JP2009153257A - Short circuit protection circuit of power converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a device capacity by shortening a delay time of voltage detection in a short circuit protection circuit of a power converter, and to use an element which is small in short circuit resistance amount. <P>SOLUTION: A voltage dividing circuit formed by serially connecting a voltage dividing part 41 composed of at least one of parallel connected circuits connected with resistors R1 to Rn and capacitors C1 to Cn, and a detecting part 42 composed of at least one of the parallel connected circuits connected with the resistor Rd and the capacitor Cd is connected to the output side of a semiconductor switching element 3A in parallel with each other, time constants of the voltage dividing part 41 and the detection part 42 are equalized, a variable resistor 24 for adjusting the displacement of these time constants is arranged, and the delay time of the detection is shortened. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a power conversion device using a voltage-driven semiconductor element as a switching element, and more particularly to a short-circuit protection circuit thereof.

As this type of conventional example, there are those shown in Patent Documents 1 and 2, for example.
FIG. 3 shows an example based on the same principle as described above. In the figure, 1 is a DC power source, 2 is a gate drive circuit (GDU) comprising an off circuit 21, a filter 22 and a protection circuit 23, and 3A and 3B are switching elements comprising self-extinguishing elements such as FETs and IGBTs (FIG. Is an example of IGBT), and 4 is a voltage dividing circuit comprising a series circuit of a voltage dividing resistor RA and a detection resistor RB.

In FIG. 3, the upper arm IGBT (3A) and the lower arm IGBT (3B) are on / off controlled by the gate drive circuit 2 (GDU), and the DC power input from the DC power source 1 is converted into AC power and output. An inverter circuit is configured. A configuration is shown in which the collector-emitter voltage (V _CE ) of the upper arm IGBT (3A) is detected via a voltage dividing circuit 4 connected in parallel between the collector and emitter on the output side of the upper arm IGBT (3A). Has been. Although not shown in FIG. 3, a short circuit protection circuit similar to that in FIG. 3 is also provided for the lower arm IGBT (3B).

The operation of the short circuit protection circuit in FIG. 3 is as follows. That is, the voltage between the collector and emitter (V _CE ) of the element 3A is detected by the voltage dividing circuit 4, and this detection signal is compared with the element firing command in the protection circuit 23 to determine whether or not protection is to be performed. In other words, when the IGBT is normal, V _CE is about several volts in the on state. However, due to the arrow I (output short circuit) or II (lower arm element failure) in FIG. Current flows, the terminal voltage V _CE of the healthy upper arm IGBT increases (see FIG. 4).

FIG. 3 uses such a characteristic. When _VCE is large even though the IGBT ignition command is on, it is determined that there is an abnormality, and a signal to that effect is sent to the off circuit 21.
Note that the protection circuit 23 has a built-in comparator function that determines the magnitude of the input _VCE detection signal based on the threshold value Vth1. In addition, a filter 22 is interposed between the protection circuit 23 and the off circuit 21 to prevent malfunction during normal switching during normal operation.

Upon introducing the detection signal of the IGBT voltage V _CE to the protection circuit 23, for capturing an IGBT voltage of the high voltage to the gate drive circuit 2 of the low voltage, it employs a circuit scheme for dividing the IGBT voltage V _CE. A resistor is used for the voltage dividing circuit 4, and a resistor RA for voltage division and a resistor RB for detection are connected in series.
5A and 5B are waveform diagrams for explaining the operation of FIG. 3. FIG. 5A shows a normal state and FIG. 5B shows a short circuit.

As shown in FIG. 5A, when the element firing command for the upper arm IGBT (3A) is switched from OFF to ON as normal switching at normal time, the voltage V _CE of the upper arm IGBT (3A) is The voltage decreases from the high voltage level in the off state to the low voltage level in the on state, but the V _CE detection signal is delayed from the decrease in the voltage V _CE itself due to the presence of the stray capacitance C _S in the voltage dividing circuit described later. descend. The protection circuit 23 is configured to output an abnormality determination signal based on an AND condition that “IGBT ignition command is ON” and “V _CE detection signal is greater than or equal to threshold Vth1”. Therefore, until the V _CE detection signal drops to a voltage level lower than the threshold Vth1 is abnormality determination signal continues to be outputted.

