JP2015154612A - control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device capable of reducing power supply harmonic currents and simplifying a configuration.SOLUTION: A controller 7 of a motor drive device generates a sine wave corresponding to a rotation number of a motor 9 and a (12n+3) order harmonic thereof (here, n=0, 1, 2, ...), and superposes the (12n+3) order harmonic on the sine wave to generate a motor voltage waveform. The controller 7 generates a motor voltage amplitude instruction value in a manner to obtain a zero degree of a phase difference between a motor current and the sine wave, to PWM-control an inverter 5 on the basis of the motor voltage waveform and the motor voltage amplitude instruction value.

Description

  The present invention relates to a control device, and more particularly to a control device that controls an inverter in a motor driving device using a small-capacitance capacitor.

  When driving a synchronous motor having a plurality of phase coils, it is important to apply a motor current to the motor at an appropriate timing and apply a voltage to the coil terminal, that is, to optimize the energization timing. As a method for detecting the reference of the energization timing, there are various methods such as a method for detecting a counter electromotive voltage and a method for detecting a zero cross current phase.

  For example, in a so-called sensorless driving method in which a motor is driven without using a motor rotor position sensor, a back electromotive voltage generated in the motor coil due to the rotation of the motor is detected from the motor coil terminal when the motor coil is energized.

  Patent Document 1 discloses a rectifier circuit that full-wave rectifies an AC voltage supplied from an AC power source through a reactor coil, a large-capacity smoothing capacitor connected between output terminals of the rectifier circuit, and a rectifier circuit. A motor drive device is disclosed that includes an inverter that converts the direct current power into alternating current power and supplies the same to a synchronous motor. The reactor coil is provided in order to improve the power factor of AC power supplied from the AC power source to the mode driving device. As the smoothing capacitor, a capacitor having a sufficiently large capacity value that can improve the ripple of the DC voltage waveform is used.

  However, in the motor drive device of Patent Document 1, the device size is large, the improvement of the input current waveform is insufficient, and it is difficult to increase the power factor. Therefore, in Patent Document 2, the reactor coil is removed, and a simple configuration using a small-capacitance capacitor is used to improve the input current waveform and increase the power factor, thereby reducing the power harmonic components. .

JP 2001-112287 A JP 2006-203963 A

  However, Patent Document 2 requires the creation of a target value of the input current waveform, calculation of an error component with the input current, and voltage generation means for eliminating the error component, which complicates the configuration of the control device. was there.

  Therefore, a main object of the present invention is to provide a control device capable of improving the input current waveform, increasing the power factor, reducing the power supply harmonic current, and simplifying the configuration.

  A control device according to the present invention includes a rectifier circuit that full-wave rectifies an AC voltage, a small-capacitance capacitor connected between output terminals of the rectifier circuit, and converts DC power from the rectifier circuit into AC power for conversion into a motor. It is for controlling an inverter in a motor drive device provided with the supplied inverter. The control device includes a first waveform generation unit, a second waveform generation unit, a command value generation unit, and a control unit. The first waveform generation unit generates a sine wave corresponding to the rotation speed of the motor. The second waveform generation unit generates a (12n + 3) -order harmonic (where n is an integer equal to or greater than 0) of the sine wave, and superimposes the generated (12n + 3) -order harmonic on the sine wave. Generate a voltage waveform. The command value generation unit generates the motor voltage amplitude command value so that the phase difference between the alternating current flowing from the inverter to the motor and the sine wave becomes 0 degree. The control unit performs PWM control on the inverter based on the motor voltage waveform and the motor voltage amplitude command value generated by the second waveform generation unit.

  According to the control device of the present invention, it is possible to improve the input current waveform, increase the power factor, reduce the power supply harmonic current, and simplify the configuration.

It is a block diagram which shows the structure of the motor drive device by one Embodiment of this invention. It is a figure which shows the waveform of the motor voltage in case the superimposition amount of a 3rd harmonic is 0, and an interphase voltage. It is a figure which shows the waveform of a motor voltage, an interphase voltage, and a 3rd harmonic in case the superposition amount of a 3rd harmonic is 0.16. It is a figure which shows the relationship between the superposition amount of a 3rd harmonic, and the maximum value of an interphase voltage. It is a time chart which shows waveforms, such as direct current, when the amount of superposition of the third harmonic is 0.16. It is a time chart which shows waveforms, such as direct current, when the amount of superposition of the third harmonic is 0.40. It is a figure which shows the relationship between the superposition amount of a 3rd harmonic, and a power supply harmonic current. It is another figure which shows the relationship between the superposition amount of a 3rd harmonic, and a power supply harmonic current. It is a figure which shows the relationship between the output of a motor, and the superposition amount of a 3rd harmonic. It is a figure which shows synthetic | combination U phase wave Vuh3, synthetic | combination V phase wave Vvh3, and U-V phase voltage Vuv at the time of using 15th harmonic Vh3. It is a figure which shows synthetic | combination U phase wave Vuh4, synthetic | combination V phase wave Vvh4, and U-V phase voltage Vuv at the time of using 27th harmonic Vh4. It is a figure which shows waveforms, such as a direct current, when a target phase difference is set to 0 degree | times when the superimposition rate of a 3rd harmonic is 0.40. It is a figure which shows the measurement result of a power supply harmonic current in the case of phase difference 0.

