Electric motor and electric compressor

Abstract

To provide an electric motor and an electric compressor capable of preventing a decrease in NV characteristics and preventing a motor from overheating.SOLUTION: A harmonic superposition frequency switching unit 44 is configured to determine whether any of phase currents Iu, Iv, and Iw exceeds a first threshold value, and to set the frequency of a harmonic wave Vh to a second frequency when any of the phase currents Iu, Iv, and Iw exceeds the first threshold value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an electric motor and an electric compressor. [Background technology]

[0002] When driving a motor using sensorless control, the control unit must estimate the position of the motor's rotor. Sensorless control is a control method that drives a motor without using a hardware position sensor by estimating the rotor position using software.

[0003] Conventionally, methods for estimating rotor position include, for example, an induced voltage method and a harmonic superposition method. The induced voltage method is a method for estimating rotor position based on an induced voltage generated by the rotation of a motor. The harmonic superposition method described in Patent Document 1 is a method for estimating rotor position based on a current (response current) that flows through a motor when a harmonic component is superimposed on a voltage command value or a current command value to the motor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-172324 Summary of the Invention [Problem to be solved by the invention]

[0005] Incidentally, motor losses increase as the frequency of the carrier wave used to control the motor with PWM (Pulse Width Modulation) and the frequency of the harmonics superimposed to estimate the rotor position increase. On the other hand, the lower the frequency of the harmonics, the worse the NV (noise and vibration) characteristics become. However, the above publication does not specifically mention how to set the frequency of the harmonics. [Means for solving the problem]

[0006] An electric motor that achieves the above-mentioned object comprises: a motor having a rotor and a stator wound with three-phase coils; a driver; and an inverter having a driver and a switching element driven by the driver, which drives the motor by driving the switching element; a temperature-related value acquisition unit that acquires a temperature-related value associated with the temperature of the motor; and a control unit that calculates a plurality of command values ​​used to control the switching element and controls the switching element, wherein the control unit is configured to superimpose a harmonic on at least one of the plurality of command values ​​and estimate the position of the rotor using a harmonic superposition method based on the harmonic superimposed on at least one of the plurality of command values, and the frequencies of the harmonic include a first frequency and a second frequency lower than the first frequency, and the control unit is configured to determine whether the temperature-related value exceeds a threshold value, and if the temperature-related value exceeds the threshold value, set the frequency of the harmonic superimposed on at least one of the plurality of command values ​​to the second frequency.

[0007] This configuration can prevent the NV characteristics from deteriorating and also prevent the motor from overheating. In the electric motor, the frequency of the harmonic may be set to the first frequency when the motor is started.

[0008] In the electric motor, the threshold value is a first threshold value, and a value smaller than the first threshold value is a second threshold value, and when the frequency of the harmonic is the second frequency, the control unit determines whether the temperature-related value has fallen below the second threshold value, and if the temperature-related value has fallen below the second threshold value, sets the frequency of the harmonic to the first frequency.

[0009] According to this configuration, by providing hysteresis when switching between the first frequency and the second frequency, it is possible to prevent the harmonic from switching frequently. In the electric motor, the temperature-related value acquisition unit may include a phase current detection unit that detects a phase current flowing through the motor, and the temperature-related value may include a detection result of the phase current detection unit.

[0010] According to this configuration, the temperature-related value of the motor can be obtained without adding any new components. In the electric motor, the temperature-related value acquisition unit may include a temperature detection unit attached to the motor and detecting the temperature of the motor, and the temperature-related value may include a detection result of the temperature detection unit.

[0011] In the electric motor, when the rotation speed of the rotor is equal to or higher than a predetermined rotation speed, the control unit estimates the position of the rotor by an induced voltage method based on induced voltages generated in the three-phase coils, and when the rotation speed is lower than the predetermined rotation speed, the control unit estimates the position of the rotor by the harmonic superposition method, and when estimating the position of the rotor by the induced voltage method, it is preferable that the control unit does not superimpose the harmonics.

[0012] According to this configuration, the rotor position can be estimated with high accuracy using an appropriate method, either the harmonic superposition method or the induced voltage method. The electric compressor that achieves the above object is characterized by comprising: a compression unit that compresses a fluid; and the electric motor according to any one of claims 1 to 6 that drives the compression unit.

