Motor drive device and air conditioner

Abstract

Provided are, for example, a motor drive device in which motor current pulsation and power supply harmonic current are suppressed. A motor drive device (100) comprises a rectifier circuit (13), a smoothing capacitor (30), an inverter circuit (40), a power supply voltage detection unit (50), a bus current detection unit (70), and a control unit (80). The control unit (80) extracts a pulsation component having a frequency six times the power supply frequency on the basis of a detection value of the power supply voltage detection unit (50), calculates a current pulsation command by multiplying a torque current command of the inverter circuit (40) by the pulsation component, and performs feedback control so that a torque current based on a detection value of the bus current detection unit (70) approaches the current pulsation command.

Description

Motor drive device and air conditioner

[0001] The present disclosure relates to a motor drive device and an air conditioner.

[0002] A known technology for a motor drive device converts AC power into DC power, and then converts the DC power back into a predetermined AC power and outputs it to a motor is described, for example, in Patent Document 1. Patent Document 1 describes correcting the phase of the output voltage of an inverter based on the phase of a three-phase AC voltage so that the d-axis voltage Vd of a pulsating component contained in the DC voltage leads the q-axis voltage Vq by 90 degrees.

[0003] Patent No. 6195003

[0004] The technology described in Patent Document 1 suppresses motor current pulsation (beat phenomenon) by correcting the phase of the inverter output voltage, but it is desirable to suppress both motor current pulsation and power supply harmonic current.

[0005] Therefore, an object of the present disclosure is to provide a motor drive device and the like that is adapted to suppress motor current pulsation and power supply harmonic currents.

[0006] In order to solve the above-mentioned problems, the motor drive device according to the present disclosure includes a rectifier circuit that converts AC voltage applied from a three-phase AC power supply into DC voltage, a smoothing capacitor that smooths the DC voltage on the output side of the rectifier circuit, an inverter circuit that converts the DC voltage of the smoothing capacitor into AC voltage and drives a motor with the AC voltage, a power supply voltage detection unit that detects the power supply voltage of the AC power supply, a current detection unit that detects the current of the inverter circuit, and a control unit that controls the inverter circuit, wherein the control unit extracts a pulsation component of a frequency six times the power supply frequency based on the detection value of the power supply voltage detection unit, multiplies the pulsation component by a torque current command of the inverter circuit to calculate a current pulsation command, and performs feedback control so that the torque current based on the detection value of the current detection unit approaches the current pulsation command.

[0007] According to the present disclosure, it is possible to provide a motor drive device and the like that is adapted to suppress motor current pulsation and power supply harmonic currents.

[0008] Fig. 1 is a configuration diagram of a motor drive device according to a first embodiment. Fig. 2 is a functional block diagram of a control unit of the motor drive device according to the first embodiment. Fig. 3 is a functional block diagram of a current pulsation suppressor of the motor drive device according to the first embodiment. Fig. 4 is a waveform diagram showing the relationship between AC voltage, line voltage, and power supply phase in the motor drive device according to the first embodiment. Fig. 5 is a waveform diagram showing waveforms of the motor current, d-axis current, q-axis current, and power supply current of the motor drive device according to the first embodiment. Fig. 6 is a configuration diagram of an air conditioner according to a second embodiment.

[0009] First Embodiment Configuration of Motor Drive Device Fig. 1 is a configuration diagram of a motor drive device 100 according to a first embodiment. The motor drive device 100 shown in Fig. 1 is a device that converts AC power supplied from an AC power source E1 into DC power, converts this DC power into predetermined AC power, and outputs it to a motor M1. The motor M1 may be, for example, a permanent magnet synchronous motor, or may be another type of motor.

[0010] 1 , motor drive device 100 includes a rectifier circuit 10, a DC reactor 20, a smoothing capacitor 30, and an inverter circuit 40. In addition to the components described above, motor drive device 100 also includes a power supply voltage detection unit 50, a DC voltage detection unit 60, a bus current detection unit 70 (current detection unit), and a control unit 80.

[0011] The rectifier circuit 10 converts AC voltage applied from a three-phase AC power source E1 into DC voltage (pulsating DC voltage). For example, a full-wave rectifying diode bridge circuit may be used as the rectifier circuit 10, but the present invention is not limited thereto. Alternatively, a switching-type rectifier circuit may be used as the rectifier circuit 10. As shown in FIG. 1 , the output side of the rectifier circuit 10 is connected to the inverter circuit 40 via a positive DC line A1 and a negative DC line A2.

[0012] The DC reactor 20 is an element for smoothing the pulsating DC voltage applied from the rectifier circuit 10 and suppressing inrush current at startup. As shown in Fig. 1, the DC reactor 20 is provided on the positive DC line A1. More specifically, the DC reactor 20 is provided between the rectifier circuit 10 and the connection point between the positive DC line A1 and the smoothing capacitor 30.

[0013] The smoothing capacitor 30 is an element that smooths the DC voltage on the output side of the rectifier circuit 10. Note that it is not necessary for the smoothing capacitor 30 to completely smooth the DC voltage, and some ripple (periodic pulsation) may be superimposed on the smoothed DC voltage. In other words, the term "smoothing" is used to mean reducing the ripple of the DC voltage to a certain extent.

[0014] 1, the smoothing capacitor 30 is connected to the DC lines A1 and K2 on the output side of the rectifier circuit 10. Specifically, the high-potential side (one lead wire) of the smoothing capacitor 30 is connected to the positive DC line A1, and the low-potential side (the other lead wire) is connected to the negative DC line A2. For example, a film capacitor is used as the smoothing capacitor 30.

