Jiwei Cao

Design of the HTS Permanent Magnet Motor With Superconducting Armature Winding

The superconducting motor generally adopts superconducting magnets to supply high flux density in the air-gap around the rotor. This structure can decrease the volume as a result of the high magnetic load, but it also creates cooling difficulty problems due to the cooling mediums spin sealing. Therefore, the superconducting magnets need frequent maintenance, and this structure cannot be applied in the industry field. So a novel high temperature superconducting motor with a superconducting armature coils is researched. This motors stator uses ferromagnetic material and the superconducting windings are located in the slots. The ferromagnetic material can decrease the magnetic field in the superconducting coils, so the current carrying ability of the superconducting coils can be increased. The rotor adopts the permanent magnets as the excitation. Such design details of the motor can ensure the superconducting coils can undertake larger current and reduce AC loss. In this paper the electromagnetic field distribution of the HTS motor stator coils is analysed. Finally, the detailed HTS motor parameters are presented to analyse the output torque characteristic. From the characteristics, it can be seen that the novel HTS motor has the same power density as the traditional HTS motor.

Design of the Cryogenic System for a 400 kW Experimental HTS Synchronous Motor

A 400 kW radial-axial flux type experimental HTS synchronous motor is designed. There are twelve armature coils used HTS wires in the motor. They are accommodated in the cooling vessels made of FRP material, and twelve cooling vessels are enclosed in the vacuum vessel. In order to cool the HTS coils of the motor, a sub-cooled liquid nitrogen cryogenic system is presented. The operation temperature is below 70 K. This system consists of HTS coils cryostats, liquid nitrogen transfer-line, liquid nitrogen dewar and a cold box with liquid nitrogen pump, G-M cryorefrigerators and some control valves inside. In this paper, different kinds of the heat loads of the system including the AC loss, current lead, supporters and radiation are presented. Basis on the heat load and operating temperature, the main parameters and equipments of the system are determined.

Design of Axial and Radial Flux HTS Permanent Magnet Synchronous Motor's Rotor

Most of superconducting motors use the superconducting coils as the excitation coils which are located in the rotor. But its cool system is complex and the cool temperature is lower than 60 K. A novel axial-radial flux HTS (high temperature superconducting) motor is presented with the liquid nitrogen cool, its armature winding in stator is superconducting coils, the excitation winding in cover is superconducting coils, permanent magnets is located in the rotor. Its cool system is simple, and easy to implement. But the electromagnetic parameters are required to ensure the armature current can flow in the winding with low voltage. Through the prototype test with the copper winding instead of the superconducting winding, a novel rotor structure fit for the HTS motor with superconducting armature winding is presented.

Magnetic Field Distribution Around Superconducting Coils in Ferromagnetic Environment

There are two kinds of high temperature superconducting motor (HTS) according to the angle of the superconductors shape, one with the superconducting bulk and the other with the superconducting tapes. Using the superconducting tapes, HTS motors, whose superconducting magnets are located in the rotor, have been researched by many researchers and institutes. This paper research a novel HTS structure that the superconducting coils are placed in the slots of the stator made of ferromagnetic materials. This paper researches the magnetic field distribution of the superconducting coil in the slots and teeth of the stator. The electromagnetic field distribution under the influence of rotating magnetic field and ferromagnetic material is presented firstly. Then, considering the effect of coupling of AC current that flow in the superconducting coils, the distribution of magnetic field is further analyzed. Finally, in order to reduce the alternating current loss, a ferromagnetic slab is added beside the superconducting coils and the improved magnetic field distribution is researched. The simulation result shows that this method is instrumental in harvesting a decrease of the perpendicular flux density from the 0.34 T to 0.06 T.

AC Loss Prediction in BSCCO-Tape Armature Winding Design of a Synchronous Motor

A permanent-magnet synchronous motor with high-Tc superconducting (HTS) armature operated at sub-cooled liquid nitrogen temperature has been designed. The prototype model has a ten-pole rotor and twelve sets of armature windings which are fabricated with BSCCO tapes, and its output power is 400 kW at the rated speed of 250 rpm. In order to decrease the AC loss of HTS coils to an appropriate level, the conventional stator iron cores are adopted. The coil design, behaviors of HTS conductors, even cooling system design will be proved in the armature case. And the prediction of AC loss in stacked tape conductor exposed to external magnetic fields with various directions have been carried out using FEA method. Based on the 3D magnetic field finite element analyses, this paper presents an AC loss analysis method for the armature winding and provides upper the limit of operating temperature for the cooling system.

