Motor drive unit

Abstract

A motor drive device (100) comprises: an inverter (32) that converts DC voltage to AC voltage and applies the AC voltage to an AC motor (1); a DC voltage detection unit (31) that detects the DC voltage applied to the inverter (32); a voltage command generation unit (21) that generates a voltage command on the basis of a torque command and the detected value of the DC voltage; and a gate signal generation unit (22) that generates a gate signal for pulse width modulation control of the inverter (32) on the basis of the result of the comparison between a modulation wave that is the waveform of the voltage command and a carrier wave. The number of slots per magnetic pole in the stator core (9) of the AC motor (1) is a natural number multiple of 3. When a numerical value obtained by normalizing the frequency of the carrier wave by the frequency of the modulation wave is denoted by Fc as a carrier wave order and n is a natural number, there is a relationship of Fc = 6n + 3 between Fc and n.

Description

[Technical Field]

[0001] The present disclosure relates to a motor drive device that drives an AC motor having a plurality of slots arranged at equal intervals along the inner circumferential surface of a stator core. [Background technology]

[0002] It is known that AC motors with multiple slots in the stator core generate torque ripples corresponding to the number of slots. Because this type of torque ripple is caused by the structure of the AC motor, AC motors are often designed to reduce torque ripples by improving their structure.

[0003] On the other hand, it is known that torque ripples are also generated by harmonics generated by pulse width modulation (PWM) control of an inverter that drives an AC motor. In order to reduce this type of torque ripple, Patent Document 1 below detects the motor current at a period longer than the inverter switching period, estimates the motor current during periods when the motor current is not detected, and calculates PWM pulses to the inverter so that the estimated motor current value matches the current command value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6407683 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the calculation process in Patent Document 1 is complicated, which increases the processing time and processing load required for the calculation.

[0006] The present disclosure has been made in view of the above, and has an object to provide a motor drive device that can reduce torque ripple while suppressing increases in processing time and processing load. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems and achieve the object, the motor drive device according to the present disclosure is a motor drive device for driving an AC motor having a stator core in which a plurality of slots are formed and arranged at equal intervals along its inner circumferential surface, and includes an inverter, a DC voltage detection unit, a voltage command generation unit, and a gate signal generation unit. The inverter converts a DC voltage into an AC voltage and applies it to the AC motor. The DC voltage detection unit detects the DC voltage applied to the inverter. The voltage command generation unit generates a voltage command based on the torque command and the detected value of the DC voltage. The gate signal generation unit generates a gate signal that pulse-width modulates and controls the inverter based on the result of comparing a modulating wave, which is the waveform of the voltage command, with a carrier wave. The number of slots per magnetic pole in the stator core is a natural number multiple of 3. Furthermore, the value obtained by normalizing the frequency of the carrier wave with the frequency of the modulating wave is represented as the carrier order Fc, and n is the natural number. Number and Then, there is a relationship between Fc and n: Fc=6n+3. [Effects of the Invention]

[0008] The motor drive device according to the present disclosure has the advantage of being able to reduce torque ripple while suppressing increases in processing time and processing load. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a diagram showing a configuration of a motor drive device according to an embodiment; [Figure 2] 2 is a diagram showing an example of a waveform of one phase of a modulated wave generated by the modulated wave generating unit of FIG. 1 and a waveform of a carrier wave generated by the carrier wave generating unit of FIG. 1; FIG. [Figure 3] 1 is a cross-sectional view of an AC motor according to an embodiment, taken along the axial direction of a shaft. [Figure 4]A cross-sectional view of the AC motor shown in Figure 3 taken along line AA in Figure 3. [Figure 5] Cross-sectional view showing one magnetic pole of the 6-pole, 36-slot reluctance motor shown in Figure 4 [Figure 6] A waveform diagram showing torque fluctuations when the 6-pole, 36-slot reluctance motor shown in Figure 4 is driven with a carrier order of 27. [Figure 7] A graph showing the frequency analysis results of the torque fluctuation waveform shown in Fig. 6. [Figure 8] This figure shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 36-slot reluctance motor shown in Figure 4 is driven with a carrier wave order of 17. [Figure 9] This figure shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 36-slot reluctance motor shown in Figure 4 is driven with a carrier wave order of 15. [Figure 10] A diagram showing the relationship between the carrier order and the orders of slot harmonics, slit harmonics, and inverter harmonics in the 6-pole, 36-slot reluctance motor shown in Figure 4. [Figure 11] A diagram showing the relationship between the carrier order and torque ripple in the 6-pole, 36-slot reluctance motor shown in Figure 4. [Figure 12] A cross-sectional view showing one magnetic pole of a 6-pole, 54-slot reluctance motor, which has a different structure from that of Figure 5. [Figure 13] A waveform diagram showing torque fluctuations when the 6-pole, 54-slot reluctance motor shown in Figure 12 is driven with a carrier order of 27. [Figure 14] FIG. 14 shows the results of frequency analysis of the torque fluctuation waveform shown in FIG. 13. [Figure 15] FIG. 13 shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 54-slot reluctance motor shown in FIG. 12 is driven with a carrier wave order of 17. [Figure 16] FIG. 13 shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 54-slot reluctance motor shown in FIG. 12 is driven with a carrier wave order of 15. [Figure 17]FIG. 13 is a diagram showing the relationship between the carrier order and torque ripple in the 6-pole, 54-slot reluctance motor shown in FIG. 12. [Figure 18] FIG. 13 is a diagram showing the relationship between the carrier order and the orders of slot harmonics, slit harmonics, and inverter harmonics in the 6-pole, 54-slot reluctance motor shown in FIG. [Figure 19] FIG. 1 is a block diagram illustrating an example of a hardware configuration for implementing the functions of a control device according to an embodiment. [Figure 20] FIG. 10 is a block diagram showing another example of a hardware configuration for realizing the functions of the control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] A motor drive device according to an embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that, although the following embodiment will be described using a motor drive device for driving a railway vehicle as an example, this does not mean that application to other uses will be excluded. Also, in the accompanying drawings, the scale of each component may differ from the actual scale for ease of understanding. The same applies to each of the drawings.