[0015] Generally, film capacitors are smaller in size (volume) than large-capacity electrolytic capacitors. Therefore, using a film capacitor as the smoothing capacitor 30 allows for the miniaturization of the circuit board of the motor drive device 100. Furthermore, because a film capacitor uses an insulating plastic film as a dielectric, there is no particular need to use an electrolyte like in an electrolytic capacitor. Therefore, there is almost no risk of malfunctioning of the film capacitor even when used in a high-temperature environment in the summer, such as in the outdoor unit of an air conditioner. Furthermore, film capacitors have the advantage of having a longer lifespan than electrolytic capacitors.

[0016] However, if a small-capacity film capacitor is used in consideration of the unit price per capacitance, the smoothing effect of the DC voltage will be weakened, resulting in larger DC voltage ripples. As a result, when the control unit 80 controls the inverter circuit 40 based on the detection value of the DC voltage detection unit 60, output errors will occur due to the DC voltage ripples, which will result in motor current pulsation. Here, "motor current pulsation" refers to periodic, low-frequency pulsations in the current (motor current) flowing through the three-phase windings of the motor M1, and is also known as the beat phenomenon.

[0017] For example, when three-phase AC power is supplied from AC power source E1, motor current pulsation occurs in DC lines A1 and A2 at a frequency six times the power supply frequency (50 Hz or 60 Hz). In other words, a sinusoidal high-frequency component that varies at a frequency six times the power supply frequency is superimposed on the fundamental component of the power supply frequency.

[0018] In addition, the sixth-order motor current pulsation in the DC lines A1 and A2 is Ｒ , K Ｓ , K Ｔ In the case of a motor, the fifth and seventh harmonic currents appear as fifth and seventh harmonic currents. Therefore, when the sixth-order motor current pulsation increases, the fifth and seventh harmonic currents also tend to increase. Therefore, in the first embodiment, the control unit 80 controls the inverter circuit 40 in a predetermined manner to suppress both the motor current pulsation and the harmonic currents. The processing by the control unit 80 will be described in detail later.

[0019] 1 is a power converter that converts the DC voltage of smoothing capacitor 30 into a predetermined AC voltage and drives motor M1 with this AC voltage. As shown in Fig. 1, inverter circuit 40 has a configuration in which a first leg including a series-connected body of switching elements S1 and S2, a second leg including a series-connected body of switching elements S3 and S4, and a third leg including a series-connected body of switching elements S5 and S6 are connected in parallel to smoothing capacitor 30.

[0020] In the first leg described above, the connection point between the pair of switching elements S1 and S2 is connected to the U-phase winding of the motor M1 via wiring. The same applies to the remaining second and third legs. In the inverter circuit 40, to prevent destruction of the switching elements S1 to S6 due to commutation, freewheeling diodes (reference numbers not shown) are connected in anti-parallel to each of the switching elements S1 to S6. Incidentally, if the switching elements S1 to S6 have parasitic diodes, these parasitic diodes function as freewheeling diodes, so there is no need to provide separate freewheeling diodes.

[0021] 1, IGBTs (Insulated Gate Bipolar Transistors) are used as the switching elements S1 to S6, but the present invention is not limited to this. In other words, MOSFETs (Metal Oxide Semiconductor Field Effect Transistors) or bipolar transistors may also be used as the switching elements S1 to S6.

[0022] The power supply voltage detection unit 50 detects the power supply voltage of the three-phase (R-phase, S-phase, T-phase) AC power supply E1, and is configured to include resistance elements R1 to R6. For example, a series connection of the resistance elements R1 and R2 has one end connected to the R-phase wiring K Ｒ The other end of the series connection of the resistance elements R1 and R2 is connected to the ground terminal of the control unit 80, and is also connected to the low-potential terminal (lead wire) of the smoothing capacitor 30 via (a part of) the DC line A2. The same applies to the series connection of the resistance elements R3 and R4 used to detect the S-phase voltage and the series connection of the resistance elements R5 and R6 used to detect the T-phase voltage.

[0023] As described above, the power supply voltage detection unit 50 has a series connection of resistance elements (for example, a series connection of resistance elements R1 and R2) connected via wiring between the input terminal (not shown) of each phase of the AC power supply E1 and the low-potential side terminal of the smoothing capacitor 30. The low-potential side of this series connection is connected to the ground terminal of the control unit 80.

[0024] As shown in Fig. 1, the connection point between the resistance elements R1 and R2 is connected to the input terminal of the control unit 80 via a wire. The voltage of one of the pair of resistance elements R1 and R2, that is, resistance element R2, is applied to the input terminal of the control unit 80 as an AC voltage signal ErN indicating the R-phase voltage. The same applies to voltage detection of the S-phase and T-phase. In this way, AC voltage signals for three phases (ErN, EsN, EtN) are input from the power supply voltage detection unit 50 to the input terminal of the control unit 80.

[0025] The control unit 80 calculates the voltage between the R-phase terminal and the ground terminal of the AC power supply E1 (R-phase AC voltage) based on the voltage of the resistance element R2 and the voltage division ratio of the resistance elements R1 and R2. Similarly, the control unit 80 calculates the power supply voltages of the S-phase and T-phase.

[0026] The DC voltage detection unit 60 detects the DC voltage across the smoothing capacitor 30 and includes resistor elements R7 and R8. In the example of Fig. 1, one end of the series connection of the resistor elements R7 and R8 is connected to the positive DC line A1. The other end of the series connection of the resistor elements R7 and R8 is connected to the negative DC line A2 and is also connected to the ground terminal of the control unit 80 via the DC line A2.

