JP2012065459A - Overcurrent detecting device, and overcurrent detecting method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an overcurrent detecting device capable of reducing failures and accurately and surely detecting short circuit, and an overcurrent detecting method.SOLUTION: When a current slowly varies just like the time when a circuit is brought into an overcurrent state, an overcurrent is detected by a voltage between both terminals of a shunt resistance 11a. When the current varies greatly just like the time when the circuit is brought into a short-circuited state, the overcurrent is detected by a voltage between both terminals of a coil 11b. A hole element or the like is not used and the shunt resistance 11a and the coil 11b are combinedly used, and the overcurrent can be thereby surely detected while maintaining reliability similar to the time when the overcurrent is detected only by the shunt resistance 11a, by reducing failures in all cases such as when the circuit is normal, overloaded, and short-circuited.

Description

  The present invention relates to an overcurrent detection device and an overcurrent detection method, and more particularly to an overcurrent detection device that detects an overcurrent of a circuit in order to operate a circuit breaker that protects the circuit when an overload state or a short circuit state occurs. The present invention relates to an overcurrent detection method.

  For example, in a power supply circuit including a DC power supply and a load that is driven by the DC power supply through a power supply line, the DC power supply is used to protect the circuit when an overload or short-circuit condition occurs. A circuit breaker is provided between the load and the load to cut off the current. In addition, there exists an overload etc. which arise by adding the load exceeding a rating, etc., and there exists a ground fault etc. in a short circuit. The circuit breaker includes various circuit breakers such as a fuse, a semiconductor breaker using a semiconductor, and a circuit breaker.

  For example, when a short circuit occurs in a power supply circuit using a semiconductor circuit breaker, current interruption is started by a switching element composed of a collector and an emitter of the semiconductor circuit breaker. At this time, an electromotive force according to the time change of the current flowing from the DC power supply and the inductance of the power feeding circuit is applied to the semiconductor circuit breaker. Thereby, since the voltage value between the collector and emitter of a semiconductor circuit breaker increases rapidly, the semiconductor circuit breaker may be damaged.

  Therefore, when using a semiconductor circuit breaker, it is necessary to avoid damage to the element due to an increase in current passing through the element. For this reason, it is important to quickly determine an overload state or a short-circuit state. In view of this, a power supply circuit using a semiconductor circuit breaker includes a current detection circuit 100 disclosed in Patent Document 1, for example, as shown in FIG. In such a current detection circuit 100, a current detection resistor (shunt resistor) 101 which is an element for detecting a current, a Hall element instead of this, or the like is used. The current detection unit 102 of the current detection circuit 100 detects a current from the voltage between both terminals of the shunt resistor 101. Based on the detected current value, for example, it is determined that a short circuit has occurred in a system having a circuit.

JP-A-63-101765

  As described above, when a shunt resistor is used for current detection, if a change in current increases due to a short circuit or the like, not only the current component to be originally measured but also the inductance component of the shunt resistor increases. In some cases, the current cannot be accurately detected due to the inductance component.

  In addition, the component due to inductance that causes an error in the detected value changes in magnitude depending on the length of the short-circuited wiring. Therefore, the current value may not be derived only by unique data processing. . Conversely, if the resistance value of the shunt resistor is increased to reduce the contribution of the inductance component, the loss due to the shunt resistor may increase.

  On the other hand, when a current detector using a Hall element is used, a DC power source for operating the Hall element, a control circuit for controlling the operation of the Hall element, and the like are required, which complicates the circuit. For this reason, there has been a problem that reliability is lowered due to an increase in the failure rate of components constituting the circuit.

  Further, the output value from the Hall element also shifts depending on the temperature or the like. Therefore, there is a problem that current detection accuracy is lacking.

  In view of the above problems, an object of the present invention is to provide an overcurrent detection device and an overcurrent detection method that can detect an overcurrent accurately and reliably with few failures.

