JP2005185003A - Protective device of power conversion apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a protector for a power converter, capable of performing protection of 3-level inverter input power supply and prompt protection of a switching element in no malfunction by detecting short-circuit current passing through bus-bar current of a 3-level inverter. <P>SOLUTION: This 3-level power converter, having DC voltage consisting of high voltage (P), medium voltage (O) and low voltage (N) and outputting three levels to phase output, includes a first current detector 101 for detecting the current passing through a medium voltage point and a second current detector 102 for detecting the current passing through a low voltage point. The 3-level power converter is configured so as to be made to stop, if the current level of a first or second current detector exceeds a first setting value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inverter / servo drive that performs variable speed driving of a motor and a power converter protection device that is connected to a grid, and in particular, a DC short-circuit fault occurs in a three-level inverter that converts a DC voltage having a neutral point into an AC voltage. Time protection device.

The three-level inverter according to the first conventional example has a circuit configuration as shown in FIG. 2, and has fuses on the high voltage side bus (P) and the low voltage side bus (N) (see, for example, Patent Document 1). ).
JP-A-9-182461 (FIG. 4). Japanese Patent No. 3391025 (FIGS. 1, 2, 3, and 4)

FIG. 2 is a diagram showing a three-level inverter described in Patent Document 1. In FIG.
The three-level inverter converts a DC voltage having a neutral point O into a high-quality AC voltage. In general, a three-level inverter device as shown in FIG. 2 has been put into practical use.
In FIG. 2, 1 is a DC power source connected between a positive potential line P and a negative potential line N, 2 and 3 are capacitors connected in series with a neutral point O in between, one terminal connected to the positive potential line P and the other Are connected to the negative potential line N. Reference numerals 4 and 5 are neutral point clamp diodes connected in series with each other with a neutral point O in between. One terminal is connected to the middle of the positive arm and the other terminal is connected to the middle of the negative arm. 6 to 9 are series connection circuits of switch elements in which flywheel diodes are connected in reverse parallel. Among the series connection circuits of switch elements 6 and 7, one terminal is a positive potential line P and the other terminal is a U-phase output line. On the other hand, the series connection circuit of the switch elements 8 and 9 has one terminal connected to the U-phase output line and the other terminal connected to the negative potential line N. Gate drivers G6 to G9 are connected to the gates of the switch elements 6 to 9, and command signals are given to the gate drivers G6 to G9 from a gate control circuit (not shown). A U-phase arm bridge is configured by the series connection circuit of the diodes 4 and 5 and the switch elements 6 to 9 described above, and the V-phase arm bridge and the W-phase arm bridge illustrated by the dotted line block are also configured as the U-phase arm bridge. It has the exact same configuration.
The positive potential line P and the negative potential line N are provided with fuses F1 and F2, respectively.

  In the three-level inverter having such a configuration, when the switch elements 6 and 7 of the positive arm among the switch elements 6 to 9 are simultaneously turned on, the potential of the positive potential P is output, and the switch element 8 of the negative arm When 9 is turned on at the same time, a negative potential N is output. When both switch elements 6 and 9 are turned off and switch elements 7 and 8 are turned on at the same time, the current is neutralized via either neutral point clamp diode 4 or 5. The potential at the sex point O is output. When a positive AC voltage is output, the switch element 7 is turned on, and the switch element 6 is turned on / off. When a negative AC voltage is output, the switch element 8 is turned on and the switch element 9 is turned on / off. Further, the switch elements 6 and 8 and 7 and 9 are complementarily turned on and off, and are not simultaneously turned on.

  However, in such a three-level inverter, when a switch element that should be non-conductive is short-circuited for some reason, when the other switch element is turned on, a large short-circuit current flows through the switch element. Therefore, the fuse F1 or F2 is blown by a short-circuit current to protect the input power supply of the inverter.

The three-level inverter according to the second conventional example has a circuit configuration as shown in FIG.
As a method for detecting a short-circuit current, each IGBT is provided with a short-circuit current detection circuit as described in Patent Document 2, and when a short circuit is detected, the gate of the IGBT is cut off for protection.
In FIG. 3, the fuses F1 and F2 are eliminated, and a short circuit detection device and a short circuit protection device are provided in the gate drivers 32a to 32d, and a logic circuit 36A is provided in the gate control circuit 36. Signal lines 34a to 34d for transmitting signals from 36 to the short circuit protection devices of gate drivers 32a to 32d and signal lines 35a to 35d for transmitting signals from the short circuit detection devices of gate drivers 32a to 32d to gate control circuit 36 are added. This is very different from FIG.