[0027] The connection point between the resistor elements R7 and R8 is connected via a wire to the input terminal of the control unit 80. The voltage of one resistor element R8 of the pair of resistor elements R7 and R8 is applied as a DC voltage signal Edc to the input terminal of the control unit 80. The control unit 80 calculates the DC voltage of the smoothing capacitor 30 based on the voltage of the resistor element R8 and the voltage division ratio of the resistor elements R7 and R8.

[0028] The bus current detection unit 70 (current detection unit) detects the current of the inverter circuit 40. Specifically, the bus current detection unit 70 detects the bus current flowing in the negative DC line A2 (bus). As shown in FIG. 1 , the bus current detection unit 70 includes a resistor element R9 provided in the DC line A2 and an amplifier 71 that amplifies the voltage across the resistor element R2. The voltage amplified by the amplifier 71 is input to an input terminal of the control unit 80 as a bus current signal Ish. The control unit 80 then calculates the bus current flowing through the DC line A2 based on the bus current signal Ish.

[0029] In addition to the above-mentioned functions, the control unit 80 has a function of controlling the inverter circuit 40. That is, the control unit 80 converts the momentarily detected values ​​(analog signals) of the power supply voltage detection unit 50, the DC voltage detection unit 60, and the bus current detection unit 70 into digital signals, and controls the inverter circuit 40 in a predetermined manner based on these digital signals.

[0030] A sample-and-hold circuit (not shown) or an A / D converter (not shown) is used as appropriate for converting an analog signal into a digital signal. The control unit 80 outputs a predetermined PWM signal based on PWM control (Pulse Width Modulation) to the switching elements S1 to S6. For example, a microcomputer or a DSP (Digital Signal Processor) may be used as the control unit 80.

[0031] 2 is a functional block diagram of a control unit 80 of the power conversion device. As shown in Fig. 2, the control unit 80 includes a current reproduction calculator 81, a three-phase / two-axis converter 82, a speed controller 83, a d-axis current command generator 84, a voltage controller 85, and a current pulsation suppressor 86. In addition to the components described above, the control unit 80 also includes a speed / phase estimator 87, a two-axis / three-phase converter 88, a PWM controller 89, a subtractor 91, and adders 92 and 93.

[0032] The current reproduction calculator 81 reproduces three-phase motor currents (Iu, Iv, Iw) based on the bus current signal Ish input from the bus current detector 70 (see FIG. 1) and predetermined three-phase voltage commands (Vu*, Vv*, Vw*).

[0033] The three-phase / two-axis converter 82 converts the three-phase motor currents (Iu, Iv, Iw) reproduced by the current reproduction calculator 81 and the control axis phase θ of the rotor of the motor M1 (see FIG. 1) estimated by the speed / phase estimator 87. ｄｃ and calculate the dc-axis current Idc and the qc-axis current Iqc based on the above. The direction of the magnetic flux of the magnet of the motor M1 is the d-axis, and the axis perpendicular to the d-axis is the q-axis. These d-axis and q-axis coordinate systems are also called rotating coordinate systems because the coordinate system itself rotates in accordance with the rotating magnetic field of the motor M1. The d-axis current (excitation current) is used to generate magnetic flux of the motor M1, while the q-axis current (torque current) is used to generate torque of the motor M1.

[0034] The d-axis assumed by the control unit 80 is the dc-axis (similar to the qc-axis). That is, the dc-axis current Idc and the qc-axis current Iqc are the motor currents of the dc and qc axes assumed by the control unit 80.

[0035] A subtractor 91 subtracts the estimated speed of the motor M1 (see FIG. 1), which is the calculation result of the speed / phase estimator 87, from a predetermined speed command input from outside. A speed controller 83 generates a qc-axis current command Iqc* (torque current command) based on the calculation result of the subtractor 91. A d-axis current command generator 84 generates a dc-axis current command idc* (excitation current command).

[0036] The voltage controller 85 calculates a dc-axis voltage command Vdc* and a qc-axis voltage command Vqc* based on the dc-axis current command idc*, the qc-axis current command iqc*, the dc-axis current Idc, the qc-axis current Iqc, the speed command, predetermined motor constants, etc.

[0037] The current pulsation suppressor 86 calculates compensation amounts ΔVd and ΔVq for suppressing motor current pulsation and power supply harmonic current. These compensation amounts ΔVd and ΔVq are compensation amounts for the dc-axis voltage command Vdc* and the qc-axis voltage command Vqc* described above, and the calculation method thereof will be described later.

[0038] The compensation amount ΔVd for the d-axis voltage calculated by the current pulsation suppressor 86 is output to an adder 92. Furthermore, the compensation amount ΔVd for the q-axis voltage calculated by the current pulsation suppressor 86 is output to another adder 93. The adder 92 generates a new dc-axis voltage command Vdc** by adding the compensation amount ΔVd to the dc-axis voltage command Vdc* input from the voltage controller 85. The other adder 93 generates a new qc-axis voltage command Vqc** by adding the compensation amount ΔVq to the qc-axis voltage command Vqc* input from the voltage controller 85.

[0039] The speed / phase estimator 87 estimates the phase difference between the dc-qc axes (the d-axis-q-axis assumed by the control unit 80) and the actual d-q axes based on the dc-axis voltage command Vdc**, the qc-axis voltage command Vqc**, the dc-axis current Idc, the qc-axis current Iqc, motor constants, etc. Then, the speed / phase estimator 87 estimates the estimated speed and control axis phase θ of the motor M1 (see FIG. 1) based on the phase difference, etc. ｄｃ Calculate.