[0013] With this configuration, the same effects as those of the electric motor described above can be obtained. [Effects of the Invention]

[0014] According to the present invention, it is possible to prevent the NV characteristics from deteriorating and also to prevent the motor from overheating. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a vehicle air conditioner. [Figure 2]FIG. 2 is a graph showing the relationship between the frequency of the harmonics switched by the control unit and the effective value of the phase current. [Figure 3] FIG. 3 is a flowchart showing an example of a series of processes related to motor control executed by the control unit. [Figure 4] FIG. 4 is a flowchart showing an example of a series of processes related to setting the frequency of harmonics, which are executed by the control unit. [Figure 5] FIG. 5 is a graph showing the relationship between the frequency of harmonics switched by a control unit and the effective value of a phase current in another example. [Figure 6] FIG. 6 is a flowchart showing an example of a series of processes related to setting the frequency of harmonics, which is executed by a control unit in another example. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Embodiment] Hereinafter, embodiments of an electric motor and an electric compressor will be described with reference to the drawings. <Overall structure> As shown in FIG. 1, a vehicle air conditioner 100 of this embodiment includes an electric compressor 101 and a refrigerant circuit 103. The electric compressor 101 includes a compression unit 102 and an electric motor M1. The electric compressor 101 compresses a refrigerant. The refrigerant circuit 103 includes, for example, a heat exchanger and an expansion valve. The vehicle air conditioner 100 cools or heats the interior of the vehicle by compressing the refrigerant with the electric compressor 101 and exchanging heat and expanding the refrigerant with the refrigerant circuit 103. The electric compressor 101 discharges oil along with the compressed refrigerant.

[0017] The compression unit 102 compresses the refrigerant. The refrigerant compressed by the compression unit 102 is discharged to the refrigerant circuit 103. The compression unit 102 may be of any type, such as a scroll type, a piston type, or a vane type.

[0018] <Electric motor> The electric motor M1 includes a motor 11. The motor 11 has a rotor 12 and a stator 13 around which three-phase coils U, V, and W are wound. The motor 11 is a three-phase motor including three coils U, V, and W. The motor 11 drives a compression unit 102. The motor 11 may be cooled by a refrigerant circulating through a refrigerant circuit 103.

[0019] The electric motor M1 includes a motor driving device 10. The motor driving device 10 includes a battery BA, a smoothing capacitor C, an inverter 21, a phase current detection unit 22, an input voltage detection unit 23, and a control unit 30.

[0020] The inverter 21 includes six switching elements Q1 to Q6, diodes D1 to D6, and a driver 51. The switching elements Q1 to Q6 are, for example, IGBTs (Insulated Gate Bipolar Transistors). If the switching elements Q1 to Q6 are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), the switching elements Q1 to Q6 and the diodes D1 to D6 are integrated together. The switching elements Q1 and Q2 are connected in series to each other. The switching elements Q3 and Q4 are connected in series to each other. The switching elements Q5 and Q6 are connected in series to each other. The diodes D1 to D6 are connected in parallel to the switching elements Q1 to Q6, respectively. A battery BA is connected to each switching element Q1 to Q6 via a smoothing capacitor C.

[0021] The connecting line connecting switching element Q1 and switching element Q2 branches off midway and is connected to coil U. The connecting line connecting switching element Q3 and switching element Q4 branches off midway and is connected to coil V. The connecting line connecting switching element Q5 and switching element Q6 branches off midway and is connected to coil W.

[0022] The driver 51 drives the switching elements Q1 to Q6. Driving the switching elements Q1 to Q6 drives the motor 11. Driving the switching elements Q1 to Q6 means the switching operation of the switching elements Q1 to Q6, that is, switching the switching elements Q1 to Q6 on and off.

[0023] The battery BA is a chargeable and dischargeable power storage device, and has a rated voltage of, for example, 800 V. The phase current detection unit 22 detects the phase currents flowing through the motor 11. The phase current detection unit 22 detects at least two phase currents. In this embodiment, the phase current detection unit 22 detects a u-phase current Iu, a v-phase current Iv, and a w-phase current Iw as phase currents. Note that, since the sum of the three phase currents is zero, the phase currents of two of the three phases may be detected and the phase current of the remaining phase may be calculated from the phase currents of the two phases. The u-phase current Iu, the v-phase current Iv, and the w-phase current Iw are actual currents flowing through the coils U, V, and W of the motor 11, respectively.

[0024] The input voltage detection unit 23 detects the input voltage Vi input to the inverter 21 from the battery BA. <Control unit> The control unit 30 includes a processor and a storage unit 80. The processor may be, for example, a central processing unit (CPU), a graphics processing unit (GPU), or a digital signal processor (DSP). The storage unit 80 includes a random access memory (RAM) and a read-only memory (ROM). The storage unit 80 stores program code or instructions configured to cause the processor to execute processes. The storage unit 80, i.e., a computer-readable medium, includes any available medium accessible by a general-purpose or special-purpose computer. The control unit 30 may be configured with hardware circuits such as an application-specific integrated circuit (ASIC) or a field-programmable gate array (FPGA). The control unit 30, which is a processing circuit, may include one or more processors operating according to a computer program, one or more hardware circuits such as an ASIC or an FPGA, or a combination thereof.

