Permanent magnet motor, method for monitoring temperature condition of rotor of permanent magnet motor and control device

Abstract

The invention relates in particular to monitoring of rotor temperature of individual electric machines in fuel cell vehicles. The invention relates to a method for monitoring the temperature condition of a rotor (11) of a permanent magnet motor, in particular of a permanent magnet synchronous motor, comprising at least the following steps: detecting a counter electromotive force parameter U1 characterizing the counter electromotive force U of the permanent magnet motor and a rotational speed omega of the rotor (11) of the permanent magnet motor; the temperature condition of the rotor (11) is indicated by means of a temperature condition monitoring mathematical model (2) on the basis of at least the counter electromotive force parameter U1 and the rotational speed omega, said temperature condition monitoring mathematical model being pre-established on the basis of a permanent magnet motor of the same specification and characterizing at least the relationship between the temperature T of the rotor (11) and the magnetic flux lambda of a permanent magnet (112) arranged on the rotor (11). A corresponding control device for a permanent magnet motor, a corresponding permanent magnet motor and a corresponding computer program product are also disclosed. The temperature of the rotor can be simply and reliably monitored at low cost.

Description

Technical Field

[0001] The invention relates to a method for monitoring the temperature condition of a rotor of a permanent magnet motor, in particular a permanent magnet synchronous motor, a corresponding control device for the permanent magnet motor, a corresponding permanent magnet motor and a corresponding computer program product. Background Art

[0002] With the development of society and the advancement of technology, more and more driving devices use electric drive devices, such as motors. In particular, in recent years, electric vehicles have been rapidly developed, and various motors are widely used in electric vehicles. For example, in the fuel cell system of an electric vehicle, the anode recirculation blower (ARB) used to circulate hydrogen is usually driven by a motor, especially a permanent magnet synchronous motor. Permanent magnet synchronous motors have higher efficiency, higher power density, smaller size and weight, lower noise, etc. because they do not require excitation.

[0003] The motor will generate heat during operation. If the heat cannot be discharged in a timely and effective manner, the accumulated heat will affect the performance of the motor at best, and will directly damage the motor at worst. In particular, for permanent magnet synchronous motors, the permanent magnets of permanent magnet synchronous motors are sensitive to temperature and will demagnetize at high temperatures. Specifically, the load capacity of permanent magnet synchronous motors is limited by the temperature of the motor. Excessive temperature of the rotor will cause the performance of the motor to be lower than expected, and may even cause safety problems. Therefore, it can be understood that for safety and other considerations, in the field of electric vehicles, reliable temperature monitoring of the rotor of synchronous permanent magnet motors is crucial to the performance and reliability of the motor, and then the safety of the entire system. In particular, every effort should be made to avoid irreversible demagnetization of the permanent magnets (also called magnetic steel) of the rotor of the motor due to excessive temperature.

[0004] However, due to the limitations of the permanent magnet synchronous motor's own structure, it is difficult to obtain the temperature of the permanent magnet by direct measurement methods when the motor is running. At present, the temperature measurement methods used include slip rings and wireless temperature sensors, but these two methods not only have high costs, but also have poor engineering implementation feasibility, so it is difficult to reliably apply them in batches. It is understandable that due to the large number of motors used in electric vehicles, the accumulation of costs will greatly reduce the cost advantage of electric vehicles in a highly competitive market environment. For example, when an infrared temperature sensor is used to measure the temperature of a permanent magnet, a special rotor with an inner hole needs to be constructed, which will result in high manufacturing costs, and the infrared sensor itself will also bring additional costs.

[0005] Therefore, corresponding improvements need to be made. Summary of the invention

[0006] In order to overcome at least one of the above-mentioned disadvantages and / or other possible disadvantages that may not be mentioned here, the object of the present invention is to provide an improved method for monitoring the temperature condition of the rotor of a permanent magnet motor, in particular a permanent magnet synchronous motor, a corresponding control device for the permanent magnet motor, a corresponding permanent magnet motor and a corresponding computer program product.

