JP7487455B2 - Load Status Monitoring Device - Google Patents

Description

The present invention relates to a load condition monitoring device.

There are known devices that monitor the state of a load that operates using power from a power supply device. For example, Patent Document 1 discloses a switching power supply device that performs an overcurrent protection operation to limit the output current by outputting an overcurrent protection operation signal to a switching element control signal control unit when the voltage of a current-voltage conversion unit reaches a threshold value due to the current flowing through the switching element.

JP 2018-113811 A

However, in a load status monitoring device that monitors the status of a load using a control device that operates by receiving power from a power supply device having an overcurrent protection circuit, when an overcurrent occurs, the overcurrent protection circuit is activated and the power supply to the control device is restricted. As a result, the control device may not be able to determine an overcurrent abnormality or respond appropriately to the occurrence of an overcurrent abnormality.

The load status monitoring device of the present invention is a load status monitoring device that monitors the load status using a control device that operates by receiving power from a power supply device having an overcurrent protection circuit, and the main purpose of the device is to appropriately determine an overcurrent abnormality and to appropriately respond to the occurrence of an overcurrent abnormality.

The load condition monitoring device of the present invention employs the following means to achieve the above-mentioned main objective.

The load condition monitoring device of the present invention comprises:
A load status monitoring device for a system including a power supply device having an overcurrent protection circuit that detects an overcurrent and limits power supply, and a load connected to a power line from the power supply device, comprising:
a current detection circuit for detecting a current flowing through the power supply line;
a relay for connecting and disconnecting the power supply line;
a control device that receives power from the power supply device and operates to drive the relay;
Equipped with
the control device drives the relay to be turned off when a state in which the current detected by the current detection circuit is equal to or greater than a predetermined value continues for a predetermined period of time;
The predetermined time is set to be shorter than a time required for the overcurrent protection circuit to detect an overcurrent.
The gist of the present invention is as follows.

The load status monitoring device of the present invention is used in a system including a power supply device having an overcurrent protection circuit that detects an overcurrent and limits the power supply, and a load connected to a power line from the power supply device. The load status monitoring device includes a current detection circuit that detects the current flowing through the power line, a relay that switches the power line on and off, and a control device that operates by receiving power from the power supply device, and the control device turns off the relay when the current detected by the current detection circuit remains at or above a predetermined value for a predetermined time. The predetermined time is set to a time shorter than the time required for the overcurrent protection circuit to detect an overcurrent. This makes it possible to determine an overcurrent abnormality and turn off the relay before the power supply to the control device is limited by the overcurrent protection circuit of the power supply device. As a result, the load status monitoring device is able to appropriately determine an overcurrent abnormality and respond appropriately to the occurrence of an overcurrent abnormality.

In the load status monitoring device of the present invention, the system includes a capacitor connected in parallel with the load to the power supply device, and the control device turns off the relay when the current detected by the current detection circuit remains equal to or greater than a predetermined value for a predetermined period of time when the power supply device starts to supply power to the load, and the predetermined period of time may be set to be longer than the time required for the capacitor to charge to a predetermined degree and shorter than the time required for the overcurrent protection circuit to detect an overcurrent. In this way, it is possible to avoid erroneously determining that an inrush current caused by the charging of the capacitor when the power supply device starts to supply power is an overcurrent abnormality.

In addition, in the load status monitoring device of the present invention, the control device may further notify the occurrence of an error when the current detected by the current detection circuit exceeds a predetermined value when the power supply device starts supplying power to the load and the state continues for a predetermined time or more. This makes it possible to respond more appropriately to the occurrence of an overcurrent abnormality.

In addition, in the load status monitoring device of the present invention, the system may be a fuel cell system, and the power supply device may be capable of supplying power generated by the fuel cell system to the load.