[0040] The two-axis / three-phase converter 88 controls the control axis phase θ ｄｃ Based on the above, the dc-axis voltage command Vdc** and the qc-axis voltage command Vdc** are converted into three-phase voltage commands (Vu*, Vv*, Vw*). The PWM controller 89 calculates a modulation factor for PWM control based on the three-phase voltage commands (Vu*, Vv*, Vw*) as well as the DC voltage signal Edc input from the DC voltage detector 60 (see FIG. 1), and generates a predetermined PWM signal. Based on the PWM signal thus generated, the on / off of the switching elements S1 to S6 (see FIG. 1) of the inverter circuit 40 (see FIG. 1) is controlled.

[0041] <Principle of suppressing motor current pulsation and power supply harmonic current> The input power P of the motor drive device 100 in FIG. ＩＮ is expressed by the following formula (1).ＤＣ is the DC voltage across the smoothing capacitor 30, and I ＤＣ is the current flowing through the DC reactor 20.

[0042] P ＩＮ =V ＤＣ ×I ＤＣ ...(1)

[0043] In addition, the output power P of the motor driving device 100 ＯＵＴ is expressed by the following equation (2): Trq included in equation (2) is the torque generated by the motor M1, and N is the rotation speed of the motor M1 in mechanical angle.

[0044] P ＯＵＴ =2π / 60×Trq×N (2)

[0045] Generally, the input power P of the motor drive device 100 (see FIG. 1) ＩＮ and output power P ＯＵＴ are approximately equal, the relationship of the following equation (3) holds approximately.

[0046] V ＤＣ ×I ＤＣ =2π / 60×Trq×N (3)

[0047] As described above, when a film capacitor with a small capacitance is used as the smoothing capacitor 30 (see FIG. 1), the DC voltage V ＤＣ For example, DC voltage V ＤＣ Remove the ripple of DC voltage V ＤＣ However, since there is a ripple in the output voltage of the rectifier circuit 10, the voltage fluctuation of the DC reactor 20 (see FIG. 1) becomes large, and power supply harmonic currents become more likely to occur.

[0048] In contrast, DC voltage V ＤＣ Instead, DC current I ＤＣThe inventors have found that when the DC voltage V approaches a constant value, not only the motor current pulsation but also the power supply harmonic current can be suppressed. In the above equation (3), since the rotation speed N of the motor M1 is approximately constant, the waveform on the right side of equation (3) is determined by the way the torque Trq changes. Therefore, ＤＣ When a pulsating component that changes in the same way as the pulsating component of the DC current I is introduced into the torque Trq (that is, when the torque Trq is intentionally pulsated), the DC current I ＤＣ approaches a constant value.

[0049] Furthermore, in the case of a three-phase AC power supply E1, the motor current pulsation includes a pulsation component of the power supply frequency x (a multiple of 6), with the influence of the pulsation component of 6 times the power supply frequency being particularly strong. Therefore, in the first embodiment, a current pulsation command including a pulsation component of a frequency 6 times the power supply frequency is used as the command value for the q-axis current (torque current) used for torque control of the motor M1. Feedback control is then performed so that the q-axis current (torque current) approaches the current pulsation command.

[0050] This results in a DC voltage V ＤＣ Since the torque of the motor M1 also pulsates in the same way as the sixth-order pulsation component of the DC current I ＤＣ The value of approaches a constant value. This type of control is called "current pulsation suppression control." Experiments and simulations have shown that "current pulsation suppression control" not only suppresses the sixth-order high-frequency component contained in the motor current pulsation, but also the fifth- and seventh-order harmonic components contained in the power supply harmonic current.

[0051] <Configuration and Processing of Current Pulsation Suppressor> Figure 3 is a functional block diagram of the current pulsation suppressor 86. As described above, the current pulsation suppressor 86 is a functional unit that calculates compensation amounts ΔVd and ΔVq for suppressing motor current pulsation and power supply harmonic current. As shown in Figure 3, the current pulsation suppressor 86 includes a line voltage calculator 86a, a phase and frequency calculator 86b, an adder 86c, a sixth-order pulsation calculator 86d, a multiplier 86e, subtractors 86f and 86g, an S-control calculator 86h for the q axis, and an S-control calculator 86i for the d axis.

[0052] The line voltage calculator 86a calculates the line voltages (Ers, Est, Etr) of the AC power supply E1 (see FIG. 1) using the AC voltage signals (ErN, EsN, EtN) based on the following equations (4) to (6). The AC voltage signals (ErN, EsN, EtN) are input from the power supply voltage detector 50 (see FIG. 1).

[0053] Ers=ErN-EsN...(4) Est=EsN-EtN...(5) Etr=EtN-ErN...(6)

[0054] The phase and frequency calculator 86b calculates the power supply phase θs using the line voltages (Ers, Est, Etr) based on the following equation (7): Here, the power supply phase θs means the phase of the power supply voltage in the AC power supply E1 (see FIG. 1 ).

[0055] θs= arctan {(-√3 Ers) / (2Est+Ers)}-30°...(7)

[0056] Furthermore, the phase and frequency calculator 86b calculates the power supply frequency ωs based on the time differential of the power supply phase θs, as shown in the following equation (8): Here, the power supply frequency ωs means the frequency of the power supply voltage in the AC power supply E1 (see FIG. 1 ).

[0057] ωs=d(θs) / dt...(8)

[0058] The adder 86c calculates the compensated power supply phase θss by adding a predetermined compensation value θs_comp to the power supply phase θs as shown in the following equation (9). Note that the compensation value θs_comp is a preset value for compensating for the element of calculation delay in the control unit 80 (cancelling the influence of the calculation delay).

