The UAV electrical system is made up of two parts: power generation consisting of a power generator and generator control unit, and power distribution that controls the unit and load distribution devices. To execute the electrical system, we use an electric motor to mechanically drag the generator in the same way the engine drags the real UAV. We also use a load bench system to apply the same load levels to the electrical system that are applied to the real plane. We needed a control system to manage all these functions. The application also includes a data acquisition system to measure certain parameters such as voltage, contactor status, control unit I/O signals, and simulation of the equipment that is not present in the electrical system but interacts with the system in the real plane.
We created an electrical rig test environment that performs two functions: excitation of the electric system so that it can be tested under the different conditions it was designed for and system status monitoring that helps determine if the equipment is correctly integrated and if the complete system fulfills the design requirements.
We use a Bosch electric engine to simulate the plane engine that moves the generator. A frequency variator attached to the electric motor has a discrete and analog I/O interface managed by a control system based on NI CompactRIO. The control system houses the start/finish logic for the driver and engine, as well as the logic for the two functioning modes: dragger and brake, which respond to the requirement of testing both the electric power generation function itself (where the engine drags the generator) and the start function (where the generator drags the engine). The system features alarms so it responds safely under unforeseen circumstances.
Dynamic load benches offer electric power to simulate the load environment. They can dynamically reproduce the load profiles applied to the electric system during a real flight.
The test environment also uses a system based on fault insertion modules from Pickering that can interrupt any signal from the electric system circulating between the equipment, for example, the status on a contactor or a voltage measurement. This device automatically simulates fault conditions on the different control software developments so we can develop new test sets with every new software release.
Another part of the application is the data acquisition system that uses an NI CompactDAQ chassis and analog and discrete I/O cards. The system monitors and records electric measurements such as voltage and current, contactor status, and system signal status. In addition, this infrastructure simulates certain plane elements that interact with the electric system using models with I/O associated with the I/O of the DAQ system.
Another pillar of this application is the software developed by our labs department. The software features analog signal acquisition at 5,000 samples per second. With this frequency, we have the correct representation of the signals in AC as well as precise calculation of sophisticated signals such as rms, frequency, and power factor.
The software features discrete signal acquisition at 1,000 samples per second so we can precisely determine the electric systems’ contactors operating sequences as well as the power transfer in different configurations. The software can also simulate hardware signals such as weight on wheels and operating switches. We connect external equipment simulations to the control units of the electric system through serial bus. The online quality analysis of electric power meets applicable MIL-STD-704. We verify this by generating the signals through software to compare them to the standard as well as to the discrete signals to check whether a certain part of the standard is fulfilled.
Technical Data Management Streaming (TDMS) recording guarantees compatibility with NI DIAdem software. We implemented synoptics and a graphical interface for the control system (CompactRIO, load benches, and Pickering system) and the acquisition system (NI CompactDAQ). We achieved integration with the automated test execution environment by using DLLs integrated in LabVIEW. We use these to communicate with the stimulation and signal acquisition system that is managed by a MathWorks, Inc. MATLAB® software automated test environment.
All the elements described above constitute the electric rig (see Figure 1). We chose a vertical rack that houses the elements of the UAV electric system, as well as the NI CompactDAQ system. The engine, driver, generator, control unit, and CompactRIO are located outside the rack connected to it.
We developed an electrical rig for a UAV that includes a control system based on CompactRIO to manage the excitation requirements typical of these applications and a data acquisition system based on NI CompactDAQ to monitor and simulate certain parameters. We used LabVIEW to develop the software in both the acquisition and control systems. With LabVIEW, we easily implemented required functions and allowed for future modifications on the test site. NI hardware and software helped us achieve a short development time and respond to the increasingly demanding time and cost requirements for these applications.
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Santiago R López Gordo