Motor drive device for suppressing LC resonance

Abstract

This motor drive device comprises: a voltage command generation unit that generates a d-axis voltage command and a q-axis voltage command; a notch filter that attenuates a component of a specific frequency related to the LC resonance with respect to the d-axis voltage command and the q-axis voltage command generated by the voltage command generation unit, and outputs a filtered d-axis voltage command and a filtered q-axis voltage command; a dq three-phase conversion unit that converts the filtered d-axis voltage command and the filtered q-axis voltage command into a three-phase voltage command and outputs the three-phase voltage command; a rectifier that converts an AC electric power supply voltage into a DC voltage and outputs the DC voltage; and an inverter that, on the basis of the three-phase voltage command, converts the DC voltage into an AC voltage for driving the motor and outputs the AC voltage.

Description

Motor drive device for suppressing LC resonance

[0001] The present disclosure relates to a motor drive device that suppresses LC resonance.

[0002] A motor drive device that drives an AC motor is provided with a rectifier and an inverter. The rectifier and inverter are electrically connected via a DC link. The rectifier converts AC voltage supplied from an AC power source into DC voltage and outputs it. The inverter converts DC voltage into AC voltage for driving the motor and outputs it.

[0003] JP 2019-058012 A, International Publication No. 2022 / 149211, JP 2022-159095 A, International Publication No. 2023 / 127034

[0004] In a motor drive device, an AC reactor is provided on the AC input side of the rectifier. A smoothing capacitor is provided in a DC link between the rectifier and the inverter. If the resonant frequency calculated from the inductance of the AC reactor and the capacitance of the smoothing capacitor matches an integer multiple (especially three times) of the power supply frequency of the AC power source and if the DC link current generated when the motor is driven contains a component at the resonant frequency, LC resonance occurs between the AC reactor and the smoothing capacitor. When LC resonance occurs, the DC link current fluctuates significantly, which could damage the rectifier. Therefore, there is a need for a motor drive device that suppresses LC resonance.

[0005] According to one aspect of the present disclosure, a motor drive device includes: a voltage command generation unit that generates a d-axis voltage command and a q-axis voltage command on a dq coordinate system; a notch filter that performs filtering on the d-axis voltage command and the q-axis voltage command generated by the voltage command generation unit to attenuate specific frequency components associated with LC resonance, and outputs the filtered d-axis voltage command and the filtered q-axis voltage command; a dq three-phase conversion unit that converts the filtered d-axis voltage command and the filtered q-axis voltage command into three-phase voltage commands on a three-phase coordinate system and outputs them; a rectifier that converts an AC power supply voltage supplied from an AC power supply into a DC voltage and outputs it; and an inverter that converts the DC voltage output from the rectifier into an AC voltage for driving the motor based on the three-phase voltage command and outputs it.

[0006] Fig. 1 is a diagram showing a motor drive device according to a first embodiment of the present disclosure; Fig. 2 is a diagram showing waveforms at each part of the motor drive device when filter processing according to the first embodiment of the present disclosure is performed; Fig. 3 is a diagram showing waveforms at each part of the motor drive device when filter processing is not performed; Fig. 4 is a diagram showing a motor drive device according to a second embodiment of the present disclosure.

[0007] A motor drive device for suppressing LC resonance according to an embodiment will be described below with reference to the drawings. In the following description, components having the same or similar functions will be assigned the same reference numerals. Duplicate descriptions of those components may be omitted. The scale of the drawings has been appropriately changed to facilitate understanding.