[0025] The control unit 30 calculates a plurality of command values. The control unit 30 controls the switching elements Q1 to Q6 based on the plurality of command values. The control unit 30 drives the motor 11 through control of the inverter 21. The control unit 30 uses sensorless control, which is a control method for driving the motor 11 without using a hardware position sensor that detects the position Hm of the rotor 12 of the motor 11. The control unit 30 controls the inverter 21 by switching between position estimation using an induced voltage method and position estimation using a harmonic superposition method. The induced voltage method is a method for estimating the position Hm of the rotor 12 based on the induced voltage generated in the three-phase coils U, V, and W. The harmonic superposition method is a method for estimating the position Hm of the rotor 12 based on the actual current (response current) that flows through the motor 11 when harmonics are superimposed on the command value. The motor 11 is driven by controlling the inverter 21. First, the position estimation by the induced voltage method and the position estimation by the harmonic superposition method will be described, and the process by which the control unit 30 switches between the two methods will be described in detail later.

[0026] <Position estimation using induced voltage method> First, the function of the control unit 30 when performing position estimation using the induced voltage method will be described. The control unit 30 includes a current coordinate conversion unit 31, a position estimation unit 32, subtraction units 33, 35, and 36, a speed control unit 34, a current control unit 37, and a PWM control unit 38.

[0027] The current coordinate converter 31 converts the phase currents Iu, Iv, and Iw into a d-axis current Id and a q-axis current Iq based on the position Hm of the rotor 12 estimated by the position estimator 32. For example, the current coordinate converter 31 converts the phase currents Iu, Iv, and Iw in a three-phase (U, V, W) fixed coordinate system into currents Iα and Iβ in a two-phase (α, β) fixed coordinate system. The current coordinate converter 31 converts the currents Iα and Iβ into a d-axis current Id and a q-axis current Iq in a two-phase (d, q) rotating coordinate system using the position Hm. The d-axis and q-axis are coordinate axes of the dq coordinate system. The dq coordinate system is a coordinate system that rotates together with the rotor 12 of the motor 11. The current coordinate converter 31 may directly convert the phase currents Iu, Iv, and Iw into the d-axis current Id and the q-axis current Iq without converting them into currents Iα and Iβ.

[0028] The position estimation unit 32 estimates the position Hm of the rotor 12 of the motor 11 based on the d-axis current Id and q-axis current Iq output from the current coordinate conversion unit 31 and the d-axis voltage command value Vd and q-axis voltage command value Vq output from the current control unit 37. The position estimation unit 32 calculates induced voltages generated in the coils U, V, and W based on, for example, the d-axis current Id and q-axis current Iq, the d-axis voltage command value Vd and q-axis voltage command value Vq acquired from the current control unit 37, and constants determined by the motor 11. The position estimation unit 32 then estimates the position Hm based on the induced voltages. The position estimation unit 32 also estimates the rotational speed Fm of the rotor 12 based on the estimated position Hm. For ease of explanation, arrows indicating the d-axis current Id, the d-axis voltage command value Vd, and the q-axis voltage command value Vq input to the position estimation unit 32 are omitted from FIG. 1.

[0029] The position estimation unit 32 estimates the position of the rotor 12 by the induced voltage method while the estimated rotation speed Fm is equal to or greater than a predetermined rotation speed Fmth. Furthermore, the position estimation unit 32 estimates the position of the rotor 12 by the harmonic superposition method while the estimated rotation speed Fm is less than the predetermined rotation speed Fmth. The predetermined rotation speed Fmth is, for example, a value indicating the rotation speed of the rotor 12 at which the position of the rotor 12 can be estimated by the induced voltage method, and indicates a value of approximately 700 rpm.

[0030] Subtraction unit 33 calculates the difference ΔFm between rotation speed command value FmRef and the rotation speed Fm estimated by position estimation unit 32. Rotation speed command value FmRef is a command value for the rotation speed of rotor 12 that is input from the outside. Rotation speed command value FmRef is input to control unit 30 from, for example, a higher-level control device of the vehicle.

[0031] The speed control unit 34 calculates a d-axis current command value IdRef and a q-axis current command value IqRef based on the difference ΔFm. The speed control unit 34 calculates the d-axis current command value IdRef and the q-axis current command value IqRef by using, for example, feedback control so that the difference ΔFm converges to 0. The feedback control is, for example, proportional-integral control.

[0032] A subtraction unit 35 calculates a difference ΔId between the d-axis current command value IdRef and the d-axis current Id. A subtraction unit 36 ​​calculates a difference ΔIq between the q-axis current command value IqRef and the q-axis current Iq.

[0033] The current control unit 37 calculates a d-axis voltage command value Vd based on the difference ΔId. The current control unit 37 calculates a q-axis voltage command value Vq based on the difference ΔIq. The current control unit 37 calculates the d-axis voltage command value Vd and the q-axis voltage command value Vq by using, for example, feedback control so that the differences ΔId and ΔIq converge to 0. The feedback control is, for example, proportional-integral control.

