Drive motor control device for electric vehicle

Abstract

To maximize the magnitude of a stator winding current of a PM motor 1 for driving an electric vehicle within a range in which irreversible demagnetization does not occur in a rotor magnet 5 when a magnitude of the stator winding current is controlled, thereby enabling larger output torque to be exerted.SOLUTION: A control device for a PM motor for driving an electric vehicle includes means for estimating a temperature of a rotor magnet of a motor, storage means for storing information capable of determining an upper limit value of a stator winding current that does not cause irreversible demagnetization in the rotor magnet at various temperatures of the rotor magnet of the motor, means for determining an upper limit value of the stator winding current at the rotor magnet temperature estimated from the information stored in the storage means, and current control means for controlling the stator winding current such that the stator winding current is limited to the upper limit value of the stator winding current.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a drive motor control device for an electric vehicle, and more particularly to a device that controls drive current so as to increase torque while minimizing demagnetization of the rotor magnet of the drive motor. [Background technology]

[0002] In a permanent magnet (PM) motor used as a drive motor for an electric vehicle, demagnetization occurs in the permanent magnet of the rotor (rotor magnet), which causes a decrease in the torque generated by the motor. Various configurations have been proposed in relation to the demagnetization of the rotor magnet. For example, Patent Document 1 proposes detecting the demagnetization of the permanent magnet that generates the excitation flux of a salient pole permanent magnet motor, and changing the phase of the torque current and the excitation current so as to obtain the maximum torque according to the demagnetization. Patent Document 2 proposes that in an embedded magnet motor, the magnet torque decreases when the magnet temperature rises, so that the phase of the current is advanced as the magnet temperature rises, and when the magnet temperature exceeds a threshold, the phase of the current is set to 0 degrees to prevent irreversible demagnetization. Patent Document 3 proposes estimating the magnetomotive force of the demagnetized magnet from the no-load induced voltage waveform of the rotating electric machine, and setting the current value and current phase for the torque command according to the estimated magnetomotive force to improve the accuracy of torque control. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 08-103093 [Patent Document 2] Patent Publication No. 2013-5503 [Patent Document 3] Patent Publication 2020-10501 Summary of the Invention [Problem to be solved by the invention]

[0004] The magnetic flux density of the rotor magnet of a PM motor changes with hysteresis relative to the magnetic field H, as shown by magnetization curve C in Figure 1(A), and when the magnetic field from the stator is not acting, i.e., when the stator winding current is not flowing, the magnetic flux density B of the rotor magnet will be the value at the intersection point (operating point P0) of the magnetization curve C and the permeance line Lp due to the demagnetizing field (H1) generated by the magnetic poles in the gap of the rotor magnet. Then, when the stator winding current flows and the magnitude of the reverse magnetic field from the stator (magnetic field in the opposite direction to the magnetization of the rotor magnet) increases, the magnetic flux density of the rotor magnet decreases from the operating point P0 along the magnetization curve C, i.e., it is demagnetized. In such demagnetization, the magnetic flux density B relative to the magnetic field H changes reversibly within the range (R) where it changes linearly from the operating point P0. If the magnitude of the reverse magnetic field of the stator is reduced, the magnetic flux density B of the rotor magnet returns to the operating point P0. However, if the magnitude of the reverse magnetic field increases beyond the bending point X of the magnetization curve C (▲), the demagnetization becomes irreversible, and even if the magnitude of the reverse magnetic field is reduced, the magnetic flux density B does not return to the magnitude of the operating point P0 (P -: The magnetic flux density increases from the reaching point in a direction substantially parallel to the linear change range R of the magnetization curve C.) Therefore, in controlling the stator winding current, in order to prevent irreversible demagnetization of the rotor magnet due to the reverse magnetic field from the stator as described above, the stator winding current is limited so that the magnitude of the reverse magnetic field from the stator does not become excessive. In this regard, the magnetization curve C of the rotor magnet changes depending on the temperature of the rotor magnet as shown in FIG. 1(B), and in particular, the higher the temperature of the rotor magnet, the smaller the magnitude of the magnetic field at which the bending point X occurs. Therefore, in the past, a large margin was set for safety so that the magnitude of the reverse magnetic field from the stator would not exceed the magnitude of the bending point X even if the temperature changed, i.e., the stator winding current was limited so that it would only reach a reverse magnetic field that was sufficiently smaller than the reverse magnetic field at which the magnetization curve reaches the bending point X. Or, even in configurations where the motor temperature is monitored, generally, there are few means for directly detecting the temperature of the rotor magnet (particularly in mass-produced motors, temperature detection means are rarely provided from the viewpoint of cost), and instead the values ​​of the stator thermistor and automatic transmission fluid (ATF) are referenced, and the rotor magnet is not monitored, so that the stator winding current is limited earlier when the motor temperature becomes high. For this reason, the output torque may be limited even if the reverse magnetic field in the rotor magnet has not yet reached the magnitude at which the bending point X occurs, and particularly in areas with relatively high temperatures and many uphill sections, there have been occasional complaints that the early torque limit makes it difficult for the vehicle to climb hills.

