A high-voltage line temperature monitoring system based on dual-mode communication and a control method thereof

Abstract

The application belongs to the technical field of safety monitoring, and provides a high-voltage line temperature monitoring system based on dual-mode communication and a control method thereof. The system adopts a low-power hardware architecture with wide and narrow band independent power supply gating. The independent power supply management of the NB-IoT communication circuit and the LTE-Cat1 communication circuit is realized through the MCU control power electronic switch. Based on the multi-factor evaluation dual-mode communication switching mode, combined with the information of the network card belonging to the operator, the hysteresis switching, the power-off reset, the heat conduction temperature backstepping and the energy state linkage control, the high-voltage line temperature monitoring based on dual-mode communication is realized. The two communication links form a cooperative control relationship in the power supply timing, fault recovery, temperature anomaly reporting and low-power sleep process, so that the monitoring system can balance the data upload stability, temperature anomaly judgment accuracy, temperature anomaly reporting timeliness and equipment low-power operation ability in the environment of weak coverage of high-voltage transmission line, strong electromagnetic interference, limited installation position and long-term unattended.

Description

Technical Field

[0001] This invention belongs to the field of safety monitoring technology and relates to the monitoring of high-voltage transmission line temperature, specifically a high-voltage line temperature monitoring system and its control method based on dual-mode communication. Background Technology

[0002] High-voltage transmission lines bear the crucial responsibility of transmitting large amounts of electrical energy over long distances. Operating in complex outdoor environments, these lines are susceptible to factors such as high-current loads, ambient temperature variations, conductor aging, poor joint contact, and icing. These factors can lead to abnormally high temperatures in the conductors or connections. The temperature of the transmission line is a critical parameter reflecting its operational status, encompassing cable current, ambient temperature, heat dissipation conditions, and insulation condition. Prolonged exposure to high temperatures can cause increased contact resistance, conductor sagging, increased leakage current, and insulation breakdown. In severe cases, it can even lead to melting at conductor joints, resulting in power outages and fires. Therefore, timely and effective monitoring of the heating status of transmission cables is essential for the stable operation of the power grid.

[0003] High-voltage transmission lines are typically erected in complex environments such as the field, high altitudes, and remote mountainous areas, placing high demands on the communication stability and low-power operation capabilities of online temperature monitoring equipment. Existing online temperature measurement equipment often employs a single wireless communication method. While narrowband wireless communication offers the advantage of low power consumption, it is prone to network instability and data transmission failures in remote mountainous areas or environments with weak coverage. Broadband wireless communication, on the other hand, while offering advantages such as strong network coverage and high transmission rates, has higher overall power consumption, making it difficult to meet the requirements for long-term low-power operation. Therefore, how to reduce the overall system power consumption while ensuring stable temperature data transmission, and achieve long-term stable operation of high-voltage transmission line temperature monitoring equipment, has become a pressing technical problem that needs to be solved in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a high-voltage line temperature monitoring system and its control method based on dual-mode communication, which can balance data transmission stability, timely reporting of abnormal temperature rise, and low power consumption operation of the equipment, and efficiently complete the high-voltage line temperature monitoring work.

[0005] The technical solution adopted by the present invention to achieve the above objectives is as follows: A high-voltage line temperature monitoring system based on dual-mode communication includes a main control circuit, a temperature acquisition circuit, an NB-IoT communication circuit, an LTE-Cat1 communication circuit, a first power gating branch, a second power gating branch, an RTC wake-up unit, and an external watchdog. The main control circuit includes an MCU, an RTC wake-up unit, and an external watchdog. The MCU is connected to the enable terminals of the temperature acquisition circuit, the RTC wake-up unit, the external watchdog, and the first and second power gating branches. The first power gating branch includes a power electronic switch S1 and a linear regulator U1, used to independently power the NB-IoT communication circuit. The second power gating branch includes a power electronic switch S2 and a linear regulator U2, used to independently power the LTE-Cat1 communication circuit. The temperature acquisition circuit includes a temperature sensor, which is installed at the planned monitoring location on the high-voltage line.

[0006] The MCU controls two power electronic switches S1 and S2 respectively, and supplies power to the NB-IoT communication circuit and the LTE-Cat1 communication circuit through linear regulators U1 and U2 respectively, thereby realizing independent power supply control for the two communication modules. In the non-working state, communication abnormal recovery state, and RTC standby state, the MCU shuts off the power supply to the corresponding communication circuit to reduce the overall power consumption of the system and avoid the superposition of standby leakage current between different communication modules.