[0008] In the following description, a rectifier that converts AC voltage supplied from an AC power source into DC voltage and outputs it is also referred to as a “rectifier device,” “rectifier circuit,” “converter,” or “forward converter.” An inverter that converts DC voltage into AC voltage and outputs it is also referred to as an “inverter.” A “DC link” refers to a circuit portion that electrically connects the DC output side of a rectifier and the DC input side of an inverter. A “DC link” is also referred to as a “DC link section,” “DC link,” “DC link section,” “DC bus,” or “DC intermediate circuit.” A “DC link voltage” refers to the potential difference between the positive potential of the positive power line and the negative potential of the negative power line of the DC link, or the voltage obtained by dividing the potential difference between the positive potential of the positive power line and the negative potential of the negative power line of the DC link using a voltage divider resistor. A “DC link current” refers to the current flowing through the DC link. A “notch filter” is also referred to as a “bandstop filter,” “band elimination filter,” or “band rejection filter.” "AC power supply voltage" refers to the AC voltage input to a rectifier from an AC power supply. "Power supply frequency" refers to the frequency of the AC voltage input to a rectifier from an AC power supply.

[0009] <Configuration of Motor Drive Device According to First Embodiment of Present Disclosure> FIG. 1 is a diagram showing a motor drive device according to a first embodiment of the present disclosure.

[0010] In the first embodiment of the present disclosure and the second embodiment described below, as an example, a case is shown in which an AC motor 3 is driven by a motor drive device 1 connected to an AC power source 2. The number of phases of the AC power source 2 and the motor 3 is not particularly limited to each embodiment, and may be, for example, three-phase or single-phase. Examples of the AC power source 2 include a three-phase 400V AC power source, a three-phase 200V AC power source, a three-phase 600V AC power source, and a single-phase 100V AC power source. Here, as an example, the AC power source 2 and the motor 3 are each three-phase. Furthermore, the number of motors 3 is not particularly limited to each embodiment, and there may be more than one. Here, as an example, there is one motor 3. Machines in which the motor 3 is provided include, for example, machine tools and robots.

[0011] A motor drive device 1 according to a first embodiment of the present disclosure includes a rectifier 100, an inverter 200, an AC reactor 300, and a smoothing capacitor 400. The motor drive device 1 also includes a voltage command generator 11, a notch filter 12, a dq three-phase converter 13, a measurement unit 14, a current detector 15, a three-phase dq converter 16, a switching signal generator 17, and a speed detector 18 as a control device that controls the power conversion operation of the inverter 200.

[0012] The rectifier 100 converts the AC power supply voltage supplied from the AC power supply 2 into a DC voltage and outputs it to a DC link. In the example shown in FIG. 1 , since the AC power supply 2 is a three-phase AC power supply, the rectifier 100 is configured as a three-phase bridge circuit. If the AC power supply 2 is a single-phase AC power supply, the rectifier 100 is configured as a single-phase bridge circuit. Examples of the rectifier 100 include a diode rectifier, a PWM switching control rectifier, and a 120-degree conduction rectifier. For example, if the rectifier 100 is configured as a diode rectifier, it is configured as a three-phase bridge circuit of diodes. If the rectifier 100 is configured as a PWM switching control rectifier or a 120-degree conduction rectifier, it is configured as a three-phase bridge circuit of switching elements and diodes connected in anti-parallel to the switching elements. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other switching elements may also be used.

[0013] An AC reactor 300 is electrically connected between the rectifier 100 and the AC power supply 2 .

[0014] A smoothing capacitor 400 is electrically connected to the DC link between the rectifier 100 and the inverter 200. The smoothing capacitor 400 is sometimes referred to as a "DC link capacitor" or a "direct-current link capacitor." The smoothing capacitor 400 has the function of suppressing oscillations in the DC output of the rectifier 100 and the function of storing DC power used by the inverter 200 to generate AC power. Examples of the smoothing capacitor 400 include an electrolytic capacitor and a film capacitor. A pre-charging circuit for pre-charging the smoothing capacitor 400 may be provided, but is not shown here.

