Study on Optimum Design of Linear Motor for Urban Transit

设计和建造了单边直线感应电机圆柱形转子(细长、三相、四极、100kVA)的拱型试验装置，作为城市轨道交通的推进系统。测试超薄由脉宽调制逆变器(PWM逆变器，三相，150kVA，1-50 Hz，40-440V)驱动。通过测量结果与计算结果的比较，发现：1.为实现上述目的而安装的细长钻具以40-50公里/小时的低速运行，安全驱动需要10 mm以上的大机械间隙，在任何电源频率下，在恒压运行下，推力都会随着滑移量的减小而减小。在恒定电源电压和频率比的速度控制中，由于大的一次阻抗压降较大，与传统的旋转感应电机相比，在低频下需要更大的电压来恒定地加速电机的速度。即使在低速细长区域，由于端部效应，气隙内的磁通密度在入口端减弱，而在出口端显著增强。由于电机出口端产生较大的垂向力(吸力)，使得实际情况下车辆的有效重量增大，因此需要采取减小垂向力的方法。对最高时速为70 km/h的城市轨道交通轻轨的设计进行了研究，提出了轻轨设计的要点：一次堆芯应设计长、窄、薄。大约2.5米的电机长度对于大约40公里/小时的瘦身来说是合适的。杆距也是最重要的维度之一。合适的取值为300 mm左右。为了减小垂直力和磁化电流，应在0.4T~0.5T之间选择较低的磁通密度。

Arch type test facility with the cylindrical rotor of single-sided linear induction motor (SLIM, 3-phase, 4-poles, 100kVA) was designed and constructed as the propulsion system for a ne urban transit. The test SLIM is driven by a pulse-width-modulate inverter (PWM Inverter, 3-phase, 150kVA, 1-50Hz, 40-440V). From the comparison between the measured results and calculated results, it was found as follows:1. As the SLIM which is installed for the purpose of the above operates with the low speed 40-50km/h and requires the large mechanical clearance over 10mm for the safety drive, the thrust decreases as the slip decreases under the constant voltage operation in any supply frequency.2. In the speed control with a constant ratio of the supply voltage and the frequency, the larger voltage is required to accelerate the motor speed constantly in the low frequency, compared with that in the conventional rotating induction motor, because of the large voltage drop by the large primary impedance.3. The flux density in the air gap is weakened at the entry end and considerably strengthened at the exit end in the small-slip region even in the low-speed SLIM, because of the end effect. As the large vertical force (attractive force) produces at the exit end of the motor, which makes the effective weight of the vehicle increase in the practical case, the method of reducing the vertical force is required.4. A study has been made on the design of the SLIMs for the urban transit with the maximum speed of 70km/h. The outline of SLIM design is given as follows: The primary core should be designed long, narrow and thin. The motor length of approximately 2.5m would be appropriate for about 40km/h SLIMs. The pole pitch is one of the most important dimensions also. The suitable value will be about 300mm. The flux density should be selected in relatively low value from 0.4T to 0.5T in order to decrease the vertical force as well as the magnetizing current.