[0034] The PWM control unit 38 converts the d-axis voltage command value Vd and the q-axis voltage command value Vq into a u-phase voltage command value Vu, a v-phase voltage command value Vv, and a w-phase voltage command value Vw based on the position Hm of the rotor 12 estimated by the position estimator 32 and the input voltage Vi. For example, the PWM control unit 38 converts the d-axis voltage command value Vd and the q-axis voltage command value Vq from the dq coordinate system to voltage command values ​​Vα and Vβ in the αβ coordinate system. The PWM control unit 38 converts the two-phase voltage command values ​​Vα and Vβ into three-phase voltage command values ​​Vu, Vv, and Vw. The PWM control unit 38 may directly convert the d-axis voltage command value Vd and the q-axis voltage command value Vq into voltage command values ​​Vu, Vv, and Vw without converting them into voltage command values ​​Vα and Vβ.

[0035] The inverter 21 is controlled based on voltage command values ​​Vu, Vv, and Vw. Specifically, the PWM control unit 38 calculates a duty command value based on the voltage command values ​​Vu, Vv, and Vw. Subsequently, the PWM control unit 38 compares the duty command value with a carrier wave such as a triangular wave or a sawtooth wave to generate a PWM signal having a duty ratio indicated by the duty command value. The PWM signal is a gate on / off signal that determines the on / off state of the switching elements Q1 to Q6. The control unit 30 controls the switching elements Q1 to Q6 by outputting the PWM signal to the corresponding switching elements Q1 to Q6 via a driver 51.

[0036] <Location estimation using harmonic superposition method> Next, the function of the control unit 30 when performing position estimation using the harmonic superposition method will be described. As shown in FIG. 1, in addition to the above-mentioned configuration, the control unit 30 further includes a harmonic superposition unit 41, an adder 42, a band-stop filter 43, and a harmonic superposition frequency switcher 44. The current coordinate converter 31, subtractors 33, 35, 36, speed controller 34, current controller 37, and PWM controller 38 have the same functions as in the case of the induced voltage method. Therefore, their description will be omitted. In FIG. 1, the band-stop filter 43 is illustrated as BSF 43.

[0037] The harmonic superimposing unit 41 generates the harmonic Vh. The harmonic Vh is defined as Va*cos2πft. Va is the amplitude of the harmonic Vh. f is the frequency of the harmonic Vh. The frequency f is, for example, a frequency that is independent of the rotation of the motor 11.

[0038] The adder 42 adds the harmonics Vh generated by the harmonic superimposing unit 41 to the d-axis voltage command value Vd. As a result, the harmonics Vh are superimposed on the d-axis voltage command value Vd. In this embodiment, the control unit 30 superimposes the harmonics Vh only on the d-axis voltage command value Vd. When the position estimator 32 estimates the position of the rotor 12 using the induced voltage method, the harmonic superimposing unit 41 does not superimpose the harmonics Vh on the d-axis voltage command value Vd. Note that the control unit 30 may estimate the position of the rotor 12 by superimposing the harmonics Vh on both the d-axis voltage command value Vd and the q-axis voltage command value Vq, both the d-axis current command value IdRef and the q-axis current command value IqRef, or a predetermined command value defined by the three-phase voltage command values ​​Vu, Vv, and Vw.

[0039] The band-stop filter 43 removes frequency components in a specific band from the d-axis current Id and the q-axis current Iq. When the harmonic superimposing unit 41 superimposes the harmonic Vh on the d-axis voltage command value Vd, the d-axis current Id and the q-axis current Iq contain frequency components based on the harmonic Vh. The band-stop filter 43 removes these frequency components.

[0040] As described above, the position estimation unit 32 estimates the position of the rotor 12 using the harmonic superposition method while the estimated rotational speed Fm is less than the predetermined rotational speed Fmth. Specifically, the position estimation unit 32 estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 from the q-axis current Iq calculated by the current coordinate conversion unit 31. When the harmonic Vh is superimposed on the d-axis voltage command value Vd, the q-axis current Iq contains current harmonics based on the harmonic Vh. The position estimation unit 32 estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 based on the current harmonics contained in the q-axis current Iq and a mathematical model of the motor 11. The position estimation unit 32 calculates, for example, an axis error Δθc from the current harmonics. The axis error Δθc is the difference between the actual position Hm of the rotor 12 and the position Hm of the rotor 12 recognized by the control unit 30. The position estimation unit 32 estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 so that the axis error Δθc becomes zero.

[0041] The harmonic superimposing frequency switching unit 44 switches the frequency of the harmonic Vh based on the phase currents Iu, Iv, Iw detected by the phase current detection unit 22 and a first threshold value Th1. <Relationship between the frequency of the harmonic Vh and the first threshold value Th1> 2 is a graph showing the correspondence between the frequency of the harmonic Vh and the effective value of the phase current of the motor 11. The frequency of the harmonic Vh includes a first frequency f1 and a second frequency f2. The second frequency f2 is lower than the first frequency f1. In the following description, the first frequency f1 may be referred to as the initial superposition frequency.

