Improvement of the technique in phase modulation for forming schemes of pole-switch windings

Electric motors that provide regulation of the rotation speed of the shaft are also designed to drive loads that allow a step change in rotational speed. The rotation speed of an asynchronous motor can be adjusted by changing the slip, the number of pole pairs, or the frequency of the current supply network. By changing rotational speed, one can change the value of the critical slip. It leads to the change in motor rotational speed. This method of regulating motor rotational speed is used in drives of woodworking machines operating in intermittent duty cycles mode, when the motor is often turned on and off. The motor rotational speed can be adjusted by changing the number of pole pairs. This is achieved by switching the stator windings. In this case, the motor rotational speed changes only in steps. The rotational speed can also be adjusted by changing the frequency of the current supply network. The motor speed reaches 18,000 rpm at a current frequency of 300 Hz. The rotational speed of the motor shaft can be changed if the motor is connected to the current supply network through an industrial electronic converter (inverter) of the electric current frequency. The main drawback is that the cost of a frequency converter can be higher than the cost of an electric motor. Multi-speed electric motors are used in electric drives for fan-type loads and other various mechanisms, where they directly make it possible to simplify the transmission and transmission system or completely abandon it. Various adjustable mechanisms see the advantage of a multi-speed motor in that, when regulating the load torque, it works at each step of the rotational speed with a slight change in it as well as a conventional electric motor does. Multi-speed electric motors can have several (two, three or four) speeds, the operation of which is to change the number of poles of the stator winding to another adjacent number. In this case, the switching is carried out in the circuit design of one winding. The purpose of the article is an analytical and graphical basis for the formation of pole-switched windings. There has been given a further development of one of the methods for the formation of pole-switched windings, a technique in phase modulation. The authors have proposed an improvement of the technique which consists in additional phase current modulation of pole-switched windings partially shortened by a third. Based on the eight-pole winding of an asynchronous squirrel-cage electric motor, the current distribution was modulated by rotary 120° steps. The result of such phase modulation is pole pairs which switch from a multiple to a non-multiple, allowing us additionally to change the phase conjugation. The performed modulation of the motor windings according to the analysis, circuit designs and the specifics of the distribution of coil systems allows us to conclude that at these certain speeds, the winding circuit of a multi-speed electric motor will correspond to the operating mode of the driven machine.