JP5153382B2 - Power regeneration converter - Google Patents

Description

  The present invention relates to a power regeneration converter, and more particularly to a power regeneration converter having a current protection function for protecting a switching circuit when an abnormal overcurrent occurs.

  The power regenerative converter is disposed between a three-phase AC power source and an inverter device for variable speed control of a three-phase induction motor that is a three-phase load, and accumulates the induced electromotive force generated when the three-phase induction motor is decelerated. A switching circuit that switches the terminal voltage of the smoothing capacitor on the inverter device side and regenerates the three-phase AC power supply is provided (for example, see Patent Document 1).

  In the conventional power regeneration converter, the amount of current flowing in the switching circuit increases in proportion to the amount of regenerative power. Therefore, in order to protect the switching circuit from an abnormal overcurrent, the switching circuit is switched to the three-phase AC power supply side. A current protection function is provided that monitors the value of the flowing current and simultaneously turns off all the switching elements constituting the switching circuit when an abnormal overcurrent exceeding the protection level flows.

JP 2004-180427 A

  However, in the switching circuit, a surge voltage is generated as the plurality of switching elements are turned on / off, and therefore a snubber capacitor that absorbs the surge voltage is provided between the positive and negative buses of the switching circuit. Therefore, the conventional current protection function as described above that simultaneously turns off all switching elements when an abnormal overcurrent occurs has the following problems.

That is, when all the switching elements are turned off simultaneously, the current in the switching circuit flows into the snubber capacitor. Assuming that the flowing current is I, the parasitic inductance in the switching circuit is L, and the capacitance value of the snubber capacitor is C, the terminal voltage V of the snubber capacitor is (1/2) LI ² = CV ² , It rises as the current I flowing in increases.

  Then, since the terminal voltage V is applied to each switching element of the upper arm and the lower arm connected in series between the positive and negative buses of the switching circuit, the terminal voltage V exceeds the rated voltage of the switching element. In this case, the switching element may be damaged.

  For this reason, conventionally, it is necessary to increase the capacitance value of the snubber capacitor to suppress the voltage rise. As a result, there is a problem that the size of the snubber capacitor is increased and the cost is increased.

  The present invention has been made in view of the above, and it is possible to realize switching circuit protection in the event of an abnormal overcurrent in a form that enables the snubber capacitor to be reduced by suppressing the increase in the terminal voltage of the snubber capacitor. The object is to obtain a power regeneration converter with a new current protection function.

  In order to achieve the above-mentioned object, a power regeneration converter according to the present invention includes a switching circuit that switches excess power generated on a three-phase load side to regenerate to a three-phase power system, the three-phase power system, and the switching A current detector that detects the magnitude and direction of each phase current flowing between the circuits, and a current value detected by the current detector is greater than or equal to a predetermined value; a plurality of switching elements that constitute the switching circuit; A control unit that outputs an instruction to turn off the switching circuit by providing a predetermined time difference in order from the switching element corresponding to the phase having the smaller current value among the phase currents detected by the current detector. It is characterized by having.

  According to the present invention, when an abnormal overcurrent occurs, not all switching elements in the switching circuit are turned off at the same time, but are turned off with a time difference in order from a certain switching element. The effect is that a power regeneration converter with a new current protection function can be obtained, which can realize switching circuit protection during current generation by suppressing the increase in the snubber capacitor terminal voltage and reducing the snubber capacitor capacity. Play.

  Exemplary embodiments of a power regeneration converter according to the present invention will be explained below in detail with reference to the drawings.

Embodiment 1 FIG.
FIG. 1 is a block diagram showing a main configuration of a power regeneration converter according to Embodiment 1 of the present invention. As shown in FIG. 1, a power regenerative converter 1a according to Embodiment 1 includes a three-phase AC power source 2 and an inverter device 4 for variable speed control of a three-phase induction motor (hereinafter referred to as “motor”) 3 that is a three-phase load. Between.

