Motor, and motor compressor

Abstract

To provide a motor capable of accurately estimating a position of a rotor, and a motor compressor.SOLUTION: A control unit 30 comprises a positional estimation unit 32, a harmonic superposing unit 41, and a harmonic superposing frequency switching unit 44. The positional estimation unit 32 estimates a position of a rotor 12 on the basis of induced voltages generated on three-phase coils, or estimates the position of the rotor 12 by a harmonic superposing method based on a harmonic which is superposed on a command value. The harmonic superposing unit 41 superposes a harmonic switched by the harmonic superposing frequency switching unit 44 on the command value. The harmonic superposing frequency switching unit 44 switches harmonic frequency so that the harmonic frequency and a noise frequency in a 6n'th order (n is a positive integer) harmonic noise component of a motor 11 do not coincide with each other.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 by sensorless control of an inverter, it is necessary to estimate the rotor position of the motor. Sensorless control is a control method that drives a motor without using a hardware position sensor by estimating the rotor position using software. Conventional methods for estimating rotor position include, for example, the induced voltage method and the harmonic superposition method. The induced voltage method estimates the rotor position by using the induced voltage generated by driving the motor. The harmonic superposition method described in Patent Document 1 estimates the rotor position by superimposing harmonic components on the voltage command value or current command value to the motor. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-172324 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, motors may generate motor noise due to torque ripple, etc. When this motor noise matches the harmonic components superimposed on the voltage command value or current command value to the motor, it can be difficult to estimate the rotor position. With the method disclosed in Patent Document 1, when the motor noise matches the harmonic components superimposed on the voltage command value or current command value to the motor, it is difficult to accurately estimate the rotor position. [Means for solving the problem]

[0005] 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, an inverter having switching elements driven by the driver and driving the motor with the switching elements, and a control unit that calculates multiple command values used to control the switching elements and controls the switching elements, wherein the control unit comprises a position estimation unit that estimates the position of the rotor using a harmonic superposition method based on harmonics superimposed on the command values, a harmonic superposition frequency switching unit that switches the harmonic frequencies of the harmonics based on the estimation results of the position estimation unit, and a harmonic superposition unit that superimposes the harmonic, the harmonic whose frequency has been switched by the harmonic superposition frequency switching unit, on the command value, and the harmonic superposition frequency switching unit switches the harmonic frequency based on the estimation results so that the harmonic frequency does not match the noise frequency of a 6nth-order (n is a positive integer) harmonic noise component of the motor.

[0006] With this configuration, the rotor position can be estimated with high accuracy. In an electric motor that achieves the above-mentioned object, the harmonic superposition frequency switching unit may switch the first harmonic, which is the harmonic superimposed on the command value, to a second harmonic having a frequency different from that of the first harmonic, when the rotor rotation speed based on the estimation result matches a switching threshold based on the 6n-th order harmonic noise component.

[0007] According to this configuration, it is possible to prevent the frequency of the harmonic from becoming close to the frequency of the 6n-th harmonic noise component. In an electric motor that achieves the above object, the harmonic superposition unit includes a first harmonic superposition unit that superimposes the first harmonic on the command value, and a second harmonic superposition unit that superimposes the second harmonic, which has a frequency lower than that of the first harmonic, on the command value; the position estimation unit includes a first position estimation unit that estimates a position of the rotor by the harmonic superposition method based on the first harmonic, and a second position estimation unit that estimates a position of the rotor by the harmonic superposition method based on the second harmonic; the control unit includes an estimation result switching unit that switches the estimation result to be output to the harmonic superposition frequency switching unit between the estimation result estimated by the first position estimation unit and the estimation result estimated by the second position estimation unit; and the harmonic superposition frequency switching unit is configured to switch the estimation result when a change over time in the rotation speed increases. When the rotation speed based on the estimation result output by the switching unit matches a switching calculation start threshold that is smaller than the switching threshold by a predetermined value, the switching unit may switch to superimposing both the first harmonic and the second harmonic on the command value, and when the rotation speed matches the switching threshold, the switching unit may switch to superimposing only the second harmonic on the command value, and when a change in the rotation speed over time is increasing, the estimation result switching unit may output the estimation result of the first position estimation unit to the harmonic superimposition frequency switching unit while only the first harmonic is superimposed on the command value and while both the first harmonic and the second harmonic are superimposed on the command value, and output the estimation result of the second position estimation unit to the harmonic superimposition frequency switching unit while only the second harmonic is superimposed on the command value.

[0008] According to this configuration, it is possible to suppress a decrease in accuracy of rotor position estimation that occurs when switching between the first harmonic and the second harmonic. In an electric motor that achieves the above-mentioned object, the harmonic superposition frequency switching unit may switch the second harmonic, which is the harmonic superimposed on the command value, to a first harmonic having a frequency different from that of the second harmonic, when the rotor rotation speed based on the estimation result matches a switching threshold based on the 6n-th order harmonic noise component.

[0009] According to this configuration, it is possible to prevent the frequency of the harmonic from becoming close to the frequency of the 6n-th harmonic noise component. In an electric motor that achieves the above object, the harmonic superposition unit includes a first harmonic superposition unit that superimposes the first harmonic on the command value, and a second harmonic superposition unit that superimposes the second harmonic, which has a frequency lower than that of the first harmonic, on the command value; the position estimation unit includes a first position estimation unit that estimates a position of the rotor by the harmonic superposition method based on the first harmonic, and a second position estimation unit that estimates a position of the rotor by the harmonic superposition method based on the second harmonic; the control unit includes an estimation result switching unit that switches the estimation result to be output to the harmonic superposition frequency switching unit between the estimation result estimated by the first position estimation unit and the estimation result estimated by the second position estimation unit; and the harmonic superposition frequency switching unit switches the estimation result when the change over time of the rotation speed is decreasing. When the rotation speed based on the estimation result output by the switching unit matches a switching calculation start threshold that is larger than the switching threshold by a predetermined value, the switching unit may switch to superimposing both the first harmonic and the second harmonic on the command value, and when the rotation speed matches the switching threshold, the switching unit may switch to superimposing only the first harmonic on the command value, and when a change over time in the rotation speed is decreasing, the estimation result switching unit may output the estimation result of the second position estimation unit to the harmonic superimposition frequency switching unit while only the second harmonic is superimposed on the command value and while both the first harmonic and the second harmonic are superimposed on the command value, and output the estimation result of the first position estimation unit to the harmonic superimposition frequency switching unit while only the first harmonic is superimposed on the command value.

