Motor control device

Abstract

To provide a motor controller capable of achieving a voltage output closer to a command value while suppressing an increase in calculation load.SOLUTION: A motor control device that controls driving of an AC motor connected to an inverter having a plurality of switching elements, the motor control device comprising: a dq-axis voltage command generation unit that generates a dq-axis voltage command value for the AC motor for each predetermined calculation cycle; A modulation factor command generation unit that generates one or more modulation factor command values, and a duty command generation unit that generates a duty command value for generating a gate signal for controlling an operation of a switching element based on the modulation factor command value are provided, and the modulation factor command generation unit switches a method of generating the modulation factor command value according to the number of times of switching when the number of times of switching is equal to or greater than a predetermined number of times.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a motor control device. [Background technology]

[0002] Higher efficiency is required in motor drive systems. Modern motor drives control output voltage using pulse width modulation (PWM), but harmonic currents generated by harmonic voltages contained in pulse voltages increase motor iron loss and magnet loss. On the other hand, in asynchronous PWM domains (PWM where the carrier signal and the motor's electrical angle are not synchronized), using a higher carrier frequency (switching frequency) is effective in reducing harmonic currents generated by PWM and suppressing motor loss. In particular, with wide bandgap semiconductors such as SiC, which have been increasingly used in recent years, inverter switching losses do not increase significantly with increasing carrier frequency, so the reduction in losses due to harmonic currents in the motor is more pronounced, expanding the range in which drive system efficiency can be improved.

[0003] In general inverter control, one switch timing in the next control cycle is calculated in one control cycle. Therefore, to improve the inverter's carrier frequency, the control cycle must be shortened. However, in reality, there is a limit to how much the control cycle can be shortened, so it is not always possible to increase the carrier frequency to the desired frequency. Therefore, it is possible to calculate multiple switch timings in one control cycle. This makes it possible to increase the effective carrier frequency to an integer multiple of the control cycle.

[0004] For example, in Patent Document 1, in synchronous PWM, multiple switch timings are calculated in advance for the modulation rate and rotation speed and output as a table, making it possible to set multiple switch timings within one control period. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-88892 Summary of the Invention [Problem to be solved by the invention]

[0006] In asynchronous PWM, to calculate multiple switch timings within one control period, consider calculating the three-phase modulation factor command value (three-phase voltage command value normalized by DC voltage) at each switch timing θ. Because the calculation of the three-phase modulation factor command value muvw* uses dq-axis / three-phase coordinate transformation, which includes trigonometric functions, the calculation load increases as the number of switch timings increases, and it becomes impossible to complete the calculation within the control period.

[0007] The present invention has been made in view of the above, and has an object to provide a motor control device that can realize a voltage output that is closer to a command value while suppressing an increase in calculation load. [Means for solving the problem]

[0008] The present application includes a plurality of means for solving the above-described problems. One example is a motor control device that controls the drive of an AC motor connected to an inverter having a plurality of switching elements, the motor control device comprising: a dq-axis voltage command generation unit that generates a dq-axis voltage command value for the AC motor for each predetermined calculation period; a modulation factor command generation unit that generates one or more modulation factor command values ​​based on the dq-axis voltage command value, a phase of the AC motor, and the number of times the switching elements perform switching within the calculation period; and a duty command generation unit that generates, based on the modulation factor command value, a duty command value for generating a gate signal that controls operation of the switching elements, wherein the modulation factor command generation unit switches a method for generating the modulation factor command value in accordance with the number of times the switching is performed when the number of times the switching is greater than or equal to a predetermined number. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress an increase in the calculation load and realize a voltage output that is closer to the command value. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 2 is a functional block diagram showing the configuration of the motor control device together with related configurations. [Figure 2] 3 is a functional block diagram showing the processing contents of a modulation factor command generating unit according to the first embodiment. FIG. [Figure 3] FIG. 10 is a diagram illustrating an example of setting a reference phase. [Figure 4] 10 is a diagram showing the relationship between a modulation factor (true modulation factor) obtained by coordinate transformation of a voltage command value and a linear approximation formula. FIG. [Figure 5] FIG. 2 is a diagram schematically illustrating the rising and falling edges of a pulse. [Figure 6] FIG. 10 is a diagram illustrating an example of conventional inverter control as a comparative example. [Figure 7] FIG. 10 is a diagram illustrating a comparative example in which a zero-order hold is applied. [Figure 8] FIG. 10 is a diagram illustrating a comparative example between the error in the present invention and the error when the reference phase is fixed. [Figure 9] FIG. 10 is a functional block diagram showing the processing contents of a modulation factor command generating unit according to a second embodiment. [Figure 10] FIG. 11 is a functional block diagram showing the processing contents of a modulation factor command generating unit according to a third embodiment. [Figure 11] FIG. 10 is a diagram showing the relationship between the true modulation factor obtained by coordinate transformation of a voltage command and an approximate expression. [Figure 12] FIG. 10 is a functional block diagram showing the processing contents of a modulation factor command generating unit according to a fourth embodiment. [Figure 13] FIG. 10 is a diagram showing the relationship between the true modulation factor obtained by coordinate transformation of a voltage command and an approximate expression. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, a three-phase AC motor and an inverter are described as examples of objects to be controlled by a motor control device, but the present invention is not limited to this, and for example, a polyphase AC motor and an inverter other than three phases may also be used as the object to be controlled.

