JP4742313B2 - Power converter protection system - Google Patents

Description

  The present invention relates to protection of a power converter in which a plurality of voltage-driven semiconductor elements are connected in series to each arm.

FIG. 6 shows a general example of a power converter in which a plurality of voltage-driven semiconductor elements are connected in series to each arm.
In FIG. 6, 25 is a three-phase AC input power supply, 26 is a rectifier circuit such as a diode bridge circuit, 27 is a smoothing capacitor, 28 to 33 are voltage-driven semiconductor elements connected in series, and 34 is a load such as a motor. It is.

  In the above configuration, when an arm short circuit occurs, the current detection circuit detects the overcurrent state of the voltage-driven semiconductor element using a current detection circuit as a conventional method for protecting the voltage-driven semiconductor element from destruction due to overcurrent. Generally, a method of shutting off the semiconductor element without breaking by gently turning off the type semiconductor element (also referred to as soft shut-off). Such a protection method is disclosed in Patent Documents 1 and 2, for example.

FIG. 7 shows a conventional example of the protection method. This shows one arm of a power conversion device in which a plurality of voltage-driven semiconductor elements are connected in series to each arm. Further, an IGBT (insulated gate bipolar transistor) element is used as a voltage-driven semiconductor element, and four IGBTs are connected in series.
In FIG. 7, 1 to 4 (Q1 to Q4) are IGBTs having diodes connected in antiparallel, 11 to 14 are overcurrent protection circuits, 15 to 18 are gate drive circuits having a soft cutoff function, and 35 to 38 are currents. It is a detector. That is, in this circuit, gate drive circuits 15 to 18 are connected to the IGBTs 1 to 4, respectively, and current detectors 35 to 38 are connected to the gate drive circuits 15 to 18 via the overcurrent protection circuits 11 to 14. Has been.

The operation will be described with reference to the case of FIG. 8 in which two IGBTs are connected in series.
In FIG. 8, when an overcurrent flows through the IGBTs 1 and 2 due to an arm short circuit or the like, the current detectors 35 and 36 detect this, and a detection signal is input to the overcurrent protection circuits 11 and 12. When a detection signal is input to the overcurrent protection circuits 11 and 12, the overcurrent protection circuits 11 and 12 determine whether or not there is an overcurrent. If it is determined that the current is overcurrent, the protection signal is output to the gate drive circuits 15 and 16. The gate drive circuits 15 and 16 are switched to the soft shut-off mode, whereby the IGBTs 1 and 2 are shut off without being destroyed.

Japanese Patent Laid-Open No. 04-079759 JP 05-308717 A

According to the method as described above, the voltage-driven semiconductor elements connected in series when an arm short circuit or the like occurs can be protected from destruction due to overcurrent. There is a problem that the voltage sharing at the time of interruption becomes unbalanced (refer to the gate voltages Q1 and Q2 in FIG. 9), and in the worst case, the voltage-driven semiconductor element to which an overvoltage is applied may be destroyed.
Accordingly, an object of the present invention is to provide a protection system that can avoid the destruction of the voltage-driven semiconductor element.

In order to solve such a problem, in the invention of claim 1, the voltage driven semiconductor element connected to the lowest voltage side is the first stage, and the voltage driven semiconductor element connected to the highest voltage side is the nth stage. (Where n is an integer), for power converters in which n voltage-driven semiconductor elements are connected in series to each arm,
Each voltage-driven semiconductor element is provided with a gate drive circuit having a function of gently turning off the voltage-driven semiconductor element when an overcurrent is detected, and the gate lines connecting the voltage-driven semiconductor element and the gate drive circuit are magnetically connected to each other. Connected by a coupling circuit, the m (m = 1 to n) stage gate drive circuit includes a current detector for detecting a current flowing in the mth stage voltage driven semiconductor element, and a detection result of the current detector And a voltage detection circuit for detecting a voltage generated based on the magnetic coupling circuit, and a voltage detection circuit for detecting a voltage generated based on the magnetic coupling circuit. And an overcurrent protection circuit that outputs a protection signal according to the detection result.

  According to the present invention, in a power conversion device in which a plurality of voltage-driven semiconductor elements are connected in series to each arm, at the same time, without overloading, the voltage sharing of each voltage-driven semiconductor element is moderately reduced. Since it can be turned off (softly interrupted), the voltage-driven semiconductor element can be reliably prevented from overcurrent breakdown when an arm short circuit occurs. In addition, since a plurality of voltage-driven semiconductor elements can be protected by a single current detection circuit, protection can be provided at a low cost.

  FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, which is an example when four IGBTs are connected in series. In FIG. 1, 1-4 are IGBTs having diodes connected in antiparallel, 5-7 are magnetic coupling circuits, 8-10 are voltage detection circuits, 11-14 are overcurrent protection circuits, and 15-18 are soft shut-off functions. Numeral 19 is a current detector.

  As shown in FIG. 1, gate drive circuits 15 to 18 are connected to the IGBTs 1 to 4, and gate lines connecting the IGBT and the gate drive circuit are connected to each other by magnetic coupling circuits 5 to 7, respectively. An overcurrent protection circuit 11 and a current detector 19 for detecting a current flowing through the IGBT are connected to the gate drive circuit 15 at the first stage, and overcurrent protection is provided to the gate drive circuits 16 to 18 other than the first stage. The circuits 12 to 14 and the voltage detection circuits 8 to 10 are connected to each other.