[0005] By the way, referring back to Fig. 1(B), the magnetic field H1 when the magnetic flux density of the rotor magnet is at the operating point and the magnetic field H2 that reaches the bending point X can be determined by specifying the temperature of the rotor magnet. The magnitude of the magnetic field H2 is the sum of the reverse magnetic field H1 due to the magnetic poles of the rotor magnet itself (the magnetic field magnitude H1 at the operating point Po) and the reverse magnetic field applied from the stator to the rotor magnet, so once the magnetic field magnitudes H1 and H2 at the operating point Po and bending point X are determined, the upper limit of the magnitude of the reverse magnetic field that can be applied from the stator to the rotor magnet without causing irreversible demagnetization is determined to be |H2-H1|. The stator magnetic field corresponds to the stator winding current and the motor output torque. Therefore, if the correspondence between the rotor magnet temperature and the magnitude of the difference between the magnetic field H1 at the operating point Po of the magnetization curve C of the rotor magnet and the magnetic field H2 at the bending point X, i.e., the upper limit of the magnitude of the reverse magnetic field that can be applied from the stator to the rotor magnet, or the correspondence with the corresponding upper limit of the winding current, can be experimentally investigated, and if the rotor magnet temperature can be specified by any method in controlling the magnitude of the stator winding current, the maximum value that can be generated in the stator winding current corresponding to the rotor magnet temperature can be determined within a range that does not cause irreversible demagnetization, and by allowing the stator winding current to increase within a range that does not exceed this maximum value, the output torque of the motor can be maximized within a range that does not cause irreversible demagnetization of the rotor magnet. This knowledge is utilized in the present invention.

[0006] Thus, a main object of the present invention is to maximize the magnitude of the stator winding current in a PM motor used to drive an electric vehicle within a range in which irreversible demagnetization does not occur in the rotor magnet, thereby enabling a greater output torque to be generated. [Means for solving the problem]

[0007] According to the present invention, the above problem is solved by a control device for a PM motor for driving an electric vehicle, a rotor magnet temperature estimation means for estimating a temperature of a rotor magnet of the motor; a rotor magnet characteristic storage means for storing information for determining an upper limit of a stator winding current that does not cause irreversible demagnetization in the rotor magnet at various temperatures of the rotor magnet of the motor; a stator winding current upper limit value determining means for determining an upper limit value of the stator winding current at the estimated rotor magnet temperature from the information stored in the rotor magnet characteristic storing means; a current control means for controlling the winding current of the stator so that the winding current is limited to an upper limit value of an allowable winding current of the stator; This is achieved by an apparatus comprising:

