JP6981437B2 - Failure detector - Google Patents

Description

The present invention relates to a failure detection device for detecting a failure of a relay in an inrush current limiting circuit.

A conventional failure detection device for detecting a failure of a relay in an inrush current limiting circuit will be described with reference to FIG. 1.

In the device shown in FIG. 1 (hereinafter referred to as AC device), the three-phase AC from the commercial power source 50 is rectified by the rectifier 40 and supplied to the DC load 42 via the pair of power lines 41p and 41n. It is a device. As shown in the figure, a smoothing capacitor 45 is provided between the power lines 41p and 41n of the AC device. Further, an inrush current limiting circuit 30 in which a current limiting resistor R0 and a relay 31 are connected in parallel is inserted in the power line 41p.

The relay 31 is a relay (mechanical relay, solid state relay) that is turned on after the power of the AC device is turned on. The on-timing of the relay 31 is determined based on the elapsed time after the power is turned on and the degree of charging of the smoothing capacitor 45.

A circuit including a resistor Rc, a photocoupler 51 (light emitting diode 51a and a phototransistor 51b), a comparator 52, and the like is a conventional failure detection device for detecting a failure of the relay 31. This failure detection device detects the failure of the relay 31 by each part functioning as follows. In the following description, the symbols R0 and Rc of each resistor are also used as symbols representing the resistance value of each resistor.

When the voltage V between both ends of the current limiting resistor R0 becomes larger than the forward voltage VF of the light emitting diode 51a of the photocoupler 51, the current Ic (= (V-VF) / Rc) flows through the light emitting diode 51a and becomes the current Ic. The light emitting diode 51a emits light with the corresponding intensity. Then, the light emitting intensity of the light emitting diode 51a according to the current Ic is converted into a voltage (hereinafter referred to as an Ic-corresponding voltage) by the phototransistor 51b and the resistor RL. After that, the Ic-corresponding voltage and the threshold voltage Vth are compared by the comparator 52, and the presence or absence of a failure of the relay 31 is determined at the level of the output signal (state signal in the figure) of the comparator 52.

Japanese Unexamined Patent Publication No. 7-23523

As is clear from the above description, the conventional failure detection device cannot detect the failure of the relay 31 unless a current Ic having a certain current value flows through the light emitting diode 51a when the relay 31 fails. .. Then, as the bus current value immediately before the failure of the relay 31 becomes smaller, the current value of the current Ic at the time of the failure of the relay 31 also becomes smaller. Therefore, the conventional failure detection device has a bus current value capable of detecting the failure of the relay 31. There is a limit value (lower limit value) determined by the specifications of each component (resistor Rc, resistance value of R0, etc.). By lowering the resistance value of the resistor Rc, the current value of the current Ic at the time of failure of the relay 31 can be made larger, but the resistor Rc with low resistance and high resistance to inrush current has a large size. turn into. Therefore, it has been extremely difficult to configure the conventional failure detection device compactly so that the failure of the relay can be detected even at a low current.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a compact failure detection device capable of detecting a failure of a relay even at a low current.

The failure detection device according to one aspect of the present invention is a device for detecting the failure of the relay of the inrush current limiting circuit in which the current limiting resistor and the relay are connected in parallel, which is inserted in the power supply line of the inrush current limiting target device. Therefore, there is a first voltage dividing circuit that divides the voltage at one end of the current limiting resistor at a predetermined voltage dividing ratio, and a second voltage dividing circuit that divides the voltage at the other end of the current limiting resistor at the predetermined voltage dividing ratio. The circuit, the differential amplifier to which the output voltage of the first voltage dividing circuit and the output voltage of the second voltage dividing circuit are input, and the output voltage and the threshold voltage of the differential amplifier are compared, and the comparison result is obtained. The voltage difference between the comparison unit that outputs the signal to be represented and the end of both the first voltage dividing circuit and the second voltage dividing circuit that are not connected to the power supply line and the power supply line is adjusted to a predetermined voltage difference. It is equipped with a standard voltage power supply.

That is, the above configuration of the failure detection device does not require a low resistance and high resistance resistor (a first and second voltage dividing circuit can be realized by a combination of two high resistance resistors). .. Therefore, if the above configuration is adopted, it is possible to realize a compact failure detection device (with a small mounting area) that can detect a relay failure even at a low current.

Even if the comparator is a comparator that compares the input voltage with one threshold voltage (reference voltage), the comparison unit compares the output voltage of the differential amplifier with the two threshold voltages, and the output voltages are the two. It may be a window comparator that outputs a signal indicating whether or not it is within the voltage range with the threshold voltage as the boundary.

The inrush current limiting circuit in which the failure of the relay is detected by the failure detection device may be a circuit inserted in the power line through which direct current flows or a circuit inserted in the power line through which alternating current flows.

According to the present invention, it is possible to provide a compact failure detection device (with a small mounting area) that can detect a relay failure even at a low current.

FIG. 1 is a schematic configuration diagram of an AC device for explaining the configuration of a conventional failure detection device. FIG. 2 is a schematic configuration diagram of an AC device in which the failure detection device according to the embodiment is used.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows a schematic configuration of an AC device 1 in which the failure detection device according to the embodiment of the present invention is used.