The operation of FIG. 1 will be described with reference to FIGS. FIG. 2 shows a case where two IGBTs are connected in series by simplifying FIG. 1, and FIG. 3 shows an example of the waveform of each part.
Now, when an overcurrent flows through the IGBTs 1 and 2 in FIG. 2, the current detector 19 detects it and a detection signal is input to the overcurrent protection circuit 11. When a detection signal is input to the overcurrent protection circuit 11 and the overcurrent protection circuit 11 determines that it is an overcurrent, a protection signal is output to the gate drive circuit 15, so that the gate drive circuit 15 is switched to the soft cutoff mode and the gate drive circuit The gate current of the IGBT 1 flows through the path 15 → the emitter of the IGBT 1 → the IGBT 1 gate → the magnetic coupling circuit 5 → the gate drive circuit 15.

  When a gate current flows through the primary winding of the magnetic coupling circuit 5, a gate current also flows through the secondary winding of the magnetic coupling circuit 5. As a result, the gate voltage VGE (Q1) of the IGBT 1 and the gate voltage VGE (Q2) of the IGBT 2 are lowered, and the IGBT 1 and the IGBT 2 start soft shutoff. At the same time, the voltage detection circuit 8 detects the voltage VTr2 generated in the secondary winding of the magnetic coupling circuit 5, and upon receiving the detection result, the overcurrent protection circuit 12 outputs a protection signal to the gate drive circuit 16, IGBT2 continues soft shutoff.

At this time, an operation delay Δt2 (see FIG. 3) may occur in the voltage detection circuit 8, but the switching timing is adjusted by the magnetic coupling circuit 5 (IGBT1 and IGBT2 have already started the soft shutoff operation). Therefore, there is no problem. Note that a method for adjusting the switching timing by such magnetic coupling is well known, for example, in Japanese Patent Application Laid-Open No. 2002-204578. By such an operation, the IGBT 1 and the IGBT 2 can be softly cut off simultaneously when an overcurrent is detected.
As described above, since the IGBT 1 and the IGBT 2 can be simultaneously softly interrupted when an overcurrent is detected, it is possible to solve the problem that the voltage sharing is unbalanced.

FIG. 4 shows another embodiment.
In FIG. 1, an overcurrent protection circuit 11 and a current detector 19 for detecting a current flowing through the IGBT are connected to the first stage gate drive circuit 15, and overcurrent is connected to the gate drive circuits 16 to 18 other than the first stage. While the protection circuits 12 to 14 and the voltage detection circuits 8 to 10 are connected, in FIG. 4, the fourth stage gate drive circuit 18 includes an overcurrent protection circuit 14 and a current detector for detecting the current flowing through the IGBT. 23, except that the overcurrent protection circuits 11 to 13 and the voltage detection circuits 20 to 22 are connected to the gate drive circuits 15 to 17 other than the fourth stage, respectively. Omitted.

FIG. 5 shows another embodiment.
In FIG. 1, an overcurrent protection circuit 11 and a current detector 19 for detecting a current flowing through the IGBT are connected to the first stage gate drive circuit 15, and overcurrent is connected to the gate drive circuits 16 to 18 other than the first stage. While the protection circuits 12 to 14 and the voltage detection circuits 8 to 10 are connected, the gate drive circuit 16 in the second stage in FIG. 5 includes the overcurrent protection circuit 12 and a current detector that detects the current flowing through the IGBT. 24 except that the overcurrent protection circuits 11, 13, and 14 and the voltage detection circuits 20, 9, and 10 are connected to the gate drive circuits 15, 17, and 18 other than the second stage, respectively. Therefore, details are omitted.

Circuit configuration diagram showing an embodiment of the present invention Simplified configuration diagram of FIG. Operation explanatory diagram of FIG. 1 is a circuit configuration diagram showing a modification of FIG. 1 is a circuit configuration diagram showing another modification of FIG. Configuration diagram showing a general example of a power converter Configuration diagram showing a conventional example of overcurrent protection Simplified configuration diagram of FIG. Operation explanatory diagram of FIG.

Explanation of symbols

  1 to 4 (Q1 to Q4) ... IGBT, 5-7 ... magnetic coupling circuit, 8-10, 20-22 ... voltage detection circuit, 11-14 ... overcurrent protection circuit, 15-18 ... gate drive circuit, 19, 24: Current detector.

Claims (1)

The voltage-driven semiconductor element connected to the lowest voltage side is the first stage, the voltage-driven semiconductor element connected to the highest voltage side is the n-th stage (n is an integer), and each arm has a voltage-driven semiconductor element. For n power converters connected in series,
Each voltage-driven semiconductor element is provided with a gate drive circuit having a function of gently turning off the voltage-driven semiconductor element when an overcurrent is detected, and the gate lines connecting the voltage-driven semiconductor element and the gate drive circuit are magnetically connected to each other. Connected by a coupling circuit, the m (m = 1 to n) stage gate drive circuit includes a current detector for detecting a current flowing in the mth stage voltage driven semiconductor element, and a detection result of the current detector And a voltage detection circuit for detecting a voltage generated based on the magnetic coupling circuit, and a voltage detection circuit for detecting a voltage generated based on the magnetic coupling circuit. An overcurrent protection circuit that outputs a protection signal according to the detection result of each of the power conversion devices is connected.

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