[0015] The inverter 200 is connected to the rectifier 100 via a DC link. The inverter 200 converts the DC voltage output from the rectifier 100 into an AC voltage for driving the motor and outputs the converted voltage. The inverter 200 is composed of a bridge circuit of switching elements and diodes connected in antiparallel to the switching elements. The inverter 200 is composed of a three-phase bridge circuit when the motor 3 is a three-phase AC motor, and is composed of a single-phase bridge circuit when the motor 3 is a single-phase AC motor. In the example shown in FIG. 1 , the motor 3 is a three-phase AC motor, so the inverter 200 is composed of a three-phase bridge circuit. Examples of switching elements include FETs, IGBTs, thyristors, GTOs, and transistors, but other switching elements may also be used. The switching signal S generated by the switching signal generating unit 17 ＊ That is, the inverter 200 controls the on / off of the switching elements in the inverter 200 in accordance with the switching signal S from the switching signal generating unit 17. ＊ The inverter 200 receives the switching signal S from the switching signal generating unit 17, converts the DC voltage in the DC link into an AC voltage for driving the motor, and outputs the AC voltage to the motor 3. As a result, the motor 3 is driven based on the AC voltage output from the inverter 200. The inverter 200 also receives the switching signal S from the switching signal generating unit 17. ＊Upon receiving this signal, the AC voltage regenerated during deceleration of the motor 3 is converted into a DC voltage and output to the DC link.

[0016] The current detection unit 15 detects the U-phase AC current i output from the inverter 200. ｕ , V-phase AC current i ｖ , and W-phase AC current i ｗ Detect.

[0017] The speed detection unit 18 detects the rotor phase angle θ of the motor 3 .

[0018] The three-phase dq conversion unit 16 converts the U-phase AC current i in the three-phase coordinate system detected by the current detection unit 15 based on the rotor phase angle θ in accordance with Equation 1. ｕ , V-phase AC current i ｖ , and W-phase AC current i ｗ is the d-axis current i on the dq coordinate system. ｄ and q-axis current i ｄ Convert it to and output it.

[0019]

[0020] The voltage command generator 11 generates a d-axis current command i ｄ ＊ and d-axis current i ｄ Based on the d-axis voltage command v ｄ１ ＊ and the q-axis current command i ｑ ＊ and q-axis current i ｑ Based on the q-axis voltage command v ｑ１ ＊ The d-axis voltage command v ｄ１ ＊ and q-axis voltage command v ｑ１ ＊ The method of generating the voltage command generator 11 does not limit the present embodiment, and may be realized by, for example, a known method. Note that the configuration of the voltage command generator 11 defined here is merely an example, and the configuration of the voltage command generator 11 may be defined by including terms such as a position command generator, a torque command generator, a current controller, PI control, and PID control.

[0021] The notch filter 12 detects the d-axis voltage command v generated by the voltage command generator 11. ｄ１＊ and q-axis voltage command v ｑ１ ＊ The notch filter 12 performs filtering to attenuate specific frequency components related to LC resonance. Each command after filtering is converted into a filtered d-axis voltage command v ｄ２ ＊ and the filtered q-axis voltage command v ｑ２ ＊ The LC resonance and notch filter 12 will be described in detail later.

[0022] The measurement unit 14 measures the power frequency f ｐ In the first embodiment of the present disclosure, the power supply frequency f ｐ The value of is used to determine the specific frequency used in the notch filter 12. Note that, if the measurement unit 14 is omitted and the power supply frequency f ｐ may be used in determining the specific frequencies used in the notch filter 12.

[0023] The dq three-phase conversion unit 13 converts the filtered d-axis voltage command v ｄ２ ＊ and the filtered q-axis voltage command v ｑ２ ＊ is expressed as the U-phase voltage command v ｕ ＊ , V-phase voltage command v ｖ ＊ , and W-phase voltage command v ｗ ＊ Convert it to and output it.

[0024]

[0025] The switching signal generator 17 generates a U-phase voltage command v ｕ ＊ , V-phase voltage command v ｖ ＊ , and W-phase voltage command v ｗ ＊ A switching signal S for controlling the switching operation of the switching element in the inverter 200 is generated based on the ＊The switching signal S in the switching signal generating unit 17 is generated. ＊ The method of generating the image data is not a limitation of the present invention, and may be realized by any known method.