  In order to achieve the above object, an overcurrent detection device and an overcurrent detection method according to the present invention are configured as follows.

  Among the present inventions, a first overcurrent detection device corresponding to claim 1 is an overcurrent detection device that detects an overcurrent in order to operate a circuit breaker that cuts off the overcurrent by an external signal. A shunt resistor for detecting current, a coil connected in series with the shunt resistor for detecting current, and first voltage detecting means for detecting a voltage between both terminals of the shunt resistor, A second voltage detecting means for detecting a voltage between both terminals of the coil; a voltage between both terminals of the shunt resistor detected by the first voltage detecting means; and a detection by the second voltage detecting means. Current detection means for detecting the current flowing through the shunt resistor and the coil and the amount of change in the current based on the voltage between the two terminals of the coil.

  According to the first overcurrent detection device, the first voltage detection unit detects the voltage between both terminals of the shunt resistor. Further, the second voltage detecting means detects the voltage between both terminals of the coil. Then, the current detecting means is configured to shunt based on the voltage between both terminals of the shunt resistor detected by the first voltage detecting means and the voltage between both terminals of the coil detected by the second voltage detecting means. The current flowing through the resistor and the coil and the amount of change in the current are detected. When the current changes slowly as in the case where the circuit is in an overcurrent state, the voltage between the two terminals of the coil does not change greatly, so the overcurrent is detected by the voltage between the two terminals of the shunt resistor. Further, when the current changes greatly as in the case where the circuit is short-circuited, the voltage between both terminals of the coil changes greatly, so that overcurrent is detected based on the voltage between both terminals of the coil. In this way, it has a shunt resistor and a coil and can accurately determine the amount of change in current when the circuit is in an overcurrent state and the amount of change in current when the circuit is in a short circuit state. For this reason, it is possible to more reliably detect an overcurrent generated when the circuit is overloaded or short-circuited.

  According to a second overcurrent detection device of the present invention, the second overcurrent detection device interrupts the circuit breaker when a change amount of the current flowing through the shunt resistor and the coil exceeds a predetermined change amount. It is characterized by comprising a cutoff start signal output means for outputting a signal for starting.

  According to the second overcurrent detection device, the breaking start signal output means starts breaking the breaker when the change amount of the current flowing through the shunt resistor or the coil exceeds a predetermined change amount. Outputs a signal to As a result, it is possible to operate the circuit breaker that interrupts the overcurrent by a signal from the outside and to interrupt the overcurrent without damaging the circuit breaker.

  A third overcurrent detection device according to a third aspect of the present invention is characterized in that the coil has an inductance larger than an inductance of a wiring to which the coil is connected.

  According to the third overcurrent detection device, the coil having an inductance larger than the inductance of the wiring to which the coil is connected is selected. As a result, the inductance component of the coil becomes larger than the noise level, and it is possible to accurately detect the amount of change in current caused by the coil and to increase the accuracy of detecting the overcurrent of the circuit.

  According to a fourth overcurrent detection device of the present invention, the circuit breaker is a semiconductor circuit breaker using a semiconductor.

  According to said 4th overcurrent detection apparatus, it becomes possible to use a semiconductor circuit breaker as a circuit breaker which interrupts | blocks an overcurrent with the signal from the outside. Even when a semiconductor circuit breaker is used, it is possible to prevent an element from being damaged due to an increase in current passing through the element and to interrupt an overcurrent of the circuit.

  An overcurrent detection method corresponding to claim 5 of the present invention is an overcurrent detection method for detecting an overcurrent in order to operate a circuit breaker that interrupts the overcurrent by an external signal, and includes a shunt. A voltage between both terminals of the resistor is detected, a voltage between both terminals of the coil connected in series with the shunt resistor is detected, and between the both terminals of the shunt resistor detected by the first voltage detecting means. Detecting a current flowing through the shunt resistor and the coil and a change amount of the current based on a voltage and a voltage between both terminals of the coil detected by the second voltage detecting unit. To do.

