Electric motor and electric compressor

Abstract

The motor includes a control unit. The control unit is configured so as to overlap the harmonics with at least one of the plurality of command values, and to estimate the position of the rotor on the basis of a harmonic overlap pattern of the harmonics that overlap with the 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 is further configured to determine whether or not the temperature-related value exceeds a threshold value, and if the temperature-related value exceeds the threshold value, set the frequency of a harmonic wave superimposed on at least one of the plurality of command values to a second frequency.

Description

Technical Field

[0001] The present disclosure relates to an electric motor and an electric compressor. Background Art

[0002] When a motor is driven using sensorless control, the control unit needs to estimate the position of the motor's rotor. Sensorless control is a control method that drives a motor by estimating the rotor's position using software, rather than using a hardware position sensor.

[0003] Conventional methods for estimating the rotor position include, for example, the induced voltage method and the harmonic superposition method. The induced voltage method estimates the rotor position based on the induced voltage generated by the motor's rotation. The harmonic superposition method, described in Japanese Patent Application Laid-Open No. 2011-172324, estimates the rotor position based on the current (response current) flowing through the motor when harmonic components are superimposed on the motor's voltage or current command values.

[0004] However, higher frequencies in the carrier used for PWM (Pulse Width Modulation) control of the motor and in the harmonics superimposed to estimate the rotor position increase motor losses. On the other hand, lower harmonic frequencies reduce noise and vibration (NV) characteristics. However, the aforementioned publication does not specifically mention the setting of harmonic frequencies. Summary of the Invention

[0005] An electric motor according to one embodiment of the present disclosure includes: 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 motor being driven by the switching element; a temperature-related value acquisition unit configured to acquire a temperature-related value associated with the temperature of the motor; and a control unit configured to calculate a plurality of command values ​​for controlling the switching element and control the switching element. 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 based on the pattern of harmonic superposition of the harmonic superimposed on the at least one of the plurality of command values. The frequency of the harmonic includes a first frequency and a second frequency lower than the first frequency. The control unit is further 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.

[0006] An electric compressor according to another aspect of the present disclosure includes: a compression unit configured to compress a fluid; and the above-mentioned electric motor configured to drive the compression unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 This is a diagram showing an example of the configuration of a vehicle air conditioning system.

[0008] Figure 2 It means by Figure 1 Graph showing the relationship between the frequency of harmonics switched by a control unit of a vehicle air conditioner and the effective value of the phase current.

[0009] Figure 3 Yes Figure 1 A flowchart showing an example of a series of processes related to motor control executed by a control unit included in a vehicle air conditioner.

[0010] Figure 4 Yes Figure 1 A flowchart showing an example of a series of processes related to setting of harmonic frequencies, which is executed by a control unit included in a vehicle air conditioner.

[0011] Figure 5 This is a graph showing the relationship between the frequency of harmonics switched by a control unit of another example and the effective value of the phase current.

[0012] Figure 6 This is a flowchart showing an example of a series of processes related to setting of harmonic frequencies executed by a control unit of another example. DETAILED DESCRIPTION

[0013] [Implementation Method]

[0014] Hereinafter, embodiments in which a motor and an electric compressor are embodied will be described with reference to the drawings.

[0015] Overall Structure

[0016] like Figure 1 As shown, a vehicle air conditioning system 100 according to an 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 the refrigerant. The refrigerant circuit 103 includes, for example, a heat exchanger and an expansion valve. The vehicle air conditioning system 100 compresses the refrigerant through the electric compressor 101, and heat exchanges and expands the refrigerant through the refrigerant circuit 103, thereby cooling and heating the vehicle interior. The electric compressor 101 discharges oil along with the compressed refrigerant.

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

[0018] <Electric Motor>

[0019] Electric motor M1 includes motor 11. Motor 11 has a rotor 12 and a stator 13 wound with three-phase coils U, V, and W. Motor 11 is a three-phase motor having three coils U, V, and W. Motor 11 drives compressor 102. Motor 11 may also be cooled by the refrigerant circulating in refrigerant circuit 103.

[0020] The electric motor M1 includes a motor drive device 10 . The motor drive 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 .

