JP2021044895A - Energy harvesting wireless sensor with charging terminal - Google Patents

Abstract

To maintain a sensor function even when an energy harvesting element is replaced in an energy harvesting wireless sensor.SOLUTION: In order to solve the above problem, in the present invention, a power supply circuit unit 2 and a sensor circuit unit 3 of an energy harvesting wireless sensor 1 are connected by a backflow prevention diode 4. A lead wire is drawn from a wireless sensor circuit so that an external power source 20 can be supplied. A power storage element 5 is separated from the power supply circuit unit 2, the lead wire is pulled out from the power storage element 5, and made to be connectable to the external power source 20. As a result, charging from the external power source 20 is enabled.SELECTED DRAWING: Figure 1

Description

The present invention relates to an energy harvesting wireless sensor that receives electric power by energy harvesting and wirelessly transmits a signal, and more particularly to a charging technique for the sensor.

In recent years, LPWA (Low Power Wide Area) communication methods capable of long-distance wireless transmission within the range of specific low-power radios that do not require a license have become practical, and energy harvesting technology has also advanced. Under such technological trends, energy harvesting wireless sensors that do not require power supply wiring and signal wiring are being put into practical use. These energy harvesting wireless sensors are expected to be used for environmental measurement of mountainous areas and rivers, which have been abandoned due to the high installation cost, taking advantage of the feature that power supply wiring and signal wiring are unnecessary. It is also used for monitoring the condition of equipment installed in remote areas.

Here, a design example of a general energy harvesting wireless sensor will be described below.

The energy harvesting wireless sensor stores the generated power obtained from the energy harvesting element in a large-capacity power storage element so that it can operate even when the amount of power generation is small.

An object of the energy harvesting wireless sensor of the present invention is to measure the environment of mountainous areas and rivers, and to monitor the condition of equipment installed in remote areas, and it is mainly installed outdoors. For example, considering the case of solar power generation, it is not always possible to obtain appropriate sunlight, and it may not be possible to obtain the required amount of power generation not only at night but also in the daytime on rainy, cloudy, or snowy days. is there. Therefore, a large-capacity power storage element is required as follows.

The actual operation when a photovoltaic power generation element is used as an energy harvesting element is examined, and the capacitance of the power storage element is calculated. As such an energy harvesting wireless sensor, a 1W class photovoltaic element is suitable in terms of price and size. In the 1W class, the size is about 150mm x 100mm. As for the power generation characteristics, the maximum rated power generation point is a voltage of 10 V and a current of about 100 mA.

As a wireless sensor as a load, the sensor power consumption is 3V, 3mA, and it is driven for 2 seconds at one measurement. The wireless transmission circuit unit operates at power consumption of 3V, 50mA, and one transmission time is about 10 seconds. Is. Under the above conditions, the power consumption when measuring and transmitting once an hour is calculated as 3V × 3mA × 2 seconds + 3V × 50mA × 10 seconds = 18m joules + 1500m joules = 1.518 joules. Then, the daily amount is 24 times this, which is 36.4 joules. Energy harvesting wireless sensors need to be able to operate with the stored power of the power storage element for about two weeks even if the weather is bad, such as during the rainy season. Then, the amount of stored power of the power storage element is 36.4 joules x 14 days = 509.6 joules. When this is stored in a power storage element with a rated voltage of 3 V, the capacitance of the power storage element is C = 2 x E / V ² = 2 x 509.6 / ^{from E = (1/2) x C x V 2.} 3 ² ≒ 113F.

Japanese Unexamined Patent Publication No. 2011-077961

The above-mentioned Patent Document 1 uses a manual generator to charge the power storage element. Since this method has a mechanical operating part, maintenance of this part is also required, and since it is a manual type, the generated voltage and current are not constant and the circuit is complicated. In addition, when the secondary battery deteriorates, replacement when the energy harvesting element deteriorates is not considered.

In addition, many energy harvesting wireless sensors are installed in remote locations, but in order to improve the efficiency of installation and post-installation tests, it is necessary to supply power immediately after installation. Furthermore, the energy harvesting wireless sensor is required to be immediately activated and to be able to perform the operation check work when checking the operation after assembly in the factory.

When a large-capacity capacitor is used as the power storage element, the capacity needs to be large, exceeding 100F, as in the above calculation example.

