JP6501266B2 - Power converter and control method thereof - Google Patents

Description

  Embodiments of the present invention relate to a power converter and a control method thereof.

  There is a power conversion device provided with a voltage type converter that converts AC power to DC power, and an inverter that converts DC power to AC power of a desired frequency and voltage and supplies the AC power to a load such as a motor. Such a power converter is used, for example, in a rolling plant.

  In a rolling plant, the load current of a power converter for a rolling mill is large. Therefore, if control of the converter is continued when an unbalanced accident such as a short-circuit single-wire ground fault or a short-circuit two-wire short circuit occurs, the phase information of the power supply shifts, causing the converter to It may lead to current failure.

  On the other hand, when abnormality of the AC power supply for a short time occurs, if the control of the converter is stopped and the output of the motor which is the load of the inverter is simultaneously suppressed, the rolling mill stalls and the rolling can not be continued. In order to continue rolling, it is necessary to have a power conversion device with no restriction on the output of the inverter even when control of the converter is stopped for a short time.

  For example, in Patent Document 1, when the DC voltage output from the converter becomes equal to or less than the lower limit value, the switching element of the converter is gated off to switch to diode rectification. Then, when the converter is in a power running operation, the output power of the load motor is made zero so that the DC voltage does not drop. If the load on the motor is a rolling mill, a reduction in the output of the motor leads to a stall on the rolling mill. Therefore, the operation can not be continued.

  For this reason, in the power conversion device, it is desirable that the operation can be continued even when an unbalanced accident such as a short-circuit one-wire ground fault or a two-wire short circuit occurs.

Patent No. 3158212 specification

  An embodiment of the present invention provides a power conversion device capable of continuing operation even when an unbalanced accident such as a short one-wire ground fault or a two-wire short circuit occurs, and a control method thereof.

According to an embodiment of the present invention, there is provided a power conversion device comprising a first converter, a plurality of smoothing capacitors, a second converter, a voltmeter, and a control unit. The first converter includes a plurality of bridge-connected switching elements, a plurality of rectifying elements connected in anti-parallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals. And converting the first three-phase AC voltage input from the three AC terminals into a DC voltage having at least three levels of positive potential, negative potential and neutral point potential by switching the plurality of switching elements. And the DC voltage is output from the at least three DC terminals. The plurality of smoothing capacitors are provided between each of the at least three DC terminals. The second converter is connected to the at least three DC terminals and is connected to an AC load, and converts the DC voltage into a second three-phase AC voltage according to the AC load, and the second three-phase converter An alternating voltage is supplied to the alternating load. The voltmeter detects a voltage value of each phase of the first three-phase AC voltage. The control unit detects the phase of each phase of the first three-phase AC voltage based on the detection result of the voltmeter, and based on the detected phase, the line voltage of the first three-phase AC voltage The switching of the plurality of switching elements of the first converter is controlled by a fixed pulse pattern method in which the modulation factor of the DC voltage and the DC voltage is 1.2 or more and 1.5 or less, and the detected phase is used as a basis. The angular velocity of each phase of the first three-phase AC voltage is detected, and when the deviation between the detected angular velocity and the angular velocity reference value is equal to or greater than a predetermined value, the plurality of switching elements are turned off.

  A power converter and its control method are provided which can continue operation even when an unbalance accident such as a short one-wire ground fault or a two-wire short circuit occurs.

It is a block diagram showing the power converter concerning a 1st embodiment typically. It is a block diagram showing the converter concerning a 1st embodiment typically. It is a graph showing the example of the pulse pattern which concerns on 1st Embodiment. It is a flow chart which expresses operation of a power converter concerning a 1st embodiment typically. It is a block diagram showing the power converter concerning a 2nd embodiment typically. It is a flowchart which represents operation | movement of the power converter device which concerns on 2nd Embodiment typically.

Hereinafter, each embodiment will be described with reference to the drawings.
The drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio of sizes between parts, and the like are not necessarily the same as the actual ones. In addition, even in the case of representing the same portion, the dimensions and ratios may be different from one another depending on the drawings.
In the specification of the present application and the drawings, the same elements as those described above with reference to the drawings are denoted by the same reference numerals, and the detailed description will be appropriately omitted.