[0021] Inverter 21 includes six switching elements Q1 to Q6, diodes D1 to D6, and a driver 51. Switching elements Q1 to Q6 are, for example, IGBTs (Insulated Gate Bipolar Transistors). If switching elements Q1 to Q6 are MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors), switching elements Q1 to Q6 and diodes D1 to D6 are integrated. Switching element Q1 and switching element Q2 are connected in series. Switching element Q3 and switching element Q4 are connected in series. Switching element Q5 and switching element Q6 are connected in series. Switching elements Q1 to Q6 are connected in parallel with diodes D1 to D6, respectively. A battery BA is connected to each switching element Q1 to Q6 via a smoothing capacitor C.

[0022] The connection line connecting switching element Q1 and switching element Q2 branches midway and is connected to coil U. The connection line connecting switching element Q3 and switching element Q4 branches midway and is connected to coil V. The connection line connecting switching element Q5 and switching element Q6 branches midway and is connected to coil W.

[0023] Driver 51 drives switching elements Q1 to Q6. Driving switching elements Q1 to Q6 drives motor 11. Driving switching elements Q1 to Q6 means switching operations of switching elements Q1 to Q6, that is, switching switching elements Q1 to Q6 on and off.

[0024] The battery BA is a chargeable and dischargeable power storage device. The rated voltage of the battery BA is, for example, 800 [V].

[0025] The phase current detection unit 22 detects the phase current flowing through the motor 11. The phase current detection unit 22 detects the phase current of at least two phases. In this embodiment, the phase current detection unit 22 detects the u-phase current Iu, the v-phase current Iv, and the w-phase current Iw. In other embodiments, based on the fact that the sum of the phase currents of the three phases becomes 0, the phase currents of two of the three phases may be detected, and the phase current of the remaining one phase may be calculated based on the phase currents of the two phases. The u-phase current Iu, the v-phase current Iv, and the w-phase current Iw are the actual currents flowing through the coils U, V, and W of the motor 11, respectively.

[0026] The input voltage detection unit 23 detects the input voltage Vi input from the battery BA to the inverter 21 .

[0027] <Control Department>

[0028] The control unit 30 includes a processor and a storage unit 80. The processor is, for example, a CPU (Central Processing Unit), a GPU (Graphics Processing Unit), or a DSP (Digital Signal Processor). The storage unit 80 includes RAM (Random Access Memory) and ROM (Read Only Memory). The storage unit 80 stores program codes or instructions configured to cause the processor to execute processes. The storage unit 80, i.e., computer-readable media, includes all available media that can be accessed by general-purpose or special-purpose computers. The control unit 30 can also be composed of hardware circuits such as ASICs (Application Specific Integrated Circuits) and FPGAs (Field Programmable Gate Arrays). The control unit 30, as a processing circuit, can include one or more processors, one or more hardware circuits such as ASICs and FPGAs, or a combination thereof that operate according to a computer program.

[0029] The control unit 30 calculates multiple command values. Based on these command values, the control unit 30 controls the switching elements Q1 to Q6. The control unit 30 drives the motor 11 by controlling the inverter 21. In this embodiment, the control unit 30 uses sensorless control, a control method that drives the motor 11 without a hardware position sensor to detect the position Hm of the rotor 12 of the motor 11. The control unit 30 controls the inverter 21 while switching between position estimation based on an induced voltage method and position estimation based on a harmonic superposition method. The induced voltage method estimates 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 estimates the position Hm of the rotor 12 based on the actual current (response current) flowing through the motor 11 when harmonics are superimposed on the command values. The motor 11 is driven by controlling the inverter 21. Position estimation based on the induced voltage method and position estimation based on the harmonic superposition method will be described first. The details of the process by which the control unit 30 switches between these two methods will be described later.

[0030] Position estimation based on induced voltage

[0031] The functions 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 converter 31 , a position estimator 32 , subtractors 33 , 35 , and 36 , a speed controller 34 , a current controller 37 , and a PWM controller 38 .

