JPH10239360A - Excess current detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excess current detection circuit which can detect an excess current corresponding to an allowable characteristic value of the excess current of a converter element. SOLUTION: An excess current detection circuit 1 detects an excess current by changing an excess current detection level and a time constant thereof in accordance with a feed direction of an input current to a converter 2. An element passing the current at the converter is identified from the feed direction. An allowance suited to the element to detect the excess current is set. Accordingly, the element of the converter can be protected properly and enhanced in durability to a change of an input power source. The circuit is provided with a feed direction detection means 11 for detecting the feed direction of the input current to the converter and a current characteristic comparison means 12 for comparing a current characteristic of the input current of the converter with a comparison value for the detection of the excess current, thereby detecting the excess current. The comparison value of the current characteristic comparison means is changed on the basis of the feed direction of the current detected by the feed direction detecting means, to detect, the excess current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an overcurrent detection circuit, and more particularly to an overcurrent detection circuit in a converter portion of an input power unit in a drive amplifier of a main shaft or a feed shaft of a machine tool.

[0002]

2. Description of the Related Art Generally, a spindle motor such as an induction motor is used for a main shaft of a machine tool, and a servo motor such as a permanent magnet synchronous motor or an induction current type three-phase synchronous motor is used for a feed shaft. I have. The control of the spindle motor and the servo motor generally controls the current flowing through each phase winding by PWM (pulse width modulation) control or the like.

FIG. 9 is a schematic block diagram for explaining a conventional motor drive and overcurrent detection. FIG. 9 shows a case in which a motor 4 such as a spindle motor or a servomotor is driven, and a DC voltage obtained by converting a three-phase input power into an AC / DC by a converter 2 is subjected to switching control by an inverter 3 for driving. ing.

[0004] The DC voltage rectified by the converter 2 is supplied to an inverter 3, and each switching element of the inverter performs switching control by a control circuit (not shown), whereby the U, V, and W phases of the motor 4 are wound. Line current is controlled. Further, in the drive control of the motor by the converter and the inverter, control by a power regeneration system is known. This power regeneration system regenerates kinetic energy on the motor side to the power supply side, thereby performing motor deceleration control and the like.

In order to perform such a power regeneration control, the converter 2 has a regenerating transistor (IGBT) 22 used as a regenerative switching element and a rectifying diode 21 connected in parallel. by this,
A current flow is formed from the motor side to the input power supply side, and a regenerative operation is performed.

[0006] In the drive control of the power regeneration system of the motor, if an excessive load or a short circuit accident occurs, an excessive current flows through the converter, which may damage the diode or the regeneration transistor.

Conventionally, in order to prevent the element from being damaged by such an overcurrent, the input / output current of the converter is compared with a set level, and an overcurrent alarm is generated when the input / output current exceeds the set level. An overcurrent detection method may be provided. In FIG. 9, in the conventional overcurrent detection method, the input / output current is detected by the current detection circuit 13 from the input power supply side, and the maximum value of the absolute value of the input / output current detected by the maximum absolute value detection circuit 14 is obtained. When the maximum value exceeds a set level by the overcurrent detection circuit 5, an overcurrent alarm output is generated.

FIG. 10 is a more detailed schematic block diagram for explaining conventional motor driving and overcurrent detection. 10, a current detection circuit 13 detects, for example, an R-phase current and an S-phase current with a current detection resistor 13a and an insulation amplifier 13b, amplifies the signals with operational amplifiers 13c and 13d, and detects an R-phase current detection value and an S-phase current detection. Find the value. Further, a current detection value corresponding to the T phase is obtained from the R-phase current detection value and the S-phase current detection value by the operational amplifier 13e. The maximum value detection circuit 14 of the absolute value
After the rectifier 14a rectifies the three-phase current obtained from the above to obtain an absolute value, the operational amplifier 14b detects the maximum value.
The overcurrent detection circuit 5 compares the output of the maximum absolute value detection circuit 14 with the comparison voltage obtained from the voltage dividing resistor 5b by an operational amplifier 5a constituting a comparator. Outputs overcurrent alarm detection signal.

[0009]

The above-described overcurrent detection circuit detects an overcurrent alarm even for a current disturbance that does not require an overcurrent alarm detection, and has a problem in terms of operational reliability.