First Embodiment
FIG. 1 is a block diagram schematically illustrating the power conversion device according to the first embodiment.
As shown in FIG. 1, the power conversion device 10 includes a first converter 11, a second converter 12, a pair of smoothing capacitors 13 and 14, a control unit 15, a voltmeter 16, and an ammeter 17. And.

  The first converter 11 has three AC terminals 11r, 11s, 11t and at least three DC terminals 11p, 11n, 11c. Each of the AC terminals 11 r, 11 s, 11 t is connected to an AC power supply 2 via a transformer 4. AC power supply 2 is a three-phase AC power supply. Each of the AC terminals 11 r, 11 s, and 11 t is connected to each phase of the three-phase AC voltage of the AC power supply 2. Thereby, a three-phase alternating current voltage is input to the first converter 11 via the respective alternating current terminals 11r, 11s, and 11t. Transformer 4 may be provided in power conversion device 10 or may be provided separately from power conversion device 10.

  The first converter 11 converts the input three-phase AC voltage (first three-phase AC voltage) into a DC voltage having at least three levels of positive potential P, negative potential N and neutral point potential C. In this example, the case of converting a three-phase AC voltage into the above three levels will be described. Hereinafter, each of the DC terminals 11p, 11n, and 11c is referred to as a positive potential terminal 11p, a negative potential terminal 11n, and a neutral point terminal 11c, respectively. The first converter 11 may convert the three-phase AC voltage into a DC voltage having more levels without limiting to three levels. In this case, the number of DC terminals may be four or more.

  The first converter 11 sets the positive potential terminal 11 p to the positive potential P, sets the negative potential terminal 11 n to the negative potential N, and sets the neutral point terminal 11 c to the neutral point potential C. The neutral point potential C is an intermediate potential between the positive potential P and the negative potential N. Thereby, the first converter 11 generates a DC voltage Vd between each of the positive potential terminal 11p and the neutral point terminal 11c and between the neutral point terminal 11c and the negative potential terminal 11n. Therefore, the voltage between the positive potential terminal 11 p and the negative potential terminal 11 n is 2 Vd.

  The smoothing capacitor 13 is provided between the positive potential terminal 11 p and the neutral point terminal 11 c. The smoothing capacitor 13 is electrically connected between the positive potential terminal 11 p and the neutral point terminal 11 c. The smoothing capacitor 14 is provided between the neutral point terminal 11 c and the negative potential terminal 11 n. The smoothing capacitor 14 is electrically connected between the neutral point terminal 11 c and the negative potential terminal 11 n. The smoothing capacitors 13 and 14 smooth the DC voltage Vd. When the first converter 11 is provided with four or more DC terminals, a smoothing capacitor is provided between each of the DC terminals. A plurality of smoothing capacitors are provided according to the number of direct current terminals.

  The second converter 12 is connected to each of the DC terminals 11p, 11n, and 11c and to the induction motor 6. The induction motor 6 is a three-phase induction motor. The second converter 12 converts the DC voltage input from the first converter 11 into a three-phase AC voltage (second three-phase AC voltage) of a desired frequency and voltage value according to the induction motor 6, and Three-phase alternating voltage is supplied to the induction motor 6. Thereby, the second converter 12 drives the induction motor 6.

  Thus, the power conversion device 10 performs the power running operation of the induction motor 6. The first converter 11 is a three-level voltage source converter. The second converter 12 is a voltage type inverter. Further, power conversion device 10 converts the three-phase AC voltage generated by induction motor 6 into a three-phase AC voltage according to AC power supply 2, and supplies the converted three-phase AC voltage to the power system. That is, the power conversion device 10 can also perform the regenerative operation of the induction motor 6. In this case, the first converter 11 functions as an inverter, and the second converter 12 functions as a converter. The AC load to which the second converter 12 supplies the three-phase AC voltage is not limited to the induction motor 6, and may be another AC load. In addition to driving the induction motor 6, the power conversion device 10 also drives, for example, a synchronous motor.