[0007] According to a first aspect of the present invention, a method for monitoring the temperature condition of a rotor of a permanent magnet motor is provided, the method comprising at least the following steps: detecting a back electromotive force parameter U1 capable of characterizing the back electromotive force U of the permanent magnet motor and a rotational speed ω of the rotor of the permanent magnet motor; and indicating the temperature condition of the rotor by means of a temperature condition monitoring mathematical model at least based on the back electromotive force parameter U1 and the rotational speed ω, wherein the temperature condition monitoring mathematical model is pre-established based on permanent magnet motors of the same specifications and is capable of at least characterizing the relationship between the temperature T of the rotor and the magnetic flux λ of the permanent magnets arranged on the rotor.

[0008] According to an optional embodiment of the present invention, the magnetic flux λ includes a component λ0 related to the temperature T, and the component λ0 is characterized by the following quadratic function of the temperature T:

[0009] λ0=aT 2 +bT+c

[0010] Among them, a, b, and c are constants.

[0011] According to an optional embodiment of the present invention, the temperature condition monitoring mathematical model also establishes a relationship between the magnetic flux λ and a first time length elapsed from the establishment time point of the temperature condition monitoring mathematical model and / or a second time length elapsed from the magnetization formation time point of the permanent magnet.

[0012] According to a second aspect of the present invention, a control device for a permanent magnet motor, in particular an inverter, is provided. The control device is configured to execute the method according to any one of the above embodiments.

[0013] According to a third aspect of the present invention, there is provided a permanent magnet motor comprising the above-mentioned control device.

[0014] According to an optional embodiment of the present invention, the control device includes: a back electromotive force acquisition unit for acquiring the back electromotive force parameter U1, a speed acquisition unit for acquiring the speed ω, and a processor for indicating the temperature condition of the rotor with the aid of the temperature condition monitoring mathematical model at least based on the back electromotive force parameter U1 and the speed ω, and the temperature condition monitoring mathematical model is at least partially implemented as computer program instructions suitable for execution in the processor.

[0015] According to a fourth aspect of the present invention, a computer program product, in particular a computer-readable storage medium, is provided, which includes or stores computer program instructions, and when the computer program instructions are executed by a processor, the method according to any of the above embodiments can be executed.

[0016] According to certain exemplary embodiments of the present invention, the temperature of a rotor of a permanent magnet synchronous motor can be monitored simply, reliably and at low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will be described in more detail below with reference to the accompanying drawings in combination with exemplary embodiments, so that the principles, features and advantages of the present invention can be better understood. The accompanying drawings include:

[0018] Figure 1 A cross-sectional view of a permanent magnet synchronous machine according to an exemplary embodiment of the present invention is schematically shown.

[0019] Figure 2 A flow chart of a method for monitoring a temperature condition of a rotor of a permanent magnet motor according to an exemplary embodiment of the present invention is shown.

[0020] Figure 3 A temperature condition monitoring mathematical model according to an exemplary embodiment of the present invention is schematically shown.

[0021] Reference numerals list

[0022] 1 Permanent Magnet Synchronous Motor

[0023] 11 Rotor

[0024] 111 Iron Core

[0025] 112 permanent magnet

[0026] 12 Stator

[0027] 121 Winding

[0028] 13 Control Devices

[0029] 131 Back EMF acquisition unit

[0030] 132 Speed ​​acquisition unit

[0031] 133 Processor

[0032] 2 Temperature condition monitoring mathematical model DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial technical effects to be solved by the present invention more clearly understood, the present invention will be further described in detail below in conjunction with the accompanying drawings and multiple exemplary embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the scope of protection of the present invention.

[0034] Figure 1 A cross-sectional view of a permanent magnet synchronous machine according to an exemplary embodiment of the present invention is schematically shown.

[0035] like Figure 1 As shown, the permanent magnet synchronous motor 1 includes a rotor 11 and a stator 12, wherein the rotor 11 is rotatably located at least partially in the stator 12, and the rotor 11 includes an iron core 111 and a plurality of permanent magnets 112 arranged on the iron core 111 as an excitation source, and a plurality of windings 121 are correspondingly arranged on the stator 12. During operation, power transmission is achieved through the magnetic force between the rotating magnetic field generated by the windings 121 on the stator 12 and the magnetic field generated by the rotor 11. Since the principle of the permanent magnet synchronous motor 1 itself is well known, it will not be described in detail here.

