Motor system

Abstract

This invention provides an improved motor system that can maintain the rotational speed of the electric motor even in low State of Charge (SOC) regions. [Solution] The motor system comprises a permanent magnet type motor 1, an inverter 10 that supplies variable frequency power to the permanent magnet type motor 1, and a vector control unit 11 that converts the three-phase current flowing from the inverter 10 to the permanent magnet type motor 1 into d-axis current and q-axis current on a dq rotating coordinate system, generates voltage command values ​​to bring the d-axis current and q-axis current closer to their respective target values, and sends the voltage command values ​​to the inverter 10. When the inductance in the d-axis direction of the coil of the permanent magnet type motor 1 is represented by Ld, the d-axis current by Id, the magnetic flux in the d-axis direction of the permanent magnet by φ, and the angular velocity of the motor rotor by ω, the permanent magnet type motor 1 is configured such that the relationship ωLdId[V]>ω0.12φ[V] holds true.

Description

Technical Field

[0005] , ,

[0001] The present invention relates to a motor system that drives a permanent magnet type motor with a battery such as a lithium ion battery, and particularly relates to a technique for reducing the power consumption of the battery.

Background Art

[0002] Electric vehicles and hybrid vehicles supply electric power from a battery such as a lithium ion battery to an electric motor to generate driving force for the vehicle. Since the battery has portability, it is used not only for automobiles but also for various transportation machines such as airplanes, trains, and ships.

[0003] In order to ensure the safety of the battery, a battery management system is applied. The battery management system is a system that monitors the state of a battery in which a plurality of cells are connected in series and / or in parallel. The main function of the battery management system is to equalize the discharge states of each cell while acquiring information on the SOC (State of Charge) and SOH (State of Health) of the battery.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The practical operating range for lithium-ion batteries is 15-95% of the State of Charge (SOC), as shown in Figure 23. However, even when the battery's SOC is within the practical operating range, the motor's rotational speed decreases as the SOC decreases. Vector control is used to maintain the motor's rotational speed, but maintaining the motor's speed is difficult in the low SOC range.

[0006] Therefore, the present invention provides an improved motor system that can maintain the rotational speed of the electric motor even in a low State of Charge (SOC) region. [Means for solving the problem]

[0007] In one embodiment, a motor system is provided comprising a motor stator having a coil made of windings wrapped around teeth, a permanent magnet type motor having a motor rotor having a permanent magnet, an inverter supplying variable frequency power to the permanent magnet type motor, a plurality of current detectors for detecting the three-phase current flowing from the inverter to the permanent magnet type motor, and a vector control unit that converts the three-phase current into d-axis current and q-axis current on a dq rotating coordinate system, generates voltage command values ​​to bring the d-axis current and q-axis current closer to their respective target values, and sends the voltage command values ​​to the inverter, wherein the permanent magnet type motor is configured such that the relationship ωLdId[V]>ω0.12φ[V] holds, when the inductance of the coil in the d-axis direction is represented by Ld, the d-axis current by Id, the magnetic flux of the permanent magnet in the d-axis direction by φ, and the angular velocity of the motor rotor by ω.

[0008] In one embodiment, the motor system further includes a battery as a DC power source that supplies DC power to the inverter. In one embodiment, if the angle from the d-axis of the composite vector, which is the sum of the d-axis current vector and the q-axis current vector, is defined as the vector angle, the vector control unit is configured to perform field weakening control within a range where the vector angle is less than 90 and greater than or equal to 70.

[0009] In one embodiment, the permanent magnet has a plurality of easy magnetization axes tilted with respect to the d axis and the q axis, the plurality of easy magnetization axes include a first easy magnetization axis close to the d axis and a second easy magnetization axis close to the q axis, the angle of the second easy magnetization axis with respect to the q axis is greater than the angle of the first easy magnetization axis with respect to the d axis. In one embodiment, the teeth are composed of a plurality of stacked amorphous plates. In one embodiment, the permanent magnet has a coercivity of 450 kA / m or more, a residual magnetic flux density of 0.7 T or more, and an energy product of 13 MGOe or more. In one embodiment, the winding has a bundle of multiple strands and an outer sheath covering the bundle of multiple strands, each of the multiple strands has a conductor and an inner sheath covering the conductor, and each of the multiple strands has a cross-sectional area corresponding to a circle with a diameter of 0.71 mm or less. In one embodiment, the thickness of the inner coating is 5 μm or less. In one embodiment, the thickness of each of the plurality of amorphous plates is less than 0.3 mm. In one embodiment, the motor stator has an annular core located outside the teeth, and the annular core is made of electromagnetic steel sheet. [Effects of the Invention]

