General Atomics Engineering teams follow a structured process when designing and evaluating a prototype. As an example, one project is a motor-development program for a three-phase brushless AC motor rated at hundreds of kilowatts for an aerospace application. The motor is very lightweight for its power rating and operates at very high inverter switching frequencies. The GA-EMS team is multidisciplinary and includes mechanical and electrical engineers as well as manufacturing engineers. The team engages outside suppliers for their expertise in areas extending down to details such as magnet wire and bearings.
GA-EMS lead electrical engineer, Matthew Zolot, described in general how the company approaches such projects. “We follow an R&D progression to develop clean-sheet prototype motors; we start with specification and requirements followed by an analytical proof of concept,” he said. “The design is iterated until we’ve converged on an optimal concept solution. At that point, we go through an internal design review before moving on to prototype production followed by experimental proof of concept.” The key verification parameters fall into three main categories: the thermal system, the electromagnetic system, and the structural or rotor-dynamic system.
According to GA-EMS, measurements on a new aerospace motor can present significant challenges. At these power, voltage, and current levels, one of the biggest challenges is measurement noise while the motor is operating. “We aim to minimize the noise coupling into the measurement signals or else we’ll have to clean the signals up while we are acquiring them or afterward,” Zolot said.
The team collects considerable amounts of data during its test. During the first article prototype operation, the focus is on the vibration (accelerometer) data to monitor the prototype’s build integrity during the initial tests. Simultaneously, GA-EMS collects data that will provide indications that the electromagnetic system is operating as expected, like back EMF and the phase currents. These early mechanical and electromagnetic tests are short duration.
As the GA-EMS team builds confidence in the prototype builds and the system’s operation, the testing effort moves onto longer duration runs. The test setup shifts focus to evaluate the thermal capabilities. Meeting thermal targets under representative profiles comprises key performance metrics. This stage of validation allows for characterization of the overall efficiency and the cooling system performance.
Aerospace applications can present unique challenges related to thermal performance. “On this type of motor, we use both liquid and air for heat removal, which isn’t necessarily something that you do in other fields that are not aviation-based,” Zolot said. “It’s different from land-based applications in that respect.”