Research on Magnetic Shield Effect of AC Superconducting Armature

The superconducting motor with superconducting armature winding has simple cooling and a high running temperature of 66 K-77 K so the motor with a superconducting armature winding and excitation has been researched by many institutes. When the superconducting armature winding was adopted in the superconducting motors, the magnetic field around the coils would influence its performance. Therefore, this paper researches the distribution of the superconducting coils in the stator tooth-slot environment which is composed of ferromagnetic material. Based on the analysis of electromagnetic distribution, a new shield method is presented for decreasing the magnetic field which is around the superconducting coils when an active current flows through the coils. The shields ferromagnetic material structure parameters are optimized by FEM (finite element method) software to seek the optimization parameters which create a minimum magnetic field. Finally, the experimental result shows the shield method can decrease the magnetic field around the superconducting coils, and the method can decrease the AC loss of the superconducting coils.

Current control for the single degree of freedom linear maglev system

The single DOF (degree of freedom) linear maglev (magnetic levitation) system is the basis of studying on the maglev guideway. Generally, the electromagnet is selected to provide the electromagnetic force, however, this force is highly nonlinear. This paper presents a linear model of the single DOF linear maglev system, and establishes the corresponding experimental platform. In order to improve the dynamic response and depress the current ripple, a predictive current control based on three-level technology is proposed. The simulation and experimental results show that the proposed method achieves excellent dynamic and static performance.

AC Current Carrying Property of High-

Current carrying capabilities of HTS tapes and coils can be defined by critical current when carrying DC current. While there is no standard criterion to judge their AC current carrying capability. In actual industrial applications, HTS tapes and coils often need to work in AC conditions. Accurately calculating the current carrying ability of tapes and coils is a precondition of designing a HTS machine. DC and AC V - I properties are measured using four-probe method under different background magnetic field. The method of measuring and obtaining the AC maximum working current is given. The applicability of the method and phenomenon of experiment is discussed based on the Anderson-Kim flux creep model. The content of this paper moderately contributes to the completion of superconducting technology. And the paper can be referenced when designing HTS machine with HTS tapes or coils carrying AC current.

T_{c}

The existing flow analysis in air gap of high speed motor commonly neglects Tooth-slots effects. The influence of whirlpools induced by the slots and teeth on flow field and heat transfer of high speed motor is investigated in this paper. According to the theory of fluid mechanics, the solved region and boundary conditions of fluid field of air gap in the high speed motor are assigned. Two kinds of flow field distributions of air gap in the high speed motor considering the air in the notches of slots in solved domain or not are presented. Then the normal flow temperature coupled field calculation model ignoring the air movements in the notch is established and calculated. And the new model in which the air in the notch is included in the calculated fluid region is solved. The result is compared with the traditional method result which approves that the proposed method can provide an accurate understanding on thermal property analysis of high speed motor. At last, the heat transfer coefficients at the air gap surface considering Tooth-slots effects are computed on the basis of calculation of flow field, and the 3D temperature field of high speed motor is analyzed.

Superconducting Tapes and Its Magnetic Field Dependence

Rotating electromagnetic voltage converter (REVC) is a new structure voltage conversion device. It has many functions including voltage change, reactive power compensation, harmonics isolation and suppression. Flywheel energy storage device possesses the characteristic of high-power and fast-speed discharge. With loading the flywheel, REVC can output mechanical energy of the flywheel when sudden power failure or voltage sag happens in the power grid, maintain uninterrupted power output to ensure the normal operation of the load. Appling mathematical model, simulation of the working status of the REVC with flywheel is completed, and the characteristics of REVC with Flywheel (REVCF) when a sudden power failure happens in the power grid are summarized. Finally, the prototype experiment proves the correctness of the simulation results.