概要 / Outline

Date:

• Tuesday, October 25, 2022 13:00-17:30

• Wednesday, October 26, 2022 09:30-14:55

Venue: Conference Room 2, Main Building, Ookayama Campus, Tokyo Institute of Technology and WEB

Presenter: Ren Sato

Presentation Number: RM-22-105

Title: Fundamental Study on Lightweight Design of Electromagnetic Motors with Carbon Nanotube Winding

発表内容 / Contents

This research aims to reduce the weight of motors in order to improve the performance of machines equipped with motors, such as industrial robots and electric vehicles. CNTs have higher electrical conductivity and lower density than conventional winding materials such as copper and aluminum (Table 1). The electrical conductivity of CNT yarns is currently lower than that of copper and aluminum, but it is expected to reach the level of copper in the 2020s due to recent improvements in manufacturing technology [4]. In this study, we design and evaluate a lightweight motor that can be designed when the electrical conductivity of CNT yarns is improved.

2. 　手法 – Methods

現在製造可能な電気伝導度10 MS/m[3]からCNTと同等の電気伝導度である100 MS/m[1]までのCNT糸を適用した表面永久磁石同期モータ (SPMSM) をPyrhönenら[6]に従って設計した．設計条件を表2に示す．

モータ形状を一意に決定するには，これらの設計条件のほかに電流密度を設定する必要がある．電流密度は一般的にモータの冷却方法から経験則的に決定するが，その値は銅コイルにのみ適用可能である．そこで，導体の体積当たりの発熱量が一定となるように電気伝導度ごとに電流密度を設定した．銅の電気伝導度64.5 MS/mで電流密度5 A/mm2として，この時の発熱量を基準として計算した電気伝導度に対する電流密度を図1に示す．

A surface permanent magnet synchronous motor (SPMSM) was designed according to Pyrhönen et al [6], applying CNT yarns with electrical conductivities ranging from 10 MS/m [3], which is currently available for production, to 100 MS/m [1], which is equivalent to CNTs. The design conditions are shown in Table 2.

In addition to these design conditions, the current density must be set to uniquely determine the motor geometry. The current density is generally determined empirically from the cooling method of the motor, but the value is only applicable to copper coils. Therefore, the current density was set for each electrical conductivity so that the amount of heat generated per volume of conductor is constant. Figure 1 shows the current densities for different electrical conductivities, calculated based on the heat generated at a copper conductivity of 64.5 MS/m and a current density of 5 A/mm2.

3.      結果 – Results

設計した4 kWモータの直径の比較を図2に示す．電気伝導度が高いほど電流密度が高く，スロット部の面積が小さく設計されることで直径が小さくなっていることが分かる．図3に銅モータを基準にしたCNT糸モータの直径の変化率を示す．出力4 kWのモータが最も電気伝導度に対する直径の変化が大きく，10 MS/mで+13.4 %，100 MS/mで-2.2 %だけ銅モータと直径が異なる．また，銅と同じ電気伝導度64.5 MS/m以前では変化率は正であり，銅モータよりも大型な設計となっている．

図4に銅モータを基準にしたCNT糸モータの質量の変化率を示す．電気伝導度30 MS/m以降ですべての出力で変化率は負となっており，銅モータよりも軽量である．つまり電気伝導度が銅以下のCNT糸でもモータの軽量化は達成されるといえる．また，図3と図4の結果を比べると30 MS以上64.5 MS/m未満の電気伝導度では銅モータよりも大型化するものの軽量化は達成されているということが分かる．

A comparison of the diameters of the designed 4 kW motors is shown in Figure 2. It can be seen that the higher the electrical conductivity, the higher the current density, and the smaller the diameter due to the smaller designed slot area. Figure 3 shows the rate of change in diameter of the CNT yarn motors with respect to the copper motor. The motor with an output of 4 kW has the largest change in diameter with respect to electrical conductivity, differing from the copper motor by +13.4 % at 10 MS/m and -2.2 % at 100 MS/m. The motor with an output of 4 kW has the largest change in diameter with respect to electrical conductivity, differing from the copper motor by +13.4 % at 10 MS/m and -2.2 % at 100 MS/m. At conductivities prior to 64.5 MS/m, which is the same as the copper motor, the rate of change is positive, indicating a larger design than the copper motor.

Figure 4 shows the rate of change in mass of the CNT yarn motor relative to the copper motor. The rate of change is negative for all outputs after the electrical conductivity of 30 MS/m, indicating that the motor is lighter than the copper motor. In other words, it can be said that motor weight reduction can be achieved even with CNT yarns whose electrical conductivity is lower than that of copper. Comparing the results of Figures 3 and 4, it can be seen that the motor is larger than the copper motor but lighter than the copper motor for conductivities between 30 MS and 64.5 MS/m.

4.      結論 – Conclusions

CNT糸の電流密度を電気伝導度ごとに設定し，モータを設計した．電気伝導度30 MS以上64.5 MS/m未満の銅に満たない電気伝導度のCNT糸を用いた設計でも，大型化はするものの軽量化は可能であることが分かった．本研究で設計したモータのなかでは出力4 kW，導体の電気伝導度100 MS/mのモータが銅モータと比較して13 %だけ軽量になり，最も軽量な設計となった．

The motor was designed by setting the current density of CNT yarns for each electrical conductivity. It was found that even designs using CNT yarns with electrical conductivities between 30 MS and 64.5 MS/m, which are less than copper, can be made lighter, although they are larger. Among the motors designed in this study, the motor with an output of 4 kW and a conductor conductivity of 100 MS/m was only 13 % lighter than the copper motor, making it the lightest design.

【関連Link】

• 一般社団法人 電気学会 (iee.jp) 

• 回転機研究会