JP5825945B2 - Inverter control device, inverter device, and air conditioner - Google Patents

Description

  The present invention relates to an inverter control device and an inverter device, and more particularly to an inverter control device and an inverter device mounted on a home or business use air conditioner.

  As a control method for a three-phase voltage source inverter used for driving an AC motor, for example, a method of switching and adopting sine wave PWM control, overmodulation PWM control, and rectangular wave voltage control has been proposed (for example, Patent Documents). 1).

  The sine wave PWM control is a control method in which a sine wave voltage command value whose phases are shifted from each other by 120 ° is compared with a carrier wave, and a PWM signal is generated from the comparison result. In this sine wave PWM control system, the duty ratio is controlled so that the fundamental wave component becomes a sine wave within a certain period.

  In addition, overmodulation PWM control, for example, as disclosed in Patent Document 2, sets the voltage command value in the overmodulation region to a voltage larger than the voltage command value of the sine wave PWM control method, thereby changing the modulation rate to sine. This control can be higher than the maximum modulation rate in the wave PWM control mode.

  Further, the rectangular wave voltage control is a control method in which one pulse of a rectangular wave having a ratio of 1: 1 between the high level period and the low level period is applied to the AC motor within the predetermined period. The modulation rate can be increased to substantially the same.

JP 2008-253000 A JP 2002-247876 A

  By the way, the sine wave PWM control system has a large switching loss and is inefficient. In addition, in the control method in which a plurality of control methods are switched and employed, there is a problem that the phase current and the phase voltage fluctuate when the control method is switched, and the switching cannot be performed smoothly.

  The present invention has been made in view of such circumstances, and provides an inverter control device, an inverter device, and an air conditioner capable of reducing switching loss and smoothly switching between control methods. For the purpose.

In order to solve the above problems, the present invention employs the following means.
The present invention adopts a two-arm modulation method, corrects a sine wave reference voltage command signal to generate a first voltage command signal, and adds a third order to the sine wave reference voltage command signal. Second signal generating means for generating a second voltage command signal by an overmodulation method in which the maximum value of the amplitude of the waveform on which the harmonic component is superimposed is equal to or greater than the amplitude of the carrier wave; and the reference of the first signal generating means The first voltage command signal is selected when the amplitude of the voltage command signal is less than the first threshold value set to the maximum amplitude value of the reference voltage command signal, and the amplitude of the reference voltage command signal is equal to the first threshold value. Inverter control comprising: selection means for selecting the second voltage command signal when equal, and PWM signal generation means for generating a pulse width modulation signal by comparing the voltage command signal selected by the selection means with a carrier wave Dress To provide.

According to the above configuration, the first signal generating unit corrects the sine wave reference voltage command signal to generate the first voltage command signal by the two-arm modulation method, and the second signal generating unit generates the sine wave reference voltage command signal. Then, a second voltage command signal is generated by an overmodulation method such that the maximum value of the amplitude of the waveform in which the third harmonic component is superimposed on is equal to or greater than the amplitude of the carrier wave. The first voltage command signal and the second voltage command signal are output to the selection means, and the amplitude of the reference voltage command signal of the first signal generation means is less than the first threshold set to the maximum amplitude value of the reference voltage command signal. In this case, the first voltage command signal is selected, and the second voltage command signal is selected when the amplitude of the reference voltage command signal is equal to the first threshold value. The selected voltage command signal is output to the PWM signal generation means, and is compared with the carrier wave to generate a pulse width modulation signal.
Here, since the maximum amplitude of the first voltage command signal by the two-arm modulation method is not set to a value exceeding the amplitude of the carrier wave, an inverter output voltage higher than that is obtained in a region where the motor rotation speed exceeds a certain rotation speed. I can't. For this reason, in the region where the inverter output voltage cannot be increased by the two-arm modulation method, the output increase in the high rotation speed region is realized by performing the PWM control of the overmodulation method by the second signal generating means. Is possible. Further, in the rotational speed region where the efficiency is lowered in the PWM control by the overmodulation method, the 2-arm modulation method PWM control by the first signal generating means is selected, so that the efficiency reduction can be suppressed. Further, in a region where the amplitude of the first voltage command signal is equal to the first threshold value, the amplitude of the reference voltage command signal used in the first signal generation unit is equal to the amplitude of the reference voltage command signal used in the second signal generation unit. Become. Since this reference voltage command signal means a phase voltage, the line voltage of the inverter output can be made equal before and after switching. Thereby, fluctuations in the line voltage of the inverter output at the time of switching the control method and distortion of the output current can be reduced, and the control method can be switched smoothly.
The said inverter control apparatus WHEREIN: The said selection means is good also as switching a 1st voltage command signal and a 2nd voltage command signal according to motor rotation speed. In this case, the motor rotational speed at the time of switching is, for example, an inverter output voltage that reaches a certain voltage value, and the rotational speed that cannot be increased any more by 2-arm modulation PWM control or a predetermined percentage from the rotational speed. It is set to a value within the range.