  The power regeneration converter 1a includes AC power terminals 11, 12, and 13. The AC power supply terminals 11, 12 and 13 are connected to the respective power supply terminals of the three-phase AC power supply 2. Further, the power regeneration converter 1 includes DC power supply terminals 14 and 15. The DC power supply terminals 14 and 15 are connected to a positive bus and a negative bus (not shown) in the inverter device 4.

  A smoothing capacitor for accumulating induced electromotive force generated during the deceleration operation of the motor 3 is connected between a positive electrode bus and a negative electrode bus (not shown) in the inverter device 4.

  In the power regeneration converter 1, a switching circuit 18 and a snubber capacitor 19 are connected in parallel between the positive bus 16 and the negative bus 17 connected to the DC power terminals 14 and 15.

  The snubber capacitor 19 is a high-frequency compatible film capacitor.

  In the switching circuit 18, three pairs of regenerative transistors TR 1 and TR 2, regenerative transistors TR 3 and TR 4, and regenerative transistors TR 5 and TR 6, which are switching elements connected in series, are connected in parallel between the positive electrode bus 16 and the negative electrode bus 17. It is a configuration. Each of the six regeneration transistors TR1 to TR6 is, for example, an IGBT. Note that diodes D1 to D6 are connected to these regenerative transistors in antiparallel.

  The series connection ends of the upper arm side regeneration transistors TR1, TR3, TR5 connected to the positive bus 16 and the lower arm side regeneration transistors TR2, TR4, TR6 connected to the negative bus 17 are the regeneration output ends. Are connected to AC power supply terminals 11, 12, 13 respectively.

  The current detectors 20, 21, and 22 are disposed on the connection lines between the three regenerative output terminals of the switching circuit 18 and the AC power supply terminals 11, 12, and 13, respectively. Is detected.

  During the regenerative operation, the control unit 23 detects each phase (R) of the three-phase AC power source 2 detected by a phase detector (not shown) while the current value detected by the current detectors 20, 21, 22 is below the protection level. On / off operation timings of the six regenerative transistors TR1 to TR6 are determined based on the phase relationship of the phase, the S phase, and the T phase. The control unit 23 outputs the determined on / off operation timings of the six regenerative transistors TR1 to TR6 to the drive circuit 24 as a first control signal instructing the regenerative operation control.

  In response to the first control signal, the drive circuit 24 generates gate signals (see FIG. 2) that individually turn on and turn off the six regeneration transistors TR1 to TR6 for a predetermined period. Each is applied to the gate terminal of the regenerative transistor.

  In addition, when the current value detected by the current detectors 20, 21, 22 exceeds the protection level during the regenerative operation, the control unit 23 detects the current of each phase detected by the current detectors 20, 21, 22 By examining the value and the direction in which the current flows, a regenerative transistor in which the current is actually flowing in the phase in which the current value is low and in the direction detected by the current detectors 20, 21, and 22 is determined in order. The timing for performing the OFF operation is determined with a time difference of (see FIGS. 3 and 4). The control unit 23 outputs the determined timing for turning off the six regenerative transistors TR1 to TR6 to the drive circuit 24 as a second control signal for instructing current protection operation control.

  Upon receiving the second control signal, the drive circuit 24 generates a gate signal that maintains the state by turning off the six regeneration transistors TR1 to TR6 at a designated timing in a designated order. Application is sequentially made to the gate terminal of the transistor.

  Hereinafter, the operation will be described with reference to FIGS. FIG. 2 is a time chart for explaining a general regenerative operation. FIG. 3 is a diagram illustrating the principle of the current protection operation performed by the control unit shown in FIG. FIG. 4 is a diagram illustrating a specific example of the current protection operation performed by the control unit illustrated in FIG. FIG. 5 is a characteristic diagram illustrating the relationship between the time difference for turning off the regenerative transistors TR1 to TR6 shown in FIG. 1 and the terminal voltage of the snubber capacitor.

