JP5506619B2 - Inverter device and control method - Google Patents

Description

  The present invention relates to an inverter device and a control method thereof.

  An inverter device that drives a three-phase induction motor or a synchronous motor with a variable voltage and variable frequency outputs a three-phase AC voltage having an arbitrary frequency to control the motor. Three-phase AC voltage is pulse width modulated (hereinafter referred to as PWM) by switching the internal DC voltage in the inverter device based on the carrier frequency and the internal phase of the three-phase internal semiconductor element based on the output frequency and output voltage command values. And obtained as a pseudo three-phase AC voltage.

  At that time, the operation of the microcomputer that performs the switching control requires a long operation time corresponding to the number of times of switching, and the built-in semiconductor element generates heat due to loss due to the number of times of switching. In order to suppress the calculation time and heat generation, a control method has been devised that can reduce the number of switching to 2/3 by resting one-phase switching among three-phase built-in semiconductor elements.

FIG. 7 shows a configuration of a main circuit portion of a general inverter device.
The inverter device has switching elements for output for three phases (hereinafter referred to as U phase, V phase, and W phase, respectively). Hereafter, it is set as 100, 101, 102, 103, 104, 105, respectively. In the inverter device, a DC voltage is stored in the electrolytic capacitor 108 from the AC power source 106 through the forward conversion unit 107. Alternatively, a DC voltage is stored in the electrolytic capacitor 108 from the DC power source 109.

  By controlling the switching elements 100, 101, 102, 103, 104, and 105 with the DC voltage, a three-phase AC voltage having an arbitrary frequency is output. At this time, the inverter device obtains the output AC voltage by the PWM method (pulse width modulation method).

  In an inverter device that controls a three-phase induction motor, the output voltage and the output frequency are proportional to each other or have a relationship proportional to a certain constant. It is generally called variable frequency variable voltage (VVVF) control, and when the output frequency is low, the output voltage is generally low, and when the output frequency is high, the output voltage is generally high. The inverter device controls the output line voltage to be a sine wave. In the conventional three-phase switching method, when the output voltage and the output frequency are increased, the utilization rate of the DC voltage stored in the electrolytic capacitor 108 is deteriorated. Therefore, switching to two-phase switching can be performed when the frequency is increased to some extent. [Patent Document 1]. Also, by switching to two-phase switching, the switching elements 100, 101, 102, 103, 104, and 105 each have a switching frequency of 2/3, and heat generation can be suppressed.

  However, when switching between two-phase switching and three-phase switching during operation of the inverter device, the output current of the inverter device pulsates during the switching. As a result, problems such as failure of the inverter device and pulsation of torque of the three-phase induction motor connected to the inverter device may occur.

  Figure 1 shows the waveform of each output phase voltage during three-phase switching. FIG. 2 shows an example of each output phase voltage waveform after transition to two-phase switching. Comparing FIG. 1 and FIG. 2, it can be seen that during two-phase switching, one phase that is not performing switching is continuously on or off for 60 degrees. This continuous on / off period is determined by alternately switching on the switching elements 100, 101, 102, 103, 104, and 105, so that it is determined to be 60 ° in six 360 ° divisions. For this reason, when the phase voltage waveform as an output has a low frequency, the wavelength of 60 ° becomes longer, so that the continuous on and off times are inevitably longer.

  If the output frequency of the inverter device reaches a certain arbitrary frequency and transitions from the waveform shown in Fig. 1 to Fig. 2, one phase that is not switching can reduce the loss caused by switching. In addition, the heat generation of the inverter device can be suppressed. However, when the switching frequency from FIG. 1 to FIG. 2 is low, the output current of the inverter device changes rapidly from a short on-time at three-phase switching to a long continuous on-time at two-phase switching. May grow momentarily.

  FIG. 11 is a block diagram of switching between two-phase switching and three-phase switching in a conventional inverter device, and FIG. 9 is a conceptual diagram thereof. Two-phase switching and three-phase switching are selected according to a switching point determined by either or both of the output voltage command and the output frequency command, and a phase voltage output is generated. In addition, this switching point may have hysteresis. As a result, as shown in FIG. 9, the two-phase switching and the three-phase switching are rapidly switched.