  The inverter control device may include a third signal generation unit that generates a third voltage command signal by a three-arm modulation method, and the selection unit may select the third voltage command signal in a startup region.

According to the above configuration, PWM control based on the third voltage command signal by the three-arm modulation method is performed when the rotation speed command value is in the startup region. In the region where the rotational speed is low, the efficiency is higher in the three-arm modulation method (sinusoidal PWM control) than in the two-arm modulation method, so that further increase in efficiency can be achieved.
For example, the activation area may be set to 15 Hz to 20 Hz or less.

The inverter control device includes phase current detection means for detecting each phase current using a detection value of a direct current flowing through a direct current bus between the direct current power source and the inverter and the pulse width modulation signal, The phase current detection means may output the previous value as the phase current for a period in which the pulse width modulation signals of all three phases are turned on or off.

According to the above configuration, since the previous value is output during the period in which the phase current detection unit cannot detect the phase current from the direct current, the PWM control can be continuously performed even during the period in which the phase current cannot be detected. Become.

  The inverter control device includes phase current detection means for detecting each phase current using a detection value of a direct current flowing through a direct current bus between the direct current power source and the inverter and the pulse width modulation signal, The phase current detection means has a predetermined current detection period in which the pulse width modulation signal of only one of the three phases is turned on or off is set according to the current detection capability of the phase current detection means When the time is shorter than the time, the previous value may be output as the phase current.

According to the above configuration, since the previous value is output during the period in which the phase current detection unit cannot detect the phase current from the direct current, the PWM control can be continuously performed even during the period in which the phase current cannot be detected. Become.

The present invention provides an inverter device comprising an inverter that converts a DC voltage from a DC power source into a three-phase AC voltage and outputs the same to a motor, and the inverter control device that controls the inverter.
The present invention provides an air conditioner suitable for home use or business use and provided with the above inverter device.

  According to the present invention, it is possible to reduce the switching loss and to smoothly switch the control method.

It is the figure which showed schematic structure of the inverter apparatus which concerns on one Embodiment of this invention. It is a figure for demonstrating the phase current detection by a phase current detection part. It is a figure for demonstrating the phase current detection by a phase current detection part. It is the block diagram which showed schematic structure of the voltage command calculating part which concerns on one Embodiment of this invention. It is the figure which showed an example of the 1st voltage command signal produced | generated by the 1st signal production | generation part. It is the figure which showed an example of the 2nd voltage command signal produced | generated by the 2nd signal generation part. It is a figure for demonstrating the inverter output voltage of a 2 arm modulation system. FIG. 6 is a diagram showing a U-phase PWM signal corresponding to a first voltage command signal by the two-arm modulation method shown in FIG. 5. It is the figure which showed the U-phase PWM signal with respect to the 2nd voltage command signal by the overmodulation system shown in FIG. PWM based on the second voltage command signal on which the third harmonic generated by the second signal generation unit is superimposed from the PWM control based on the first voltage command signal of the two-arm modulation method generated by the first signal generation unit It is the figure which showed the U-phase electric current when switched to control. It is the figure which showed the U-phase electric current at the time of control system switching at the time of using the 2nd voltage command signal which does not superimpose a 3rd harmonic in a 2nd signal generation part. It is the figure which showed schematic structure of the inverter apparatus at the time of applying a 3 shunt electric current detection system. It is the figure which showed schematic structure of the inverter apparatus at the time of applying a motor current detection system.

