New Cascade Speed Control System

The slip energy recovery induction motor driving systems have been used for many years for the speed control of large wound rotor induction motors. It provides us a simple and efficient form of AC variable-speed drive, which is of special interest for pumps, fans and other loads whose torque is proportional to the square of the speed. Since it absorbs the reactive power from power line, the whole system has a lower power factor, which affects its application in wide ranges. In this paper, the basic principle of the conventional slip energy recovery induction motor drive is discussed. Two kinds of slip energy recovery induction motor driving systems with high factors are discussed, and the performance analysis of these methods is compared. On the basis of above, a new type of three-phase and four-line slip energy recovering drive is proposed. Its special feature is that the rotor circuit doesn抰 absorb reactive power from power line, and on the other hand it can provide reactive power, which raises the power factor of the whole system greatly. This paper makes a concrete analysis of the working principles of this new method. The improvements of power factor with this new method are studied in greater detail. The parameter of each segment is calculated, and the particular formulas are given. A new type of numerical slip energy recovering drive systems controlled by 80C 196 Single-Chip microcomputer is composed. Be aimed at the pulse signal of this new method, a numerical trigger is designed and verified by means of simulation and tests. The results produced by calculation and simulation shows that the news scheme can raise power factor of the whole system in a great degree. In addition, the capacity of the reverse transformer is smaller than that of conventional system, so the pollution of power line caused by harmonics are restrained in certain degrees.