[0011] Embodiment 1 is a diagram showing the configuration of a motor driving device 100 according to an embodiment. In FIG. 1, the motor driving device 100 according to the embodiment is made up of an inverter 32 and a control device 20.

[0012] 1, AC motor 1 is a propulsion motor mounted on a railway vehicle. AC motor 1 generates torque for driving the railway vehicle using AC power supplied from inverter 32. AC motor 1 is an induction motor or a synchronous motor.

[0013] The DC power supply unit 30 is a supply source of DC power to be supplied to the inverter 32. The DC power supply unit 30 is composed of an overhead line, a pantograph, a filter capacitor, etc. The inverter 32 converts the DC voltage applied from the DC power supply unit 30 into an AC voltage and applies it to the AC motor 1.

[0014] A DC voltage detection unit 31 is provided between the DC power supply unit 30 and the inverter 32 to detect the DC voltage output by the DC power supply unit 30. The detection value of the DC voltage detected by the DC voltage detection unit 31 is output to the control device 20.

[0015] FIG. 1 shows an example in which the main circuit of inverter 32 is a two-level inverter. In inverter 32, six semiconductor switching elements Su, Sv, Sw, Sx, Sy, and Sz are provided, and arm circuits in which two of the semiconductor switching elements are connected in series and an intermediate potential, which is the potential at the connection end, is provided for each output phase. In FIG. 1, in order to obtain three-phase AC voltages Vu, Vv, and Vw, a u-phase arm consisting of semiconductor switching elements Su and Sx, a v-phase arm consisting of semiconductor switching elements Sv and Sy, and a w-phase arm consisting of semiconductor switching elements Sw and Sz are configured. Note that the main circuit of inverter 32 does not need to be a two-level inverter and may be, for example, a three-level inverter.

[0016] The control device 20 includes a voltage command generation unit 21 and a gate signal generation unit 22. The gate signal generation unit 22 includes a modulated wave / carrier wave selection unit 23, a modulated wave generation unit 24, a carrier wave generation unit 25, and a comparison unit 26.

[0017] The voltage command generation unit 21 generates a voltage command based on a torque command and a detected value of the DC voltage. The gate signal generation unit 22 generates a gate signal for PWM control of the inverter 32 based on the voltage command output by the voltage command generation unit 21. In the example of FIG. 1 , gate signals for PWM control of six semiconductor switching elements Su, Sv, Sw, Sx, Sy, and Sz, i.e., gate signals for six elements, are generated and output to the inverter 32. The inverter 32 generates PWM-controlled three-phase AC voltages Vu, Vv, and Vw and applies them to the AC motor 1.

[0018] In the gate signal generating unit 22, the modulated wave generating unit 24 generates a modulated wave based on the voltage command output by the voltage command generating unit 21 and the selection signal output by the modulated wave / carrier wave selecting unit 23. The carrier wave generating unit 25 generates a carrier wave based on the voltage command output by the voltage command generating unit 21 and the selection signal output by the modulated wave / carrier wave selecting unit 23.

[0019] Fig. 2 is a diagram showing an example of the waveform of one phase of the modulated wave generated by the modulated wave generating unit 24 in Fig. 1 and the waveform of the carrier wave generated by the carrier wave generating unit 25 in Fig. 1. Here, the modulated wave is a waveform signal obtained by normalizing the command waveform of the motor applied voltage to be applied to the AC motor 1 with the DC voltage of the DC power supply unit 30 in order to generate a gate signal.

[0020] As shown in FIG. 2, the frequency of the carrier wave is greater than the frequency of the modulating wave. FIG. 2 shows an example in which the frequency of the carrier wave is 27 times the frequency of the modulating wave. In this paper, the value obtained by normalizing the frequency of the carrier wave with the frequency of the modulating wave is called the "carrier order" and is represented by the symbol "Fc." That is, FIG. 2 shows an example in which a selection signal that sets the carrier order Fc to 27 is output from the modulating wave / carrier wave selection unit 23 to the modulating wave generation unit 24 and the carrier wave generation unit 25. Note that the example in FIG. 2 is just one example, and the carrier order may be selected to a value other than 27 by the selection signal.

[0021] The modulating wave / carrier wave selection unit 23 determines a selection signal that reduces torque ripple generated in the AC motor 1 and outputs the selection signal to the modulating wave generation unit 24 and the carrier wave generation unit 25. The modulating wave generation unit 24 generates a modulating wave in accordance with the selection signal output from the modulating wave / carrier wave selection unit 23. The carrier wave generation unit 25 generates a carrier wave in accordance with the selection signal output from the modulating wave / carrier wave selection unit 23.