[0010] According to this configuration, it is possible to suppress a decrease in accuracy of rotor position estimation that occurs when switching between the first harmonic and the second harmonic. The electric compressor that achieves the above object is characterized by including a compression section that compresses a fluid, and any one of the electric motors described above that drives the compression section.

[0011] With this configuration, the same effects as those of the electric motor described above can be obtained. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide an electric motor and an electric compressor that are capable of estimating the rotor position with high accuracy. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a vehicle air conditioner according to the first embodiment. [Figure 2] FIG. 2 is a graph showing the relationship between motor noise and the rotation speed of the motor. [Figure 3] FIG. 3 is a flowchart used to explain a series of processes performed by the control unit. [Figure 4] FIG. 4 is a diagram showing an example of the configuration of a vehicle air conditioner according to the second embodiment. [Figure 5] FIG. 5 is a graph showing the relationship between motor noise and the rotation speed of the motor. [Figure 6] FIG. 6 is a graph showing the relationship between motor noise and the rotation speed of the motor. DETAILED DESCRIPTION OF THE INVENTION

[0014] [First embodiment] Hereinafter, a first embodiment of an electric motor and an electric compressor will be described with reference to the drawings.

[0015] <Overall structure> As shown in FIG. 1, a vehicle air conditioner 100 of the first 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 has, 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 by performing heat exchange and expansion of the refrigerant with the refrigerant circuit 103. The electric compressor 101 discharges oil together with the compressed refrigerant.

[0016] 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.

[0017] <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 the compression unit 102.

[0018] 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, a control unit 30, and a storage unit 80.

[0019] The inverter 21 includes six switching elements Q1 to Q6, diodes D1 to D6, and a driver 51. For example, IGBTs (Insulated Gate Bipolar Transistors) are used as the switching elements Q1 to Q6. When the switching elements Q1 to Q6 and the diodes D1 to D6 are integrated, MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used. 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.

[0020] The connection line between switching element Q1 and switching element Q2 branches off midway and is connected to coil U. The connection line between switching element Q3 and switching element Q4 branches off midway and is connected to coil V. The connection line between switching element Q5 and switching element Q6 branches off midway and is connected to coil W.

[0021] The driver 51 drives the switching elements Q1 to Q6, thereby driving the motor 11. The battery BA is a chargeable and dischargeable power storage device. The rated voltage of the battery BA is, for example, 800 V.

[0022] The phase current detection unit 22 detects the phase currents flowing through the motor 11. The phase current detection unit 22 detects the phase currents for at least two phases. 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. The phase currents for two of the three phases may be detected, and the phase current for the remaining phase may be calculated from the phase currents for 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 respective phases of the motor 11.

[0023] 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 is realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware. The program may be stored in advance in a storage device (not shown) that includes a non-transitory storage medium such as an HDD (Hard Disk Drive) or flash memory provided in the storage unit 80.

[0024] The storage unit 80 may be realized by the various storage devices described above, or an EEPROM (Electrically Erasable Programmable Read Only Memory), a ROM (Read Only Memory), a RAM (Random Access Memory), or the like.

[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 controls the inverter 21 using sensorless control. Sensorless control is a method of controlling the inverter 21 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 using sensorless control 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 of estimating the position Hm of the rotor 12 based on induced voltages generated in three-phase coils U, V, and W. The harmonic superposition method is a method of estimating the position Hm of the rotor 12 by superimposing harmonics on a command value. The motor 11 is driven by controlling the inverter 21. First, position estimation using the induced voltage method and position estimation using the harmonic superposition method will be described, and the process by which the control unit 30 switches between the 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 a 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 a rotational speed Fm of the rotor 12 based on the induced voltages.

[0029] 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.

[0030] 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. As the feedback control, for example, proportional-integral control can be used.

[0031] 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.

[0032] 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. For example, proportional-integral control can be used as the feedback control.

[0033] 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 into voltage command values Vα and Vβ in coordinates from the dq coordinate system to 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 for three phases. The PWM control unit 38 may also 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.

[0034] The inverter 21 is controlled based on the voltage command values Vu, Vv, and Vw. Specifically, the PWM control unit 38 generates a PWM signal based on the voltage command values Vu, Vv, and Vw and a carrier frequency, and controls the switching elements Q1 to Q6 by the PWM signal.

[0035] <Location estimation using harmonic superposition method> Next, the functions of the control unit 30 when performing position estimation using the harmonic superposition method will be described. As shown in Fig. 1, 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, a PWM control unit 38, a harmonic superposition unit 41, an addition unit 42, a band-stop filter 43, and a harmonic superposition frequency switching unit 44. The current coordinate conversion unit 31, the subtraction units 33, 35, and 36, the speed control unit 34, the current control unit 37, and the PWM control unit 38 have the same functions as in the case of the induced voltage method. Therefore, their description will be omitted.

[0036] 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 harmonic frequency f is, for example, a frequency that is independent of the rotation of the motor 11.

[0037] 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 in the harmonic superimposing method. The control unit 30 may superimpose the harmonics Vh on a predetermined command value defined by any one of the command values of 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 only the three-phase voltage command values Vu, Vv, and Vw, and cause the position estimator 32 to estimate the position of the rotor 12.

[0038] 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 due to the harmonic Vh. The band-stop filter 43 removes these frequency components.

[0039] 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 an axis error Δθc from, for example, the current harmonics. The axis error Δθc is the error 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.

[0040] The harmonic superposition frequency switching unit 44 switches the harmonics Vh that the harmonic superposition unit 41 superimposes on the d-axis voltage command value Vd, based on the rotation speed Fm estimated by the position estimator 32. Specifically, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonics Vh so that the frequency of the harmonics Vh superimposed on the d-axis voltage command value Vd does not match the frequency of motor noise of the motor 11 caused by torque ripple or the like.

