The following describes in detail a power line patrol UAV navigation system based on GPS RTK technology provided by the present invention with reference to the accompanying drawings and specific embodiments.
 In the following description, a number of different aspects of the present invention will be described. However, for those of ordinary skill in the art, only some or all of the structures or processes of the present invention can be used to implement the present invention. For clarity of explanation, specific numbers, configurations, and sequences are described, but it is obvious that the present invention can also be implemented without these specific details. In other cases, in order not to obscure the present invention, some well-known features will not be described in detail.
 With the rapid development of satellite positioning technology, people's demand for fast and high-precision location information is becoming stronger. At present, the most widely used high-precision positioning technology is the real-time dynamic positioning technology (Real-TimeKinematic, RTK). The key of RTK technology is the use of GPS carrier phase observation and the use of the observation error between the reference station and the mobile station. Spatial correlation removes most of the errors in the observation data of the mobile station by means of difference, thereby achieving high-precision positioning.
 The biggest problem encountered in the application of RTK technology is the effective range of the reference station calibration data. The spatial correlation of GPS errors gradually loses linearity as the distance between the base station and the mobile station increases, so at a longer distance (single frequency> 10km, dual frequency> 30km), the mobile station data after differential processing still contains large observation errors, which leads to the reduction of positioning accuracy and the inability to resolve the whole-cycle ambiguity of the carrier phase. For power line inspection, this effect is fatal. Therefore, in order to ensure satisfactory positioning accuracy, the operating distance of the traditional stand-alone RTK is very limited.
 In order to overcome the shortcomings of traditional RTK technology, network RTK technology is proposed. In the network RTK technology, the linearly attenuated single-point GPS error model is replaced by the regional GPS network error model, that is, the GPS network composed of multiple reference stations is used to estimate the GPS error model of an area, and the GPS error model for the network coverage area The mobile station provides correction data. And what the mobile station receives is not the observation data of an actual reference station, but the data of a virtual reference station, and the correction data of a reference grid that is closer to its own location, so the network RTK technology is also called Virtual reference station technology (Virtual Reference).
 In the first embodiment of the present invention, a GPS RTK technology-based UAV navigation system for power line patrol is provided. The GPS RTK navigation system integrates technologies such as differential GPS, wireless communication, computer display and control, and is The power line patrol drone provides high-precision navigation and position display, and provides monitoring and control information for the ground station. The GPS RTK navigation system sends GPS differential data to the mobile station (drone) through a wireless data link through multiple reference stations set up on the transmission line. The drone’s navigation system uses GPS RTK differential technology to obtain centimeter-level precision navigation At the same time, the UAV's flight control system realizes real-time monitoring of the mobile station (UAV) and each reference station by the ground station through wireless communication technology.
 Specifically, in this embodiment, as figure 1 As shown, the GPS RTK navigation system includes one or more mobile stations (unmanned aerial vehicles), multiple reference station subsystems and a ground station monitoring subsystem, the multiple reference station subsystems are respectively arranged on the power line tower . Among them, the UAV's navigation system uses GPSRTK differential technology to achieve high-precision positioning and navigation of the UAV, providing a reliable guarantee for the power line patrol UAV to perform line patrol operations according to the precise flight trajectory.
 Among them, the ground station monitoring subsystem is used to start the work of each reference station through the wireless data transmission system at the beginning of the power line inspection operation, and to monitor the mobile station (UAV) in real time through the wireless data transmission system during the power line inspection operation. ) And the working status of each base station. Among them, each reference station subsystem is used to send GPS differential data in real time through the wireless data transmission system, which can be once a second. Among them, the mobile station (drone) is used to receive the GPS differential data sent by each reference station in real time through the wireless data transmission system, and obtain high-precision navigation information through real-time calculation and processing of GPS RTK differential technology. The control system transmits its own position and speed information and the working status information of each reference station to the ground station through the wireless data transmission system.
 Among them, the reference station subsystem is used to continuously receive all visible GPS satellite signals, and send the station coordinates, pseudorange observations, carrier phase observations, satellite tracking status, and receiver operating status to the mobile station. Among them, the GPS RTK navigation system can accommodate more than 30 reference stations, and has scalability. Among them, the speed accuracy of the system is better than 5 cm/s, the system time synchronization accuracy is better than 50 nanoseconds, the cold start time of the system is better than 60 seconds, and the hot start time is better than 15 seconds.