[0022] The comparator 26 generates the gate signal based on the comparison result between the modulated wave and the carrier wave. Specifically, the comparator 26 compares the modulated wave output from the modulated wave generator 24 with the carrier wave output from the carrier wave generator 25 for each phase, (i) If the amplitude of the modulating wave is greater than the amplitude of the carrier wave, the upper element is ON, and the lower element is OFF. (ii) If the amplitude of the modulating wave is less than the amplitude of the carrier wave, the upper element is OFF, and the lower element is ON. The upper elements correspond to the semiconductor switching elements Su, Sv, and Sw, and the lower elements correspond to the semiconductor switching elements Sx, Sy, and Sz. The inequality signs in (i) and (ii) above may be reversed.

[0023] As explained in the section on background art, torque ripple also increases due to harmonics generated by PWM control of the inverter 32 that drives the AC motor 1. In this paper, these harmonics are called "inverter harmonics." Inverter harmonics are harmonics that are included in the AC voltage applied to the AC motor 1 by PWM control of the inverter 32. High As described above, the modulated wave / carrier wave selection unit 23 determines a selection signal that reduces the torque ripple generated in the AC motor 1. A specific method for determining a selection signal that reduces the torque ripple generated in the AC motor 1 will be described later.

[0024] Fig. 3 is a cross-sectional view of AC motor 1 according to the embodiment, taken along the axial direction of shaft 4. Dashed line B in Fig. 3 is the axis of shaft 4. Fig. 4 is a cross-sectional view of AC motor 1 shown in Fig. 3, taken along line AA in Fig. 3. Figs. 3 and 4 show the structure of a three-phase reluctance motor as an example of AC motor 1. Note that frame 5 is not shown in Fig. 4.

[0025] The AC motor 1 has an annular stator 6 and a cylindrical rotor 7 that are inserted and fixed into a frame 5 by a method such as press fitting or shrink fitting. The annular stator 6 and the cylindrical rotor 7 are arranged to be relatively rotatable using bearings 8 via a magnetic gap 19, which is a mechanical gap.

[0026] The stator 6 is configured by windings 10 around a circular stator core 9 made of an iron core. The rotor 7 is formed by inserting the shaft 4 into the center of a cylindrical rotor core 11 made of an iron core by a method such as press fitting or shrink fitting.

[0027] The stator core 9 is composed of an annular core back 12 and teeth 13 that protrude radially inward from the core back 12 and are arranged at equal intervals. A plurality of slots 14 are formed at equal intervals between the plurality of teeth 13 provided on the radially inner side of the stator core 9. The slots 14 house windings 10. The teeth 13 and slots 14 are also provided at the same angle in the circumferential direction of the annulus. In this document, the plurality of slots 14 as a whole may be referred to as the "slot portion."

[0028] In Fig. 4, if the number of slots provided in stator core 9 is S and the number of magnetic poles in rotor core 11 is P, then S = 36 and P = 6. That is, Fig. 4 shows the cross-sectional structure of a three-phase reluctance motor with 6 poles and 36 slots. Note that the numbers of slots and magnetic poles shown in Fig. 4 are merely examples and are not limited to the example in Fig. 4.

[0029] Fig. 5 is a cross-sectional view showing one magnetic pole of the 6-pole, 36-slot reluctance motor shown in Fig. 4, and is an enlarged view of 1 / 6 of the area in Fig. 4. As shown in Fig. 5, the stator 6 of the 6-pole, 36-slot reluctance motor has six slots 14 per magnetic pole.

[0030] 5, on the cross sections of the stator core 7 and rotor core 11, the d-axis is defined in the direction of the center lines of the magnetic poles, and the q-axis is defined in the direction of the center lines between the magnetic poles. The direction of the center lines of the magnetic poles is the direction in which magnetic flux easily passes, while the direction of the center lines between the magnetic poles is the direction in which magnetic flux does not easily pass. The d-axis direction is sometimes called the "salient pole direction," and the q-axis direction is sometimes called the "non-salient pole direction."

[0031] The d-axis and q-axis have an electrical phase difference of 90 degrees. The rotor 7 rotates due to the inductance torque generated based on the difference in inductance between the d-axis and q-axis directions. In other words, a reluctance motor generates output torque by utilizing the difference in magnetic resistance in the rotational direction. Therefore, the greater the difference in inductance between the d-axis and q-axis, the higher the output torque a reluctance motor can generate.

[0032] In FIG. 5, when viewed in the direction of the central axis of the cylinder, rotor core 11 is provided with a plurality of slits 15, each of which is an arc-shaped opening that protrudes toward the cylindrical center O of rotor core 11 for each magnetic pole of rotor core 11 and has each vertex located on the q-axis. The plurality of slits 15 creates space in rotor core 11. In other words, the slits 15 give rotor core 11 a structure in which magnetic portions made of magnetic material, i.e., the electromagnetic steel sheet material, and non-magnetic portions made of air appear alternately. Furthermore, slits 15 are provided symmetrically about the q-axis for each magnetic pole. Note that in this document, the entire set of slits 15 may be referred to as the "slit portion."

[0033] While FIG. 5 shows a case where the number of slits 15 is three, the number is not limited to three and may be two or four or more. That is, the number of slits 15 may be any number as long as it is plural. Also, in FIG. 5, the ends of slits 15 are formed linearly along the side of rotor core 11 that is located on the magnetic gap 19 side, but the shape is not limited to this. The ends of slits 15 may be chamfered in an arc shape. Note that an approximation of the arc shape using, for example, a straight line can also be considered to be the same shape.