[0010] When the d-axis inductance Ld of the coil, the d-axis current Id flowing through the coil, and the magnetic flux φ in the d-axis direction of the permanent magnet satisfy the above relationship, the inverter can rotate the permanent magnet motor at the target speed even if the voltage applied from the battery to the inverter decreases. In one example, the motor's rotational speed can be maintained even in the range where the State of Charge (SOC) is around 10%. Furthermore, since the power required for the permanent magnet motor to rotate at the target speed is reduced, the battery's power consumption can be lowered. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing one embodiment of a motor system. [Figure 2]It is a block diagram showing an embodiment of a vector control unit. [Figure 3] It is a cross-sectional view showing an embodiment of a permanent magnet type motor. [Figure 4] It is a schematic diagram showing the d-axis current Id and q-axis current Iq on the dq rotating coordinate system converted from three-phase currents. [Figure 5] It is a graph of a sin curve showing the relationship between the torque of a permanent magnet type motor and the vector angle. [Figure 6] It is a schematic diagram showing another embodiment of a motor system. [Figure 7] It is a block diagram showing another embodiment of a vector control unit. [Figure 8] It is a cross-sectional view showing another embodiment of a permanent magnet type motor. [Figure 9] It is a cross-sectional view showing a part of a motor rotor as seen from the axial direction of the rotating shaft. [Figure 10] It is a diagram showing an embodiment of the easy magnetization axis of a permanent magnet. [Figure 11] It is a diagram showing another embodiment of the easy magnetization axis of a permanent magnet. [Figure 12] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 13] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 14] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 15] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 16] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 17] It is a diagram showing yet another embodiment of the easy magnetization axis of a permanent magnet. [Figure 18] It is a cross-sectional view showing an embodiment of a motor stator. [Figure 19] It is a cross-sectional view showing an embodiment of a winding. [Figure 20] It is a cross-sectional view showing an embodiment of a strand. [Figure 21] This graph shows the relationship between the heat loss caused by electrical resistance when a direct current flows through a wire and the diameter of the wire, and the relationship between the heat loss caused by eddy currents when an alternating current flows through a wire and the diameter of the wire. [Figure 22] This graph shows the relationship between the diameter of the wire strand and the loss of that strand. [Figure 23] This graph shows the relationship between the State of Charge (SOC) and Open Circuit Voltage (OCV) of a lithium-ion battery. [Modes for carrying out the invention]

[0012] Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a schematic diagram showing one embodiment of a motor system. As shown in Figure 1, the motor system includes a permanent magnet type electric motor 1, an inverter 10 that supplies variable frequency power to the permanent magnet type electric motor 1, a vector control unit 11 that determines the voltage command value to the inverter 10, and a plurality of current detectors (ammeters or current sensors) 12 that detect the current flowing from the inverter 10 to the permanent magnet type electric motor 1. The permanent magnet type electric motor 1 includes a motor rotor having permanent magnets.

[0013] The inverter 10 basically consists of an inverter circuit 10A as a power conversion unit and a gate driver 10B that drives the inverter circuit 10A. In the inverter circuit 10A, three sets of upper and lower arms are connected in parallel between the positive line P and the negative line N, which are connected to the battery 5 as a DC power source. Switching elements (IGBTs) S1 to S6 and diodes D1 to D6 are incorporated into the upper and lower arms of each phase. Symbol C1 is a capacitor. The inverter circuit 10A is composed of these switching elements S1 to S6, diodes D1 to D6, and capacitor C1. The gate driver 10B drives the switching elements S1 to S6 of the inverter circuit 10A so that a voltage is generated according to the voltage command value sent from the vector control unit 11.

[0014] The current detector 12 measures the three-phase currents Iu, Iv, and Iw supplied from the inverter 10 to the permanent magnet motor 1. These measured values ​​are input to the vector control unit 11. The vector control unit 11 generates three-phase voltage command values ​​Vu*, Vv*, and Vw* based on the three-phase currents Iu, Iv, and Iw and the speed command value input from an external source. Furthermore, the vector control unit 11 generates PWM signals corresponding to these three-phase voltage command values ​​Vu*, Vv*, and Vw*, and sends these PWM signals to the gate driver 10B. The gate driver 10B generates a gate drive PWM signal based on the PWM signals corresponding to the three-phase voltage command values ​​Vu*, Vv*, and Vw*. The six switching elements S1 to S6 are operated (on and off) based on the gate drive PWM signals. In this way, the inverter 10 generates voltages based on the three-phase voltage command values ​​from the vector control unit 11 and applies them to the permanent magnet motor 1.

[0015] Figure 2 is a block diagram showing one embodiment of the vector control unit 11. The vector control unit 11 in this embodiment is a sensorless vector control unit that estimates the position of the motor rotor of the permanent magnet motor 1 from the feedbacked motor current without using a position sensor. The basic operation of the vector control unit 11 is as follows: The three-phase current flowing from the inverter 10 to the permanent magnet motor 1 is detected by the current detector 12. This detected three-phase current is converted into two-phase currents Id and Iq on the dq rotation coordinate system by the 3 / 2 phase conversion unit 17 and the stationary / rotating coordinate conversion unit 18, and then input to the magnetization voltage control unit 22 and the torque voltage control unit 21. The magnetization voltage control unit 22 determines the magnetization voltage command value Vd* by PI calculation to minimize the difference between the current magnetization current Id and the magnetization current command value (target magnetization current) Id*. The torque voltage control unit 21 determines the torque voltage command value Vq* by PI calculation to minimize the difference between the current torque current Iq and the torque current command value Iq*.

[0016] The target torque current determination unit 24 determines a torque current command value Iq* by PI calculation to minimize the difference between the externally input speed command value ω* and the current angular velocity ω. The current angular velocity ω is determined by the axis error estimator 29 and the differentiator 32 based on the voltage command values ​​Vd*, Vq* and the feedback currents, which are two-phase currents Id, Iq. The axis error estimator 29 calculates the rotation angle θ of the motor rotor of the permanent magnet motor 1 from the two-phase currents Id, Iq, and the differentiator 32 calculates the angular velocity ω of the motor rotor from the rotation angle θ. The magnetization current command value Id* is the target magnetization current calculated using the motor model. The voltage command values ​​Vd*, Vq* are converted to three-phase voltage command values ​​on a fixed coordinate system via the rotation / stationary coordinate transformation unit 35 and the two- / three-phase transformation unit 36, and then sent to the inverter 10.

[0017] The configuration of the vector control unit 11 that performs vector control is not limited to the embodiment shown in Figure 2, and known vector control configurations can be applied, as long as it is configured to convert the three-phase current flowing from the inverter to the permanent magnet motor into d-axis current and q-axis current, and to generate voltage command values ​​to bring the d-axis current and q-axis current closer to their respective target values. For example, the vector control unit 11 may have the configuration disclosed in Japanese Patent Application Publication No. 2012-50285. In other embodiments, the vector control unit 11 may be a sensorless vector control unit that estimates the position of the motor rotor of the permanent magnet motor 1 from the induced voltage of the permanent magnet motor 1 detected by a voltage sensor.