In general, a short-time withstand voltage representing an allowable value of an element with respect to a current flowing in a short time is defined by a product I ² t determined by a square value I ² of a current I and a conduction time t, and a regenerating transistor (IGBT) Is a level (usually twice the rated current) that must not be exceeded in a short time. In a converter that performs power regeneration control, the current flowing in the converter differs between the elements flowing during charging and during regeneration, and therefore, the allowable characteristics for overcurrent differ.

FIG. 11 is a schematic diagram showing the short-time tolerance I ² t of the diode and the regenerating transistor (IGBT).
Normally, in FIG. 11, the short-time tolerance I ² t of the diode
Is the short-time withstand capability I ² t of the regenerating transistor (IGBT)
Therefore, as the overcurrent allowable value I2 of the diode at a certain time t1, a current value larger than the overcurrent allowable value I1 of the regenerating transistor (IGBT) can be used.

Therefore, in the conventional overcurrent detection circuit, by setting the permissible value of the regenerating transistor having a small overcurrent permissible value to a set level, both the diode of the converter and the regenerating transistor are protected against overcurrent. It is carried out.

On the other hand, even in a normal operation state, the input / output current is disturbed due to the distortion of the power supply voltage, the imbalance of the inter-phase voltage, and the like.

Therefore, in the conventional overcurrent detection circuit, as described above, since the overcurrent detection is always performed with the overcurrent detection level set to a small overcurrent allowable value, an element capable of allowing a large overcurrent allowable value is used. Even when current flows through, overcurrent detection will be performed with a small overcurrent allowable value, and depending on the element, even if the current fluctuation is within the allowable range,
It is determined that an overcurrent has occurred.

As described above, if an alarm is output by always detecting an overcurrent based on a small allowable value of the overcurrent, an alarm is output even when it is not necessary to generate an alarm. If the system is stopped by this alarm output, unnecessary system stoppage occurs, and the operation reliability of the system including the converter is reduced.

Further, the conventional overcurrent detection circuit performs overcurrent detection by comparing only the current level, and does not judge the overcurrent detection based on the conduction time during which the current flows. FIG. 11
, The allowable time during which a certain overcurrent allowable value I2 is allowed is that the regenerating transistor (IGBT) is t1 while the diode is t2 longer than t1, and the diode is longer than the regenerating transistor (IGBT). Can withstand overcurrent for a long time. However, in the conventional overcurrent detection circuit, protection against overcurrent is performed for both the diode of the converter and the regenerative transistor by setting the time constant circuit to the shorter allowable time.

Therefore, in the conventional overcurrent detection circuit, as in the case of the above-described detection level, overcurrent detection is performed with a short overcurrent permissible time even for an element that allows a long overcurrent permissible time. However, depending on the element, even if the current varies within an allowable range, it is determined that an overcurrent occurs.

Therefore, the present invention solves the above-mentioned problems of the conventional overcurrent detection circuit, and provides an overcurrent detection circuit capable of detecting an overcurrent according to an allowable characteristic value of the converter element with respect to overcurrent. The purpose is to provide.

[0019]

SUMMARY OF THE INVENTION An overcurrent detection circuit according to the present invention performs overcurrent detection by changing an overcurrent detection level and a detection circuit time constant according to the direction of input current of a converter. Direction identifies the element in the converter where current is flowing, sets the tolerance for overcurrent detection adapted to that element, thereby properly protecting the converter element and immunity to input power fluctuations Is to increase.

The overcurrent detection circuit according to the present invention, in a first configuration for performing the above operation, includes a conduction direction detecting means for detecting a conduction direction of an input current of the converter in a converter for performing power regeneration control; A current characteristic comparing means for comparing the current characteristic of the input current with a comparison value for detecting the overcurrent to perform overcurrent detection, and a current characteristic based on the conducting direction of the current detected by the conducting direction detecting means. The comparison value of the comparison means is changed, and the overcurrent detection is performed with the comparison value corresponding to the energization direction by changing the comparison value. According to this configuration, it is determined which element of the converter the current is flowing through based on the energizing direction detected by the energizing direction detecting means, and the comparison value for overcurrent detection of the current characteristic comparing means is determined based on the energizing direction. Is changed to set an overcurrent allowable value suitable for the element. Then, by performing overcurrent detection using an overcurrent allowable value adapted to the element, it is possible to appropriately protect the element of the converter and increase the resistance to input power supply fluctuation (corresponding to claim 1).

