摘要
本文所讨论的是双闭环三相异步电动机的串级调速的基本原理与实现方法。对于一般交流电动机的调速，我们都是从电动机的定子侧引入控制变量（改变定子供电电压、频率）来实现的，这对于转子处于短路状态的交流鼠笼型转子异步电动机是唯一途径。但是，对于绕线式异步电动机来说，由于其转子绕组能通过变量以实现调速。转子侧的控制变量有电流、电动势、电阻等。通常转子电流随负载的大小决定，不能任意调节；而转子回路阻抗的调节属于耗能型调速，缺点较多，所以转子侧的控制变量只能是电动势，这也是本文所要讨论的重点之一。在发挥绕线式异步电动机转子的可控性优势的基础上，提高调速性能需要从两方面着手：
1从节能角度考虑，应将损耗在转子附加电阻上的能量吸收，转化成别的有用的能量或反馈到电网，以提高传动系统的效率
2从高性能调速要求考虑，应用控制理论，将其组成闭环调速控制系统，满足调速精度、动态响应等指标的要求。
综合所述，利用串级调速系统，就是使绕线式异步电动机实现高性能调速的有效办法。用转子串反电动势来代替电阻，吸收转差功率；用双闭环控制提高系统的静、动态性能。把这种用附加电动势的方法将转差功率回收利用的调速称为双闭环串级调速。这是本文所必须讨论的，也是本文的核心所在。
Abstract
This paper discusses the mechanisms and implementation details of concatenation control in a three - phase asynchronous motor with double closed loop. To control speeds for a typical alternating current motor, we usually take control variables (to change voltage and frequency of the stator power supply) from the stator side in an electric motor, which is also the only way for squirrel-cage asynchronous motor with rotor in a short-circuit state. However, with wound rotor series, asynchronous motors can adjust speeds through control variables, which include electric current, electromotive force and resistance, etc. on the rotor side. Typically, the rotor current is determined by the load and cannot be adjusted freely. In contrast, adjusting rotor’s return circuit impedance tends to consume more power along with other disadvantages. Therefore, electromotive force should be the only control variable on the rotor side, which is also one of the major points discussed in this paper. In order to increase speed control, we need to take the following two measures while fully utilizing the adjustable nature of rotors in series-wound asynchronous motor:
1. In order to save energy, power wasted on rotor’s additional resistance should be absorbed and converted into other forms of usable energy or sent back to electric grid to increase the efficiency of transmission systems.
2. Considering high control ability and the applied control theory, it should be formed into a closed-loop control system in order to meet the requirements of such criteria as control accuracy and dynamic response
In summary, concatenation control system is one effective means to realize high control ability in series-wound asynchronous motors. Specifically, it is used to replace resistance with rotor’s electromotive force and absorb slip power; and to enhance the static and dynamic capabilities of the system using double closed loop. We refer to this method of utilizing additional electromotive force to recycle slip power as concatenation control with double close loop, which is also the focus of this paper.