[0034] The center point W is the midpoint in the circumferential direction of the arc-shaped end portion along the outer surface of rotor core 11 at the arc-shaped opening of the closest slit 15 with respect to the d-axis passing through the cylindrical center O of rotor core 11. Also, the angle formed by the center points W of each slit 15 provided within one magnetic pole and the cylindrical center O of rotor core 11 between adjacent slits is defined as θ.

[0035] In the examples of FIGS. 4 and 5, the slits 15 are arranged so that the angle θ is evenly spaced between adjacent slits. The angle between the d-axis and a line connecting the center point W of the slit closest to the d-axis and the cylindrical center O of the rotor core 11 is set to θ / 2. When the angle θ is evenly spaced between adjacent slits, θ is set to 6.67 (=360 / 54) degrees. In this document, this angle θ is referred to as the "slit spacing θ," and the number of angles θ around the entire circumference of the rotor core 11 is sometimes referred to as the "number of pitches." In the configuration of FIG. 5, the number of pitches is 54. The configuration of FIG. 5 is merely an example, and the slit spacing θ does not necessarily have to be equal between adjacent slits.

[0036] As mentioned above, rotor core 11 is configured such that core sections with low magnetic resistance, through which magnetic flux can easily pass, and slit sections with high magnetic resistance, through which magnetic flux cannot easily pass, alternate in the direction of rotation. Such fluctuations in magnetic resistance in rotor core 11 cause harmonics to be superimposed on winding 10. In this paper, harmonics generated by fluctuations in magnetic resistance in rotor core 11 in the direction of rotation are referred to as "slit harmonics."

[0037] 5, when stator core 9 is viewed from rotor core 11, core sections with low magnetic resistance, through which magnetic flux can easily pass, and slot sections with high magnetic resistance, through which magnetic flux cannot easily pass, alternate in the direction of rotation. Such fluctuations in magnetic resistance in stator core 9 cause harmonics to be superimposed on winding 10. In this paper, harmonics generated by fluctuations in magnetic resistance in stator core 9 in the direction of rotation are referred to as "slot harmonics."

[0038] FIG. 6 is a waveform diagram showing torque fluctuations when the 6-pole, 36-slot reluctance motor shown in FIG. 4 is driven with a carrier wave order of 27. The horizontal axis of FIG. 6 represents the electrical angle, and the vertical axis represents the normalized magnitude of the torque applied to the AC motor 1. FIG. 7 is a diagram showing the results of frequency analysis of the torque fluctuation waveform shown in FIG. 6. The horizontal axis of FIG. 7 represents the order of the torque ripple, and the vertical axis represents the torque ripple amplitude, which is the amplitude value of the torque ripple. The order of the torque ripple is a numerical value obtained by normalizing one of the frequencies of the torque ripple with the frequency of the modulating wave and displaying it as a multiple. The vertical axis represents the value of the amplitude of each order of the torque ripple normalized with the overall magnitude of the torque ripple across all frequency bands.

[0039] First, as shown in Figure 6, the torque value fluctuates depending on the electrical angle, which is equivalent to the rotational position of the rotor 7. Furthermore, Figure 7 also shows that, excluding the sixth and lower orders, the torque ripple is large at the 12th, 18th, 24th, 30th, and 36th orders. Of the torque ripple at these orders, the 12th, 24th, and 36th harmonics are slot harmonics. The AC motor 1 shown in Figure 4 has a six-pole, 36-slot configuration, with six slots per pole. Therefore, the fundamental frequency of the slot harmonics is the 12th order, and the 24th and 36th orders, which are integer multiples of the 12th order, are also slot harmonics. Furthermore, the AC motor 1 shown in Figure 4 has a pitch count of 54, which corresponds to 1.5 times the number of slots S (36) around the entire circumference of the stator core 9. Therefore, the fundamental frequency of the slit harmonics is the 18th order, and the 36th order, which is an integer multiple of the 18th order, is also a slit harmonic.

[0040] Through this study, the inventors of the present application found that, among multiple inverter harmonics, the orders of inverter harmonics that have a significant impact on torque ripple are (Fc-3), (Fc+3), and 2Fc. In the case of Figure 7, the 24th order corresponds to the (Fc-3) order, and the 30th order corresponds to the (Fc+3) order. Note that the 2Fc order is a large order value and is not included in the analysis results of Figure 7.

[0041] According to the analysis results in Fig. 7, the 30th-order component appears significantly, and it can be seen that the (Fc+3)-order is an inverter harmonic. On the other hand, the 24th-order, which corresponds to the (Fc-3)-order, overlaps with the slot harmonic and cannot be distinguished. Therefore, frequency analysis was performed by further varying the carrier order. The analysis results are shown in Figs. 8 and 9. Specifically, Fig. 8 shows the frequency analysis results of the torque fluctuation waveform when the 6-pole, 36-slot reluctance motor shown in Fig. 4 is driven with a carrier order of 17, and Fig. 9 shows the frequency analysis results of the torque fluctuation waveform when the 6-pole, 36-slot reluctance motor shown in Fig. 4 is driven with a carrier order of 15.

