Control device for electric motor

Abstract

To provide a control device of an electric motor capable of suppressing occurrence of a detection error of a resolver due to electromagnetic noise generated by controlling the electric motor while suppressing complication of switching control of an inverter.SOLUTION: A frequency of electromagnetic noise generated when switching elements are controlled based on a predetermined switching frequency fc0 corresponding to an operation state required for an AC motor is estimated, a frequency of a detection signal of a detection coil when the AC motor is driven in the required operation state is estimated, and the predetermined switching frequency fc0 is corrected so that the estimated frequency of the electromagnetic noise and the frequency of the detection signal of the detection coil become different frequencies (steps S4, S6, and S7).SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a control device for an electric motor configured to exchange power with a power storage device by converting DC current and AC current using an inverter, and more particularly to a control device for an electric motor configured to control the inverter based on a signal from a resolver that detects the rotation angle of the electric motor. [Background technology]

[0002] Patent Document 1 describes a control system for an AC motor that is driven by controlling the power supplied to it based on the rotation angle detected by a resolver. This AC motor control system is configured to match the carrier frequency for generating AC current supplied to the AC motor with the frequency of the excitation current applied to the excitation coil provided in the resolver, in order to prevent electromagnetic noise generated by supplying current to the AC motor from affecting the signal detected by the detection coil of the resolver and causing a detection error in the resolver. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-118689 Summary of the Invention [Problem to be solved by the invention]

[0004] The control system for an AC motor described in Patent Document 1 is configured to match the frequency of an excitation current applied to an excitation coil provided in a resolver with the carrier frequency, thereby matching the frequency of electromagnetic noise generated by energizing the AC motor with the frequency of a resolver detection signal and suppressing resolver detection errors. Meanwhile, the initial characteristics of inverters that generate AC current to energize the AC motor vary from one inverter to another, and the frequency of electromagnetic noise may change due to deterioration over time. In such cases, it may be impossible to perfectly match the carrier frequency with the frequency of the excitation current, and electromagnetic noise may affect the resolver detection signal, resulting in resolver detection errors. Furthermore, in order to perfectly match the carrier frequency with the frequency of the excitation current while taking into account the inverter's initial characteristics and deterioration over time, a sensor that detects the current supplied to the AC motor with relatively high accuracy is required. Furthermore, the inverter's switching signal may need to be corrected based on the detection value of the sensor, which may complicate inverter switching control.

[0005] The present invention has been made with a focus on the above-mentioned technical problems, and aims to provide a motor control device that can suppress the occurrence of resolver detection errors due to electromagnetic noise generated by controlling the motor, while suppressing the complexity of inverter switching control. [Means for solving the problem]

[0006] In order to achieve the above object, the present invention provides a motor control device including: a DC power supply; an AC motor that operates when an AC voltage is applied to it; an inverter having a plurality of switching elements and that converts the DC voltage to the AC voltage by controlling the plurality of switching elements at a predetermined switching frequency according to an operating state required of the AC motor; a rotor connected to an output shaft of the AC motor; an excitation coil that excites the rotor when an AC voltage of a predetermined excitation frequency is applied to it; and a resolver having a detection coil that generates an induced voltage according to the magnetic flux of the rotor, the motor control device including a controller that controls the switching elements, the controller estimating a frequency of electromagnetic noise that is generated when the switching elements are controlled based on the predetermined switching frequency, estimating a frequency of a detection signal from the detection coil when the AC motor is driven in the required operating state, and correcting at least one of the predetermined switching frequency and the predetermined excitation frequency so that the estimated frequency of the electromagnetic noise and the frequency of the detection signal from the detection coil are different frequencies.

[0007] In the present invention, the frequency of the electromagnetic noise may include a frequency of a sideband wave corresponding to a carrier wave generated by controlling the switching element.

[0008] In the present invention, the frequency of the electromagnetic noise may include a frequency of a sideband wave corresponding to a high-order carrier wave generated by controlling the switching element.

[0009] In addition, in the present invention, the frequency of the electromagnetic noise may include an upper frequency obtained by adding a rotational frequency based on the rotational speed of the AC motor and the number of poles of the AC motor to the frequency of a carrier wave generated by controlling the switching element, and a lower frequency obtained by subtracting the rotational frequency from the frequency of the carrier wave.

[0010] In addition, in the present invention, the frequency of the electromagnetic noise may include an upper frequency obtained by adding a rotational frequency based on the rotational speed of the AC motor and the number of poles of the AC motor to the frequency of a high-order carrier wave generated by controlling the switching element, and a lower frequency obtained by subtracting the rotational frequency from the frequency of the carrier wave.

[0011] In addition, in the present invention, the frequency of the detection signal of the detection coil may include an upper output frequency obtained by adding a rotational frequency based on the rotational speed of the AC motor and the number of poles of the resolver to the predetermined excitation frequency, and a lower output frequency obtained by subtracting the rotational frequency from the predetermined excitation frequency.