  Hereinafter, an embodiment in which an inverter device according to the present invention is applied to a permanent magnet synchronous motor used in a compressor of a home air conditioner or a commercial air conditioner will be described with reference to the drawings. In addition to the permanent magnet synchronous motor, the inverter device according to the present invention can be widely applied to general three-phase AC motors such as an induction motor, an induction synchronous motor, a synchronous reluctance motor, and a switched reluctance motor.

  FIG. 1 is a diagram showing a schematic configuration of an inverter device according to an embodiment of the present invention. As shown in FIG. 1, the inverter device 1 includes an inverter 2 to which a DC voltage is input from a DC power supply 5 and an inverter control device 3 that controls the inverter 2. In FIG. 1, reference numeral 4 denotes a compressor motor driven by the inverter device 1.

  A DC voltage is supplied to the inverter 2 from the DC power source 5 through the DC bus L. The inverter 2 generates a three-phase AC voltage from the DC voltage and supplies the generated three-phase AC voltage to the compressor motor 4. Specifically, the inverter 2 includes upper-arm switching elements 2a, 2b, and 2c and lower-arm switching elements 2d, 2e, and 2f provided corresponding to the respective phases, and these switching elements. Is controlled by the inverter control device 3 to control the three-phase AC voltage (inverter output) supplied to the compressor motor 4.

The inverter device 1 also includes a current sensor 6 for detecting a direct current Idc flowing through the direct current bus L.
The direct current Idc detected by the current sensor 6 is output to the inverter control device 3. Here, an example of the current sensor 6 is a shunt resistor. In FIG. 1, the current sensor 6 is provided on the negative electrode side of the DC power source 5, but may be provided on the positive electrode side.

  The inverter control device 3 is, for example, an MPU (Micro Processing Unit), and includes a computer-readable recording medium in which a program for executing each process described below is recorded. The following processing is realized by reading the program recorded in the main memory device such as a RAM and executing it. Examples of the computer-readable recording medium include a magnetic disk, a magneto-optical disk, and a semiconductor memory.

  The inverter control device 3 generates PWM signals Su, Sv, Sw for each phase so as to make the rotation speed of the compressor motor 4 coincide with a rotation speed command value given from a host control device (not shown). The inverter 3 is controlled by giving to the switching element corresponding to each phase of the inverter 2, and a desired three-phase AC voltage is supplied to the compressor motor 4.

The inverter control device 3 includes a phase current detection unit (phase current detection unit) 11 that detects each phase current Iu, Iv, Iw using the DC current Idc detected by the current sensor 6, and a phase current detection unit 11 that detects the phase current. The voltage command calculation unit 12 that generates the voltage command signals Vu ^* , Vv ^* , and Vw ^* for each phase using the phase currents Iu, Iv, and Iw thus generated, and the voltage command signal Vu generated by the voltage command calculation unit 12 A PWM signal generation unit 13 that generates PWM signals (pulse width modulation signals) Su, Sv, Sw by comparing ^* , Vv ^* , Vw ^* and a carrier wave is provided as a main configuration.

  The phase current detection unit 11 detects the current of each phase from the DC current Idc using a known technique disclosed in, for example, Japanese Patent Application Laid-Open No. 2008-220117. For example, the phase current detection unit 11 uses the fact that two-phase current information flows in the DC current Idc, and uses the DC sensor detected by the current sensor 6 based on the on / off information of the switching elements 2a to 2f of the inverter 3. Each phase is distributed and detected as a three-phase current detection value. Here, as shown in FIG. 2, the phase current detection unit 11 obtains a phase current from a DC current detected using the fact that the PWM signal corresponding to any one of the three phases is turned on or off. However, the phase current cannot be detected during the period in which all the three-phase PWM signals are on (mode 0 in FIG. 2) or off (mode 7 in FIG. 2).

