Magnetization and Losses for an Improved Architecture of Trapped-Flux Superconducting Rotor

Abstract

A hybrid electric configuration for aircraft propulsion yields several advantages, such as reducing the fuel consumption and takeoff distance, improving control, and decreasing emissions. For such a scenario to occur, advances designed to increase the power-to-weight ratio of actual electric motors must be developed. Superconducting technologies offer the prospect of achieving such performances but at a cost of increased design and construction complexities. In that sense, stacks of high temperature superconductors have proven to trap high-current vortexes that provide a source of magnetic flux density for torque production without the need of current leads or other equipment in the rotor. However, these macroscopic currents must be induced prior to operation and remain undisturbed by variations in the magnetic flux density of the airgap, such as the ones caused by heating and demagnetization. This work presents the results of numerical computations on a new rotor architecture designed to facilitate the magnetization of stacks from a superconducting stator and prevent their demagnetization during torque production. The machine performance is assessed, and the expected survivability of the trapped-flux in stacks is compared to laboratory measurements.

Time constant of the transverse-field demagnetization of superconducting stacks of tapes

“…Also, the analytical results are found using the Critical State Model, so with higher n values for the E − J Power Law, the numerical results will get closer to the analytical ones ( Figure 9). Numerical calculations also agree for higher number of tapes (Figure 9), validating equation (16) for its direct use in quick approximation of time constants for a stack.…”

“…For a finite stack with ferromagnetic material with high permeability present on both top and bottom sides, the system is similar to a stack with infinite number of tapes, and thus this formula can be used in this case too, which is also the case of a stack in a motor with a magnetic circuit (see figure 2) [15,16]. Figure 2: When a superconducting stack is kept between soft ferromagnets (left), it can be assumed to be acting as an infinite stack (right).…”

“…The main benefits of such motors over conventional ones are reduction of size (upto 70 percent), weight, noise, and vibration. Increased efficiency is one of its another benefits and the superconducting stacks of tapes can be used in rotors of HTS motors [13][14][15][16]. Recent advances in high temperature superconductivity and cryogenic systems have led to the use of HTS motors in various new applications, such as in aviation for future electric aircraft ( Hybrid Distributed Electric Propulsion) [17,18], generators [19] (with HTS coils), marine propulsion, and wind turbines [20] [21].…”

Modeling cross-field demagnetization of superconducting stacks and bulks for up to 100 tapes and 2 million cycles

“…In contrast, stacks do not lose much magnetization if the runtime of the application involve low number of cycles, even if the ripple field amplitudes are high. In motors for aviation, where ripple fields can range from few hundreds of Hertz to kilo-Hertz, the asymptotic value could be reached in times much shorter than the flight-times, being bulks more reliable for these applications, unless the ripple fields in the stack are strongly reduced 61 .…”

Superconducting Magnetic Heterostructured Components for Electric Motor Applications

“…The rotor yoke shields them producing a mostly a DC electromagnetic environment in what is known as an interior mounted magnet configuration. Based on this idea, a novel rotor layout specifically tailored for stacks operating in a fully superconducting synchronous motor was proposed in [12]. However, the rotor yoke's ferromagnetic material reduces the reluctance between the center and the edges of the magnet, increasing again the leakage flux, as seen in [12].…”