<First Embodiment>
[overall structure]
As shown in FIG. 1, the motor drive device according to one embodiment of the present invention includes a rectifier circuit 1, a capacitor 2, a DC voltage sensor 3, a DC current sensor 4, an inverter 5, an AC current sensor 6, and a controller 7. . This motor drive device converts single-phase AC power from the AC power supply 8 into three-phase AC power and supplies it to the synchronous motor 9 to drive the synchronous motor 9 to rotate.

  The rectifier circuit 1 includes four diodes D1 to D4, and full-wave rectifies the single-phase AC voltage from the AC power supply 8. The capacitor 2 is connected between the positive output terminal 1a and the negative output terminal 1b of the rectifier circuit 1. As the capacitor 2, a capacitor having a capacitance value of about 1/100 (for example, 10 to 20 μF) of a normal smoothing capacitor is used. The capacitor 2 is provided to prevent the inverter 5 from being destroyed by the regenerative energy of the synchronous motor 9. No reactor coil is provided.

  The DC voltage sensor 3 detects an instantaneous value of the DC voltage Vdc appearing between the terminals of the capacitor 2 and outputs a signal indicating the detected value to the controller 7. The direct current sensor 4 detects an instantaneous value of the direct current Idc flowing from the rectifier circuit 1 to the inverter 5 and outputs a signal indicating the detected value to the controller 7.

  The inverter 5 is PWM (pulse width modulation) controlled by the controller 7, converts the DC power from the rectifier circuit 1 into three-phase AC power, and supplies it to the synchronous motor 9. The inverter 5 includes six switching elements s1 to s6 and six diodes d1 to d6. The switching elements s1 to s3 are connected between the positive output terminal 1a of the rectifier circuit 1 and the three-phase input terminals 9w, 9v, 9u of the synchronous motor 9, respectively. The switching elements s4 to s6 are respectively connected between the three-phase input terminals 9w, 9v, 9u of the synchronous motor 9 and the negative output terminal 1b of the rectifier circuit 1. The diodes d1 to d6 are connected in antiparallel to the switching elements s1 to s6, respectively. Each of switching elements s1 to s6 is formed of, for example, an IGBT (Insulated Gate Bipolar Transistor).

  The AC current sensor 6 detects an instantaneous value of the AC current Iu flowing through a predetermined input terminal (9u in FIG. 1) among the three-phase input terminals 9w, 9v, and 9u of the synchronous motor 9, and indicates the detected value. The signal is output to the controller 7. The synchronous motor 9 includes a stator including a three-phase coil and a rotor including a permanent magnet. When three-phase AC power is supplied to the three-phase coil via the three-phase input terminals 9w, 9v, 9u, the rotor is rotationally driven at a rotational speed corresponding to the frequency of the three-phase AC power.

  The controller 7 is constituted by a microcomputer, and performs PWM control of each of the switching elements s1 to s6 of the inverter 5 based on the output signals of the sensors 3, 4 and 6. The controller 7 includes a rotation speed setting unit 10, a sine wave generation unit 11, a motor output detection unit 12, a superimposition amount setting unit 13, a harmonic generation unit 14, and an adder 15.

  The rotation speed setting unit 10 sets a target rotation speed of the synchronous motor 9. The rotational speed (rpm) of the synchronous motor 9 is equal to the target rotational speed set by the rotational speed setting unit 10.

  The sine wave generation unit 11 includes a sine wave data table including a predetermined number of data. The sine wave generator 11 reads sine wave data corresponding to the U phase, V phase, and W phase of the synchronous motor 9 from the sine wave data table according to the target rotational speed set by the rotational speed setting unit 10 and the passage of time. And outputs U-phase motor voltage phase information based on the U-phase sine wave data.

  When the harmonic wave generation unit 14 uses a sine wave corresponding to the target rotational speed of the motor (a sine wave generated by the sine wave generation unit 11) as a fundamental wave, the harmonic generation unit 14 calculates the order Hn calculated from the following equation. Generate harmonics.

Hn = 12n + 3 (where n = 0, 1, 2,...) (1)
Specifically, the harmonic generation unit 14 includes a sine wave data table including a predetermined number of data, like the sine wave generation unit 11. The harmonic generation unit 14 reads the sine wave data from the sine wave data table according to the number of revolutions (12n + 3) times the target number of revolutions set by the revolution number setting unit 10 and the passage of time. Further, the harmonic generation unit 14 multiplies the read sine wave data by the superposition amount k set by the superposition amount setting unit 13 to generate (12n + 3) -order harmonic data.

  For the sake of simplicity in the description of the following embodiments, first, a case where n = 0, that is, H0 = 3 (third harmonic) will be described.

  The motor output detector 12 detects the output P of the synchronous motor 9 based on the output signals of the DC voltage sensor 3 and the DC current sensor 4, and gives a signal indicating the detected value to the superposition amount setting unit 13. The superposition amount setting unit 13 is based on the output signal of the motor output detection unit 12, that is, the output P of the synchronous motor 9, and the superposition amount of the third harmonic (more generally, the (12n + 3) th harmonic) with respect to the sine wave. Set k. This superposition amount k is the ratio of the amplitude of the third harmonic to the amplitude of the sine wave.