A second configuration of the overcurrent detection circuit according to the present invention is as follows.
The comparison value for detecting the overcurrent is a current level, and the current characteristic comparing means changes the voltage level for detecting the overcurrent based on the conducting direction detected by the conducting direction detecting means. According to this configuration, by performing overcurrent detection using an allowable current level adapted to the element, it is possible to appropriately protect the element of the converter and increase the resistance to input power supply fluctuations.
Corresponding to).

A third configuration of the overcurrent detection circuit according to the present invention is as follows.
The comparison value for detecting the overcurrent is a time constant, and the current characteristic comparing means changes the time constant for detecting the overcurrent based on the energizing direction detected by the energizing direction detecting means. According to this configuration, by performing overcurrent detection using the time constant of the detection circuit adapted to the element, it is possible to appropriately protect the element of the converter and increase the resistance to input power supply fluctuations. Corresponding to).

Further, in a fourth configuration of the overcurrent detection circuit according to the present invention, the comparison value for detecting the overcurrent is a current level and a time constant, and the current characteristic comparing means includes an energizing direction detected by the energizing direction detecting means. , The voltage level and the time constant for detecting the overcurrent are changed. According to this configuration, by performing overcurrent detection using an allowable current level adapted to the element, it is possible to appropriately protect the element of the converter and increase the resistance to input power supply fluctuations. ).

In a fifth configuration of the overcurrent detection circuit according to the present invention, the current compared by the current characteristic comparison means is set to the maximum current of the input current of the converter. By performing overcurrent detection with this configuration, overcurrent detection can be performed for all levels of current flowing through each element of the converter (corresponding to claim 5).

[0025]

Embodiments of the present invention will be described below in detail with reference to the drawings. A configuration example of an embodiment of the present invention will be described with reference to a schematic block diagram for explaining the overcurrent detection circuit circuit of the present invention in FIG. FIG.
Shows a case in which a motor 4 such as a spindle motor or a servomotor is driven, and a three-phase input power is
The inverter 3 drives the DC voltage obtained by the AC / DC conversion by switching control of the DC voltage.

The DC voltage rectified by the converter 2 is supplied to an inverter 3, and the switching elements of the inverter perform switching control by a control circuit (not shown), whereby the U, V, and W phases of the motor 4 are wound. Controls line current. The power regeneration system is a control system that regenerates kinetic energy on the motor side to the power supply side, thereby performing deceleration control and the like of the motor. In order to perform such power regeneration control, the converter 2 connects a regenerating transistor (IGBT) 22 in parallel with a rectifying diode 21, thereby forming a current flow from the motor side to the input power source side, Regenerative operation is being performed.

In the drive control of the power regeneration system of the motor described above, the present invention provides an overcurrent detection circuit to prevent an overcurrent caused by an excessive load or a short circuit accident from flowing into the converter and damaging the diode and the regeneration transistor. 1 is provided.

An overcurrent detection circuit 1 according to the present invention comprises an energization direction detection circuit 1 for detecting an energization direction of a current flowing through a converter.
1 and a current characteristic comparison circuit 12 for comparing the current characteristic of the input current with a comparison value for overcurrent detection to perform overcurrent detection. The comparison value of the current characteristic comparison circuit 12 is determined based on the conduction direction. The overcurrent alarm is output when the current characteristic of the input current exceeds the comparison value, and the comparison value of the current characteristic comparison circuit 12 is changed according to the energization direction, so that it is optimal for the element of the converter. Overcurrent detection is performed according to an allowable value.

The input current of the converter is detected by a circuit configuration of a current detection overcurrent 13 connected to an input power supply and a maximum absolute value detection overcurrent 14 for detecting a maximum absolute value of the detection current. Then, the detected current is compared in the current characteristic comparison circuit 12 with an allowable value which is a comparison value. FIG. 1 shows a configuration example in which a three-phase current is detected by detecting a two-phase current with respect to a three-phase input power supply. The overcurrent 14 can be constituted by the circuit shown in FIG.