1 is a diagram showing an outline of the configuration of a fuel cell system including a load state monitoring device according to an embodiment of the present invention; 10 is a flowchart illustrating an example of an overcurrent monitoring process. 4 is an explanatory diagram showing how a power supply voltage and a supply current change over time. FIG. FIG. 2 is an explanatory diagram showing an equivalent circuit of a circuit including a power supply circuit and a capacitor.

The embodiment of the present invention will be described with reference to the drawings.

Figure 1 is a schematic diagram showing the configuration of a fuel cell system including a load status monitoring device of this embodiment. As shown in the figure, the fuel cell system 10 is connected to a power receiving facility (not shown) such as a house, and is connected to a commercial power system 1 to supply AC power (e.g., AC 100V or AC 200V) to electrical appliances connected to an indoor AC outlet. This fuel cell system 10 includes a fuel cell 11 that generates DC power, a DC/DC converter 12 that converts the voltage of the DC power from the fuel cell 11, an inverter 13 that converts the DC power from the DC/DC converter 12 to AC power, a parallel-off relay 14 that connects and disconnects a power line connecting a wiring 2 connected to the commercial power system 1 and an output terminal of the inverter 13, a power supply circuit 15 that supplies DC power to auxiliary equipment provided in the fuel cell system 10, a load status monitoring device 20 of this embodiment, and a control device 30 that forms part of the load status monitoring device 20 and controls the entire system. These are housed in a housing installed outdoors.

The power supply circuit 15 includes a DC/DC converter that converts the voltage of the DC power from the fuel cell 11 and an AC/DC converter that converts the AC power of the commercial power system 1 into DC power, and supplies power to the auxiliary devices (including the auxiliary load 17) of the fuel cell system 10 and to the control device 30. The power supply circuit 15 also includes an overcurrent protection circuit 15a that limits (cuts off) the power supply when a current exceeding a predetermined value continues to flow in the circuit for a predetermined period of time.

In this embodiment, the auxiliary load 17 is a remote control device that operates by receiving power from the power supply circuit 15, and is equipped with an operation switch for instructing the start and stop of the fuel cell 11 and setting the operation mode of the fuel cell 11. A capacitor 18 is connected in parallel to the power supply circuit 15 between the terminals of the auxiliary load 17.

The load status monitoring device 20 of this embodiment monitors the status (mainly short circuits) of the auxiliary load 17. This load status monitoring device 20 includes a current detection circuit 21 for detecting the current flowing through the power supply line 16 from the power supply circuit 15 to the auxiliary load 17, a load disconnection relay 22 for disconnecting the power supply line 16, and the control device 30 described above.

The current detection circuit 21 has a current detection resistor 21a attached to the power supply line 16 and a differential amplifier 21b that amplifies and outputs the differential voltage between the terminals of the current detection resistor 21a. The output signal of the differential amplifier 21b is input to the control device 30 via an A/D converter (not shown).

The control device 30 is configured as a microprocessor centered on a CPU, and operates by receiving power from the power supply circuit 15. In addition to the CPU, the control device 30 also includes a ROM for storing processing programs, a RAM that functions as a work memory, a non-volatile memory, an input/output port, and a communication port. The supply current I from the current detection circuit 21 is input to the control device 30 via the input port. On the other hand, the control device 30 outputs a drive signal to the load disconnection relay 22 and a display signal to the display device 31 that displays various information via the output port. The control device 30 also includes a communication circuit, and communicates with the auxiliary load 17 (remote control device) by superimposing communication data on the power supply line 16.

Next, the operation of the load state monitoring device 20 provided in the fuel cell system 10 configured in this manner will be described. FIG. 2 is a flow chart showing an example of an overcurrent monitoring process executed by the CPU of the control device 30. This process is executed when power supply from the power supply circuit 15 is started.