Let's calculate the charging time when charging this capacitor with, for example, a photovoltaic power generation element with a rated output of 10V and 100mA. Let the capacitor capacity be 100F, the rated voltage be 3V, and the time required to charge to a voltage of 3V be t. MPPT (Maximum Power Point Tracking) control is adopted for the power generation control of the photovoltaic power generation element, and it is assumed that the battery is charged with a power of 10 V and 100 mA. Then, the stored energy E of the capacitor with a capacity of 100F and a rating of 3V is E = (1/2) x C x V ² joules (C: capacitor capacity, V: capacitor voltage) = (1/2) x 100 x 3 ² Since = 450 joules, t = E / (10V × 100mA) = 450 / (1W) = 450s = 7.5 minutes.

The rating of the photovoltaic power generation element is ^{the one under the condition of irradiance of 1000 W / m 2} , which corresponds to the sunlight in the daytime in fine weather, which is about 100,000 lux in terms of illuminance, which is 1,000 in a normal office. When charging with an illuminance of about lux, it simply takes 100 times 7.5 times longer, and it is not efficient to shine light on the photovoltaic power generation element to charge the power storage element.

In addition, even after installation, in the case of some change in the power generation environment, for example, in the case of solar power generation, the amount of electricity stored due to the construction of a new building, the overgrowth of branches and leaves of surrounding trees, and the constant shade, or the deterioration of the power storage element It may be necessary to take measures due to the decline. In such a case, it is necessary to change the installation location, cut down the branches and leaves of the trees, or replace the power storage element to fully charge and restore the power storage element. In addition, since the amount of power generation has decreased due to the deterioration of the energy harvesting element, the amount of electricity stored may decrease and countermeasures may be required. If data loss is not tolerated due to highly public and important measurement data, power is supplied to the device and operation continues even when the installation location is changed, the branches and leaves of trees are cut down, the power storage element, and the energy harvesting element are replaced. Need to be done.

An object of the present invention is to continue and maintain the detection function of the energy harvesting wireless sensor even in various operating conditions such as when charging is required. For example, it is possible to charge a power storage element while supplying operating power to an energy harvesting wireless sensor so that a post-assembly test, a post-installation test, and an operation in a factory can be performed promptly. This is an example of the object of the present invention. Further, as another example of the object of the present invention, it is included that the replacement of parts constituting the energy harvesting wireless sensor can maintain the detection function or shorten the period during which the function cannot be exhibited.

In order to solve the above problems, the present invention has a configuration in which an energy harvesting wireless sensor for measuring and detecting a physical quantity is connected to the following external power sources. The sensor unit has a sensor unit that detects a physical quantity, an environmental power generation unit that supplies power generated by environmental power generation to the sensor unit, and an external power supply connection unit that connects to an external power source. When the electrical connection with the environmental power generation unit is disconnected, the physical quantity is detected by using the power supply supplied through the external power generation connection unit. More specifically, the power supply circuit section and the sensor circuit section of the environmental power generation wireless sensor are connected by a backflow prevention diode, and a lead wire is pulled out from the wireless sensor circuit section so that external power can be supplied, and electricity is stored from the power supply circuit section. The element is separated and a lead wire is pulled out from the power storage element so that it can be connected to an external power source so that it can be charged from the external power source.

In addition, one aspect of the present invention includes performing any of replacement, charging, and replacement of the energy harvesting element of the energy harvesting element that stores the energy harvesting power when the energy harvesting wireless sensor is operated. In this case, the sensor unit further has a charging unit that stores power supplied via the external power generation connection unit, and the sensor unit has the physical quantity when the connection with the energy harvesting unit is electrically disconnected. It is also included in the present invention that the detection uses the power source directly supplied from the external power source connection unit or the power source stored in the charging unit.

According to the present invention, by using an external power source, it is possible to continue and sustain the operation of the energy harvesting wireless sensor even in various situations.

Configuration diagram of the energy harvesting wireless sensor 1 and the external power supply 20 for explaining the procedure for exchanging the energy harvesting element 17 in one embodiment of the present invention. Configuration diagram of the energy harvesting wireless sensor 1 external power supply 20 for explaining the replacement procedure of the power storage element 5 in the embodiment of the present invention. The figure which shows the state in the normal operation of the energy harvesting wireless type sensor 1 in one Example of this invention. The figure which shows one example of the external power supply circuit 20 of one Example of this invention. The figure which simplified the charging circuit to the power storage element of one Example of this invention A graph showing the charging time of the power storage element according to the embodiment of the present invention.