[0059] θss=θs+θs_comp (9)

[0060] For example, voltage and current sampling is performed once per cycle at the timing of a peak or valley of the carrier of the PWM signal, and the result is output at the timing of the next sampling. Therefore, if the above-mentioned compensation is not performed, a phase delay equivalent to one sampling occurs. In contrast, in this embodiment, the power supply phase is compensated based on equation (9), so the effect of calculation delay can be suppressed.

[0061] In this way, the control unit 80 (see FIG. 1) calculates the power supply phase θs based on the AC voltage signals (ErN, EsN, EtN) that are the detection values ​​of the power supply voltage detection unit 50 (see FIG. 1), and calculates the compensated power supply phase θss by adding a predetermined compensation value θs_comp, which is a compensation element for the calculation delay, to the power supply phase θs. Then, the control unit 80 (see FIG. 1) extracts the sixth-order ripple component k based on the compensated power supply phase θss, as will be described next.

[0062] The sixth-order pulsation calculator 86d extracts the sixth-order pulsation component k from the compensated power supply phase θss based on the following equation (10): Ka included in equation (10) is a control constant for adjusting the magnitude of the sixth-order pulsation component, and is set in advance so as to minimize the fifth-order and seventh-order harmonic components of the power supply current.

[0063] k=Ka×sin(6×θss) (10)

[0064] The sixth-order pulsation component k extracted by the sixth-order pulsation calculator 86d has a sinusoidal waveform that changes at a frequency six times the power supply frequency. The multiplier 86e calculates a current pulsation command Iqc_r by multiplying the qc-axis current command Iqc* input from the speed controller 83 by the pulsation component k, as shown in the following equation (11). This current pulsation command Iqc_r intentionally pulsates the torque Trq of the motor M1 (see FIG. 1) at a frequency six times the power supply frequency, and as a result, the DC current I ＤＣ is a q-axis current command value for making the value of Iqc* in equation (11) approach a constant value (see also equation (3)). Note that, since the qc-axis current command Iqc* in equation (11) is often a substantially constant value, the current ripple command Iqc_r has a sinusoidal waveform that changes at a frequency six times the power supply frequency.

[0065] Iqc_r=k×Iqc*...(11)

[0066] In this way, the current pulsation suppressor 86 (i.e., the control unit 80: see FIG. 2) extracts the pulsation component k having a frequency six times the power supply frequency based on the detection value of the power supply voltage detection unit 50 (see FIG. 1), and calculates the current pulsation command Iqc_r by multiplying this pulsation component k by the qc-axis current command Iqc* (torque current command) of the inverter circuit 40 (see FIG. 1).

[0067] The subtractor 86f subtracts the qc-axis current Iqc from the current pulsation command Iqc_r. The qc-axis current Iqc is input from the three-phase / two-axis converter 82 (see FIG. 2). The difference (Iqc_r−Iqc), which is the calculation result of the subtractor 86f, is output to the q-axis S control calculator 86h.

[0068] Another subtractor 86g subtracts the dc-axis current Idc from the value "0" which is the target value of the d-axis current. The dc-axis current Idc is input from the three-phase / two-axis converter 82 (see FIG. 2). The difference (0-Idc) calculated by the subtractor 86g is output to an S control calculator 86i for the d-axis.

[0069] The S control calculator 86h calculates the q-axis voltage compensation amount ΔVq based on the power supply frequency ωs and the difference (Iqc_r - Iqc) so as to bring this difference (Iqc_r - Iqc) closer to zero. Note that, because the response frequency of a typical motor control system is often 100 Hz or less, the response performance may be insufficient for pulsating components with a frequency six times the power supply frequency (300 Hz or 360 Hz). Therefore, in the first embodiment, the S control calculators 86h and 86i amplify pulsating components near a frequency six times the power supply frequency, thereby ensuring sufficient response performance.

[0070] Specifically, the S control calculator 86h calculates the voltage compensation amount ΔVq (torque voltage compensation amount) based on the transfer function of the following equation (12) so as to greatly amplify the pulsation component of a frequency six times the power supply frequency (50 [Hz] or 60 [Hz]). Note that s included in equation (12) is a Laplace operator. Also, K １ , K ２ , K ３is a predetermined control gain, which is set in advance based on the motor constants, etc. Also, ω included in the equation (12) ０ is the center frequency six times the power supply frequency. Control gain K １ , K ２ , K ３ is pre-adjusted to the center frequency ω ０ The magnitude of the gain, bandwidth, and phase characteristics at

[0071]

[0072] The transfer function G(s) shown in equation (12) has a center frequency ω ０ It has the characteristic of having sensitivity (gain) to a frequency six times the power supply frequency, and almost no sensitivity to other frequencies. This makes it possible to achieve high sensitivity (high gain) to pulsating components without increasing the sensitivity to frequencies other than the pulsating component of six times the power supply frequency. It is also possible to make the difference (Iqc_r - Iqc) approach zero.

[0073] The center frequency ω included in equation (12) ０ is calculated based on equation (13) using the power supply frequency ωs input from the phase & frequency calculator 86b.

[0074] ω ０ = 6 × ωs (13)

[0075] In this way, the S control calculator 86h (i.e., the control unit 80: see FIG. 2) performs feedback control so that the qc-axis current Iqc (torque current) based on the detection value of the bus current detector 70 (current detector: see FIG. 1) approaches the current pulsation command Iqc_r. Specifically, the S control calculator 86h (control unit 80: see FIG. 2) calculates the voltage compensation amount ΔVq (torque voltage compensation amount) by amplifying the value in the range including six times the power supply frequency in the waveform of the difference (Iqc_r - Iqc) between the current pulsation command Iqc_r and the qc-axis current Iqc (torque current). The voltage compensation amount ΔVq has a sinusoidal waveform that pulsates at a frequency six times the power supply frequency.