[0012] In the present invention, the controller may correct at least one of the predetermined switching frequency and the predetermined excitation frequency when a current value required for the AC motor is equal to or greater than a predetermined current value. [Effects of the Invention]

[0013] According to this invention, the frequency of electromagnetic noise generated when switching elements are controlled based on a predetermined switching frequency and the frequency of the detection signal of the detection coil when driven in an operating state required for the AC motor are estimated, and at least one of the predetermined switching frequency and the predetermined excitation frequency is corrected so that the estimated frequency of electromagnetic noise and the frequency of the detection signal of the detection coil are different frequencies. By correcting at least one of the predetermined frequency and the predetermined excitation frequency in this manner, it is possible to suppress detection errors of the resolver caused by electromagnetic noise being superimposed on the detection signal of the detection coil. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a configuration diagram for explaining an example of an electrical system including a DC power supply, an inverter, and an AC motor according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram for explaining the configuration of a resolver. [Figure 3] 4A and 4B are diagrams showing AC waveforms of an excitation coil and a detection coil. [Figure 4] 3 is a flowchart illustrating an example of control executed by a control device according to an embodiment of the present invention. [Figure 5] FIG. 10 is a diagram illustrating an example in which a lower noise frequency and an upper output frequency match. [Figure 6] FIG. 1(a) shows an example in which a lower noise frequency corresponding to a secondary carrier wave matches an upper output frequency, and FIG. 1(b) shows an example in which an upper noise frequency matches a lower output frequency. [Figure 7] 10 is a diagram showing an example in which an upper noise frequency corresponding to a second carrier wave matches a lower output frequency. FIG. [Figure 8] 10 is a flowchart illustrating an example of control for correcting a reference carrier frequency in accordance with a motor current. DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 shows an example of an electrical system 1 including a DC power supply, an inverter, and an AC motor according to an embodiment of the present invention. This DC power supply (hereinafter simply referred to as the power supply) 2 is a power supply that outputs a DC voltage, similar to power supplies provided in conventional electric vehicles and hybrid vehicles. This power supply 2 can be configured using a secondary battery such as a lithium-ion battery or a nickel-metal hydride battery, or an electric double layer capacitor. Note that this power supply 2 may also be configured using a battery pack in which multiple batteries are arranged in series.

[0016] The electric motor (hereinafter simply referred to as motor) 3 can be configured as a three-phase AC synchronous motor with multiple permanent magnets in the rotor, similar to motors used as driving power sources in conventional electric vehicles and hybrid vehicles. That is, motor 3 operates when AC voltage is applied. The motor 3 shown in FIG. 1 is configured as a star-connected AC motor and includes a U-phase coil 3u, a V-phase coil 3v, and a W-phase coil 3w. One end of each of these coils 3u, 3v, and 3w is connected to a neutral point 4. This motor 3 corresponds to the "AC motor" in this embodiment of the present invention.

[0017] A positive bus bar 5 is connected to the positive terminal of the power supply 2, and a negative bus bar 6 is connected to the negative terminal of the power supply 2. A smoothing capacitor (hereinafter simply referred to as capacitor) 7 is connected between the positive bus bar 5 and the negative bus bar 6 to suppress fluctuations in the voltage output from the power supply 2 and to suppress fluctuations in the voltage input to the power supply 2. Specifically, the positive terminal of the capacitor 7 is connected to the positive bus bar 5, and the negative terminal is connected to the negative bus bar 6.

[0018] An inverter 8 is further connected between the positive bus bar 5 and the negative bus bar 6. This inverter 8 includes an upper arm switch (element) 9 and a lower arm switch (element) 10. The collector, which is the high potential terminal of this upper arm switch 9, is connected to the positive bus bar 5, the emitter, which is the low potential terminal, is connected to the collector, which is the high potential terminal of the lower arm switch 10, and the emitter, which is the low potential terminal of the lower arm switch 10, is connected to the negative bus bar 6. In other words, the upper arm switch 9 and the lower arm switch 10 are connected in series.

[0019] 1 is a three-phase AC motor, each of the upper arm switch 9 and the lower arm switch 10 is composed of three switches. Specifically, the upper arm switch 9 is composed of a first switch Q1 connected to the U-phase coil 3u, a third switch Q3 connected to the V-phase coil 3v, and a fifth switch Q5 connected to the W-phase coil 3w. The lower arm switch 10 is composed of a second switch Q2 connected to the U-phase coil 3u, a fourth switch Q4 connected to the V-phase coil 3v, and a sixth switch Q6 connected to the W-phase coil 3w.

[0020] Each of these switches Q1 to Q6 is configured by a conventionally known insulated gate bipolar transistor (IGBT), and flywheel diodes D1 to D6 are connected in anti-parallel to each of the switches Q1 to Q6. Note that each of the switches Q1 to Q6 is not limited to an IGBT, and may be configured by other switching elements such as a metal oxide semiconductor field effect transistor (MOSFET). These switches Q1 to Q6 correspond to the "switching elements" in the embodiments of the present invention.