[0012] First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

[0013] FIG. 1 is a functional block diagram showing the configuration of a motor control device according to this embodiment together with related configurations.

[0014] 1, an AC motor 2, which is the object of control of the motor control device 1, is connected to the motor control device 1 via an inverter 3 having multiple switching elements. The inverter 3 controls the three-phase AC voltage supplied to the AC motor 2 by switching the switching elements ON / OFF in response to gate drive signals output by the motor control device 1.

[0015] The AC motor 2 is a synchronous motor that is rotationally driven by a three-phase AC voltage supplied from an inverter 3. The AC motor 2 has a rotational position sensor 2a to control the phase of the three-phase AC voltage applied from the inverter 3 to match the phase of the induced voltage of the AC motor 2. Here, the rotational position sensor 2a can be, for example, a resolver composed of an iron core and a winding. Alternatively, the rotational position sensor 2a can be configured using a GMR (Giant Magneto Resistive effect) sensor or a Hall element.

[0016] The motor control device 1 includes a voltage command generator 4, a modulation factor command generator 5, a duty command generator 6, a gate command generator 7, and a rotational position detector 8.

[0017] Based on the output signal of rotational position sensor 2a, rotational position detection unit 8 detects the rotational position θ of the rotor in AC motor 2. Note that instead of detecting the rotational position θ of the rotor from the output signal of rotational position sensor 2a, the rotational position θ of the rotor of AC motor 2 may be estimated from the currents and voltages of various parts, and this value may be used as the detection value.

[0018] The voltage command generation unit 4 has a control function for controlling the output of the AC motor 2, and generates and outputs voltage command values ​​(Vd*, Vq*) (dq-axis voltage command values) so that the output (motor output) of the AC motor 2 matches a command value input from a higher-level control device (details omitted) that controls the entire system including the motor control device 1, the AC motor 2, the inverter 3, etc. The voltage command generation unit 4 recalculates and updates the voltage command values ​​(Vd*, Vq*) at each update period (control period). Note that the control variables for the motor output can be, for example, current, magnetic flux, rotation speed, torque, etc.

[0019] The switching count storage unit 9 is a storage function unit such as a memory that stores the switching count determined by the higher-level control device and input to the motor control device 1. The switching count stored in the switching count storage unit 9 is the number of times the switching elements of the inverter 3 are switched ON / OFF during one control period. For example, if the switching count is 3 times, the switching elements of the inverter 3 are switched ON / OFF three times during one control period.

[0020] The modulation factor command generating unit 5 generates modulation factor command values ​​(three-phase modulation factor command values) equal to the number of switching times for each of the U, V, and W phases using the voltage command values ​​(Vd*, Vq*) generated by the voltage command generating unit 4, the DC voltage DCV connected to the inverter 3, the rotational position θ of the AC motor 2 detected by the rotational position detecting unit 8, and the number of switching times stored in the switching count memory unit 9.