  According to the overcurrent detection method, it is possible to obtain the same action as the first overcurrent detection device.

  According to the present invention, by using a combination of a shunt resistor and a coil, while maintaining the same reliability as when detecting a current by a shunt resistor alone, any state during normal operation, overload, or short circuit However, it is possible to reliably detect a short circuit. In addition, since no element such as a Hall element is used, a circuit for operating the Hall element is not required, so that the failure rate can be kept low.

  Furthermore, by using a coil in addition to the shunt resistor, it is possible to determine that the current changes greatly as when the circuit is in a short circuit state, so it is possible to detect a short circuit rather than detecting a short circuit using only the shunt resistor. It is possible to reduce the time required to detect Thereby, the failure of the circuit breaker can be further avoided.

It is a circuit block diagram which shows the circuit structure of the electric power feeding circuit 10 to which the overcurrent detection apparatus 11 which concerns on this invention is applied. It is a flowchart which shows the flow of the process which detects the overcurrent in the control part 11e. It is a circuit block diagram which shows the circuit structure of the conventional overcurrent detection apparatus 100.

  Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In each drawing referred to in the following description, components equivalent to those in the other drawings are denoted by the same reference numerals.

(Embodiment)
(Circuit configuration of the power supply circuit 10 to which the overcurrent detection device 11 is applied)
FIG. 1 is a circuit configuration diagram showing a circuit configuration of a power feeding circuit 10 to which an overcurrent detection device 11 according to the present invention is applied.

  A power supply circuit 10 illustrated in FIG. 1 includes an overcurrent detection device 11 and a semiconductor circuit breaker 12. A DC power source 21 that outputs a DC current and a load 22 that is operated by the DC power source 21 are connected to each other by a power supply line including a positive electrode line 23 and a positive electrode line 24. Then, a current flows from the DC power source 21 to the load 22 through the feeder line.

  The overcurrent detection device 11 is connected on the positive line 23 and detects the current value of the current flowing through the connection point. Then, when the detected current value reaches a predetermined current value, the overcurrent detection device 11 outputs a signal for starting the breaking of the semiconductor circuit breaker 12 to the semiconductor breaker 12.

  The overcurrent detection device 11 includes a shunt resistor 11a, a coil 11b, voltage detection units 11c and 11d, and a control unit 11e.

  The shunt resistor 11a is an element that is connected to the positive electrode line 23 and is provided for detecting a current. A voltage is generated in the shunt resistor 11a when a current flows.

  The coil 11b is an element that is connected on the positive electrode line 23 and is used to detect a current, like the shunt resistor 11a. The coil 11b generates a voltage corresponding to the amount of change when the current changes greatly during a unit time. That is, no voltage is generated when the amount of change in current is small. Since the inductance of the coil 11b needs to be larger than the noise level of the output of the coil 11b, the coil 11b has an inductance that is several times larger than the inductance of the power supply line connected to the coil 11b. Choose what you have.

  The shunt resistor 11a and the coil 11b described above are connected in series with each other on the positive line 23 between the semiconductor circuit breaker 12 and the load 22 as shown in the figure.

  The voltage detector 11c is connected between both terminals of the shunt resistor 11a, and detects a voltage between both terminals of the shunt resistor 11a.

  The voltage detection unit 11d is connected between both terminals of the coil 11b and detects a voltage between both terminals of the coil 11b.

  The control unit 11e includes a current detection unit 11f and a cutoff start signal output unit 11g. Based on the voltage between both terminals of the shunt resistor 11a detected by the voltage detector 11c and the voltage between both terminals of the coil 11b detected by the voltage detector 11d, the current detector 11f The current flowing through the coil 11b and the amount of change in the current are detected. The cutoff start signal output unit 11g outputs a signal for causing the semiconductor circuit breaker 12 to start blocking current when the change amount of the current detected by the current detection unit 11f exceeds a predetermined change amount, that is, The gate voltage of the semiconductor circuit breaker 12 is controlled so that the overcurrent can be interrupted by the semiconductor circuit breaker 12.