 Among them, the system uses 902-928MHz ultrashort wave frequency hopping digital radio communication, and the communication distance is greater than 50 kilometers under the condition of visibility. Among them, the UAV navigation position output update rate is up to 5Hz, the GPS differential data output update rate is 1Hz, and the aircraft position return update rate is 1HZ. Among them, for the data transmission rate, the GPS serial transmission rate is up to 2304000bps, and the air data link transmission rate is up to 38400bps, which fully meets the rate of GPS differential and aircraft position output and return.
 Further, such as figure 2 As shown, the mobile station subsystem includes UAV GPS navigation system, wireless data transmission system and control equipment. Among them, the wireless data transmission system includes radio and radio antenna. Among them, the control device is used to provide centimeter-level high-precision navigation information for the UAV autopilot system through GPS RTK differential technology. Specifically, the control device connects the GPS mobile station and the radio station, receives the GPS differential data sent by each reference station in real time through the GPS mobile transmission system, and obtains high-precision navigation information through real-time calculation and processing of the GPS RTK differential technology. At the same time, the control equipment transmits its own position and speed information and the working status information of each reference station to the ground station through the radio's wireless data transmission system. The power conversion device can be connected to the onboard battery equipment.
 Among them, when the mobile station (UAV) receives data from the base station, it synchronously observes and collects GPS satellite carrier phase data, and solves the carrier phase ambiguity through differential processing in the GPS RTK system. According to the base station and the mobile station (without Based on the spatial correlation between human and machine, the differential observation values are formed in the system for real-time calculation and processing, and the centimeter-level accurate plane coordinates x, y and elevation h of the mobile station (UAV) are obtained.
 Wherein, in this embodiment, when the time system used by the GPS RTK differential technology is GPS, the coordinate system is the WGS-84 coordinate system (World Geodetic System-1984 Coordinate System). The processing method includes: eliminating ionospheric errors and calculating satellite positions. Among them, to eliminate the ionospheric error is to obtain the actual ionospheric delay value through the ionospheric grid delay algorithm to eliminate the ionospheric error. It includes: calculating the ephemeris to get the satellite position; finding the ionospheric penetration point position, finding the corresponding grid point, finding the ionospheric delay correction number of the 4 vertices of the grid; interpolating to obtain the penetration point vertical delay correction number , Find the actual delay value of the penetration point.
 Among them, calculating the satellite position includes calculating the ephemeris data, adding ephemeris correction and difference information to calculate the satellite position. Furthermore, the binary-encoded ephemeris data stream received from the GPS OEM board must be calculated according to the standard data structure, and then converted into decimal-encoded data according to the IEEE-754 standard. Here, the parameters to be solved are: the square root of the semi-major axis of the orbit (sqrta), the correction of the mean anomaly (dn), the ephemeris reference time (toe), the mean anomaly at toe (m0), and the eccentricity Rate (e), perigee angular distance (w), satellite orbit perturbation correction parameters (cus CUC cis cic crs crc), orbit inclination (i0), ascending node right ascension (omg0), ascending node right ascension change rate (odot) .
 Among them, the positioning accuracy of the GPS RTK navigation system in RTK working mode, the plane accuracy is better than 2CM+1PPM (CEP, the distance increases by 1 km, the error increases by 1 mm), and the elevation is better than 5CM (CEP).
 Among them, such as image 3 As shown, the base station subsystem includes GPS differential base station host, wireless data transmission system and base station control equipment. Among them, the base station also includes a backup base station host for backing up GPS data. Among them, the wireless data transmission system includes high-power frequency hopping radio and radio antenna. Among them, the base station host and control equipment are all erected on the towers of the transmission line corridor. Several sets of base stations form the base station subsystem, which provides GPS differential data for the mobile station subsystem (UAV).