[0008] In the above configuration, the "electric vehicle" may be any type of vehicle using a PM motor for driving, such as an electric vehicle, a hybrid vehicle, a plug-in hybrid vehicle, or a fuel cell vehicle. The "rotor magnet temperature estimation means" may be a means for estimating the temperature of the rotor magnet by any method, and as described later, for example, the real-time temperature of the rotor magnet may be estimated based on the resistance value of the stator coil, or a machine learning algorithm of any type may be used to predict the required torque of the motor from the running conditions of the vehicle, and the future temperature of the rotor magnet may be estimated (predicted) based on the predicted required torque. As can be understood from the above explanation, the upper limit of the stator winding current that does not cause irreversible demagnetization in the rotor magnet is ultimately a function of the rotor magnet temperature, so the "information capable of determining the upper limit of the stator winding current that does not cause irreversible demagnetization in the rotor magnet at various temperatures of the rotor magnet of the motor" stored in the "rotor magnet characteristic storage means" is, in short, information that can be used to determine the upper limit of the stator winding current from the rotor magnet temperature, and may be collected experimentally in advance. Specifically, the information stored in the rotor magnet characteristic storage means may be, for example, the magnetic field at the operating point (the intersection of the magnetization curve (BH) and the permeance line) and the bending point (the point where the magnetic flux density begins to drop sharply when the magnitude of the magnetic field in the rotor magnet changes in the direction of demagnetization) in the magnetization curve of the rotor magnet at each rotor magnet temperature. In this case, in the "stator winding current upper limit value determination means", the magnitude of the difference between the magnetic field at the operating point and the magnetic field at the bending point in the rotor magnet temperature estimate value extracted from the rotor magnet characteristic storage means is calculated as the upper limit value of the magnitude of the stator's reverse magnetic field (reverse magnetic field upper limit value) that does not cause irreversible demagnetization in the rotor magnet, and the stator winding current corresponding to the reverse magnetic field upper limit value is calculated as the upper limit value of the stator winding current. Note that the correspondence between the stator's reverse magnetic field upper limit value and the corresponding allowable upper limit value of the winding current may be determined in advance experimentally or theoretically.Alternatively, the information stored in the rotor magnet characteristic storage means may be the upper limit of the reverse magnetic field of the stator at each rotor magnet temperature, in which case the "stator winding current upper limit value determination means" may calculate the stator winding current corresponding to the upper limit of the reverse magnetic field of the stator at the estimated rotor magnet temperature as the upper limit of the stator winding current. Furthermore, the information stored in the rotor magnet characteristic storage means may be the upper limit of the stator winding current that does not cause irreversible demagnetization in the rotor magnet at each rotor magnet temperature.

[0009] In the present invention, to put it simply, based on the knowledge that the difference in the magnitude of the magnetic fields at the operating point and the bending point of the rotor magnet changes depending on the temperature of the rotor magnet, the upper limit of the winding current that gives the upper limit of the reverse magnetic field that can be applied from the stator to the rotor magnet without causing irreversible demagnetization in the rotor magnet (stator reverse magnetic field upper limit) is determined, and the stator winding current is controlled so as not to exceed the upper limit of the current corresponding to the stator reverse magnetic field upper limit. With this configuration, the stator winding current can be increased according to the rotor magnet temperature to the limit at which irreversible demagnetization does not occur in the rotor magnet, and the motor torque can be maximized within the range where irreversible demagnetization does not occur in the rotor magnet.

[0010] In the above configuration, since the rotor magnet temperature depends on the temperature of the stator coil winding, and the coil resistance value changes depending on the coil winding temperature, the rotor magnet temperature may be estimated by experimentally investigating the correspondence between the coil resistance value and the rotor magnet temperature in advance, preparing a map that gives the rotor magnet temperature for the coil resistance value, and detecting the coil resistance value when the motor is in use, and selecting the rotor magnet temperature corresponding to the detected coil resistance value in the map as the estimated value of the rotor magnet temperature. With this configuration, the rotor magnet temperature value (estimated value) can be obtained without providing a temperature sensor on the rotor magnet, and an upper limit value of the stator winding current that does not cause irreversible demagnetization in the rotor magnet can be determined.