  For example, as shown in FIG. 3, if the current detection times Tvw and Tuv are short, the current detection performance cannot catch up and current detection may not be performed. As described above, in the period in which the phase current cannot be detected, the phase current detection unit 11 uses the previous value as the current value of the phase. That is, during the period in which the phase current cannot be detected, the previously obtained phase current is output from the phase current detection unit 11 to the voltage command calculation unit 12.

  As shown in FIG. 4, the voltage command calculation unit 12 includes a first signal generation unit (first signal generation unit) 21 that generates a first voltage command signal by a two-arm modulation method as described later, and a later-described A second signal generation unit (second signal generation unit) 22 that generates a second voltage command signal by the overmodulation method, a first voltage command signal generated by the first signal generation unit, and a second signal generation unit. And a selection unit (selection means) 23 that switches and employs the second voltage command signal.

  For example, the first signal generation unit 21 corrects a sinusoidal reference voltage command signal to generate a first voltage command signal as shown in FIG. In the two-arm modulation method, the operation of one-phase switching elements (for example, the switching elements 2a and 2d in the case of the U phase) is turned on or off in a plurality of saturation sections set during one period of each phase output voltage. The first voltage command signal is generated so as to modulate only the other two phases. In other words, in the two-arm modulation method, control is performed so that the line voltage has a desired waveform while distorting the potential of each phase. This PWM control by the two-arm modulation method can reduce the switching frequency by 2/3 times compared with the PWM control by the three-arm modulation method that generates and uses a sine-wave voltage command signal. Can be made. The two-arm modulation method is a known modulation method and is disclosed in, for example, Japanese Patent Laid-Open Nos. 6-233546 and 2011-91907.

  The second signal generator 22 generates a second voltage command signal by an overmodulation method. For example, as shown in FIG. 6, the second signal generation unit 22 makes the maximum value of the amplitude of the waveform obtained by superimposing the third-order harmonic component on the sinusoidal reference voltage command signal equal to or larger than the amplitude of the carrier wave. A second voltage command signal is generated. By setting it as such a 2nd voltage command signal, a motor output voltage higher than the maximum motor output voltage obtained by control based on the 1st voltage command signal of the 1st signal generation part 21 can be obtained.

  In the first signal generation unit 21 and the second signal generation unit 22, as a specific control method, for example, a known vector control method using a current in a dq axis two-phase coordinate system, It is possible to employ a known V / f control method disclosed in Japanese Patent No. -93931.

  The selection unit 23 includes a first signal generation unit 21 and a second signal generation unit 22 that are calculated by the vector control method, the V / f control method, and the like based on the rotational speed command value of the compressor motor 4 and the detected motor current. The voltage command signal from any one of these is selected and output to the PWM signal generator 13.

  Specifically, the selection unit 23 sets the amplitude of the sinusoidal reference voltage command signal used to generate the first voltage command signal in the first signal generation unit 21 to the maximum amplitude value of the reference voltage command signal. When the first voltage command signal from the first signal generation unit 21 is selected when the threshold value is less than the set first threshold value and the amplitude of the sinusoidal reference voltage command signal is equal to the first threshold value, the second signal The second voltage command signal from the generator 22 is selected.

  Here, in the two-arm modulation method, in the normal operation region where the motor rotation speed is equal to or less than a certain rotation speed ω1, the amplitude of the sine wave-shaped reference voltage command signal used in the first signal generation unit 21 gradually increases in proportion to the rotation speed. Therefore, as shown in FIG. 7, the inverter output voltage, that is, each of the U-phase voltage, the V-phase voltage, and the W-phase voltage increases in proportion to the rotational speed. However, when the motor rotation speed exceeds a certain rotation speed ω1, the amplitude of the reference voltage command signal used to generate the first voltage command signal becomes constant at the maximum value, so that the inverter output voltage becomes constant. , You can not get any more output. At this time, the maximum output voltage of the inverter can be obtained by Vdc / √2, where the value of the voltage of the DC power supply 5 is Vdc. The rotational speed ω1 is determined from the relationship between the induced voltage constant of the permanent magnet synchronous motor and the maximum output voltage of the inverter.