[0026] In the example shown in FIG. 1 and FIG. 4 described later, the inverter 200 is configured as a three-phase bridge circuit, and therefore has six switching elements. ＊ are generated for each of these six switching elements. In the example shown in FIG. 1 and FIG. 4 described later, for the sake of simplicity, the six electrical wirings extending from the switching signal generating unit 17 to the inverter 200 are represented by a combination of one line "-" and six diagonal lines " / / / / / / " according to convention.

[0027] <LC Resonance> A resonance frequency f defined by the inductance L of the AC power supply 2 and the AC reactor 300 and the capacitance C of the smoothing capacitor 400 ｒ can be expressed as in Equation 3.

[0028]

[0029] In the motor drive device 1, a closed circuit is formed that runs from the AC power supply 2 through the AC reactor 300, the rectifier 100, the smoothing capacitor 400, the rectifier 100, and the AC reactor 300, and then returns to the AC power supply 2 again, so that LC resonance may occur. Since the AC reactor 300 is included in the closed circuit twice, as shown in Equation 3, the value obtained by multiplying the inductance L by two is the resonance frequency f ｒ will be related to.

[0030] The above equation 3 is the inductance L of the AC power supply 2 Ｓ This holds true when the inductance L of the AC reactor 300 is sufficiently large compared to the inductance L of the AC power supply 2. Ｓ is so large as to be non-negligible compared with the inductance L of the AC reactor 300, the resonant frequency f ｒ can be expressed as in Equation 4.

[0031]

[0032] The DC link current generated when the motor 3 is driven by the motor drive device 1 has a resonance frequency f ｒ LC resonance may occur if the frequency component is close to the resonant frequency f ｒ is the power frequency f ｐ LC resonance becomes apparent when the resonant frequency f ｒ is the power frequency f ｐ and the DC link current generated when the motor 3 is driven by the motor drive device 1 has a resonance frequency f ｒ When the component (a) is included, a very large LC resonance occurs. The oscillation of the DC link current caused by the LC resonance causes the current flowing through the rectifier 100 to oscillate significantly, which may damage the rectifier 100.

[0033] <Configuration of Notch Filter> As described above, the resonant frequency f ｒ is the power frequency f ｐ LC resonance becomes apparent when the resonant frequency f ｒ is the power frequency f ｐ and the DC link current generated when the motor 3 is driven by the motor drive device 1 has a resonance frequency f ｒ When the component of d-axis current i is included, a very large LC resonance occurs. When LC resonance occurs, the DC link voltage oscillates. The d-axis current i on the dq coordinate system, which is the current feedback from the inverter output, ｄ and q-axis current i ｑ Since the d-axis voltage command v on the dq coordinate system generated by the voltage command generator 11 oscillates at the same frequency as the oscillation frequency of the DC link voltage, ｄ１ ＊ and q-axis voltage command v ｑ１ ＊ The oscillation frequency of the DC link voltage also occurs.

[0034] Therefore, in the first embodiment of the present disclosure, the d-axis voltage command v generated by the voltage command generating unit 11 is ｄ１ ＊ and q-axis voltage command v ｑ１ ＊For power frequency f ｐ The notch filter 12 attenuates frequency components that are approximately integer multiples of the above.

[0035] The notch filter 12 is a band-stop filter that attenuates a specific frequency component by reducing the gain of that specific frequency, while passing other frequency components unchanged. The notch filter 12 has a very narrow rejection band (also called a "stop band"), which is the range of specific frequencies that defines the components to be attenuated, and a high Q value.

