8 电梯拖动系统Lift driving system电梯的电力拖动系统对电梯的起动加速、稳速运行、制动减速起着控制作用。拖动系统的优劣直接影响电梯的起动、制动加减速度、平层精度、乘坐的舒适感等指标。早期的电梯原动机都是直流电动机，在19世纪中叶之前，直流拖动是当时电梯唯一的电力拖动方式，19世纪末，电力系统出现了三相制交流电源，同时又发明了实用的交流感应电动机，因而从20世纪初开始交流电力拖动在电梯上得到了应用。Controlling lift start-up speed, smooth operation and deceleration, electrical driving system plays a decisive role in such index as start-up, acceleration / deceleration, leveling accuracy and riding comfort. Before the middle of 19s century, adopting DC motor, DC driving system was the only mode for lift; by the end of 19s century, with the development of AC inductive motor, AC driving system was applied in lift from the beginning of 20s century. 8-1 拖动系统分类Driving system types 目前用于电梯的电力拖动系统有两大类，即：直流电梯拖动系统和交流电梯拖动系统。直流电梯拖动系统通常分为二种：一是用发电机组构成的可控硅励磁的发电机-电动机驱动系统；二是可控硅直接供电的可控硅-电动机系统。Currently, electrical driving system is classified into two types, i.e. DC driving system and AC driving system. DC driving system has two types, one is driven by controllable silicon excitation multiple dynamos motor, the other by controllable silicon motor. 交流拖动系统又可分为三种：交流变极调速系统、交流变压调速系统和变频变压调速系统。AC driving system includes three types: AC polar-speed-variable system, AC voltage-speed-variable system and frequency-voltage-speed-variable system.8-2 直流拖动系统DC driving system直流电梯速度快、舒适感好、平层精度高。但由于其对电网的影响较大，所以在2m/s速度以下的电梯已不再应用，但目前在2m/s速度以上的电梯仍有应用（包括有齿轮的和无齿轮的）。Featuring high running speed, good riding comfort and high leveling accuracy, DC lift has a great influence on electrical network, therefore, lift with speed of less than 2m/s is not out of use, but lift with speed of more than 2m/s is still in use (including geared and gearless). 直流电动机的转速可由下式表示：DC motor speed is indicated as follows: 8-1？ 式中： Where:Ua 电机进线端的电压 Ua Inlet voltage of motor Ia 电枢电流 Ia Armature current Ra 电枢电阻 Ra Armature resistance Rt 外接调整电阻 Rt Varistor Ce 电势常数 Ce Potential constant 励磁磁通 Excitation flux由上式可知，直流电机的转速主要与输入电机的端电压、外接调整电阻及励磁磁通有关，只要改变其中的某个参数，均可改变电机转速。其中改变端电压Ua比较理想，因为在不同电压下的特性曲线均是平行的，即在同一电压下负载变化时，其转速变化不大。直流电梯的两种拖动系统都是利用调整电动机端电压Ua的方法进行调速。发电机-电动机组是通过调节发电机的励磁改变发电机的输出电压（即电动机的端电压）进行调速，故称可控硅励磁系统。可控硅-电动机系统是利用三相可控硅整流器，把交流电变为可控的直流电，供给直流电动机的调速系统，省去了发电机组，因此降低了能耗和造价，使结构更加紧凑。图8-1为可控硅励磁的发电机-电动机拖动系统示意图；图8-2为可控硅直接供电的电机拖动系统。From the above formula, we learn that DC motor speed is mainly related to inlet voltage of motor, varistor and excitation flux, therefore, changing one of the three factors will alter motor speed. It is preferable to change Ua, i.e. inlet voltage of motor, since character curve is parallel under different voltages, i.e. motor speed does not change noticeably under the same voltage when load varies. Both two driving systems of DC lift change speed by adjusting Ua, i.e. inlet voltage of motor. Dynamo-motor changes speed by adjusting excitation of motor to change outlet voltage of dynamo, i.e. inlet voltage of motor, and this process is called silicon excitation system. By means of three-phase controllable rectifier, controllable silicon motor system converts AC to DC, providing speed-adjusting system of DC motor, sparing dynamo, reducing power consumption and cost, making structure more compact. In figure 8-1 is shown controllable silicon excitation dynamo-motor driving system, while in figure8- 2 controllable silicon motor driving system.8-2-1 可控硅励磁的发电机-电动机组拖动系统Controllable silicon excitation dynamo motor driving system图8-3为快速直流电梯拖动系统原理图Figure 8-3 is a sketch of the mechanism of high-speed DC driving system.给定电源经积分转换变成梯形信号。测速发电机取与电梯速度成正比的电压信号。速度给定信号与测速反馈信号相比较后得到的误差信号，加到具有比例积分的速度调节器进行放大调节，然后输出加到反并联的两组可控硅触发器上，使两组触发器同时得到两个符号相反、大小相等的控制信号，控制两组触发器的输出脉冲同时向相反方向作相等角度的移动，用以控制可控硅整流器的输出电压的大小和极性。可控硅整流器的输出电压控制直流发电机的励磁磁通，使发电机电枢输出电压随之变化，电动机转速随发电机输出电压而变化，最终使速度跟随给定的速度曲线变化，达到速度自动调节的目的。Given power is converted to trapezoid signal after integration. Tachogenerator selects voltage signal in directly proportional to lift speed. Comparing given speed signal and feedback signal will produce a error signal, which is added to PI speed controller to be amplified, then the outlet is added to two counter-parallel controllable silicon triggers, which can obtain two control signals that are equal in magnitude but have opposite codes. Outlet pulse controlling two triggers moves toward opposite directions simultaneously at equal angle degree, so as to control the outlet voltage and polarity of controllable silicon rectifier. The outlet voltage of controllable silicon rectifier controls the excitation flux of DC dynamo, changing dynamo armature outlet voltage and motor speed. Consequently, speed will vary according to given speed curve, achieving the goal of speed self-adjusting. 当给定正电压与测速反馈电压相比较使速度调节器输出一个负电压给触发器，使正向组可控硅工作在整流状态，反向组可控硅工作在待逆变状态，供给发电