[0041] <Relationship between harmonic Vh frequency and motor noise> 2 shows a waveform W11 indicating 18th-order harmonic noise of motor 11, a waveform W12 indicating 12th-order harmonic noise of motor 11, and a waveform W13 indicating 6th-order harmonic noise. Here, motor 11 generates motor noise due to torque ripple and the like. Specifically, motor 11 generates motor noise with a frequency component that is 6n times the fundamental frequency of the motor voltage (n is a positive integer). Therefore, harmonic noise that is 6n times the fundamental frequency of the motor 11 voltage is superimposed on the detection result of phase current detection unit 22. As waveforms W11 to W13 show, the frequency of the 6n-order harmonic noise component increases as the rotation speed of rotor 12 increases.

[0042] 2 also shows waveforms W21 and W22 indicating the frequency of the harmonic Vh switched by the harmonic superposition frequency switching unit 44. As shown by waveform W21, the harmonic superposition frequency switching unit 44 selects 1000 Hz as the frequency of the harmonic Vh when the rotation speed of the rotor 12 is between 0 and 600 rpm. In the following description, 1000 Hz will also be referred to as the initial superposition frequency. As shown by waveform W11, the 18th or 6nth harmonic noise component becomes 1000 Hz when the rotation speed of the rotor 12 is approximately 650 rpm. In this case, it is difficult for the position estimator 32 to estimate the position of the rotor 12 using the harmonic superposition method based on the detection results of the phase current detector 22 on which noise is superimposed. Therefore, the harmonic superimposing frequency switching unit 44 switches the frequency of the harmonic Vh so that the frequency of the harmonic Vh does not match the 6n-th harmonic noise component.

[0043] 2, the harmonic superposition frequency switching unit 44 determines whether the rotation speed of the rotor 12 based on the rotation speed Fm of the rotor 12 estimated by the position estimator 32 matches a switching threshold. The switching threshold is, for example, a value smaller than a value indicating the rotation speed of the rotor 12 at the timing when the frequency of the 6n-th harmonic noise component matches the frequency of the harmonic Vh. In this example, the rotation speed of the rotor 12 at the timing when the frequency of the 18th or 6n-th harmonic noise component becomes 1000 [Hz], matching the frequency of the harmonic Vh, is approximately 650 [rpm]. Accordingly, the switching threshold is set to 600 [rpm], which is smaller than 650 [rpm].

[0044] Information indicating the switching threshold is pre-stored in, for example, the storage unit 80. The harmonic superposition frequency switching unit 44 compares the switching threshold read from the storage unit 80 with the rotation speed based on the estimated rotation speed Fm. If the rotation speed is increasing over time, the harmonic superposition frequency switching unit 44 maintains the frequency of the harmonic Vh at 1000 [Hz] until the rotation speed increases from 0 [rpm] and reaches the switching threshold of 600 [rpm]. As shown by waveform W22, when the rotation speed reaches the switching threshold as the rotation speed Fm increases, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to 750 [Hz], which is lower than 1000 [Hz]. In the first embodiment, the harmonic Vh with a frequency of 1000 [Hz] is an example of a first harmonic. The harmonic Vh with a frequency of 750 [Hz] is an example of a second harmonic. As a result, the harmonic superimposing frequency switching unit 44 switches the frequency of the harmonic Vh so that the frequency of the harmonic Vh does not match the frequency of the 6n-th harmonic noise component.

[0045] Furthermore, when the rotation speed based on the estimated rotation speed Fm is less than a predetermined threshold, the position estimation unit 32 estimates the position of the rotor 12 using the harmonic superposition method, and when the estimated rotation speed is equal to or greater than the predetermined threshold, the position estimation unit 32 estimates the position of the rotor 12 using the induced voltage method. Here, the lower the speed of the electric motor M1, 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 if the speed of the electric motor M1 is low. Therefore, the predetermined threshold is, for example, a value indicating the rotation speed of the rotor 12 at which the position of the rotor 12 can be estimated using the induced voltage method.

[0046] 2, the predetermined threshold is set to 700 rpm. Information indicating the predetermined threshold is stored in advance in, for example, the storage unit 80. The position estimation unit 32 compares the predetermined threshold read from the storage unit 80 with the rotation number based on the estimated rotation speed Fm, and if the rotation number is less than the predetermined threshold, estimates the position of the rotor 12 using the harmonic superposition method, while if the rotation number is equal to or greater than the predetermined threshold, estimates the position of the rotor 12 using the induced voltage method.

[0047] When the position estimation unit 32 estimates the position of the rotor 12 using the induced voltage method, the harmonic superposition frequency switching unit 44 switches so as not to superimpose the harmonics Vh on the d-axis voltage command value Vd. Accordingly, the harmonic superposition unit 41 does not generate the harmonics Vh and does not superimpose the harmonics Vh on the d-axis voltage command value Vd.

[0048] Here, the 6n-th harmonic noise components indicated by waveforms W11 to W13 vary in appearance depending on the characteristics of the electric motor M1. Therefore, information indicating a switching threshold value according to the characteristics of the electric motor M1 is pre-stored in the storage unit 80. Furthermore, the rotational speed of the rotor 12 at which the position of the rotor 12 can be estimated by the induced voltage method varies depending on the characteristics of the electric motor M1. Therefore, information indicating a predetermined threshold value according to the characteristics of the electric motor M1 is pre-stored in the storage unit 80.

[0049] <Processing of the control unit 30> A series of processes executed by the control unit 30 will be described with reference to Fig. 3. The processes of the flowchart shown in Fig. 3 are executed when the operation of the electric motor M1 starts. In parallel with the processes of the flowchart shown in Fig. 3, the PWM control unit 38 executes basic processes related to the control of the switching elements Q1 to Q6 using PWM signals.

[0050] First, the harmonic superposition unit 41 superimposes the harmonic Vh of the initial superposition frequency onto the d-axis voltage command value Vd when the electric motor M1 starts operating (step S100). Next, the position estimation unit 32 estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 using a harmonic superposition method (step S102). 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 onto the d-axis voltage command value Vd by the process of step S100, 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.