[0036] There are many types of materials for the permanent magnet 112, and aluminum-nickel-cobalt permanent magnet alloys, iron-chromium-cobalt permanent magnet alloys, rare earth permanent magnet materials, and composite permanent magnet materials can usually be used. The magnetism of these magnetic materials usually changes with temperature. Generally speaking, as the temperature increases, the magnetism of the permanent magnet 112 will decrease accordingly, because the increase in temperature will lead to a decrease in magnetic retention and magnetic moment. The size of the temperature coefficient of the permanent magnet 112 is related to factors such as the type, composition, and preparation process of the permanent magnet material. In particular, when the temperature is high, the permanent magnet material may even undergo irreversible demagnetization, so it is necessary to monitor the temperature of the rotor 11, especially the permanent magnet 112, during operation. The iron core 111 has good thermal conductivity. During the operation of the permanent magnet synchronous motor 1, the temperature of the permanent magnet 112 is roughly the same as the temperature of the iron core 111, so their temperatures can be simply considered as the temperature of the rotor 12. No distinction is made in this article.

[0037] During the operation of the permanent magnet synchronous motor 1, the rotation of the rotor 11 will cut the magnetic field to generate an induced electromotive force. This induced electromotive force is opposite to the power supply voltage of the permanent magnet synchronous motor 1, so it is called back electromotive force, which can be detected. The magnitude of the back electromotive force is proportional to the speed of the motor, and is also related to the magnetism of the permanent magnet 112. The greater the magnetism, the greater the back electromotive force generated. As mentioned above, the magnetism of the permanent magnet 112 (which can be represented by the magnetic flux of the magnetic field it generates) is related to its temperature. Therefore, the inventor of this application creatively uses this relationship to provide a non-contact measurement and non-direct measurement technical route for temperature monitoring of the rotor 11.

[0038] The back electromotive force U has the following relationship (1) with the magnetic flux λ of the magnetic field generated by the permanent magnet 112 and the rotation speed ω of the rotor 11 (here, exemplarily represented by angular velocity):

[0039] U=λω (1)

[0040] The magnetic flux λ and the temperature T of the rotor 11 can be expressed by the following functional relationship (2):

[0041] λ=f(T) (2)

[0042] Here, f(T) represents the magnetic flux λ as a function of the temperature T of the rotor 11 .

[0043] Therefore, the following relationship (3) can be obtained:

[0044] U= f(T)·ω (3)

[0045] Therefore, it can be understood that if the temperature T of the rotor 11 is to be determined indirectly through the back electromotive force U, the function f(T) also needs to be determined.

[0046] However, many factors, such as the different magnetic materials of the permanent magnet 112 itself, the different rotors 11 (e.g., different arrangements of the permanent magnet 112), the different stators 12 (e.g., different arrangements of the windings 121), and the structural dimensions of the permanent magnet synchronous motor 1, will affect the magnetic coupling relationship between the permanent magnet 112 and the windings 121. The difference in this magnetic coupling relationship will directly correspond to the difference in magnetic flux λ. Therefore, when the rotation speed ω of the rotor 11 remains unchanged, it seems that there is a relationship between the temperature of the rotor 11 and the measurable back electromotive force U, but it is difficult to establish a relationship that can indirectly and reliably determine the temperature of the rotor 11 from the back electromotive force U, because this relationship is affected by multiple factors, especially factors that are coupled to each other.

[0047] In this case, the inventors of the present application creatively discovered that, for a permanent magnet synchronous motor 1 of predetermined specifications or models (i.e., having a predetermined design), since other influencing parameters are relatively fixed and the influencing parameters of these aspects of each permanent magnet synchronous motor 1 of the same design do not differ much, a temperature condition monitoring mathematical model of the rotor 11 can be established for the permanent magnet synchronous motor 1 of the predetermined design, and the temperature condition monitoring mathematical model can at least characterize the relationship λ=f(T) between the temperature T of the rotor 11 and the magnetic flux λ of the permanent magnet 112.