JP-A-8-289588

In an inverter device for driving a three-phase induction motor, a control method for resting one-phase switching among the three phases is introduced in (Patent Document 1). However, when the control method shifts from the control for switching all three phases to the control for two-phase switching in which one-phase switching is stopped, the output current of the inverter device may pulsate and an excessive current may flow. This current may fluctuate the output torque of the three-phase induction motor, operate the overcurrent protection function of the inverter device, stop the inverter device, or cause a failure of the inverter device. This invention makes it a subject to suppress the pulsation of the said electric current from said reason.

  In performing the control as disclosed in Patent Document 1, a transition period is provided at the time of switching from two-phase switching to three-phase switching, or from three-phase switching to two-phase switching, and gradually from two-phase switching to two-phase switching time This is achieved by extending the switching time, or gradually shortening the switching time in two phases from switching in two phases and switching to switching in three phases.

  According to the present invention, the transition from switching in three phases to switching in two phases, or the transition from switching in two phases to switching in three phases is smooth, and the pulsation of the output current generated during the transition Can be suppressed.

Phase voltage waveform during three-phase switching Phase voltage waveform during two-phase switching Phase voltage waveform during transition between two-phase switching and three-phase switching according to the present invention Phase voltage waveform during transition between two-phase switching and three-phase switching according to the present invention Phase voltage waveform during transition between two-phase switching and three-phase switching according to the present invention Phase voltage waveform during transition between two-phase switching and three-phase switching according to the present invention Hardware configuration diagram of the inverter device Phase voltage command generation block diagram in the inverter device of the present invention Conceptual diagram of switching between two-phase and three-phase switching in conventional inverter devices Conceptual diagram of switching between two-phase and three-phase switching in the inverter device of the present invention Phase voltage command generation block diagram in a conventional inverter device

  Embodiments will be described below with reference to the drawings.

  FIG. 8 is a block diagram of switching between two-phase switching and three-phase switching in the inverter device of the present invention, and FIG. 10 is a conceptual diagram thereof. The addition of the three-phase / two-phase transition transient process 203 as shown in FIG. 8 provides a transition period during the transition from the two-phase switching to the three-phase switching as shown in FIG. As a result, the pulsation of the output current of the inverter device can be suppressed.

  FIG. 3 is an example of a waveform of a transition period inserted during the transition from FIG. 1 to FIG. 2 according to the present invention. The time during which the switch is continuously turned on is only 5 degrees at the beginning and the end of the 60 ° period in which the two-phase switching is performed in FIG. 2, and the other 50 ° is to perform the three-phase switching. For example, when the output frequency of the inverter device is between 0 Hz and 10 Hz, the three-phase switching shown in FIG. 1 is used, and this waveform is applied between 10 Hz and 20 Hz.

  FIG. 4 shows the waveform of the transition period after the transition of FIG. In FIG. 3, it is 5 °, but in FIG. 4, it is assumed to be continuously turned on for a period of 10 °. Therefore, the remaining 40 ° is three-phase switching. For example, this waveform is applied when the output frequency of the inverter device is 20 Hz to 30 Hz, and when it exceeds 30 Hz, the output voltage waveform of FIG. 2 is obtained.

  For this reason, since the continuous ON time can be shorter than the two-phase switching in the whole period, the rapid growth of the output current can be suppressed. In this embodiment, two transition periods are added. However, even if an arbitrary number of stages is added, the intention of the present invention does not change.

  In the present embodiment, as an operation of the three-phase / two-phase transition transient process 203 in FIG. 8, an example will be described in which transition is made to two-phase switching continuously instead of stepwise transition to two-phase switching. When the phase voltage waveform transitions from Fig. 1 to Fig. 2, the continuous on-time t2 at the time of transition to Fig. 2 is fixed, and the total of the continuous on-time t3 and t4 in Fig. 3 and Fig. 4 is always t2. The intent of the present invention is achieved even when controlled to be equal.

  In the present embodiment, as the operation of the three-phase / two-phase transition transient process 203 in FIG. 8, in the phase voltage waveform in the transition period between the three-phase switching and the two-phase switching, the period for performing the two-phase switching is 60 ° two-phase switching. An example of providing in the center of the period will be described. The hardware of the inverter device is shown in FIG.