[0042] According to the analysis results of FIG. 8, as in FIG. 7, 12th, 24th, and 36th slot harmonics and 18th and 36th slit harmonics are generated. Furthermore, the analysis results of FIG. 8 also show that 14th, 20th, and 34th harmonics are generated, with the 14th corresponding to (Fc-3), the 20th corresponding to (Fc+3), and the 34th corresponding to (2Fc). Here, it can be seen that the 14th is an order component that does not belong to either slot harmonics or slit harmonics, and is the (Fc-3) order of inverter harmonics. Furthermore, the 34th is also an order component that does not belong to either slot harmonics or slit harmonics, and it can be seen that the 34th, which is 2Fc order as an inverter harmonic, also has a significant impact on torque ripple.

[0043] Furthermore, according to the analysis results in Fig. 9, as in Fig. 7, 12th, 24th, and 36th slot harmonics and 18th and 36th slit harmonics are generated. Furthermore, the analysis results in Fig. 9 show that 12th, 18th, and 30th inverter harmonics are generated, with the 12th corresponding to (Fc-3), the 18th corresponding to (Fc+3), and the 30th corresponding to (2Fc). The 12th and 18th harmonics cannot be distinguished from slot harmonics and slit harmonics, respectively, but the 30th is a component that is only an inverter harmonic, and from these results it can be seen that the 30th component, which is 2Fc, has a significant impact on torque ripple.

[0044] FIG. 10 shows the relationship between the carrier order Fc and the orders of slot harmonics, slit harmonics, and inverter harmonics in the 6-pole, 36-slot reluctance motor shown in FIG. 4. Although coincident orders do appear at higher orders, they are not shown because they do not become the main components of torque ripple. Also, FIG. 10 only shows the case where the carrier order Fc is odd, i.e., the carrier frequency is an odd multiple of the modulating wave frequency. This is because when the carrier order Fc is even, the north and south magnetic poles are not symmetrical, and the pulses of the PWM signal do not become synchronous pulses.

[0045] In FIG. 10, the circled areas indicate that the order overlaps with at least one of the slot harmonic and slit harmonic. When the carrier order Fc=27, as explained with reference to FIG. 7, the 24th order (2x) of the slot harmonic coincides with Fc-3 (24th order) of the inverter harmonic. When the carrier order Fc=17, as explained with reference to FIG. 8, there is no coincident order. When the carrier order Fc=15, as explained with reference to FIG. 9, the 12th order (1x) of the slot harmonic coincides with Fc-3 (12th order) of the inverter harmonic, and the 18th order (1x) of the slit harmonic coincides with Fc+3 (18th order) of the inverter harmonic.

[0046] FIG. 11 shows the relationship between the carrier order Fc and torque ripple in the 6-pole, 36-slot reluctance motor shown in FIG. 4. The horizontal axis of FIG. 11 represents the carrier order Fc, and the vertical axis represents the torque ripple normalized by the 29th order, which is the highest carrier order Fc. FIG. 11 shows that the torque ripple decreases as the carrier order Fc increases. It also shows that the torque ripple reaches a minimum when the carrier order Fc is 6n+3, where n is a natural number. Specifically, FIG. 11 shows that the torque ripple reaches a minimum when Fc=9 (n=1), Fc=15 (n=2), Fc=21 (n=3), and Fc=27 (n=4).

[0047] Considering the results of FIGS. 10 and 11, the following can be said. First, as shown in FIG. 10, when the carrier wave order Fc is 6n+3 (n=1 to 4), there is an order that matches the inverter harmonic in at least one of the slot harmonics and slit harmonics. Furthermore, comparing the analysis results of FIG. 8, in which the carrier wave order Fc is 17, with the analysis results of FIG. 9, in which the carrier wave order Fc is 15, and further referring to the results of FIG. 11, it can be seen that torque ripple is reduced when an order that matches the inverter harmonic exists in at least one of the slot harmonics and slit harmonics. This means that when an order that matches the inverter harmonic exists in at least one of the slot harmonics and slit harmonics, the number of orders at which torque ripple occurs is reduced when viewed from the perspective of the overall torque ripple. This is thought to have reduced torque ripple.

[0048] Furthermore, when the carrier wave order Fc is 27, although there is no matching order between the inverter harmonics and the slit harmonics, as shown in the results of FIG. 11, the torque ripple is minimized, and the torque ripple reduction effect is obtained. Therefore, it can be seen that the method described in this embodiment is effective for any AC motor having a stator core with multiple slots formed on its inner circumferential surface. Therefore, the method of this embodiment is not limited to reluctance motors, and the torque ripple reduction effect can also be obtained when applied to permanent magnet motors or induction motors.

[0049] The above explanation was about the 6-pole, 36-slot reluctance motor shown in Figures 4 and 5. To confirm the above explanation, we also analyzed reluctance motors with other structures. The results are explained below.

[0050] Figure 12 is a cross-sectional view showing one magnetic pole of a 6-pole, 54-slot reluctance motor with a different structure from that of Figure 5. The rotor core 11 has a pitch of 72, and the slit spacing θ is θ = 5.0 (= 360 / 72) degrees. With this structure, the fundamental frequency of the slit harmonics is 4 / 3 times the fundamental frequency of the slot harmonics.

[0051] Fig. 13 is a waveform diagram showing torque fluctuations when the 6-pole, 54-slot reluctance motor shown in Fig. 12 is driven with a carrier order of 27. The notations on the vertical and horizontal axes are the same as those in Fig. 6. As in Fig. 6, it can be seen that the torque value fluctuates when the electrical angle, which is equivalent to the rotational position of the rotor 7, changes.