[0036] In the first embodiment of the present disclosure, a stop band, which is a specific frequency range for components to be attenuated by the notch filter 12, is set to a power supply frequency f ｐ (for example, the power supply frequency f ｐ More preferably, the stop band of the notch filter 12 is set to a value within a range of, for example, a few percent of an integer multiple of the power supply frequency f ｐ Approximately three times the power frequency f ｐ Here, as an example, the stop band of the notch filter 12 is set to a value three times the power supply frequency f ｐ The stop band of the notch filter 12 is set to "plus or minus a few percent" of an integer multiple (preferably three times) of the input signal. The stop band of the notch filter 12 is not limited to this numerical value and may be set to another numerical value. The stop band of the notch filter 12 may be set appropriately taking into consideration the operational status, control accuracy, cost, etc. of the motor drive device 1. The gain that determines the attenuation rate of the components included in the stop band of the notch filter 12 may also be set appropriately taking into consideration the operational status, control accuracy, cost, etc. of the motor drive device 1. The stop band and gain of the notch filter 12 may be set while checking the waveform of the DC link voltage, the waveform of the DC link current, or the waveform of the AC current of each phase input to the rectifier 100 using an oscilloscope or the like.

[0037] <Experimental Waveforms> Fig. 2 is a diagram showing waveforms at various parts of the motor drive device when filter processing according to the first embodiment of the present disclosure is performed, and Fig. 3 is a diagram showing waveforms at various parts of the motor drive device when filter processing is not performed.

[0038] In the experiments for measuring the waveforms shown in Figures 2 and 3, various parameters and conditions were set the same, except for whether or not filtering by a notch filter was applied. The AC power supply frequency was set to a nominal value of 50 Hz. In the experiments on the motor drive device according to the first embodiment of the present disclosure shown in Figure 2, the center frequency of the stop band of the notch filter was set to 150 Hz ± a few percent, and the gain was set so that the attenuation rate in the stop band of the notch filter was 60%.

[0039] 2 and 3 each show waveforms of a DC link voltage, a DC link current, a motor current of each phase flowing from the inverter to the motor, and an R-phase AC current input to the rectifier from an AC power supply. A comparison of the waveforms in FIG. 2 (filtered) with those in FIG. 3 (unfiltered) reveals the following. First, looking at the waveforms of the DC link voltage and the DC link current, it can be seen that the first embodiment of the present disclosure shown in FIG. 2 has less oscillation than the example without filtering shown in FIG. 3. Furthermore, looking at the waveform of the R-phase AC current, it can be seen that the peak value is nearly stable in the first embodiment of the present disclosure shown in FIG. 2, whereas the peak value varies in the example without filtering shown in FIG. 3. The greater the variation in the peak value, the more likely the rectifier is to be damaged. As can be seen from the comparison between FIG. 2 and FIG. 3, LC resonance can be suppressed according to the first embodiment of the present disclosure.

[0040] <Configuration of Motor Drive Device According to Second Embodiment of Present Disclosure> FIG. 4 is a diagram showing a motor drive device according to a second embodiment of the present disclosure.

[0041] In the first embodiment described above, the stop band, which is a specific frequency range for the components to be attenuated by the notch filter 12, is set to the power supply frequency f ｐ In contrast to this, in the second embodiment of the present disclosure, the stop band of the notch filter 12 is set to a resonant frequency f ｒ Set it to a value close to .

[0042] A motor drive device 1 according to the second embodiment of the present disclosure includes a rectifier 100, an inverter 200, an AC reactor 300, and a smoothing capacitor 400. The motor drive device 1 also includes a voltage command generator 11, a notch filter 12, a dq three-phase converter 13, a current detector 15, a three-phase dq converter 16, a switching signal generator 17, a speed detector 18, and a calculator 19 as a control device that controls the power conversion operation of the inverter 200.

[0043] The rectifier 100, inverter 200, AC reactor 300, and smoothing capacitor 400 are as described in relation to the first embodiment shown in Fig. 1. The voltage command generator 11, dq three-phase converter 13, current detector 15, three-phase dq converter 16, switching signal generator 17, and speed detector 18 are as described in relation to the first embodiment shown in Fig. 1.