[0021] One end of U-phase coil 3u is connected to the connection point between first switch Q1 and second switch Q2, one end of V-phase coil 3v is connected to the connection point between third switch Q3 and fourth switch Q4, and one end of W-phase coil 3w is connected to the connection point between fifth switch Q5 and sixth switch Q6. The other ends of U-phase coil 3u, V-phase coil 3v, and W-phase coil 3w are connected to neutral point 4 as described above.

[0022] The electrical system 1 described above is provided with a phase current sensor 11 that detects the current flowing through each of the coils 3u, 3v, and 3w, a resolver 12 that detects the rotation speed of the motor 3, and an inverter control device (hereinafter referred to as a controller) 13 that controls each of the switches Q1 to Q6 based on data detected by these sensors 11 and 12. Note that since the sum of the instantaneous values ​​of the three-phase currents iu, iv, and iw is zero, in the example shown in Fig. 1, phase current sensors 11u and 11v are provided to detect motor currents for two phases, the U-phase current iu and the V-phase current iv.

[0023] This controller 13 is an electronic control device mainly composed of a microcomputer, similar to controllers installed in conventional electric vehicles and hybrid vehicles equipped with a motor as a driving power source, and is configured to PWM control the inverter 8.

[0024] Therefore, the controller 13 is configured to receive signals such as a signal Sθ related to the rotation angle θ of the motor 3 output from the R / D converter 16 described later, a current value Im required for the motor 3 (i.e., the target torque of the motor 3), and a target rotation number (rotational speed) Nm of the motor 3.

[0025] The controller 13 also stores a map for calculating (selecting) a carrier frequency (hereinafter referred to as reference carrier frequency) fc0 according to the current value (hereinafter referred to as motor current) Im required for the motor 3 and the target rotation speed (hereinafter referred to as motor rotation speed) Nm of the motor 3. This reference carrier frequency fc0 is a frequency determined by conducting experiments and simulations in advance using the motor current Im and the motor rotation speed Nm as variables, and is determined so as to suppress vibrations and abnormal noise when the motor 3 is driven and to improve controllability. This reference carrier frequency fc0 corresponds to the "predetermined switching frequency" in the embodiments of the present invention.

[0026] Furthermore, the controller 13 is configured to correct the reference carrier frequency fc0 when electromagnetic noise generated by PWM control of the inverter 8 affects the output signal of the resolver 12. An example of control for correcting the reference carrier frequency fc0 will be described later.

[0027] The controller 13 is configured to determine a signal to be output to each of the switches Q1 to Q6 based on the corrected carrier frequency (hereinafter referred to as the command carrier frequency) fc. Specifically, the controller 13 is configured to determine a pulse width (on-duty ratio) for turning on each of the switches Q1 to Q6 from a voltage command value required of the motor 3 and a carrier signal based on the command carrier frequency fc, and to output a signal corresponding to that signal to each of the switches Q1 to Q6. Note that PWM control can be performed in the same manner as in the conventional case, and therefore a detailed description thereof will be omitted.

[0028] Fig. 2 shows a schematic diagram for explaining the configuration of the resolver 12. The resolver 12 shown in Fig. 2 is a one-phase excitation, two-phase output type resolver, and includes a stator 14, a rotor 15, a resolver digital converter (hereinafter referred to as an R / D converter) 16, an excitation coil 17, and detection coils 18a and 18b.

[0029] The R / D converter 16 is composed of a signal generating circuit 16a that generates an excitation current and a microcomputer 16b that performs signal calculations.

[0030] The rotor 15 is a ferromagnetic material having an elliptical cross section, and is engaged with the output shaft (rotor shaft) 3a of the motor 3 by a spline or the like so as to rotate integrally with the output shaft 3a. Therefore, the rotation angle θ of the output shaft 3a of the motor 3 can be detected by detecting the rotational angle position of the rotor 15. The rotor 15 is not limited to one having an elliptical cross section, and may be, for example, a member having a cross-sectional shape with four protrusions formed at 90-degree intervals from each other, and the shape of the rotor 15 is not particularly limited.

[0031] The excitation coil 17 and the detection coils 18a, 18b are built into the stator 14, and the detection coils 18a, 18b are positioned with an electrical angle of 90 degrees apart. The excitation coil 17 is also connected to a signal generating circuit 16a. Therefore, when the signal generating circuit 16a applies an AC voltage, which is an excitation signal Sr, to the excitation coil 17, an AC current having a frequency corresponding to the AC voltage is supplied to the excitation coil 17. In principle, the AC voltage applied to the excitation coil 17 is an AC voltage having a predetermined frequency (hereinafter referred to as the excitation frequency) fr, and the excitation frequency fr corresponds to the "predetermined excitation frequency" in this embodiment of the present invention. While FIG. 2 shows one excitation coil 17 and a pair of detection coils 18a, 18b, multiple sets of the excitation coil 17 and the detection coils 18a, 18b may be attached to the stator 14.

[0032] Fig. 3 shows the AC waveforms of the excitation coil 17 and the detection coils 18a and 18b. The horizontal axis in Fig. 3 represents the rotation angle θ of the rotor 15, and the vertical axis represents the voltage value. The excitation signal Sr is a signal generated by, for example, an oscillator (not shown) provided in the signal generating circuit 16a, and is an AC voltage with a constant amplitude and a constant frequency. Therefore, an excitation current, which is an AC current with the same frequency as the excitation signal Sr, is generated in the excitation coil 17, thereby exciting the rotor 15, which is made of a ferromagnetic material.