[0007] The control method for the high-voltage line temperature monitoring system based on dual-mode communication includes: The system controls the NB-IoT and LTE-Cat1 communication circuits to power on and operate according to an adaptive switching strategy, and shuts off the power supply to the corresponding communication circuits after communication is completed, enabling the high-voltage line temperature monitoring system to dynamically switch between low-power standby and reliable upload. The adaptive switching strategy is based on multi-factor evaluation, which includes at least the CSQ signal strength of the NB-IoT and LTE-Cat1 communication modules, network registration status, network access time, MQTTS connection result, number of valid AT command responses, number of consecutive upload failures, recent upload success rate, IoT card operator information, and network frequency band information of the currently camped cell or searchable cell. The MCU generates link priorities based on the evaluation factors and selects the current upload link according to the link priorities.

[0008] Furthermore, the MCU controls the power electronic switches S1 and S2 to turn on or off via logic levels, thereby controlling the connection or disconnection of the corresponding linear regulator input power supply. When any communication circuit is in a non-working state, a communication abnormality recovery state, or an RTC standby state, the MCU shuts down the corresponding power gating branch, so that the NB-IoT communication circuit and the LTE-Cat1 communication circuit are in a mutually independent power-off isolation state.

[0009] Furthermore, the link priority strategy of the monitoring system is as follows: The monitoring system prioritizes NB-IoT communication circuit for network access and data transmission. When the NB-IoT communication module experiences network connection abnormalities, data transmission failures, failure to complete network access within a preset time, AT command retransmission counts reaching a preset limit, or the recent upload success rate falling below a preset threshold, the MCU shuts off the power supply to the NB-IoT communication circuit and switches to the LTE-Cat1 communication circuit for data transmission. After switching from the NB-IoT communication circuit to the LTE-Cat1 communication circuit, the monitoring system sets a link recovery hysteresis condition. Only when the NB-IoT communication circuit continuously meets the preset CSQ threshold, network access time threshold, and upload success condition in subsequent monitoring will the monitoring system restore the communication priority to the NB-IoT communication circuit, thus forming a hysteresis handover mechanism to avoid additional power consumption and communication failures caused by frequent handovers in weak coverage environments.

[0010] Furthermore, the monitoring system pre-stores or receives updated IoT card operator frequency band priority information. This operator frequency band priority information includes at least the IoT card's owner operator, the priority frequency band corresponding to the NB-IoT communication standard, and the priority frequency band corresponding to the LTE-Cat1 communication standard. The monitoring system prioritizes low-power uploads to the NB-IoT frequency band that the IoT card's owner operator can search for or has already registered at the current location. When the NB-IoT frequency band does not meet the preset access or upload conditions, the system then selects the LTE-Cat1 frequency band that the IoT card's owner operator can search for or has already registered at the current location for uploads, thereby reducing invalid cross-standard searches and unnecessary high-power connection attempts.

[0011] Furthermore, the AT command interaction between the NB-IoT communication module and the LTE-Cat1 communication module is configured with error detection and retransmission mechanisms and power-off reset mechanisms. When the main control circuit of the monitoring system starts working, it prioritizes powering the NB-IoT module in the NB-IoT communication circuit through logic level control. After the NB-IoT module completes power-on initialization, it monitors the network connection status. When the network connection is normal, the NB-IoT module establishes an MQTTS connection with the server and sends the collected temperature data to the server. During this period, the system sets up an error detection and retransmission mechanism for each AT command. After sending the AT command, the main control circuit monitors the validity of the returned message. When an erroneous message, an illegal message, or no response is received within a specified time, the current message is cleared and the corresponding AT command is retransmitted. When a single AT command exceeds the maximum number of retransmissions or the communication module does not respond, the MCU shuts down the corresponding power gating branch, and after a preset discharge waiting time, it re-initializes. If data upload is still not completed after power-off reset, it switches to another communication circuit.