[0048] Although the above description is for the permanent magnet synchronous motor 1, the above association also exists for any other possible type of motor (including motors developed in the future) whose rotor 11 has permanent magnets 112. Therefore, the present invention is not entirely limited to the permanent magnet synchronous motor 1.

[0049] To this end, according to one aspect of the present invention, Figure 2 As shown, a method for monitoring the temperature condition of a rotor 11 of a permanent magnet motor is provided, the method comprising at least the following steps:

[0050] S1: Detecting a back electromotive force parameter U1 capable of characterizing the back electromotive force U of the permanent magnet motor and a rotation speed ω of the rotor 11 of the permanent magnet motor; and

[0051] S2: Based at least on the back electromotive force parameter U1 and the rotation speed ω, the temperature condition of the rotor 11 is indicated by means of a temperature condition monitoring mathematical model, wherein the temperature condition monitoring mathematical model is established based on permanent magnet motors of the same specification, and can at least characterize the relationship between the temperature T of the rotor 11 and the magnetic flux λ of the permanent magnets 112 arranged on the rotor 11. It can be understood by those skilled in the art that "the same specification" means having the same design, at least having the same key design parameters, and thus the established temperature condition monitoring mathematical model is also reliable for other permanent magnet motors of the same specification.

[0052] Those skilled in the art can understand that the detected back electromotive force parameter U1 can be the back electromotive force U itself, or other parameters related to the back electromotive force U. For example, it can be a parameter detected after amplifying (for example, amplifying by an amplifier) ​​the back electromotive force U. In any case, as long as the back electromotive force U can be determined deterministically by the back electromotive force parameter U1, it will suffice.

[0053] Here, those skilled in the art can understand that, in principle, the rotation speed ω of the rotor 11 can be expressed in terms of angular velocity or rpm (revolutions per minute). Using different expressions may only result in different corresponding coefficients.

[0054] Figure 3 A schematic diagram of a temperature condition monitoring mathematical model 2 according to an exemplary embodiment of the present invention is shown.

[0055] Preferably, if Figure 3 As shown, the input parameters of the temperature condition monitoring mathematical model 2 can be the back electromotive force parameter U1 and the speed ω, and the output parameter can be directly the temperature T of the rotor 11, or other parameters that can indicate the temperature condition of the rotor 11. For example, the corresponding alarm signal can be output only when the temperature T of the rotor 11 exceeds the predetermined threshold value T0, and the output parameter can be the alarm signal or both. The temperature T of the rotor 11 can be monitored in real time, and the subsequent speed change trend of the rotor 11 can be dynamically predicted based on the monitoring results, so as to take measures in advance to prevent the temperature T from rising uncontrollably above the predetermined threshold value.

[0056] There are many ways to establish the temperature condition monitoring mathematical model 2. One way is to fill the rotor 11 of the permanent magnet motor of the same specification with fluids of different temperatures (for example, 25°C, 65°C, 85°C), such as coolants, so that the rotor 11 is at a predetermined temperature, and at the same time measure the back electromotive force parameter U1 and the rotor speed ω at the corresponding temperature, and the temperature condition monitoring mathematical model can be established through multiple sets of data.

[0057] In addition, in principle, a temperature condition monitoring mathematical model for a permanent magnet motor corresponding to the specific specifications can also be established through simulation (using corresponding simulation software) according to the specific specifications of the permanent magnet motor. Even a permanent magnet motor prototype with the same specifications using a direct measurement method can be trial-produced to obtain a temperature condition monitoring mathematical model 2.

[0058] Those skilled in the art will appreciate that the present invention is not limited to this, and any method may be used as long as a corresponding temperature condition monitoring mathematical model 2 can be established for a permanent magnet motor of a predetermined specification.

[0059] The temperature condition monitoring mathematical model 2 may be a certain functional relationship, or a corresponding relationship presented in other forms, such as an artificial neural network.