[0018] Figure 3 is a cross-sectional view showing one embodiment of a permanent magnet electric motor 1. The permanent magnet electric motor 1 comprises a rotating shaft 42, a motor rotor 46 having a plurality of permanent magnets 45, and a motor stator 47 for generating a rotating magnetic field. The plurality of permanent magnets 45 are fixed to the rotor core 49 of the motor rotor 46. The motor rotor 46, including the plurality of permanent magnets 45 and the rotor core 49, is fixed to the rotating shaft 42 and rotates integrally with the rotating shaft 42.

[0019] The permanent magnet type electric motor 1 further comprises bearings 51 and 52 that rotatably support the rotating shaft 42, and a motor housing 55 to which the bearings 51 and 52 are fixed. The bearings 51 and 52 are positioned on both sides of the motor rotor 46 in the axial direction of the rotating shaft 42. The motor rotor 46, motor stator 47, and bearings 51 and 52 are housed within the motor housing 55. The bearings 51 and 52 are ball bearings, and conductive oil is used to lubricate the balls of the bearings 51 and 52. In one embodiment, the balls of the bearings 51 and 52 are made of ceramic. The use of conductive oil or ceramic balls prevents galvanic corrosion.

[0020] The motor stator 47 is positioned adjacent to the motor rotor 46. The motor stator 47 comprises multiple teeth (or pole teeth) 60 and windings 63 wound around these teeth 60. The windings 63, when wound around the multiple teeth 60, constitute multiple coils 65.

[0021] The permanent magnet 45 is covered by an outer cylinder 70, which prevents the permanent magnet 45 from flying out due to centrifugal force when the motor rotor 46 is rotating at high speed. To further secure the outer cylinder 70 and prevent the permanent magnet 45 from scattering in the axial direction, end plates 71 are positioned on both sides of the permanent magnet 45 in the axial direction of the rotating shaft 42. The permanent magnet 45 is positioned between the end plates 71 of the motor rotor 46. The outer cylinder 70 is fixed to the outer circumferential surface of the end plates 71.

[0022] Figure 4 is a schematic diagram showing the d-axis current Id and q-axis current Iq, which are two-phase currents on a dq rotating coordinate system converted from three-phase (u-phase, v-phase, w-phase) currents by the vector control unit 11. The d-axis extends in the direction of the magnetic flux of the permanent magnets 45 of the motor rotor 46, and the q-axis is perpendicular to the d-axis. The three-phase winding 64 is converted into a two-phase winding by the vector control unit 11 and rotates in synchronization with the motor rotor 46. In Figure 4, R represents the resistance of the winding 63 forming the coil 65, Ld represents the inductance of the coil 65 in the d-axis direction, Lq represents the inductance of the coil 65 in the q-axis direction, and ω represents the angular velocity of the motor rotor 46. The number of permanent magnets 45 of the motor rotor 46 shown in Figure 4 is an example and is not limited to the embodiment shown in Figure 4.

[0023] The permanent magnet type electric motor 1 is configured such that the following relationship holds true. ωLdId[V]>ω0.12φ[V] (1) Here, φ represents the magnetic flux of the permanent magnet 45 in the d-axis direction.

[0024] When the inductance Ld in the d-axis direction of coil 65, the d-axis current Id flowing through the coil, and the magnetic flux φ in the d-axis direction of permanent magnet 45 satisfy the above relationship, the inverter 10 can rotate the permanent magnet motor 1 at the target speed even if the voltage applied from battery 5 to inverter 10 decreases. In one example, the rotational speed of the permanent magnet motor 1 can be maintained even in the region where the SOC (State of Charge) is around 10%. Furthermore, since the power required for the permanent magnet motor 1 to rotate at the target speed is reduced, the power consumption of battery 5 can be lowered.

[0025] The d-axis inductance Ld is proportional to the square of the number of turns (windings) of the coil 65, so the d-axis inductance Ld can be adjusted by changing the number of turns of the coil 65. The magnetic flux φ in the d-axis direction of the permanent magnet 45 can be adjusted by changing the magnetic flux density, surface area, mass, etc. of the permanent magnet 45 used. Therefore, by adjusting at least one of the number of turns of the coil 65 and the specifications of the permanent magnet 45 used, the above relationship (1) can be made to hold.

[0026] Figure 5 is a sine curve graph showing the relationship between the torque of the permanent magnet motor 1 and the vector angle. The torque of the permanent magnet motor 1 depends on the q-axis current Iq. If the vector angle θi is the angle from the d-axis of the composite vector I, which is the sum of the d-axis current vector and the q-axis current vector, then when the vector angle θi is 90 degrees, the q-axis current Iq is I × sin90 = I, and the torque is at its maximum. The vector control unit 11 in this embodiment is configured to perform field weakening control when the vector angle θi is less than 90 and within the range of 70 or more.

[0027] In this embodiment, the vector angle θi in field weakening control is, for example, 75 degrees. In this case, the d-axis current Id and the torque current q-axis current Iq in the above relation (1) are expressed as follows. Id = Icos75 = I × 0.2588 Iq = Isin75 = I × 0.9659 From the above, it can be seen that if field weakening control is performed with a vector angle θi of 75 degrees, the torque reduction rate is only about 3.4%. Therefore, in this embodiment, the rotational speed of the permanent magnet type motor 1 can be maintained with only a slight torque reduction.