  The superposition amount setting unit 13 maintains or increases the superposition amount k according to the increase in the output P of the motor 9. The superposition amount setting unit 13 changes the superposition amount k within a range of 0.16 or more and 0.40 or less. By superimposing the third harmonic on the sine wave, it is possible to increase the output voltage of the inverter 5 or reduce the harmonic component of the power supply current. This point will be described in detail later.

  The adder 15 adds the sine wave data corresponding to the U phase, the V phase, and the W phase from the sine wave generation unit 11 and the third harmonic data from the harmonic generation unit 14, respectively. Motor voltage waveform data corresponding to the V phase and the W phase is generated.

  The controller 7 includes a phase difference detection unit 16, a target phase difference storage unit 17, a PI (Proportional Integral) calculation unit 18, a voltage limiting unit 19, and a PWM signal generation unit 20.

  The phase difference detection unit 16 is based on the U-phase motor voltage phase information from the sine wave generation unit 11 and the signal indicating the U-phase current Iu from the AC current sensor 6 and the U-phase motor voltage Vu and the current Iu. And a signal indicating the detected value is output.

  For example, the phase difference detection unit integrates each current sampling data sampled every two motor voltage phase periods to obtain a motor current signal area, and calculates the phase difference from the area ratio of both motor current signal areas (Japanese Patent Application Laid-Open No. 2005-318867). 2001-112287).

  The target phase difference storage unit 17 stores target phase difference information. The target phase difference information stored in the target phase difference storage unit 17 is output to the PI calculation unit 18. In the present embodiment, the target phase difference is preferably 0 degree. By setting the target phase difference to 0 degree, the voltage phase of the motor and the current phase of the motor are in phase, and the motor operates at a power factor of 1. The reason for setting the target phase difference to 0 degree will be described later with reference to FIGS.

  The PI calculation unit 18 calculates error data between the phase difference detected by the phase difference detection unit 16 and the target phase difference information stored in the target phase difference storage unit 17, and performs proportional control and control on the error data. Execute integration control to output motor output voltage amplitude value.

The voltage limiting unit 19 limits the motor voltage amplitude command value generated by the PI calculation unit 18 to an upper limit value PWMmax or less corresponding to the superposition amount k set by the superposition amount setting unit 13. Assuming that PWMmax when k = 0 is 1, PWMmax = 3 [12k / (3k + 1)] ^0.5 / (6k + 2) in the range of k ≧ 0.16. A method for deriving this mathematical expression will be described later.

  The PWM signal generation unit 20 includes six motor voltage waveform data corresponding to the U phase, the V phase, and the W phase from the adder 15 and the motor voltage amplitude command value generated by the PI calculation unit 18. PWM signals are generated, and those PWM signals are supplied to the inverter 5. Switching elements s1 to s6 of inverter 5 are turned on and off according to six PWM signals, respectively. Thereby, three-phase alternating current power is supplied to the synchronous motor 9, and the roller of the synchronous motor 9 is rotationally driven.

[Relationship between third harmonic and amplitude of motor phase voltage]
Next, the relationship between the superposition amount k of the third harmonic and the amplitude of the motor phase voltage will be described. Here, the relationship between the superposition amount k and the amplitude of the U-V phase voltage Vuv when the third harmonic Vh is superimposed on the U-phase motor voltage Vu and the V-phase motor voltage Vv will be described. The same applies to the W phase and the U phase.

  When the third harmonic data is not superimposed on the sine wave data generated by the sine wave generator 11, that is, when k = 0, the amplitudes of the U-phase motor voltage Vu and the V-phase motor voltage Vv are shown in FIG. Is 1.0 (100%), the U-V phase voltage Vuv, which is the voltage between the U phase and the V phase, is a sine wave having an amplitude of 1.73. Here, for simplification of explanation, it is assumed that the sine wave data is a sine wave having a maximum value of 1 and an amplitude of 1, and the maximum value of the output data of the PWM signal generation unit 20 is 1.

  Further, by superimposing the third harmonic data on the sine wave data, it is possible to maximize the amplitude of the U-V interphase voltage Vuv. That is, as shown in FIG. 3, when the U-phase and V-phase motor output voltage amplitudes are 1.0 (100%) and the superposition amount k is 0.16 (16%, 1/6), U− The V-phase voltage Vuv is a sine wave having an amplitude of 1.73. That is, the U-V phase voltage Vuv is the same whether or not the third harmonic Vh is superimposed on the U-phase motor voltage Vu and the V-phase motor voltage Vv. Further, since the phases are shifted by 120 degrees between the U phase and the V phase, the third harmonic Vh does not affect the waveform of the U-V phase voltage Vuv, and the waveform of the U-V phase voltage Vuv is a sine wave. Become.

  What is characteristic is that the maximum value of the combined U-phase wave Vuh after superimposing the third-order harmonic Vh on the U-phase motor voltage Vu becomes 0.86, and after the third-order harmonic Vh is superimposed on the V-phase motor voltage Vv. The maximum value of the combined V-phase wave Vvh is 0.86. That is, when the third harmonic Vh is superimposed on the sine wave, the maximum values of the combined U-phase wave Vuh and the combined V-phase wave Vvh are smaller than 1. Therefore, by setting the amplitudes of the combined U-phase wave Vuh and the combined V-phase wave Vvh to 1, the amplitude of the U-V phase voltage Vuv can be made larger than 1.73.