  First, a general regenerative operation will be briefly described with reference to FIG. FIG. 2 (1) shows the voltage waveform of the three-phase AC power supply, and FIG. 2 (2) shows the gate signal waveform given individually to the six regenerative transistors TR1 to TR6.

  The regenerative transistor TR1, which is the upper arm, is turned on during a period from the timing at which it intersects with the T phase voltage to the timing at which it intersects with the S phase voltage during the period when the R phase voltage is “+”. On the other hand, the regenerative transistor TR2, which is the lower arm, is turned on during the period from the timing of crossing the T-phase voltage to the timing of crossing the S-phase voltage in the period in which the R-phase voltage is “−”.

  The regenerative transistor TR3, which is the upper arm, is turned on during a period from the timing at which the S phase voltage intersects with the R phase voltage to the timing at which it intersects with the T phase voltage in the period when the S phase voltage is “+”. On the other hand, the regenerative transistor TR4, which is the lower arm, is turned on during the period from the timing of crossing the R phase voltage to the timing of crossing the T phase voltage in the period in which the S phase voltage is “−”.

  The regenerative transistor TR5, which is the upper arm, is turned on during the period from the timing at which it intersects the S phase voltage to the timing at which it intersects the R phase voltage during the period when the T phase voltage is “+”. On the other hand, the regenerative transistor TR6, which is the lower arm, is turned on during a period from the timing at which the T-phase voltage intersects with the R-phase voltage to the timing at which it intersects with the R-phase voltage in the period when the T-phase voltage is “−”.

  As shown in FIG. 2 (2), the regenerative operation is performed by changing the DC voltage appearing between the positive electrode bus 16 and the negative electrode bus 17 to which the terminal voltage of the smoothing capacitor (not shown) on the inverter device 4 side is applied to three. Of the upper arm and the three lower arms, the upper arm regenerative transistor connected to the phase with the highest voltage and the lower arm regenerative transistor connected to the phase with the lowest voltage are turned on, and the other This is realized by repeatedly switching while maintaining the relationship in which the regenerative transistor is turned off.

Then, the current protection function of the control unit 23 monitors the magnitude of the regenerative current of each phase during the above-described regenerative operation, and when it is detected that the regenerative current of a certain phase has exceeded the protection level, off operation to the regenerative transistors have smaller phase with a predetermined time difference in sequence.

  Hereinafter, the current protection operation according to the first embodiment will be described with reference to FIGS. In FIG. 3, the currents IR, IS, and IT are assumed to be IR + IS = IT, where IR <IS. In this case, the regenerative transistor is turned off in the order of TR1 → TR2 → TR3 → TR4 → TR6 → TR5 from the R phase, the S phase, and the T phase in the order of decreasing current value and in the order in which the current actually flows. Let Specifically, the control is performed as shown in FIG.

  In FIG. 4, one set of upper and lower arms is shown. As shown in FIG. 4 (1), when the regenerative current 26 directed from the switching circuit 18 to the three-phase AC power supply 2 is a phase having a low current value, first, the regenerative current 26 actually directed to the three-phase AC power supply 2 is The upper arm regenerative transistor TR1 that is flowing is turned off (shut off), and the lower arm regenerative transistor TR2 is turned off after a predetermined time in each set of upper and lower arms.

  In addition, as shown in FIG. 4B, when the regenerative current 27 directed from the three-phase AC power source 2 to the switching circuit 18 is a phase having a low current value, first, the regenerative current 27 actually directed to the switching circuit 18 is The upper arm regenerative transistor TR2 is turned off, and the upper arm regenerative transistor TR1 is turned off after a predetermined time in each set of upper and lower arms.