[0021] FIG. 2 is a functional block diagram showing the processing contents of the modulation factor command generating unit.

[0022] 2, the modulation factor command generating unit 5 is made up of a reference phase output unit 51, a coefficient calculating unit 52, a differentiator 53, a phase calculating unit 54, and a modulation factor calculating unit 55. In the following explanation, the U phase will be explained as a representative of the three phases, U phase, V phase, and W phase, but similar operations are performed for the V phase and W phase.

[0023] The reference phase output unit 51 sets two phases θ0 and θ1, starting from the control period, as reference phases in accordance with the switching count N stored in the switching count storage unit 9. FIG. 3 is a diagram showing an example of setting the reference phases. Note that the reference phases θ0 and θ1 are different from the "phase representing the n-th control period" described later.

[0024] The coefficient calculation unit 52 uses the reference phases θ0 and θ1 set by the reference phase output unit 51 to calculate the coefficients of an approximation formula for the modulation factor used in the modulation factor calculation unit 55 at the subsequent stage.

[0025] Specifically, for the reference phases θ0 and θ1, the voltage command values ​​(Vd*, Vq*) from the voltage command generation unit 4 are first coordinate-converted to three-phase voltages using the following (Equation 1), and the coordinate-converted values ​​are divided by the DC voltage DCV to calculate the three-phase modulation factor command values.

[0026]

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[0027] FIG. 4 is a diagram showing the relationship between the modulation factor (true modulation factor) obtained by coordinate transformation of the voltage command value and the linear approximation formula.

[0028] As shown in FIG. 4, when the modulation factor command values ​​of the U phase at the reference phases θ0 and θ1 are respectively set to mu0* and mu1*, a set of (θ0, mu0*) and (θ1, mu1*) is obtained.

[0029] A linear approximation formula showing the change in modulation factor m is expressed by the following (Formula 2) with phase θ as a variable.

[0030]

number

[0031] By substituting the set of (θ0, mu0*) and (θ1, mu1*) for the modulation factor m and phase θ in the above (Equation 2), the simultaneous equations in the following (Equation 3) are obtained.

[0032]

number

[0033] By solving the above (Equation 3), the coefficients a and b can be obtained as shown in the following (Equation 4).

[0034]

number

[0035] The coefficients a and b obtained as in (Equation 4) above are output to the modulation factor calculation unit 55.

[0036] A phase calculation unit 54 sets N phases for which modulation factor command values ​​should be calculated in a modulation factor calculation unit 55 at a subsequent stage, based on the number of switching times from a switching count storage unit 9, the detection result (electrical angle) from a rotational position detection unit 8, and the electrical angular velocity ω obtained by differentiating the electrical angle with a differentiator 53. Here, a case is considered where one control period is equally divided into N and phases for which modulation factor command values ​​should be calculated are set.

[0037] In the case shown in FIG. 4, the phase θn representing the n-th control period for which the modulation factor is to be calculated can be calculated using the following equation (5), where T is the control period, ω is the electrical angular velocity, and θS is the phase corresponding to the start of the control period.

[0038]

number

[0039] In this embodiment, the electrical angular velocity ω is obtained by differentiating the electrical angle using differentiator 53, but an electrical angle obtained by another method may be used, for example, a command value in speed control may be used. Also, in this embodiment, the explanation is given assuming that the electrical angular velocity is constant, but this is not limiting, and for example, the angular acceleration may be obtained in advance, and the phase θn may be obtained on the assumption that the electrical angular velocity changes gradually.

[0040] The modulation factor calculation unit 55 reflects the coefficients a and b shown in the above (Equation 4) obtained by the coefficient calculation unit 52 in the above (Equation 2), and by substituting the phase θn obtained in the above (Equation 5) into this formula, calculates the modulation factor command value mun* corresponding to the nth phase and outputs it to the duty command generation unit 6.