  The voltmeter 16 detects the voltage value of each phase of the three-phase alternating current of the alternating current power supply 2. The voltmeter 16 inputs the detected voltage value of each phase to the control unit 15. The ammeter 17 detects the current value of each phase of the three-phase alternating current of the alternating current power supply 2. The ammeter 17 inputs the detected current value of each phase to the control unit 15.

  The control unit 15 controls the operation of the first converter 11 and the second converter 12 based on the detection results of the voltmeter 16 and the ammeter 17. The control unit 15 controls the conversion of the three-phase AC voltage to the DC voltage by the first converter 11. The control unit 15 controls the conversion from the DC voltage to the three-phase AC voltage by the second converter 12. The operation of the second converter 12 may be controlled by a control unit separate from the control unit 15.

FIG. 2 is a block diagram schematically showing the converter according to the first embodiment.
As shown in FIG. 2, the first converter 11 includes a plurality of bridge-connected switching elements 21 and a plurality of rectifying elements 22 connected to the respective switching elements 21 in antiparallel. In this example, the first converter 11 further includes a plurality of rectifying elements 23.

  The switching element 21 has a pair of main terminals and a control terminal. The control terminal is used to switch between an on state in which current flows between the respective main terminals and an off state in which no current substantially flows between the respective main terminals. For the switching element 21, for example, a self arc extinguishing element such as a gate turned off thyristor (GTO) or an insulated gate bipolar transistor (IGBT) is used. The control terminal is, for example, a gate terminal.

  The first converter 11 is a three-phase bridge type and has six arms AR, AS, AT, AX, AY, AZ. The configurations of the respective phase arms AR, AS, AT, AX, AY, AZ connected to the respective AC terminals 11r, 11s, 11t are substantially the same. Therefore, the two arms AR and AX connected to the AC terminal 11r (R phase) will be described here as an example.

  The positive side arm AR is a series of two switching elements SR1 and SR2 connected in series, rectifying elements DR1 and DR2 connected in anti-parallel to the switching elements SR1 and SR2, and a series of switching elements SR1 and SR2 And a rectifying element DR3 connected between the connection point and the neutral point terminal 11c.

  Similarly, the negative arm AX includes two switching elements SX1 and SX2 connected in series, rectifying elements DX1 and DX2 connected in anti-parallel to the switching elements SX1 and SX2, and switching elements SX1, A rectifying element DX3 connected between the series connection point of SX2 and the neutral point terminal 11c.

  Both arms AR and AX are connected in series between the positive potential terminal 11p and the negative potential terminal 11n, and the series connection point of both arms AR and AX is connected to the AC phase terminal 11r of R phase. The potential at the series connection point of the switching elements SR1 and SR2 is clamped to the neutral point potential C via the rectifying element DR3. Similarly, the potential at the series connection point of the switching elements SX1 and SX2 is clamped to the neutral point potential C via the rectifying element DX3. The rectifying elements DR1, DR2, DX1, DX2 (each rectifying element 22) are so-called reflux diodes. The rectifying elements DR3 and DX3 (each rectifying element 23) are so-called clamp diodes.

  The configuration of the arms AS, AT is substantially the same as the configuration of the arms AR. The configuration of arms AY and AZ is substantially the same as the configuration of arm AX. Thereby, according to switching of each switching element 21, the potentials of AC terminals 11r, 11s and 11t are clamped to any of three levels of potentials of positive potential terminal 11p, negative potential terminal 11n and neutral point terminal 11c. Be done.

  The configuration of the second converter 12 is substantially the same as the configuration of the first converter 11, so a detailed description will be omitted. In the second converter 12, the side connected to the smoothing capacitors 13 and 14 is the DC side (corresponding to the positive potential terminal 11p, the negative potential terminal 11n, and the neutral point terminal 11c), and the side connected to the induction motor 6 is the side It becomes an alternating current side (equivalent to alternating current terminals 11r, 11s, 11t). The control unit 15 controls the switching of each switching element of the second converter 12 to control the conversion from the DC voltage to the three-phase AC voltage by the second converter 12.