[0012] Furthermore, the monitoring system uses a lithium battery as an energy storage unit, combined with a photovoltaic panel to continuously power the lithium battery; the MCU dynamically adjusts the temperature acquisition cycle, data upload cycle, and communication link selection based on the lithium battery voltage, photovoltaic charging status, planned monitoring location temperature, temperature threshold, and temperature rise rate. The specific logic is as follows: When the lithium battery voltage is lower than the preset low charge threshold and the temperature is not abnormal, the acquisition cycle is extended and the NB-IoT communication circuit is used for uploading. When the temperature at the planned monitoring location exceeds the preset alarm threshold or the temperature rise rate exceeds the preset change rate threshold, the system is immediately activated and the communication link with the higher upload success rate is selected for alarm data upload.

[0013] Furthermore, after completing temperature data acquisition and uploading, the MCU controls the power gating branch to shut down the power supply to the NB-IoT communication circuit, LTE-Cat1 communication circuit, and temperature acquisition circuit. After configuring the RTC wake-up timer, it enters a low-power mode, waiting for the RTC wake-up timer to reach the set time before waking up again and starting work. When the RTC wake-up timer reaches the set time, the MCU wakes up again and starts the next round of temperature data acquisition and uploading. During the MCU's low-power mode, the external watchdog remains active. When the MCU experiences a program error, communication error, or wake-up failure, the external watchdog automatically resets the MCU, thereby improving the stability and reliability of the system operation.

[0014] Furthermore, when the installation location of the temperature sensor is limited by factors such as fixture structure, safety distance, and wiring structure, resulting in a distance offset from the planned monitoring location and making direct installation at the planned monitoring location impossible, the monitoring system executes a heat conduction temperature back-calculation algorithm to compensate for the installation offset distance. The cloud server sends the distance parameters from the installation location to the planned monitoring location to the MCU of the main control circuit. Based on the installation location temperature, ambient temperature, and distance parameters measured by the temperature acquisition circuit, the system uses a preset heat conduction attenuation model to back-calculate the temperature at the planned monitoring location and uses the back-calculated temperature at the planned monitoring location for temperature alarm judgment, acquisition cycle adjustment, and communication link selection.

[0015] The beneficial effects of this invention are: (1) The present invention adopts a low-power hardware architecture with independent power gating for wide and narrow bands. The MCU controls the power electronic switch to realize independent power supply management of NB-IoT communication circuit and LTE-Cat1 communication circuit. In non-working state, communication abnormal recovery state and RTC standby state, the power supply of the corresponding communication module can be turned off, thereby effectively reducing the overall standby power consumption of the system.

[0016] (2) The present invention adopts a wide and narrow band dual-mode communication switching method based on multi-factor evaluation, which uses signal strength, network access time, connection result, AT command response, number of upload failures, historical upload success rate, operator information and network frequency band information together for link selection. Compared with the single CSQ judgment method, it can more accurately reflect the real communication availability under the complex environment of high voltage lines.

[0017] (3) This invention prioritizes the selection of the NB-IoT or LTE-Cat1 frequency band available at the current location by the operator’s frequency band priority information, which can reduce invalid network scanning, repeated access across standards and high power consumption connection attempts, and improve the access efficiency of mobile IoT cards in different high-voltage line scenarios.

[0018] (4) The present invention uses the thermal conduction temperature back-calculation method with installation offset distance compensation, so that the estimated temperature of the planned monitoring position can still be obtained when the equipment cannot be directly installed at the planned monitoring position. This can reduce the impact of installation position deviation on temperature alarm judgment and improve the applicability and accuracy of high-voltage line temperature monitoring.

[0019] (5) After communication failure, the present invention restores communication sequentially through error detection and retransmission, power failure and reset and link switching, and sets NB-IoT link recovery hysteresis conditions, which can reduce invalid reconnection and frequent switching in weak coverage environment and improve the reliability of temperature data upload.

[0020] (6) The present invention dynamically adjusts the acquisition cycle, upload cycle and communication link selection based on lithium battery voltage, photovoltaic charging status, temperature threshold, temperature rise rate and planned monitoring location temperature. It can reduce power consumption when the battery is low and increase the priority of alarm data upload when the temperature is abnormal. It is suitable for long-term online temperature monitoring scenarios of high voltage transmission lines.