In this way, when the overcurrent is abnormal, the six regenerative transistors TR1 to TR6 are turned off (shut off) with a time difference in order from a certain regenerative transistor determined from the magnitude and direction of the regenerative current. The flowing overcurrent flows back while decreasing in the switching circuit. That is, as can be understood from the relational expression of (1/2) LI ² = CV ² , the current I that greatly affects the increase in the terminal voltage V of the snubber capacitor 19 decreases, and therefore the increase in the terminal voltage of the snubber capacitor 19 is suppressed. Is done.

  Hereinafter, how the increase in the terminal voltage of the snubber capacitor 19 is suppressed will be specifically described with reference to FIG. FIG. 5 shows the relationship between the time difference and the terminal voltage of the snubber capacitor when the three-phase AC power supply 2 is an AC 220V power supply.

  As shown in FIG. 5, in the conventional technique in which the six regenerative transistors TR1 to TR6 are turned off simultaneously, the terminal voltage of the snubber capacitor 19 has been increased to 592V, but the six regenerative transistors TR1 to TR6 are individually connected. It has been found that the terminal voltage rise of the snubber capacitor 19 can be reduced to 523 V when the off operation is performed with a time difference of 200 ns at the maximum.

  As described above, according to the first embodiment, when an abnormal overcurrent occurs, not all switching elements (regenerative transistors) in the switching circuit are turned off simultaneously, but the magnitude and direction of the regenerative current. Since a time difference is provided in order from a certain switching element determined from the above and the off operation is performed, an increase in the terminal voltage of the snubber capacitor 19 can be suppressed. That is, the snubber capacitor can be reduced in capacity, and the switching element can be prevented from being damaged, so that the cost can be reduced.

Embodiment 2. FIG.
FIG. 6 is a block diagram showing a main configuration of a power regeneration converter according to Embodiment 2 of the present invention. In FIG. 6, components that are the same as or equivalent to the components shown in FIG. 1 (Embodiment 1) are assigned the same reference numerals. Here, the description will be focused on the portion related to the second embodiment.

  As shown in FIG. 6, in the power regeneration converter 1b according to the second embodiment, in the configuration shown in FIG. 1 (the first embodiment), the current detectors 30, 21, 22 are replaced with the current detectors 20, 21, 22. 32 is provided, and a control unit 33 is provided instead of the control unit 23.

  The current detectors 30, 31, and 32 detect the magnitudes of the respective phase currents that flow through the connection lines between the three regenerative output terminals of the switching circuit 18 and the AC power supply terminals 11, 12, and 13.

  The control unit 33 includes a current protection table 34. During the regenerative operation, the control unit 33 is the first control signal having the same contents as described in the first embodiment while the current value detected by the current detectors 30, 31, and 32 is equal to or lower than the protection level. Is output to the drive circuit 24. If the current value detected by the current detectors 30, 31, 32 exceeds the protection level, the six regenerative transistors TR1-TR6 determined with reference to the current protection table 34 are connected. The timing for performing the off operation is output to the drive circuit 24 as a second control signal for instructing the current protection operation control.

  Upon receiving the second control signal, the drive circuit 24 generates a gate signal that maintains the state by turning off the six regeneration transistors TR1 to TR6 at a designated timing in a designated order. Application is sequentially made to the gate terminal of the transistor.

  Hereinafter, the current protection operation according to the second embodiment will be described with reference to FIG. FIG. 7 is a diagram for explaining the relationship between the contents of the current protection table provided in the control unit shown in FIG. 6 and the switching pattern.

  The switching pattern shown in FIG. 7 (1) is the same as that shown in FIG. 2 (2). As described with reference to FIG. 2, six regenerative transistors TR1 to TR6 form a set, and two regenerative transistors are turned on and the remaining four regenerative transistors are turned off. Switching patterns (a) to (f) are created.

  In the current protection table 34, as shown in FIG. 7 (2), six regenerative transistors TR1 to TR6 are initially turned off corresponding to each of the six sets of switching patterns (a) to (f). From the regenerative transistor to be operated (shut off) to the regenerative transistor to be finally turned off (shut off) are set.