  The control unit 15 has a phase detector 30, an active / reactive current detector 32, and a gate control unit 34. The detection result of the voltmeter 16 is input to the phase detector 30. The phase detector 30 detects the phase of each phase of the three-phase AC voltage of the AC power supply 2 based on the detection result of the voltmeter 16.

  Further, the phase detector 30 detects the angular velocity of each phase of the three-phase AC voltage of the AC power supply 2 based on the amount of change per unit time of the detected phase. In other words, the phase detector 30 detects the frequency of each phase of the three-phase AC voltage of the AC power supply 2. The phase detector 30 inputs the detected phase information and angular velocity information of each phase to the gate control unit 34.

  The detection result of the voltmeter 16 and the detection result of the ammeter 17 are input to the active component / ineffective component current detector 32. Based on the detection results of the voltmeter 16 and the ammeter 17 inputted, the active component / reactive component current detector 32 detects the effective current Ip of the current supplied from the AC power supply 2 side to the first converter 11 and the invalid current. Calculate the current Iq. The active / ineffective current detector 32 inputs the calculated active current Ip and reactive current Iq to the gate control unit 34.

  The gate control unit 34 generates a control signal (for example, a gate signal) for controlling switching of each switching element 21 of the first converter 11 by a fixed pulse pattern method. The gate control unit 34 inputs the generated control signals to the control terminals of the switching elements 21. Thereby, the gate control unit 34 switches on / off of each switching element 21 and controls the operation of the first converter 11.

  The fixed pulse pattern method is a method of continuously generating the same pulse pattern every cycle. The fundamental frequency of the pulse pattern is synchronized with the frequency of the AC power supply 2. The gate control unit 34 synchronizes the fundamental frequency of the pulse pattern with the frequency of the AC power supply 2 based on the phase information detected by the phase detector 30. The fixed pulse pattern method is described in detail, for example, in Japanese Patent No. 3630621, Japanese Patent No. 4015795, and Japanese Patent No. 5411031.

  Further, the gate control unit 34 sets, for example, the deviation between the active current Ip and the reference current of the reactive current Iq to zero based on the active current Ip and the reactive current Iq detected by the active component / reactive component current detector 32. The amount of phase correction to be calculated is calculated. Then, the gate control unit 34 generates a pulse pattern in which the phase is shifted by the correction amount from the phase of the AC power supply 2. The phase of the pulse pattern may be determined only by the phase information of the phase detector 30.

FIG. 3 is a graph showing an example of a pulse pattern according to the first embodiment.
FIG. 3 shows an example of control signals GR1, GR2, GX1, GX2 input to the R-phase switching elements SR1, SR2, SX1, SX2 and a voltage waveform Vsr of the R-phase. As shown in FIG. 3, the waveform of the 1⁄4 cycle of the pulse pattern is symmetrical about 90 °. Also, the positive and negative pulses for the tri-level converter are vertically symmetrical. Furthermore, the pulse patterns of the three-phase respective phases are identical pulse patterns shifted by 120 ° from each other. Therefore, if a pulse pattern of 1⁄4 cycle is determined, all pulse patterns are determined. Although FIG. 3 illustrates the case of three pulses per AC power supply half cycle, the number of pulses may be arbitrary.

The gate control unit 34 sets the modulation factor of the line voltage of the AC power supply 2 and the positive or negative DC voltage Vd to 1.2 or more in the control of the fixed pulse pattern method. Assuming that the modulation factor is m and the line voltage of the AC power supply 2 is Va, the modulation factor m can be obtained by the following equation (1).
m = (√2 // 3) Va / Vd (1)
That is, the DC voltage Vd is made smaller than the line voltage Va. Thereby, the modulation factor m can be made 1.2 or more.

That is, the DC voltage Vd is made smaller than the value of the following equation (1A) with respect to the line voltage Va. Thereby, the modulation factor m can be made 1.2 or more.
Vd = (√2 // 3 / 1.2) Va (1A)

  The modulation factor m can be changed, for example, by adjusting the timing of the pulse P1 of FIG. When the timing of the pulse P1 is delayed, the central pulse width decreases and the modulation factor m decreases accordingly. On the contrary, when the timing of the pulse P1 is advanced, the central pulse width increases and the modulation factor m also increases. Thereby, the modulation factor m can be set arbitrarily. Further, the gate control unit 34 sets, for example, the modulation factor m to 1.5 or less.