[0021] (7) The present invention adopts a low-power operation mechanism based on RTC wake-up and dynamic power-off control of the communication module, and realizes automatic reset of system abnormalities through an external watchdog, which can improve the long-term operation stability of the system in the event of program abnormality, communication abnormality or wake-up failure. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 A schematic diagram of the hardware architecture of a high-voltage line temperature monitoring system based on dual-mode communication provided in an embodiment of the present invention; Figure 2 The schematic diagram of the main control circuit provided in the embodiment of the present invention; Figure 3 A schematic diagram of the enable control circuit provided in an embodiment of the present invention; Figure 4 This is a schematic diagram of the adaptive dual-mode communication switching strategy provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of the ultra-low power operation mechanism of the system provided in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the embodiments and accompanying drawings: like Figure 1 As shown, a high-voltage line temperature monitoring system based on dual-mode communication includes a main control circuit, a temperature acquisition circuit, an enable control circuit, an NB-IoT communication circuit, and an LTE-Cat1 communication circuit.

[0025] The main control circuit is connected to the temperature acquisition circuit, the enable control circuit, the NB-IoT communication circuit, and the LTE-Cat1 communication circuit, respectively. The enable control circuit is connected to the NB-IoT communication circuit and the LTE-Cat1 communication circuit, respectively.

[0026] Main control circuit section such as Figure 2 As shown, the device includes an MCU, an external watchdog and download circuit, a decoupling circuit, an external low-speed active crystal oscillator, a boot circuit, and a temperature acquisition circuit. The MCU chip uses an STM32L4 series low-power microcontroller, which supports multiple low-power operating modes and has an independent RTC function, which can meet the device's long-term low-power operation requirements. The lowest power mode, Shutdown, consumes only 200nA when the RTC is enabled as the wake-up source. The external watchdog timer uses the TPL5010DDCR, an ultra-low power external watchdog chip with a typical operating current of only 35nA. It can automatically reset the chip in case of MCU communication abnormalities, program crashes, or wake-up failures, thereby improving the stability of system operation.

[0027] The temperature acquisition circuit mainly includes a temperature sensor, which is a DS18B20 digital temperature sensor. Due to the strong electromagnetic field environment around high-voltage transmission lines, which can easily interfere with signal acquisition, a single-bus digital temperature sensor is used for temperature acquisition. The DS18B20 has the characteristics of simple interface circuit, strong anti-interference ability and low power consumption, which can meet the requirements of low power consumption and stable operation of high-voltage line temperature monitoring equipment.

[0028] Enable control circuit such as Figure 3As shown, the system includes two power switches and two linear regulators. The lithium battery VBAT is connected to the input VIN of each power switch, and the output VOUT of each power switch is connected to the input VIN of the corresponding linear regulator. The outputs of the two linear regulators provide regulated power to the NB-IoT communication circuit and the LTE-Cat1 communication circuit, respectively. The enable terminals SW1 and SW2 of the two power switches are controlled by the MCU to achieve on-demand power management for the communication circuits, thereby reducing system standby power consumption. The power switches use the TPS22916BYFPR, which has low static power consumption and low shutdown leakage current, with a typical operating current of 35nA. It can cut off power to peripherals when the communication module stops working, thus reducing overall system power consumption. Because the NB-IoT communication module has low power consumption, its power supply linear regulator is ME6231C33M5G, which has a maximum output current of 500mA and low quiescent current. Because the LTE-Cat1 communication module has a high peak operating current, its power supply linear regulator is TLV75733PDBVR, which can provide a maximum output current of 1A to ensure stable operation of the LTE-Cat1 communication circuit.

[0029] The NB-IoT communication circuit mainly consists of an NB-IoT module, a level converter, an RF antenna, and a SIM card interface. The NB-IoT module and the level converter are powered by an enable circuit. The NB-IoT module uses the BC660K and supports MQTTS communication based on TLS encryption, which can improve the security of temperature data transmission.

[0030] The LTE-Cat1 communication circuit mainly consists of an LTE-Cat1 module, a level converter, an RF antenna, and a SIM card interface. The LTE-Cat1 module and the level converter are also powered by an enable circuit. The LTE-Cat1 module uses the EG800Z and supports MQTTS communication based on TLS encryption.