On the other hand, a filter 22 having a time constant element is provided on the output side of the protection circuit 23, and a signal having a waveform in which the rise of the abnormality determination signal from the protection circuit 23 is delayed is output from the filter 22 to the off circuit 21. Is done. Then, V _CE until the detection signal is output from the abnormality judgment signals from the protection circuit 23 decreases the voltage level lower than the threshold Vth1 is stopped, the level of the output signal of the filter 22 is more than the threshold value Vth2 of the off-circuit 21 and By setting the time constant of the filter 22 so as not to occur, an erroneous OFF operation is prevented from occurring in normal switching at the normal time.

Next, as shown in FIG. 5B, when an output short circuit occurs when the element firing command for the upper arm IGBT (3A) is on, the voltage V _{CE of the} upper arm IGBT (3A) Increases from a normal low voltage level in the ON state to a high voltage level in an abnormal state, but the V _CE detection signal is higher than the increase in the terminal voltage V _CE itself due to the presence of the stray capacitance C _S in the voltage dividing circuit. Ascend late. The protection circuit 23 is configured to output an abnormality determination signal based on an AND condition that “IGBT ignition command is ON” and “V _CE detection signal is greater than or equal to threshold Vth1”. Therefore, the abnormality judgment signal rises when V _CE detection signal reaches the threshold value Vth1.

  Then, since the filter 22 outputs a signal having a waveform obtained by delaying the rise of the abnormality determination signal from the protection circuit 23 toward the off circuit 21, the level of the output signal of the filter 22 is the threshold value of the off circuit 21. The timing when the OFF operation starts after reaching Vth2 is further delayed. The operation described with reference to FIG. 5B is the same when an element failure occurs in the lower arm while the element firing command for the upper arm IGBT (3A) is on.

Japanese Patent Laid-Open No. 10-257779 Japanese Patent Laid-Open No. 05-219752

By the way, in FIG. 3, V _CE is detected by the partial voltage of the resistor alone. Therefore, if the stray capacitance C _S as shown by the dotted line in FIG. 3 exists, if the voltage division ratio is large, the low voltage side is affected. Although so that delay in detection of V _CE, when the delay is large, the following problems occur.

For example, in the normal state of FIG. 5, when the delay of the _VCE detection signal becomes large due to the presence of the stray capacitance C _S in the voltage dividing circuit, the upper arm IGBT (3A) is turned on by the ignition command being turned on in normal switching. The response delay of the _VCE detection signal that decreases toward a low voltage level corresponding to the on state of the IGBT (3A) increases. In this case, the state in which the V _CE detection signal is equal to or higher than the threshold value Vth1 of the protection circuit 23 continues for a long time, and during that time, “IGBT ignition command is ON” and “ _VCE detection signal is equal to or higher than the threshold value Vth1. The abnormality determination signal based on the AND condition “is that” is continuously output from the protection circuit 23. For this reason, depending on the setting of the time constant of the filter 22, the output signal of the filter 22 may be equal to or higher than the threshold value Vth2 of the off circuit 21, and the off circuit 21 may malfunction. In order to prevent such malfunction during normal switching, the time constant of the filter 22 must be increased.

In the above point, if a fixed constant (delay) determined by the voltage dividing resistor and the stray capacitance C _S that causes a delay of the V _CE detection signal can be defined as a device, the time constant of the filter 22 In this setting, based on the above-mentioned fixed constant (delay), the time constant value can be made as small as possible within a range in which malfunction in normal switching can be surely prevented. However, in actuality, the value of the stray capacitance C _S in the voltage dividing circuit varies depending on the structure of the voltage dividing resistor and the installation conditions. Therefore, a fixed constant (delay) determined by the voltage dividing resistor and the stray capacitance C _S is used as the device. It cannot be specified. For this reason, in order to surely prevent malfunction in normal switching, the time constant of the filter 22 is included with a larger margin in consideration of the fact that the fixed constant (delay) is different for each device. Therefore, it is necessary to set the actual time constant of the filter 22 to be larger.