  When the power control operation of the induction motor 6 is performed, the gate control unit 34 determines whether the deviation between the detected angular velocity and the angular velocity reference value is equal to or more than a predetermined value based on the angular velocity information input from the phase detector 30. Determine if The gate control unit 34 performs the above determination for each phase of the three-phase AC voltage. The angular velocity reference value is determined, for example, according to the frequency of the AC power supply 2. For example, when the frequency of the AC power supply 2 is 50 (Hz), the angular velocity reference value is 100π (rad / s). The gate control unit 34 determines, for example, ± 10% of the angular velocity reference value as a constant value. For example, when the frequency of the AC power supply 2 is 50 (Hz), the gate control unit 34 has a predetermined value or more when the deviation between the detected angular velocity and the angular velocity reference value is ± 10π (rad / s) or more. It is determined that

  When the gate control unit 34 determines that each phase is less than a predetermined value, switching of each switching element 21 of the first converter 11 is performed with the fixed pulse pattern method having a modulation factor of 1.2 or more as described above. Control.

  On the other hand, when the gate control unit 34 determines that at least one of the phases is equal to or more than a predetermined value, the gate control unit 34 turns off the switching elements 21 of the first converter 11. The gate control unit 34 generates a control signal to turn off each switching element 21 and inputs the control signal to the control terminal of each switching element 21 to turn off each switching element 21. As a result, the gate control unit 34 operates the first converter 11 as a diode converter with the rectifying elements 22.

  Thus, the gate control unit 34 operates the first converter 11 as a voltage source converter according to a fixed pulse pattern method with a modulation factor of 1.2 or more, and the diode operates the first converter 11 as a diode converter. And a rectification mode.

  The gate control unit 34 returns the operation of the first converter 11 from the diode rectification mode to the converter mode when determining that the deviation is equal to or more than a predetermined value and then returning to the state less than the predetermined value. That is, the gate control unit 34 resumes control of the plurality of switching elements 21 according to the fixed pulse pattern method when the deviation returns to a state less than a predetermined value after the plurality of switching elements 21 are turned off.

FIG. 4 is a flowchart schematically illustrating the operation of the power conversion device according to the first embodiment.
FIG. 4 schematically shows the operation of the induction motor 6 in the power running mode.
As shown in FIG. 4, in the power conversion device 10, when performing the powering operation of the induction motor 6, the gate control unit 34 of the control unit 15 uses the fixed pulse pattern method of the modulation factor of 1.2 or more as the first converter The switching of each of the 11 switching elements 21 is controlled to operate the first converter 11 in the converter mode. Thereby, the gate control unit 34 converts the three-phase AC voltage of the AC power supply 2 into a DC voltage. The control unit 15 also controls the operation of the second converter 12 and converts the DC voltage output from the first converter 11 into a three-phase AC voltage corresponding to the induction motor 6. The second converter 12 supplies the converted three-phase AC voltage to the induction motor 6. Thus, the induction motor 6 is driven in power.

  The gate control unit 34 controls the operation of the first converter 11 when the induction motor 6 is in a power running operation, and the deviation between the detected angular velocity and the angular velocity reference value for each phase of the three-phase AC voltage is It is determined whether or not it is a fixed value or more.

  When it is determined that each of the phases is less than the predetermined value, the gate control unit 34 continues the operation of the first converter 11 in the converter mode.

  On the other hand, when the gate control unit 34 determines that at least one of the phases is equal to or larger than a predetermined value, the gate control unit 34 turns off the switching elements 21 and switches the operation of the first converter 11 from the converter mode to the diode rectification mode. .

  If it is determined that the deviation between the detected angular velocity and the angular velocity reference value is greater than or equal to a predetermined value in one or two phases of the three-phase AC voltage of AC power supply 2, an imbalance accident occurs in AC power supply 2 it seems to do. If an unbalance accident occurs in the AC power supply 2, a phase shift may occur in phase detection in the phase detector 30. For this reason, if the first converter 11 continues to operate in the converter mode at the time of unbalance accident, the first converter 11 or the second converter 12 may fail due to a DC overcurrent or the like in some cases.