[0076] Similarly, the other S control calculator 86i calculates the d-axis voltage compensation amount ΔVd based on the power supply frequency ωs and the aforementioned difference (0-Idc). The aforementioned equations (12) and (13) are used to calculate this voltage compensation amount ΔVd. The voltage compensation amount ΔVd also has a sinusoidal waveform that pulsates at a frequency six times the power supply frequency. By reflecting the d-axis voltage compensation amount ΔVd in the control, the influence of interference from the q-axis to the d-axis is suppressed, thereby suppressing pulsation of the d-axis current.

[0077] The d-axis compensation amount ΔVd, which is the calculation result of the S control calculator 86i, is output to an adder 92 (see FIG. 2). As described above, the adder 92 generates a new dc-axis voltage command Vdc** by adding the compensation amount ΔVd to the dc-axis voltage command Vdc*. Similarly, the q-axis compensation amount ΔVq, which is the calculation result of the other S control calculator 86h, is output to another adder 93 (see FIG. 2). The adder 93 generates a new qc-axis voltage command Vqc** by adding the compensation amount ΔVq to the qc-axis voltage command Vdc*.

[0078] In this way, the control unit 80 generates a new qc-axis voltage command Vqc** (new torque voltage command) by adding the compensation amount ΔVq (torque voltage compensation amount) to the qc-axis voltage command Vdc* (torque voltage command), and controls the inverter circuit 40 (see FIG. 1) based on the new qc-axis voltage command Vqc**. This series of processes is the above-mentioned "current pulsation suppression control."

[0079] <Simulation Results> FIG. 4 is a waveform diagram showing the relationship between AC voltage, line voltage, and power supply phase. The horizontal axis of each waveform diagram shown in FIG. 4 represents time. The vertical axis of each waveform diagram represents, from top to bottom, the AC voltage (i.e., AC voltage signal (ErN, EsN, EtN)), the line voltage (Ers, Est, Etr), and the power supply phase θs of the AC voltage. When the line voltages (Ers, Est, Etr) are calculated from the AC voltage signals (ErN, EsN, EtN) based on the above-described equations (4) to (6), a sinusoidal waveform as shown in FIG. 4 is obtained. With respect to the power supply phase θs, a change occurs repeatedly in which the value linearly increases from −π [rad] to +π [rad] over time, then drops back to −π [rad] and linearly increases again (i.e., a sawtooth-shaped waveform is obtained).

[0080] FIG. 5 is a waveform diagram showing the waveforms of the motor current, d-axis current, q-axis current, and power supply current. The horizontal axis of each waveform diagram in FIG. 5 represents time. The vertical axis of each waveform diagram, from top to bottom, represents the motor currents (Iu, Iv, Iw) for three phases (U, V, and W phases), the u-phase motor current Iu, the q-axis current, the d-axis current, the power supply currents (Ir, Is, It) for three phases (R, S, and T phases), and the R-phase power supply current Ir. In other words, the second waveform diagram from the top of FIG. 5 represents only the U-phase motor current Iu from the three-phase motor currents (Iu, Iv, Iw) shown in the topmost row. The bottom waveform diagram in FIG. 5 represents only the R-phase power supply current Ir from the three-phase power supply currents (Ir, Is, It) shown in the second waveform diagram from the bottom.

[0081] Also, assume that the current pulsation suppression control is switched from off to on at time t1 in Figure 5. As shown in the second waveform diagram from the top of Figure 5, the U-phase motor current Iu pulsates periodically at a low frequency until the current pulsation suppression control is started, and motor current pulsation (i.e., beat phenomenon) occurs. It can also be seen that the motor current pulsation is reduced some time after the start of the current pulsation suppression control (time t1). The same is true for the remaining V-phase and W-phase motor currents.

[0082] After the current pulsation suppression control is initiated, the d-axis current value approaches zero (command value). Meanwhile, the q-axis current pulsates as indicated by the dashed-dotted frame Q1. This is because the q-axis current is controlled based on the current pulsation command Iqc_r (see FIG. 3 ) that includes a pulsation component with a frequency six times the power supply frequency.

[0083] Furthermore, as shown in the bottom row of FIG. 5, after a while from the start of the current pulsation suppression control (time t1), the R-phase power supply current Ir assumes a waveform close to a square wave, indicating that the power supply harmonic current is suppressed. The remaining S-phase and T-phase also assume similar waveforms. Furthermore, as shown by the dashed-dotted frame Q2, when the largest value (i.e., DC current) of the R-phase, S-phase, and T-phase power supply currents is extracted, it becomes a substantially constant value. In other words, as described above, the DC current Ir in equation (3) ＤＣ It can be seen that approaches a constant value.

[0084] <Effects> According to the first embodiment, the control unit 80 compensates the current command using a pulsation component having a frequency six times the power supply frequency. This makes it possible to suppress motor current pulsation (especially the sixth-order pulsation) and power supply harmonic current (especially the fifth-order and seventh-order components).

[0085] In addition, suppressing motor current pulsation not only prevents overcurrent but also reduces losses, resulting in more stable and efficient control. Furthermore, suppressing power supply harmonic currents allows operation to comply with power supply harmonic regulations.