[0032] The current coordinate conversion unit 31 converts the phase currents Iu, Iv, and Iw into the d-axis current Id and the q-axis current Iq based on the position Hm of the rotor 12 estimated by the position estimation unit 32. For example, the current coordinate conversion unit 31 converts the phase currents Iu, Iv, and Iw in a fixed coordinate system for three phases (U, V, and W) into currents Iα and Iβ in a fixed coordinate system for two phases (α and β). Using the position Hm, the current coordinate conversion unit 31 converts the currents Iα and Iβ into the d-axis current Id and the q-axis current Iq in a rotating coordinate system for two phases (d, q). The d-axis and q-axis are coordinate axes of the dq coordinate system, which rotates with the rotor 12 of the motor 11. The current coordinate conversion unit 31 may also directly convert the phase currents Iu, Iv, and Iw into the d-axis current Id and the q-axis current Iq, rather than converting them into the currents Iα and Iβ.

[0033] 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 the q-axis current Iq output from the current coordinate conversion unit 31, and the d-axis voltage command value Vd and the q-axis voltage command value Vq output from the current control unit 37. The position estimation unit 32 calculates the induced voltage generated in the coils U, V, and W based on, for example, the d-axis current Id and the q-axis current Iq, the d-axis voltage command value Vd and the q-axis voltage command value Vq obtained from the current control unit 37, and the constants determined by the motor 11. Then, the position estimation unit 32 estimates the position Hm based on the induced voltage. In addition, the position estimation unit 32 estimates the rotation speed Fm of the rotor 12 based on the estimated position Hm. In addition, for the sake of convenience, in Figure 1 In FIG. 1 , 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 estimating unit 32 are omitted.

[0034] Position estimating unit 32 estimates the position of rotor 12 using the induced voltage method while estimated rotational speed Fm is equal to or greater than predetermined rotational speed Fmth. Furthermore, position estimating unit 32 estimates the position of rotor 12 using the harmonic superposition method while estimated rotational speed Fm is less than predetermined rotational speed Fmth. Predetermined rotational speed Fmth represents, for example, a rotational speed of rotor 12 at which the position of rotor 12 can be estimated using the induced voltage method, and represents a value of approximately 700 rpm.

[0035] Subtraction unit 33 calculates a difference ΔFm between rotational speed command value FmRef and rotational speed Fm estimated by position estimation unit 32. Rotational speed command value FmRef is an externally inputted rotational speed command value for rotor 12. Rotational speed command value FmRef is inputted to control unit 30 from, for example, a higher-level control device of the vehicle.

[0036] The speed control unit 34 calculates the d-axis current command value IdRef and the 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, for example, using feedback control so that the difference ΔFm converges to zero. The feedback control is, for example, proportional-integral control.

[0037] The subtraction unit 35 calculates a difference ΔId between the d-axis current command value IdRef and the d-axis current Id. The subtraction unit 36 ​​calculates a difference ΔIq between the q-axis current command value IqRef and the q-axis current Iq.

[0038] The current control unit 37 calculates the d-axis voltage command value Vd based on the difference ΔId. The current control unit 37 calculates the 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, for example, using feedback control so that the difference ΔId and the difference ΔIq converge to zero. The feedback control is, for example, proportional-integral control.

[0039] Based on the position Hm of the rotor 12 estimated by the position estimating unit 32 and the input voltage Vi, 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. 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 into 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. Alternatively, the PWM control unit 38 may directly convert the d-axis voltage command value Vd and the q-axis voltage command value Vq into the voltage command values ​​Vu, Vv, and Vw without converting them into the voltage command values ​​Vα and Vβ.

[0040] Inverter 21 is controlled based on voltage command values ​​Vu, Vv, and Vw. Specifically, PWM control unit 38 calculates a duty cycle command value based on voltage command values ​​Vu, Vv, and Vw. Next, PWM control unit 38 compares the duty cycle command value with a carrier wave (such as a triangular wave or sawtooth wave) to generate a PWM signal having the duty cycle indicated by the duty cycle command value. The PWM signal is a gate on / off signal that specifies the on / off state of switching elements Q1-Q6. Control unit 30 outputs the PWM signal to the corresponding switching elements Q1-Q6 via driver 51, thereby controlling switching elements Q1-Q6.

[0041] Position estimation based on the harmonic superposition method

[0042] Next, the function of the control unit 30 in the case of performing position estimation based on the harmonic superposition method will be described. Figure 1 As shown, in addition to the above-described configuration, the control unit 30 further includes a harmonic superimposition unit 41, an addition unit 42, a band rejection filter 43, and a harmonic superimposition frequency switching unit 44. The current coordinate converter 31, subtraction units 33, 35, and 36, speed controller 34, current controller 37, and PWM controller 38 have the same functions as those of the induced voltage method. Therefore, their description will be omitted.