[0044] The calculation unit 19 calculates a resonance frequency f defined by the inductance L of the AC power supply 2 and the AC reactor 300 and the capacitance C of the smoothing capacitor 400. ｒ is calculated according to the above-mentioned formula 3 or formula 4. ｒ The calculation unit 19 for calculating the resonance frequency f may be provided in a calculation device (for example, a computer or a calculator) external to the motor drive device 1. In this case, the resonance frequency f calculated by the external calculation device is used. ｒ The data on the above may be input to the notch filter 12.

[0045] The center frequency of the stop band, which is a specific frequency range for the components to be attenuated by the notch filter 12, is defined as the resonant frequency f ｒ A value in the vicinity of (for example, the resonant frequency f ｒ Here, as an example, the center frequency of the stop band of the notch filter 12 is set to a value within ±several percent of the resonant frequency f ｒ Although the range was set to "± several percent" of the resonance frequency f ｒ It may be set to any other value as long as it is within the range including the above.

[0046] The second embodiment can also achieve the same effects as the first embodiment. For example, if the inductance L of the AC power supply 2 and the AC reactor 300 and the capacitance C of the smoothing capacitor 400 are known, the notch filter 12 according to the second embodiment can be adopted, and if the inductance L and the capacitance C are not known, the notch filter 12 according to the first embodiment can be adopted.

[0047] 1 and 4 , a power line for supplying power to a control device including the voltage command generation unit 11, the notch filter 12, the dq three-phase conversion unit 13, the measurement unit 14, the current detection unit 15, the three-phase dq conversion unit 16, the switching signal generation unit 17, the speed detection unit 18, and the calculation unit 19 is a separate system from a power line for supplying power from the AC power supply 2 to the rectifier 100. In other words, even before the rectifier 100 is powered on, power is supplied to drive the control device in preparation for operation when the inverter 200 is powered on.

[0048] The motor drive device 1 includes at least one processor, which is an arithmetic processing device. Examples of the arithmetic processing device include an IC, an LSI, a CPU, an MPU, and a DSP. The arithmetic processing device includes a voltage command generator 11, a notch filter 12, a dq three-phase converter 13, a measurement unit 14, a three-phase dq converter 16, a switching signal generator 17, a calculation unit 19, and other processing units. Each of these units included in the arithmetic processing device is a functional module implemented by, for example, a program executed on the processor. For example, if the voltage command generator 11, the notch filter 12, the dq three-phase converter 13, the measurement unit 14, the three-phase dq converter 16, the switching signal generator 17, the calculation unit 19, and other processing units are implemented in the form of a program, the functions of each unit can be realized by operating the arithmetic processing device in accordance with the program. The programs for executing the processes in the voltage command generation unit 11, the notch filter 12, the dq three-phase conversion unit 13, the measurement unit 14, the three-phase dq conversion unit 16, the switching signal generation unit 17, the calculation unit 19, and other processing units may be provided in a form recorded on a computer-readable recording medium such as a semiconductor memory, a magnetic recording medium, or an optical recording medium. Alternatively, the voltage command generation unit 11, the notch filter 12, the dq three-phase conversion unit 13, the measurement unit 14, the three-phase dq conversion unit 16, the switching signal generation unit 17, the calculation unit 19, and other processing units may be realized as semiconductor integrated circuits in which programs for realizing the functions of the respective units are written.

[0049] The motor drive device 1 also includes at least one memory serving as a storage device. The memory includes the voltage command generator 11, the notch filter 12, the dq three-phase converter 13, the measurement unit 14, the three-phase dq converter 16, the switching signal generator 17, the calculation unit 19, and various other storage units within the processing units. Examples of the memory include electrically erasable and recordable nonvolatile memories such as EEPROM (registered trademark), or high-speed read / write random access memories such as DRAM and SRAM. The storage unit may also have a configuration such as an HDD (hard disk drive) or SSD (solid state drive). The memory stores programs for operating the voltage command generator 11, the notch filter 12, the dq three-phase converter 13, the measurement unit 14, the three-phase dq converter 16, the switching signal generator 17, the calculation unit 19, and the other processing units. The memory also stores a power supply frequency f detected by the measurement unit 14. ｐ the rotor phase angle θ detected by the speed detection unit 18, and the resonant frequency f calculated by the calculation unit 19. ｒ The memory also stores various programs and data related to the motor drive device 1.