In such a configuration, it is assumed that the switch element 8 is erroneously turned on to cause an arm short circuit when flowing along the route passing through the switch elements 6 and 7. In this case, a short circuit is detected by the gate drivers 32a to 32c, and this is transmitted to the gate control circuit 36 through the signal lines 35a to 35c. The gate control circuit 36 knows that a short circuit has occurred in the switch elements 6 to 8, and outputs an on signal to the gate drivers 32a and 32b and an off signal to the gate drivers 32c and 32d. It can be determined that the element 8 has been misfired for some reason. Accordingly, the gate control circuit 36 first causes the gate driver 32a to start the protection operation and locks the gate drive of other switch elements so that they are not operated by the normal on / off signal.
Next, after a predetermined time, the gate driver 32b of the switch element 7 starts a protection operation. These protection operation and lock signals are performed by dedicated signal lines 34a to 4d in order to distinguish them from normal on / off signals.

However, since the protection device using the fuse of the first conventional example has a long time until the fuse is blown and cannot be protected at a high speed, the switch elements other than the failed switch element are destroyed by a short-circuit current. was there.
Further, the method of providing the short-circuit detection circuit in each switch element of the second conventional example has a problem that a large number of detection circuits are required, the apparatus becomes complicated, and the cost increases.
The present invention has been made in view of such problems, and can detect a short-circuit current at high speed and can protect a non-failing switch element at high speed. Therefore, it is an object of the present invention to provide a protection device for a power conversion device that is simple, reliable, small, and low in cost.

In order to solve the above problem, the present invention is configured as follows.
The invention described in claim 1 is a three-level power converter that includes a DC voltage of a high voltage (P), a medium voltage (O), and a low voltage (N), and outputs the ternary level as a phase output. A first current detector for detecting a current flowing through the intermediate voltage point, and a second current detector for detecting a current flowing through the low voltage point, and the current of the first or second current detector When the level exceeds the first set value, the three-level power conversion device is stopped, and the power conversion device protection device is provided.
According to a second aspect of the present invention, there are provided four switch elements connected in series to a DC power supply, a free wheel diode connected in reverse parallel to each of the switch elements, and a voltage dividing capacitor connected in series to the DC power supply. A connection point of the first and second switch elements from the high voltage side of the switch element, a first clamp diode connected to a voltage dividing point of the voltage dividing capacitor, and a high voltage side of the switch element In a three-level power converter having a connection point between the third and fourth switch elements and a second clamp diode connected to the voltage dividing point of the voltage dividing capacitor, a current flowing through the intermediate voltage point is detected. A first current detector and a second current detector for detecting a current flowing through a low voltage point, and when a current level of the first or second current detector exceeds a first set value, Previous Stopping the three-level power converting apparatus in which a protection system for a power converter according to claim.
According to a third aspect of the present invention, in the protection device for a power conversion device according to the first or second aspect, the configuration of the power conversion device is a single phase or more multiphase, and the first current detector and the first Two current detectors are shared by each phase.

According to the first and second aspects of the invention, it is possible to detect the short-circuit current flowing through the bus bar by the detector and turn off the switch element, and that other non-failed switches are destroyed by the short-circuit current. Can be prevented.
According to the third aspect of the present invention, the circuit can be simplified and the reliability can be improved at low cost by sharing the current detector in the multiphase configuration.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit configuration diagram of a protection device for a three-phase three-level inverter according to an embodiment of the present invention.
In the figure, 1 is a DC power source connected between a positive potential line P and a negative potential line N, 2 and 3 are capacitors connected in series with a neutral point O in between, one terminal connected to the positive potential line P and the other The terminal is connected to the negative potential line N. Reference numerals 4 and 5 are neutral point clamp diodes connected in series with each other with the neutral point D1 interposed therebetween. One terminal is connected to the middle of the positive arm and the other terminal is connected to the middle of the negative arm. Reference numerals 6 to 9 denote switch elements in which flywheel diodes 6a to 9a are connected in reverse parallel, and constitute a series connection circuit. Among them, the series connection circuit of the switch elements 6 and 7 has one terminal connected to the positive potential line P and the other terminal connected to the U-phase output line, while the series connection circuit of the switch elements 8 and 9 has one terminal connected to the U-phase output line. The other terminal of the U-phase output line is connected to the negative potential line N. As the switch elements 6 to 9, a bipolar transistor, an insulated gate bipolar transistor (IGBT), a gate turn-off thyristor (GTO), or the like is used. Here, an IGBT is used.
Gate drivers G6 to G9 are connected to the gates of the switch elements 6 to 9, and command signals are given to the gate drivers G6 to G9 from a gate control circuit (not shown).
A U-phase arm bridge is configured by the series connection circuit of the diodes 4 and 5 and the switch elements 6 to 9 described above, and the V-phase arm bridge and the W-phase arm bridge illustrated by the dotted line block are also configured as the U-phase arm bridge. It has the exact same configuration.
In such a main circuit configuration, the feature of the present invention is between the connection point D1 of the neutral point clamp diodes 4 and 5 connected in series with each other and the connection point O of the capacitors 1 and 2 connected in series with each other. The first current detector 101 is provided, the second current detector 102 is also provided on the negative potential line N, and the detection values of the current detectors 101 and 102 are sent to the signal processing circuit 100. It is. The output of the signal processing circuit 100 can invalidate the turn-on signal from the gate control circuit and turn off the switch elements 6-9.