[0051] Next, the position estimation unit 32 determines whether the rotation speed based on the rotation speed Fm matches the switching threshold based on the estimated rotation speed Fm (step S104). If the harmonic superposition frequency switching unit 44 determines that the rotation speed estimated by the position estimation unit 32 does not match the switching threshold (step S104; NO), the harmonic superposition frequency switching unit 44 does not switch the frequency of the harmonic Vh and proceeds to step S102. If the position estimation unit 32 determines that the rotation speed matches the switching threshold as the rotation speed Fm increases (step S104; YES), the position estimation unit 32 determines whether the rotation speed is equal to or greater than a predetermined threshold (step S106). If the position estimation unit 32 determines that the rotation speed is less than the predetermined threshold (step S106; NO), the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to a frequency lower than the previous frequency (in this case, the initial superposition frequency) (step S108) and proceeds to step S102. If the position estimation unit 32 determines that the rotation speed is equal to or greater than the predetermined threshold value (step S106: YES), it proceeds to estimate the position of the rotor 12 using the induced voltage method (step S110), and ends the series of processes.

[0052] [Effects of the first embodiment] According to the first embodiment, the following effects can be obtained. (1-1) The control unit 30 includes a position estimation unit 32, a harmonic superposition unit 41, and a harmonic superposition frequency switching unit 44. The position estimation unit 32 estimates the position of the rotor 12 based on induced voltages generated in the three-phase coils U, V, and W, or estimates the position of the rotor 12 using a harmonic superposition method based on harmonics Vh superimposed on the d-axis voltage command value Vd. The harmonic superposition frequency switching unit 44 switches the harmonics Vh to be superimposed on the d-axis voltage command value Vd based on the estimation result of the position estimation unit 32. The harmonic superposition unit 41 superimposes the harmonic Vh switched by the harmonic superposition frequency switching unit 44 on the d-axis voltage command value Vd. Furthermore, the position estimation unit 32 estimates the position of the rotor 12 using the induced voltage method when the rotation speed of the rotor 12 based on the estimation result is equal to or greater than a predetermined threshold. Furthermore, when the rotation speed of the rotor 12 based on the estimation result is less than a predetermined threshold, the position estimation unit 32 estimates the position of the rotor 12 using a harmonic superposition method based on the harmonic Vh. When the rotation speed of the rotor 12 based on the estimation result of the position estimation unit 32 matches the switching threshold in a case where the change over time of the rotor 12 is increasing, the harmonic superposition frequency switching unit 44 switches the first harmonic, which is the harmonic Vh superimposed on the d-axis voltage command value Vd, to a second harmonic having a different frequency from the first harmonic. Specifically, when the change over time of the rotation speed of the rotor 12 is increasing, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to the second harmonic, which is lower than the frequency of the first harmonic. More specifically, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to 750 [Hz], which is lower than 1000 [Hz]. Furthermore, when the position estimator 32 estimates the position of the rotor 12 using the induced voltage method, the harmonic superposition frequency switcher 44 does not superimpose the harmonic Vh on the d-axis voltage command value Vd.

[0053] With this configuration, the position estimator 32 can accurately estimate the position of the rotor 12 using the harmonic superposition method without being affected by the frequency of motor noise of the motor 11 due to torque ripple, etc. Furthermore, when switching of the first harmonic is required, the frequency of the first harmonic and the frequency of the 6n-th harmonic noise component become close to each other. Therefore, when the rotation speed of the rotor 12 is changing rapidly over time, using the second harmonic, which has a frequency lower than the frequency of the first harmonic, can prevent the frequency of the second harmonic and the frequency of the 6n-th harmonic noise component from becoming close to each other. Therefore, with this configuration, the harmonic superposition frequency switcher 44 can superimpose an appropriate harmonic Vh on the d-axis voltage command value Vd in accordance with the change over time of the rotation speed of the rotor 12.

[0054] (1-2) The electric compressor 101 includes a compression unit 102 that compresses a fluid refrigerant, and an electric motor M1 that drives the compression unit 102. Here, the electric compressor 101 can appropriately drive the motor 11 by accurately estimating the position of the rotor 12 using a harmonic superposition method. Therefore, the motor 11 operates while reducing noise and vibration. With this configuration, the vehicle air conditioner 100 equipped with the electric compressor 101 can make noise and vibration less noticeable to passengers in the vehicle cabin.

[0055] [Second embodiment] In the first embodiment described above, the position estimation unit 32 starts estimating the position of the rotor 12 based on the harmonic Vh after switching at the timing when the harmonic Vh is switched in accordance with the determination based on the switching threshold. In the second embodiment, the position estimation unit 32 starts estimating the position of the rotor 12 based on the harmonic Vh after switching in advance.

[0056] <Overall structure> 4, the vehicle air conditioner 100 of the second embodiment includes a control unit 30a instead of the control unit 30 included in the vehicle air conditioner 100 of the first embodiment. The position estimator 32 included in the control unit 30a includes a first position estimator 32a and a second position estimator 32b. The harmonic superimposing unit 41 included in the control unit 30a includes a first harmonic superimposing unit 41a and a second harmonic superimposing unit 41b. The control unit 30a also includes an estimation result switcher 47 in addition to the components included in the control unit 30.

[0057] The first harmonic superimposing unit 41a generates the harmonic Vh based on an instruction from the harmonic superimposing frequency switching unit 44. In the following description, the harmonic Vh generated by the first harmonic superimposing unit 41a will be referred to as the harmonic Vha, and the harmonic Vh generated by the second harmonic superimposing unit 41b will be referred to as the harmonic Vhb. Furthermore, when the harmonic Vha and the harmonic Vhb are not to be distinguished from each other, they will simply be referred to as the harmonic Vh. The adder 42 adds the harmonic Vha generated by the first harmonic superimposing unit 41a to the d-axis voltage command value Vd. As a result, the harmonic Vha is superimposed on the d-axis voltage command value Vd. The second harmonic superimposing unit 41b generates the harmonic Vhb based on an instruction from the harmonic superimposing frequency switching unit 44. The adder 42 adds the harmonic Vhb generated by the second harmonic superimposing unit 41b to the d-axis voltage command value Vd, thereby superimposing the harmonic Vhb on the d-axis voltage command value Vd.