[0050] <Advantages of the First and Second Embodiments of the Present Disclosure> According to the first and second embodiments of the present disclosure, it is possible to realize a motor drive device that suppresses LC resonance caused by an AC reactor and a smoothing capacitor.

[0051] According to a first embodiment of the present disclosure, the stopband of a notch filter is set to a range that is approximately an integer multiple (preferably approximately three times) of the power supply frequency. Then, filtering by the notch filter is applied to a d-axis voltage command and a q-axis voltage command in a dq coordinate system. The filtered d-axis voltage command and the filtered q-axis voltage command are converted into three-phase voltage commands in a three-phase coordinate system, and the power conversion operation of an inverter is controlled based on these three-phase voltage commands. This makes it possible to realize a motor drive device that suppresses LC resonance caused by an AC reactor and a smoothing capacitor.

[0052] According to a second embodiment of the present disclosure, the stopband of a notch filter is set to a value near a resonance frequency defined based on the inductance of an AC power supply and an AC reactor and the capacitance of a smoothing capacitor. Then, filtering by the notch filter is applied to a d-axis voltage command and a q-axis voltage command on a dq coordinate system. The filtered d-axis voltage command and the filtered q-axis voltage command are converted into three-phase voltage commands on a three-phase coordinate system, and the power conversion operation of an inverter is controlled based on these three-phase voltage commands. This makes it possible to realize a motor drive device that suppresses LC resonance caused by the AC reactor and the smoothing capacitor.

[0053] In conventional motor drive devices, in order to suppress LC resonance caused by the AC reactor and smoothing capacitor, the inductance of the AC reactor is increased or the capacitance of the smoothing capacitor is increased so that the value three times the power supply frequency is shifted from the resonance frequency. However, increasing the inductance of the AC reactor or the capacitance of the smoothing capacitor, which are hardware, leads to problems such as an increase in the size and cost of the motor drive device.

[0054] In contrast, according to the first and second embodiments of the present disclosure, filtering using a notch filter is applied to the d-axis voltage command and the q-axis voltage command on software, which makes it possible to reduce the size and cost of the motor drive device and simplify its design.

[0055] Although the present disclosure has been described in detail above, the present disclosure is not limited to the individual embodiments and individual variations described above. Various additions, substitutions, modifications, partial deletions, etc. are possible for these embodiments and variations within the scope of the gist of the present disclosure, or within the scope of the gist of the present disclosure derived from the content of the claims and their equivalents. These embodiments and variations can also be implemented in combination. For example, in the above-described embodiments and variations, the order of each operation and the order of each process are shown as examples and are not limited to these. The same applies when numerical values ​​or mathematical formulas are used in the description of the above-described embodiments and variations.

[0056] <Supplementary Notes> The following supplementary notes are further disclosed regarding the above-described embodiment and modifications.