[0011] In another aspect of estimating the rotor magnet temperature, the future output torque or stator winding current may be predicted while the vehicle is running, and the rotor magnet temperature may be estimated based on the predicted future output torque or stator winding current. With this configuration, the future rotor magnet temperature is estimated while the vehicle is running, so that it is possible to prevent the stator winding current from exceeding the upper limit of the winding current for the actual stator reverse magnetic field upper limit value due to a time lag in estimating the rotor magnet temperature. In predicting the future output torque or stator winding current while the vehicle is traveling, a discrimination calculator may be prepared that uses training data in which the vehicle's traveling route (incline angle, curvature, and other road information), the presence or absence of a preceding vehicle, the lane in which the vehicle is traveling, the number of passengers, and other traveling conditions as input data, and outputs the output torque or stator winding current in each traveling condition according to a machine learning algorithm when the input data is given, and the output torque or stator winding current in that condition may be predicted using the discrimination calculator while the vehicle is traveling in accordance with the future traveling conditions from moment to moment. Then, a predicted estimated value of the rotor magnet temperature for the predicted output torque or stator winding current may be determined using a map prepared in advance that indicates the correspondence between the output torque or stator winding current and the rotor magnet temperature. Effect of the Invention

[0012] Thus, according to the device of the present invention, the stator reverse magnetic field is allowed to increase to a maximum value that does not cause irreversible demagnetization of the rotor magnet in accordance with the rotor magnet temperature, taking into account the temperature characteristics of the magnetization curve of the rotor magnet, thereby enabling the motor to generate a larger torque. In particular, in the case where the rotor magnet temperature is predicted according to future running conditions from moment to moment using an identification calculator prepared according to a machine learning algorithm, the upper limit value of the winding current corresponding to the stator reverse magnetic field upper limit value can be advantageously controlled in a feedforward manner.

[0013] Other objects and advantages of the present invention will become apparent from the following description of preferred embodiments of the invention. [Brief description of the drawings]

[0014] [Figure 1] Figure 1(A) shows an example of the magnetization curve (only the second quadrant at 100°C) of a rotor magnet of a PM motor for driving an electric vehicle to which this embodiment is applied. In the figure, the horizontal axis and vertical axis respectively represent the magnetic field H and magnetic flux density B inside the magnet. Figure 1(B) shows examples of the magnetization curves (only the second quadrant) of the rotor magnet at various temperatures. [Diagram 2] FIG. 2 is a cross-sectional view (1 / 4 portion) of a PM motor for driving an electric vehicle to which this embodiment is applied. [Diagram 3] FIG. 3 is a block diagram showing the configuration of a control device for a PM motor for driving an electric vehicle to which this embodiment is applied. [Figure 4] Fig. 4(A) is a block diagram showing the configuration of a rotor magnet temperature estimating unit in an embodiment in which the temperature of the rotor magnet is estimated from the winding resistance of the stator, and Fig. 4(B) is a block diagram showing the configuration of a rotor magnet temperature estimating unit in an embodiment in which the future temperature of the rotor magnet is predicted from the running conditions of the vehicle. [Explanation of symbols]

[0015] 1...PM motor, 2...stator, 2a...stator salient pole, 3...coil (winding), 4...rotor, 5...rotor magnet (permanent magnet) BEST MODE FOR CARRYING OUT THEINVENTION

[0016] The present invention will now be described in detail with reference to some preferred embodiments thereof with reference to the accompanying drawings, in which like reference numerals indicate like parts.

[0017] Motor Configuration The drive motor control device according to this embodiment is applied to the stator winding current of a PM motor 1 for driving an electric vehicle, which is illustrated in Fig. 2. In the PM motor 1, a plurality of salient poles 2a are provided along the inner circumferential direction of a hollow cylindrical stator (core) 2 in a normal manner, coils 3 are wound around the salient poles 2a, a cylindrical rotor 3 is rotatably mounted in the inner cavity of the stator 2, and a plurality of permanent magnets 3 may be embedded or attached along the circumferential direction on the surface of the rotor 3, facing the inner ends of the salient poles 2a. As a result, a magnetic circuit φ is formed that circulates from the rotor magnet 3 through the two stator salient poles 2a to the rotor magnet 3, as illustrated.

