Tadashi Hirayama

Drive performance evaluation of linear switched reluctance motor using a current source inverter

This paper presents drive performance evaluations of a linear switched reluctance motor (LSRM) driven by a current source inverter (CSI). First, we describe a new drive circuit with CSI for the LSRM drive. For deliberations of drive performance evaluations, a simulation model is built by a circuit simulator. The drive performances of the LSRM with the proposed drive circuit are compared with a traditional voltage source inverter. As a result, it is confirmed that a deterioration of thrust with increase in velocity and an efficiency characteristics are improved by using the proposed drive circuit.

AC Loss Measurement of High-Tc Superconducting Coils Wound With Stacked Conductors

In order to elucidate the ac loss characteristics of high-Tc superconducting coils wound with stacked conductors, we measured ac losses of Bi-2223 sample coils under the various electromagnetic conditions by a nitrogen boil-off method. The sample coils were wound with stacked conductors, which were composed of two Bi-2223 tapes. Each tape of stacked conductors was wrapped with polyimide tape, and the ends were made into the open circuit or short circuit. The coils with transposition and the coils without transposition were prepared as sample coils. We measured the magnetic amplitude dependence and the frequency dependence of ac losses of sample coils under external magnetic fields, and evaluated the magnetization losses and coupling current losses. Measured data were compared with theoretical values. Based on the obtained results, ac loss characteristics of high-Tc superconducting coils wound with stacked conductors under external magnetic fields were discussed.

Measurement of Transport Characteristics in HTS Conductors With Large Current Capacity by Using an HTS Current Transformer

In order to quantitatively elucidate the transport characteristics of HTS conductors with large current capacities, we minutely investigated the relation between the current distributions in the sample conductor and the circuit parameters such as joint resistance and sample inductance. A high temperature superconducting current transformer (HTS-CT) was used to energize a large current in the sample conductor. No change in the joint resistance was observed with an increase of the sample current. On the other hand, the current ratio of the HTS-CT decreased with an increase in the sample current. This is considered to be equivalent to the inductance becoming large with an increase in the sample current. From the measured current distributions, we see that the current in the central area of the conductor is increased with increasing sample current. Based on these experimental results, the relation between the change of the current distributions and the increase of the sample inductance is discussed.

Development of a Compact Measurement System of Transport Characteristics in HTS Conductors by Using an HTS Current

In order to realize HTS power machines and devices with high performance, it is important to evaluate the characteristics of HTS conductors quantitatively. We developed a compact system to measure the transport characteristics of HTS conductors under various experimental conditions. This system enables us to measure the transport characteristics of straight HTS conductors up to a current capacity of 1 kA class at 77 K, 66 K, and 4.2 K. The measurement of transport current losses is done by the Poynting vector method. The distribution of Poynting vectors around the sample conductor can be obtained by using many sets of both potential leads and pickup coils. An HTS current transformer (HTS-CT) is used to feed current to the sample conductor for the measurement. A secondary current of about 1 kA at 77 K can be induced when the primary current is 40 A. The sample conductor is connected to the secondary coil of this transformer. As a sample conductor, we used a conductor consisting of 16 parallel Ag-sheathed Bi-2223 multifilamentary tapes. The joint method between the HTS-CT and sample conductors is also examined. Based on these results, the usefulness of this measurement system is discussed.

Output characteristics of linear switched reluctance motor with YBCO tape conductors

This paper presents output characteristics of a linear switched reluctance motor (LSRM) with excitation windings wound high-temperature superconducting (HTS) tapes. In a double-sided LSRM, Bi-2223 or YBCO tape conductors are used for the excitation windings. The characteristics of the LSRM are obtained by a finite element method analysis. We can obtain large thrust compared with a conventional LSRM by using YBCO tape conductors. Also, the effect of a configuration of the YBCO coil on the thrust is calculated. We discuss a suitable coil configuration for the average thrust upgrading.