[0042] As shown in FIG. 2, when any of the phase currents Iu, Iv, and Iw of the motor 11 is between 0 and less than a first threshold value Th1, the harmonic superposition frequency switching unit 44 causes the harmonic superposition unit 41 to generate harmonics Vh at a first frequency f1, thereby superimposing the harmonics Vh at the first frequency f1 on the d-axis voltage command value Vd. When any of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 exceeds the first threshold value Th1, the harmonic superposition frequency switching unit 44 changes the frequency of the harmonics Vh generated by the harmonic superposition unit 41 from the first frequency f1 to a second frequency f2. As a result, the harmonics Vh at the second frequency f2 are superimposed on the d-axis voltage command value Vd. The first threshold value Th1 is a value based on the heat resistance temperature of the motor 11. The first threshold value Th1 indicates the value of the phase current when the temperature of the motor 11 becomes a predetermined value higher than the average temperature during normal operation.

[0043] Here, the temperature of the motor 11 rises as the phase currents Iu, Iv, and Iw of the motor 11 increase. In other words, the phase currents Iu, Iv, and Iw of the motor 11 correlate with the temperature of the motor 11. Therefore, the phase current detection unit 22 is an example of a temperature-related value acquisition unit, and the detection results of the phase currents Iu, Iv, and Iw are an example of a temperature-related value associated with the temperature of the motor 11. In other words, the process of determining that any of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 has exceeded the first threshold value Th1 is an example of the process of determining that the temperature of the motor 11 has exceeded the first threshold value Th1.

[0044] <Processing of the control unit 30> A series of processes related to the control of the motor 11 executed by the control unit 30 will be described with reference to Fig. 3. The process of the flowchart shown in Fig. 3 is executed at a predetermined calculation cycle from when the motor 11 starts until when the motor 11 stops.

[0045] For example, the motor 11 starts when the air conditioner 100 for a vehicle starts, and stops when the air conditioner 100 for a vehicle stops. In a series of processes related to the control of the motor 11, first, the control unit 30 acquires the rotation speed Fm of the rotor 12 (step S1). In the first calculation cycle after the start of the motor 11, the control unit 30 may estimate the rotation speed Fm using the harmonic superposition method or the induced voltage method.

[0046] Next, the control unit 30 determines whether the rotation speed Fm is equal to or greater than a predetermined rotation speed Fmth (step S2). If the rotation speed Fm is equal to or greater than the predetermined rotation speed Fmth (step S2; YES), the control unit 30 estimates the rotation position of the rotor 12 using the induced voltage method (step S3). On the other hand, if the rotation speed Fm is less than the predetermined rotation speed Fmth (step S2; NO), the control unit 30 estimates the rotation position of the rotor 12 using the harmonic superposition method (step S4). Then, the control unit 30 generates a PWM signal as described above based on the rotation speed Fm estimated in step S3 or step S4, and drives the motor 11 through control of the inverter 21 (step S5).

[0047] Furthermore, the control unit 30 executes a series of processes related to setting the frequency of the harmonic wave Vh shown in Fig. 4 in parallel with the flowchart shown in Fig. 3. The processes of the flowchart shown in Fig. 4 may be executed in the same calculation cycle as the flowchart shown in Fig. 3, or may be executed in a different calculation cycle. Note that the processes of the flowchart shown in Fig. 4 do not have to be a series of processes executed in parallel with the flowchart shown in Fig. 3, and may be, for example, a subroutine executed within the flowchart shown in Fig. 3 (for example, executed before step S4).

[0048] The frequency of the harmonic wave Vh is set to the initial superposition frequency (first frequency f1) when the motor 11 is started. Therefore, if the motor 11 is stopped after the frequency of the harmonic wave Vh has been set to the second frequency f2 and then restarted, the frequency of the harmonic wave Vh is reset from the second frequency f2 to the initial superposition frequency.

[0049] In a series of processes related to setting the frequency of the harmonic wave Vh, first, the phase current detection unit 22 acquires the phase currents Iu, Iv, and Iw (step S102). Next, the harmonic superimposition frequency switching unit 44 determines whether the phase currents Iu, Iv, and Iw are increasing based on the detection results of the phase current detection unit 22 (step S104). If none of the phase currents Iu, Iv, and Iw are increasing (step S104; NO), the harmonic superimposition frequency switching unit 44 ends the series of processes because there is no need to switch the frequency of the harmonic wave Vh.

[0050] When the harmonic superposition frequency switching unit 44 determines that any one of the phase currents Iu, Iv, and Iw is increasing (step S104; YES), it determines whether any one of the phase currents Iu, Iv, and Iw has exceeded the first threshold value Th1 (step S106). When the harmonic superposition frequency switching unit 44 determines that none of the phase currents Iu, Iv, and Iw has exceeded the first threshold value Th1 (step S106; NO), it ends the series of processes. When the harmonic superposition frequency switching unit 44 determines that any one of the phase currents Iu, Iv, and Iw has exceeded the first threshold value Th1 (step S106; YES), it switches the frequency of the harmonic Vh from the first frequency f1 to the second frequency f2 (step S108). As a result, the harmonic superposition unit 41 superimposes the harmonic Vh of the second frequency f2 on the d-axis voltage command value Vd. Then, the control unit 30 ends the series of processes.