When the power is turned on, the AC device 1 is a device in which the three-phase AC from the commercial power source 50 is rectified by the rectifier 40 and supplied to the DC load 42 via the pair of power supply lines 41p and 41n. The rectifier 40 of the AC device 1 is a diode bridge rectifier, and the DC load 42 is a load (system) composed of a three-phase motor and an inverter. Further, "the power of the AC device 1 is turned on" means "a state in which a current flows through the pair of power lines 41p and 41n". Therefore, the AC device 1 is controlled so that the DC load 42 consumes power even if the power is turned on by turning on the breaker or the like provided between the commercial power source 50 and the rectifier 40. The power may be turned on by this.

As shown in the figure, the AC device 1 includes a smoothing capacitor 45 arranged between the power supply lines 41p and 41n, and an inrush current limiting circuit 30 inserted in the power supply line 41p. The inrush current limiting circuit 30 is a circuit in which the current limiting resistor R0 and the relay 31 are connected in parallel, and the AC device 1 controls the on / off of the relay 31 of the inrush current limiting circuit 30 and the DC load 42. It also has a microcontroller (MCU) 18 for control.

The failure detection device according to the present embodiment is a device for detecting a failure (open failure) of the relay 31, and is a voltage dividing unit 10, a differential amplifier 11, a window comparator 12, a standard voltage power supply 13, and a signal transmission circuit 15. It is composed of and.

The standard voltage power supply 13 is a power supply that outputs a standard voltage because the differential amplifier 11 is used within the common mode input voltage range. As the standard voltage power supply 13, for example, one that outputs the voltage of the power supply line 41p in a state where the relay 31 is turned on after the power of the AC device 1 is turned on and the voltage between the power supply lines 41p and 41n is stable is used.

As shown, the standard voltage power supply 13 is arranged between the power supply line 41p and the end of the voltage divider circuits 10a and 10b that are not connected to the power supply line. Therefore, the standard voltage power supply 13 adjusts the voltage difference between the power supply line 41p and the end of the voltage dividing circuits 10a and 10b that are not connected to the power supply line to the standard voltage.

The voltage dividing unit 10 is a circuit for converting the voltage at each end of the current limiting resistor R0 into a voltage having a magnitude suitable for input to the differential amplifier 11. The voltage dividing portion 10 includes a first voltage dividing circuit 10a composed of a resistor R1 and a resistor R2 connected to one end (the end on the DC load 42 side) of the current limiting resistor R0, and a current limiting resistor. It is composed of a second voltage dividing circuit 10b composed of a resistor R3 and a resistor R4 connected to one end of R0. Hereinafter, the resistance value of the resistor Rn (n = 1 to 4) is also referred to as Rn.

As each resistor of the voltage dividing unit 10, those having the same voltage dividing ratio r of each voltage dividing circuit 10a and 10b (for example, 0.01) are adopted. That is, resistors R1 to R4 that satisfy "R1 / (R1 + R2) = R3 / (R3 + R4)" are adopted in the voltage dividing unit 10. Further, the voltage dividing portion 10 is composed of resistors R1 to R4 having relatively high resistance (that is, resistors R1 to R4 having a small size).

As shown in the figure, the voltage signal Vout1 output from the first voltage divider circuit 10a is input to the + input terminal (non-inverting input terminal) of the differential amplifier 11. Further, the voltage signal Vout2 output from the second voltage dividing circuit 10b is input to the − input terminal (inverting input terminal) of the differential amplifier 11. Hereinafter, the voltage value of the voltage signal Vx (x = out1, out2, etc.) is also referred to as Vx.

The differential amplifier 11 is an amplifier that amplifies the difference "Vout1-Vout2" of the input voltage to the two input terminals with a predetermined differential gain Ad. When the voltage dividing ratio of each voltage dividing circuit 10a and 10b of the voltage dividing unit 10 is expressed as r, it can be expressed as Vout1 = V1 × r and Vout2 = V2 × r. Therefore, the voltage Vout of the output signal Vout of the differential amplifier 11 is a value represented by the following equation (1), that is, a value proportional to the voltage difference “V1-V2” across the current limiting resistor R0.

Vout = Ad × r × (V1-V2)… (1)
The voltage signal Vout output by the differential amplifier 11 is input to the window comparator 12. A positive reference voltage Vp and a negative reference voltage Vm are given to the window comparator 12. The reference voltage Vp is a voltage predetermined as a threshold value on the positive side of the detection voltage (value of Vout) to be determined that the relay 31 has failed. The reference voltage Vm is a voltage predetermined as a threshold value on the negative side of the detection voltage at which the relay 31 should be determined to have failed. The reference voltage Vp is determined based on an estimated value or an experimental value of the detected voltage when the relay 31 fails in a state where a desired amount of current is flowing to the DC load 42 side in the power supply line 41p. Similarly, the reference voltage Vm is determined based on an estimated value or an experimental value of the detected voltage when the relay 31 fails in a state where a desired amount of current is flowing to the rectifier 40 side in the power supply line 41p. The current flows through the power line 41p to the rectifier 40 side when the regenerative power is generated on the DC load 42 side. Further, the desired amount of current is the minimum amount of current that can detect the failure of the relay 31.