  When the current value detected by the current detectors 30, 31, 32 is equal to or higher than the protection level, the control unit 33 refers to the current protection table 34 and sets the overcurrent detection timing of the current detectors 30, 31, 32. A second control signal for instructing the drive circuit 24 to perform current protection operation control at a timing for providing a predetermined time difference in order from the regenerative transistors determined in the corresponding switching patterns (a) to (f). Output as.

For example, over-current detection timing of the current detector 30, 31, 32, if the timing of the switching pattern (a), 6 pieces of the regenerative transistors TR1~TR6, as shown in FIG. 7 (2), current protection The regenerative transistor TR5 → the regenerative transistor TR1 → the regenerative transistor TR3 → the regenerative transistor TR6 → the regenerative transistor TR2 → the regenerative transistor TR4, which are set in the table 34, are turned off (cut off) with a predetermined time difference.

  Therefore, also in the second embodiment, as shown in FIG. 5, the increase in the terminal voltage of the snubber capacitor 19 can be suppressed, so that the capacity of the snubber capacitor can be reduced as in the first embodiment. In addition to this, it is possible to reduce damage to the switching element (regenerative transistor), so that the cost can be reduced.

  Further, in the second embodiment, as shown in FIG. 7, since the current protection table 34 is provided with six interrupt patterns obtained by dividing one cycle into six, simple current protection can be performed from the current voltage waveform.

  As described above, the power regenerative converter according to the present invention realizes switching circuit protection in the event of an abnormal overcurrent in a form that enables the snubber capacitor capacity to be reduced by suppressing the increase in the snubber capacitor terminal voltage. Useful for.

It is a block diagram which shows the principal part structure of the power regeneration converter by Embodiment 1 of this invention. It is a time chart explaining general regeneration operation. It is a figure explaining the principle of the current protection operation which the control part shown in FIG. 1 performs. It is a figure explaining the specific example of the electric current protection operation which the control part shown in FIG. 1 performs. It is a characteristic view explaining the relationship between the time difference which makes the regeneration transistors TR1-TR6 shown in FIG. 1 perform an OFF operation, and the terminal voltage of the snubber capacitor. It is a block diagram which shows the principal part structure of the power regeneration converter by Embodiment 2 of this invention. It is a figure explaining the relationship between the content of the table for a current protection with which the control part shown in FIG. 6 is provided, and a switching pattern.

Explanation of symbols

1a, 1b Power regeneration converter 2 Three-phase AC power supply 3 Three-phase induction motor (motor)
4 inverter device 11, 12, 13 AC power supply terminal 14, 15 DC power supply terminal 16 positive electrode bus 17 negative electrode bus 18 switching circuit 19 snubber capacitor 20, 21, 22 current detector 23 control unit 24 drive circuit 30, 31, 32 current detection 33 Control unit 34 Current protection table TR1, TR2, TR3, TR4, TR5, TR6 Regenerative transistor D1-D6 Diode

Claims (2)

A switching circuit that switches the surplus power generated on the three-phase load side and regenerates it to the three-phase power supply system;
A current detector for detecting the magnitude and direction of each phase current flowing between the three-phase power supply system and the switching circuit;
When the current value detected by the current detector is greater than or equal to a predetermined value, among the plurality of switching elements constituting the switching circuit, the current corresponding to the phase having the smaller current value among the phase currents detected by the current detector A control unit for outputting an instruction to perform an off operation with a predetermined time difference in order from the switching element to the drive circuit of the switching circuit;
A power regeneration converter characterized by comprising:   When the current value detected by the current detector is greater than or equal to a predetermined value, the control unit includes a current value of the phase currents detected by the current detector among the plurality of switching elements constituting the switching circuit. A switching element corresponding to a small phase and outputting an instruction to turn off the switching circuit by providing a predetermined time difference in order from the switching element in which current is actually flowing in the direction detected by the current detector. The power regeneration converter according to claim 1.

Images