  The modulation factor m when the first converter 11 is operated in the diode rectification mode is, for example, about 1.21. Therefore, when the difference between the modulation factor m in the converter mode and the modulation factor m in the diode rectification mode is large, the DC voltage becomes excessively large when the first converter 11 is switched to the diode rectification mode. Or become smaller.

  For example, when the modulation factor m in the converter mode is smaller than 1.2, when the first converter 11 is switched to the diode rectification mode, the DC voltage Vd becomes smaller, and the power running operation of the induction motor 6 can be continued. It will not be possible. For example, when the first converter 11 is operated by PWM control, it is considered that the modulation factor m becomes maximum at the time of so-called two-phase modulation in which one of the three phases is kept on for 120 °. The modulation factor m at this time is 1.15, which is smaller than 1.2.

  On the other hand, if the modulation factor m in the converter mode is larger than 1.5, the DC voltage Vd becomes large when the first converter 11 is switched to the diode rectification mode, and the first converter 11 or the second converter 12 failures are a concern.

  In the power conversion device 10 according to the present embodiment, in the converter mode, the first converter 11 is operated by the fixed pulse pattern method having a modulation factor of 1.2 or more. Thereby, it is possible to suppress the fluctuation of the DC voltage Vd when the first converter 11 is switched to the diode rectification mode. Therefore, in the power conversion device 10, the power running operation of the induction motor 6 can be continued by switching the first converter 11 to the diode rectification mode even when an imbalance accident for a short time occurs.

  Further, in the power conversion device 10 according to the present embodiment, the modulation factor m in the converter mode is set to 1.5 or less. Thereby, it is possible to more appropriately suppress the fluctuation of the DC voltage Vd when the first converter 11 is switched to the diode rectification mode. When the DC voltage Vd in the converter mode is made larger than the DC voltage Vd in the diode rectification mode, the modulation factor m is, for example, 1.2 or more and less than 1.35.

  After switching the first converter 11 to the diode rectification mode, the gate control unit 34 determines whether or not the deviation between the detected angular velocity and the angular velocity reference value has returned to a state less than a predetermined value. The gate control unit 34 returns the operation of the first converter 11 from the diode rectification mode to the converter mode when it is opposed to returning to the state less than the predetermined value.

  Further, after switching the first converter 11 to the diode rectification mode, the control unit 15 determines whether or not a predetermined time has elapsed from the timing of switching to the diode rectification mode. If the imbalance accident continues for a predetermined time or more, it is considered that an abnormality occurs in the AC power supply 2. Therefore, when the control unit 15 determines that the predetermined time has elapsed, that is, when the deviation is a predetermined value or more continues for a predetermined time, the operation of the second converter 12 is stopped, and the power running operation of the induction motor 6 is performed. Stop. Thereby, for example, the power conversion device 10, the induction motor 6, and the like can be protected from the abnormality of the AC power supply 2.

Second Embodiment
FIG. 5 is a block diagram schematically showing the power conversion device according to the second embodiment.
As shown in FIG. 5, the control unit 15 of the power conversion device 110 further includes a voltage detector 36. The same reference numerals are given to components substantially the same in function and configuration as the first embodiment, and the detailed description will be omitted.

  The detection result of the voltmeter 16 is input to the voltage detector 36. The voltage detector 36 detects, based on the detection result of the voltmeter 16, the decrease of the three-phase AC voltage of the AC power supply 2 by a predetermined value or more. The voltage detected by the voltage detector 36 may be a phase voltage of each phase of the three-phase AC voltage, or may be a line voltage of each phase of the three-phase AC voltage. The threshold value of the voltage is, for example, 20% to 30% of the rated voltage of the three-phase AC voltage of the AC power supply 2. The voltage detector 36 detects, for example, a decrease equal to or more than a predetermined value when any of the three-phase AC voltages of the AC power supply 2 becomes 20% or less of the rated voltage. The voltage detector 36 inputs a voltage drop detection signal indicating detection of a voltage drop to the gate control unit 34 when the voltage detector 36 detects a drop of the three-phase AC voltage by a predetermined value or more.