[0031] The control method for a high-voltage line temperature monitoring system based on dual-mode communication, and its control flow are as follows: Figure 4 As shown, it includes: When the system is working, the main control circuit prioritizes the enable circuit to power the NB-IoT module in the NB-IoT communication circuit; after the NB-IoT module completes power-on initialization, it monitors the current network connection status; when the network connection is normal, the NB-IoT module establishes an MQTTS connection with the server and uploads the collected temperature data. During the establishment of network connection and data upload by the NB-IoT module, the system sets up an error detection and retransmission mechanism for each AT command; after sending the AT command, the main control circuit monitors the validity of the returned message; when an abnormal message is detected or no response is received within the specified time, the system clears the current message and retransmits the corresponding AT command; the maximum number of retransmissions for a single AT command is set to 5, and the timeout for a single response is set to 10 seconds. When any AT command exceeds the maximum number of retransmissions, the system determines that the current NB-IoT communication has failed. When the NB-IoT network connection is abnormal, data transmission fails, or network access is not completed within a preset time, the main control circuit controls the enable circuit to shut down the power supply to the NB-IoT module and switches to power supply to the LTE-Cat1 module in the LTE-Cat1 communication circuit. Subsequently, the LTE-Cat1 module establishes an MQTTS connection with the server and completes the temperature data upload.

[0032] During the handover process between the NB-IoT and LTE-Cat1 communication links, the system establishes link evaluation parameters for both the NB-IoT and LTE-Cat1 communication links. These parameters include the current CSQ value, network registration status, network access time, MQTTS connection result, number of valid AT command responses, number of consecutive upload failures, recent upload success rate, IoT card operator information, and network frequency band information of the currently active or searchable cell. The system scores these parameters according to preset weights and uses the communication link with the higher score as the current upload link. When the score difference does not reach the preset handover threshold, the original communication link is maintained to avoid frequent handovers caused by instantaneous signal fluctuations.

[0033] In one embodiment, the monitoring system pre-stores and receives updated IoT card operator frequency band priority information. This information includes the IoT card's operator, the priority frequency band corresponding to the NB-IoT communication standard, and the priority frequency band corresponding to the LTE-Cat1 communication standard. When the monitoring system uses a mobile operator's IoT card, the MCU uses the operator identifier, network registration information, and cell frequency band information returned by the communication module to first determine whether the NB-IoT frequency band that the mobile operator can search for or has already registered at the current location meets the access and upload conditions. If the conditions are not met, the system switches to the LTE-Cat1 frequency band that the mobile operator can search for or has already registered at the current location to complete the upload.

[0034] In one embodiment, after the communication module is powered on and initialized, the MCU can read the currently registered operator, access standard, cell frequency band or frequency point information via AT commands, and match the reading results with the operator's frequency band priority table; when the current frequency band belongs to the priority frequency band of the operator to which the IoT card belongs and the link score meets the threshold, the current communication link is maintained; when the current frequency band does not belong to the priority frequency band or the link score is lower than the threshold, the MCU re-executes the network search, link score or dual-mode switching process to reduce invalid network scanning and high-power access attempts.

[0035] When the system switches from the NB-IoT communication circuit to the LTE-Cat1 communication circuit, the MCU records the reasons for and number of NB-IoT link failures and sets link recovery hysteresis conditions. Only when the NB-IoT communication circuit continuously meets the preset CSQ threshold, network access time threshold, and upload success conditions in subsequent monitoring will the MCU restore the NB-IoT communication priority; otherwise, the LTE-Cat1 communication circuit will continue to be used to complete data upload, thereby improving communication stability in weak coverage environments.

[0036] When the temperature data exceeds the preset alarm threshold or the temperature rise rate per unit time exceeds the preset change rate threshold, the system marks the current data as alarm data and shortens or skips the normal RTC sleep waiting process, immediately starting the communication upload process; if the priority communication link fails to complete the alarm data upload within the preset time, the system directly switches to another communication link to improve the alarm timeliness in high-voltage line abnormal temperature rise scenarios.

[0037] This monitoring system has been tested in different high-voltage line scenarios, and the system has been able to stably complete temperature data acquisition and wireless transmission in all cases.

[0038] Through actual operation tests, it was observed that in urban and suburban environments, both the NB-IoT module and the LTE-Cat1 module have good network coverage capabilities, with CSQ values ​​of NB-IoT and LTE-Cat1 modules both above 25. In remote mountainous environments, the NB-IoT communication network coverage is relatively stable, with CSQ values ​​maintained between 19 and 25, while the LTE-Cat1 communication signal strength decreases, with CSQ values ​​maintained between 17 and 20. In indoor or heavily obstructed environments, the LTE-Cat1 communication network exhibits better communication quality, with CSQ values ​​generally maintained above 27, while the NB-IoT communication network's CSQ values ​​remain between 17 and 21.

