Tech Briefs

Computer program helps UAVs avoid collisions with overhead wires.

Army Research Laboratory, Adelphi, Maryland

The Army Research Laboratory Power-Line Unmanned Aerial Vehicle (UAV) Modeling and Simulation (ARL-PLUMS) Software Tool allows a user to model, compute, and analyze the quasistatic electric and magnetic fields around alternating current (AC) power lines. ARL-PLUMS comes with an interactive graphical user interface (GUI), which accesses a compute engine to calculate these fields around these lines due to various ground and line geometries and load conditions. ARLPLUMS allows the user to rapidly define all significant model parameters and compute the electric and magnetic fields along a UAV path or in a cutting plane. In addition, a set of false-color plots can be created to show the time-varying nature of the fields as a movie. ARL-PLUMS also comes with an application programming interface (API) for accessing some of these features from MATLAB without using the GUI.

Example of 2D power-line model created in ARLPLUMS

ARL-PLUMS uses a right-handed coordinate system. When seated at the computer and looking at the monitor, the positive x direction is out of the screen, toward the user; the positive y direction is to the right; and the positive z direction is up, toward the ceiling. The power lines run parallel to the x axis and positive current runs in the positive x direction. Sea level is always at z = 0 m, and all other geometry is referenced to this. An example 2-D power-line model created in ARL-PLUMS is shown in the figure. In this example, there is a single 3-phase circuit 20 m above the ground, and the wires are spaced 4.4 m apart.

Generally, the electric and magnetic fields around power lines are treated separately and independently as quasistatic entities. This is permissible because at typical power-line frequencies (50 or 60 Hz) or low (e.g., 3rd or 5th) harmonics, the corresponding electromagnetic wavelengths are 1,000–6,000 km. Only the behavior of the fields in the vicinity of the power lines is of interest. This is generally 0–10 km away, which is a fraction of these wavelengths. In this region, coupled electromagnetic effects (such as wave propagation) are negligible compared to the effects of the quasistatic sources, themselves.

In the quasistatic case, the voltages on the lines give rise to an electric field around the lines, and the currents on the lines give rise to a magnetic field around the lines. However, while the currents are the sources of the magnetic field, the voltages do not directly source the electric field. Instead, through capacitive coupling, the voltages induce linear charge densities on the lines and an image charge distribution on the ground, and this charge distribution is the actual source of the electric field. In either case, the total (measured) field at any point is the superposition of the constituent fields from each line source at that point.

Various combinations of the electric and magnetic fields, such as rms magnitudes, derivatives with respect to time and/or distance, ratios, and percent changes, can be used by a UAV to detect power lines. Each of these quantities has a specific structure around the lines, which can be exploited to determine how close to the lines the UAV is. No matter the direction of approach, the UAV will measure larger and larger fields as it moves closer and closer to the lines. Once the UAV has detected the lines, it can take action to avoid crashing into them.

This work was done by Ross N. Adelman and David M. Hull of the Army Research Laboratory. ARL-0192

This Brief includes a Technical Support Package (TSP).

US Army Research Laboratory Power-Line UAV Modeling and Simulation (ARL-PLUMS Ver 2.x) (reference ARL-0192) is currently available for download from the TSP library.

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