; step two, collecting a real-time temperature T of the motor and judging a relationship between the real-time temperature T of the motor and a preset temperature; step three, when the real-time temperature T of the motor is not less than the preset temperature, step two is continuously executed; when the real-time temperature T of the motor is less than the preset temperature, a current value of the motor is controlled according to a real-time permanent magnet flux linkage of the motor. According to the application, the technical problem that irreversible demagnetization of a motor permanent magnet occurs when the motor starts in a low-temperature environment in the prior art can be solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of motors, and in particular relates to a method for protecting a motor from low temperatures. Background Art

[0002] With increasing attention to environmental protection and efficient energy use, the trend toward electric vehicles is gaining momentum. For new energy vehicles, battery technology, motor technology, and motor controller technology are considered the three key electric technologies. Given the current lack of breakthroughs in battery technology, improving the efficiency, power density, safety, and reliability of motor drive systems has become a key research direction for new energy vehicle motor drive systems.

[0003] Permanent magnet synchronous motors (PMSMs) are widely used in pure electric and hybrid new energy vehicles due to their high power density, wide speed range, compact size, and high efficiency. While PMSMs offer several unparalleled advantages over other motor types, they also have some disadvantages. For example, ferrite magnets, commonly used in PMSMs, have low remanent magnetic density and coercivity. These magnets are susceptible to irreversible demagnetization at low temperatures, affecting normal motor operation.

[0004] When a motor is started in a low-temperature environment, excessive starting current can cause irreversible demagnetization of the motor's permanent magnets, severely impacting motor performance. The increased flux linkage of the motor's permanent magnets causes a rise in terminal voltage, potentially exceeding the inverter's limits and limiting the motor's output performance.

[0005] Since the motor in the prior art may cause irreversible demagnetization of the motor's permanent magnet when it is started in a low-temperature environment, which may affect the motor's performance, the present invention studies and designs a motor low-temperature protection method. Summary of the Invention

[0006] Therefore, the present invention provides a motor low-temperature protection method, which can solve the technical problem in the prior art that when the motor is started in a low-temperature environment, the permanent magnet of the motor may be irreversibly demagnetized.

[0007] In order to solve the above problem, the present invention provides a motor low temperature protection method, which is implemented according to the following steps:

[0008] Step 1: Collect the initial magnetic flux value λ of the motor init , and collect the critical point when the motor enters the weak magnetic condition;

[0009] Step 2: Collect the real-time temperature T of the motor and determine the relationship between the real-time temperature T of the motor and the preset temperature;

[0010] Step three, when the real-time temperature T of the motor is not less than the preset temperature, continue to execute step two; when the real-time temperature T of the motor is less than the preset temperature, control the current value of the motor according to the real-time permanent magnet flux linkage of the motor.

[0011] In some embodiments, controlling the current value of the motor according to the real-time permanent magnet flux linkage of the motor further comprises calculating the real-time permanent magnet flux linkage according to the following formula:

[0012] λ real= λ init *(1+K λ *(T-T ref ))

[0013] wherein,

[0014] λ real : real-time flux linkage value;

[0015] λ init : initial permanent magnet flux linkage value;

[0016] K λ : flux linkage temperature coefficient;

[0017] T: real-time temperature;

[0018] T ref : reference temperature.

[0019] In some embodiments, the reference temperature is 25°C.

[0020] In some embodiments, controlling the current value of the motor according to the real-time permanent magnet flux linkage of the motor further comprises judging whether the motor is in a field weakening working condition according to the critical point of the motor entering the field weakening working condition and the real-time permanent magnet flux linkage; when the critical point of the motor entering the field weakening working condition is less than the real-time permanent magnet flux linkage, the motor is in the field weakening working condition; and when the critical point of the motor entering the field weakening working condition is not less than the real-time permanent magnet flux linkage, the motor is not in the field weakening working condition.

[0021] In some embodiments, when the motor is in the field weakening working condition, the method further comprises the following steps of controlling the motor controller MCU to gradually increase the current control angle beta, thereby increasing the direct-axis current id and reducing the quadrature-axis current iq, until the terminal voltage reaches the maximum voltage limit value U=U max .

[0022] In some embodiments, when the motor is not in the field weakening working condition, the method further comprises the following steps of judging whether the motor is in a starting working condition; when the motor is in the starting working condition, driving the motor controller MCU to reduce the maximum starting current value according to the variation of the real-time flux linkage value; and when the motor is not in the starting working condition, driving the motor controller MCU to reduce the input current in each working condition according to the real-time flux linkage value of the motor.