[0028] Figure 6 is a schematic diagram showing another embodiment of the motor system. The configuration of this embodiment, which is not specifically described, is the same as that of the embodiment described with reference to Figures 1 to 5, so redundant explanations are omitted. As shown in Figure 6, the motor system of this embodiment is equipped with a position sensor 66 that detects the position (angular position) of the motor rotor 46 (see Figure 3) of the permanent magnet type electric motor 1. An example of the position sensor 66 is a magnetic sensor such as a Hall sensor. The position sensor 66 is attached to the permanent magnet type electric motor 1. The position sensor 66 is electrically connected to the vector control unit 11, and a signal indicating the angular position of the motor rotor 46 is sent to the vector control unit 11.

[0029] Figure 7 is a block diagram showing one embodiment of the vector control unit 11 shown in Figure 6. The configuration of this embodiment, which is not specifically described, is the same as that of the embodiment described with reference to Figure 2, so the redundant explanation is omitted. The vector control unit 11 of this embodiment is equipped with a rotation angle calculator 67 instead of an axis error estimator 29. The rotation angle calculator 67 calculates the rotation angle θ of the motor rotor 46 of the permanent magnet type electric motor 1 from a signal indicating the angular position of the motor rotor 46 sent from the position sensor 66, and the differentiator 32 calculates the angular velocity ω of the motor rotor 46 from the rotation angle θ.

[0030] The vector control unit 11 in the embodiment shown in Figure 7 performs vector control based on the angular position of the motor rotor detected by the position sensor 66. However, the configuration of vector control using the position sensor 66 is not limited to the embodiment shown in Figure 7, and known vector control configurations can be applied.

[0031] Next, other embodiments of the permanent magnet type motor 1 that satisfy the above relation (1) will be described with reference to Figure 8. The configuration of this embodiment, which is not specifically described, is the same as that of the embodiment described with reference to Figure 3, so the redundant explanation will be omitted. The permanent magnet type motor 1 of this embodiment is a multi-pole electric motor with 4 or more poles.

[0032] The motor stator 47 is positioned adjacent to the motor rotor 46. The motor stator 47 comprises a plurality of teeth (or pole teeth) 60, windings 63 wound around these teeth 60, and an annular core 64 positioned outside the plurality of teeth 60. The windings 63 are wound around the plurality of teeth 60 to form a plurality of coils 65. In the embodiment shown in Figure 8, the motor stator 47 is positioned radially outward from the motor rotor 46 and surrounds the motor rotor 46. There is a radial gap between the motor rotor 46 and the motor stator 47. Such an electric motor is a radial gap electric motor.

[0033] Figure 9 is a cross-sectional view showing a portion of the motor rotor 46 as seen from the axial direction of the rotating shaft 42. Multiple permanent magnets 45 are arranged along the circumferential direction of the motor rotor 46 such that the north poles and south poles are arranged alternately. In one embodiment, the multiple permanent magnets 45 are arranged without gaps along the circumferential direction of the motor rotor 46. Gaps of about 1 mm for manufacturing purposes, or the application of adhesive, are included in the category of "without gaps."

[0034] Each permanent magnet 45 has a coercivity of 450 kA / m or more, a residual magnetic flux density of 0.7 T or more (preferably 0.9 T or more), and an energy product of 13 MGOe or more (B × H, where B is the magnetic flux density and H is the magnetic field). In one embodiment, the permanent magnet 45 is a rare earth magnet containing samarium (Sm), neodymium (Nd), praseodymium (Pr), cerium (Ce), didymium, etc. For example, the permanent magnet 45 is produced by a sintering method using samarium cobalt. In another embodiment, the permanent magnet 45 is an iron nitride (FeN) magnet having an L10 structure.

[0035] Each permanent magnet 45 has a different crystal orientation in the d-axis and q-axis. More specifically, the permanent magnet 45 has multiple easy magnetization axes M1, M2 tilted at different angles with respect to the radial direction of the motor rotor 46. Here, the d-axis is a virtual radial axis passing through the pole center of each permanent magnet 45, and the q-axis is a virtual radial axis passing through the inflection point of the pole. The q-axis extends along both ends of each permanent magnet 45.

[0036] As shown in Figure 9, each permanent magnet 45 has multiple easy magnetization axes M1, M2 tilted with respect to the d-axis and q-axis. The multiple easy magnetization axes M1, M2 include a first easy magnetization axis M1 that is close to the d-axis and a second easy magnetization axis M2 that is close to the q-axis. Here, "close" does not mean absolutely close, but relatively close. That is, the first easy magnetization axis M1 is closer to the d-axis than the second easy magnetization axis M2, and the second easy magnetization axis M2 is closer to the q-axis than the first easy magnetization axis M1. The first easy magnetization axis M1 and the second easy magnetization axis M2 are tilted toward the d-axis.

[0037] The angle of the second easy magnetization axis M2 with respect to the q-axis is greater than the angle of the first easy magnetization axis M1 with respect to the d-axis. In addition, the second easy magnetization axis M2 is more inclined with respect to the d-axis than the first easy magnetization axis M1. That is, the angle of the second easy magnetization axis M2 with respect to the d-axis is greater than the angle of the first easy magnetization axis M1 with respect to the d-axis. The first easy magnetization axis M1 may be approximately parallel to the d-axis. The second easy magnetization axis M2 is inclined away from the q-axis. Such easy magnetization axes M1 and M2 can be realized by controlling the crystal orientation when forming the magnetic powder by sintering.