[0043] The harmonic superimposing unit 41 generates a harmonic Vh. The harmonic Vh is defined by 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.

[0044] The adding unit 42 adds the harmonic Vh generated by the harmonic superposition unit 41 to the d-axis voltage command value Vd. As a result, the harmonic Vh is superimposed on the d-axis voltage command value Vd. In the present embodiment, the control unit 30 superimposes the harmonic Vh only on the d-axis voltage command value Vd. When the position estimating 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. In other embodiments, the control unit 30 may also estimate the position of the rotor 12 by superimposing the harmonic Vh on both the d-axis voltage command value Vd and the q-axis voltage command value Vq, on both the d-axis current command value IdRef and the q-axis current command value IqRef, or on a given command value defined by the three-phase voltage command values ​​Vu, Vv, and Vw.

[0045] Band-rejection filter 43 removes frequency components in a specific frequency band from d-axis current Id and q-axis current Iq. When harmonic superimposition unit 41 superimposes harmonic Vh on d-axis voltage command value Vd, d-axis current Id and q-axis current Iq contain frequency components based on harmonic Vh. Band-rejection filter 43 removes these frequency components.

[0046] As described above, the position estimating unit 32 estimates the position of the rotor 12 using a harmonic superposition method while the estimated rotational speed Fm is less than the predetermined rotational speed Fmth. Specifically, the position estimating unit 32 estimates the position Hm and the rotational speed Fm of the rotor 12 based on 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 includes current harmonics based on the harmonic Vh. The position estimating unit 32 estimates the position Hm and the rotational speed Fm of the rotor 12 based on the current harmonics included in the q-axis current Iq and the mathematical model of the motor 11. For example, the position estimating unit 32 calculates an axial error Δθc based on the current harmonics. The axial 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 estimating unit 32 estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 so that the axial error Δθc becomes zero.

[0047] The harmonic superimposition frequency switching unit 44 switches the frequency of the harmonic Vh based on the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 and the first threshold value Th1 .

[0048] <Relationship between the frequency of harmonic Vh and the first threshold Th1>

[0049] Figure 2This 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.

[0050] like Figure 2 As shown, the harmonic superposition frequency switching unit 44 causes the harmonic superposition unit 41 to generate harmonics Vh of the first frequency f1 while the phase currents Iu, Iv, and Iw of the motor 11 are all between zero and less than the first threshold Th1. This causes the harmonics Vh of the first frequency f1 to be superimposed on the d-axis voltage command value Vd. If any of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 exceeds the first threshold Th1, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonics Vh generated by the harmonic superposition unit 41 from the first frequency f1 to the second frequency f2. This causes the harmonics Vh of the second frequency f2 to be superimposed on the d-axis voltage command value Vd. The first threshold Th1 is a value based on the heat-resistant temperature of the motor 11. The first threshold Th1 represents the phase current value when the temperature of the motor 11 is higher than the average temperature under normal conditions by a predetermined value.

[0051] Here, as the phase currents Iu, Iv, and Iw of the motor 11 increase, the temperature of the motor 11 rises. In other words, the phase currents Iu, Iv, and Iw of the motor 11 are correlated 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 temperature-related values ​​correlated with the temperature of the motor 11. In other words, determining that any one of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 exceeds the first threshold value Th1 is an example of determining that the temperature of the motor 11 exceeds the first threshold value Th1.

[0052] <Processing by the Control Unit 30>

[0053] Reference Figure 3 , a series of processes related to the control of the motor 11 executed by the control unit 30 are described. From the time the motor 11 is started to the time the motor 11 is stopped, a given operation cycle is executed. Figure 3 The motor 11 is started, for example, when the vehicle air conditioner 100 is started, and is stopped when the vehicle air conditioner 100 is stopped.

[0054] In the series of processes related to controlling motor 11, control unit 30 first obtains rotational speed Fm of rotor 12 (step S1). In the initial calculation cycle after motor 11 is started, control unit 30 can estimate rotational speed Fm using either a harmonic superposition method or an induced voltage method.