[0023] In some embodiments, the drive motor controller MCU reduces the starting maximum current value according to the real-time flux linkage value change size, and the input current calculation formula is:

[0024] I adj= I ref* (1-(△λ / λ init )*K normal )

[0025] Wherein,

[0026] I adj : adjusted input current;

[0027] I ref : original reference current;

[0028] △λ=λ real -λ init : permanent magnet flux linkage difference;

[0029] K normal : conventional working condition current adjustment proportionality coefficient.

[0030] In some embodiments, the drive motor controller MCU reduces the starting maximum current value according to the real-time flux linkage value change size, and the input current calculation formula is:

[0031] I start-adj =I start-max *(1-(△λ / λ init )*K start )

[0032] Wherein,

[0033] I start-adj : adjusted starting current;

[0034] I start-max : original maximum starting current;

[0035] △λ=λ real -λ init : permanent magnet flux linkage difference;

[0036] K start : starting current adjustment proportionality coefficient.

[0037] In some embodiments, when the motor is not in the starting condition, the motor is in the normal running condition, and the motor is not in the field weakening condition, the drive motor controller MCU reduces the input current under each working condition according to the real-time flux linkage value of the motor.

[0038] In some embodiments, in step one, the initial flux linkage value at 25°C of the motor is collected.

[0039] The motor low-temperature protection method has the following beneficial effects:

[0040] In the technical scheme, when the motor is in a low-temperature environment, the current value of the motor is controlled according to the real-time permanent magnet flux of the motor, so as to prevent irreversible demagnetization of the motor. The motor can still output greater torque at high speed, and the range of the external characteristic curve is ensured, and the output performance of the motor is ensured. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the embodiments of the present application or the technical schemes in the prior art, the drawings needed to be used in the following embodiment or prior art description will be briefly introduced. The drawings in the following description are only exemplary, and other embodiment drawings can be obtained by the provided drawings without creative labor for those skilled in the art.

[0042] Figure 1 is a flowchart of the motor low-temperature protection method of the present application;

[0043] Figure 2 is a motor current-torque curve diagram of the motor using the motor low-temperature protection method of the present application and the motor of the prior art;

[0044] Figure 3 is a motor current-torque simulation experiment data of the motor using the motor low-temperature protection method of the present application and the motor of the prior art. DETAILED DESCRIPTION

[0045] The technical schemes in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. The description of the at least one exemplary embodiment is actually only illustrative, but not as any limitation on the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0046] In the description of the present application, it should be understood that the orientation words such as “front, back, up, down, left, right”, “transverse, vertical, perpendicular, horizontal” and “top, bottom” and the like indicate the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate and imply that the indicated device or element must have a specific orientation or be constructed and operated in a specific orientation, therefore it cannot be understood as a limitation on the scope of protection of the present application; the orientation words “inner, outer” refer to the inner and outer of the contour of each component itself.

[0047] For purposes of the description hereinafter, spatial relations terms, such as "above", "below", "top", "bottom", and the like, are used with reference to the exemplary illustrations as shown in the drawings. However, it is to be understood that the spatial terms are intended to encompass different orientations of the device in use or operation in addition to the orientations depicted in the drawings. For example, if the device described is turned over, the components described as "above" other components or "below" other components would then be oriented "below" other components or "above" other components, respectively. Accordingly, the exemplary terms "above" and "below" can encompass both an orientation of above and below. The device can be otherwise oriented (rotated 90 degrees or at other orientations) and the spatial descriptions modified accordingly.

[0048] In addition, it should be pointed out that the use of the words "first", "second" and the like to define parts is only for the convenience of distinguishing the corresponding parts, and the above words have no special meaning unless otherwise stated, and therefore cannot be understood as limiting the scope of protection of the present application.

[0049] For reference Figure 1 As shown, according to the embodiment of the present application, a motor low temperature protection method is provided, which is implemented according to the following steps:

[0050] Step one, collect the initial flux linkage value λ of the motor init And collect the critical point of the motor entering the field weakening working condition;

[0051] Step two, collect the real-time temperature T of the motor, and judge the relationship between the real-time temperature T of the motor and the preset temperature;

[0052] Step three, when the real-time temperature T of the motor is not less than the preset temperature, continue to execute step two; when the real-time temperature T of the motor is less than the preset temperature, control the current value of the motor according to the real-time permanent magnet flux linkage of the motor.