[0051] [Effects of the embodiment] According to the above embodiment, the following effects can be obtained. (1) The position estimation unit 32 estimates the position of the rotor 12 using a harmonic superposition method. The frequency of the harmonic Vh is set to a first frequency f1 when the motor 11 is started. When any one of the phase currents Iu, Iv, and Iw exceeds a first threshold value Th1, the harmonic superposition frequency switching unit 44 determines that the temperature of the motor 11 has exceeded the first threshold value Th1, and changes the frequency of the harmonic Vh to be superimposed on the d-axis voltage command value Vd from the first frequency f1 to a second frequency f2.

[0052] According to this configuration, when the harmonic superposition method starts to estimate the position of the rotor 12, the frequency of the harmonics Vh is increased, thereby preventing the NV characteristics from deteriorating. On the other hand, when the temperature of the motor 11 increases, the frequency of the harmonics Vh is decreased, thereby preventing the motor 11 from overheating.

[0053] (2) The detection results of the phase current detector 22 that detects the phase currents Iu, Iv, and Iw flowing through the motor 11 are used as temperature-related values ​​associated with the temperature of the motor 11. According to this configuration, the temperature-related value of the motor 11 can be obtained without adding a new component for detecting the temperature of the motor 11.

[0054] (3) The position estimation unit 32 estimates the position of the rotor 12 by the harmonic superposition method or the induced voltage method. Specifically, when the rotation speed Fm of the rotor 12 based on the estimation result is equal to or greater than a predetermined rotation speed Fmth, the position estimation unit 32 estimates the position of the rotor 12 by the induced voltage method. Furthermore, when the rotation speed Fm of the rotor 12 based on the estimation result is less than the predetermined rotation speed Fmth, the position estimation unit 32 estimates the position of the rotor 12 by the harmonic superposition method. When the position estimation unit 32 estimates the position of the rotor 12 by the induced voltage method, the harmonic superposition unit 41 does not superimpose the harmonic Vh on the d-axis voltage command value Vd.

[0055] Here, the lower the rotation speed Fm of the rotor 12, the lower the induced voltage. Therefore, when the position estimation unit 32 estimates the position of the rotor 12 using the induced voltage method, the estimation accuracy decreases when the rotation speed Fm of the rotor 12 is low. In this regard, with this configuration, the position estimation unit 32 can accurately estimate the position of the rotor 12 using either the harmonic superposition method or the induced voltage method, whichever is appropriate depending on the rotation speed Fm of the rotor 12. On the other hand, when the rotation of the motor 11 circulates a coolant used to cool the motor 11 itself, a low rotation speed Fm of the rotor 12 reduces the coolant flow rate, making the motor 11 more likely to overheat. Therefore, when the temperature of the motor 11 is high, as in this embodiment, lowering the frequency of the harmonics Vh is highly effective.

[0056] (4) The electric compressor 101 includes a compression unit 102 that compresses a refrigerant fluid, and an electric motor M1 that drives the compression unit 102. By switching the frequency of the harmonics Vh when estimating the position of the rotor 12 using the harmonic superposition method as described above, it is possible to suppress overheating of the motor 11 and to suppress degradation of the NV characteristics. With this configuration, the vehicle air conditioner 100 equipped with the electric compressor 101 can suppress overheating of the motor 11 while making it difficult for passengers in the vehicle cabin to perceive noise and vibration.

[0057] The above embodiment may be modified as follows: The above embodiment and each of the following modifications may be combined with each other within the scope of technical compatibility. Although the harmonic superposition frequency switching unit 44 changed the frequency of the harmonic Vh from the first frequency f1 to the second frequency f2 when the phase currents Iu, Iv, and Iw of the motor 11 are increasing, this is not limiting. The harmonic superposition frequency switching unit 44 may change the frequency of the harmonic Vh from the second frequency f2 to the first frequency f1 when the phase currents Iu, Iv, and Iw of the motor 11 are decreasing. Details will be described below with reference to FIGS. 5 and 6.

[0058] The harmonic superposition frequency switching unit 44 maintains the frequency of the harmonic Vh at the second frequency f2 while the phase current Iu, Iv, or Iw of the motor 11 remains equal to or greater than the second threshold value Th2 after the phase current Iu, Iv, or Iw of the motor 11 falls below the first threshold value Th1. The second threshold value Th2 is smaller than the first threshold value Th1. When the frequency of the harmonic Vh is the second frequency f2, the harmonic superposition frequency switching unit 44 sets the frequency of the harmonic Vh to the first frequency f1 after the phase current Iu, Iv, or Iw of the motor 11 falls below the second threshold value Th2. As described above, when the frequency of the harmonic Vh is the first frequency f1, the harmonic superposition frequency switching unit 44 sets the frequency of the harmonic Vh to the second frequency f2 if the phase current Iu, Iv, or Iw of the motor 11 exceeds the first threshold value Th1. In other words, hysteresis is provided in the switching of the frequency of the harmonic Vh. The process of determining that any of the phase currents Iu, Iv, Iw detected by the phase current detection unit 22 has fallen below the second threshold value Th2 is an example of a process of determining that a temperature-related value of the motor 11 has fallen below the second threshold value Th2.