[0052] FIG. 14 shows the results of frequency analysis of the torque fluctuation waveform shown in FIG. 13. The notations on the vertical and horizontal axes are the same as those in FIG. 7. FIG. 14 shows that, excluding the sixth and lower orders, the torque ripple is large at the 12th, 18th, 24th, and 30th orders. Of the torque ripple at these orders, the 18th order harmonic corresponds to a slot harmonic, and the 30th order harmonic corresponds to an inverter harmonic. Furthermore, the 24th order harmonic is considered to correspond to both a slot harmonic and an inverter harmonic, but this cannot be distinguished from the analysis results in FIG. 14 alone. Therefore, frequency analysis was performed by changing the carrier order. The analysis results are shown in FIGS. 15 and 16. Specifically, FIG. 15 shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 54-slot reluctance motor shown in FIG. 12 is driven with a carrier order of 17, and FIG. 16 shows the results of frequency analysis of the torque fluctuation waveform when the 6-pole, 54-slot reluctance motor shown in FIG. 12 is driven with a carrier order of 15.

[0053] According to the analysis results of Figure 15, an 18th slot harmonic and a 24th slit harmonic are generated. Furthermore, the analysis results of Figure 15 also show that 14th, 18th, 20th, 24th, 30th, and 34th harmonics are generated, with the 14th corresponding to (Fc-3), the 20th corresponding to (Fc+3), and the 34th corresponding to (2Fc). Here, it can be seen that the 14th is an order component that does not belong to either slot harmonics or slit harmonics, and is the (Fc-3) inverter harmonic. Furthermore, it can be seen that the 20th is an order component that does not belong to either slot harmonics or slit harmonics, and is the (Fc+3) inverter harmonic. Furthermore, it can be seen that the 34th order is an order that does not belong to either the slot harmonic or the slit harmonic, and is the (2Fc) order of the inverter harmonic.

[0054] Furthermore, according to the analysis results of FIG. 16, 18th and 36th slot harmonics and 24th slit harmonic are generated. Furthermore, according to the analysis results of FIG. 16, 12th, 18th, 24th, 30th, and 36th harmonics are generated, with the 12th corresponding to the (Fc-3) order and the 30th corresponding to the (2Fc) order. Here, it can be seen that the 12th order is an order component that does not belong to either the slot harmonic or the slit harmonic, and is the (Fc-3) order of the inverter harmonic. Furthermore, it can be seen that the 30th order is an order component that does not belong to either the slot harmonic or the slit harmonic, and is the (2Fc) order of the inverter harmonic. Furthermore, from the above explanation, it can be seen that the 18th order is a fundamental component of the slot harmonic and also the (Fc-3) order of the inverter harmonic.

[0055] Fig. 17 is a diagram showing the relationship between the carrier order Fc and torque ripple in the 6-pole, 54-slot reluctance motor shown in Fig. 12. As in Fig. 11, the horizontal axis represents the carrier order Fc, and the vertical axis represents the torque ripple normalized by the 29th order, which is the largest carrier order Fc. As in Fig. 11, Fig. 17 also shows that the torque ripple decreases as the carrier order Fc increases. Also, as in Fig. 11, the relationship in which the torque ripple reaches a minimum value when the carrier order Fc is 6n+3, where n is a natural number, is maintained.

[0056] Fig. 18 is a diagram showing the relationship between the carrier order Fc and the orders of the slot harmonics, slit harmonics, and inverter harmonics in the 6-pole, 54-slot reluctance motor shown in Fig. 12. As with Fig. 10, higher-order components are not shown. Also, as with Fig. 10, only the case where the carrier order Fc is an odd number is shown.

[0057] Considering the results shown in FIGS. 10, 11, 17, and 18, the following can be said. First, whether the stator core 9 has a 6-pole, 36-slot structure or a 6-pole, 54-slot structure, the torque ripple remains at its minimum when the carrier wave order Fc is 6n+3. This relationship is believed to be due to the fact that the number of slots per magnetic pole is a natural number multiple of 3 for both the 6-pole, 36-slot structure and the 6-pole, 54-slot structure. In fact, the number of slots per magnetic pole is 6 for the 6-pole, 36-slot structure, and 9 for the 6-pole, 54-slot structure, so the number of slots per magnetic pole is a natural number multiple of 3. When the stator core 9 is viewed from the rotor core 11, core portions with low magnetic resistance and slot portions with high magnetic resistance alternate in the direction of rotation. This means that the torque ripple has a periodicity where it reaches its minimum at natural number multiples of 6.

[0058] Based on the above description, the gate signal generating unit 22 provided in the control device 20 according to the embodiment performs the following control. Note that, here, the value obtained by normalizing the frequency of one of the multiple inverter harmonics by the frequency of the modulating wave is called the "first order," the value obtained by normalizing the frequency of one of the multiple slot harmonics by the frequency of the modulating wave is called the "second order," and the value obtained by normalizing the frequency of one of the multiple slit harmonics by the frequency of the modulating wave is called the "third order."

[0059] First, when generating a gate signal for PWM control of the inverter 32, the gate signal generator 22 generates the gate signal so that the first order matches the second order. This control method makes it possible to match the frequency of at least one of the slot harmonics with the frequency of at least one of the inverter harmonics. This reduces the number of orders at which torque ripple occurs, thereby enabling torque ripple to be reduced.