[0055] Next, the control unit 30 determines whether the rotational speed Fm is greater than or equal to the predetermined rotational speed Fmth (step S2). If the rotational speed Fm is greater than or equal to the predetermined rotational speed Fmth (step S2: Yes), the control unit 30 estimates the rotational position of the rotor 12 using the induced voltage method (step S3). On the other hand, if the rotational speed Fm is less than the predetermined rotational speed Fmth (step S2: No), the control unit 30 estimates the rotational position of the rotor 12 using the harmonic superposition method (step S4). The control unit 30 then generates the PWM signal as described above based on the rotational speed Fm estimated in step S3 or step S4, and drives the motor 11 by controlling the inverter 21 (step S5).

[0056] In addition, the control unit 30 and Figure 3 The flowchart shown is executed in parallel with Figure 4 A series of processes related to setting the frequency of the harmonic Vh is shown. Figure 4 The processing of the flowchart shown can be performed with Figure 3 The flowchart shown in the figure can be executed in the same operation cycle, or it can be executed in different operation cycles. Figure 4 The processing of the flowchart shown may not be the same as Figure 3 The series of processing performed in parallel by the flowchart shown in FIG. Figure 3 A subroutine executed within the flowchart shown (eg, executed before step S4).

[0057] The frequency of the harmonic Vh is set to the initial superposition frequency (first frequency f1) when the motor 11 is started. Therefore, after the frequency of the harmonic Vh is switched to the second frequency f2, the motor 11 stops. When the motor 11 is restarted, the frequency of the harmonic Vh switches from the second frequency f2 to the initial superposition frequency.

[0058] In the series of processes related to setting the frequency of harmonics Vh, the phase current detection unit 22 first obtains 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 the harmonic-superimposition frequency switching unit 44 determines that none of the phase currents Iu, Iv, and Iw are increasing (step S104: No), there is no need to switch the frequency of harmonics Vh, and the series of processes ends.

[0059] If the harmonic superposition frequency switching unit 44 determines that any of the phase currents Iu, Iv, and Iw has increased (step S104: Yes), it then determines whether any of the phase currents Iu, Iv, and Iw has exceeded the first threshold value Th1 (step S106). If 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), the series of processes ends. If the harmonic superposition frequency switching unit 44 determines that any 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). The harmonic superposition unit 41 thereby superimposes the harmonic Vh of the second frequency f2 on the d-axis voltage command value Vd. The control unit 30 then ends the series of processes.

[0060] [Effects of implementation]

[0061] According to the above-described embodiment, the following effects can be obtained.

[0062] (1) The position estimating 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 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 exceeds the first threshold value and switches the frequency of the harmonic Vh superimposed on the d-axis voltage command value Vd from the first frequency f1 to the second frequency f2.

[0063] This configuration increases the frequency of harmonics Vh when starting rotor 12 position estimation using the harmonic superposition method, thereby suppressing degradation of NV characteristics. Furthermore, when the temperature of the motor 11 rises, the frequency of harmonics Vh is reduced, thereby suppressing overheating of the motor 11.

[0064] (2) The detection result of the phase current detection unit 22 that detects the phase currents Iu, Iv, and Iw flowing through the motor 11 is used as a temperature-related value associated with the temperature of the motor 11 .

[0065] According to this configuration, the temperature-related value of the motor 11 can be acquired without adding a new configuration for detecting the temperature of the motor 11 .

[0066] (3) The position estimating unit 32 estimates the position of the rotor 12 using a harmonic superposition method or an induced voltage method. Specifically, the position estimating unit 32 estimates the position of the rotor 12 using the induced voltage method when the rotational speed Fm of the rotor 12 based on the estimation result is greater than or equal to the predetermined rotational speed Fmth. Furthermore, the position estimating unit 32 estimates the position of the rotor 12 using the harmonic superposition method when the rotational speed Fm of the rotor 12 based on the estimation result is less than the predetermined rotational speed Fmth. When the position estimating unit 32 estimates the position of the rotor 12 using the induced voltage method, the harmonic superposition unit 41 does not superimpose the harmonic Vh on the d-axis voltage command value Vd.