  FIG. 5 is an example of a waveform of a transition period inserted during the transition from FIG. 1 to FIG. 2 according to the present invention. The continuous ON period is the center of the 60 ° period for two-phase switching in FIG. 2, for example, 30 °. The other 30 ° performs three-phase switching. For example, this waveform is applied when the output frequency of the inverter device is 10 Hz to 20 Hz.

  FIG. 6 shows the waveform of the transition period that transitions next to FIG. In FIG. 5, it is 30 °, but in FIG. 6, it is assumed to be continuously turned on for a period of 50 °. Therefore, the remaining 10 ° is three-phase switching. For example, this waveform is applied when the output frequency of the inverter device is 20 Hz to 30 Hz, and when it exceeds 30 Hz, the output voltage waveform of FIG. 2 is obtained.

  In the present embodiment, as an operation of the three-phase / two-phase transition transient process 203 in FIG. 8, an example will be described in which transition is made to two-phase switching continuously instead of stepwise transition to two-phase switching.

  When the phase voltage waveform transitions from Fig. 1 to Fig. 2, the continuous on-time t2 at the time of transition to Fig. 2 is fixed, and the continuous on-time t5 in Figs. 5 and 6 is always equal to t2. The purpose of the present invention can be achieved even when the control is performed.

  In addition, this invention is not a thing limited to an above-described Example, Various modifications are included. For example, the above-described embodiments have been described in detail for easy understanding of the present invention, and are not necessarily limited to those having all the configurations described. Further, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

  Further, the control lines and information lines indicate objects that are considered necessary for the explanation, and do not necessarily indicate all control lines and information lines on the product.

100 Switching element QU (U phase upper side)
101 Switching element QV (V phase upper side)
102 Switching element QW (W phase upper side)
103 Switching element QX (U phase lower side)
104 Switching element QY (V phase lower side)
105 Switching element QZ (W phase lower side)
106 Three-phase AC power supply
107 Forward conversion part
108 Smoothing capacitor
109 DC power supply
200 Inverter device
201 Three-phase PWM generation processing block
202 Two-phase PWM generation processing block
203 Three-phase ⇔ Two-phase transition transient processing block
204 Switching judgment processing block
205 PWM output switching block
206 Carrier generation block
207 PWM output generation block

Claims (7)

In the inverter device having a forward conversion unit for converting the input AC voltage into DC, and a plurality of switching elements for converting the DC voltage into an AC voltage of an arbitrary frequency by PWM control by two-phase switching and three-phase switching, When switching between two-phase switching and three-phase switching, a transition period in which two-phase switching and three-phase switching are mixed is provided. In the transition period, a voltage command generated by a transient processing unit between three-phase switching and two-phase switching is provided. An inverter device characterized by the output of 2. The inverter device according to claim 1, wherein the transient processing unit provides a two-phase switching range at the beginning and the end in a range of 60 ° centered on a peak of a phase voltage waveform of each phase, and an output frequency An inverter device characterized by changing the two-phase switching period step by step according to the command. 2. The inverter device according to claim 1, wherein in the transient processing unit, a two-phase switching period is provided at the beginning and end in a range of 60 ° centered on a peak of a phase voltage waveform of each phase, An inverter device characterized in that the time for two-phase switching is fixed and the output frequency is changed to continuously change to two-phase switching. 2. The method for controlling an inverter device according to claim 1, wherein the transient processing section provides a two-phase switching range at the beginning and end of the range of 60 ° centered on the peak of the phase voltage waveform of each phase. The control method is characterized by changing the two-phase switching period step by step according to the output frequency command. 2. The method of controlling an inverter device according to claim 1, wherein the transient processing section is provided with a two-phase switching period at the beginning and at the end in a range of 60 [deg.] Around the peak of the phase voltage waveform of each phase. The control method is characterized in that the time for the two-phase switching is fixed and the output frequency is changed to continuously change to the two-phase switching. The method for controlling an inverter device according to claim 1, wherein the transient processing unit performs two-phase switching in a range of 60 ° centered on a peak of a phase voltage waveform of each phase in a constant period of the center. A control method characterized by performing the two-phase switching period step by step. The method for controlling an inverter device according to claim 1, wherein the transient processing unit performs two-phase switching in a range of 60 ° centered on a peak of a phase voltage waveform of each phase in a constant period of the center. The control method is characterized in that it is continuously changed to two-phase switching by fixing the time and changing the output frequency.

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