[0060] Furthermore, in the above control method, since the frequency of the modulating wave is determined by the voltage command value, by appropriately setting the frequency of the carrier wave, it is possible to generate a gate signal that matches the first order with the second order. Furthermore, this control method does not significantly affect existing control, and does not require the complex arithmetic processing described in Patent Document 1. Therefore, by using this control method, it is possible to reduce torque ripple while suppressing increases in processing time and processing load. Furthermore, by using this control method, it is not necessary to modify the structure of the AC motor, so it is possible to promote the use of existing AC motors in various applications with diverse torque ripple requirements, while satisfying torque ripple requirements through inverter control.

[0061] Furthermore, when the AC motor is a reluctance motor having a rotor core with multiple slits, the gate signal generator 22 generates gate signals for PWM control of the inverter 32 so that the first order matches at least one of the second order and the third order. This control method makes it possible to match the frequency of at least one of the slot harmonics and the slit harmonics with the frequency of at least one of the inverter harmonics. This reduces the number of orders at which torque ripple occurs, thereby reducing torque ripple. Furthermore, this control method does not significantly affect existing control and does not require complex arithmetic processing as in Patent Document 1. Therefore, torque ripple can be reduced while suppressing increases in processing time and processing load.

[0062] Next, a hardware configuration for realizing the functions of the control device 20 described above will be described with reference to Fig. 19 and Fig. 20. Fig. 19 is a block diagram showing an example of a hardware configuration for realizing the functions of the control device 20 according to the embodiment. Fig. 20 is a block diagram showing another example of a hardware configuration for realizing the functions of the control device 20 according to the embodiment.

[0063] When realizing some or all of the functions of the control device 20 in the embodiment, the configuration can include a processor 300 that performs calculations, a memory 302 that stores programs read by the processor 300, and an interface 304 that inputs and outputs signals, as shown in Figure 19.

[0064] The processor 300 is a computing means. The processor 300 may be a computing means called a microprocessor, a microcomputer, a CPU (Central Processing Unit), or a DSP (Digital Signal Processor). Examples of the memory 302 include non-volatile or volatile semiconductor memories such as RAM (Random Access Memory), ROM (Read Only Memory), flash memory, EPROM (Erasable Programmable ROM), and EEPROM (registered trademark) (Electrically EPROM), as well as magnetic disks, flexible disks, optical disks, compact disks, minidisks, and DVDs (Digital Versatile Discs).

[0065] The memory 302 stores a program that executes the functions of the control device 20 in the embodiment. The processor 300 exchanges necessary information via the interface 304, executes the program stored in the memory 302, and refers to the data stored in the memory 302, thereby performing the above-mentioned processing. The calculation results by the processor 300 can be stored in the memory 302.

[0066] Furthermore, when realizing part of the functions of the control device 20 in the embodiment, a processing circuit 303 shown in Fig. 20 can be used. The processing circuit 303 may be a single circuit, a composite circuit, an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a combination thereof. Information input to and output from the processing circuit 303 can be obtained via an interface 304.

[0067] It is also possible that some of the processing in the control device 20 is performed by the processing circuit 303, and the processing that is not performed by the processing circuit 303 is performed by the processor 300 and the memory 302.

[0068] As described above, the motor drive device according to the embodiment includes an inverter, a DC voltage detection unit, a voltage command generation unit, and a gate signal generation unit. The inverter converts a DC voltage into an AC voltage and applies it to the AC motor. The DC voltage detection unit detects the DC voltage applied to the inverter. The voltage command generation unit generates a voltage command based on the torque command and the detected value of the DC voltage. The gate signal generation unit generates a gate signal that performs pulse width modulation control of the inverter based on the result of comparing a modulation wave, which is the waveform of the voltage command, with a carrier wave. The AC motor has an annular stator core in which a plurality of slots are formed and arranged at equal intervals along the inner circumferential surface. The number of slots per magnetic pole in the stator core of the AC motor is a natural number multiple of 3. The frequency of the carrier wave normalized by the frequency of the modulation wave is represented as the carrier order Fc, and n is the natural number. Number and In this case, the gate signal generator generates a gate signal such that the relationship between Fc and n is Fc=6n+3. When the inverter is controlled by this gate signal, the frequency of at least one of the slot harmonics can be made to match the frequency of at least one of the inverter harmonics. This makes it possible to obtain a motor drive device that can reduce torque ripple while suppressing increases in processing time and processing load.

[0069] In the motor drive device according to the embodiment, the inverter is subjected to pulse width modulation control to generate a voltage included in the AC voltage applied to the AC motor. ComplexThe first order is the value obtained by normalizing the frequency of one of the multiple inverter harmonics by the frequency of the modulating wave. The second order is the value obtained by normalizing the frequency of one of the multiple slot harmonics generated by fluctuations in magnetic resistance in the rotational direction of the stator core by the frequency of the modulating wave. A gate signal generator provided in the motor drive device generates a gate signal so that the first order matches the second order. This allows the frequency of at least one of the slot harmonics to match the frequency of at least one of the inverter harmonics, thereby reducing the number of orders at which torque ripple occurs and enabling torque ripple reduction.

[0070] In the above control, the first order is the carrier order. et al. 3 The order subtracted from the carrier order 3 to or an order obtained by doubling the carrier wave order. The second order is one of an order corresponding to the frequency of the fundamental wave among the multiple slot harmonics, an order corresponding to twice the frequency of the fundamental wave among the multiple slot harmonics, or an order corresponding to three times the frequency of the fundamental wave among the multiple slot harmonics. These components are the main components of the inverter harmonics and slot harmonics. Therefore, control to reduce torque ripple can be effectively performed.