An embodiment of the present invention will be described with reference to FIGS. 1 to 6.

In FIGS. 1, 2, and 3, 1 is an environmental power generation wireless sensor, 2 is a power supply circuit unit, 3 is a sensor circuit unit, 4 is a backflow prevention diode, 5 is a power storage element, 6 is a backflow prevention diode, 7, 8 , 9 is a resistor, 18 is an external power supply connection terminal, 10 is switch SW1, 11 is switch SW2, 12 is switch SW3, 13 is a resistor, 14 and 15 are storage element connection terminals, 16 is an environmental power generation element connection terminal, 17 is an environmental power generation element, 18 is an external power supply connection terminal, and 20 is an external power supply.

FIG. 1 shows a state in which the energy harvesting wireless sensor 1 is connected to the external power supply 20 to supply power to the sensor circuit unit 3 and charge the power storage element 5 while continuing the operation. In this state, switch SW1-10 is open, switch SW2-11 is closed, and switch SW3-12 is open. Power is supplied from the external power supply 20 to the sensor circuit unit 3 through the a terminal of the external power supply connection terminal 18, and the operation as a wireless sensor is continued. Then, power is supplied from the external power source 20 to the power storage element 5 through the c terminal of the external power supply connection terminal 18, and the power storage element 5 is charged. Here, the d terminal of the external power supply connection terminal 18 is for feeding back the terminal voltage of the power storage element 5 to control the charging of the power storage element 5.

The resistor 9 is for connecting the terminal voltage of the power storage element 5 to the voltmeter 31 of the external power supply 20 through the terminal b of the external power supply connection terminal 18 and monitoring the charging state of the power storage element 5.

The power supply circuit unit 2 is composed of an energy harvesting element 17 and a power generation / charge control circuit, charges the power storage element 5, and supplies power to the sensor circuit unit. The energy harvesting element 17 is, for example, a solar power generation element. The power generation / charge control circuit is, for example, an MPPT (Maximum Power Point Tracking) control circuit and a charge circuit of the power storage element 5.

The sensor circuit unit 3 is composed of a boost / constant voltage circuit, a wireless sensor circuit, and a system control circuit. The boost / constant voltage circuit boosts the terminal voltage of the power storage element 5 that has not been made constant to the operating voltage of the wireless sensor circuit and the system control circuit to make it constant. The wireless sensor circuit is composed of a wireless communication circuit and a sensor circuit. The system control circuit controls the entire sensor circuit unit, such as measurement cycle control of the sensor circuit in the wireless sensor circuit and transmission cycle control of the wireless communication circuit.

The backflow prevention diode 4 supplies power only to the sensor circuit unit 3 to prevent current from flowing to the power supply circuit unit 2 and the power storage element 5. Since the backflow prevention diode 4 is inserted between the power supply circuit unit 2 and the power storage element 5, a loss occurs due to the forward voltage drop even during the normal operation of the energy harvesting wireless sensor 1.

However, in recent years, a diode having a very low forward voltage has been developed, and when the operating current of the sensor circuit unit is about 50 mA, the forward voltage can be suppressed to 0.2 to 0.3 V, so that a large loss does not occur. The backflow prevention diode 6 is for preventing the power storage element 5 from being discharged when the c terminal and the e terminal of the external power supply connection terminal 18 are short-circuited, such as when the external power supply 20 is in an abnormal state. Is. Since the power storage element 5 has a large capacity exceeding 100 F, a large current flows when the terminals are short-circuited, the power storage element 5 overheats abnormally, and the power storage element 5 may be damaged or ignite. Is for. The normal operation refers to the case where the detection function as the energy harvesting wireless sensor 1 is operated and the power is not supplied from the external power source 20 or is extremely small.

The replacement work procedure of the energy harvesting element 17 and the power supply process from the external power source 20 for that purpose will be described with reference to FIG.

The energy harvesting wireless sensor 1 receives a replacement instruction of the energy harvesting element 17 from the user, and the connection state of each switch is set to the state shown in FIG. The user may manually connect (open / close) these switches. As a result, power is supplied from the external power source 20 to the sensor circuit unit 3 including the wireless sensor circuit, and the operation is maintained. In addition, power is also supplied from the external power source 20 to the power storage element 5.