[0067] Here, the lower the rotational speed Fm of the rotor 12, the lower the induced voltage. Therefore, when the position estimating unit 32 estimates the position of the rotor 12 using the induced voltage method, the estimation accuracy decreases when the rotational speed Fm of the rotor 12 is low. In this regard, according to this structure, the position estimating unit 32 can estimate the position of the rotor 12 with high accuracy using an appropriate method, either the harmonic superposition method or the induced voltage method, based on the rotational speed Fm of the rotor 12. On the other hand, when the refrigerant used to cool the motor 11 itself circulates through the rotation of the motor 11, if the rotational speed Fm of the rotor 12 is low, the refrigerant flow rate decreases, and the motor 11 is prone to overheating. Therefore, when the temperature of the motor 11 is high, as in the present embodiment, the effect of reducing the frequency of the harmonic Vh is greater.

[0068] (4) The electric compressor 101 includes a compression section 102 for compressing a refrigerant serving as a fluid, and an electric motor M1 for driving the compression section 102. As described above, by switching the frequency of the harmonic Vh when estimating the position of the rotor 12 using the harmonic superposition method, overheating of the motor 11 can be suppressed, and degradation of the NV characteristics can be prevented. With this configuration, the vehicle air conditioning system 100 equipped with the electric compressor 101 can suppress overheating of the motor 11 and reduce the perception of noise and vibration by passengers in the vehicle cabin.

[0069] The above-mentioned embodiment may also be modified as follows. In addition, the above-mentioned embodiment and the following other examples may be combined with each other within the scope of no technical contradiction.

[0070] ○ When the phase currents Iu, Iv, and Iw of the motor 11 increase, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh from the first frequency f1 to the second frequency f2, but the present invention is not limited thereto. The harmonic superposition frequency switching unit 44 may also switch 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 decrease. Figures 5 and 6 The details are explained.

[0071] The harmonic superposition frequency switching unit 44 maintains the frequency of the harmonic Vh at the second frequency f2 while any one of the phase currents Iu, Iv, and Iw of the motor 11 falls below the first threshold value Th1 and while the frequency remains above the second threshold value Th2. The second threshold value Th2 is a value smaller than the first threshold value Th1. When the frequency of the harmonic Vh is at the second frequency f2, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to the first frequency f1 after any one of the phase currents Iu, Iv, and Iw of the motor 11 falls below the second threshold value Th2. As described above, when the frequency of the harmonic Vh is at the first frequency f1, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to the second frequency f2 if any one of the phase currents Iu, Iv, and Iw of the motor 11 exceeds the first threshold value Th1. In other words, a hysteresis is provided in the switching of the frequency of the harmonic Vh. The process of determining that any one of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22 is lower than the second threshold value Th2 is an example of the process of determining that the temperature-related value of the motor 11 is lower than the second threshold value Th2.

[0072] Reference Figure 6 , another example of a series of processes related to setting the frequency of the harmonic Vh will be described. Figure 6 The flowchart shown is Figure 4 In addition to the processing in the flowchart shown, the processing of steps S200 to S202 is also included.

[0073] If the phase currents Iu, Iv, and Iw are not increasing (step S104: No), the harmonic superposition frequency switching unit 44 determines that the phase currents Iu, Iv, and Iw are decreasing, and determines whether any of the phase currents Iu, Iv, and Iw is below the second threshold Th2 (step S200). If the harmonic superposition frequency switching unit 44 determines that none of the phase currents Iu, Iv, and Iw is below the second threshold Th2 (step S200: No), the series of processes ends. If the harmonic superposition frequency switching unit 44 determines that any of the phase currents Iu, Iv, and Iw is below the second threshold Th2 (step S200: Yes), the frequency switching unit 44 switches the frequency of the harmonic Vh from the second frequency f2 to the first frequency f1 (step S202). The harmonic superposition unit 41 thus superimposes the harmonic Vh of the first frequency f1 on the d-axis voltage command value Vd. The control unit 30 then ends the series of processes.

[0074] According to this configuration, the frequency of the harmonic Vh can be switched appropriately according to the temperature of the motor 11. Furthermore, by providing hysteresis in the switching of the frequency of the harmonic Vh, it is possible to suppress frequent switching of the frequency of the harmonic Vh.

[0075] In this other example, the frequency of the harmonic Vh may be set to the second frequency f2 when the motor 11 is started.