On the other hand, at the time of a short circuit, the increase in the _VCE detection signal during the ON command of the healthy element is detected at high speed, and the short circuit withstand capability of the IGBT, that is, the off time is shorter than the time from the start of overcurrent flow due to the short circuit It is necessary to prevent a short circuit accident of the device. Here, the short circuit withstand capability of the IGBT is about several tens of μs. If the delay of the V _CE detection signal is large due to the presence of the stray capacitance C _S in the voltage dividing circuit, the delay of the rise of the V _CE detection signal with respect to the increase of the voltage V _CE of the upper arm IGBT (3A) due to the output short circuit becomes large. delay timing V _CE detection signal reaches the threshold value Vth1 of the protection circuit 23 also increases the delay of the rising timing of the output signal of the protection circuit 23 is also increased.

The timing at which the output signal of the filter 22 reaches the threshold value Vth2 of the off circuit 21 and the off operation by the off circuit 21 starts is a timing further delayed by the delay due to the time constant of the filter 22, as described above. When the delay of the V _CE detection signal due to the presence of the stray capacitance C _S in the voltage dividing circuit is large, the time constant of the filter 22 for reliably preventing malfunction in normal switching is also set large. The delay due to the time constant of the filter 22 is also increased.

As described above, when the delay of the _VCE detection signal due to the presence of the stray capacitance C _S in the voltage dividing circuit is large, the delay of the off operation corresponding to the output short circuit is also large, which exceeds the short circuit withstand capability of the device. In order to prevent the short-circuit protection from becoming impossible, there is a problem that it is necessary to select an element having a large short circuit resistance (long) as a switching element such as an IGBT.

  Accordingly, an object of the present invention is to reduce the time of voltage detection delay in a short circuit protection circuit of a power conversion device so that the device capacity can be reduced, and to enable use of an element having a short circuit resistance (short). Etc.

In order to solve such a problem, the invention according to claim 1 detects the output voltage of the semiconductor switching element constituting each arm of the power converter, and short-circuit protection based on the relationship between the detected voltage and the element firing command. In the short circuit protection circuit of the power conversion device that operates,
A voltage dividing circuit formed by serially connecting a voltage dividing unit composed of at least one of a parallel connection circuit of a resistor and a capacitor and a detection unit consisting of at least one of a parallel connection circuit of a resistor and a capacitor. In addition to being connected in parallel to the output side of the element, there is provided adjusting means for making the time constants of the voltage dividing section and the detecting section equal to each other and adjusting the deviation of these time constants.
In the invention of claim 1, the adjusting means can be a variable resistor (invention of claim 2).

(A) In the short circuit protection circuit of the power conversion device according to the present invention, the short circuit protection method “performs the short circuit protection operation based on the relationship between the output voltage of the semiconductor switching element of each arm and the element firing command” is a conventional short circuit protection method. Compared to the short-circuit protection method, it has the following advantages.
(A1) Since a fuse for short circuit protection is unnecessary, the inductance in the device can be reduced.
(A2) Since the protection operation can be performed at a higher speed than the fuse, the device capacity can be reduced.
(A3) Since the protection operation can be performed at a speed higher than that of the fuse, it can be cut off with a smaller current at the time of the short circuit, so that the electromagnetic mechanical force generated by the current flowing at the time of the short circuit is reduced, and the size of the bus bar in the apparatus is also reduced Can be small.

  (B) The present invention has the advantage of the above (a) compared with the method using a fuse. Further, in consideration of the output voltage detection delay due to the stray capacitance of the voltage detection voltage dividing circuit, each of the voltage detection voltage dividing circuit and the detection unit is at least one of a parallel circuit of a resistor and a capacitor. The time constants of the voltage dividing unit and the detection unit are made equal to each other, and adjustment means for adjusting the deviation of these time constants is provided. As a result, the present invention shortens the detection delay time of the output voltage, can be cut off with a smaller current at the time of short circuit, and can further reduce the device capacity of the power converter, Since a smaller (shorter) element can be used, the configuration is more suitable as a short circuit protection circuit for a power converter.

FIG. 1 is a circuit diagram showing an embodiment of the present invention.
As is clear from FIG. 3, this is different from the conventional example of FIG. 3 in that a variable resistor 24 (Rv) is connected to the gate drive circuit (GDU) 2 and each of the series resistors R1 to Rn of the voltage divider 41. in parallel, with a capacitor C1~Cn sufficiently large capacitance negligible stray capacitance C _S, it is characterized such that connecting the capacitor Cd in parallel with the resistor Rd of the detector 42. Capacitors C1 to Cn and Cd function for phase compensation. Similarly to FIG. 3, the voltage dividing circuit 4 is connected in parallel between the collector and emitter on the output side of the upper arm IGBT (3A), and is connected in parallel between the collector and emitter of the upper arm IGBT (3A). The voltage V _CE of the upper arm IGBT (3A) is detected via the voltage dividing circuit 4.