[0033] The magnetic flux of the rotor 15 caused by such excitation varies according to the excitation frequency fr. Therefore, as the magnetic flux of the rotor 15 changes, an AC voltage (induced voltage) having the same frequency as the excitation frequency fr is generated in the detection coils 18a and 18b.

[0034] Furthermore, as the gap between the detection coils 18a, 18b and the rotor 15 increases, the magnetic flux density passing through the detection coils 18a, 18b decreases, thereby decreasing the voltage induced in the detection coils 18a, 18b. Because the cross section of the rotor 15 is elliptical as described above, the gap between the detection coils 18a, 18b and the rotor 15 changes as the rotor 15 rotates. Therefore, the amplitude of the voltage detected by the detection coils 18a, 18b changes according to the gap. Therefore, the amplitude of the voltage detected by the detection coils 18a, 18b changes periodically with different phases according to the change in the rotation angle θ of the motor 3.

[0035] The voltage detected by the detection coils 18a and 18b can be calculated by adding together the AC voltages generated in the detection coils 18a and 18b by passing an AC excitation current through the excitation coil 17 and the AC voltages generated in the detection coils 18a and 18b by the rotation of the excited rotor 15. In other words, the voltages detected by the detection coils 18a and 18b are AC voltages obtained by combining the AC voltages generated in the detection coils 18a and 18b by applying a current to the excitation coil 17 and the AC voltages generated in the detection coils 18a and 18b in accordance with the rotation (angular velocity) of the rotor 15. Therefore, the AC voltages output from the detection coils 18a and 18b include multiple frequency components. In the following description, the AC voltages output from the detection coils 18a and 18b will be referred to as AC voltage signals Sa and Sb.

[0036] The virtual waveform Wa obtained by connecting the peak points of the AC voltage signal Sa is an AC waveform that corresponds to changes in the gap between the stator 14 and the rotor 15. Similarly, the virtual waveform Wb obtained by connecting the peak points of the AC voltage signal Sb is an AC waveform that corresponds to changes in the gap between the stator 14 and the rotor 15.

[0037] Here, the rotational angle position of rotor 15 can be determined from the difference between the values ​​of each virtual waveform Wa, Wb. Furthermore, a phase difference equivalent to an electrical angle of 90 degrees occurs between each virtual waveform Wa, Wb, and the rotation direction (positive rotation / negative rotation) of rotor 15 can be determined from the polarity of the phase difference between the virtual waveforms (which phase of the virtual waveforms is leading).

[0038] The microcomputer 16b provided in the R / D converter 16 described above is configured to generate a signal Sθ corresponding to the rotation angle θ of the rotor 15 and output it to the controller 13. Therefore, the microcomputer 16b receives the excitation signal Sr of the excitation coil 17 from the signal generating circuit 16a and the AC voltage signals Sa and Sb from the detection coils 18a and 18b, and generates virtual waveforms Wa and Wb based on these signals. The microcomputer 16b then generates a signal Sθ corresponding to the rotation angle θ of the rotor 15 based on the generated virtual waveforms Wa and Wb and outputs it to the controller 13.

[0039] As described above, each of the switches Q1 to Q6 is PWM controlled based on the carrier frequency. Therefore, when the inverter 8 is operating, in addition to a carrier wave according to the carrier frequency, a lower sideband wave with a frequency lower than the carrier frequency and an upper sideband wave with a frequency higher than the carrier frequency are generated as electromagnetic noise. Hereinafter, the frequency of the electromagnetic noise based on the lower sideband wave will be referred to as the lower noise frequency fnol, and the frequency of the electromagnetic noise based on the upper sideband wave will be referred to as the upper noise frequency fnoh.

[0040] Furthermore, the AC voltage signals Sa and Sb described above have peaks at the voltage value of a frequency component obtained by adding a frequency (hereinafter referred to as the rotational frequency) fm corresponding to the angular velocity of the rotor 15 to the excitation frequency fr, and at the voltage value of a frequency component obtained by subtracting the rotational frequency fm from the excitation frequency fr. Hereinafter, the frequency obtained by adding the rotational frequency fm to the excitation frequency fr will be referred to as the upper output frequency foh, and the frequency obtained by subtracting the rotational frequency fm from the excitation frequency fr will be referred to as the lower output frequency fol. The upper output frequency foh and the lower output frequency fol correspond to the "frequency of the detection signal of the detection coil" in this embodiment of the present invention.

[0041] Therefore, when the upper output frequency foh or the lower output frequency fol coincides with the upper noise frequency fnoh or the lower noise frequency fnol, the virtual waveforms Wa and Wb generated by the microcomputer 16b are waveforms that are affected by electromagnetic noise, and an error occurs in the rotation angle θ of the motor 3 due to this influence.