[0039] Based on the network coverage in different areas, the system can dynamically adjust the switching strategy between broadband and narrowband dual-mode communication, and change the priority of NB-IoT communication and LTE-Cat1 communication to improve the stability of data transmission and the reliability of communication in complex environments.

[0040] In one embodiment, such as Figure 5 As shown, the control process of the high-voltage line temperature monitoring system based on dual-mode communication includes an ultra-low power operation mechanism based on RTC wake-up and dynamic power-off control of the communication module, which is mainly implemented by the MCU and an external watchdog. When the system is working, the main control circuit controls the power supply of the temperature acquisition circuit, NB-IoT communication circuit and LTE-Cat1 communication circuit through the enable circuit. After completing the acquisition and uploading of temperature data and receiving messages from the server, the power supply of the relevant functional circuits is turned off to reduce the overall power consumption of the system. Then, the MCU initializes the RTC timer, configures the wake-up time and turns off the peripherals to enter the low power mode, waiting for the RTC timer to end to wake up the MCU and start the next round of temperature data acquisition and uploading.

[0041] During the system's low-power mode, the external watchdog remains active. When the system experiences communication abnormalities, program crashes, or wake-up failures, the external watchdog can automatically reset the MCU, thereby improving the long-term stability and reliability of the system.

[0042] In the above embodiments, the main power consumption of the high-voltage line temperature monitoring system based on dual-mode communication during data transmission comes from the MCU, temperature acquisition circuit, and wireless communication module. When the system uses NB-IoT communication to upload temperature data, the MCU, DS18B20 temperature sensor, NB-IoT module BC660K, and related peripheral circuits work simultaneously, with an average system operating current of approximately 20mA to 80mA, and a peak current of approximately 200mA during network connection and data transmission. When the system switches to LTE-Cat1 communication, due to the higher transmission power of the LTE-Cat1 module, the average system operating current is approximately 100mA to 300mA, and the instantaneous peak current can reach approximately 1A.

[0043] In low-power standby mode, the system shuts down the NB-IoT communication circuit, LTE-Cat1 communication circuit, temperature acquisition circuit, and other non-essential peripherals, retaining only the MCU's RTC wake-up function and the external watchdog timer. The STM32L431CCT6's static power consumption in low-power mode can be as low as microamps or even nanoamps, the TPL5010DDCR external watchdog timer has a typical operating current of approximately 35nA, and the TPS22916BYFPR power switch has extremely low turn-off leakage current. Therefore, the overall standby current of the system can be controlled below 10uA, thus meeting the low-power operation requirements of long-term online monitoring equipment for high-voltage transmission lines.

[0044] In this embodiment, during actual operation and testing, the monitoring system uses a 1500mAh lithium battery as an energy storage unit, and uses a photovoltaic panel to continuously power the lithium battery. The device periodically collects temperature data and uploads wireless data at 5-minute intervals. During several days of continuous operation and testing, the lithium battery voltage changes to 3.69V, 3.81V, 3.86V, 3.91V, 3.95V, 4.00V, 4.06V, and 4.15V, respectively. Subsequently, the battery voltage remained stable at around 4.15V for a long period of time.

[0045] Actual operation tests show that the system can continuously provide a stable energy input to the equipment through photovoltaic power generation. Its energy harvesting power is sufficient to cover the energy consumed by the equipment's periodic communication, data acquisition, and standby operation, and gradually completes the charging of the lithium battery. After the equipment reaches a stable operating state, the lithium battery voltage can be maintained near full charge for a long time, indicating that the overall energy balance of the system is basically achieved, and it has high micro-energy harvesting efficiency and energy utilization efficiency.

[0046] Because the system adopts a low-power operating mode, the communication circuit and unnecessary peripherals are turned off during non-operation periods, and the standby current can be controlled at a low level. Therefore, under normal lighting conditions, the system can achieve long-term self-powered operation. Under the condition that the lithium battery cycle life meets the requirements, the device can theoretically achieve continuous online operation for several years. Its actual service life mainly depends on the aging life of the lithium battery and external environmental conditions.

[0047] In one embodiment, when the device cannot be directly installed at the planned monitoring location due to installation limitations, the system configures the distance parameter L from the installation location to the planned monitoring location through a cloud server. The unit of the distance parameter L is cm. After receiving the distance parameter L, the MCU inputs the installation location temperature, ambient temperature, and distance parameter L measured by the temperature acquisition circuit into a preset heat conduction attenuation model to infer the temperature at the planned monitoring location.