When the overcurrent monitoring process is executed, the CPU of the control device 30 first inputs the supply current I detected by the current detection circuit 21 (step S100) and determines whether the input supply current I is equal to or greater than the predetermined value Iref (step S110). If it is determined that the supply current I is not equal to or greater than the predetermined value Iref, the process returns to step S100. On the other hand, if it is determined that the supply current I is equal to or greater than the predetermined value Iref, the process returns to step S100 and, if it is determined that the predetermined time Tref has not continued, the process returns to step S100. If it is determined that the predetermined time Tref has continued, the load disconnection relay 22 is turned off (step S130), a warning display indicating that an overcurrent abnormality (short circuit abnormality) has occurred in the auxiliary load 17 is displayed on the display device 31, and error information is stored in the non-volatile memory (step S140), and the process ends.

Figure 3 is an explanatory diagram showing the change in the power supply voltage and the supply current over time. As shown in the figure, when power supply circuit 15 starts supplying power to auxiliary load 17, an inrush current occurs due to charging of capacitor 18. Then, the power supply voltage temporarily drops due to the impedance of power line 16. Here, considering the circuit of Figure 4 as an equivalent circuit of a power supply circuit including power supply circuit 15 and capacitor 18, the power supply voltage of power supply circuit 15 is E, the capacitance of capacitor 18 is C, the impedance (resistance) of power line 16 is R, and the elapsed time from turning on switch SW is t, the supply current I flowing through power line 16 is calculated by the following formula (Equation 1). The predetermined time Tref is set to a time longer than the time from when the inrush current exceeds a predetermined value Iref, which is a threshold value for determining an overcurrent abnormality, until it falls below the predetermined value Iref, that is, the time T1 (see Figure 3) required to charge capacitor 18 to a predetermined extent. This makes it possible to avoid erroneously determining that the inrush current generated by the charging of the capacitor 18 when the power supply circuit 15 starts supplying power is an overcurrent abnormality. In addition, the predetermined time Tref is set to a time shorter than the time T2 (see FIG. 3) required for the overcurrent protection circuit 15a of the power supply circuit 15 to detect the occurrence of an overcurrent. This allows the control device 30 to determine an overcurrent abnormality before the overcurrent protection circuit 15a of the power supply circuit 15 limits (cuts off) the power supply due to the occurrence of an overcurrent, that is, before the power supply voltage falls below the reset voltage Vres due to the limit on the power supply of the power supply circuit 15 and the control device 30 is reset. Therefore, the control device 30 can disconnect the auxiliary load 17 from the power line 16 due to the occurrence of an overcurrent abnormality, and can appropriately respond to the abnormality of the auxiliary load 17.

The load state monitoring device 20 of the present embodiment described above is used in a fuel cell system 10 including a power supply circuit 15 having an overcurrent protection circuit 15a that detects an overcurrent and limits the power supply, an auxiliary load 17 connected to a power supply line 16 from the power supply circuit 15, and a capacitor 18 connected in parallel with the auxiliary load 17 to the power supply circuit 15. The load state monitoring device 20 includes a current detection circuit 21 that detects the current flowing through the power supply line 16, a load disconnection relay 22 that disconnects the power supply line 16, and a control device 30 that operates by receiving power from the power supply circuit 15. When the power supply circuit 15 starts supplying power to the auxiliary load 17, the control device 30 turns off the load disconnection relay 22 when the supply current I detected by the current detection circuit 21 becomes equal to or greater than a predetermined value Iref and continues for a predetermined time Tref. The predetermined time Tref is set to a time longer than the time T1 required to charge the capacitor 18 and shorter than the time T2 required for the overcurrent protection circuit 15a to detect an overcurrent. This makes it possible to determine an overcurrent abnormality before the overcurrent protection circuit 15a of the power supply circuit 15 limits the power supply to the control device 30. It also makes it possible to avoid erroneously determining that an inrush current that occurs when the power supply circuit 15 starts supplying power is an overcurrent abnormality. As a result, it becomes possible to properly determine an overcurrent abnormality and to properly respond to the occurrence of an overcurrent abnormality.

