Brushless Non-Salient-Pole Synchronous Motor
Abstract Generated abstract
This paper proposes a low-power, general-purpose brushless non-salient-pole synchronous motor intended to avoid the application limits imposed by sliding contacts in conventional synchronous machines. The design uses a three-phase stator winding shunted by diodes and a resistance, a rotor excitation winding supplied through a rectifier, and a short-circuited rotor winding that provides asynchronous starting and functions as a generator for the rotor rectifier. The authors explain how a direct current component in the stator phases creates a stationary six-pole excitation flux, inducing voltage in the rotor winding and enabling rectified excitation so the motor can pull into synchronism. The proposed arrangement offers a brushless synchronous motor configuration suited to industrial uses where sliding contacts are undesirable.
Full Text
BRUSHLESS NON-SALIENT-POLE SYNCHRONOUS MOTOR
A. I. Skorospeshkin, A. B. Tsukublin, E. N. Podborskii
(Presented by the seminar of the Department of Electrical Machines and General Electrical Engineering)
The presence of sliding contacts in existing synchronous motors limits the fields of their application. The proposed synchronous motor is a non-salient-pole, brushless, low-power motor of general application.
The construction and operating principle of the motor are explained in Fig. 1. A three-phase winding 1 with the number of pole pairs \(P=1\), connected in a star, is placed on the stator. All three phases are shunted by diodes 2 and resistance 3. A single-phase winding 4 with the number of pole pairs \(P=1\), which is supplied from rectifier 5, is placed on the rotor. It occupies \(3/4\) of the pole pitch.
In addition, winding 6 with the number of pole pairs \(P=1\), short-circuited, is placed in the rotor slots. It performs two tasks:
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It serves for asynchronous starting of the motor, i.e., it is its secondary winding.
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It plays the role of a three-phase generator feeding the rotor rectifier.
Let us explain this by Fig. 2.
In this figure only one phase \(A_x\) of the generator of the rotor winding is shown, consisting of \(a_2=3\) parallel branches, which are at the same time phases of the short-circuited winding of the motor. If the number of generator phases is equal to three, then the total number of phases of the motor part of the winding with respect to the rotating field with the number of pole pairs \(P=1\) is \(m_{1p}=3a_2\). The ends of the three generator phases are connected in a star, and the three beginnings of the generator part of the rotor, indicated by dots in Fig. 1, are connected to rectifier 5. When a field with the number of pole pairs \(P=3\) arises, an e.m.f. with frequency \(f_2\) is induced in winding 6, but no e.m.f. with slip frequency is induced at the generator terminals \(A_x\).
When winding 1 is connected to the mains, the motor accelerates as an asynchronous short-circuited motor. In order for the motor to pull into synchronism, it is necessary to close switch 7. In this case, in all phases of winding 1 a direct component of current will appear, directed from the beginning of the phases toward
Fig. 1.
Fig. 2
to their ends, which creates a flux stationary in space with the number of pole pairs \(P=3\). This flux induces an e.m.f. in winding 6, and rectifier 5 rectifies it and feeds winding 4 with direct current. The motor is pulled into synchronism. Resistance 3 makes it possible to regulate the magnitude of the direct component of the current in winding 1, i.e., the degree of compounding.
Thus, the proposed synchronous motor has the following features: the three-phase stator winding 1, on the one hand, creates a rotating magnetic flux with the number of pole pairs \(P=1\), as in an ordinary synchronous motor; on the other hand, with the aid of diodes this same winding creates a stationary six-pole excitation flux in space, which distinguishes the proposed brushless synchronous motor from existing ones.
Such a motor may find application in a wide variety of branches of industry, especially where the presence of sliding contact is inadmissible.