  Specifically, when the motor output voltage amplitude of the combined U-phase wave Vuh and the combined V-phase wave Vvh is 1.16 (= 1 / 0.86, 116%), the U-V interphase voltage Vuv has an amplitude of 2. 0.0 sine wave. Thus, by superimposing the third harmonic Vh on the U-phase motor voltage Vu and the V-phase motor voltage Vv by 16%, the amplitude of the U-V interphase voltage Vuv is increased by 16% compared to the case where the third harmonic Vh is not superimposed. The DC voltage Vdc can be utilized to the maximum. However, if the motor output voltage amplitudes of the combined U-phase wave Vuh and the combined V-phase wave Vvh are larger than 1.16, the waveforms of the combined U-phase wave Vuh and the combined V-phase wave Vvh are distorted. Must be limited to 1.16 or less.

  FIG. 4 is a diagram showing the relationship between the superposition amount k of the third harmonic Vh and the maximum value Auv of the U-V interphase voltage Vuv. In FIG. 4, the maximum value Auv of the U-V phase voltage Vuv when k = 0 is set to 1. As can be seen from FIG. 4, the maximum value Auv of Vuv that increases k from 0 gradually increases, and the maximum value Auv of Vuv peaks when k = 0.16. As k is increased from 0.16, the maximum value Auv of Vuv gradually decreases, and when k = 0.4, the maximum value of Vuv Auv becomes substantially equal to the value when k = 0 (ie, 1).

[Relationship between amount of superposition of third harmonic and upper limit of motor output voltage amplitude]
As described above, when the motor output voltage amplitude of the combined U-phase wave Vuh and the combined V-phase wave Vvh is 1.16 (= 1 / 0.86, 116%), the U-V phase voltage Vuv has an amplitude of 2 0.0 sine wave. However, if the motor output voltage amplitudes of the combined U-phase wave Vuh and the combined V-phase wave Vvh are larger than 1.16, the amplitudes of the combined U-phase wave Vuh and the combined V-phase wave Vvh exceed 1 and exceed 1. Since these parts are limited to 1, their waveforms are distorted. Therefore, in this case, it is necessary to limit the motor output voltage amplitude to 1.16 or less. Here, the relationship between the superposition amount k of the third harmonic and the upper limit value of the motor output voltage amplitude will be described.

When the sine wave is sin θ, the third harmonic is sin 3θ, and the combined wave of the sine wave and the third harmonic is y, y is expressed by the following equation (2).
y = sin θ + ksin 3θ (2)
Differentiating the above equation (2) yields y ′ = cos θ + 3 k cos 3θ = cos θ (1 + 12 k cos ² θ−9 k). Assuming that y has an extreme value and y ′ = 0, θ = π / 2 and 3π / 2 from cos θ = 0, and cos ² θ = (9k−1) from 1 + 12 kcos ² θ−9k = 0. / 12k. When θ = π / 2, 3π / 2, y is a minimum value, and when cos ² θ = (9k−1) / 12k, y is a maximum value.

Since 1 ≧ cos ² θ ≧ 0, 1 ≧ (9k−1) / 12k ≧ 0. Since 9k-1 ≧ 0, k ≧ 1/9. Further, since 9k-1 ≦ 12k, k ≧ −1 / 3. Therefore, k ≧ 1/9. k ≧ 1/9 is a condition in which y peaks are dispersed into two in a half cycle of y. When k <1/9, the peak of y is only θ = θ = π / 2, 3π / 2, and the peak is not dispersed into two in the half cycle of y.

Further, when the above equation (2) is modified, y = sin θ + k (4 cos ² θ−1) sin θ. Here, when cos ² θ = (9k−1) / 12k, y becomes a maximum value, and sin ² θ = 1−cos ² θ = (3k + 1) / 12k. The maximum value ymax of y is expressed by the following equation (3).
ymax = [(3k + 1) / 12k] ^0.5 (6k + 2) / 3 (3)
When the reciprocal of ymax is PWMmax, PWMmax is expressed by the following equation (4). The motor output voltage amplitude must be limited to PWMmax or less.
PWMmax = 3 [12k / (3k + 1)] ^0.5 / (6k + 2) (4)
For example, when k = 0.16, ymax = 0.86, and when the motor output voltage amplitude is 1 / 0.86 = 1.16, the interphase voltage becomes maximum. However, if the motor output voltage amplitude exceeds 1.16, the waveform of the composite wave is distorted, so it is necessary to limit the motor output voltage amplitude to 1.16 or less.

  When the motor output voltage amplitude exceeds the upper limit value PWMmax, the interphase voltage does not become a sine wave but voltage distortion occurs, and many harmonic components are superimposed on the motor current and the power supply harmonics increase. Therefore, in the present embodiment, the voltage limiter 19 limits the motor output voltage amplitude to the upper limit value PWMmax or less.