As for the input current of the converter, the direction of current flow differs between charging and regeneration, and the elements through which the current flows also differ. FIG. 2 and FIG. 3 are schematic block diagrams for explaining the energizing direction during charging and during regeneration. In FIG. 2, at the time of charging, a current flows through the diode 21 of the converter 2 (broken arrow in the figure). As described above, the diode is usually connected to the regenerative transistor (I
Compared with (GBT), the short-time withstand amount I ² t is large, and the shorter the energization time t, the larger the energization current withstand amount I can be set.

Therefore, when the overcurrent is detected by comparing the charging current with the comparison value in the current characteristic comparing circuit 12, the overcurrent flowing through the diode can be detected. Since the short-time capability of the diode is large, the detection level of the comparison value of the current characteristic comparison circuit 12 can be set high, and the detection time constant of the circuit can be set large. The detection time constant varies depending on the diode used, but can be generally several ms to several tens ms.

In FIG. 3, at the time of regeneration, a current flows through the regeneration transistor 22 of the converter 2 (broken arrow in the figure). As described above, the allowable current value of the normal regenerating transistor (IGBT) is smaller than that of the diode, and must not exceed this allowable value even for a moment.
The detection time constant cannot be set large.

Therefore, when the regenerative current is compared with a comparison value by the current characteristic comparing circuit 12 to detect an overcurrent,
An overcurrent flowing through the regenerating transistor (IGBT) is detected, so that the detection level of the current characteristic comparison circuit 12 is set to a small value corresponding to the regenerating transistor (IGBT), and the detection time constant of the circuit is set to a small value. Need to be. The detection time constant varies depending on the regenerating transistor (IGBT) used, but is generally several μs or less.

The energization direction detection circuit 11 shown in FIG. 1 detects the direction in which the input current of the converter 2 flows,
The current characteristic comparing circuit 1 discriminates whether the current direction is a current direction during charging or a current direction during regeneration.
2, and sets the detection level or the detection time constant, or both the detection level and the detection time constant, to a set value corresponding to the element through which the current flows.

Next, a more detailed configuration of the overcurrent detection circuit of the present invention will be described with reference to FIG. In FIG. 4, the point that the motor 4 is drive-controlled by a circuit configuration for performing power regeneration control including the converter 2 and the inverter 3 is the same as in FIG.
Includes an energization direction detection circuit 11 and a current characteristic comparison circuit 12. 4 omits the current detection circuit and the maximum absolute value detection circuit, and shows only a configuration in which the maximum current value is input to the current characteristic comparison circuit 12.

The conduction direction detecting circuit 11 is a comparator 11
a, the input current of one of the converters detected by the voltage detector 5 is input to the other input terminal. As a result, the comparator 11 detects the energizing direction of the converter, and inputs a signal having a different sign to the current characteristic comparing circuit 12 according to the energizing direction.

The current characteristic comparison circuit 12 includes a time constant circuit 20 that can change the detection time constant and an overcurrent level comparison circuit 30 that can change the detection level. Switching element 40
Is switched. The time constant circuit 20 includes a first time constant circuit 21 and a second time constant circuit 22 having different detection time constants, and the maximum current value is commonly input to both time constant circuits. The second time constant circuit 22 in FIG. 4 is grounded via the switching element 40. The switching element 40 is on / off controlled by a detection signal from the energization direction detection circuit 11, and when turned on, one of the time constant circuits (the second time constant circuit 22 in FIG. 4).
Is short-circuited to stop the operation of this time constant circuit, and only the other time constant circuit (the first time constant circuit 21 in FIG. 4) is operable.

Here, the detection time constant of the first time constant circuit 21 is set large, and the detection time constant of the second time constant circuit 22 is set small. According to this setting, the switching element 4
By turning on 0, the first time constant circuit 21 is operated to increase the detection time constant. On the other hand, by turning off the switching element 40, both the time constant circuits of the first time constant circuit 21 and the second time constant circuit 22 are operated. At this time, since both input terminals of the both time constant circuits are connected, the output is mainly output from the detection of the second time constant circuit 22 having a small detection time constant, and the detection is performed by operating the second time constant circuit 22 substantially. The time constant can be reduced. Thus, the detection time constant of the time constant circuit 20 can be changed.