Since the power source from the external power source 20 or the power storage element 5 can be used instead of the energy harvesting element 17, the energy harvesting element 17 can be replaced. More specifically, if the user monitors the voltmeter 31 of the external power source 20 and determines that the terminal voltage of the power storage element 5 has reached the rated voltage and is in a stable state, the charging of the power storage element 5 is completed. Then, the energy harvesting wireless sensor 1 supplies power from the power storage element 5 or the external power source 20 to the sensor circuit unit 3 including the wireless sensor circuit, and maintains its operation. Therefore, the energy harvesting element 17 can be replaced by the user's work while maintaining the operation.

Next, the energy harvesting wireless sensor 1 detects the user's designation or the end of replacement, closes the switch SW1-10, and opens the switch SW2-11. Then, the user can remove the external power supply 20. The user may open and close the switch.

When charging only the power storage element 5, charge the battery in the connected state shown in FIG. 1, and when charging is completed, close the switch SW1-10 and open the switch SW2-11, and the user must remove the external power supply 20. Make it possible.

Next, the procedure for replacing the power storage element 5 will be described with reference to FIG. When the power storage element 5 is replaced, the switch SW3-12 discharges the stored energy of the power storage element 5 before the replacement so that it can be safely removed and handled.

FIG. 2 shows a configuration in which the energy harvesting wireless sensor 1 and the external power supply 20 are connected. More specifically, the connection state of the switch that discharges the energy stored in the power storage element 5 in order to replace the power storage element 5 while the external power supply 20 supplies power to the wireless sensor circuit unit is shown. .. At this time, the energy harvesting wireless sensor 1 discharges the stored energy of the power storage element 5 by opening the switches SW1-10 and SW2-11 and closing the switches SW3-12 according to the user's designation. Therefore, the user monitors the voltmeter 31 of the external power supply 20, determines that the discharge is complete when the terminal voltage of the power storage element 5 reaches 0V, and specifies the energy harvesting radio to open the switch SW3-12. Perform on formula sensor 1.

Subsequently, the procedure after the replacement of the power storage element 5 will be described. The energy harvesting wireless sensor 1 detects the designation from the user or the replacement of the power storage element 5, and closes the switch SW2-11 to start charging the power storage element 5. Then, the user monitors the voltmeter of the external power supply 20 and determines whether the terminal voltage of the power storage element 5 has reached the rated voltage and is stable. When it is stable, charging is completed, so the energy harvesting wireless sensor 1 closes the switch SW1-10 and opens the switch SW2-11 to disconnect from the external power supply.

FIG. 3 shows the normal operating state of the energy harvesting wireless sensor 1. At this time, the switch SW1-10 is closed, and the switch SW2-11 and the switch SW3-12 are in the open state. With this configuration, in addition to the energy harvesting element 17, the power source of the power storage element 5 can be used in the wireless sensor circuit to operate its function.

FIG. 4 shows an example of the internal circuit of the external power supply 20. In FIG. 4, 21 is a battery, 22 and 27 are transistors, 23 and 28 are operational amplifiers, 24 is a reference voltage source, 25, 26, 29 and 30 are resistors, 31 is a voltmeter and 32 is a connection terminal. Such a circuit makes it possible to supply power to the energy harvesting wireless sensor 1, but the configuration of the external power supply 20 is not limited to this circuit as long as it has a function of supplying power.

Next, the power supply to the sensor circuit unit and the charging operation to the power storage element 5 will be described with reference to FIGS. 4, 5, and 6.

As shown in FIG. 4, the power supply to the sensor circuit unit 3 is performed by converting the voltage of the battery 21 to a constant voltage in a circuit including a transistor 27, an operational amplifier 28, a constant voltage source 24, and resistors 29 and 30. .. The charging circuit of the power storage element 5 is a circuit including a transistor 22, an operational amplifier 23, a constant voltage source 24, and resistors 25 and 26, and is performed by controlling the voltage of the battery 21. A voltage obtained by dividing the terminal voltage of the power storage element 5 by the resistors 7 and 8 of FIG. 1 is input to the terminal d of the connection terminal 32, and the terminal voltage of the power storage element 5 is set by the operational amplifier 23 of the power storage element 5. It is controlled to reach the rated voltage.