 Among them, the GPS host and the radio adopt a separate design, the reference station is powered by a solar battery, and the power supply of the control device is composed of two modules: the power supply of the signal receiving module is in a normally open state; and the power switch of the signal transmitting module adopts a remote control method. When the power line inspection operation is not performed, the base station transmitter module is in a sleep state, and only the receiver module is in a normal working state. At the beginning of the power line inspection operation, the operator operates the ground station system and starts the work of each reference station through the wireless data transmission system, and monitors the working status of the mobile station (drone) and each reference station in real time; the power line inspection operation is completed Operators operate the ground station system and turn off the power of the signal transmitter module of each base station through the wireless data transmission system.
 Among them, such as Figure 4 As shown, the ground station monitoring system includes a wireless data transmission system and a monitoring host. The wireless data transmission system includes a radio station and a radio antenna. Among them, the ground station monitoring host is used to start the work of each reference station through the wireless data transmission system at the beginning of the power line inspection operation, and to monitor the mobile station (drone) in real time through the wireless data transmission system during the power line inspection operation. The working status and the working status of each base station.
 Among them, such as Figure 5 As shown, for the wireless data transmission system of the present application, the network is formed through wireless communication. The wireless communication network structure of the present application adopts the wireless communication of the frequency hopping radio network to make the time base of the radio unified, which is directly related to the wireless communication. Whether there is a collision between human and machine in the process of power line inspection. This system selects the 1PPS signal output by GPS as the time base unified reference. It has the characteristics of high precision and strong reliability, which fully meets the needs of large-capacity data transmission and networking.
 Among them, the wireless communication network includes several wireless communication devices, including a mobile station (unmanned aerial vehicle), multiple reference stations and a ground station system radio. Among them, the data transmission between the mobile station and the base station is a point-to-multipoint (P2M) network composed of several frequency hopping radio stations. Among them, the ground station monitoring system needs to transmit data with the GPS equipment of the mobile station and the reference station to form a point-to-multipoint (P2M) network. In the P2M network, the transmission and reception timing of each station is controlled by the ground station system, and the control mechanism adopts TDMA. The ground station allocates transmission time slots for each communication device and itself. Any station only transmits in its own transmitting time slot and automatically enters the receiving state during the rest of the time. In order to realize TDMA, the radio station in the network realizes the clock synchronization automatically at first, and keeps it all the time, can keep the clock synchronization through 1PPS output by GPS, its synchronization precision can reach 50NS.
 When entering the transmission time slot of the communication equipment of a certain site, the communication equipment of the site starts to transmit, and the communication equipment of the other sites remain silent, and the ground station system receives the data transmitted by the communication equipment of the site. If the data transmission is not complete in a time slot, the station will continue to transmit after entering the time slot of the machine next time. By selecting the appropriate port rate, each radio station can complete data transmission and reception without causing data overflow. The radio itself is networked according to the TDMA mode, and the ground station system allocates receiving and transmitting time slots for each station in the network. When configuring the network, you need to input the number of radio stations in the network and the port rate to the radio. The ground station system will automatically form a time slot allocation strategy based on these parameters. The final result of the execution of the time slot strategy is to ensure that the ground station system and each station work according to the set port rate, and then ensure that all stations can achieve the data rate and total transmission required by each station.
 According to the system of this application, the MTBF (mean time between failures) of the main equipment of the system is greater than 2000 hours, the drone's on-board GPS navigation equipment uses on-board power batteries, and the reference station equipment uses solar batteries, and the power consumption is less than 8W. The UAV airborne GPS and radio adopt an integrated design, the weight does not exceed 1Kg, and the size does not exceed 80mm (length) × 50mm (width) × 30mm (height), which can be designed according to the user's airborne type. The reference station GPS and radio adopt an integrated design, the weight does not exceed 2Kg, and the size does not exceed 200mm (length) × 150mm (width) × 100mm (height), which can be customized according to user needs. The working temperature of the airborne GPS equipment is -40℃~+55℃, and the storage temperature is -55℃~+65℃; the working temperature of GPS reference station is -30℃~+55℃, and the storage temperature is -40℃~+65 ℃, and the humidity of GPS equipment and radio is 95% non-condensing.
 Finally, it should be noted that the above embodiments are only used to describe the technical solutions of the present invention and not to limit the technical methods. The application of the present invention can be extended to other modifications, changes, applications and embodiments, and therefore all such Modifications, changes, applications, and embodiments of are all within the spirit and teaching scope of the present invention.