[0038] As can be seen from Figure 9, the permanent magnet 45 has magnetic field lines (easy magnetization axes) that are longer than its radial width, which allows for a high permeance Pc. The effective magnetic flux density Bd of the magnet is given by the following formula Bd = Br / (1 + 1 / Pc) The formula is given by , where Br is the residual magnetic flux density. The above formula shows that as the permeance coefficient approaches infinity, the effective magnetic flux density Bd approaches Br. The permeance coefficient is a value proportional to the thickness of the magnet, that is, a value proportional to the length of the easy magnetization axis. Therefore, the magnetic flux can be increased by lengthening the easy magnetization axis. In other words, this embodiment improves the coercivity of the magnet by increasing the denominator m of the unit [A / m] relative to the performance value of the magnet's coercivity [A / m], making it possible for the permanent magnet to operate without irreversible demagnetization even in the region of a large magnetic field.

[0039] In this embodiment, the permanent magnet 45 having such easy magnetization axes M1 and M2 can generate magnetic field lines that cross its thickness direction longer than the radial thickness of the permanent magnet 45. In other words, even with a permanent magnet of the same size, longer magnetic field lines can be generated. As a result, the permanent magnet type motor 1 can generate high torque and can be miniaturized.

[0040] Figures 10 to 17 show various embodiments of the easy magnetization axis of the permanent magnet 45. In Figure 10, the easy magnetization axes M1 and M2 are curved. The easy magnetization axes M1 and M2 are tilted toward the d-axis at different angles, while also tilting toward the q-axis. In Figure 11, the easy magnetization axes M1 and M2 extend in a straight line, but the easy magnetization axis M2 extends toward the easy magnetization axis M1. In Figure 12, both ends of the permanent magnet 45 are inclined with respect to the q-axis. More specifically, both ends 45a, 45a of the permanent magnet 45 are inclined radially outward from the permanent magnet 45, away from the q-axis. Therefore, an air gap exists between two adjacent permanent magnets 45. Since the corners of the permanent magnets 45, where the magnetic flux lines are short, are cut off, demagnetization can be prevented.

[0041] In Figure 13, there is a recess 45b in the center of the inner edge of the permanent magnet 45. The recess 45b is on the d-axis and has a wedge shape. This recess 45b prevents the magnetic flux lines on both sides of the center of the permanent magnet 45 from colliding, thereby preventing demagnetization. Figure 14 is an example similar to Figure 12, but the outer portions 45c, 45c of both ends 45a, 45a of the permanent magnet 45 are tilted inward. In Figure 15, the inner portions 45d, 45d of the permanent magnet 45, adjacent to its two ends 45a, 45a, are tilted inward. The inward tilt of the inner portions 45d, 45d allows the lengths of the magnetic flux lines to be made more uniform.

[0042] Figure 16 shows a modified version of Figure 15. Specifically, a magnetic material (e.g., metal) 75 is attached to the inwardly inclined inner portions 45d, 45d. In Figure 17, the permanent magnet 45 has a shape divided along the d-axis. In this example, the permanent magnet 45 is composed of two divided parts, but it may be composed of three or more divided parts. For example, if it is composed of 10 divided parts, a curved easy magnetization axis can be formed, and a smooth change in magnetic flux can be achieved, so demagnetization can be effectively prevented.

[0043] Furthermore, the gaps between the magnets created by the q-axis line and reference numeral 45a in Figure 12, the gap formed by reference numeral 45b in Figure 13, the gap formed by the q-axis and reference numeral 45c in Figure 14, the gap formed by the q-axis and reference numeral 45d in Figure 15, and the gap near the d-axis in Figure 17 can be constructed by installing wedges from the axial direction to prevent the permanent magnets 45 from scattering, or by filling the gaps with resin adhesive, thereby creating an annular magnet set, which improves manufacturability and makes it easier to handle.

[0044] In summary, the permanent magnet 45 of this embodiment has fewer higher-order components, such as third-order components, compared to conventional radially or linearly oriented sintered magnets, and its magnetic flux waveform is closer to a sine wave. That is, the permanent magnet 45 of this embodiment has a magnetic flux waveform that increases the magnetic flux linked to the motor coil in accordance with the Biot-Savart equation. In Halbach arrays and linearly oriented magnet arrangements, the orientation angle of the dq axis is set to suppress the phenomenon in which the magnetic flux waveform becomes close to a rectangle at the end of the magnet that is most oriented towards the stator in the array, and to increase the first-order component of the magnetic flux that responds more effectively to the first-order current waveform. Specifically, by defining the entire range of the flux outflow surface of one pole pair of magnets as 360 degrees in order to avoid third-order waveforms, it is possible to reduce low-order harmonic flux waveforms such as the third-order flux waveform at 120 degrees, the fifth-order flux waveform at 72 degrees, the seventh-order flux waveform at approximately 51.4 degrees, and the eleventh-order at approximately 32.7 degrees and the thirteenth-order at approximately 27.7 degrees, which tend to occur as twice the order of the stator pole teeth.

[0045] If the q-axis portion is cut off by a curved surface (see reference numeral 45e in Figure 14) facing the stator of the permanent magnet 45 as shown in Figure 14, the central angle determined by the arc of the curved surface 45e between the permanent magnet 45 and the stator is preferably 120 degrees, 72 degrees, 51.4 degrees, 32.7 degrees, 27.7 degrees, or twice the higher frequency, such as 144 degrees, 102.8 degrees, 65.4 degrees, 55.4 degrees, or three times the higher frequency, such as 154.2 degrees, 98.1 degrees, 83.1 degrees, or four times the higher frequency, such as 130.8 degrees, 110.8 degrees, or five times the higher frequency, such as 163.5 degrees, 138.5 degrees, or six times the higher frequency, such as 166.2 degrees. Furthermore, considering manufacturing precision, it is preferable that the angle be ±1 degree of these values. If the permanent magnet 45 is manufactured at the above angle, the permanent magnet motor 1 will not need to have any of the aforementioned 3rd, 5th, 7th, 11th, or 13th order higher frequency elements. In particular, when configured at 120 degrees in a three-phase motor, the circulating current caused by the 3rd order electromotive force generated when the permanent magnet motor 1 is delta-connected can be suitably suppressed. When the permanent magnet 45 is divided into multiple parts, it is preferable that the angular range occupied by the magnet that is relatively strongly angularly oriented in the d-axis direction, such as M1, is the above angle.