  The semiconductor circuit breaker 12 is connected on the positive line 23 between the DC power source 21 and the load 22, and starts interrupting current based on a signal output from the overcurrent detection device 11.

  First, a current flows through the shunt resistor 11a and the coil 11b. When the current flows, a voltage is generated in the shunt resistor 11a by multiplying the current flowing through the shunt resistor 11a by the resistance value of the shunt resistor 11a. However, since there is almost no change in current in an overload state or a normal state that is not short-circuited, no voltage is generated in the coil 11b. For this reason, it is possible to accurately measure the current based on the voltage across the terminals of the shunt resistor 11a and determine that the current state is not an overload state or a short-circuit state.

  Further, even when the load current gradually increases and becomes an overcurrent state due to the addition of a load exceeding the rating, the current can be accurately measured by the shunt resistor 11a as in the normal state described above. Therefore, when the voltage across the terminals of the shunt resistor 11a exceeds a predetermined voltage value, it can be determined that an overload condition is present.

  In addition, when a short circuit occurs and the current flowing through the circuit suddenly increases and an overcurrent state occurs, the shunt resistor 11a has the sum of the resistance component voltage and the inductance component voltage as described above. Is output. On the other hand, a voltage corresponding to the amount of change in current per unit time is generated in the coil 11b as represented by V = L × di / dt. That is, the phenomenon that the voltage is generated in the coil 11b occurs when the current changes greatly. For this reason, when a large voltage is generated in the coil 11b, it can be determined that the coil 11b is in a short-circuit state. Further, by using the coil 11b, it is possible to detect a short-circuited state in a shorter time than detecting a short-circuit only by the shunt resistor 11a.

(Overcurrent detection process flow in the control unit 11e)
Next, the flow of overcurrent detection processing in the control unit 11e will be described with reference to FIG.

  First, the control unit 11e inputs a voltage between both terminals of the shunt resistor 11a detected by the voltage detection unit 11c and a voltage between both terminals of the coil 11b detected by the voltage detection unit 11d (step S101). . The current detection unit 11f detects the current flowing through the shunt resistor 11a and the coil 11b and the amount of change in the current based on the voltage between both terminals of the shunt resistor 11a and the voltage between both terminals of the coil 11b ( Step S102).

  When the change amount of the current flowing through the coil 11b detected by the current detection unit 11f exceeds a predetermined change amount (YES in step S103), the cutoff start signal output unit 11g determines that the circuit is in a short circuit state. to decide. The interruption start signal output unit 11g outputs a signal for causing the semiconductor breaker 12 to start breaking, that is, controls the gate voltage so that the overcurrent is interrupted by the semiconductor breaker 12 (step S104).

  The interruption start signal output unit 11g is a case where the amount of change in the current flowing through the coil 11b by the current detection unit 11f does not exceed the predetermined change amount (NO in step S103), and the current detection unit 11f If the amount of change in the current flowing through the resistor 11a exceeds a predetermined amount of change (YES in step S105), it is determined that the circuit has been overloaded. Then, the interruption start signal output unit 11g outputs a signal for causing the semiconductor breaker 12 to start breaking, that is, controls the gate voltage so that the overcurrent is interrupted by the semiconductor breaker 12 (step S106).

  When the change amount of the current flowing through the shunt resistor 11a by the current detection unit 11f does not exceed the predetermined change amount (NO in step S105), it is a normal state that is not overloaded or short-circuited. Therefore, the process returns to step S101, and the above-described overcurrent detection process is continued.