  Then, the filter time constants of the voltage divider 41 and the detector 42 are set to be equal to each other as shown by the following formula 1. However, since there is an error in each resistor and capacitor, a variable resistor 24 (Rv) as an adjusting means is connected to the entrance of the gate drive circuit (GDU) 2 in order to correct the deviation of both time constants. The variable resistor 24 (Rv) is connected in parallel to the resistor Rd of the detection unit 42 in the voltage dividing circuit 4. Further, the adjustment of the filter time constant by the variable resistor 24 (Rv) can be performed by looking at the step response waveform of the voltage dividing circuit 4, for example.

When the filter time constants of the voltage dividing unit 41 and the detecting unit 42 are made equal to each other by adjusting the variable resistor 24 (Rv) as described above, the voltage dividing ratio of the voltage dividing circuit 4 is the DC voltage and the DC voltage. Is maintained at a constant value, that is, a constant voltage dividing ratio determined by the ratio of the resistance values of the voltage dividing unit 41 and the detecting unit 42, so that the V _CE detection by the voltage dividing circuit 4 itself is performed. Signal delay can be eliminated. Even in this case, in the configuration in which a noise filter (not shown) is provided on the input side of the protection circuit 23 in the detection signal line from the voltage dividing circuit 4 to the off circuit 21, for example, the delay due to the noise filter is a delay in the _VCE detection. Although there is a delay element other than the voltage dividing circuit 4 such as causing a delay, the delay time can be defined when selecting a circuit element such as the noise filter.

Accordingly, in the configuration of FIG. 3, the fixed constant (delay) that causes the delay of the _VCE detection signal cannot be defined as a device due to the presence of the stray capacitance C _S in the voltage dividing circuit. In the present invention, a fixed constant (delay) that causes a delay of the V _CE detection signal can be defined as a device.
Further, by adding a parallel capacitor and adjusting the filter time constants of the voltage dividing unit 41 and the detecting unit 42, the filter time constants of both are made equal to each other, and the delay of the V _CE detection signal by the voltage dividing circuit 4 is eliminated. Delay time can be shortened. Even if there is a difference in the filter time constant between the voltage divider 41 and the detector 42 after adjustment of the variable resistor 24 (Rv), if the difference is small, the delay of the V _CE detection signal by the voltage divider 4 Since it is small, there is an effect of reducing the detection delay time.

As a result, if the time constant of the filter 22 is set corresponding to a fixed constant (delay) defined as a device, malfunctions in normal switching at normal times can be reliably prevented. The margin included in the set value of the time constant can be made smaller than in the configuration of FIG. 3, and the time constant of the filter 22 can be made smaller.
Further, since the delay time of the _VCE detection is shortened, the delay of the off operation corresponding to the output short circuit can be reduced, so that the short circuit protection can be realized even with an element having a short circuit resistance (short).
In addition, according to the present invention, even when an element abnormality occurs, for example, in the unit of the power conversion device that causes an abnormality in the lower arm element, the increase in the _VCE of the upper arm element in the unit is reduced with a short delay time. Since it can detect and perform a high-speed protection operation, it is possible to reliably avoid the influence on other units and reduce the influence on equipment and operation.

In addition, the short circuit protection circuit of the power conversion device according to the present invention employs a method of “performing a short circuit protection operation based on the relationship between the output voltage of the semiconductor switching element of each arm and the element firing command”, so Compared to the conventional short-circuit protection circuit used, it has the following advantages, and is more suitable for space saving and reliability improvement of the device.
(A) Since no fuse for short-circuit protection is required, the number of parts can be reduced, and space can be saved by deleting the number of parts.
(B) Since a fuse for short circuit protection is unnecessary, the inductance in the device can be reduced.
(C) Since the protection operation can be performed at a speed higher than that of the fuse, the device capacity can be reduced.
(D) Since the protection operation can be performed at a speed higher than that of the fuse, it can be cut off with a smaller current at the time of the short circuit, so that the electromagnetic mechanical force generated by the current flowing at the time of the short circuit is reduced, and the size of the bus bar in the device Can also be reduced.