On the other hand, the PWM control based on the second voltage command signal generated by the second signal generation unit 22 has a large loss and poor efficiency in a region where the rotational speed is low, but in the region where the rotational speed is equal to or higher than ω1, A voltage equal to or higher than the inverter output voltage obtained by PWM control by the first signal generator 21 can be obtained. This is because in the region where the rotation speed exceeds ω1, the maximum amplitude of the waveform of the second voltage command signal is set to a value exceeding the amplitude of the carrier wave.
As described above, depending on whether the amplitude of the reference voltage command signal used in the first signal generation unit 21 is the maximum value, in other words, the control method is switched depending on whether the motor rotation speed is less than or equal to the rotation speed ω1. By doing so, it is possible to make use of the advantages of each signal generation unit and increase the efficiency.

  Further, at the time of switching between the first voltage command signal and the second voltage command signal, the amplitude of the reference voltage command signal used for generating the first voltage command signal and the second voltage command signal are generated. Since the amplitude of the reference voltage command signal used has the same value, the line voltage of the inverter output voltage can be set to the same value. Thus, since the line voltage at the time of switching the control method becomes equal, the fluctuation of the line voltage at the time of switching the control method can be reduced, and the control method can be switched smoothly.

The PWM signal generation unit 13 compares the voltage command signals Vu ^* , Vv ^* , Vw ^* selected by the selection unit 23 of the voltage command calculation unit 12 with a carrier wave that is a triangular wave to obtain the PWM signals Su, Sv, Sw. It is generated and output to a gate drive (not shown) that drives each switching element included in the inverter 2. FIG. 8 is a diagram showing a U-phase PWM signal corresponding to the first voltage command signal by the two-arm modulation method shown in FIG. 5, and FIG. 9 shows the second voltage command signal by the over-modulation method shown in FIG. It is the figure which showed the U-phase PWM signal.

Next, operations of the motor control device 3 and the motor device 1 according to the present embodiment having the above-described configuration will be described.
When a start command for the compressor motor 4 is issued, detection of a direct current is started by the current sensor 6, and the detected direct current is output to the phase current detector 11. The phase current detection unit 11 detects each phase current Iu, Iv, Iw using the detected value of the direct current, and outputs it to the voltage command calculation unit 12. When current detection is impossible, the phase current detection unit 11 outputs the previous value.

The first signal generation unit 21 (see FIG. 4) and the second signal generation unit 22 of the voltage command calculation unit 12 respectively use the phase currents Iu, Iv, and Iw to generate the first voltage command signal and the second voltage command signal, respectively. Generate and output to the selection unit 23. The selection unit 23 selects the first voltage command signal from the first signal generation unit 21 until the amplitude of the reference voltage command signal used to generate the first voltage command signal from the start reaches the first threshold, When the amplitude of the reference voltage command signal becomes equal to the first threshold value, the second voltage command signal from the second signal generator 22 is selected, and the selected voltage command signals Vu ^* , Vv ^* , Vw ^* are generated as PWM signals. It outputs to the part 13 (refer FIG. 1). In other words, the first voltage command signal is selected in a region where the motor rotational speed is less than the rotational speed ω1, and the second voltage command signal is selected in a region where the motor rotational speed is the rotational speed ω1 or more.
The PWM signal generation unit 13 compares the input voltage command signals Vu ^* , Vv ^* , Vw ^* with the carrier wave to generate PWM signals Su, Sv, Sw corresponding to each phase, and supplies them to the inverter 2. Output.
When the second voltage command signal is selected and the amplitude of the reference voltage command signal is smaller than the first threshold, the second voltage command signal is switched to the first voltage command signal. Even in this case, since the inverter output voltage at the time of switching takes the same value, fluctuations in the line voltage can be reduced.