[0053] In this technical solution, when the motor is in a low temperature environment, the current value of the motor is controlled according to the real-time permanent magnet flux linkage of the motor, so as to prevent irreversible demagnetization of the motor. The motor can still output greater torque at high speed, and the range of the external characteristic curve is ensured, and the output performance of the motor is ensured.

[0054] In some embodiments, controlling the current value of the motor according to the real-time permanent magnet flux linkage of the motor further includes calculating the real-time permanent magnet flux linkage according to the following formula:

[0055] λ real= λ init *(1+K λ *(T-Tref ))

[0056] wherein,

[0057] λ real : real-time flux value;

[0058] λ init : initial permanent magnet flux value;

[0059] K λ : flux temperature coefficient;

[0060] T: real-time temperature;

[0061] T ref : reference temperature.

[0062] According to the critical point of the field weakening working condition collected at normal temperature, it is judged whether the motor has entered the field weakening working condition. If the motor is not in the field weakening working condition, the real-time permanent magnet flux of the motor is calculated.

[0063] In some embodiments, the reference temperature is 25℃.

[0064] In some embodiments, the control of the current value of the motor according to the real-time permanent magnet flux of the motor further comprises: judging whether the motor is in the field weakening working condition according to the critical point of the motor entering the field weakening working condition and the real-time permanent magnet flux. When the critical point of the motor entering the field weakening working condition is less than the real-time permanent magnet flux, the motor is in the field weakening working condition. When the critical point of the motor entering the field weakening working condition is not less than the real-time permanent magnet flux, the motor is not in the field weakening working condition.

[0065] In some embodiments, when the motor is in the field weakening working condition, the motor controller MCU gradually increases the current control angle beta, thereby increasing the direct-axis current id and reducing the quadrature-axis current iq, until the terminal voltage reaches the maximum voltage limit value U=U max .

[0066] If the motor is normally running and is in the field weakening working condition, the low-temperature environment field weakening working condition protection control strategy is entered. The motor controller MCU gradually increases the current control angle beta, thereby increasing the direct-axis current id and reducing the quadrature-axis current iq, until the terminal voltage reaches the maximum voltage limit value U=U max .

[0067] Since the permanent magnet flux of the motor increases in the low-temperature environment, compared with the normal temperature, the terminal voltage of the motor is larger under the same working condition. Therefore, the terminal voltage of the motor is more likely to reach the maximum voltage limit value. For reference, see Figure 2 and Figure 3As shown, the motor external characteristic curve range is reduced, the terminal voltage is too large, and the inverter may be damaged in severe cases. By gradually increasing the current control angle beta of the motor controller MCU, the direct-axis current id is increased, the field weakening is deepened, and the permanent magnet field is reduced to meet the maximum voltage limit requirement, so that the maximum torque output by the motor under high speed working condition is increased, the motor output power is improved, the output performance of the motor under field weakening working condition is ensured, and the motor external characteristic curve range is not reduced

[0068] The motor low temperature protection method of the application adjusts the starting maximum current value according to the real-time flux linkage value of the motor to prevent irreversible demagnetization of the motor in a low temperature environment. In a low temperature environment, the flux linkage of the motor permanent magnet is increased, and the input current under each working condition (non-field weakening working condition) is reduced by the driving motor controller MCU according to the real-time flux linkage value of the motor to reduce the motor loss and improve the motor efficiency. The flux linkage of the motor permanent magnet is increased, which causes the terminal voltage to rise and may exceed the limit of the inverter, thereby limiting the output performance of the motor. In order to solve this problem, the application deepens the field weakening, increases the current control angle beta (increases the direct-axis current id), weakens the permanent magnet field, and reduces the terminal voltage to ensure that it is within a safe range. The motor can still output greater torque under high speed, the range of the external characteristic curve is ensured, and the output performance of the motor is ensured.

[0069] In some embodiments, when the motor is not in the field weakening working condition, it is judged whether the motor is in the starting working condition. When the motor is in the starting working condition, the driving motor controller MCU reduces the starting maximum current value according to the real-time flux linkage value. When the motor is not in the starting working condition, the driving motor controller MCU reduces the input current under each working condition according to the real-time flux linkage value of the motor.