[0046] As shown in Figure 9, the permanent magnet 45 is covered by an outer cylinder 70 made of carbon fiber reinforced plastic (CFRP). In one embodiment, the thickness of the outer cylinder 70 is 1 mm or less, and the stress generated in the outer cylinder 70 is 0.2% yield stress or less. To withstand low temperatures, it is desirable that the composite resin be thermoplastic. Multiple permanent magnets 45 are fixed to the outer circumferential surface of the rotor core 49 with adhesive to form a ring-shaped magnet. Since adhesive alone may cause the permanent magnets 45 to detach when the motor rotor 46 rotates at high speed, the permanent magnets 45 are covered by the outer cylinder 70. The ring-shaped permanent magnets 45 are press-fitted into the outer cylinder 70.

[0047] The pressure applied during this press-fitting should preferably be higher than the stress on the outer cylinder 70 due to centrifugal force within the rated rotational speed range of the motor rotor 46. The centrifugal force can be calculated from the expected rotational speed of the motor rotor 46 and the structure of the motor rotor 46. For example, in the case of a motor for a vehicle, it is desirable that the press-fitting pressure be equal to or greater than the stress generated on the outer cylinder 70 due to centrifugal force at the rotational speed output by cluster analysis of 5 to 10 points, such as WLTC mode driving. In this way, the outer cylinder 70 of an inner rotor type rotor will not theoretically bulge even when subjected to centrifugal force, and the protrusion of the outer cylinder 70 into the air gap between the rotor and stator, which affects the quality of the motor, can be suppressed. As a secondary effect, in the case of IPM type rotors in which magnets are embedded in electromagnetic steel sheets, the inductance and magnetic flux obtained at low speeds can change due to the protrusion of the laminated steel sheet into the air gap by tens of microns at high speeds, causing changes in the back electromotive force constant and inductance, but this phenomenon can be suppressed. This ensures that there are no changes in gains, etc., when performing PI control at low speeds or at arbitrary rated rotational speeds, enabling good proportional control and allowing for cheaper and simpler control, or even motor operation with a microcontroller.

[0048] The outer cylinder 70 is made of non-magnetic, high-strength materials such as carbon fiber reinforced plastic (CFRP), glass fiber reinforced plastic (GFRP), titanium, austenitic stainless steel, metals, or combinations thereof. The outer cylinder 70 prevents the magnetic flux loop of the permanent magnet 45 from being completed within the motor rotor 46, suppresses eddy current losses due to the alternating magnetic field generated from the motor stator 47, and enables high reliability. When the outer cylinder 70 is made from the aforementioned fibrous materials, the orientation of the fibers is in the circumferential direction of the motor rotor 46. This orientation increases the strength of the outer cylinder 70. The outer cylinder 70 can prevent the outer diameter of the motor rotor 46 from changing due to centrifugal force and can prevent slippage of the permanent magnet.

[0049] If sufficient magnetic force can be obtained without suppressing magnetic flux leakage, the outer cylinder 70 may be made of materials such as martensitic SUS or iron-based alloys. In this case, the outer cylinder 70 is easy to manufacture. Furthermore, if the eddy currents generated in the motor rotor 46 are negligible, the outer cylinder 70 may be formed from a conductive material such as copper or iron. In this case as well, grooves may be cut into the outer surface of the outer cylinder 70, or grooving or knurling may be performed to reduce eddy current losses. In one embodiment, the outer cylinder 70 may be made of a composite material of carbon fiber reinforced plastic (CFRP) and metal.

[0050] Figure 18 is a cross-sectional view showing one embodiment of a motor stator 47. As shown in Figure 18, the motor stator 47 has T-shaped teeth 60 (also called pole teeth) that form slots 81 for winding the windings 63. These teeth 60 play a role in more effectively circulating the magnetic flux from the motor rotor 46. The motor stator 47 has an annular core 64 positioned outside the multiple teeth 60. The windings 63 are wound around the multiple teeth 60 to form multiple coils. The motor stator 47 and windings 63 in Figure 18 employ a so-called concentrated winding configuration. In an inner rotor type radial gap electric motor, the annular core 64 is positioned radially outward from the multiple teeth 60.

[0051] In this embodiment, the tooth 60 is composed of a plurality of laminated amorphous plates, and the thickness of each of the plurality of amorphous plates is less than 0.3 mm (preferably 0.2 mm or less, and more preferably 0.1 mm or less). In one embodiment, the thickness of each of the plurality of amorphous plates is 0.025 mm to 0.035 mm.

[0052] The annular core 64 is constructed of a laminated structure of multiple electromagnetic steel sheets made of silicon-containing alloy steel. The thickness of the electromagnetic steel sheets is greater than the thickness of the amorphous sheets, and in one example it is 0.35 mm. In one embodiment, the teeth 60 and the annular core 64 may be integrally constructed to form a stator core. In this case, the stator core including the multiple teeth 60 has a laminated structure of multiple amorphous sheets.

[0053] The amorphous tooth 60 has a configuration that satisfies the relationship B50 × Ast > Br × Am. Here, B50 represents the magnetic flux density when the magnetization force is 5000 A / mm, Ast represents the product of the width of the stator pole tooth 60 and the core axis length facing the permanent magnet 45 within an electrical angle of 180, Br represents the residual magnetic flux density, and Am represents the product of Ast and the opposing surfaces of the permanent magnet 45.