[0018] Range of stator winding current that does not cause irreversible demagnetization of the rotor magnet As already mentioned, when no current flows through the stator coil 3 of the PM motor 1, the magnetic flux density in the rotor magnet 5 is at the operating point Po, which is the intersection point of the magnetization curve C and the permeance line Lp, as shown in Figure 1(A), due to the demagnetizing field created by its own magnetic poles, and the magnetic field in the magnet is H1. When current flows through the coil 3 of the stator 2 to rotate the rotor 4, a reverse magnetic field is applied from the stator salient pole 2a, whose magnetic field is in the opposite direction to the magnetization direction of the rotor magnet 5, causing "demagnetization" in which the magnetic flux density in the rotor magnet 5 decreases from the operating point Po along the magnetization curve C. At that time, if the change in the magnetic field H in the rotor magnet is within the range R before the bending point X of the magnetization curve C (the point where the magnetic flux density begins to decrease rapidly), when the magnitude of the reverse magnetic field created by the stator becomes smaller, the magnetic flux density in the rotor magnet 5 returns to the operating point Po along the magnetization curve C. However, when the magnetic field H in the rotor magnet reaches a point (▲) that deviates from the range R to the negative side, when the magnitude of the reverse magnetic field by the stator becomes small, the magnetic flux density in the rotor magnet 5 increases from the reached point ▲ in parallel to the magnetization curve C, and reaches a point P lower than the operating point Po. -The magnetization of the rotor magnet 5 is only restored up to the bending point X, and the demagnetization becomes irreversible. When the irreversible demagnetization of the rotor magnet 5 occurs, the generated torque decreases thereafter. In order to avoid this, the stator winding current needs to be controlled so that the magnetic field in the rotor magnet 5 does not exceed the bending point X on the negative side. In this regard, as shown in FIG. 1(B), the magnetization curve C of the rotor magnet generally shifts to the positive side of the magnetic field as the rotor magnet temperature increases, and the magnetic fields H1 and H2 at the operating point Po and bending point X change in a direction in which their magnitudes become smaller (|H2-H1| also becomes smaller). Therefore, in the past, the stator winding current was generally limited with a sufficient margin so that irreversible demagnetization does not occur even if the rotor magnet temperature changes, or limited when the motor temperature rises. However, in that case, the torque may be limited even if there is a margin until the magnetic field in the rotor magnet 5 reaches the bending point X.

[0019] Therefore, in the device of this embodiment, information is stored that can determine an upper limit of the stator winding current that does not cause irreversible demagnetization at various rotor magnet temperatures that have been experimentally investigated in advance, and when the motor is used, the rotor magnet temperature is estimated or predicted, and the stored information that can determine an upper limit of the stator winding current at each rotor magnet temperature is referenced, and the stator winding current is controlled so that it does not exceed the stator winding current upper limit that corresponds to the estimated rotor magnet temperature, thereby enabling the motor to generate maximum torque within a range that does not cause irreversible demagnetization.

[0020] The magnetic field inside the rotor magnet is the sum of the magnetic field (H1) due to the magnetic poles of the rotor magnet itself and the magnetic field due to the stator, so the upper limit of the magnitude of the reverse magnetic field due to the stator that does not cause irreversible demagnetization is given by |H2-H1|. Also, the stator magnetic field Hs is Hs·l=N·I …(1) Since the above relationship holds (l is the magnetic path distance (air gap x 2 + magnet thickness), and N is the number of coil turns), the upper limit Imax of the stator winding current that does not cause irreversible demagnetization is Imax = (|H2-H1|)·l / N … (2) Thus, the control allows the stator winding current to increase up to an upper limit Imax that is determined based on the rotor magnet temperature.

[0021] Configuration for controlling stator winding current 3, in the control device for the stator winding current according to the present embodiment, first, a torque requirement determination unit determines a torque requirement for the motor in response to the depression amount of the accelerator pedal of the vehicle, and a stator winding current determination unit determines a winding current requirement Ir corresponding to the torque requirement. On the other hand, when the rotor magnet temperature is estimated by the rotor magnet temperature estimation in any of the modes described later, the estimated value is sent to the rotor magnet characteristic storage unit. The rotor magnet characteristic storage unit stores information for determining an upper limit value of the stator winding current (which does not cause irreversible demagnetization) for each rotor magnet temperature experimentally examined in advance, such as the magnetic fields at the operating point and the bending point, and the upper limit value of the reverse magnetic field that can be generated in the stator, which is the magnitude of the difference between them, or the winding current corresponding thereto, and information corresponding to the estimated value of the rotor magnet temperature is extracted there, and the stator winding current upper limit value determination unit determines the upper limit value Imax of the stator winding current using the extracted value (for example, according to the above formula (2)). Then, the stator winding current limiting section actually issues a command to the stator winding. Ia = min(Imax, Ir) ... (3) and the inverter control is executed to drive the motor in a normal manner so that the maximum value of the stator winding current is Ia. With this configuration, the stator winding current is allowed to increase to its maximum within the range where irreversible demagnetization does not occur in the rotor magnet, so that a larger torque can be generated.