[0041] Returning to Fig. 1, duty command generator 6 of motor control device 1 generates a duty command value based on the modulation factor command value obtained from modulation factor command generator 5. For example, looking at the U phase as a representative, duty command generator 6 uses the following (Equation 6) to convert the modulation factor command value mun* to a duty command value Dun*, assuming that the case where the phase is always ON in one control cycle is 1.

[0042]

number

[0043] The gate command generation unit 7 calculates and sets the timing at which the switching elements of the inverter 3 should be switched ON / OFF (switching timing) in a format suitable for a microcomputer or the like based on the duty command value Dun* generated by the duty command generation unit 6, and outputs the calculated timing as a gate drive signal to the inverter 3. The calculation of the switch timing Tswn in the gate command generation unit 7 is performed by the following (Equation 7).

[0044]

number

[0045] Here, in the above (Equation 7), (pos edge) corresponds to the case where the pulse rises at that phase, and (nega edge) corresponds to the case where the pulse falls at that phase.

[0046] FIG. 5 is a diagram showing a schematic diagram of the rising and falling edges of a pulse in the case where the above (Equation 7) applies, with the horizontal axis representing time t.

[0047] For example, in the case of a microcontroller that generates PWM on a time basis, this can be achieved by setting a program counter that corresponds to the switch timing. Also, a similar concept can be applied to a microcontroller that generates PWM on an angle basis, and the switch timing can be calculated. By using an angle base, errors can be reduced even when the speed changes suddenly.

[0048] The effects of the present embodiment configured as above will be described.

[0049] FIG. 6 is a diagram showing an example of conventional inverter control as a comparative example with the present invention. In FIG. 6, for example, in the case of a normal pulse waveform, one switch timing in the next control period is calculated in one control period. Therefore, in order to improve the carrier frequency of the inverter, it is necessary to shorten the control period. However, in reality, there is a limit to how much the control period can be shortened, and it is therefore not always possible to increase the carrier frequency to the desired frequency.

[0050] Therefore, it is possible to calculate multiple switch timings in one control period, as shown by multiple pulse waveforms in Figure 6. This makes it possible to increase the effective carrier frequency to an integer multiple of the control period. For example, in synchronous PWM, by calculating multiple switch timings for the modulation rate and rotation speed in advance and outputting them as a table, it is possible to set multiple switch timings within one control period.

[0051] Furthermore, in asynchronous PWM, in order to calculate multiple switch timings within one control period, we consider calculating the three-phase modulation factor command value (three-phase voltage command value normalized by DC voltage) at each switch timing θ. Because the calculation of the three-phase modulation factor command value muvw* uses the dq-axis / three-phase coordinate transformation including the trigonometric functions shown above in (Equation 2), the calculation load increases as the number of switch timings increases, and it becomes impossible to complete the calculation within the control period.

[0052] Fig. 7 is a diagram illustrating the application of zero-order hold as a comparative example to the present invention. As shown in Fig. 7, if zero-order hold is applied to reduce the calculation load and the same modulation factor is used at all switch timings, an error will occur in the actual modulation factor command value, and it will not be possible to output a voltage that matches the command value.

[0053] In contrast, in this embodiment, a motor control device 1 controls the drive of an AC motor 2 connected to an inverter 3 having a plurality of switching elements, and includes: a voltage command generation unit 4 that generates a voltage command value for the AC motor 2 for each predetermined calculation period; a modulation factor command generation unit 5 that generates one or more modulation factor command values ​​based on the voltage command value, the phase of the AC motor 2, and the number of times N the switching elements perform switching within the calculation period; and a duty command generation unit 6 that generates, based on the modulation factor command value, a duty command value for generating a gate signal that controls the operation of the switching elements, and the modulation factor command generation unit 5 is configured to switch the method of generating the modulation factor command value in accordance with the number of switching times N when the number of switching times N is equal to or greater than a predetermined number. In this way, by calculating multiple switch timings within one control period, it is possible to improve the carrier frequency while suppressing an increase in calculation load, and to achieve a voltage output closer to the command value.

[0054] That is, in this embodiment, by replacing the coordinate transformation that has conventionally been performed N times using trigonometric functions (see (Equation 1) above) with a simple approximation formula (see (Equation 2) above), it is possible to reduce the number of coordinate transformations and the calculation processing load.