[0058] Here, the harmonic Vha and the harmonic Vhb have different harmonic frequencies f. In the following description, it is assumed that the frequency of the harmonic Vha is 1000 [Hz] and the frequency of the harmonic Vhb is 750 [Hz]. In the second embodiment, the harmonic Vha is an example of a first harmonic, and the harmonic Vhb is an example of a second harmonic.

[0059] The harmonic superimposing frequency switching unit 44 controls the first harmonic superimposing unit 41a and the second harmonic superimposing unit 41b based on the rotation speed Fm output by the estimation result switching unit 47. Specifically, the harmonic superimposing frequency switching unit 44 controls the first harmonic superimposing unit 41a and the second harmonic superimposing unit 41b according to one of a first pattern, a second pattern, and a third pattern.

[0060] In the first pattern, the harmonic superposition frequency switching unit 44 instructs only the first harmonic superposition unit 41a to generate the harmonic Vha and superimpose the harmonic Vha on the d-axis voltage command value Vd. In the second pattern, the harmonic superposition frequency switching unit 44 instructs both the first harmonic superposition unit 41a and the second harmonic superposition unit 41b to generate the harmonic Vh and superimpose the harmonic Vha and Vhb on the d-axis voltage command value Vd. In the third pattern, the harmonic superposition frequency switching unit 44 instructs only the second harmonic superposition unit 41b to generate the harmonic Vhb and superimpose the harmonic Vhb on the d-axis voltage command value Vd.

[0061] The first position estimator 32a 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 converter 31. As described above, 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 first position estimator 32a 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 harmonic Vh used for estimation by the first position estimator 32a is the harmonic Vha superimposed on the d-axis voltage command value Vd by the first harmonic superimposing unit 41a. Therefore, the first position estimator 32a estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 only in the first pattern and the second pattern.

[0062] Furthermore, the second position estimator 32b 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 converter 31. As described above, 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 second position estimator 32b 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 harmonic Vh used for estimation by the second position estimator 32b is the harmonic Vhb superimposed on the d-axis voltage command value Vd by the second harmonic superimposing unit 41b. Therefore, the second position estimator 32b estimates the position Hm of the rotor 12 and the rotational speed Fm of the rotor 12 only in the second pattern and the third pattern. In the following description, when the first position estimation unit 32a and the second position estimation unit 32b are not to be distinguished from each other, they will be simply referred to as the position estimation unit 32.

[0063] When both the first position estimation unit 32a and the second position estimation unit 32b output the rotation speed Fm (i.e., the second pattern), the estimation result switching unit 47 outputs information that was output in the pattern immediately before the transition to the second pattern. Specifically, when the pattern immediately before the transition to the second pattern is the first pattern, the estimation result switching unit 47 outputs the rotation speed Fm based on the estimation result of the first position estimation unit 32a to the harmonic superposition frequency switching unit 44. On the other hand, when the pattern immediately before the transition to the second pattern is the third pattern, the estimation result switching unit 47 outputs the rotation speed Fm based on the estimation result of the second position estimation unit 32b to the harmonic superposition frequency switching unit 44.

[0064] Furthermore, in the first pattern, since only first position estimator 32a outputs rotation speed Fm, estimation result switcher 47 outputs rotation speed Fm based on the estimation result of first position estimator 32a to harmonic superposition frequency switcher 44. Furthermore, in the third pattern, since only second position estimator 32b outputs rotation speed Fm, estimation result switcher 47 outputs rotation speed Fm based on the estimation result of second position estimator 32b to harmonic superposition frequency switcher 44.

[0065] <Switching timing for each pattern> Fig. 5 shows a waveform W11 indicating the 18th-order noise of the motor 11, a waveform W12 indicating the 12th-order noise of the motor 11, and a waveform W13 indicating the 6th-order noise of the motor 11. Fig. 5 also shows waveforms W31 and W32 indicating the frequency of the harmonic Vh switched by the harmonic superimposition frequency switching unit 44. Specifically, the waveform W31 is a waveform indicating the harmonic Vha, and the waveform W32 is a waveform indicating the harmonic Vhb.

[0066] When switching the frequency of the harmonics Vh, the harmonic superposition frequency switching unit 44 of this embodiment also superimposes the post-switching harmonics Vh on the d-axis voltage command value Vd before the switching timing so that the frequency of the harmonics Vh superimposed on the d-axis voltage command value Vd does not match the frequency of motor noise of the motor 11 caused by torque ripple, etc. In other words, when switching the harmonics Vh from the harmonic Vha to the harmonic Vhb, the harmonic superposition frequency switching unit 44 transitions to the third pattern via the first and second patterns.

[0067] First, the harmonic superposition frequency switching unit 44 determines whether the rotation speed of the rotor 12 based on the rotation speed Fm output by the estimation result switching unit 47 matches the switching calculation start threshold. The switching calculation start threshold is a threshold that is smaller than the switching threshold by a predetermined value. In the example shown in Fig. 5, the switching threshold is a value indicating 600 [rpm], and the switching calculation start threshold is a value indicating 550 [rpm].

[0068] Information indicating the switching calculation start threshold is stored in advance in, for example, the storage unit 80. The harmonic superposition frequency switching unit 44 compares the switching calculation start threshold read from the storage unit 80 with the rotation speed, and controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the first pattern until the rotation speed Fm matches the switching calculation start threshold. As shown by the waveform W31, when the rotation speed Fm is between 0 and 550 rpm, control is performed according to the first pattern, and therefore only the first harmonic superposition unit 41a generates the harmonic Vha and superimposes the harmonic Vha on the d-axis voltage command value Vd. Furthermore, in the first pattern, only the first position estimator 32a estimates the position of the rotor 12.

[0069] When the rotation speed Fm increases and coincides with the switching calculation start threshold, the harmonic superposition frequency switching unit 44 controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the second pattern. As shown by waveforms W31 and W32, between 550 and 600 rpm, the first harmonic superposition unit 41a and the second harmonic superposition unit 41b both generate harmonics Vh and superimpose the harmonics Vh on the d-axis voltage command value Vd due to control according to the second pattern. Furthermore, in the second pattern, both the first position estimator 32a and the second position estimator 32b estimate the position of the rotor 12.