[0042] Therefore, the electric motor control device in this embodiment of the present invention is configured to correct the reference carrier frequency fc0 and determine the command carrier frequency fc so that the upper noise frequency fnoh and the lower noise frequency fnol generated by controlling the motor 3 do not match the frequency of the output signal of the resolver 12 (i.e., the upper output frequency foh and the lower output frequency fol).

[0043] A flowchart illustrating an example of this control is shown in Figure 4. In the example shown in Figure 4, first, command values ​​corresponding to the operating state required of motor 3, i.e., motor current Im and motor rotation speed Nm, are calculated (step S1). If motor 3 is a motor provided as a driving force source for a vehicle, step S1 calculates the torque required of motor 3 based on, for example, accelerator operation amount and vehicle speed, and calculates the current value (motor current) Im for outputting the calculated required torque, and also calculates the target rotation speed (motor rotation speed) Nm of motor 3 based on the gear ratio between motor 3 and the drive wheels and the vehicle speed. Note that step S1 may involve calculating the motor current Im and motor rotation speed Nm using a controller other than controller 13, and reading the signals thereof into controller 13.

[0044] Next, a reference carrier frequency fc0 is calculated based on the command value of the motor 3 calculated in step S1 (step S2). The reference carrier frequency fc0 in step S2 can be determined based on the map stored in the controller 13 as described above, and the motor current Im and motor rotation speed Nm calculated in step S1.

[0045] By calculating the reference carrier frequency fc0 as described above, it is possible to estimate the frequencies fnoh and fnol of the electromagnetic noise that occurs when the inverter 8 is controlled in accordance with the reference carrier frequency fc0. It is also possible to estimate the frequencies (upper output frequency foh and lower output frequency fol) of the AC voltage signals Sa and Sb of the resolver 12 when the rotation speed of the motor 3 is the motor rotation speed Nm calculated in step S1.

[0046] Specifically, the upper noise frequency fnoh can be calculated by the following equation (1), the lower noise frequency fnol can be calculated by the following equation (2), the upper output frequency foh can be calculated by the following equation (3), and the lower output frequency fol can be calculated by the following equation (4). fnoh=fc0+nc×Nm×pm …(1) fnol=fc0-nc×Nm×pm …(2) foh = fr + Nm × pr …(3) fol = fr - Nm × pr …(4)

[0047] Here, nc in equations (1) and (2) is an integer coefficient determined according to the magnitude of the electromagnetic noise, and is determined to have a larger value as the magnitude of the electromagnetic noise increases, in other words, as the current value passing through the motor 3 increases. Furthermore, pm in equations (1) and (2) is the number of poles of the motor 3, and pr in equations (3) and (4) is the number of poles of the resolver 12. That is, the upper noise frequency fnoh and the lower noise frequency fnol can be obtained by adding or subtracting the rotational frequency (nc × Nm × pm) based on the rotational speed (rotational speed) of the motor 3 and the number of poles of the motor 3 to or from the reference carrier frequency fc0, and the upper output frequency foh and the lower output frequency fol can be obtained by adding or subtracting the rotational frequency (Nm × pr) based on the rotational speed (rotational speed) of the motor 3 and the number of poles of the resolver 12 to or from the excitation frequency fr.

[0048] As described above, the control example shown here is configured to suppress interference of the electromagnetic noise frequencies fnoh and fnol with the AC voltage signals Sa and Sb, i.e., to change the electromagnetic noise frequencies fnoh and fnol by correcting the reference carrier frequency fc0.

[0049] Therefore, following step S2, it is determined whether the reference carrier frequency fc0 is higher than the excitation frequency fr (step S3). This step S3 is a step for determining whether there is a possibility that the lower noise frequency fnol matches the upper output frequency foh, as shown in Fig. 5. Therefore, if the reference carrier frequency fc0 is higher than the excitation frequency fr and the determination in step S3 is affirmative, the reference carrier frequency fc0 is corrected so that the lower noise frequency fnol becomes a frequency higher than the upper output frequency foh.

[0050] Specifically, the command carrier frequency fc for controlling the inverter 8 is set to a frequency that satisfies the following equation (5) (step S4). Here, equation (5) is an equation obtained by rearranging equation (6) with respect to the command carrier frequency fc. fc>fr+Nm×pr+nc×Nm×pm…(5) fc-nc×Nm×pm>fr+Nm×pr …(6)

[0051] That is, the command carrier frequency fc is set so that the difference between the command carrier frequency fc and the excitation frequency fr is greater than the difference between the reference carrier frequency fc0 and the excitation frequency fr. In order to suppress an increase in vibration and abnormal noise during PWM control of the inverter 8, it is preferable to set the command carrier frequency fc to a frequency that satisfies equation (5) and has a small difference from the reference carrier frequency fc0.

[0052] Conversely, if the reference carrier frequency fc0 is equal to or lower than the excitation frequency fr and therefore the result of step S3 is negative, the frequencies of the AC voltage signals Sa and Sb (i.e., the upper output frequency foh and the lower output frequency fol) will be between the upper noise frequency fnoh and the frequency of the electromagnetic noise (sideband) corresponding to the secondary carrier wave, or will be equal to or higher than the frequency of the electromagnetic noise corresponding to the secondary carrier wave.