[Relationship between third harmonic and DC current]
Next, the relationship between the third harmonic and the direct current Idc flowing through the inverter 5 will be described. FIGS. 5A and 5B are time charts showing waveforms of the direct current Idc and the like when the third harmonic superposition amount k is 0.16. In particular, FIG. 5A shows waveforms of the combined U-phase wave Vuh, the combined V-phase wave Vvh, the combined W-phase wave Vwh, and the triangular wave Vt, and FIG. 5B shows the U-phase current Iu and the V-phase current. The waveforms of Iv, W-phase current Iw, DC current Idc, and AC voltage Vac are shown. 5A and 5B, the phase difference between the motor voltage and the motor current is 45 degrees.

  In the present embodiment, since the capacitance value of capacitor 2 is small, DC voltage Vdc has substantially the same waveform as AC voltage Vac, and fluctuates at a frequency twice that of AC voltage Vac. Further, the maximum value of the direct current Idc changes in the same manner as the combined waves Vuh, Vvh, Vwh.

  The terminal voltage of each phase is controlled by a PWM signal modulated at a carrier frequency according to the voltage of each phase. In accordance with the PWM-modulated inverter output voltage, the DC current Idc is observed with a motor current in the maximum voltage phase of U, V, and W phases and an inverse sign component of the motor current in the minimum voltage phase. For example, in the section where the U-phase motor voltage Vu is the maximum voltage and the W-phase motor voltage Vw is the minimum voltage, the U-phase current Iu and the opposite sign components of the W-phase current Iw are observed in the DC current Idc.

  FIGS. 6A and 6B are time charts showing waveforms of the direct current Idc and the like in the case where the superposition amount k of the third harmonic is 0.4, and are compared with FIGS. 5A and 5B. FIG. 6A and 6B, the phase difference between the motor voltage and the motor current is 45 degrees. As can be seen from FIGS. 6A and 6B, it is clear that the peak of the voltage waveform of each phase is dispersed into two by increasing the amount of superposition. In addition, since the peak of each phase is dispersed into two, the PWM waveform of each phase subjected to carrier modulation changes in the same manner, and the dispersion effect is also clearly seen in the DC current Idc as compared with the case of k = 0.16. It has become.

  Since the peak of the voltage waveform is dispersed into two, fluctuations in the terminal voltage of each phase are mitigated, and fluctuations in the on / off width in carrier frequency units are also mitigated in the PWM-modulated DC current waveform, and the DC current Idc The density is dispersed. Thus, by superimposing the third harmonic on the sine wave of the fundamental wave of each phase, it is possible to intentionally generate a sparse / dense distribution of the direct current Idc and disperse the density.

  In the motor drive device of the present embodiment, the reactor coil is removed and the small-capacitance capacitor 2 is used. Therefore, the motor currents Iu, Iv, Iw that are output currents of the inverter 5 and the input current of the inverter 5 A certain direct current Idc generates a harmonic current Ih in an alternating current that is an input current of the rectifier circuit 1.

  The motor current of the phase having the maximum motor voltage waveform of each phase and the inverse sign component of the motor current of the minimum phase appear in the DC current Idc. Therefore, when the maximum and minimum two currents appear in the three-phase current waveform whose phases are shifted by 120 degrees, the DC current Idc fluctuates six times of three phases × 2 in one cycle of the motor voltage waveform. That is, the direct current Idc fluctuates at a frequency six times the motor electrical angular frequency. Since the mechanical angle makes one revolution with a period of ½ of the number of motor poles, in the case of a four-pole motor, it makes one revolution with two electrical angles.

  As described above, the fluctuation of the DC current Idc occurs during one rotation of the mechanical angle (number of motor phases × 2) × (number of poles / 2) times, and the pulsation of the current waveform is converted into frequency (number of motor phases) × It is represented by (number of poles) × (number of rotations) and appears as a power supply harmonic current Ih in the alternating current.

[Relationship between third harmonic and power supply harmonic current]
Next, the relationship between the third harmonic and the power supply harmonic current Ih will be described. The power supply harmonic current Ih refers to a current having a frequency component that is an integral multiple of the sine wave waveform of the AC power supply 8. In electronic equipment, a regulation value is provided for the harmonic current Ih. .

  In the motor drive device of the present embodiment, the reactor coil is removed and the small-capacitance capacitor 2 is used. Therefore, the harmonic current Ih is changed into the AC current due to the influence of the motor currents Iu, Iv, Iw and the DC current Idc. Occur. For this reason, if the pulsation of the alternating current has a frequency that is an integral multiple of the sinusoidal waveform of the alternating current power supply 8, the restriction value Ihmax may not be satisfied. Therefore, in the present embodiment, by adjusting the superposition amount k of the third harmonic according to the output P of the motor, the power supply harmonic current Ih caused by the current pulsation generated in the inverter 5 is suppressed and the regulation value Ihmax is set. clear.

  Specifically, the third harmonic is largely superimposed on the sine wave of the fundamental wave of each phase to intentionally generate a sparse / dense distribution of the DC current Idc, and the density is dispersed, thereby (the number of motor phases) × The harmonic component of the frequency represented by (the number of poles) × (the number of rotations) is suppressed.