[0076] 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, but this is not limiting. 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 above-described configuration, the motor drive device 10 may include a temperature detection unit attached to the motor 11 to detect the temperature of the motor 11. The temperature detection unit may be implemented, for example, by a thermocouple and a functional unit that performs A / D conversion on the measurement results obtained by the thermocouple.

[0077] In this case, the detection result of the temperature detection unit is used as the temperature-related value of the motor 11. Furthermore, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh by comparing the temperature-related value of the motor 11 based on the detection result of the temperature detection unit with the first threshold value Th1 and the second threshold value Th2. In this case, the first threshold value Th1 and the second threshold value Th2 are values ​​based on the heat-resistant temperature of the motor 11. Specifically, the first threshold value Th1 indicates a temperature higher than the average temperature of the motor 11 during normal operation. Furthermore, the second threshold value Th2 is a value lower than the first threshold value Th1.

[0078] The first threshold value Th1 is based on the average temperature of the motor 11 during normal operation, but is not limited to this. The first threshold value Th1 may also be based on a statistical value such as the median, average, or mode of the temperature range that the motor 11 can take. Furthermore, the first threshold value Th1 may also be based on a statistical value such as the median, average, or mode of the heat-resistant temperature range of the motor 11.

[0079] The harmonic-superimposition frequency switching unit 44 switches 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, but the present invention is not limited to this. The harmonic-superimposition frequency switching unit 44 may also switch the frequency of the harmonic Vh based on a statistical value such as the median value, average value, maximum value, or minimum value of the phase currents Iu, Iv, and Iw detected by the phase current detection unit 22.

[0080] The position estimating unit 32 estimates the position of the rotor 12 using a harmonic superposition method or an induced voltage method, but the present invention is not limited thereto. The position estimating unit 32 may estimate the position of the rotor 12 using only the harmonic superposition method.

[0081] The harmonic superimposing unit 41 superimposes the harmonic Vh on the d-axis voltage command value Vd, but the present invention is not limited to this. The harmonic superimposing unit 41 may superimpose the harmonic Vh on the current command values ​​IdRef and IqRef.

Claims

1. An electric motor comprising: A motor including a rotor and a stator wound with three-phase coils; an inverter including a driver and a switching element driven by the driver, and configured to drive the motor by driving the switching element; a temperature-related value acquiring unit configured to acquire a temperature-related value associated with the temperature of the motor; and a control unit configured to calculate a plurality of command values ​​for controlling the switching element and control the switching element; 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 based on a harmonic superposition pattern of the harmonic superimposed on at least one of the plurality of command values. The electric motor is characterized in that The frequencies of the harmonics include a first frequency and a second frequency lower than the first frequency, The control unit is further configured to determine whether the temperature-related value exceeds a threshold value, and set the frequency of the harmonic superimposed on at least one of the plurality of command values ​​to the second frequency if the temperature-related value exceeds the threshold value.

2. The electric motor according to claim 1, wherein The frequency of the harmonic is set to the first frequency when the motor is started.

3. The electric motor according to claim 1, wherein The threshold is a first threshold, and a value smaller than the first threshold is a second threshold. The control unit is further configured to determine whether the temperature correlation value is lower than the second threshold value when the frequency of the harmonic is the second frequency, and set the frequency of the harmonic to the first frequency when the temperature correlation value is lower than the second threshold value.

4. The electric motor according to claim 1, wherein The temperature-related value acquisition unit includes a phase current detection unit configured to detect a phase current flowing through the motor. The temperature-related value includes a detection result of the phase current detection unit.

5. The electric motor according to claim 1, wherein The temperature-related value acquisition unit includes a temperature detection unit installed on the motor and configured to detect the temperature of the motor. The temperature-related value includes a detection result of the temperature detection unit.

6. The electric motor according to claim 1, wherein The control unit is further configured to estimate the position of the rotor by an induced voltage method based on the induced voltage generated in the three-phase coils when the rotation speed of the rotor is greater than a given rotation speed, and to estimate the position of the rotor by the harmonic superposition method when the rotation speed is less than the given rotation speed. When estimating the position of the rotor by the induced voltage method, the harmonics are not superimposed.

7. An electric compressor, characterized in that: have: a compression unit configured to compress the fluid; and The electric motor according to any one of claims 1 to 6 is configured to drive the compression unit.

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