[0053] Therefore, if the determination in step S3 is negative, it is determined whether the frequencies of the AC voltage signals Sa and Sb (i.e., the upper output frequency foh and the lower output frequency fol) are between the upper noise frequency fnoh and the frequency of the electromagnetic noise corresponding to the secondary carrier wave, specifically, whether the reference carrier frequency fc0 is higher than 1 / 2 the excitation frequency fr (step S5).

[0054] If the reference carrier frequency fc0 is higher than half the excitation frequency fr and thus a positive determination is made in step S5, the frequency of the electromagnetic noise corresponding to the secondary carrier wave may match the frequencies foh and fol of the AC voltage signals Sa and Sb, and the upper noise frequency fnoh may match the lower output frequency fol. Specifically, as shown in FIG. 6(a), the lower noise frequency f'nol corresponding to the secondary carrier wave may match the upper output frequency foh, or as shown in FIG. 6(b), the upper noise frequency fnoh may match the lower output frequency fol. Note that in FIGS. 5 to 7, the frequency of the secondary carrier wave is denoted as 2fc0.

[0055] Therefore, if the answer to step S5 is affirmative, the reference carrier frequency fc0 is corrected so that the lower noise frequency f'nol corresponding to the secondary carrier wave becomes a higher frequency than the upper output frequency foh, and the upper noise frequency fnoh becomes a lower frequency than the lower output frequency fol.

[0056] Specifically, the command carrier frequency fc for controlling the inverter 8 is set to a frequency that satisfies the following equations (7) and (9) (step S6). Here, equation (7) is an equation obtained by rearranging equation (8) with respect to the command carrier frequency fc, and equation (9) is an equation obtained by rearranging equation (10) with respect to the command carrier frequency fc. fc>(fr+Nm×pr+nc×Nm×pm) / 2 …(7) 2fc-nc×Nm×pm>fr+Nm×pr…(8) fc <fr-Nm×pr-nc×Nm×pm …(9) fc+nc×Nm×pm <fr-Nm×pr …(10)

[0057] In other words, the command carrier frequency fc is set so that the difference between the frequency of the secondary carrier wave (twice the frequency of the command carrier frequency fc) and the excitation frequency fr is larger than the difference between the frequency of the secondary carrier wave before correction (twice the frequency of the reference carrier frequency fc0) and the excitation frequency fr, or the command carrier frequency fc is set so that the difference between the command carrier frequency fc and the excitation frequency fr is larger than the difference between the reference carrier frequency fc0 and the excitation frequency fr. Note that, in order to suppress an increase in vibration and abnormal noise during PWM control of the inverter 8, it is preferable to set the command carrier frequency fc to a frequency that satisfies equations (7) and (9) and has a small difference from the reference carrier frequency fc0.

[0058] On the other hand, if the reference carrier frequency fc0 is equal to or less than half the excitation frequency fr and the result of step S5 is negative, the frequencies of the AC voltage signals Sa and Sb (i.e., the upper output frequency oh and the lower output frequency fol) will be equal to or greater than the frequency of the electromagnetic noise corresponding to the secondary carrier wave. In this case, the upper noise frequency f'noh corresponding to the secondary carrier wave may coincide with the frequencies foh and fol of the AC voltage signals Sa and Sb. Specifically, as shown in FIG. 7, the upper noise frequency f'noh corresponding to the secondary carrier wave may coincide with the lower output frequency fol.

[0059] Therefore, if the determination in step S5 is negative, the reference carrier frequency fc0 is corrected so that the upper noise frequency f'noh corresponding to the secondary carrier wave becomes higher than the lower output frequency fol.

[0060] Specifically, the command carrier frequency fc for controlling the inverter 8 is set to a frequency that satisfies the following equation (11) (step S7). Here, equation (11) is an equation obtained by rearranging equation (12) with respect to the command carrier frequency fc. fc<(fr-Nm×pr-nc×Nm×pm) / 2 …(11) 2fc+nc×Nm×pm <fr-Nm×pr …(12)

[0061] In other words, the command carrier frequency fc is set so that the difference between the frequency of the secondary carrier wave (twice the command carrier frequency fc) and the excitation frequency fr is greater than the difference between the frequency of the secondary carrier wave before correction (twice the reference carrier frequency fc0) and the excitation frequency fr. Note that, in order to suppress an increase in vibration and abnormal noise during PWM control of the inverter 8, it is preferable to set the command carrier frequency fc to a frequency that satisfies equation (11) and has a small difference from the reference carrier frequency fc0.

[0062] Then, the inverter 8 is PWM controlled based on the command carrier frequency fc set in any one of steps S4, S6, and S7 (step S8), and this routine is temporarily ended.

