Method and an arrangement for starting an electrical machine hav

Electricity: motive power systems – Synchronous motor systems – Hysteresis or reluctance motor systems

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318254, 318721, H02P 800

Patent

active

053152247

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a method for starting an electrical machine having varying reluctance and being of the kind set forth in the preamble of claim 1, and also to an arrangement for carrying out the method. Examples of machines of this kind are stepping motors and so-called switched reluctance motors (SR-motors).


BACKGROUND ART

Machines having varying reluctance, hereinafter called reluctance machines, may be rotating or linear machines, meaning that when a movable part rotates or moves linearly, the reluctance in the magnetic circuit of the machine will vary. In the following, this movable part is called the rotor, irrespective of the type of machine concerned. The position of this movable part is thus called the rotor position.
Normally, in order to utilize a reluctance machine optimally, the position of the movable part, i.e. the rotor position, is sensed and the machine is controlled on the basis of this sensed position. The position is often sensed with the aid of position sensors mounted on the machine, these sensors producing an output signal which denotes the absolute position. Sensors of a simpler kind which provide relative positional information, for instance increment sensors, are also used.
In recent times, methods have been proposed for controlling reluctance machines which do not include the use of physical sensors. Two such methods are described in U.S. Pat. No. 4,868,478 and S.E. 8604307-2. All of the embodiments described in these publications use different methods of sensing or measuring the inductance in a machine phase.
However, one problem which is not resolved satisfactorily by the methods described in these publications, is how the machine shall be started.
Since the inductance is indirectly a measure of the reluctance, the drive circuits described in said publications constitute examples of embodiments which can be used in practice as the basis of starting a reluctance machine. These drive circuits are not described in detail here. The invention, however, is not restricted to its use together with these drive circuits, but applies to all systems in which the reluctance or a magnitude connected thereto can be measured or sensed in the various magnetic circuits of the machine.
Machines of the kind to which the invention relates include a stationary part, here referred to as the stator, irrespective of whether the machine concerned is a rotating machine or a linear machine, and a movable part, the rotor. Both the stator and the rotor are normally made from a soft magnetic material, such is soft magnetic iron, with embossed, toothlike poles.
Flux generating windings for the different phases and poles are normally applied to the stator, which gives favourable operation with respect to mechanical construction, operational reliability, working temperature, etc., although these windings may alternatively be mounted on the rotor instead, if so desired. In the case of specific machine designs, there is used a combination of varying reluctance and permanent magnets. An example of one such design is the socalled hybrid-stepping motor.
A common feature of machines which employ varying reluctance is that these machines shall be controlled so that current will flow through the machine windings only when the reluctance for each individual winding circuit either increases with a change in rotor position, which applies to generator operation, or decreases with a change in the rotor position, which applies to motor operation. The aforesaid rotor-position-dependency derives from this.
For the sake of simplicity, the following description will be made solely with reference to rotating machines. It will be understood, however, that what is described applies also to linear machines.
The object of the invention is to provide a method for engaging and starting a machine having varying reluctance, with the intention of establishing which phase circuit or phase circuits shall be activated in order to obtain torque in a desired direction.
The aforesaid object is achieved with a method having th

REFERENCES:
patent: 4520302 (1985-05-01), Hill et al.
patent: 4868478 (1989-09-01), Hedlund et al.
patent: 4959596 (1990-09-01), MacMinn et al.
patent: 5012172 (1991-04-01), Sember
patent: 5051680 (1991-09-01), Belanger
patent: 5107195 (1992-04-01), Lyons et al.
patent: 5173651 (1992-12-01), Buckley et al.
patent: 5196775 (1993-03-01), Harris et al.

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