As described above, the differential amplifier 11 outputs a voltage signal Vout having a voltage Vout proportional to the voltage difference “V1-V2” across the current limiting resistor R0. The reference voltages Vp and Vm are given to the window comparator 12 to which the voltage signal Vout is input. Therefore, if an open failure occurs in the relay 31 during the operation of the AC device 1, the level of the voltage signal Vs output by the window comparator 12 changes to a different level (low level in the configuration of FIG. 2). Will be done.

The signal transmission circuit 15 is a circuit for transmitting the voltage signal Vs from the window comparator 12 to the MCU 18 while being electrically isolated by the photocoupler 16. While the relay 31 is on (during the operation of the AC device 1), the MCU 18 monitors the state of the relay 31 (presence or absence of failure) based on the voltage signal Vs, and if the relay 31 fails, the MCU 18 monitors the state of the relay 31 (whether or not there is a failure). A process for stopping the operation of the AC device 1 and a process for notifying the user that the relay 31 has failed are performed. Due to the circuit configuration, during the period from when the power of the AC device 1 is turned on until the relay 31 is turned on, a voltage signal Vs at a level indicating that the relay 31 has failed is input to the MCU 18. Since this voltage signal Vs does not indicate that the relay 31 has failed, the MCU 18 particularly processes even if a voltage signal Vs at a level indicating that the relay 31 has failed is input before the relay 31 is turned on. Do not do.

As described above, the configuration adopted in the failure detection device according to the present embodiment detects the failure of the relay 31 without using a low resistance and high resistance resistor, and also detects the failure of the relay 31. There is no particular limitation on the current value that can detect the failure of. Therefore, if the above configuration is adopted, it is possible to realize a compact failure detection device (with a small mounting area) that can detect a relay failure even at a low current.

《Transformation form》
The above-mentioned failure detection device can perform various modifications. For example, the failure detection device may be used as a device for detecting a failure of a relay in an inrush current limiting circuit for limiting an AC inrush current. Further, the inrush current limiting circuit to be detected by the failure detection device may be provided in any device.

The failure detection device may be transformed into a device equipped with a comparator instead of the window comparator 12. However, if the failure detection target of the failure detection device is the relay of the inrush current limiting circuit that limits the DC inrush current of the device that generates regenerative power, by adopting the window comparator 12, the relay can be relayed even during regeneration. It is preferable to be able to detect the failure of the.

<< Additional notes >>
A current limiting resistor (R0) inserted in the power line (41p) of the inrush current limiting target device (1).
) And the relay (31) are connected in parallel to detect the failure of the relay (31) of the inrush current limiting circuit (30).
A first voltage dividing circuit (10a) that divides the voltage at one end of the current limiting resistor (R0) at a predetermined voltage dividing ratio, and
A second voltage dividing circuit (10b) that divides the voltage at the other end of the current limiting resistor (R0) at the predetermined voltage dividing ratio.
A differential amplifier (11) to which the output voltage of the first voltage divider circuit (10a) and the output voltage of the second voltage divider circuit (10b) are input.
A comparison unit (12) that compares the output voltage of the differential amplifier (11) with the threshold voltage and outputs a signal representing the comparison result.
The voltage difference between the end of both the first voltage divider circuit (10a) and the second voltage divider circuit (10b) not connected to the power supply line (41p) and the power supply line (41p) is a predetermined voltage. A standard voltage power supply (13) that adjusts to the difference, and
A failure detection device.

10 Voltage divider 11 Differential amplifier 12 Window comparator 13 Standard voltage power supply 15 Signal transmission circuit 16 Photocoupler 18 Microcontroller 30 Inrush current limit circuit 31 Relay 40 Rectifier 42 DC load

Claims (2)

It is a failure detection device that detects the failure of the relay of the inrush current limiting circuit in which the current limiting resistor and the relay are connected in parallel, which is inserted in the power supply line of the device subject to inrush current limitation.
A first voltage divider circuit that divides the voltage at one end of the current limiting resistor at a predetermined voltage divider ratio, and
A second voltage divider circuit that divides the voltage at the other end of the current limiting resistor at the predetermined voltage divider ratio, and
A differential amplifier to which the output voltage of the first voltage divider circuit and the output voltage of the second voltage divider circuit are input, and
A comparison unit that compares the output voltage of the differential amplifier with the threshold voltage and outputs a signal representing the comparison result.
A standard voltage power supply that adjusts the voltage difference between the power supply line and the end of both the first voltage divider circuit and the second voltage divider circuit that are not connected to the power supply line to a predetermined voltage difference.
A failure detection device. The comparator compares the output voltage of the differential amplifier with the two threshold voltages, and outputs a signal indicating whether or not the output voltage is within the voltage range with the two threshold voltages as boundaries. Is a window comparator
The failure detection device according to claim 1.

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