[0071] In addition, in the motor drive device according to the embodiment, the AC motor to be driven is a reluctance motor having a rotor core with a plurality of slits, each of which is formed by an arc-shaped opening and convex toward the center of the cylinder when viewed in the direction of the central axis of the cylinder, with each apex located on the q-axis. Furthermore, the third order is defined as the value obtained by normalizing the frequency of one of the plurality of slit harmonics generated by fluctuations in magnetic reluctance in the rotor core in the rotational direction by the frequency of the modulation wave. In this case, a gate signal generator included in the motor drive device generates a gate signal such that the first order matches at least one of the second and third orders. This allows the frequency of at least one of the slot harmonics and slit harmonics to match the frequency of at least one of the inverter harmonics, thereby reducing the number of orders at which torque ripple occurs and thereby reducing torque ripple.

[0072] In the above control, the first order is the carrier order. et al. 3 The order subtracted from the carrier order 3 to The second order is one of the orders obtained by adding the above components, or the order obtained by doubling the carrier order. The second order is one of the orders corresponding to the frequency of the fundamental wave among the multiple slot harmonics, the orders corresponding to twice the frequency of the fundamental wave among the multiple slot harmonics, or the orders corresponding to three times the frequency of the fundamental wave among the multiple slot harmonics. The third order is one of the orders corresponding to the frequency of the fundamental wave among the multiple slit harmonics, or the orders corresponding to twice the frequency of the fundamental wave among the multiple slit harmonics. These components are the main components of inverter harmonics, slot harmonics, and slit harmonics. Therefore, control to reduce torque ripple can be effectively performed.

[0073] The configurations shown in the above embodiments are merely examples, and may be combined with other known technologies, and parts of the configurations may be omitted or modified without departing from the spirit of the invention. [Explanation of symbols]

[0074] 1 AC motor, 4 shaft, 5 frame, 6 stator, 7 rotor, 8 bearing, 9 stator core, 10 winding, 11 rotor core, 12 core back, 13 teeth, 14 slot, 15 slit, 19 magnetic gap, 20 control device, 21 voltage command generation unit, 22 gate signal generation unit, 23 modulation wave / carrier wave selection unit, 24 modulation wave generation unit, 25 carrier wave generation unit, 26 comparison unit, 30 DC power supply unit, 31 DC voltage detection unit, 32 inverter, 100 motor drive device, 300 processor, 302 memory, 303 processing circuit, 304 interface, Su, Sv, Sw, Sx, Sy, Sz semiconductor switching elements.

Claims

1. A motor drive device for driving an AC motor having a stator core in which a plurality of slots are formed and arranged at equal intervals along an inner circumferential surface, an inverter that converts a DC voltage into an AC voltage and applies the AC voltage to the AC motor; a DC voltage detection unit that detects the DC voltage applied to the inverter; a voltage command generating unit that generates a voltage command based on a torque command and the detected value of the DC voltage; a gate signal generating unit that generates a gate signal for pulse width modulation control of the inverter based on a comparison result between a modulated wave, which is the waveform of the voltage command, and a carrier wave; Equipped with the number of slots per magnetic pole in the stator core is a natural number multiple of 3, When the frequency of the carrier wave normalized by the frequency of the modulating wave is represented as a carrier order Fc, and n is a natural number, there is a relationship between Fc and n: Fc = 6n + 3, a first order is a value obtained by normalizing the frequency of one of a plurality of inverter harmonics included in the AC voltage applied to the AC motor by pulse width modulation control of the inverter with the frequency of the modulated wave; When the second order is a value obtained by normalizing the frequency of one of a plurality of slot harmonics generated by fluctuations in magnetic resistance in the rotational direction of the stator core with the frequency of the modulated wave, The gate signal generating unit generates the gate signal so that the first order coincides with the second order. A motor drive device characterized by:

2. The first order is any one of an order obtained by subtracting 3 from the carrier order, an order obtained by adding 3 to the carrier order, or an order obtained by doubling the carrier order, The second order is any one of an order corresponding to a frequency of a fundamental wave among a plurality of slot harmonics, an order corresponding to a frequency twice as high as the fundamental wave among a plurality of slot harmonics, or an order corresponding to a frequency three times as high as the fundamental wave among a plurality of slot harmonics.

2. The motor drive device according to claim 1.

3. the AC motor is a reluctance motor having a rotor core that has a cylindrical shape, is disposed on the inner surface side of the stator core, and is provided with a plurality of slits each having an arc-shaped opening that is convex toward the center of the cylinder for each magnetic pole when viewed in the direction of the central axis of the cylinder, and each apex of which is located on the q axis; When the third order is a value obtained by normalizing the frequency of one of a plurality of slit harmonics generated by fluctuations in magnetic resistance in the rotational direction of the rotor core with the frequency of the modulated wave, The gate signal generating unit generates the gate signal so that the first order coincides with the third order.

3. The motor drive device according to claim 1 or 2.

4. The third order is either an order corresponding to a frequency of a fundamental wave among a plurality of slit harmonics or an order corresponding to a frequency twice that of the fundamental wave among a plurality of slit harmonics.

4. The motor drive device according to claim 3.

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