[0060] The inventors of the present application have found that for currently commonly used permanent magnetic materials, the magnetic flux λ generally has a quadratic function relationship with the temperature T, which can be expressed by the following formula (4):

[0061] λ=aT 2 +bT+c (4)

[0062] Among them, a, b, and c are constants.

[0063] As mentioned above, the magnetic flux λ is related to the back electromotive force U and the rotational speed ω, that is, it can be obtained by λ=U / ω, which can be seen from the relationship (1). Therefore, in principle, the three parameters a, b, and c can be obtained by measuring three groups of parameters (T1, λ1), (T2, λ2), and (T3, λ3), thereby establishing the corresponding temperature condition monitoring mathematical model 2.

[0064] Those skilled in the art will understand that after determining the three parameters a, b, c, the temperature T of the rotor 11 can be calculated using formula (4) based on the magnetic flux λ, i.e., based on the measured back electromotive force U (or in a more general sense, the back electromotive force parameter U1) and the rotational speed ω.

[0065] According to mathematical knowledge, there may be two solutions for formula (4), but one of the two solutions is either a negative number or another impossible value, and therefore does not affect the determination of the temperature of the rotor 11 .

[0066] The magnetism of the currently commonly used permanent magnetic materials hardly decays or decays very limitedly over time, but for some permanent magnetic materials, there will still be a certain degree of decay. Obviously, if there is decay and this decay is completely ignored, it may affect the reliable determination of the temperature T of the rotor 11. Therefore, according to an exemplary embodiment of the present invention, the temperature condition monitoring mathematical model 2 also considers the time length of the permanent magnet 112 from the time point of establishing the temperature condition monitoring mathematical model 2, which can be called the model establishment time length t0.

[0067] In this case, the change in magnetic flux λ may be caused by both the temperature T of the rotor 11 and the model establishment time t0. Therefore, when determining the change in magnetic flux λ, not only the change in temperature T but also the model establishment time t0 should be considered. At this time, the part related to temperature T can be a part of magnetic flux λ, that is, component λ0.

[0068] For a specific type of permanent magnetic material, the decay of its magnetism over time is known, so the known decay characteristics can be introduced when constructing the temperature condition monitoring mathematical model 2.

[0069] If the magnetic decay of the permanent magnetic material over time is linear, in theory, it is not necessary to consider the time elapsed since the time point of initial magnetization of the permanent magnetic material, but only the model establishment time t0 elapsed since the time point of establishing the temperature condition monitoring mathematical model 2 is considered. If not, introducing the time elapsed since the time point of initial magnetization is obviously beneficial to improving the calculation accuracy of the temperature T of the rotor 11.

[0070] Of course, the magnetic change of the permanent magnet 112 may also be affected by other factors. Figure 3 The input parameters of the temperature condition monitoring mathematical model 2 shown may not be limited to U1 and ω, but may also include other determinable parameters.

[0071] Those skilled in the art will appreciate that if the temperature condition monitoring mathematical model 2 can be updated regularly, those parameters that change slowly over time may also be ignored.

[0072] Obviously, according to another aspect of the present invention, Figure 1 As shown, a control device 13 for a permanent magnet motor 1 is provided, wherein the control device 13 is configured to execute a method according to any of the above embodiments. The control device 13 may be a part of the permanent magnet motor.

[0073] In order to be able to execute the above method, the control device 13 includes a back electromotive force acquisition unit 131 for acquiring a back electromotive force parameter U1, a speed acquisition unit 132 for acquiring a speed ω of the rotor 11, and a processor 133 for indicating the temperature condition of the rotor 11 with the help of a temperature condition monitoring mathematical model 2 based at least on the back electromotive force parameter U1 and the speed ω, wherein the temperature condition monitoring mathematical model 2 is at least partially implemented as computer program instructions suitable for execution in the processor 133.

[0074] Those skilled in the art will appreciate that a permanent magnet synchronous motor generally includes an inverter. Through the inverter, direct current power (for example, direct current power provided by a lithium battery) can be converted into constant frequency and constant voltage or frequency and voltage regulated alternating current and / or other aspects of control can be achieved. Therefore, the control device 13 can directly utilize the inverter of the permanent magnet motor itself, or construct a control device including an inverter to achieve comprehensive control.