(Modification)
Note that the occurrence of a short circuit in the circuit is detected by the fact that the current flowing through the coil 11b suddenly increases as described above, and a voltage is generated between both terminals of the coil 11b. However, if a short circuit occurs partially in the circuit or the length of the feeder line is long, the rise of the current flowing through the coil 11b may be gradual even if a short circuit occurs in the circuit. In this case, it can be determined that the circuit is short-circuited based on the magnitude of the voltage between both terminals of the shunt resistor 11a. Therefore, it is possible to improve the detection accuracy of the short circuit by detecting the short circuit using the shunt resistor 11a and the coil 11b in combination rather than detecting the short circuit only by the voltage between both terminals of the coil 11b.

  In addition, as described above, the coil 11b having an inductance several times larger than the inductance of the power supply line connected to the coil 11b is usually used, but there are cases where the output from the coil contains a lot of noise components. In this case, for example, an integration circuit in which a shunt resistor 11a and a capacitor are connected may be provided in parallel with the coil 11b. Then, it is possible to determine an overcurrent state or a short-circuit state based on the output value of the integrating circuit, that is, the integrated value.

(Summary)
As described above, in the overcurrent detection device 11 according to the present embodiment, when the current changes slowly as in the overcurrent state, the overcurrent is detected by the voltage across the shunt resistor 11a. Further, when the current changes greatly as when a short circuit occurs, an overcurrent is detected by the voltage between both terminals of the coil 11b.

  Thus, by using a combination of the shunt resistor 11a and the coil 11b without using a Hall element or the like, the same reliability as when detecting an overcurrent of the circuit with only the shunt resistor 11a is maintained, and normal operation is performed. It is possible to reduce the number of failures in any of the states of overload, overload, and short circuit, and reliably detect the overcurrent of the circuit. Further, by using the coil 11b in addition to the shunt resistor 11a, the time required to detect a short circuit can be shortened. Thereby, the failure of the circuit breaker can be further avoided.

  INDUSTRIAL APPLICABILITY The present invention can be used as an overcurrent detection device that detects an overcurrent in order to operate a circuit breaker such as a semiconductor circuit breaker that cuts off a current using an external signal.

DESCRIPTION OF SYMBOLS 11 Overcurrent detection apparatus 11a Shunt resistance 11b Coil 11c, 11d Voltage detection part 11e Control part 11f Current detection part 11g Breaking start signal output part

Claims (5)

An overcurrent detection device that detects an overcurrent in order to operate a circuit breaker that interrupts the overcurrent by a signal from the outside,
A shunt resistor for detecting the current,
A coil connected in series with the shunt resistor for detecting current;
First voltage detecting means for detecting a voltage between both terminals of the shunt resistor;
Second voltage detecting means for detecting a voltage between both terminals of the coil;
Based on the voltage between both terminals of the shunt resistor detected by the first voltage detection means and the voltage between both terminals of the coil detected by the second voltage detection means, the shunt resistance and Current detection means for detecting the current flowing through the coil and the amount of change in the current;
An overcurrent detection device comprising:   When the amount of change in the current flowing through the shunt resistor and the coil exceeds a predetermined amount of change, the device includes a break start signal output means for outputting a signal for causing the breaker to start break. The overcurrent detection device according to claim 1.   The overcurrent detection device according to claim 1, wherein the coil has an inductance larger than an inductance of a wiring to which the coil is connected.   The overcurrent detection device according to claim 1, wherein the circuit breaker is a semiconductor circuit breaker using a semiconductor. An overcurrent detection method for detecting an overcurrent in order to operate a circuit breaker that interrupts an overcurrent by an external signal,
Detect the voltage between both terminals of the shunt resistor,
Detecting the voltage between both terminals of the coil connected in series with the shunt resistor;
Based on the voltage between both terminals of the shunt resistor detected by the first voltage detection means and the voltage between both terminals of the coil detected by the second voltage detection means, the shunt resistance and An overcurrent detection method comprising detecting a current flowing through the coil and a change amount of the current.

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