[0070] In some embodiments, the driving motor controller MCU reduces the starting maximum current value according to the real-time flux linkage value, and the input current calculation formula is:

[0071] I adj= I ref* (1-(△λ / λ init )*K normal )

[0072] Wherein,

[0073] I adj : adjusted input current;

[0074] I ref : original reference current (set according to different working conditions);

[0075] △λ=λ real -λ init : permanent magnet flux linkage difference;

[0076] K normal : Normal working condition current adjustment proportionality coefficient.

[0077] If the motor is not in the starting condition, but in the normal running condition, and not in the field weakening condition, the driving motor controller MCU reduces the input current in each working condition according to the real-time flux value of the motor, inputs the current calculation formula, and because the motor permanent magnet flux increases, the output torque under the unit current increases. Compared with the normal temperature, the motor permanent magnet flux increases in the low temperature environment, and can output greater torque under the same current. Therefore, by driving the motor controller MCU to reduce the input current in each working condition according to the real-time flux value of the motor, the motor loss is reduced and the motor efficiency is improved.

[0078] In some embodiments, the driving motor controller MCU reduces the starting maximum current value according to the real-time flux value change size, and inputs the current calculation formula:

[0079] I start-adj =I start-max *(1-(△λ / λ init )*K start )

[0080] Wherein,

[0081] I start-adj : Adjusted starting current;

[0082] I start-max : Original maximum starting current;

[0083] △λ=λ real -λ init : Permanent magnet flux difference;

[0084] K start : Starting current adjustment proportionality coefficient.

[0085] If the motor is in the starting condition, the driving motor controller MCU reduces the starting maximum current value according to the real-time flux value change size, inputs the above formula, and the motor permanent magnet is ferrite magnetic steel. The ferrite magnetic steel is more likely to cause irreversible demagnetization in the low temperature environment, which seriously affects the performance of the motor. Therefore, by driving the motor controller MCU to reduce the starting maximum current value according to the real-time flux value change size, it is prevented that the excessive starting current causes irreversible demagnetization of the motor permanent magnet in the low temperature environment.

[0086] The motor low-temperature protection method of the application prevents irreversible demagnetization of the motor by adjusting the maximum starting current value according to the change in the real-time flux linkage value of the motor when the motor is in a low-temperature environment, so as to ensure the output performance of the motor.

[0087] The motor low-temperature protection method of the application also solves the problem that excessive starting current may cause irreversible demagnetization of the permanent magnet of the motor when the motor starts in a low-temperature environment, thereby seriously affecting the performance of the motor.

[0088] The motor low-temperature protection method of the application reduces the input current in each working condition (non-field weakening working condition) according to the real-time flux linkage value of the motor by using the motor controller MCU, thereby reducing the motor loss and improving the motor efficiency.

[0089] In a low-temperature environment, the flux linkage of the permanent magnet of the motor increases, resulting in an increase in the terminal voltage, which may exceed the limit of the inverter, thereby limiting the output performance of the motor. In order to solve this problem, the motor low-temperature protection method of the application deepens the field weakening, increases the current control angle beta (increases the direct-axis current id), weakens the magnetic field of the permanent magnet, reduces the terminal voltage, and ensures that it is within a safe range. The motor can still output greater torque at high speed, the range of the external characteristic curve is ensured, and the output performance of the motor is ensured.

[0090] In some embodiments, when the motor is not in the starting working condition, the motor is in the normal running working condition, and the motor is not in the field weakening working condition, the motor controller MCU reduces the input current in each working condition according to the real-time flux linkage value of the motor.

[0091] In some embodiments, in step one, the initial flux linkage value of the motor at 25 DEG C is collected.

[0092] The motor low-temperature protection method of the application uses ferrite as the magnetic steel material of the permanent magnet synchronous motor, and the residual magnetism temperature coefficient of the magnetic steel of this material is usually negative. In a low-temperature environment, the residual magnetism of the ferrite magnetic steel is greater. In a low-temperature environment, irreversible demagnetization is more likely to occur in a reverse magnetic field.

[0093] When the motor starts in a low-temperature environment, excessive starting current may cause irreversible demagnetization of the motor permanent magnet, thereby seriously affecting the performance of the motor. The application proposes a permanent magnet motor low-temperature protection method, which adjusts the maximum starting current value according to the motor real-time flux value change size through the driving motor controller MCU, to prevent irreversible demagnetization of the motor.

[0094] The motor permanent magnet flux increases, and the output torque of the motor per unit current increases. The application reduces the input current under each working condition (non-field weakening working condition) through the driving motor controller MCU according to the motor real-time flux value, reduces the motor loss, and improves the motor efficiency.