[0054] In one embodiment, the thickness of each of the stacked amorphous plates is less than 0.2 mm, and the magnetic flux density B50 is 1.5 T (Tesla) or higher. In another embodiment, the thickness of each of the stacked amorphous plates is 0.1 mm or less, and the magnetic flux density B50 is 2.0 T (Tesla) or higher.

[0055] When the magnetic flux generated by the motor rotor 46 is φm[Wb], it is appropriate to set B50×Ast≧φm[Wb]. Alternatively, if the motor system is an axial gap type or the component is a compacted magnetic core, it is appropriate to set B100×Ast≧φm[Wb].

[0056] Amorphous materials have high magnetic permeability and, in terms of material properties, possess a saturation magnetic flux density (Bs) approximately 20% lower than that of general electromagnetic soft iron. Such amorphous materials were subjected to SST (Solid State Test) and single-sheet magnetic measurement tests (JIS C 2556) using measurement samples measuring 30 mm wide x 120 mm long x 35 μm thick. When B50 is measured with such materials, a magnetic flux exceeding Bs is measured. This is because Bs is reached below B50, and then a situation similar to that of coreless materials occurs, with the magnetic flux increasing due to the permeability in air. The preferred material in this invention is such an amorphous material; it is desirable to use an amorphous material that reaches Bs below B50, then undergoes a magnetic flux increase due to the permeability in air, and measures B50 ≥ 1.7 [T] as a result of the aforementioned tests. This means that a magnetic flux density exceeding that of electromagnetic steel can be achieved in the magnetic flux range handled by typical permanent magnet motors of approximately 400 kW or less.

[0057] The motor stator 47 has its windings 63 wound in a distributed winding pattern within its slots 81. As a result, the motor's winding coefficient is high because all sections are wound, reducing the harmonic flux supplied to the motor rotor 46 and lowering the overall loss of the motor components.

[0058] Figure 19 is a cross-sectional view showing one embodiment of the winding 63. As shown in Figure 19, the winding 63 is made up of multiple strands 90 twisted together. The multiple strands 90 are compressed to form a single bundle. Since each of the multiple strands 90 has a rectangular or square cross-section, there is almost no gap between the strands 90.

[0059] A bundle of multiple strands 90 is covered by an insulating film 92. The insulating film 92 is made of glass fiber or engineering plastic (e.g., PEEK or PPS). Since the winding 63 is made up of a collection of multiple strands 90, the generation of eddy currents in each strand 90 is suppressed, and the eddy currents in the winding 63 can be reduced. In addition, because the multiple strands 90 are twisted together, the parasitic inductance component can be minimized and the stray capacitance between adjacent strands 90 can be canceled out.

[0060] As shown in Figure 19, the winding 63 has a rectangular cross-section. Since the winding 63 can be treated as a square wire, the space factor of the winding 63 within the slot 81 can be increased. In one embodiment, the space factor of the winding 63 excluding the outer sheath 92 is 90% or more, when the cross-sectional area of ​​the winding 63 including the four corners is defined as 100%. In this embodiment, the motor stator 47 has a three-phase winding structure, but the winding structure is not limited to this embodiment. For example, the motor stator 47 may have a two-phase winding structure, or a five-phase winding structure, or a seven-phase winding structure, or any number of phases as long as it is a commercially available motor.

[0061] Figure 20 is a cross-sectional view showing one embodiment of the wire strand 90. As shown in Figure 20, the wire strand 90 has a rectangular or square cross-section. The wire strand 90 has a conductor 95 and an inner sheath 98, which is an insulating film covering the conductor 95. The conductor 95 is made of a low-resistance material, and examples of materials for the conductor 95 include aluminum, aluminum alloy, copper, and carbon nanotubes (CNTs).

[0062] The inner coating 98 covers the entire outer surface of the conductor 95. Examples of materials for the inner coating 98 include enamel resins made of oxide insulating material, polyamide-imide, and polyimide. Oxide insulating material is preferred because it allows for a thinner inner coating 98. The inner coating 98 may also have an air insulating layer with partial voids.

[0063] The thickness of the inner coating 98 of each strand 90 is 5 μm or less. In the case of an inner coating 98 made of enamel resin, the thickness of the inner coating 98 can be controlled to 1-3 μm, 3-5 μm, etc., by the number of times the enamel resin is applied during the manufacturing process of the strand 90. The strand 90 has a cross-sectional area equivalent to the cross-sectional area of ​​a circle with a diameter of 0.71 mm or less. The cross-sectional area of ​​the strand 90 is the total cross-sectional area of ​​the strand 90, including the conductor 95 and the inner coating 98. In particular, as will be explained below, the strand 90 has a cross-sectional area equivalent to the cross-sectional area of ​​a circle with a diameter of 0.126 mm to 0.71 mm.

[0064] Figure 21 is a graph showing the relationship between the loss due to heat generated by electrical resistance when a DC current flows through the wire 90 (hereinafter referred to as DC loss) and the cross-sectional area of ​​the wire 90, and the relationship between the loss due to eddy currents generated when an AC current flows through the wire 90 (hereinafter referred to as AC loss) and the cross-sectional area of ​​the wire 90. As can be seen from this graph, the larger the cross-sectional area of ​​the wire 90, the smaller the DC loss, while on the other hand, the larger the cross-sectional area of ​​the wire 90, the larger the AC loss. Therefore, there is a trade-off relationship between DC loss and AC loss.

[0065] Therefore, in this embodiment, a wire 90 having a cross-sectional area that can reduce the sum of DC loss and AC loss is used. Figure 22 is a graph showing the relationship between the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the wire 90 and the loss of the wire 90. The vertical axis represents the sum of DC loss and AC loss, and the horizontal axis represents the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the wire 90 including the conductor 95 and the inner sheath 98.