[0022] Rotor magnet temperature estimation (1) Estimation of rotor magnet temperature using stator coil resistance The rotor magnet temperature is determined by the surface area of ​​the stator-rotor air gap from the coil, the thermal conductivity of the silicon steel plate, the air, and the ATF oil, etc. On the other hand, the electric resistance value of the coil changes in response to the coil temperature. That is, the rotor magnet temperature is a function of the electric resistance value of the coil. Therefore, in one aspect of the present embodiment, the relationship between the rotor magnet temperature and the coil electric resistance value is experimentally investigated in advance, and during use of the motor, as shown in FIG. 4(A), the electric resistance value of the coil is detected (determined from the voltage and current applied to the coil), and the rotor magnet temperature corresponding to the detected electric resistance value may be selected as an estimated value. In this case, the stator winding current is controlled in real time according to the rotor magnet temperature within a range in which irreversible demagnetization does not occur in the rotor magnet.

[0023] (2) Estimation of rotor magnet temperature using future driving conditions In another aspect of this embodiment, the rotor magnet temperature may be predicted based on the predicted torque after predicting the torque to be generated in the future based on the future driving conditions of the vehicle using a machine learning algorithm. Specifically, a discrimination calculator is prepared using input data of driving conditions such as map information such as the inclination angle and curvature of the road, detection information from a sensor that recognizes a preceding vehicle ahead of the vehicle, information on the lane the vehicle is traveling in (whether the lane is an overtaking lane or not), and the number of occupants in the vehicle, and using the torque generated by the motor after a predetermined time period that may be set arbitrarily as output data of the driving conditions. Such a discrimination calculator can be prepared using an arbitrary machine learning algorithm (e.g., a neural network, a support vector machine, etc.). When the torque generated by the motor is given, the current that will flow through the stator winding is determined, which determines the Joule heat to be generated, which is reflected in the temperature of the stator. In the end, the rotor magnet temperature is a function of the torque generated by the motor. Thus, while the motor is in use, as shown in Fig. 4(B), the torque predicted to be generated by the motor in the future may be calculated from the vehicle's running conditions using an identification calculator, the stator winding current may be predicted from the predicted torque, and the rotor magnet temperature may be predicted and estimated from the predicted value. With this configuration, when the vehicle's running conditions from the present onward are predicted, for example, when the accelerator pedal is predicted to be depressed and torque increases, the rotor magnet temperature from the present onward is predicted and the upper limit of the stator winding current is determined in a feedforward manner in response to the estimated rotor magnet temperature, and the stator winding current is controlled within a range in which irreversible demagnetization does not occur in the rotor magnet. In other words, since the rotor magnet temperature can be quickly estimated, the upper limit of the stator winding current can be increased or decreased without delay in response to the rotor conditions, and a larger torque can be generated within a range in which irreversible demagnetization does not occur.

[0024] The above description has been given in relation to the embodiment of the present invention, but it will be apparent to those skilled in the art that many modifications and changes can be easily made thereto, and that the present invention is not limited to the embodiment exemplified above, but can be applied to various devices without departing from the concept of the present invention.

Claims

[Claim 1] A control device for a PM motor for driving an electric vehicle, a rotor magnet temperature estimation means for estimating a temperature of a rotor magnet of the motor; a rotor magnet characteristic storage means for storing information for determining an upper limit of a stator winding current that does not cause irreversible demagnetization in the rotor magnet at various temperatures of the rotor magnet of the motor; a stator winding current upper limit value determining means for determining an upper limit value of the stator winding current at the estimated rotor magnet temperature from the information stored in the rotor magnet characteristic storing means; a current control means for controlling the winding current of the stator so that the winding current is limited to an upper limit value of the stator winding current; An apparatus comprising:

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