[0095] In a low-temperature environment, the flux of the motor permanent magnet increases, causing the terminal voltage to rise, which may exceed the limit of the inverter, thereby limiting the output performance of the motor. To solve this problem, the application deepens the field weakening, increases the current control angle beta (increases the direct-axis current id), weakens the permanent magnet magnetic field, and reduces the terminal voltage to ensure that it is within the safe range. The motor can still output greater torque at high speed, ensuring the range of the external characteristic curve and the output performance of the motor.

[0096] As can be easily understood by those skilled in the art, the advantageous technical features of the above-mentioned methods can be freely combined and superimposed without conflict.

[0097] The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the application shall be included in the protection scope of the application. The above only describes the preferred embodiments of the application and is not intended to limit the application. Any modifications, equivalent replacements and improvements made within the spirit and principle of the application shall be included in the protection scope of the application.

Claims

1. A method for protecting a motor from low temperature, characterized by: Follow these steps to implement: Step 1: Collect the initial magnetic flux value λ of the motor init , and collect the critical point when the motor enters the weak magnetic condition; Step 2: Collect the real-time temperature T of the motor and determine the relationship between the real-time temperature T of the motor and the preset temperature; Step 3: When the real-time temperature T of the motor is not less than the preset temperature, continue to execute step 2; when the real-time temperature T of the motor is less than the preset temperature, control the current value of the motor according to the real-time permanent magnet flux of the motor; Controlling the motor current value according to the real-time permanent magnet flux of the motor also includes calculating the real-time permanent magnet flux using the following formula: l real= l init *(1+K λ *(TT ref )) in, λ real : Real-time magnetic linkage value; λ init : Initial permanent magnet flux value; K λ : magnetic flux temperature coefficient; T: real-time temperature; T ref : Reference temperature.

2. The motor low temperature protection method according to claim 1, characterized in that: The reference temperature is 25°C.

3. The motor low temperature protection method according to claim 1, characterized in that: Controlling the current value of the motor according to the real-time permanent magnet flux of the motor also includes judging whether the motor is in a weak magnetic working condition based on the critical point at which the motor enters the weak magnetic working condition and the real-time permanent magnet flux. When the critical point at which the motor enters the weak magnetic working condition is less than the real-time permanent magnet flux, the motor is in a weak magnetic working condition. When the critical point at which the motor enters the weak magnetic working condition is not less than the real-time permanent magnet flux, the motor is not in a weak magnetic working condition.

4. The motor low temperature protection method according to claim 3, characterized in that: When the motor is in a weak magnetic condition, the following steps are also included: controlling the motor controller MCU to gradually increase the current control angle beta, thereby increasing the direct axis current id and reducing the quadrature axis current iq until the terminal voltage reaches the maximum voltage limit value U=U max .

5. The motor low temperature protection method according to claim 3, characterized in that: When the motor is not in a weak magnetic condition, it is determined whether the motor is in a starting condition. When the motor is in a starting condition, the motor controller MCU is driven to reduce the maximum starting current value according to the change in the real-time magnetic flux value. When the motor is not in a starting condition, the motor controller MCU is driven to reduce the input current under each condition according to the real-time magnetic flux value of the motor.

6. The motor low temperature protection method according to claim 5, characterized in that: The drive motor controller MCU reduces the maximum starting current value according to the change in the real-time magnetic flux value. The input current calculation formula is: I adj= I ref* (1-(△λ / λ init )*K normal ) in, I adj : Adjusted input current; I ref : original reference current; △λ=λ real -λ init : permanent magnet flux difference; K normal : Current adjustment proportional coefficient under normal working conditions.

7. The motor low temperature protection method according to claim 5, characterized in that: The drive motor controller MCU reduces the maximum starting current value according to the change in the real-time magnetic flux value. The input current calculation formula is: I start-adj =I start-max *(1-(△λ / λ init )*K start ) in, I start-adj : Adjusted starting current; I start-max : original maximum starting current; △λ=λ real -λ init : permanent magnet flux difference; K start : Starting current adjustment proportional coefficient.

8. The motor low temperature protection method according to claim 5, characterized in that: When the motor is not in the starting condition, the motor is in the normal operating condition, and the motor is not in the weak magnetic condition, the motor controller MCU is driven to reduce the input current under each condition according to the real-time magnetic flux value of the motor.

9. The motor low temperature protection method according to claim 1, characterized in that: In the step 1, the initial flux value of the motor at 25° C. is collected.

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