[0086] Furthermore, since a film capacitor can be used as the smoothing capacitor 30, the board of the motor drive device 100 can be made smaller, and the cost of the smoothing capacitor 30 can be reduced and its lifespan can be extended.

[0087] In the first embodiment, the q-axis current (torque current) is controlled to approach a predetermined current pulsation command based on feedback control. Therefore, the influence of constant errors is reduced compared to when feedback control is not performed, and the motor M1 can be controlled with high precision.

[0088] Second Embodiment In the second embodiment, an air conditioner W1 (see FIG. 6) including the motor drive device 100 (see FIG. 1) configured as described in the first embodiment will be described. Note that the configuration and processing content of the motor drive device 100 are the same as those in the first embodiment, and therefore description thereof will be omitted.

[0089] Fig. 6 is a configuration diagram of an air conditioner W1 according to a second embodiment. The air conditioner W1 is a device that performs air conditioning, such as cooling operation. As shown in Fig. 6, the air conditioner W1 includes an outdoor unit U1 that is provided with a compressor 1, an outdoor heat exchanger 2, an outdoor fan 3, and an expansion valve 4, as well as a motor drive device 100. The air conditioner W1 also includes an indoor unit U2 that is provided with an indoor heat exchanger 5 and an indoor fan 6.

[0090] The compressor 1 is a device that compresses a low-temperature, low-pressure gas refrigerant and discharges it as a high-temperature, high-pressure gas refrigerant, and is equipped with a motor M1 as a drive source. For example, a scroll compressor or a rotary compressor is used as this compressor 1. Although not shown in Fig. 6 , an accumulator for separating the refrigerant into gas and liquid is connected to the suction side of the compressor 1. The motor M1 shown in Fig. 6 is also connected to the output side of an inverter circuit 40 (see Fig. 1 ) as a drive source for the compressor 1.

[0091] The outdoor heat exchanger 2 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer tubes and the outside air sent in by the outdoor fan 3. The outdoor fan 3 is a fan that sends outside air to the outdoor heat exchanger 2 and is installed near the outdoor heat exchanger 2. The expansion valve 4 is a valve that reduces the pressure of the refrigerant condensed in the outdoor heat exchanger 2 (condenser). The refrigerant reduced in pressure by the expansion valve 4 is led to the indoor heat exchanger 5 (evaporator).

[0092] The indoor heat exchanger 5 is a heat exchanger in which heat is exchanged between the refrigerant flowing through its heat transfer pipes (not shown) and the indoor air (air in the air-conditioned room) sent in by the indoor fan 6. The indoor fan 6 is a fan that sends indoor air to the indoor heat exchanger 5, and is installed near the indoor heat exchanger 5.

[0093] As shown in Fig. 6, a compressor 1, an outdoor heat exchanger 2, an expansion valve 4, and an indoor heat exchanger 5 are connected in sequence via piping 7. The refrigerant circulates sequentially through the compressor 1, the outdoor heat exchanger 2 (condenser), the expansion valve 4, and the indoor heat exchanger 5 (evaporator). The air cooled by heat exchange with the refrigerant flowing through the indoor heat exchanger 5 is blown out from the indoor unit U2 into the air-conditioned room.

[0094] <Effects> According to the second embodiment, the air conditioner W1 is provided with the motor drive device 100 having the same configuration as in the first embodiment, and therefore the performance and reliability of the air conditioner W1 are improved.

[0095] <<Modifications>> The motor drive device 100 and the air conditioner W1 according to the present disclosure have been described above in various embodiments. However, they are not limited to these and various modifications can be made. For example, in the first embodiment, the control unit 80 (see FIG. 1 ) suppresses sixth-order motor current pulsation and fifth-order and seventh-order power supply harmonic currents. However, this is not limiting. That is, the control unit 80 may extract a pulsation component having a frequency six times the power supply frequency based on the detection value of the power supply voltage detection unit 50, and may also extract a pulsation component having a frequency (6×n) times the power supply frequency (where n is a natural number greater than or equal to 2). In this case, the control unit 80 multiplies each pulsation component by a torque current command to calculate multiple current pulsation commands corresponding to the respective pulsation components. The control unit 80 then generates a new torque voltage command by adding multiple torque voltage compensation amounts corresponding to the multiple current pulsation commands to the torque voltage command, and controls the inverter circuit 40 based on this new torque voltage command. It should be noted that a plurality of S-control calculators for the q-axis are provided in one-to-one correspondence with the pulsation components of the 6th, 12th, 18th, etc., and each S-control calculator calculates the voltage compensation amount ΔVq for the q-axis individually (the same applies to the d-axis). The above-mentioned processing does not necessarily have to be performed for all orders of the 6th, 12th, 18th, etc., as long as at least one order other than the 6th order is included.

[0096] In the first embodiment, the DC reactor 20 is provided on the positive DC line A1 (see FIG. 1 ), but this is not limiting. That is, the DC reactor 20 may be omitted as appropriate. In the embodiment, the smoothing capacitor 30 is a film capacitor, but this is not limiting. For example, the smoothing capacitor 30 may be another type of capacitor, such as an electrolytic capacitor.

[0097] In the first embodiment, the compensated power supply phase θss is calculated by adding a predetermined compensation value θs_comp to the power supply phase θs, but this is not limiting. For example, if the effect of calculation delay is minor, the above-described process may be omitted.

[0098] In the first embodiment, the feedback control is performed by the S-control calculators 86h and 86i (see FIG. 3) based on the transfer function of the above-described equation (12), but the present invention is not limited to this. That is, other transfer functions may be used as long as they have sensitivity to a specific center frequency.