[0063] Note that electromagnetic noise corresponding to third-order or higher-order carrier waves has a small amplitude, and therefore has little effect on the detection value of the resolver 12 even if the frequency of the electromagnetic noise matches the frequency of the AC voltage signals Sa and Sb. Therefore, the above control example does not include a step of correcting the reference carrier frequency fc0 based on the electromagnetic noise corresponding to the higher-order carrier waves. However, the motor control device in the embodiment of the present invention may correct the reference carrier frequency fc0 based on the frequency of the electromagnetic noise corresponding to the above-mentioned higher-order carrier waves.

[0064] The above-described equations (5) to (12) calculate the frequency of electromagnetic noise generated when the switching elements are controlled based on the reference carrier frequency fc0 and the frequency of AC voltage signals Sa, Sb when motor 3 rotates at the motor rotation speed Nm required for motor 3, and calculate a command carrier frequency fc at which the estimated frequency of electromagnetic noise and the frequency of AC voltage signals Sa, Sb differ. By determining the command carrier frequency fc in this way based on the estimated frequency of electromagnetic noise and the estimated frequency of AC voltage signals, it is possible to prevent detection errors in the resolver 12 from occurring due to electromagnetic noise being superimposed on the AC voltage signals Sa, Sb.

[0065] Furthermore, as described above, by setting the command carrier frequency so that the difference between the carrier frequency or the frequency of the secondary carrier wave and the excitation frequency is large, the degree of freedom in setting the command carrier frequency can be improved. In other words, when setting the command carrier frequency taking into consideration the initial characteristics and aging degradation of each switch Q1 to Q6, a range of settable command carrier frequencies can be provided, which prevents the frequency of electromagnetic noise from matching the frequency of the AC voltage signals Sa and Sb due to changes in the characteristics of those switches Q1 to Q6. In other words, the command carrier frequency fc for suppressing detection errors of the resolver 12 can be easily set, simplifying control.

[0066] Furthermore, the frequency of electromagnetic noise generated when switching elements are controlled based on the reference carrier frequency fc0 and the frequency of AC voltage signals Sa, Sb when motor 3 rotates at the motor rotation speed Nm required for motor 3 are estimated taking into account the number of poles of motor 3 and the number of poles of resolver 12. Therefore, even if the number of poles of motor 3 differs from the number of poles of resolver 12, by setting command carrier frequency fc based on the estimated frequency of electromagnetic noise and the frequency of AC voltage signals Sa, Sb, it is possible to prevent the frequency of electromagnetic noise and AC voltage signals Sa, Sb from matching. In other words, it is possible to prevent a reduction in design freedom, such as by limiting the number of poles of motor 3 or resolver 12, in order to prevent the frequency of electromagnetic noise and AC voltage signals Sa, Sb from matching.

[0067] Furthermore, as described above, the command carrier frequency fc can be set to a frequency different from the frequency of electromagnetic noise and the frequency of AC voltage signals Sa and Sb, in other words, the influence of electromagnetic noise on AC voltage signals Sa and Sb can be suppressed, so the motor 3 and resolver 12 can be arranged close to each other, and there is no need to provide a member such as a shield to block electromagnetic noise.As a result, the motor assembly including the motor 3 and resolver 12 can be made smaller.

[0068] On the other hand, the magnitude of the electromagnetic noise increases according to the magnitude of the current flowing through the motor 3. Therefore, when the torque required of the motor 3 is small and therefore the current flowing through the motor 3 is small, the electromagnetic noise generated by controlling the motor 3 is also small. In other words, the degree of influence of the electromagnetic noise on the AC voltage signals Sa, Sb of the resolver 12 is small. Therefore, when the current flowing through the motor 3 is large and the degree of influence of the electromagnetic noise on the AC voltage signals Sa, Sb of the resolver 12 is greater than a predetermined level, the reference carrier frequency fc0 may be corrected.

[0069] An example of this control is shown in Fig. 8. Note that the control example shown in Fig. 8 is obtained by adding step S11 and step S12 to the control example shown in Fig. 4, and therefore the same steps as those in the control example shown in Fig. 4 are denoted by the same reference numerals and their explanations will be omitted.

[0070] 8, following step S2, it is determined whether the motor current Im is less than a predetermined current I1 (step S11). This step S11 is a step for determining whether electromagnetic noise generated by controlling the motor 3 affects the AC voltage signals Sa and Sb of the resolver 12 to such an extent that the detection error of the rotation angle of the motor 3 by the resolver 12 becomes equal to or greater than a predetermined difference. Therefore, the predetermined current I1 in step S11 is a current value that is set in advance by conducting experiments or simulations, taking into consideration the arrangement (distance) between the motor 3 and the resolver 12, etc.

[0071] If the motor current Im is equal to or greater than the predetermined current I1 and therefore a negative determination is made in step S11, electromagnetic noise generated by controlling the motor 3 is superimposed on the AC voltage signals Sa and Sb of the resolver 12, increasing the detection error of the rotation angle of the motor 3 by the resolver 12. Therefore, if a negative determination is made in step S11, steps S4 to S7 are executed to correct the reference carrier frequency fc0.