The first time constant circuit 21 and the second time constant circuit 22 can be constituted by CR circuits.
The time constant can be adjusted by changing the value of each element.

The overcurrent level comparison circuit 30 comprises two comparators having a configuration including a first operational amplifier 31, a second operational amplifier 32, and a voltage dividing resistor 33. One input terminal of each of the operational amplifiers has a first operational amplifier. The outputs of the constant circuit 21 and the second time constant circuit 22 are input, and different comparison voltages set by the voltage dividing resistor 33 are input to the other input terminals. One of the time constant circuits (in FIG. The two operational amplifier 32) is grounded via the switching element 40. The switching element 40 is controlled to be turned on and off by a detection signal from the energization direction detection circuit 11. When the switching element 40 is turned on, one of the operational amplifiers (the second operational amplifier 32 in FIG. 4) is short-circuited, the comparison operation by this operational amplifier is stopped, and the other operational amplifier ( FIG.
Enables the comparison operation by the first operational amplifier 31),
When off, the comparison operation by both operational amplifiers is enabled.

Here, the detection level of the first operational amplifier 31 is set high, and the detection level of the second operational amplifier 32 is set low. According to this detection level setting,
When the switching element 40 is turned on, the comparison operation of the first operational amplifier 31 is performed, and the overcurrent can be detected at a large detection level. On the other hand, by turning off the switching element 40, both the first operational amplifier 31 and the second operational amplifier 32 are operated. At this time, the comparison levels of the two operational amplifiers are set differently, and the detection is performed in order from the comparator which normally sets the lower detection level.
, A detection circuit having a low detection level can be operated to reduce the detection level. Thereby, the detection level of the overcurrent level comparison circuit 30 can be changed.

Next, the operation of the overcurrent detection circuit according to the present invention will be described with reference to FIGS. FIGS. 5 and 6 show the operation during charging and detect the current flowing through the diode. FIGS. 7 and 8 show the operation during regeneration and detect the current flowing through the regenerating transistor. And a time constant circuit output and an alarm output.

In each of the figures, Ic represents the allowable value of the diode during charging, and Ib represents the allowable value of the regenerating transistor during regeneration. Note that the allowable value Ic is equal to the allowable value I.
b, and the time constant T1 at the time of charging is larger than the time constant T2 at the time of regeneration.

In the charging shown in FIGS. 5 and 6, the time constant is set to a large time constant T1, and the detection level is also set to a large allowable value Ic. FIG. 5A shows a case where the upper limit of the input current is the allowable value Ic during charging. In this case, the output of the time constant circuit reaches the allowable value Ic after the time constant T1, and at this point, an overcurrent alarm is output. FIG. 5B shows a case where the upper limit of the input current is larger than the allowable value Ic during charging. In this case, the output of the time constant circuit exceeds the allowable value Ic before the time constant T1 elapses, and reaches the input current level after the time constant T1. The overcurrent alarm is output when the value exceeds the allowable value Ic.

FIG. 6A shows a case where the upper limit of the input current is larger than the allowable value Ic during charging and shorter than the time constant T1. In this case, the output of the time constant circuit is the allowable value Ic.
Before it exceeds, and no overcurrent alarm is output.
FIG. 6B shows a case where the upper limit of the input current is smaller than the allowable value Ic during charging and longer than the time constant T1. Also in this case, the output of the time constant circuit does not exceed the allowable value Ic, and no overcurrent alarm is output.

Therefore, according to the overcurrent detection circuit of the present invention, as shown in FIG. 6A, even if the detection level exceeds the allowable value during charging, it is shorter than the detection time constant. Can prevent the output of an overcurrent alarm.

6 and 7, when the input current is at the level at the time of regeneration, neither the detection level nor the detection time constant will exceed the detection level at the time of charging.

