Stress calculation is a key link in evaluating whether the structure of a superconducting magnet is safe. A 35-kV/3.5-MVA single-phase high temperature superconductivity-controllable reactor (HTS-CR) with the HTS winding wound by HTS double pancakes is being developed. The effect on the local stress and temperature rise of HTS double pancakes, which determines the design of the strengthening structure of the HTS double pancake, is studied in this paper. Furthermore, the multiprocess stress development for HTS double pancakes from manufacturing to power-on is also investigated, which discloses the model and the results of the stress calculation. This study can provide a reference for developing HTS-CR with large capacity in the future.

In the five-phase-inverter adjustable speed system, a five-phase two-level inverter usually adopts the nearest-two vector SVPWM (NTV-SVPWM) or the nearest-four vector SVPWM (NFV-SVPWM). The former one has a high-output-current harmonic, which increases the power losses, while the latter one has a low harmonic, but its sinusoidal voltage transfer ratio (VTR) is 0.812, which decreases load capacity. To improve the loading capacity and decrease the power losses of the five-phase-inverter adjustable speed system, a new space vector over-modulation method based on multi-vector weighting is proposed in this paper, and harmonic characteristics of the proposed over-modulation method are analyzed. The simulation results indicate that the proposed over-modulation method has a lower output voltage error than that with the traditional NFV-SVPWM and has a lower output current THD than that with the traditional NTV-SVPWM. The experimental results verify that the proposed method is correct and feasible.

Aiming at the chattering issue in speed observation for sensorless control, this paper proposes a sliding mode observer based on an improved double-power reaching law for high-performance speed estimation in five-phase induction motors. Traditional constant-rate reaching law observers exhibit significant chattering, while the double-power reaching law, though offering certain “variable-gain” adjustment effects, still has limited chattering suppression capability. To address this, the paper introduces a state variable related to the stator current into the conventional double-power observer, further enhancing the ability of the sliding mode gain to vary with the system state. This approach effectively suppresses chattering while maintaining convergence speed. The stability of the observer system employing the new reaching law is proven using Lyapunov stability theory, and the value ranges of key parameters are determined. Simulation results demonstrate that, compared to traditional constant-rate reaching law and conventional double-power reaching law observers, the proposed improved method significantly reduces speed observation chattering and effectively enhances the observation accuracy of the observer.

As a novel inverter topology for multiphase motor drives, the m-phase series winding inverter (SWI) can reach 100% DC-link utilization similar to m-phase H-bridge inverters, while SWIs' power switches count is close to that of half-bridge inverters. Yet, existing laws for forming winding connection sequence (WCS) and judging the WCS's feasibility in SWIs can't deal with situations where part of motor windings are connected in the reverse direction. In this paper, a phase angle difference parameter Δn is proposed. Combined with the voltage vector diagram, Δn provides a more straightforward method for forming all possible WCSs with windings connected either all in forward direction or partially in reverse direction for m-phase SWIs. Moreover, it is derived that the coprime relationship between Δn and m serves as a criterion for determining the feasibility of the corresponding WCS. Based on this criterion, a counting function is introduced to quantify the number of feasible WCSs, thereby preventing omissions during enumeration. Further investigation reveals that the DC-link utilization of the SWI improves as Δn increases, while the leg current stress also rises with larger Δn. Experimental validation on a five-phase induction motor platform and a nine-phase resistive-inductive load confirms the completeness and generality of the proposed principles.