In the three-level inverter having such a configuration,
(1) U-phase switch element 6 is off, switch element 7 is on, switch element 8 is on, and switch element 9 is off. When the V-phase or W-phase switch element 6 is off, the switch element 7 is on, the switch element 8 is on, and the switch element 9 is off, the output voltage is 0,
(2) U-phase switch element 6 is on, switch element 7 is on, switch element 8 is off, and switch element 9 is off. When the V-phase or W-phase switch element 6 is off, the switch element 7 is on, the switch element 8 is on, and the switch element 9 is off, the output voltage is + E level,
(3) U-phase switch element 6 is on, switch element 7 is on, switch element 8 is off, and switch element 9 is off. When the V-phase or W-phase switch element 6 is off, the switch element 7 is off, the switch element 8 is on, and the switch element 9 is on, the output voltage is + 2E level,
(4) U-phase switch element 6 is off, switch element 7 is off, switch element 8 is on, and switch element 9 is on. When the V-phase or W-phase switch element 6 is off, the switch element 7 is on, the switch element 8 is on, and the switch element 9 is off, the output voltage is -E level,
(5) U-phase switch element 6 is off, switch element 7 is off, switch element 8 is on, and switch element 9 is on. When the V-phase or W-phase switch element 6 is on, the switch element 7 is on, the switch element 8 is off, and the switch element 9 is off, the output voltage is -2E level,
(6) U-phase switch element 6 is off, switch element 7 is off, switch element 8 is off, and switch element 9 is off. When the V-phase or W-phase switch element 6 is off, the switch element 7 is off, the switch element 8 is off, and the switch element 9 is off, the output voltage is open (non-conductive state).

In the usage pattern as described above, when a switch element that should be non-conductive among the switch elements 6 to 9 is short-circuited for some reason, when another switch element is turned on, a large short-circuit current is generated in the switch element. It will flow.
Since the short-circuit current flows through at least one of the first current detector 101 and the second current detector 102, the first current detector 101 or the second current detector 102 that detects the short-circuit current performs signal processing on the detected value. The signal processing circuit 100 determines that an abnormality has occurred, turns off the gate signal of each switch element, and immediately cuts off the short-circuit current.
Since the present invention does not use the fuses F1 and F2 in the part different from the first conventional example in FIG. 2, the short-circuit current flowing through the switch element can be cut off at high speed, and the destruction of the non-failed switch element is prevented. be able to.
Moreover, since the part different from FIG. 3 of the second conventional example can be composed of two short-circuit current detection circuits, it is possible to improve the reliability and provide a low-cost protection device.
When the current capacity of the switch element is large, the switching order may be adopted, and the switch element may be blocked in the order that requires urgent protection.
However, when the current capacity of the switch elements is small, when a short-circuit current flows, it is better to shut off all the switch elements at a high speed at the same time, rather than ordering them.
As described above, the power conversion device having the protection device according to the present invention can detect the IGBT short-circuit current at high speed and shut off the IGBT, thereby preventing the destruction of the IGBT that has not failed and the power supply short-circuit. Therefore, a reliable and low-cost protection device can be provided.

It is a block diagram of the protection apparatus which shows 1st Example of this invention. It is a block diagram of the protection apparatus of a 1st prior art example. It is a block diagram of the protection apparatus of the 2nd prior art example.

Explanation of symbols

1 DC power supply 2, 3 Capacitor 4, 5 Neutral point clamp diode 6-9 Switch element (IGBT)
6a to 9a Flywheel diode G6 to G9 Gate driver 100 Signal processing circuit 101, 102 Current detector

Claims (3)

In a three-level power converter that includes a high voltage (P), a medium voltage (O), and a low voltage (N) DC voltage, and outputs the ternary level to the phase output,
A first current detector for detecting a current flowing through a middle voltage point; and a second current detector for detecting a current flowing through a low voltage point; and a current level of the first or second current detector. When the value exceeds the first set value, the three-level power converter is stopped. Four switch elements connected in series to the DC power supply, a freewheeling diode connected in reverse parallel to each of the switch elements, a voltage dividing capacitor connected in series to the DC power supply, and the switch element from the high voltage side. A connection point of the first and second switch elements, a first clamp diode connected to the voltage dividing point of the voltage dividing capacitor, and a connection point of the third and fourth switch elements from the high voltage side of the switch elements And a three-level power converter comprising a second clamp diode connected to the voltage dividing point of the voltage dividing capacitor,
A first current detector for detecting a current flowing through a middle voltage point; and a second current detector for detecting a current flowing through a low voltage point; and a current level of the first or second current detector. When the value exceeds the first set value, the three-level power converter is stopped.   3. The power conversion according to claim 1, wherein the configuration of the power conversion device is a single phase or more multiphase, and the first current detector and the second current detector are shared by each phase. 4. Device protection device.

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