[0055] Furthermore, in this embodiment, errors in the modulation factor command value can be suppressed compared to when zero-order hold is used.

[0056] Furthermore, in this embodiment, the control period of the reference phase used in coefficient calculation unit 52 is configured to be changed according to the number of switching times N, so that errors can be suppressed more effectively than when the control period is not changed. Fig. 8 is a diagram showing a comparison between the error in the present invention and the error when the reference phase is fixed, with the horizontal axis representing N and the vertical axis representing N approximated modulation factor command values ​​and the maximum value of the error between the modulation factor calculated by coordinate transformation. As shown in Fig. 8, it can be seen that by changing the reference phase as in the present invention, modulation factor errors can be suppressed more effectively than when the reference phase is not changed according to the number of switching times N.

[0057] When the coefficients of the approximation formula (polynomial) of the modulation factor are found from a reference phase that minimizes the error in the modulation factor and the modulation factor corresponding to the reference phase, the reference phase that minimizes the maximum value of the modulation factor error may be calculated, for example, by solving the minimization problem of the following (Equation 8) in real time.

[0058]

number

[0059] However, from the viewpoint of reducing the calculation load, it is desirable to have a table of reference phases calculated in advance based on the above (Equation 8) and to set the reference phases using this table.

[0060] Furthermore, for example, a reference phase may be specified as a relative position, with the start point of the control period being 0 and the end point being 1, and a specific phase may be obtained by substituting the relative phase θ0 or θ1 in place of the (2n-1) / 2N term in the above (Equation 5).

[0061] <Second embodiment> A second embodiment of the present invention will be described with reference to FIG.

[0062] This embodiment shows a case where the order of the approximation formula is changed depending on the operating conditions. In this embodiment, the same members as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted as appropriate.

[0063] FIG. 9 is a functional block diagram showing the processing contents of the modulation factor command generating unit according to this embodiment.

[0064] 9, modulation factor command generation unit 5A is made up of reference phase output unit 51A, coefficient calculation unit 52A, differentiator 53, phase calculation unit 54, and modulation factor calculation unit 55A. In addition, an order determination unit 10 is provided outside modulation factor command generation unit 5A in motor control device 1. In the following explanation, the U phase will be described as a representative of the three phases, U phase, V phase, and W phase, but similar operations are performed for the V phase and W phase.

[0065] The order determination unit 10 determines the order p of the approximation formula used to calculate the modulation factor in the modulation factor calculation unit 55A according to the operating conditions of the AC motor 2. The operating conditions that the order determination unit 10 refers to when determining the order p include, for example, the rotation speed.

[0066] The reference phase output unit 51A sets two phases θ0 and θ1 starting from the control period as reference phases according to the number of switching times N stored in the number of switching times memory unit 9 and the order p determined by the order determination unit.

[0067] The coefficient calculation unit 52A uses the reference phases θ0 and θ1 set by the reference phase output unit 51A to calculate the coefficients of an approximation equation (p-th order polynomial) of the modulation factor used in the subsequent modulation factor calculation unit 55A. When (Equation 2) shown in the first embodiment is generalized to a p-th order polynomial, the following (Equation 9) is obtained.

[0068]

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[0069] To find the coefficients ap,...,a0 of the pth-order polynomial such as (Equation 9) above, (p+1) or more equations are required, so it is necessary to calculate (p+1) pairs of phase and modulation factor (θNn, muNn*) and set up simultaneous equations such as those shown in (Equation 10) below.

[0070]

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[0071] In the above (Equation 10), the coefficient vector a is determined by multiplying the modulation factor vector m by the inverse matrix of Θ from the left.

[0072] The modulation factor calculation unit 55A reflects the coefficient vector a obtained by the coefficient calculation unit 52A using the above (Equation 10) in the pth-order polynomial shown in the above (Equation 9), and by substituting the phase θn obtained by the phase calculation unit 54 into this pth-order polynomial, calculates the modulation factor command value mun* corresponding to the nth phase and outputs it to the duty command generation unit 6.