FIG. 6 is a flowchart schematically illustrating the operation of the power conversion device according to the second embodiment.
As shown in FIG. 6, the gate control unit 34 operates the first converter 11 in the converter mode, and a voltage drop is detected by the voltage detector 36 in a state where the induction motor 6 is in a power running operation. In this case, each switching element 21 is turned off, and the first converter 11 is switched from the converter mode to the diode rectification mode. That is, in this example, the gate control unit 34 determines that an unbalance accident has occurred in the alternating current power supply 2 when any of the phases of the three-phase alternating current voltage of the alternating current power supply 2 lowers by a predetermined value or more.

  The gate control unit 34 operates the first converter 11 in the diode rectification mode when the voltage detector 36 detects a drop in the three-phase AC voltage and then returns to a state in which the three-phase AC voltage is larger than a predetermined value. Return to converter mode from. That is, when the three-phase AC voltage of AC power supply 2 is restored to a state larger than a predetermined value after the plurality of switching elements 21 are turned off, gate control unit 34 switches the plurality of switching elements according to the fixed pulse pattern method. Resume control of 21. Further, when a predetermined time has elapsed since the switching to the diode rectification mode, the control unit 15 stops the operation of the second converter 12 and stops the power running operation of the induction motor 6.

  Depending on the condition of the unbalance accident of the AC power supply 2, the voltage detector 36 may detect an abnormality prior to the detection of the abnormality by the phase detector 30. Therefore, in the power conversion device 110 according to the present embodiment, the first converter 11 is switched from the converter mode to the diode rectification mode when a voltage drop is detected during powering operation. Thereby, for example, the unbalance accident of AC power supply 2 can be detected more appropriately. For example, it is possible to more appropriately suppress the failure of the first converter 11 or the second converter 12 due to the unbalance accident of the AC power supply 2.

  Thus, in this example, during powering operation of induction motor 6, at least one of the angular velocity based on the detection result of phase detector 30 and the voltage based on the detection result of voltage detector 36 Detect a balancing accident. The detection of the unbalance accident of the AC power supply 2 may be performed with only the angular velocity as shown in the first embodiment, or may be performed with only the voltage as shown in FIG.

  Although the modulation factor is 1.2 or more in the above description, if there is a margin in the current rating of the first converter 11, the necessary amount of power can be increased by increasing the current against the drop of the DC voltage Vd. It is possible to supply the second converter 12. That is, even when the modulation factor is less than 1.2, the current rating of the first converter 11 has a margin that is the inverse of the degree of decrease in the DC voltage Vd when the first converter 11 enters the diode rectification mode For example, implementation of the present invention is possible.

  While certain embodiments of the present invention have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and the gist of the invention, and are included in the invention described in the claims and the equivalent scope thereof.

  DESCRIPTION OF SYMBOLS 2 ... AC power supply, 4 ... Transformer, 6 ... Induction motor, 10, 110 ... Power converter, 11 ... 1st converter, 12 ... 2nd converter, 13, 14 ... Smoothing capacitor, 15 ... Control unit, 16 ... Voltmeter 17 17 Ammeter 21 Switching element 22 Rectifying element 23 Rectifying element 30 Phase detector 32 Active current / reactive current detector 34 Gate control section 36 Voltage Detector

Claims (7)