  Note that as the superposition amount k of the third harmonic becomes larger, the density distribution of the direct current Idc becomes larger and the effect of reducing the power supply harmonic current Ih becomes higher. However, as shown in FIG. 4, k = 0.16. The phase-to-phase voltage amplitude decreases at the boundary. Therefore, if the third harmonic is superposed with an extremely large superposition amount k, the interphase voltage amplitude decreases, the motor phase current increases due to insufficient voltage, and as a result, the power harmonic current Ih may increase conversely. is there. Therefore, in consideration of a tradeoff between an increase in the density distribution of the direct current Idc and an increase in the motor phase current, the superposition amount k is determined by confirmation through experiments.

  FIGS. 7A and 7B are diagrams illustrating changes in the power harmonic currents Ih of the 2nd to 40th orders when the superposition amount k is changed in three stages of 0, 0.16, and 0.30. In particular, FIG. 7A shows the harmonic current Ih of the 0th to 40th order, and FIG. 7B shows the harmonic current Ih of the 10th to 22nd order. The power supply frequency is 50 Hz. In the experiment, a 4-pole motor was used, the rotation speed was 4500 rpm, and the motor output voltage amplitude was set to 1.0 (100%) of the maximum value. In this case, the power supply harmonic current Ih resulting from the rotational speed is 18th order (3 phases × 4 poles × 4500 rpm / 60/50 Hz).

  As can be seen from FIGS. 7 (a) and 7 (b), the harmonic component in the vicinity of the frequency due to the rotational speed becomes smaller as the amount of superposition of the third harmonic superimposed on the motor applied voltage is increased. For example, when the superposition amount k of the third harmonic is increased from 0 to 0.30, the component of the 17th harmonic current is decreased from 0.17 A to 0.07 A. FIG. 8 is a diagram showing the relationship between the superposition amount k, the 15th harmonic current Ih (15), and the 17th harmonic current Ih (17). As can be seen from FIG. 8, the harmonic current Ih monotonously decreased as the amount of superposition k increased.

[Relationship between motor output and superposition amount]
When the superposition amount k is kept constant and the output P of the motor 9 is increased, the direct current Idc increases and the power supply harmonic current Ih also increases. Therefore, in the present embodiment, the superposition amount k is increased in accordance with the increase in the output P of the motor 9, and the increase in the power supply harmonic current Ih is suppressed.

  FIG. 9 is a diagram showing the relationship between the output P of the motor 9 and the superposition amount k. As shown in FIG. 9, the superposition amount setting unit 13 changes the superposition amount k according to the output P of the motor 9. The output P of the motor 9 is detected by the motor output detection unit 12 based on signals from the DC voltage sensor 3 and the DC current sensor 4. When the output P of the motor 9 is 0 to 800 [W], k = 0.16 is constant. As a result, the maximum voltage at which the interphase voltage becomes a sine wave can be increased, and the motor 9 can be driven at high speed.

  When the output P of the motor 9 is 800 to 1600 [W], k is monotonously increased from 0.16 to 0.40 in proportion to the output P of the motor 9. Thereby, the increase in the power supply harmonic current Ih accompanying the output P of the motor 9 can be suppressed. When the output P of the motor 9 is 1600 to 2000 [W], k = 0.40 is constant. Thereby, the superposition of an excessive third-order harmonic is suppressed, and the harmonic current Ih is prevented from being suppressed more than necessary, so that a sinusoidal interphase voltage can be increased and the motor 9 can be driven at a higher speed.

[For 15th and 27th harmonics]
The Hn-order harmonic described in the above equation (1) is n = 0, 1, 2,.
sin (Hn · θ) = sin (3 (4n + 1) · θ) (5)
It is expressed as Here, when θ = 90 degrees at which the fundamental wave sin (θ) is maximized, the phase of the Hn-order harmonic represented by Expression (5) is 270 degrees. That is, when the fundamental wave is maximal, the Hn-order harmonic becomes minimal. On the other hand, when θ = 270 degrees (or −90 degrees) at which the fundamental wave sin (θ) is minimized, the phase of the Hn-order harmonic represented by the equation (5) is 90 degrees. That is, when the fundamental wave is minimum, the Hn-order harmonic becomes maximum. Therefore, the magnitude of the peak value (maximum value and minimum value) of the fundamental wave can be reduced by superimposing the Hn-order harmonic on the fundamental wave. This is considered to reduce the power supply harmonic current. Specifically, the case of the 15th harmonic of n = 1 and the case of the 27th harmonic of n = 2 will be described.

  FIG. 10 is a diagram illustrating the combined U-phase wave Vuh3, the combined V-phase wave Vvh3, and the U-V phase voltage Vuv when the 15th harmonic Vh3 is used. FIG. 11 is a diagram showing a combined U-phase wave Vuh4, a combined V-phase wave Vvh4, and a U-V phase voltage Vuv when the 27th harmonic Vh4 is used. In any case, the power supply harmonic current Ih can be reduced by dispersing the peak of the motor phase voltage from one to a plurality.

  However, since the peak dispersion effect becomes smaller when n becomes excessive, it is preferable to measure the suppression effect of the power supply harmonic current Ih and determine n based on the measurement result.

  Further, as shown in FIGS. 10 and 11, even when the amplitude of the motor voltages Vu, Vv, Vw is 1.0 (100%), the maximum value of the combined waves Vuh, Vvh, Vwh is 1. It will exceed zero. When the maximum value of the synthesized waves Vuh, Vvh, Vwh exceeds 1.0, the waveforms of the synthesized waves Vuh, Vvh, Vwh are distorted and the power supply harmonics are increased. Therefore, when n is 1 or more, the amplitudes of the motor voltages Vu, Vv, and Vw are set to 1.0 (100%) or less so that the maximum value of the combined waves Vuh, Vvh, and Vwh does not exceed 1.0. Need to be restricted.