[0073] The other configurations are the same as those in the first embodiment.

[0074] The present embodiment configured as above can also achieve the same effects as the first embodiment.

[0075] Furthermore, for example, when the fundamental wave period of the true three-phase modulation factor command value is close to the control period T, first-order approximation may not be able to ensure the required modulation factor approximation accuracy. In such cases, it is necessary to increase the order p to improve the required modulation factor approximation accuracy. In this embodiment, by dynamically switching the order p, it is possible to ensure approximation accuracy, particularly in areas where the control period T and the fundamental wave frequency of the three-phase modulation factor are close, such as in the high rotation area.

[0076] The polynomial may include a variable other than the reference phase or a term with a non-integer exponent.

[0077] <Third embodiment> A third embodiment of the present invention will be described with reference to FIGS.

[0078] In this embodiment, two systems of modulation factor command generators with the same configuration are provided, with each system taking charge of the first and second halves of the control period. In this embodiment, the same members as in the first embodiment are given the same reference numerals, and their explanations will be omitted where appropriate.

[0079] FIG. 10 is a functional block diagram showing the processing contents of the modulation factor command generating unit according to this embodiment.

[0080] 10, the modulation factor command generator 5B has two systems of modulation factor command generators 5B1 and 5B2. The modulation factor command generators 5B1 and 5B2 have the same configuration, and each is composed of a reference phase output unit 51, a coefficient calculation unit 52, a differentiator 53, a phase calculation unit 54, and a modulation factor calculation unit 55.

[0081] FIG. 11 is a diagram showing the relationship between the true modulation factor obtained by coordinate transformation of the voltage command and the approximation formula.

[0082] As shown in FIG. 11, modulation factor command generators 5B1 and 5B2 correspond to two dashed approximate straight lines (approximation formulas) when the control period T is divided into two. For example, consider a case where modulation factor command generator 5B1 is responsible for the first half of the control period and modulation factor command generator 5B2 is responsible for the second half of the control period. In this case, modulation factor command generator 5B1, which is responsible for the first half of the control period, outputs phases θ0 and θ' as reference phases. Similarly, modulation factor command generator 5B2, which is responsible for the second half of the control period, outputs θ' and θ1 as reference phases. Because three-phase modulated waves are generally symmetric, θ' is best set in the center of the control period, but it can also be shifted from the center. Alternatively, the control period may be divided into two or more parts, with multiple modulation factor command generators each responsible for each part.

[0083] The other configurations are the same as those in the first embodiment.

[0084] The present embodiment configured as above can also achieve the same effects as the first embodiment.

[0085] Furthermore, since this is equivalent to approximating the three-phase modulation factor with a multi-step broken line, modulation factor errors can be suppressed compared to approximating with a single straight line (first-order approximation).

[0086] <Fourth embodiment> A fourth embodiment of the present invention will be described with reference to FIGS.

[0087] This embodiment shows a case where the coefficients of an approximation equation for the modulation factor are calculated using modulation factor command values ​​for the reference phase calculated in the previous control cycle and the current control cycle. In this embodiment, the same members as in the first embodiment are given the same reference numerals, and their explanations will be omitted as appropriate.

[0088] FIG. 12 is a functional block diagram showing the processing contents of the modulation factor command generating unit according to this embodiment.

[0089] As shown in FIG. 12, the modulation factor command generating section 5C is made up of a reference phase output section 51C, a coefficient calculating section 52C, a differentiator 53, a phase calculating section , a modulation factor calculating section 55, and a previous value storing section .

[0090] The reference phase output section 51C outputs one constant reference phase θf regardless of the number N of switching operations.

[0091] FIG. 13 is a diagram showing the relationship between the true modulation factor obtained by coordinate transformation of the voltage command and the approximation formula.

[0092] The previous value storage unit 56 stores the modulation factor command value muf* calculated for the reference phase θf by the coefficient calculation unit 52 in the previous control period T′ as the previous modulation factor command value muf*′.

[0093] The coefficient calculation unit 52C calculates the coefficient of (Equation 2) shown in the first embodiment from the following (Equation 11) using the modulation factor command value muf*' calculated in the previous control cycle T' and the modulation factor command value muf* calculated in the current control cycle T.