A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in anti-parallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals; The first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of positive potential, negative potential and neutral point potential by switching of the switching element, and the DC voltage is converted to the DC voltage A first converter outputting from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
It is connected to the at least three DC terminals and connected to an AC load, converts the DC voltage to a second three-phase AC voltage according to the AC load, and converts the second three-phase AC voltage to the AC load. Supplying a second converter,
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
The phase of each phase of the first three-phase AC voltage is detected based on the detection result of the voltmeter, and the inter-line voltage of the first three-phase AC voltage and the DC voltage are detected based on the detected phase. Controlling the switching of the plurality of switching elements of the first converter by a fixed pulse pattern method in which the modulation factor of the first converter is 1.2 or more and 1.5 or less, and based on the detected phase, A control unit that detects angular velocity of each phase of three-phase alternating current voltage, and turns off the plurality of switching elements when a deviation between the detected angular velocity and an angular velocity reference value is equal to or greater than a predetermined value;
Power converter equipped with.   The control unit resumes control of the plurality of switching elements by the fixed pulse pattern method when the deviation returns to a state less than the predetermined value after the plurality of switching elements are turned off. The power converter according to 1.   The power conversion device according to claim 1 or 2, wherein the control unit turns off the plurality of switching elements when the first three-phase AC voltage detected by the voltmeter decreases by a predetermined value or more.   When the control unit returns to a state where the first three-phase AC voltage is larger than the predetermined value after the plurality of switching elements are turned off, the control unit is configured to use the plurality of switching elements according to the fixed pulse pattern method. The power converter according to claim 3, wherein control is resumed. A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in anti-parallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals; The first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of positive potential, negative potential and neutral point potential by switching of the switching element, and the DC voltage is converted to the DC voltage A first converter outputting from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
It is connected to the at least three DC terminals and connected to an AC load, converts the DC voltage to a second three-phase AC voltage according to the AC load, and converts the second three-phase AC voltage to the AC load. Supplying a second converter,
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
The phase of each phase of the first three-phase AC voltage is detected based on the detection result of the voltmeter, and the inter-line voltage of the first three-phase AC voltage and the DC voltage are detected based on the detected phase. Controlling the switching of the plurality of switching elements of the first converter by the fixed pulse pattern method in which the modulation factor of the first converter is 1.2 or more and 1.5 or less, and the first three phases detected by A control unit that turns off the plurality of switching elements when the AC voltage decreases by a predetermined value or more;
Power converter equipped with. A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in anti-parallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals; The first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of positive potential, negative potential and neutral point potential by switching of the switching element, and the DC voltage is converted to the DC voltage A first converter outputting from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
It is connected to the at least three DC terminals and connected to an AC load, converts the DC voltage to a second three-phase AC voltage according to the AC load, and converts the second three-phase AC voltage to the AC load. Supplying a second converter,
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
And a control method of a power converter including:
Detecting the phase of each phase of the first three-phase AC voltage based on the detection result of the voltmeter;
The first converter according to the fixed pulse pattern method in which the modulation ratio between the line voltage of the first three-phase AC voltage and the DC voltage is 1.2 or more and 1.5 or less based on the detected phase. Controlling switching of the plurality of switching elements of
Detecting an angular velocity of each phase of the first three-phase AC voltage based on the detected phase;
Turning the plurality of switching elements off when the deviation between the detected angular velocity and the angular velocity reference value is equal to or greater than a predetermined value;
And controlling the power converter. A plurality of bridge-connected switching elements, a plurality of rectifying elements connected in anti-parallel to each of the plurality of switching elements, three AC terminals, and at least three DC terminals; The first three-phase AC voltage input from the three AC terminals is converted into a DC voltage having at least three levels of positive potential, negative potential and neutral point potential by switching of the switching element, and the DC voltage is converted to the DC voltage A first converter outputting from at least three DC terminals;
A plurality of smoothing capacitors provided between each of the at least three DC terminals;
It is connected to the at least three DC terminals and connected to an AC load, converts the DC voltage to a second three-phase AC voltage according to the AC load, and converts the second three-phase AC voltage to the AC load. Supplying a second converter,
A voltmeter for detecting a voltage value of each phase of the first three-phase AC voltage;
And a control method of a power converter including:
Detecting the phase of each phase of the first three-phase AC voltage based on the detection result of the voltmeter;
The first converter according to the fixed pulse pattern method in which the modulation ratio between the line voltage of the first three-phase AC voltage and the DC voltage is 1.2 to 1.5 based on the detected phase. Controlling switching of the plurality of switching elements of
Turning the plurality of switching elements off when the first three-phase alternating voltage detected by the voltmeter decreases by a predetermined value or more;
And controlling the power converter.

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