Energy-Efficient Control Strategy for PMSM With Superconductive Stator Winding

This paper proposes a new control approach for inverter-fed permanent-magnet synchronous machines with superconductive stator winding (SPMSM) to minimize the ac losses in the superconductors. Particularly in electrical machines with ac-driven superconductors, the losses in the superconductor dominate the system behavior. In comparison to normal conductive materials, the losses in high-temperature superconductors, which are operating with alternating currents, are strongly coupled with the frequency of the current, the magnetic flux leakage, and the current shape. The frequency and the magnetic flux leakage are mainly design parameters of the machine. In contrast, the current shape can be influenced by an inverter with an intelligent control strategy that is based on separate current controllers with a cascaded voltage controller. The mathematical model of a SPMSM in a/b/c and in alpha/beta is used and takes the topology of the inverter with common-mode injection into account. This paper describes the details of the control scheme in which the magnitude of the current is controlled and the position of the current space vector is directly locked at the synchronous generated voltage, with the effects at resulting ac losses in the stator coils. Different kinds of loss measurements at single superconductive stator coils show the loss reduction in comparison to the state-of-the-art control scheme without losing the dynamic performance. The results from the single coil measurements will also be transferred to a prototype electrical 80-kW SPMSM.