FIG. 5 is a simplified diagram of the charging circuit of the power storage element 5. When charging from a state in which the power storage element 5 is completely discharged, even if the charging circuit is controlled at a constant voltage, the capacitance of the power storage element 5 is very large, so that the rated voltage of the power storage element 5 is immediately reached. The transient state continues for a long time. As shown in FIG. 5, this transient state is represented by a state in which the battery 21 is connected to the power storage element 5 by the resistor 25. Here, assuming that the forward voltage of the backflow prevention diode 6 in FIG. 2 is 0.7V and the Vbe of the transistor in FIG. 4 is 0.7V, the voltage of the battery 21 is 10.4V. Assuming that the resistor 25 is 4.7Ω, the capacitance of the power storage element 5 is 100F, and the rated voltage is 3V, the terminal voltage of the power storage element 5 rises with time as shown in FIG. Then, when the terminal voltage of the power storage element reaches 3V, the constant voltage control works and it is fixed at 3V.

Here, the number of chargeable times when a small battery of 12V and 2.3Ah for a motorcycle is used as the battery 21 is estimated. Assuming that the capacitance of the power storage element 5 is 100F and the rated voltage is 3V, the amount of energy E required to fully charge is E = (1/2) × C × V ² and E = (1/2) ×. 100 x 3 ² = 450 joules. On the other hand, the energy amount Eb of the 12V, 2.3Ah battery is Eb = 12 × 2.3 × 60 × 60 ≒ 9.9 × 10 ⁴ joules. Ignoring the loss caused by the resistor 25 in Fig. 4, and considering only the energy transfer, the number of times this battery can be charged is (9.9 x 10 ⁴ ) / 450 ≒ 220 times, which is sufficient for maintenance use. ..

For factory tests, the battery 21 in FIG. 4 may be a DC power supply device powered by AC100V.

According to the above embodiment, it is possible to start up the energy harvesting wireless sensor at a higher speed. In addition, the power storage element can be quickly charged from an external power source regardless of the power generated by the energy harvesting element. Therefore, for example, a test at the time of assembly in a factory, a test at the time of shipment, a test after installation, and an operation can be carried out promptly. That is, it is possible to maintain and continue the operation of the energy harvesting wireless sensor even in various situations such as the start of operation at the time of startup.

Furthermore, even in the installation location change work when the amount of energy harvesting cannot be sufficiently obtained due to environmental changes after installation and operation, and the replacement work when the power storage element and the energy harvesting element deteriorate, the device is stopped while supplying operating power. It can be made possible to work without.

1 ... Environmental power generation wireless sensor, 2 ... Power supply circuit section, 3 ... Sensor circuit section, 4, 6 ... Backflow prevention diode, 5 ... Charging element, 7, 8, 9, 13 ... Resistor, 18 ... External power supply connection terminal , 10 ... Switch SW1, 11 ... Switch SW2, 12 ... Switch SW3, 14, 15 ... Power storage element connection terminal, 16 ... Environmental power generation element connection terminal, 17 ... Environmental power generation element, 18 ... External power supply connection terminal, 20 ... External power supply

Claims (5)

A sensor unit that detects physical quantities and
An energy harvesting unit that supplies power generated by energy harvesting to the sensor unit,
It has an external power supply connection part that connects to an external power supply,
The sensor unit is characterized in that when the electrical connection with the energy harvesting unit is disconnected, the physical quantity is detected by using the power supply supplied through the external power generation connection unit. Power generation sensor device. In the energy harvesting type sensor device according to claim 1.
Further, it has a charging unit for storing power supplied via the external power supply connection unit.
The sensor unit is an energy harvesting type sensor device characterized in that when the electrical connection with the energy harvesting unit is cut off, the power source stored in the charging unit is used to detect the physical quantity. In the energy harvesting type sensor device according to claim 1.
Further, it has a charging unit for storing power supplied via the external power supply connection unit.
The sensor unit is an energy harvesting type that uses a power source directly supplied from the external power generation connection unit to detect the physical quantity when the electrical connection with the energy harvesting unit is disconnected. Sensor device. In the energy harvesting type sensor device according to any one of claims 1 to 3.
It has a switch for disconnecting the connection between the energy harvesting unit and the sensor unit when the sensor unit uses the power supply supplied via the external power supply connection unit.
An energy harvesting sensor device characterized in that the energy harvesting unit can be replaced when the connection is disconnected by the switch. In the energy harvesting type sensor device according to any one of claims 1 to 4.
An energy harvesting sensor device characterized in that the sensor unit and the energy harvesting unit are connected via a backflow prevention diode.

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