  As described above, according to the inverter control device 3 and the inverter device 1 according to the present embodiment, the amplitude of the sinusoidal reference voltage command signal used to generate the first voltage command signal is the reference voltage. When the first voltage command signal from the first signal generator 21 is selected and the amplitude of the reference voltage command signal is equal to the first threshold value when the maximum amplitude value of the command signal is less than the first threshold value The second voltage command signal from the second signal generator 22 is selected. In other words, a PMW signal is generated based on the first voltage command signal generated by the two-arm modulation method in a region where the rotational speed command value is lower than ω1, and overmodulation is performed in a region where the rotational speed command value is ω1 or more. A PWM signal is generated based on the second voltage command signal generated by the method. Here, the rotational speed command value ω1 is a maximum output voltage of a two-arm modulation type inverter (Vdc / √2 if the value of the voltage of the DC power supply 5 is Vdc), an induced voltage constant of the permanent magnet synchronous motor, and It is a value determined from the relationship.

  As a result, in the region where the inverter output voltage cannot be increased by the two-arm modulation method, the output increase in the high rotation speed region can be realized by performing the PWM control by the overmodulation method. In addition, in the rotational speed region where the efficiency decreases in the PWM control by the overmodulation method, the PWM control by the two-arm modulation method is selected, so that the efficiency reduction can be suppressed.

  Further, when the rotational speed is ω1, the line voltage by PWM control based on the two-arm modulation method and the line voltage by PWM control based on the overmodulation method in which the third-order harmonics are superimposed coincide. Therefore, it is possible to reduce the fluctuation of the line voltage when switching the control method, and to smoothly switch the control method.

  In FIG. 10, the second harmonic in which the third harmonic generated by the second signal generator 22 is superimposed from the PWM control based on the first voltage command signal of the two-arm modulation method generated by the first signal generator 21. A U-phase current when switched to PWM control based on a voltage command signal is shown. As shown in FIG. 10, it can be seen that the U-phase current is not distorted or fluctuated before and after switching, and switching is performed smoothly.

  FIG. 11 shows the U-phase current before and after the method switching when the reference voltage command signal that does not superimpose the third harmonic is used in the second signal generation unit 22. In the U-phase current shown in FIG. 11, it can be seen that the current waveform is distorted after switching. Thus, by using the second voltage command signal in which the third harmonic is superimposed on the sinusoidal reference voltage command signal, distortion and fluctuation of the U-phase current can be eliminated.

  In the present embodiment, the case where the control method is switched based on the amplitude of the sinusoidal reference voltage command signal used to generate the first voltage command signal has been described. The selection unit 23 may switch the control method by comparing the motor rotation speed or the motor rotation speed command with a preset rotation speed threshold value. In this case, the rotation speed threshold is set, for example, to the same value as the rotation speed ω1 or within a predetermined percentage range of the rotation speed ω1.

  In this embodiment, the case of switching between the 2-arm modulation method and the over-modulation method has been described. Further, a third voltage command unit that employs the 3-arm modulation method to generate a third voltage command signal is provided. It is good as well. In this case, the selection unit 23 selects the third voltage command signal in the start-up region (for example, the rotation speed region from 15 Hz to 20 Hz or less) where the rotation speed command value is set to a value smaller than ω1. Thus, the third voltage command signal based on the three-arm modulation method is used in the start-up region where the rotational speed is low, and the first voltage command signal based on the two-arm modulation method is used in the rotational speed region where the rotational speed is equal to or higher than the rotational speed. In the rotation speed region, the second voltage command signal by the overmodulation method is selected. Since the efficiency of the 3-arm modulation method is higher than that of the 2-arm modulation method in the region where the rotational speed is low, it is possible to realize further higher efficiency by adopting the configuration as described above.

  Further, even when PWM control based on the second voltage command signal by the second signal generator 22 is performed, if the output does not catch up and the motor rotation speed does not match the rotation speed command, the flux weakening control It is good also as controlling so that motor rotation speed may correspond to rotation speed command.