  The present invention has the advantages (a) to (d) as compared with the method using a fuse. “Short-circuit protection operation based on the relationship between the output voltage of the semiconductor switching element of each arm and the element firing command” In the short-circuit protection method, the voltage detection voltage dividing circuit and the detection unit each include at least one parallel circuit of a resistor and a capacitor, and the voltage dividing unit and the detection unit Each time constant is made equal to each other, and adjustment means for adjusting the deviation of these time constants is provided. As a result, the present invention shortens the detection delay time of the output voltage, can be cut off with a smaller current at the time of short circuit, and can further reduce the device capacity of the power converter, Smaller (shorter) elements can be used, and the configuration is more suitable as a short circuit protection circuit for a power converter.

FIG. 2 is a waveform diagram of each part for explaining the operation of FIG. Note that (a) shows a normal state and (b) shows a short circuit.
FIG. 2 shows the operation when the filter time constants of the voltage dividing unit 41 and the detecting unit 42 are adjusted to be equal as shown in Equation 1 above. It can be seen that the detection delay time is significantly shortened compared to the case.

Further, in this way, when the filter time constants of the voltage divider 41 and the detector 42 are adjusted to be equal to greatly reduce the detection delay time, a filter provided to prevent malfunction in normal switching Since the time constant of the circuit 22 can be significantly reduced, the off operation corresponding to the output short-circuit can be made faster.
In FIGS. 1 and 2, the voltage V of the upper arm IGBT is connected via the voltage dividing circuit 4 connected in parallel between the collector and emitter of the upper arm IGBT, as in FIGS. _A configuration is shown in which a _CE detection signal is input to the protection circuit 23 for the upper arm IGBT and the short arm protection of the upper arm IGBT is performed in combination with the element firing command. The same applies to the short arm protection of the lower arm IGBT. This can be done with a configuration.

That is, a lower arm IGBT voltage dividing circuit having the same configuration as that of the voltage dividing circuit 4 in FIG. 1 is provided in parallel between the collector and emitter of the lower arm IGBT (3B), and is provided in the gate drive circuit 2 (GDU). Is equipped with a protection circuit for the lower arm IGBT, etc., so that the _VCE detection signal of the lower arm IGBT is input to the protection circuit for the lower arm IGBT through the lower arm IGBT voltage dividing circuit. By forming a short-circuit protection circuit for the lower arm IGBT, the short-arm protection of the lower arm IGBT based on the _VCE detection signal of the lower arm IGBT and the element firing command, that is, when the lower arm IGBT is normal, The operation of protecting the lower arm IGBT when an accident current flows through the lower arm IGBT due to an element failure or the like of the upper arm can be performed similarly to the short-circuit protection of the upper arm IGBT.

Circuit diagram showing an embodiment of the present invention Waveform diagram of each part for explaining the operation of FIG. Circuit diagram showing a conventional example FIG. 3 is a characteristic diagram showing the relationship between current and voltage flowing through the element of FIG. Waveform diagram of each part for explaining the operation of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... DC power supply, 2 ... Gate drive circuit (GDU), 21 ... Off circuit, 22 ... Filter, 23 ... Protection circuit, 24 ... Variable resistor, 3A, 3B ... Switching element (IGBT: Insulated gate bipolar transistor), 4 ... voltage divider circuit, 41 ... voltage divider, 42 ... detector.

Claims (2)

In the short circuit protection circuit of the power conversion device that detects the output voltage of the semiconductor switching element that constitutes each arm of the power conversion device and performs the short circuit protection operation based on the relationship between the detected voltage and the element firing command,
A voltage dividing circuit formed by serially connecting a voltage dividing unit composed of at least one of a parallel connection circuit of a resistor and a capacitor and a detection unit consisting of at least one of a parallel connection circuit of a resistor and a capacitor. Power conversion characterized by being connected in parallel to the output side of the element, and having adjusting means for making the time constants of the voltage dividing unit and the detecting unit equal to each other and adjusting the deviation of these time constants Device short circuit protection circuit.   The short circuit protection circuit for a power converter according to claim 1, wherein the adjusting means is a variable resistor.

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