[0099] Although the first embodiment has been described with reference to a case where three-phase AC power is supplied from the AC power supply E1 (see FIG. 1 ), the present invention is not limited to this. For example, the first embodiment can also be applied to a case where single-phase AC power is supplied from the AC power supply. In this case, a pulsation component having a frequency that is 2×n times the power supply frequency (n is a natural number) is multiplied by the q-axis current command to generate a predetermined current pulsation command.

[0100] In addition, in each embodiment, the bus current detector 70 (see FIG. 1: current detector) detects the current in the DC line A2 (see FIG. 1), but this is not limiting. For example, a current detector (not shown) may detect the current flowing through the wiring between the inverter circuit 40 and the three-phase windings of the motor M1. In addition, in each embodiment, the DC voltage detector 60 (see FIG. 1) includes the resistive elements R1 to R6 (see FIG. 1), but this is not limiting. For example, a voltage sensor may be used as the DC voltage detector 60.

[0101] In the second embodiment (see FIG. 6 ), the motor drive device 100 is connected to the motor M1 of the compressor 1, but the present invention is not limited to this. For example, the motor drive device 100 may be connected to an outdoor fan motor (not shown).

[0102] In the second embodiment (see FIG. 6 ), the air conditioner W1 is described as not particularly including a four-way valve (not shown), but this is not limiting. That is, a four-way valve that switches the refrigerant flow path between the cooling cycle and the heating cycle may be provided. Furthermore, the second embodiment (see FIG. 6 ) can be applied to various types of air conditioners, such as commercial air conditioners and multi-air conditioners for buildings, in addition to room air conditioners. Furthermore, each embodiment can be applied to other devices (refrigeration cycle devices) such as freezers and chillers, in addition to water heaters and hot water supply air conditioners.

[0103] Furthermore, each embodiment has been described in detail to clearly explain the present disclosure, and is not necessarily limited to having all of the described configurations. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. Furthermore, the mechanisms and configurations described above are those considered necessary for the explanation, and do not necessarily represent all mechanisms and configurations in the product. Furthermore, the control lines and information lines are those considered necessary for the explanation, and do not necessarily represent all control lines and information lines in the product. In reality, it can be assumed that almost all configurations are interconnected.

[0104] REFERENCE SIGNS LIST 1 Compressor 2 Outdoor heat exchanger 3 Outdoor fan 4 Expansion valve 5 Indoor heat exchanger 6 Indoor fan 10 Rectifier circuit 20 DC reactor 30 Smoothing capacitor 40 Inverter circuit 50 Power supply voltage detection section 60 DC voltage detection section 70 Bus current detection section (current detection section) 80 Control section 100 Motor drive device A1, A2 DC line E1 AC power supply M1 Motor R1, R2, R3, R4, R5, R6 Resistance element W1 Air conditioner

Claims

1. A motor drive device comprising: a rectifier circuit that converts AC voltage applied from a three-phase AC power supply into DC voltage; a smoothing capacitor that smooths the DC voltage on the output side of the rectifier circuit; an inverter circuit that converts the DC voltage of the smoothing capacitor into AC voltage and drives a motor with the AC voltage; a power supply voltage detection unit that detects the power supply voltage of the AC power supply; a current detection unit that detects the current of the inverter circuit; and a control unit that controls the inverter circuit, wherein the control unit extracts a pulsation component of a frequency six times the power supply frequency based on the detection value of the power supply voltage detection unit, multiplies the pulsation component by a torque current command of the inverter circuit to calculate a current pulsation command, and performs feedback control so that the torque current based on the detection value of the current detection unit approaches the current pulsation command.

2. The motor drive device of claim 1, wherein the control unit calculates a torque voltage compensation amount by amplifying a value in a range including six times the power supply frequency in the waveform of the difference between the current ripple command and the torque current, generates a new torque voltage command by adding the torque voltage compensation amount to the torque voltage command, and controls the inverter circuit based on the new torque voltage command.

3. The motor drive device according to claim 2, wherein the torque voltage compensation amount is calculated based on the transfer function of equation (12), where s in equation (12) is a Laplace operator, and K １ , K ２ , K ３ is the control gain, and ω ０ is the center frequency six times the power supply frequency.

4. The motor drive device of claim 1, wherein the control unit calculates the power supply phase based on the detection value of the power supply voltage detection unit, calculates the compensated power supply phase by adding a predetermined compensation value that is a compensation element for calculation delay to the power supply phase, and extracts the pulsating component based on the compensated power supply phase.

5. The motor drive device according to claim 1, wherein the power supply voltage detection unit has a series connection of resistive elements connected via wiring between the input terminal of each phase of the AC power supply and the low-potential side terminal of the smoothing capacitor, and the low-potential side of the series connection is connected to the ground terminal of the control unit.

6. The motor drive device according to claim 1, wherein the control unit extracts a pulsation component having a frequency six times the power supply frequency based on the detection value of the power supply voltage detection unit, and also extracts a pulsation component having a frequency (6 x n) times the power supply frequency (where n is a natural number of 2 or more), multiplies the torque current command by each of the pulsation components, calculates a plurality of current pulsation commands corresponding to each of the pulsation components, adds a plurality of torque voltage compensation amounts corresponding to the plurality of current pulsation commands to the torque voltage command, and generates a new torque voltage command, and controls the inverter circuit based on the new torque voltage command.

7. An air conditioner comprising the motor drive device according to any one of claims 1 to 6, a compressor, an outdoor heat exchanger, an expansion valve, and an indoor heat exchanger, wherein the motor is connected to the output side of the inverter circuit as a drive source for the compressor.

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