[0048] The preset heat conduction attenuation model can be expressed as T(L)=T∞+(T0-T∞)e^(-kL), where T(L) is the measured temperature at a distance L from the planned monitoring location, T0 is the temperature at the planned monitoring location, T∞ is the ambient temperature, and k is the heat conduction attenuation coefficient; in one embodiment, k is taken as 0.154cm^-1.

[0049] When the MCU knows T(L), T∞, and L, it can inversely calculate the planned monitoring location temperature T0 using T0 = T∞ + (T(L) - T∞)e^(kL). The MCU compares the inversely calculated planned monitoring location temperature T0 with a preset alarm threshold and determines whether to trigger an alarm upload based on the temperature rise rate. When T0 reaches the alarm condition, the MCU shortens the acquisition cycle or immediately wakes up the communication module and selects the communication link with the higher upload success rate to send alarm data according to the link scoring results.

[0050] In one embodiment, the MCU also adjusts the data acquisition and upload cycle based on the lithium battery voltage and photovoltaic charging status. When the lithium battery voltage is detected to be lower than a preset low battery threshold and the temperature has not reached the alarm condition, the MCU extends the RTC wake-up cycle and prioritizes using the low-power NB-IoT communication circuit to complete the data upload; when the photovoltaic charging status is good or the temperature data reaches the alarm condition, the MCU restores or shortens the acquisition cycle and selects the communication link with a higher upload success rate based on the link evaluation results.

[0051] This invention provides a high-voltage line temperature monitoring system and its control method based on dual-mode communication. Through multi-factor link scoring, operator frequency band priority, communication failure power-off reset, link recovery hysteresis, heat conduction temperature inference, RTC wake-up, and energy status linkage control, it achieves high-voltage line temperature monitoring based on dual-mode communication. This monitoring system does not simply set up NB-IoT and LTE-Cat1 communication modules in parallel, but rather establishes a collaborative control relationship between the two communication links during power supply timing, fault recovery, temperature anomaly reporting, and low-power sleep processes. This allows the monitoring system to balance data upload stability, temperature anomaly judgment accuracy, temperature anomaly reporting timeliness, and low-power operation capability even in environments with weak coverage, strong electromagnetic interference, limited installation location, and long-term unattended operation of high-voltage transmission lines.

Claims

1. A high-voltage line temperature monitoring system based on dual-mode communication, characterized in that: The system includes a main control circuit, a temperature acquisition circuit, an NB-IoT communication circuit, an LTE-Cat1 communication circuit, a first power gating branch, a second power gating branch, an RTC wake-up unit, and an external watchdog timer. The main control circuit includes an MCU, an RTC wake-up unit, and an external watchdog timer. The MCU is connected to the enable terminals of the temperature acquisition circuit, the RTC wake-up unit, the external watchdog timer, and the first and second power gating branches. The first power gating branch includes a power electronic switch S1 and a linear regulator U1, used to independently power the NB-IoT communication circuit. The second power gating branch includes a power electronic switch S2 and a linear regulator U2, used to independently power the LTE-Cat1 communication circuit. The temperature acquisition circuit includes a temperature sensor, which is installed at the planned monitoring location of the high-voltage line.

2. The control method for a high-voltage line temperature monitoring system based on dual-mode communication as described in claim 1, characterized in that: The high-voltage line temperature monitoring system controls the NB-IoT communication circuit and the LTE-Cat1 communication circuit to power on and operate according to an adaptive switching strategy, and shuts off the power supply to the corresponding communication circuit after communication is completed, so that the high-voltage line temperature monitoring system dynamically switches between low-power standby and reliable upload. The adaptive switching strategy is based on multi-factor evaluation, and the evaluation factors include at least the CSQ signal strength of the NB-IoT communication module and the LTE-Cat1 communication module, network registration status, network access time, MQTTS connection result, number of valid AT command responses, number of consecutive upload failures, success rate of the most recent uploads, IoT card operator information, and network frequency band information of the currently camped cell or searchable cell. The MCU generates a link priority based on the evaluation factors and selects the current upload link according to the link priority.

3. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 2, characterized in that: The MCU controls the power electronic switch S1 and the power electronic switch S2 to turn on or off through logic levels, thereby controlling the connection or disconnection of the corresponding linear regulator input power supply. When any communication circuit is in a non-working state, a communication abnormality recovery state, or an RTC standby state, the MCU shuts down the corresponding power gating branch, so that the NB-IoT communication circuit and the LTE-Cat1 communication circuit are in a mutually independent power-off isolation state.

4. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 2, characterized in that: The link priority strategy of the monitoring system is as follows: The monitoring system prioritizes NB-IoT communication circuit for network access and data transmission. When the NB-IoT communication module experiences network connection abnormalities, data transmission failures, failure to complete network access within a preset time, AT command retransmission counts reaching a preset limit, or the recent upload success rate falling below a preset threshold, the MCU shuts off the power supply to the NB-IoT communication circuit and switches to the LTE-Cat1 communication circuit for data transmission. After switching from the NB-IoT communication circuit to the LTE-Cat1 communication circuit, the monitoring system sets a link recovery hysteresis condition. Only when the NB-IoT communication circuit continuously meets the preset CSQ threshold, network access time threshold, and upload success condition in subsequent monitoring will the monitoring system restore the communication priority to the NB-IoT communication circuit, so as to avoid frequent switching between the NB-IoT communication circuit and the LTE-Cat1 communication circuit in weak coverage environments.

5. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 4, characterized in that: The monitoring system pre-stores or receives updated IoT card operator frequency band priority information. The operator frequency band priority information includes at least the IoT card's owner operator, the priority frequency band corresponding to the NB-IoT communication standard, and the priority frequency band corresponding to the LTE-Cat1 communication standard. The monitoring system prioritizes the NB-IoT frequency band that the IoT card's owner operator can search for or has already registered at the current location for low-power uploading. When the NB-IoT frequency band does not meet the preset access or uploading conditions, the system then selects the LTE-Cat1 frequency band that the IoT card's owner operator can search for or has already registered at the current location for uploading.

6. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 4, characterized in that: The AT command interaction between the NB-IoT communication module and the LTE-Cat1 communication module is configured with error detection, retransmission, and power-off reset mechanisms. After sending an AT command, the monitoring system checks the validity of the returned message. If an erroneous message, an illegal message, or no response is received within a specified time, the current message is cleared and the corresponding AT command is retransmitted. If a single AT command exceeds the maximum number of retransmissions or the communication module does not respond, the MCU shuts down the corresponding power gating branch, and after a preset discharge waiting time, it is powered on and initialized again. If data upload is still not completed after power-off reset, it switches to another communication circuit.

7. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 4, characterized in that: The monitoring system uses lithium batteries as energy storage units, combined with photovoltaic panels to continuously power the lithium batteries; the MCU dynamically adjusts the temperature acquisition cycle, data upload cycle, and communication link selection based on the lithium battery voltage, photovoltaic charging status, temperature threshold, and temperature rise rate. The specific logic is as follows: When the lithium battery voltage is lower than the preset low charge threshold and the temperature is not abnormal, the temperature acquisition cycle is extended and the NB-IoT communication circuit is used to upload data first. When the temperature exceeds the preset alarm threshold or the rate of temperature rise exceeds the preset rate of change threshold, the system will immediately wake up and prioritize the communication link with the higher success rate of uploading to upload alarm data.

8. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 2, characterized in that: After completing temperature data acquisition and uploading, the MCU controls the power gating branch to shut down the power supply to the NB-IoT communication circuit, LTE-Cat1 communication circuit, and temperature acquisition circuit, and enters low-power mode after configuring the RTC wake-up timer. When the RTC wake-up timer reaches the set time, the MCU is re-wake up and starts the next round of temperature data acquisition and uploading. When the MCU experiences program abnormalities, communication abnormalities, or wake-up failures, the external watchdog automatically resets the MCU.

9. The control method for a high-voltage line temperature monitoring system based on dual-mode communication according to claim 2, characterized in that: When there is a distance deviation between the installation location of the temperature sensor and the planned monitoring location, the monitoring system executes a heat conduction temperature back-calculation algorithm to compensate for the installation offset distance. The cloud server sends the distance from the installation location to the planned monitoring location to the MCU of the main control circuit. Based on the installation location temperature, ambient temperature, and distance measured by the temperature acquisition circuit, the monitoring system uses a preset heat conduction attenuation model to back-calculate the temperature at the planned monitoring location. The back-calculated temperature at the planned monitoring location is then used for temperature alarm judgment, acquisition cycle adjustment, and communication link selection.

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