[0070] When the rotation speed Fm further increases and coincides with the switching threshold, the harmonic superposition frequency switching unit 44 controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the third pattern. As shown by waveform W32, between 600 and 700 rpm, control is performed according to the third pattern, and only the second harmonic superposition unit 41b generates the harmonic Vhb and superimposes it on the d-axis voltage command value Vd. Furthermore, in the third pattern, only the second position estimator 32b estimates the position of the rotor 12.

[0071] The process of switching between the harmonic superposition method and the induced voltage method is performed by the first position estimation unit 32a when the pattern immediately before switching is the first pattern, and by the second position estimation unit 32b when the pattern immediately before switching is the third pattern. Furthermore, the process of switching between the harmonic superposition method and the induced voltage method is performed by the first position estimation unit 32a when the pattern immediately before switching is the second pattern and the pattern immediately before switching is the first pattern, and by the second position estimation unit 32b when the pattern immediately before switching is the third pattern. The process of switching between the harmonic superposition method and the induced voltage method by the first position estimation unit 32a or the second position estimation unit 32b based on a predetermined threshold is the same as in the above-described embodiment, and therefore will not be described again.

[0072] [Effects of the second embodiment] According to the second embodiment, the following effects can be obtained. (2-1) The harmonic superimposing unit 41 includes a first harmonic superimposing unit 41a and a second harmonic superimposing unit 41b. The first harmonic superimposing unit 41a superimposes the harmonic Vha on the d-axis voltage command value Vd. The second harmonic superimposing unit 41b superimposes the harmonic Vhb on the d-axis voltage command value Vd. The position estimating unit 32 includes a first position estimating unit 32a and a second position estimating unit 32b. The first position estimating unit 32a estimates the position of the rotor 12 using a harmonic superimposing method based on the harmonic Vha. The second position estimating unit 32b estimates the position of the rotor 12 using a harmonic superimposing method based on the harmonic Vhb. The control unit 30a includes an estimation result switching unit 47. The estimation result switching unit 47 switches between the estimation result estimated by the first position estimating unit 32a and the estimation result estimated by the second position estimating unit 32b, and outputs the result to the harmonic superimposing frequency switching unit 44.

[0073] When the change over time of the rotor 12 is increasing, and when the rotor 12 based on the estimation result output by the estimation result switching unit 47 matches the switching calculation start threshold, the harmonic superposition frequency switching unit 44 switches to superimposing both the harmonics Vha and Vhb on the d-axis voltage command value Vd, and when the rotor 12 matches the switching threshold, switches to superimposing only the harmonic Vhb on the d-axis voltage command value Vd.

[0074] When the change over time of the rotor 12 is increasing, the estimation result switching unit 47 outputs the estimation result of the first position estimator 32a to the harmonic superposition frequency switching unit 44 while only the harmonic Vha is superimposed on the d-axis voltage command value Vd and while both the harmonics Vha and Vhb are superimposed on the d-axis voltage command value Vd, and outputs the estimation result of the second position estimator 32b to the estimation result switching unit 47 while only the harmonic Vhb is superimposed on the d-axis voltage command value Vd.

[0075] As described above, the position estimator 32 calculates the position error Δθc from the current harmonics contained in the q-axis current Iq and estimates the position of the rotor 12 so that the position error Δθc becomes zero. Therefore, when estimating the position of the rotor 12 based on the harmonic Vh, the position estimator 32 performs the estimation process multiple times before the result stabilizes. Therefore, if the pattern is suddenly shifted from the first pattern to the third pattern, the result of the position estimation based on the harmonic Vhb by the second position estimator 32b will not be stable. Therefore, the accuracy of the position estimation of the rotor 12 may decrease immediately after the pattern shift.

[0076] According to this configuration, the transition is made from the first pattern to the second pattern to the third pattern, thereby preventing a decrease in the accuracy of the position estimation of the rotor 12 due to switching between the harmonics Vha and Vhb.

[0077] The above-described embodiments may be modified as follows: The above-described embodiments and the following modifications may be combined with each other within the scope of technical compatibility. 2 and 5, the case where the sixth-order harmonic noise component and the frequency of the harmonic Vh are prevented from matching is described above, but this is not limited thereto. As described above, the manner in which the 6n-th order harmonic noise component occurs varies depending on the characteristics of the electric motor M1. Therefore, in addition to the sixth-order harmonic noise component, there are also cases where it is required to prevent the 12th order harmonic noise component from matching the frequency of the harmonic Vh.

[0078] 6 shows a waveform W14 indicating the 18th-order noise of the motor 11, a waveform W15 indicating the 12th-order noise of the motor 11, and a waveform W1 indicating the 6th-order noise of the motor 11. As shown by waveforms W14 to W16, the frequency of the 6nth-order harmonic noise component increases as the rotation speed of the rotor 12 increases. In the electric motor M1 having the characteristics shown in FIG. 6, the 6nth-order harmonic noise component exhibits a greater increase in frequency relative to the rotation speed of the rotor 12 than in the electric motor M1 having the characteristics shown in FIGS. 2 and 5. Therefore, it is preferable that the harmonic superposition frequency switching unit 44 switch between two or more harmonics Vh between 0 [rpm] and the predetermined threshold value of 700 [rpm].

[0079] In the example shown in Fig. 6, the switching thresholds are set to 360 [rpm] and 460 [rpm], and the predetermined threshold is set to 700 [rpm]. The harmonic superposition frequency switching unit 44 selects 1000 [Hz] as the frequency of the harmonic Vh when the rotation speed of the rotor 12 is between 0 and 360 [rpm]. Furthermore, the harmonic superposition frequency switching unit 44 selects 800 [Hz] as the frequency of the harmonic Vh when the rotation speed of the rotor 12 is between 360 and 460 [rpm]. Furthermore, the harmonic superposition frequency switching unit 44 selects 680 [Hz] as the frequency of the harmonic Vh when the rotation speed of the rotor 12 is between 460 and 700 [rpm].

[0080] When the frequency of the harmonic wave Vh is switched from 1000 Hz to 800 Hz, 1000 Hz is an example of the first harmonic wave, and 800 Hz is an example of the second harmonic wave. When the frequency of the harmonic wave Vh is switched from 800 Hz to 680 Hz, 800 Hz is an example of the first harmonic wave, and 680 Hz is an example of the second harmonic.