[0072] Conversely, if the motor current Im is less than the predetermined current I1 and therefore the answer in step S11 is affirmative, the degree to which electromagnetic noise generated by controlling the motor 3 affects the AC voltage signals Sa, Sb of the resolver 12 is small. In other words, even if electromagnetic noise is superimposed on the AC voltage signals Sa, Sb of the resolver 12, the detection error in the rotation angle of the motor 3 is small, and the degree to which it affects the controllability of the motor 3 is low.

[0073] Therefore, if the answer to step S11 is affirmative, the reference carrier frequency fc0 calculated in step S2 is set as the command carrier frequency fc (step S12), and the process proceeds to step S8.

[0074] As described above, the reference carrier frequency fc0 is corrected when the value of the current flowing through the motor 3 is large. In other words, the reference carrier frequency fc0 is not corrected when the value of the current flowing through the motor 3 is small. This not only prevents the occurrence of increased vibrations and abnormal noise when the motor 3 is operated under low load, but also prevents deterioration of controllability.

[0075] In the above-described control examples, the reference carrier frequency fc0 is corrected to suppress superposition of electromagnetic noise on the AC voltage signals Sa and Sb. However, the excitation frequency fr may be corrected in addition to or instead of the reference carrier frequency fc0. That is, the excitation frequency fr may be corrected to satisfy the above equations (5), (7), (9), and (11). Specifically, for example, if the correction amount is relatively large and the corrected commanded carrier frequency fc deviates from the allowable frequency band, the commanded carrier frequency fc may be corrected within the allowable frequency band, and the excitation frequency fr may be corrected based on the correction amount that is insufficient to satisfy the above equations (5), (7), (9), and (11). Alternatively, when the vehicle equipped with the motor 3 is traveling at a low speed and is intolerant of vibrations and abnormal noise, the excitation frequency fr may be corrected instead of the reference carrier frequency fc0. [Explanation of symbols]

[0076] 1. Electrical System 2 Power supply 3 motors 3a Output shaft 3u, 3v, 3w coils 8 inverters 9 Upper arm switch 10 Lower arm switch 11 Phase Current Sensor 12 Resolver 13 Controller 14 Stator 15 rotors 16 R / D converter 16a Signal generation circuit 16b Microcomputer 17 Excitation coil 18a, 18b detection coil Q1~Q6 switches Sa, Sb AC voltage signal Sr excitation signal Wa,Wb Virtual waveform fnoh Upper noise frequency fnol Lower noise frequency fc command carrier frequency fc0 Reference carrier frequency fm rotation frequency foh Upper output frequency fol Lower output frequency fr excitation frequency

Claims

1. a motor control device including a DC power supply, an AC motor that operates when an AC voltage is applied to it, an inverter that has a plurality of switching elements and converts the DC voltage to the AC voltage by controlling the plurality of switching elements at a predetermined switching frequency according to an operating state required of the AC motor, and a resolver that has a rotor connected to an output shaft of the AC motor, an excitation coil that excites the rotor when an AC voltage of a predetermined excitation frequency is applied to it, and a detection coil that generates an induced voltage according to the magnetic flux of the rotor, a controller for controlling the switching element; The controller estimating a frequency of electromagnetic noise that will be generated when the switching element is controlled based on the predetermined switching frequency; estimating a frequency of a detection signal from the detection coil when the AC motor is driven in the required operating state; At least one of the predetermined switching frequency and the predetermined excitation frequency is corrected so that the estimated frequency of the electromagnetic noise and the frequency of the detection signal of the detection coil are different frequencies. A control device for an electric motor.

2. The motor control device according to claim 1, The frequency of the electromagnetic noise includes the frequency of a sideband wave corresponding to a carrier wave generated by controlling the switching element. A control device for an electric motor.

3. The motor control device according to claim 1, The frequency of the electromagnetic noise includes the frequency of a sideband wave corresponding to a high-order carrier wave generated by controlling the switching element. A control device for an electric motor.

4. The motor control device according to claim 1, The frequency of the electromagnetic noise includes an upper frequency obtained by adding a rotation frequency based on the rotation speed of the AC motor and the number of poles of the AC motor to the frequency of a carrier wave generated by controlling the switching element, and a lower frequency obtained by subtracting the rotation frequency from the frequency of the carrier wave. A control device for an electric motor.

5. The motor control device according to claim 1, The frequency of the electromagnetic noise includes an upper frequency obtained by adding a rotation frequency based on the rotation speed of the AC motor and the number of poles of the AC motor to the frequency of a high-order carrier wave generated by controlling the switching element, and a lower frequency obtained by subtracting the rotation frequency from the frequency of the carrier wave. A control device for an electric motor.

6. The motor control device according to claim 1, The frequency of the detection signal of the detection coil includes an upper output frequency obtained by adding a rotation frequency based on the rotation speed of the AC motor and the number of poles of the resolver to the predetermined excitation frequency, and a lower output frequency obtained by subtracting the rotation frequency from the predetermined excitation frequency. A control device for an electric motor.

7. The motor control device according to claim 1, The controller When a current value required for the AC motor is equal to or greater than a predetermined current value, at least one of the predetermined switching frequency and the predetermined excitation frequency is corrected. A control device for an electric motor.

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