[0066] In this graph, the wire strand 90 has an inner coating 98 with a thickness of 5 μm or less that is guaranteed and can be manufactured as an insulating coating. The range of 0.126 mm to 0.71 mm is an effective dimensional range for reducing total loss when the decrease in AC loss (loss due to eddy currents) of the wire strand 90 is subtracted from the increase in DC loss (loss due to heat generated by electrical resistance) of the wire strand 90. In one embodiment, the diameter of a circle with a cross-sectional area equal to the cross-sectional area of ​​the wire strand 90 is in the range of 0.2 mm to 0.71 mm.

[0067] The winding 63 is fixed in place within the slot 81 with varnish or the like to prevent it from moving. In this embodiment, the winding 63 is fixed to the slot 81 with epoxy resin. Here, the relationship between the coefficients of linear expansion of the varnish, the inner coating 98 of the wire strands 90, and the outer coating 92 of the winding 63 is varnish > outer coating 92 > inner coating 98. According to this relationship between the coefficients of linear expansion, the coefficient of linear expansion gradually changes in the direction in which heat generated from the motor rotor 46 or motor stator 47 or heat generated within the winding 63 is transferred, thus avoiding dimensional changes due to rapid temperature changes, and preventing cracks and chips in the varnish, outer coating 92, inner coating 98, and motor stator 47.

[0068] The configuration employing the amorphous teeth 60 and winding 63 described above allows for control of the d-axis and q-axis, enabling a large magnetic flux for the primary component. The amorphous teeth 60 minimize high-frequency losses caused by excessively large magnetic flux, thus minimizing iron loss. The eddy current loss generated within the winding 63 due to the larger-than-usual magnetic flux leakage is reduced compared to conventional conductors. As a result, it becomes possible to select a larger number of poles and inverters operating at higher frequencies, achieving a smaller and lighter overall system.

[0069] The embodiments described above are intended to enable persons with ordinary skill in the art to implement the present invention. Various modifications of the above embodiments can be made naturally by those skilled in the art, and the technical idea of ​​the present invention can be applied to other embodiments as well. Therefore, the present invention is not limited to the embodiments described, but is to be interpreted in the broadest sense according to the technical idea defined by the claims. [Explanation of Symbols]

[0070] 1 Permanent magnet electric motor 5 batteries 10 Inverters 10A Inverter Circuit 10B Gate Driver 11 Vector Control Unit 12 Current detector 17 3 / 2 Phase Conversion Section 18 Stationary / Rotational Coordinate Transformation Unit 21 Torque Voltage Control Unit 22 Magnetization Voltage Control Unit 24 Target Torque Current Determination Unit 29 Axis error estimator 32 Differentiator 35 Rotation / Standby Coordinate Transformation Unit 36 2 / 3 Phase Conversion Section 42 Rotation axis 45 Permanent Magnets 46 Motor Rotor 47 Motor Stator 49 Rotor core 51, 52 Bearings 55 Motor Housing 60 teeth 63 Winding 64 Circular Core 65 coils 66 Position Sensor 67. Rotation Angle Calculator 70 Outer cylinder 71 End plate 75 Magnetic materials 81 slots 90 strands 92 Outer coat 95 Conductor 98 Inner coating

Claims

1. A permanent magnet type electric motor comprising a motor stator having a coil consisting of windings wrapped around teeth, and a motor rotor having permanent magnets, An inverter that supplies variable frequency power to the aforementioned permanent magnet type motor, Multiple current detectors for detecting the three-phase current flowing from the inverter to the permanent magnet motor, The vector control unit converts the three-phase current into d-axis current and q-axis current on a dq rotating coordinate system, generates voltage command values ​​to bring the d-axis current and q-axis current closer to their respective target values, and sends the voltage command values ​​to the inverter. When the inductance of the coil in the d-axis direction is Ld, the d-axis current is Id, the magnetic flux of the permanent magnet in the d-axis direction is φ, and the angular velocity of the motor rotor is ω, the permanent magnet type electric motor is: A motor system configured such that the relationship ωLdId[V] > ω0.12φ[V] holds true.

2. The motor system according to claim 1, further comprising a battery as a DC power source that supplies DC power to the inverter.

3. The motor system according to claim 1, wherein the vector control unit is configured to perform field weakening control when the vector angle from the d-axis is the angle of the composite vector, which is the sum of the d-axis current vector and the q-axis current vector, to the d-axis, and the vector angle is defined as the vector angle, and the vector control unit is configured to perform field weakening control when the vector angle is less than 90 and within the range of 70 or more.

4. The permanent magnet has a plurality of easy magnetization axes tilted with respect to the d axis and the q axis, The motor system according to claim 1, wherein the plurality of easy magnetization axes include a first easy magnetization axis close to the d axis and a second easy magnetization axis close to the q axis, and the angle of the second easy magnetization axis with respect to the q axis is greater than the angle of the first easy magnetization axis with respect to the d axis.

5. The motor system according to claim 1, wherein the teeth are composed of a plurality of stacked amorphous plates.

6. The motor system according to claim 1, wherein the permanent magnet has a coercivity of 450 kA / m or more, a residual magnetic flux density of 0.7 T or more, and an energy product of 13 MGOe or more.

7. The winding has a bundle of multiple strands and an outer sheath covering the bundle of multiple strands. Each of the aforementioned plurality of strands has a conductor and an inner sheath covering the conductor, The motor system according to claim 1, wherein each of the plurality of strands has a cross-sectional area corresponding to a circle with a diameter of 0.71 mm or less.

8. The motor system according to claim 7, wherein the thickness of the inner coating is 5 μm or less.

9. The motor system according to claim 5, wherein the thickness of each of the plurality of amorphous plates is less than 0.3 mm.

10. The motor system according to claim 1, wherein the motor stator has an annular core located outside the teeth, and the annular core is made of an electromagnetic steel sheet.

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