[0057] (Supplementary Note 1) A motor drive device comprising: a voltage command generation unit that generates a d-axis voltage command and a q-axis voltage command on a dq coordinate system; a notch filter that performs filtering on the d-axis voltage command and the q-axis voltage command generated by the voltage command generation unit to attenuate a specific frequency component associated with LC resonance, and outputs the filtered d-axis voltage command and the filtered q-axis voltage command; a dq three-phase conversion unit that converts the filtered d-axis voltage command and the filtered q-axis voltage command into three-phase voltage commands on a three-phase coordinate system and outputs them; a rectifier that converts an AC power supply voltage supplied from an AC power supply into a DC voltage and outputs it; and an inverter that converts the DC voltage output from the rectifier based on the three-phase voltage commands into an AC voltage for driving the motor and outputs it. (Supplementary Note 2) The motor drive device according to Supplementary Note 1, wherein the specific frequency is approximately an integer multiple of the power supply frequency of the AC power supply. (Supplementary Note 3) The motor drive device according to Supplementary Note 2, wherein the specific frequency is approximately three times the power supply frequency of the AC power supply. (Supplementary Note 4) The motor drive device according to Supplementary Note 2, comprising a measurement unit that measures a power supply frequency, wherein the specific frequency is determined based on the power supply frequency measured by the measurement unit. (Supplementary Note 5) The motor drive device according to Supplementary Note 1, comprising: an AC reactor electrically connected between an AC power supply and a rectifier; and a smoothing capacitor electrically connected between the rectifier and the inverter and smoothing the DC voltage output from the rectifier, wherein the specific frequency is a value close to a resonance frequency determined based on the inductance of the AC power supply and the AC reactor and the capacitance of the smoothing capacitor. (Supplementary Note 6) The motor drive device according to any one of Supplements 1 to 5, comprising: a current detection unit that detects three-phase AC current output from the inverter, and a three-phase dq conversion unit that converts the three-phase AC current detected by the current detection unit into d-axis current and q-axis current on a dq coordinate system and outputs the current, wherein the voltage command generation unit generates a d-axis voltage command based on the d-axis current command and the d-axis current, and generates a q-axis voltage command based on the q-axis current command and the q-axis current.

[0058] REFERENCE SIGNS LIST 1 Motor drive device 2 AC power supply 3 Motor 11 Voltage command generation unit 12 Notch filter 13 dq three-phase conversion unit 14 Measurement unit 15 Current detection unit 16 Three-phase dq conversion unit 17 Switching signal generation unit 18 Speed ​​detection unit 19 Calculation unit 100 Rectifier 200 Inverter 300 AC reactor 400 Smoothing capacitor

Claims

1. A motor drive device comprising: a voltage command generation unit that generates a d-axis voltage command and a q-axis voltage command on a dq coordinate system; a notch filter that performs filtering on the d-axis voltage command and the q-axis voltage command generated by the voltage command generation unit to attenuate specific frequency components associated with LC resonance, and outputs a filtered d-axis voltage command and a filtered q-axis voltage command; a dq three-phase conversion unit that converts the filtered d-axis voltage command and the filtered q-axis voltage command into three-phase voltage commands on a three-phase coordinate system and outputs them; a rectifier that converts an AC power supply voltage supplied from an AC power supply into a DC voltage and outputs it; and an inverter that converts the DC voltage output from the rectifier based on the three-phase voltage command and outputs it as an AC voltage for driving a motor.

2. The motor drive device according to claim 1, wherein the specific frequency is a frequency that is approximately an integer multiple of the power supply frequency of the AC power supply.

3. The motor drive device according to claim 2, wherein the specific frequency is approximately three times the power supply frequency of the AC power supply.

4. The motor drive device according to claim 2, further comprising a measurement unit that measures the power supply frequency, and the specific frequency is determined based on the power supply frequency measured by the measurement unit.

5. The motor drive device according to claim 1, comprising: an AC reactor electrically connected between said AC power supply and said rectifier; and a smoothing capacitor electrically connected between said rectifier and said inverter for smoothing the DC voltage output from said rectifier, wherein said specific frequency is a value close to a resonance frequency defined based on the inductance of said AC power supply and said AC reactor and the capacitance of said smoothing capacitor.

6. A motor drive device according to any one of claims 1 to 5, comprising: a current detection unit that detects three-phase AC current output from the inverter; and a three-phase dq conversion unit that converts the three-phase AC current detected by the current detection unit into a d-axis current and a q-axis current on a dq coordinate system and outputs the current, wherein the voltage command generation unit generates the d-axis voltage command based on a d-axis current command and the d-axis current, and generates the q-axis voltage command based on a q-axis current command and the q-axis current.