[Relationship between motor power factor and harmonic current]
Next, the relationship between the phase difference (motor power factor) between the motor voltage and motor current and the harmonic current will be described.

  As described with reference to FIGS. 5 and 6, the peak of the voltage waveform is largely dispersed into two by superimposing the third harmonic component on the fundamental wave. As a result, fluctuations in the terminal voltage of each phase are alleviated, fluctuations in the ON / OFF width in carrier frequency units are also mitigated in the PWM-modulated DC current waveform, and the DC current density is dispersed. As described above, the third harmonic is largely superimposed on the sine wave of the fundamental wave of each phase, so that the density of DC current is intentionally generated and the density is dispersed.

  However, in the case of FIG. 5 and FIG. 6, since the phase difference between the motor voltage and the motor current is 45 degrees, the DC current still exists, and as a result, the power supply harmonic current increases. It is thought that. Hereinafter, a specific example will be described.

  FIG. 12 is a diagram showing a waveform of a direct current or the like when the target phase difference is 0 degree when the superposition ratio of the third harmonic is 0.40. The waveform diagrams of FIGS. 12 (a) and 12 (b) are compared with the waveform diagrams of FIGS. 6 (a) and 6 (b).

  As can be seen from FIGS. 12 (a) and 12 (b), the density distribution of the DC current is more dispersed than in the case of the phase difference of 45 degrees shown in FIG. The reason is considered as follows. In the case of FIG. 12, since the phase difference is 0 degree, the motor voltage and the motor current are synchronized (motor power factor = 1), and the motor current is in a section where the pulse width of the PWM signal for motor voltage control is wide. The motor current is small in a section where the pulse width of the PWM signal for controlling the motor voltage is large. On the other hand, in the case of FIG. 6, since the phase difference between the motor voltage and the motor current is 45 degrees, the motor current is small in the section where the pulse width of the PWM signal for motor voltage control is wide. The motor current is large in the section where the pulse width of the PWM signal is narrow. For this reason, in the case of FIG. 6, it is thought that the density of DC current exists.

  FIG. 13 is a diagram illustrating a measurement result of the power supply harmonic current when the phase difference is zero. In the experiment, a 4-pole motor was used, and the rotation speed was 5166 rpm. With respect to the amplitude of the motor output voltage, an experiment was performed both when set to 0.9 (DUTY 90%) and when set to a maximum value of 1.0 (DUTY 100%).

  In FIG. 13, the vertical axis indicates the magnitude [A] of the power supply harmonic current Ih, and the horizontal axis indicates the order of the power supply harmonic current Ih. A case where the amplitude of the motor output voltage is 0.9 is indicated by a thin solid line, and a case where the amplitude is 1.0 is indicated by a broken line. Furthermore, the regulation value Ihmax of the power supply harmonic current is represented by a thick solid line.

  From the experimental conditions, the power supply harmonic current Ih resulting from the rotational speed is the 31st order (3 phases × 4 poles × 5166 rpm / 60/50 Hz). Referring to the experimental results shown in FIG. 13, the harmonic component near the frequency (31st order) due to the rotational speed is higher when the applied voltage of the motor is closer to 1 (the amplitude is 1.0). You can see that it has become smaller.

[effect]
As described above, in the present embodiment, the amount of superposition of the (12n + 3) -order harmonic is increased in accordance with the increase in the output P of the motor 9, so that an increase in the power supply harmonic current Ih can be suppressed. Further, since the motor voltage amplitude is limited to the upper limit value PMWmax or less corresponding to the superposition amount k, it is possible to prevent the waveform of the motor voltage from being distorted and the power supply harmonic current Ih from increasing. Therefore, the power supply harmonic current Ih can be reduced and suppressed to the regulation value Ihmax or less while using the capacitor 2 having a small capacity without using the reactor coil.

  In particular, by setting the target value of the phase difference between the motor voltage and the motor current to 0 degree (that is, bringing the power factor of the motor closer to 1), the distribution of the DC current density can be further dispersed. Thereby, the power supply harmonic current Ih can be further reduced.

  In addition, since the capacitor 2 having a small capacity is used without using the reactor coil, the input current waveform can be improved and the power factor can be increased. In addition, since it is unnecessary to create a target value of the input current waveform, calculate an error component with the input current, and voltage generation means for eliminating the error component, the device configuration is compared with the device described in Patent Document 2. Can be simplified.

<Second Embodiment>
In the first embodiment, the superposition amount k is changed according to the output P of the motor 9, but the superposition amount k may be fixed to a constant value. In the experiment by the inventor of the present application, the case where k = 0.35 is optimal, the power supply harmonic current Ih can be reduced, and a high motor voltage can be obtained. In this case, if the sine wave data on which the third harmonic is superimposed in advance is stored in the sine wave generator 11, the calculation process necessary for the superposition of the third harmonic can be omitted, and the load on the calculation process is reduced. can do. In addition, the motor output detection unit 12, the harmonic generation unit 14, and the adder 15 can be removed, and the configuration can be simplified.