[0081] With this configuration, even if the frequency of the 6n-th harmonic noise component increases significantly with respect to the rotation speed of the rotor 12, the position of the rotor 12 can be estimated with high accuracy by appropriately setting the harmonic Vh. Note that, although the above description has been given of the cases where there is one switching threshold and two switching thresholds, this is not limiting. Two or more switching thresholds may be provided.

[0082] In the above description, when the rotation speed of the rotor 12 increases over time, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to the second harmonic, which is lower than the frequency of the first harmonic. However, this is not limited to this. The rotation speed of the rotor 12 may not necessarily increase over time, but may also decrease. In this case, the harmonic superposition frequency switching unit 44 may switch the frequency of the harmonic Vh from the low-frequency harmonic Vhb to the high-frequency harmonic Vha.

[0083] In this case, when the change in the rotation speed of the rotor 12 over time decreases and the rotation speed of the rotor 12 based on the estimation result of the position estimation unit 32 matches the switching threshold, the harmonic superposition frequency switching unit 44 switches the second harmonic, which is the harmonic Vh, superimposed on the d-axis voltage command value Vd to the first harmonic, which has a different frequency from the second harmonic. Specifically, when the change in the rotation speed of the rotor 12 over time decreases, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to the first harmonic, which has a higher frequency than the second harmonic. More specifically, the harmonic superposition frequency switching unit 44 switches the frequency of the harmonic Vh to 1000 Hz, which is higher than 750 Hz. Furthermore, when the position estimation unit 32 estimates the position of the rotor 12 using the induced voltage method, the harmonic superposition frequency switching unit 44 does not superimpose the harmonic Vh on the d-axis voltage command value Vd.

[0084] According to this configuration, when switching of the second harmonic is required, the frequency of the second harmonic and the frequency of the 6n-th harmonic noise component become closer to each other. Therefore, when the change in the rotation speed of the rotor 12 over time is decreasing, by using the first harmonic having a frequency higher than the frequency of the second harmonic, it is possible to prevent the frequency of the first harmonic and the frequency of the 6n-th harmonic noise component from becoming closer to each other. Therefore, according to this configuration, the harmonic superposition frequency switching unit 44 can superimpose an appropriate harmonic Vh on the d-axis voltage command value Vd in accordance with the change in the rotation speed of the rotor 12 over time.

[0085] Furthermore, when the change over time of the rotor 12 is decreasing, the harmonic superposition frequency switching unit 44 may transition to the first pattern via the third pattern and the second pattern when switching the harmonic Vh from the harmonic Vhb to the harmonic Vha.

[0086] In this case, the harmonic superposition frequency switching unit 44 determines whether the rotation speed of the rotor 12 based on the rotation speed Fm output by the estimation result switching unit 47 matches the switching calculation start threshold. In this case, the switching calculation start threshold is a threshold that is larger than the switching threshold by a predetermined value. For example, if the switching threshold is a value indicating 600 [rpm], the switching calculation start threshold is a value indicating 650 [rpm].

[0087] Information indicating the switching calculation start threshold is stored in advance in, for example, the storage unit 80. The harmonic superposition frequency switching unit 44 compares the switching calculation start threshold read from the storage unit 80 with the rotation speed, and controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the third pattern until the rotation speed Fm matches the switching calculation start threshold. As a result of being controlled according to the third pattern, only the second harmonic superposition unit 41b generates the harmonic Vhb and superimposes the harmonic Vhb on the d-axis voltage command value Vd. Furthermore, in the third pattern, only the second position estimator 32b estimates the position of the rotor 12.

[0088] When the rotation speed Fm decreases and coincides with the switching calculation start threshold, the harmonic superposition frequency switching unit 44 controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the second pattern. As a result of being controlled according to the second pattern, both the first harmonic superposition unit 41a and the second harmonic superposition unit 41b generate the harmonic Vh and superimpose the harmonic Vh on the d-axis voltage command value Vd. Furthermore, in the second pattern, both the first position estimator 32a and the second position estimator 32b estimate the position of the rotor 12.

[0089] When the rotation speed Fm further decreases and coincides with the switching threshold, the harmonic superposition frequency switching unit 44 controls the first harmonic superposition unit 41a and the second harmonic superposition unit 41b according to the first pattern. As a result of being controlled according to the third pattern, only the first harmonic superposition unit 41a generates the harmonic Vha and superimposes the harmonic Vha on the d-axis voltage command value Vd. In addition, in the first pattern, only the second position estimator 32b estimates the position of the rotor 12.

[0090] The process of switching between the harmonic superposition method and the induced voltage method is the same as in the above-described embodiment, and therefore a description thereof will be omitted. In this example, when the change over time of the rotor 12 is decreasing and the rotor 12 based on the estimation result output by the estimation result switching unit 47 matches the switching calculation start threshold, the harmonic superposition frequency switching unit 44 switches to superimposing both the harmonics Vha and Vhb on the d-axis voltage command value Vd, and when the rotor 12 matches the switching threshold, switches to superimposing only the harmonic Vha on the d-axis voltage command value Vd.

[0091] When the change over time of the rotor 12 is decreasing, the estimation result switching unit 47 outputs the estimation result of the second position estimator 32b to the harmonic superposition frequency switching unit 44 while only the harmonic Vhb is superimposed on the d-axis voltage command value Vd and while both the harmonics Vha and Vhb are superimposed on the d-axis voltage command value Vd, and outputs the estimation result of the first position estimator 32a to the estimation result switching unit 47 while only the harmonic Vha is superimposed on the d-axis voltage command value Vd.

[0092] According to this configuration, the transition is made from the third pattern to the second pattern and then to the first pattern, thereby preventing a decrease in the accuracy of the position estimation of the rotor 12 due to switching between the harmonics Vha and Vhb.

[0093] Although the above description has been given of a case in which the harmonic superposition frequency switching unit 44 switches between the first and second harmonic based on a switching threshold, this is not limitative. The harmonic superposition frequency switching unit 44 may switch between the first and second harmonic by a method other than the method using a switching threshold, as long as the frequency of the harmonic superposed in the harmonic superposition method does not match the noise frequency of the 6n-th harmonic noise component of the motor 11.