[0059] A series of processes relating to setting the frequency of the harmonic wave Vh in another embodiment will be described with reference to Fig. 6. The flowchart shown in Fig. 6 includes steps S200 to S202 in addition to the processes in the flowchart shown in Fig. 4.

[0060] If the phase currents Iu, Iv, and Iw have not increased (step S104; NO), the harmonic superposition frequency switching unit 44 determines that the phase currents Iu, Iv, and Iw have decreased, and determines whether any of the phase currents Iu, Iv, and Iw has fallen below the second threshold value Th2 (step S200). If the harmonic superposition frequency switching unit 44 determines that none of the phase currents Iu, Iv, and Iw have fallen below the second threshold value Th2 (step S200; NO), the harmonic superposition frequency switching unit 44 ends the series of processes. If the harmonic superposition frequency switching unit 44 determines that any of the phase currents Iu, Iv, and Iw has fallen below the second threshold value Th2 (step S200; YES), the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh from the second frequency f2 to the first frequency f1 (step S202). As a result, the harmonic superposition unit 41 superimposes the harmonic Vh of the first frequency f1 on the d-axis voltage command value Vd. Then, the control unit 30 ends the series of processes.

[0061] With this configuration, the harmonic superposition frequency switching unit 44 can appropriately set the frequency of the harmonic wave Vh in accordance with the temperature of the motor 11. Furthermore, by providing hysteresis in the switching of the frequency of the harmonic wave Vh, it is possible to prevent the frequency of the harmonic wave Vh from switching too frequently. In this other embodiment, the frequency of the harmonic wave Vh may be set to the second frequency f2 when the motor 11 starts.

[0062] Although the detection results of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 are used as the temperature-related values ​​of the motor 11, this is not limitative. Instead of (or in addition to) the detection results of the phase currents Iu, Iv, and Iw, other information may be used as the temperature-related values ​​of the motor 11. For example, in addition to the configuration described above, the motor drive device 10 may include a temperature detection unit attached to the motor 11 that detects the temperature of the motor 11. The temperature detection unit is realized by, for example, a thermocouple and a functional unit that performs AD conversion of the results measured by the thermocouple.

[0063] In this case, the detection result of the temperature detection unit is used as the temperature-related value of the motor 11. The harmonic superposition frequency switching unit 44 compares the temperature-related value of the motor 11 based on the detection result of the temperature detection unit with a first threshold value Th1 and a second threshold value Th2 to switch and set the frequency of the harmonics Vh. In this case, the first threshold value Th1 and the second threshold value Th2 are values ​​based on the heat resistance temperature of the motor 11. Specifically, the first threshold value Th1 is a value indicating a temperature higher than the average temperature of the motor 11 under normal conditions. The second threshold value Th2 is a value smaller than the first threshold value Th1.

[0064] Although the first threshold value Th1 is a value based on the average temperature of the motor 11 under normal conditions, this is not limited to this. The first threshold value Th1 may be a value based on a statistical value such as the median, average, or mode of the temperature range that the motor 11 can reach. Furthermore, the first threshold value Th1 may be a value based on a statistical value such as the median or average of the heat-resistant temperature range of the motor 11.

[0065] Although the harmonic superposition frequency switching unit 44 switches and sets the frequency of the harmonic Vh based on the effective value of any one of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22, this is not limitative. The harmonic superposition frequency switching unit 44 may switch the frequency of the harmonic Vh based on a statistical value such as the median, average, maximum, or minimum value of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22.

[0066] The position estimation unit 32 estimates the position of the rotor 12 using the harmonic superposition method or the induced voltage method, but this is not limiting. The position estimation unit 32 may estimate the position of the rotor 12 using only the harmonic superposition method.

[0067] Although the harmonic superimposing unit 41 superimposes the harmonic Vh on the d-axis voltage command value Vd, this is not limiting. The harmonic superimposing unit 41 may superimpose the harmonic Vh on the current command values ​​IdRef and IqRef.