<Third Embodiment>
The inverter control apparatus for driving a motor according to the first and second embodiments includes, for example, an air conditioner, an refrigerator, an electric washing machine, an electric dryer, a vacuum cleaner, a blower, a heat pump water heater and the like equipped with an inverter circuit. It is applicable to. For any product, the motor drive inverter device can be reduced in size and weight to increase the degree of freedom in product design, reduce the number of parts, improve product quality and life, and make it cheaper. Can be provided.

[Appendix]
Hereinafter, a part of the contents described in each of the above embodiments will be listed.

  [1] The control device (7) includes a rectifier circuit (1) for full-wave rectification of an AC voltage, a small-capacitance capacitor (2) connected between output terminals of the rectifier circuit (1), and a rectifier circuit (1 The inverter (5) is controlled in a motor drive device that includes an inverter (5) that converts the DC power from) into AC power and supplies it to the motor (9). The control device (7) includes a first waveform generation unit (11) that generates a sine wave corresponding to the rotational speed of the motor, and a (12n + 3) -order harmonic of the sine wave (where n is an integer of 0 or more) ) And a second waveform generator (14, 15) that generates the motor voltage waveform by superimposing the generated (12n + 3) -order harmonic on the sine wave. The control device (7) further includes a command value generation unit (18) that generates a motor voltage amplitude command value so that the phase difference between the alternating current flowing from the inverter (5) to the motor (9) and the sine wave becomes 0 degrees. And a control unit (20) that PWM-controls the inverter based on the motor voltage waveform and the motor voltage amplitude command value generated by the second waveform generation unit (14, 15).

  According to the above configuration, the (12 + 3) -order harmonic is superimposed on the fundamental wave and the motor voltage is controlled so that the phase difference between the motor voltage and the motor current becomes zero. Can be reduced.

[2] In the control device (7) of [1], n is 0.
[3] The control device (7) according to [1] or [2] includes a superposition amount setting unit (13) that sets a superposition amount of the (12n + 3) -order harmonic with respect to the sine wave, and a command value generation unit (18). A voltage limiting unit (19) for limiting the generated motor voltage amplitude command value to an upper limit value or less corresponding to the superposition amount set by the superposition amount setting unit (13); The control unit (20) generates an inverter based on the motor voltage waveform generated by the second waveform generation unit (14, 15) and the motor voltage amplitude command value limited to the upper limit value or less by the voltage limiting unit (19). (5) is PWM controlled.

  According to the above configuration, the motor voltage waveform can be prevented from being distorted by limiting the amplitude of the motor voltage in accordance with the harmonic superposition rate.

  [4] The control device (7) according to [3] further includes a motor output detection unit (12) that detects the output of the motor. The superposition amount setting unit (13) sets the superposition amount based on the motor output detected by the motor output detection unit (12).

  According to said structure, by setting the suitable superimposition rate according to a motor output, superimposition of an excessive 3rd harmonic can be suppressed and a motor can be driven at higher speed.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  1 rectifier circuit, 2 capacitor, 3 DC voltage sensor, 4 DC current sensor, 5 inverter, 6 AC current sensor, 7 controller, 8 AC power supply, 9 synchronous motor, D1 to D4, d1 to d6 diode, s1 to s6 switching element 10 rotational speed setting unit, 11 sine wave generation unit, 12 motor output detection unit, 13 superposition amount setting unit, 14 harmonic generation unit, 15 adder, 16 phase difference detection unit, 17 target phase difference storage unit, 18 PI Arithmetic unit, 19 voltage limiter, 20 PWM signal generator.

Claims (4)

A rectifier circuit for full-wave rectification of an AC voltage, a small-capacitance capacitor connected between output terminals of the rectifier circuit, and an inverter that converts DC power from the rectifier circuit into AC power and supplies the AC power to a motor. A control device for controlling the inverter in the motor drive device,
A first waveform generator that generates a sine wave corresponding to the rotational speed of the motor;
A (12n + 3) order harmonic of the sine wave (where n is an integer greater than or equal to 0) is generated, and the motor voltage waveform is generated by superimposing the generated (12n + 3) order harmonic on the sine wave. Two waveform generators;
A command value generator for generating a motor voltage amplitude command value so that the phase difference between the alternating current flowing from the inverter to the motor and the sine wave is 0 degree;
A control apparatus comprising: a control unit that performs PWM control of the inverter based on the motor voltage waveform generated by the second waveform generation unit and the motor voltage amplitude command value.   The control device according to claim 1, wherein n is 0. A superposition amount setting unit for setting a superposition amount of the (12n + 3) -order harmonic with respect to the sine wave;
A voltage limiting unit that limits the motor voltage amplitude command value generated by the command value generation unit to an upper limit value or less according to the superposition amount set by the superposition amount setting unit;
The control unit performs PWM control of the inverter based on a motor voltage waveform generated by the second waveform generation unit and a motor voltage amplitude command value limited to the upper limit value or less by the voltage limiting unit. Item 3. The control device according to Item 1 or 2. A motor output detector for detecting the output of the motor;
The control device according to claim 3, wherein the superposition amount setting unit sets the superposition amount based on an output of the motor detected by the motor output detection unit.

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