[0094] For example, a switching range may be used instead of the switching threshold. The switching range ranges from a value that is a predetermined value smaller than the switching threshold to a value that is a predetermined value larger than the switching threshold. When the rotation speed of the rotor 12 matches the switching range, the harmonic superposition frequency switching unit 44 determines that the harmonic frequency matches the noise frequency of the 6n-th harmonic noise component of the motor 11, and switches the harmonic Vh that has been superimposed to a harmonic Vh of a different frequency.

[0095] Although the above description has been given of the case where the harmonic wave Vh is superimposed on the d-axis voltage command value Vd, this is not limiting. The harmonic wave superimposing unit 41, the first harmonic wave superimposing unit 41a, and the second harmonic wave superimposing unit 41b may superimpose the harmonic wave Vh on the current command values IdRef and IqRef. [Explanation of symbols]

[0096] 10...motor drive device, 11...motor, 12...rotor, 13...stator, 21...inverter, 22...phase current detection unit, 23...input voltage detection unit, 30, 30a...control unit, 31...current coordinate conversion unit, 32...position estimation unit, 32a...first position estimation unit, 32b...second position estimation unit, 33...subtraction unit, 34...speed control unit, 35...subtraction unit, 36...subtraction unit, 37...current control unit, 38...PWM control unit, 41...harmonic superposition unit, 41a...first harmonic superposition unit Harmonic superposition unit, 41b...second harmonic superposition unit, 42...addition unit, 43...bandstop filter, 44...harmonic superposition frequency switching unit, 47...estimation result switching unit, 51...driver, 80...storage unit, 100...vehicle air conditioning device, 101...electric compressor, 102...compression unit, 103...refrigerant circuit, Fm...rotational speed, FmRef...rotational speed command value, Hm...position, M1...electric motor, Vd...d-axis voltage command value, Vh, Vha, Vhb...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, and driving the motor by the switching element; a control unit that calculates a plurality of command values used to control the switching elements and controls the switching elements, The control unit a position estimation unit that estimates a position of the rotor by a harmonic superposition method based on harmonics superposed on the command value; a harmonic superposition frequency switching unit that switches the harmonic frequency of the harmonic based on the estimation result of the position estimation unit; a harmonic superposition unit that superimposes the harmonic, the harmonic frequency of which has been switched by the harmonic superposition frequency switching unit, on the command value, the harmonic superposition frequency switching unit switches the harmonic frequency based on the estimation result so that the harmonic frequency does not match a noise frequency of a 6n-th order (n is a positive integer) harmonic noise component of the motor. Electric motor.

2. when the rotation speed of the rotor based on the estimation result matches a switching threshold based on the 6n-th order harmonic noise component, the harmonic superposition frequency switching unit switches the first harmonic, which is the harmonic superimposed on the command value, to a second harmonic having a frequency different from that of the first harmonic.

2. The electric motor according to claim 1.

3. The harmonic superimposing unit a first harmonic superimposing unit that superimposes the first harmonic on the command value; a second harmonic superimposing unit that superimposes the second harmonic, which has a frequency lower than that of the first harmonic, on the command value; The position estimation unit a first position estimation unit that estimates a position of the rotor by the harmonic superposition method based on the first harmonic; a second position estimation unit that estimates the position of the rotor by the harmonic superposition method based on the second harmonic, The control unit an estimation result switching unit that switches the estimation result to be output to the harmonic superposition frequency switching unit between the estimation result estimated by the first position estimation unit and the estimation result estimated by the second position estimation unit, the harmonic superposition frequency switching unit switches to superimposing both the first harmonic and the second harmonic on the command value when the change over time of the rotation speed is increasing and the rotation speed based on the estimation result output by the estimation result switching unit matches a switching calculation start threshold that is smaller than the switching threshold by a predetermined value, and switches to superimposing only the second harmonic on the command value when the rotation speed matches the switching threshold; When the change over time of the rotation speed is increasing, the estimation result switching unit outputs the estimation result of the first position estimation unit to the harmonic superposition frequency switching unit while only the first harmonic is superimposed on the command value and while both the first harmonic and the second harmonic are superimposed on the command value, and outputs the estimation result of the second position estimation unit to the harmonic superposition frequency switching unit while only the second harmonic is superimposed on the command value.

3. The electric motor according to claim 2.

4. when the rotation speed of the rotor based on the estimation result matches a switching threshold based on the 6n-th order harmonic noise component, the harmonic superposition frequency switching unit switches the second harmonic, which is the harmonic superimposed on the command value, to a first harmonic having a frequency different from that of the second harmonic.

2. The electric motor according to claim 1.

5. The harmonic superimposing unit a first harmonic superimposing unit that superimposes the first harmonic on the command value; a second harmonic superimposing unit that superimposes the second harmonic, which has a frequency lower than that of the first harmonic, on the command value; The position estimation unit a first position estimator that estimates a position of the rotor by the harmonic superposition method based on the first harmonic, and a second position estimator that estimates a position of the rotor by the harmonic superposition method based on the second harmonic, The control unit an estimation result switching unit that switches the estimation result to be output to the harmonic superposition frequency switching unit between the estimation result estimated by the first position estimation unit and the estimation result estimated by the second position estimation unit, the harmonic superposition frequency switching unit switches to superimposing both the first harmonic and the second harmonic on the command value when the change over time of the rotation speed is decreasing and when the rotation speed based on the estimation result output by the estimation result switching unit matches a switching calculation start threshold that is larger than the switching threshold by a predetermined value, and switches to superimposing only the first harmonic on the command value when the rotation speed matches the switching threshold; When the change over time of the rotation speed is decreasing, the estimation result switching unit outputs the estimation result of the second position estimation unit to the harmonic superposition frequency switching unit while only the second harmonic is superimposed on the command value and while both the first harmonic and the second harmonic are superimposed on the command value, and outputs the estimation result of the first position estimation unit to the harmonic superposition frequency switching unit while only the first harmonic is superimposed on the command value.

5. The electric motor according to claim 4.

6. a compression section that compresses the fluid; the electric motor according to claim 3 or claim 5 that drives the compression unit; An electric compressor comprising:

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