  In the present embodiment, the case where each phase current is detected from a direct current using one single shunt resistor has been described. However, the method for detecting each phase current is not limited to this method. For example, as shown in FIG. 12, shunt resistors 6a, 6b, and 6c that detect currents flowing through the switching elements 2d, 2e, and 2f of the lower arm included in the inverter 2 are provided, and the shunt resistors 6a, 6b, and 6c Each of the three-phase currents may be obtained based on the detected current value. Further, as shown in FIG. 13, current sensors 6d and 6e for detecting two phases of the respective phase currents output from the inverter 2 to the compressor motor 4 are provided, and based on current detection values by the current sensors 6d and 6e. Thus, the three-phase current may be obtained.

DESCRIPTION OF SYMBOLS 1 Inverter apparatus 2 Inverter 2a, 2b, 2c, 2d, 2e, 2f Switching element 3 Inverter control apparatus 4 Compressor motor 5 DC power supply 11 Phase current detection part 12 Voltage command calculating part 13 PWM signal generation part 21 1st signal generation part 22 Second signal generator 23 Selector

Claims (6)

An inverter control device that controls an inverter that converts a DC voltage from a DC power source into a three-phase AC voltage and outputs it to a motor,
A first signal generating means that adopts a two-arm modulation method and corrects a sinusoidal reference voltage command signal to generate a first voltage command signal;
Second signal generation for generating a second voltage command signal by an overmodulation method in which the maximum value of the amplitude of the waveform obtained by superimposing the third harmonic component on the sinusoidal reference voltage command signal is equal to or greater than the amplitude of the carrier wave. Means,
The first voltage command signal is selected when the amplitude of the reference voltage command signal of the first signal generating means is less than a first threshold value set to the maximum amplitude value of the reference voltage command signal, and the reference voltage command Selecting means for selecting the second voltage command signal when the amplitude of the signal is equal to the first threshold;
An inverter control device comprising PWM signal generation means for generating a pulse width modulation signal by comparing the voltage command signal selected by the selection means with a carrier wave. A third signal generating means for generating a third voltage command signal by a three-arm modulation method;
The inverter control device according to claim 1, wherein the selection unit selects the third voltage command signal in a startup region. Phase current detection means for detecting each phase current using a detected value of a DC current flowing through a DC bus between the DC power supply and the inverter and the pulse width modulation signal,
3. The inverter control device according to claim 1, wherein the phase current detection unit outputs a previous value as a phase current for a period in which the pulse width modulation signals of all three phases are turned on or off. Phase current detection means for detecting each phase current using a detected value of a DC current flowing through a DC bus between the DC power supply and the inverter and the pulse width modulation signal,
The phase current detection means has a predetermined current detection period in which the pulse width modulation signal of only one of the three phases is turned on or off is set according to the current detection capability of the phase current detection means The inverter control device according to claim 1, wherein the previous value is output as the phase current when the time is shorter than the time. An inverter that converts a DC voltage from a DC power source into a three-phase AC voltage and outputs it to the motor;
An inverter control device for controlling the inverter;
The inverter control device
A first signal generating means that adopts a two-arm modulation method and corrects a sinusoidal reference voltage command signal to generate a first voltage command signal;
Second signal generation for generating a second voltage command signal by an overmodulation method in which the maximum value of the amplitude of the waveform obtained by superimposing the third harmonic component on the sinusoidal reference voltage command signal is equal to or greater than the amplitude of the carrier wave. Means,
The first voltage command signal is selected when the amplitude of the reference voltage command signal of the first signal generating means is less than a first threshold value set to the maximum amplitude value of the reference voltage command signal, and the reference voltage command Selecting means for selecting the second voltage command signal when the amplitude of the signal is equal to the first threshold;
An inverter device comprising PWM signal generation means for generating a pulse width modulation signal by comparing the voltage command signal selected by the selection means with a carrier wave.   An air conditioner suitable for home use or business use and equipped with the inverter device according to claim 5.

Images