At the time of regeneration in FIGS. 7 and 8, the time constant is set to a small time constant T2, and the detection level is also set to a small allowable value Ib. FIG. 7A shows a case where the upper limit of the input current is the allowable value Ic during regeneration. In this case, the output of the time constant circuit reaches the allowable value Ic after the time constant T2, and outputs an overcurrent alarm at this time. FIG. 7B shows a case where the upper limit of the input current is larger than the allowable value Ib during regeneration. In this case, the output of the time constant circuit exceeds the allowable value Ib before the time constant T2 elapses, and reaches the input current level after the time constant T2. The overcurrent alarm is output when the value exceeds the allowable value Ib.

FIG. 8A shows a case where the upper limit of the input current is larger than the allowable value Ib during regeneration and shorter than the time constant T2. In this case, the output of the time constant circuit is the allowable value Ib.
Before it exceeds, and no overcurrent alarm is output.
FIG. 8B shows a case where the upper limit of the input current is smaller than the allowable value Ib during regeneration and longer than the time constant T2. Also in this case, the output of the time constant circuit does not exceed the allowable value Ib, and no overcurrent alarm is output.

Therefore, according to the overcurrent detection circuit of the present invention, as shown in FIG. 8A, even when the detection level exceeds the allowable value during regeneration, it is shorter than the detection time constant. Can prevent the output of an overcurrent alarm.

[0051]

As described above, according to the overcurrent detection circuit of the present invention, overcurrent detection can be performed in accordance with the allowable characteristic value of the converter element for overcurrent.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram for explaining an overcurrent detection circuit according to the present invention.

FIG. 2 is a schematic block diagram for explaining an energizing direction during charging.

FIG. 3 is a schematic block diagram for explaining an energizing direction during regeneration.

FIG. 4 is a more detailed schematic block diagram illustrating an overcurrent detection circuit according to the present invention.

FIG. 5 is a diagram for explaining an operation during charging of the overcurrent detection circuit of the present invention.

FIG. 6 is a diagram for explaining an operation at the time of charging of the overcurrent detection circuit of the present invention.

FIG. 7 is a diagram for explaining an operation during regeneration of the overcurrent detection circuit of the present invention.

FIG. 8 is a diagram for explaining an operation during regeneration of the overcurrent detection circuit of the present invention.

FIG. 9 is a schematic block diagram for explaining a conventional motor drive and overcurrent detection.

FIG. 10 is a more detailed schematic block diagram for explaining driving and overcurrent detection of a conventional motor.

FIG. 11 shows a diode and a regeneration transistor (IGB).
It is a schematic diagram showing a short tolerance I ² t of T).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Overcurrent detection circuit 2 Comparator 3 Inverter 4 Motor 11 Energization direction detection circuit 12 Current characteristic comparison circuit 13 Current detection circuit 14 Maximum absolute value detection circuit 15 Current detector 20 Time constant circuit 21 First time constant circuit 22 Second Time constant circuit 30 Circuit level comparison circuit 31, 32 Comparator 33 Voltage dividing resistor 40 Switching element

Claims (5)

[Claims] In a converter for performing power regeneration control, an energizing direction detecting means for detecting an energizing direction of an input current of the converter, and a current characteristic of an input current of the converter being compared with a comparison value for detecting an overcurrent. Current characteristic comparing means for performing current detection, wherein the comparison value of the current characteristic comparing means is changed based on the current flowing direction detected by the current flowing direction detecting means, and the comparison value is changed according to the current direction. An overcurrent detection circuit characterized in that overcurrent detection is performed based on a value. 2. A comparison value for detecting an overcurrent is a current level, and the current characteristic comparing means changes a voltage level for detecting an overcurrent based on an energizing direction detected by an energizing direction detecting means. The overcurrent detection circuit according to claim 1, wherein 3. A comparison value for detecting an overcurrent is a time constant, and the current characteristic comparing means changes a time constant for detecting an overcurrent based on a conduction direction detected by a conduction direction detection means. The overcurrent detection circuit according to claim 1, wherein 4. A comparison value for detecting the overcurrent is a current level and a time constant, and the current characteristic comparing means includes a voltage for detecting an overcurrent based on a conduction direction detected by the conduction direction detection means. 2. The overcurrent detection circuit according to claim 1, wherein the level and the time constant are changed. 5. The overcurrent detection circuit according to claim 1, wherein the current compared by the current characteristic comparison means is a maximum current of an input current of the converter.