In this embodiment, the control device 30 determines that an overcurrent abnormality (short circuit abnormality) has occurred when the supply current I detected by the current detection circuit 21 becomes equal to or greater than the predetermined value Iref when the power supply circuit 15 starts supplying power (while the capacitor 18 is being charged) and this state continues for a predetermined time Tref. However, the control device 30 can also determine that an overcurrent abnormality (short circuit abnormality) has occurred when the supply current I detected by the current detection circuit 21 becomes equal to or greater than the predetermined value Iref and this state continues for a predetermined time Tref even after the charging of the capacitor 18 is completed. In this case, the predetermined time Tref does not need to take into account the inrush current generated when the capacitor 18 is charged, and it is sufficient that it is shorter than the time required for the overcurrent protection circuit 15a to detect the overcurrent. In addition, after the charging of the capacitor 18 is completed, the control device 30 can also monitor the state of the auxiliary load 17 by determining whether the supply current I detected by the current detection circuit 21 is within an appropriate range.

The correspondence between the main elements of the embodiment and the main elements of the invention described in the section on means for solving the problem will be explained. In the embodiment, the power supply circuit 15 corresponds to the "power supply device", the auxiliary load 17 corresponds to the "load", the capacitor 18 corresponds to the "capacitor", the fuel cell system 10 corresponds to the "system", the current detection circuit 21 corresponds to the "current detection circuit", the load disconnection relay 22 corresponds to the "relay", and the control device 30 corresponds to the "control device".

The correspondence between the main elements of the embodiment and the main elements of the invention described in the Means for Solving the Problem column does not limit the elements of the invention described in the Means for Solving the Problem column, since the embodiment is an example for specifically explaining the form for implementing the invention described in the Means for Solving the Problem column. In other words, the interpretation of the invention described in the Means for Solving the Problem column should be based on the description in that column, and the embodiment is merely a specific example of the invention described in the Means for Solving the Problem column.

The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment in any way, and it goes without saying that the present invention can be carried out in various forms without departing from the spirit of the present invention.

The present invention can be used in the manufacturing industry of load condition monitoring devices and fuel cell systems.

1 Commercial power system, 2 Wiring, 10 Fuel cell system, 11 Fuel cell, 12 DC/DC converter, 13 Inverter, 14 Parallel-off relay, 15 Power supply circuit, 15a Overcurrent protection circuit, 16 Power supply line, 17 Auxiliary load, 18 Capacitor, 20 Load status monitoring device, 21 Current detection circuit, 21a Current detection resistor, 21b Differential amplifier, 22 Load disconnection relay, 30 Control device, 31 Display device.

Claims (3)

A load status monitoring device for a system including a power supply device having an overcurrent protection circuit that detects an overcurrent and limits power supply, a load connected to a power line from the power supply device, and a capacitor connected in parallel with the load to the power supply device, comprising:
a current detection circuit for detecting a current flowing through the power supply line;
a relay for connecting and disconnecting the power supply line;
a control device that receives power from the power supply device and operates to drive the relay;
Equipped with
when the power supply device starts supplying power to the load and an inrush current detected by the current detection circuit remains equal to or greater than a predetermined value for a predetermined period of time, the control device determines that a short circuit has occurred in the load and turns off the relay;
The predetermined time is set to a time that is longer than a time that is normally required for the capacitor to be charged to a predetermined extent, that is, a time that is required for an inrush current to fall below the predetermined value after exceeding the predetermined value in a state in which there is no short-circuit abnormality in the load, and is shorter than a time that is required for the overcurrent protection circuit to detect an overcurrent.
Load condition monitoring device. The load condition monitoring device according to claim 1,
The control device further notifies the occurrence of an error when a state in which the current detected by the current detection circuit is equal to or greater than a predetermined value continues for a predetermined period of time or more.
Load condition monitoring device. The load state monitoring device according to claim 1 or 2,
the system is a fuel cell system;
The power supply device is capable of supplying the power generated by the fuel cell system to the load.
Load condition monitoring device.

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