[0068] The technical ideas that can be understood from the above-described embodiment and modified examples will be described. [Aspect 1] An electric motor comprising: a motor having a rotor and a stator wound with three-phase coils; an inverter having a driver and switching elements driven by the driver, and driving the motor by driving the switching elements; a temperature-related value acquisition unit that acquires temperature-related values ​​associated with the temperature of the motor; and a control unit that calculates multiple command values ​​used to control the switching elements and controls the switching elements, wherein the control unit superimposes harmonics on at least one of the multiple command values ​​and estimates the position of the rotor using a harmonic superposition method based on the harmonics superimposed on at least one of the multiple command values, the frequencies of the harmonics including a first frequency and a second frequency lower than the first frequency, and the control unit is configured to determine whether the temperature-related value exceeds a threshold value, and if the temperature-related value exceeds the threshold value, set the frequency of the harmonics superimposed on at least one of the multiple command values ​​to the second frequency.

[0069] [Aspect 2] The electric motor according to [Aspect 1], wherein the frequency of the harmonic is set to the first frequency when the motor is started. [Aspect 3] An electric motor as described in [Aspect 1] or [Aspect 2], wherein the threshold value is a first threshold value, a value smaller than the first threshold value is a second threshold value, and the control unit determines whether the temperature-related value falls below the second threshold value when the frequency of the harmonic is the second frequency, and if the temperature-related value falls below the second threshold value, sets the frequency of the harmonic to the first frequency.

[0070] [Aspect 4] An electric motor described in any one of [Aspect 1] to [Aspect 3], wherein the temperature-related value acquisition unit includes a phase current detection unit that detects a phase current flowing through the motor, and the temperature-related value includes the detection result of the phase current detection unit.

[0071] [Aspect 5] An electric motor described in any one of [Aspect 1] to [Aspect 3], wherein the temperature-related value acquisition unit includes a temperature detection unit attached to the motor and detecting the temperature of the motor, and the temperature-related value includes the detection result of the temperature detection unit.

[0072] [Aspect 6] An electric motor described in any one of [Aspect 1] to [Aspect 5], wherein the control unit estimates the position of the rotor using an induced voltage method based on induced voltages generated in the three-phase coils when the rotational speed of the rotor is equal to or greater than a predetermined rotational speed, and estimates the position of the rotor using the harmonic superposition method when the rotational speed is less than the predetermined rotational speed, and does not superpose the harmonics when estimating the position of the rotor using the induced voltage method.

[0073] [Aspect 7] An electric compressor comprising a compression section that compresses a fluid and an electric motor according to any one of [Aspect 1] to [Aspect 6] that drives the compression section. [Explanation of symbols]

[0074] 11...motor, 12...rotor, 13...stator, 21...inverter, 22...phase current detection unit as temperature-related value acquisition unit, 30...control unit, 51...driver, 101...electric compressor, 102...compression unit, f1...first frequency, f2...second frequency, Fm...rotational speed, Fmth...predetermined rotational speed, M1...electric motor, Q1, Q2, Q3, Q4, Q5, Q6...switching elements, Th1...first threshold, Th2...second threshold, U...coil, V...coil, W...coil, Vh...harmonics.

Claims

1. a motor having a rotor and a stator wound with three-phase coils; an inverter having a driver and a switching element driven by the driver, the inverter driving the motor by driving the switching element; a temperature-related value acquisition unit that acquires a temperature-related value associated with the temperature of the motor; a control unit that calculates a plurality of command values ​​used to control the switching elements and controls the switching elements; The control unit superimposing a harmonic on at least one of the plurality of command values; an electric motor that estimates a position of the rotor by a harmonic superposition method based on the harmonic superposed on at least one of the plurality of command values, the frequencies of the harmonics include a first frequency and a second frequency lower than the first frequency, The control unit determining whether the temperature-related value exceeds a threshold; When the temperature-related value exceeds the threshold value, a frequency of the harmonic superimposed on at least one of the plurality of command values ​​is set to the second frequency. Electric motor.

2. the frequency of the harmonic is set to the first frequency at the start of the motor; 2. The electric motor according to claim 1.

3. the threshold is a first threshold, and a value smaller than the first threshold is a second threshold, The control unit determining whether the temperature-related value is lower than the second threshold value when the frequency of the harmonic is the second frequency; If the temperature-related value falls below the second threshold, setting the frequency of the harmonic to the first frequency.

2. The electric motor according to claim 1.

4. the temperature-related value acquisition unit includes a phase current detection unit that detects a phase current flowing through the motor; the temperature-related value includes a detection result of the phase current detection unit; 2. The electric motor according to claim 1.

5. the temperature-related value acquisition unit includes a temperature detection unit attached to the motor and detecting a temperature of the motor; the temperature-related value includes a detection result of the temperature detection unit; 2. The electric motor according to claim 1.

6. the control unit estimates the position of the rotor by an induced voltage method based on induced voltages generated in the three-phase coils when the rotation speed of the rotor is equal to or higher than a predetermined rotation speed; When the rotation speed is less than the predetermined rotation speed, estimating the position of the rotor using the harmonic superposition method; When the rotor position is estimated by the induced voltage method, the harmonics are not superimposed.

2. The electric motor according to claim 1.

7. a compression section that compresses the fluid; The electric motor according to any one of claims 1 to 6, which drives the compression unit; An electric compressor comprising:

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