[0075] According to another aspect of the present invention, a computer program product, in particular a computer-readable storage medium, such as a memory, is provided, which includes or stores computer program instructions, and when the computer program instructions are executed by a processor, the method according to any of the above embodiments can be executed.

[0076] In particular, the computer program product can be presented as computer software that can be loaded into the control device 13 for execution. In this case, the computer software can be provided to the user together with the permanent magnet motor as needed, or provided to the user as a separate additional function. This provides a more flexible business operation model.

[0077] Moreover, the computer software can also be updated according to the specific situation to achieve a more accurate temperature condition monitoring mathematical model 2 or give the permanent magnet motor more other functions. This software method is convenient for upgrading operations.

[0078] The permanent magnet synchronous motor of the present invention can be applied to the anode circulation fan, electric air compressor (EAC), electric motor (e-motor) and the like of fuel cell electric vehicles. The temperature monitoring result can directly participate in the control of the whole vehicle. The monitoring of the rotor temperature can not only ensure the thermal safety of the motor, but also improve the peak performance of the motor. The actual measurement results show that the temperature of the rotor can be determined more accurately by the method of the present invention, and the actual error is within the range of ±5%.

[0079] Although specific embodiments of the present invention are described in detail herein, they are provided for the purpose of explanation only and should not be considered to limit the scope of the present invention. Various substitutions, changes and modifications may be conceived without departing from the spirit and scope of the present invention.

Claims

1. A method for monitoring the temperature condition of a rotor (11) of a permanent magnet motor, the method comprising at least the following steps: S1: detecting a back electromotive force parameter U1 capable of characterizing a back electromotive force U of the permanent magnet motor and a rotation speed ω of a rotor (11) of the permanent magnet motor; and S2: Based at least on the back electromotive force parameter U1 and the rotational speed ω, the temperature condition of the rotor (11) is indicated by means of a temperature condition monitoring mathematical model (2), wherein the temperature condition monitoring mathematical model (2) is pre-established based on a permanent magnet motor of the same specification and is at least capable of characterizing the relationship between the temperature T of the rotor (11) and the magnetic flux λ of the permanent magnet (112) arranged on the rotor (11).

2. The method according to claim 1, wherein: The magnetic flux λ includes a component λ0 that is related to the temperature T, and the component λ0 is characterized by the following quadratic function of the temperature T: λ0=aT 2 +bT+c Among them, a, b, and c are constants.

3. The method according to claim 1 or 2, wherein: The temperature condition monitoring mathematical model (2) also establishes a relationship between the magnetic flux λ and a first time period that has passed since the establishment time point of the temperature condition monitoring mathematical model (2) and / or a second time period that has passed since the magnetization formation time point of the permanent magnet (112).

4. The method according to any one of claims 1 to 3, wherein: The temperature condition monitoring mathematical model (2) is established through software simulation and / or experimental data.

5. The method according to any one of claims 1 to 4, wherein: The temperature condition is indicated by a temperature and / or an alarm signal.

6. A control device (13) for a permanent magnet electric machine, the control device (13) being configured to execute the method according to any one of claims 1-5.

7. A permanent magnet motor, comprising: A control device (13) according to claim 6.

8. The permanent magnet motor according to claim 7, wherein: The control device (13) comprises: a back electromotive force acquisition unit (131) for acquiring the back electromotive force parameter U1, a speed acquisition unit (132) for acquiring the speed ω, and a processor (133) for indicating the temperature condition of the rotor (11) at least based on the back electromotive force parameter U1 and the speed ω with the aid of the temperature condition monitoring mathematical model (2), wherein the temperature condition monitoring mathematical model (2) is at least partially implemented as computer program instructions suitable for execution in the processor (133).

9. The permanent magnet motor according to claim 7 or 8, wherein: The control device (13) comprises an inverter; and / or The permanent magnet motor is configured as a synchronous permanent magnet motor.

10. A computer program product, in particular a computer-readable storage medium, comprising or storing computer program instructions, which are capable of executing the method according to any one of claims 1 to 5 when the computer program instructions are executed by a processor.

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