[0094]

number

[0095] It should be noted that the previous control period T' and the current control period T do not necessarily coincide, and therefore the above (Equation 11) also includes a correction for this.

[0096] The other configurations are the same as those in the first embodiment.

[0097] The present embodiment configured as above can also achieve the same effects as the first embodiment.

[0098] In addition, in this embodiment, coordinate transformation is performed only once within a control period, which allows for a significant reduction in the amount of calculation. Note that, since the approximation error of the modulation factor tends to increase, it is more effective to use this method in the low to medium speed range where the fundamental wave period of the three-phase modulation factor is sufficiently long relative to the control period and the modulation factor changes gradually, or in the fast control period range.

[0099] <Additional Notes> The present invention is not limited to the above-described examples, and various modifications are possible within the scope of the gist of the present invention. For example, the above-described embodiments have been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to those having all of the described configurations.

[0100] For example, the values ​​and numbers of reference phases are determined according to the number of switching operations as in the first embodiment, or according to the degree of a polynomial as in the second embodiment. However, the present invention is not limited to this, and the values ​​and numbers of reference phases may be determined according to the magnitude of the allowable error in the modulation rate or the rotation speed of the motor.

[0101] Furthermore, the above-described configurations, functions, processing units, processing procedures, etc. may be partly or entirely realized in hardware, for example, by designing them as integrated circuits, etc. Furthermore, the above-described configurations, functions, etc. may be realized in software, by a processor interpreting and executing a program that realizes each function.

[0102] Furthermore, the signal lines and information lines shown are those considered necessary for explanation, and do not necessarily represent all control lines and information lines. Furthermore, the above-mentioned configurations, functions, processing units, processing procedures, etc. do not necessarily need to be located in the same physical location; for example, some may be located on a network or in the cloud via communication, etc. [Explanation of symbols]

[0103] 1...motor control device, 2...AC motor, 2a...rotational position sensor, 3...inverter, 4...voltage command generation unit, 5, 5A, 5B, 5C...modulation rate command generation unit, 6...duty command generation unit, 7...gate command generation unit, 8...rotational position detection unit, 9...switching count memory unit, 10...order determination unit, 51, 51A, 51C...reference phase output unit, 52, 52A, 52C...coefficient calculation unit, 53...differentiator, 54...phase calculation unit, 55, 55A...modulation rate calculation unit, 56...previous value memory unit

Claims

1. A motor control device that controls driving of an AC motor connected to an inverter having a plurality of switching elements, a dq-axis voltage command generating unit that generates dq-axis voltage command values ​​for the AC motor at every predetermined calculation period; a modulation factor command generating unit that generates one or more modulation factor command values ​​based on the dq-axis voltage command value, a phase of the AC motor, and the number of times the switching element performs switching within the calculation period; a duty command generating unit that generates a duty command value for generating a gate signal that controls an operation of the switching element based on the modulation factor command value, The motor control device is characterized in that, when the number of switching times is equal to or greater than a predetermined number, the modulation factor command generating unit switches a generation method of the modulation factor command value in accordance with the number of switching times.

2. 2. The motor control device according to claim 1, The motor control device, wherein the modulation factor command generating unit generates at least one of the one or more modulation factor command values ​​using a polynomial that is set based on the number of switching times.

3. 3. The motor control device according to claim 2, The motor control device is characterized in that the modulation factor command generating unit determines the coefficients of the polynomial from a reference phase that minimizes an error in the modulation factor and the modulation factor corresponding to the reference phase.

4. 4. The motor control device according to claim 3, A motor control device characterized in that the value and number of the reference phases are determined based on at least one of the magnitude of an allowable error in the modulation rate, the number of switching times, the degree of the polynomial, and the motor rotation speed.

5. 4. The motor control device according to claim 3, A motor control device characterized in that a plurality of polynomials are set within the calculation period and switched depending on a switching position.

6. 4. The motor control device according to claim 3, The motor control device is characterized in that the polynomial includes variables other than the reference phase and terms with non-integer exponents.

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