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1. WO1997043820 - ELECTROMOTEUR A COURANT CONTINU TRIPHASE SANS BALAIS A COMMUTATION ELECTRONIQUE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

THREE-PHASE ELECTRONICALLY COMMUTATED
BRUSHLESS DC-ELECTROMOTOR

The invention concerns a three-phase electronically commutated brushless DC-electromotor provided with a rotational speed regulation, in which electromotor an unsteady or steady rotational speed variation is possible and thus also a variation of the output power of the electromotor without any additional control circuit, this being feasible by adding just a microswitch or a potentiometer.

There have been known several technical solutions providing for electronic commutation of electromotors. The most common are the electromotors to be mounted centrally within electronic cooling fans to cool various systems where low DC voltage power supply is provided for. The said electromotors are provided with an external rotor made of permanent magnets and with a salient poles stator. A two phase stator winding is excited by means of an electronic circuit performing a simple commutation without any possibility of the rotational velocity regulation and of starting or stopping the regulation of the electromotor.

Wide spread electronically commutated electromotors are electric servomotors having a separate control circuit which must be connected to the electromotor windings by power lines; a connection of rotor position sensors to the electronic circuit for the commutation of the electromotor windings is required. A disadvantage of these electromotors exists in the connection of the electronic circuit to the electromotor windings.

The sensing of the rotor position in electronically commutated electromotors applied in the industry is mainly accomplished by means of position marking elements attached to the rotor. The position marking elements like encoders, optical sensors, gear wheels or magnetic rings surrounded by contactless sensors are used. The disadvantage of such sensing exists in that the marking elements are attached to the rotor, which attachement requires technologically exacting solutions as regards local coincidence with the rotor magnetic poles. The attachement of the rotor position sensors is carried out, e.g. in three-phase electromotors, with a positional angle spacing 120°, to which purpose a large holder is required; a wired connection to an electronic circuit, however, is made difficult due to a considerable distance between the sensors.

The technical problem to be solved by the present invention is such construction of a DC-electromotor that it makes possible a simple starting and stopping and the regulation of rotational speed - i.e. is the electromotor output power - by means of just one microswitch or potentiometer directly connected to the input of an electronic circuit on the electromotor so that the regulation of starting/stopping as well as of the rotational speed is provided and no additional low or heavy current control circuit and usual wiring between them is needed, at the same time, however, the electromotor has no other mechanically wearable parts besides rotor bearings, which contributes to a longer lifetime, high reliability of operation and quiet operation, its construction is compact and its assembling is simple.

The invention will now be described by way of an example and with reference to the accompanying drawings representing in:
Fig. 1 the axial cross-section through the electromotor of the invention,
Fig. 2 the cross-section through the rotor of the electromotor of the invention
trahsversally with respect to the rotor axis,
Fig. 3 a block diagram of the electronic circuit for turning on/off the windings of the electromotor of the invention and for the regulation of its rotational speed.

The electromotor of the invention comprises only five main components distinguished by the following solutions shown in Fig. 1: - a stator made of laminated plates 1 and with three-phase windings 2; the poles are non-salient ones;
- a rotor with a core 3 and with permanent magnets 4, its pole number being equal to the number of poles excited by the 'stator winding;
- a front casing part provided with a bearing;
- a rear casing part provided with a bearing;
- a compact electronic circuit provided with rotor position sensors 6; OD1, OD2,
OD3, a circuit 5 for the control and regulation of rotational speed and
with an output power stage 7 for three-phase excitation.

The stator is made of laminated plates 1 with equidistant slots wherein three-phase windings k are placed. These windings are delta-connected or star-connected as usual in stators of AC-generators and electromotors. The beginnings of the stator windings for particular phases are spatially distributed along the periphery with respect to each other so that the created magnetic field is shifted from phase to phase for 2/3 T where T is the pole pitch as shown in Fig. 2.

The rotor is consists of a shaft with the core 3 made of magnetically conductive material of a cylindric shape and of the magnets 4, N and S denote their poles, mounted on the cylinder periphery, the magnets being of the same length as the core and with such radius that they match the core surface as well as possible, thus enabling an efficient magnetic contact between next positioned magnetically opposite polarized poles. The length of the rotor and magnetic poles exceeds that length of the stator laminated plates 1 so that on the side, where the rotor position sensors 6; OD1, OD2, OD3 are placed, the rotor juts out from the region of the stator plates 1.

Above this part of the rotor periphery surface the three rotor position sensors 6; OD1, OD2, OD3 are placed controlling the commutation of the electromotor windings via electronic circuit. Between the neighbouring rotor position sensors 6; ODl, OD2, OD3 there is a distance
A = (n2T + 2T/3) where n= 0, 1, 2, ... Their state is directly influenced by the rotor magnetic poles; hence the electromotor has no additional rotor position sensors.

The electronic circuit is represented in Fig. 3 by a block diagram. A supply circuit b is switched on and off by means of a switch a. An analog input e is conducted to the electronic circuit provided with an amplifier f and a pulse-width modulator g. The rotor position sensors 6; OD1, OD2, OD3 arid the pulse-width modulator g are connected to a circuit h for signal processing and transmission, the outputs of the circuit h being connected to inputs of a matching circuit i. The matching circuit i is connected through an output stage j to the electromotor windings k. The output stage j is connected to feeding source terminals -B, +B and is, for the reasons of current limitation via a comparator 1 providing for voltage drop limitation, also connected to the input of the circuit h for the processing and transmission of the signals originating from the sensors 6; OD1, OD2, OD3.

The electronic circuit as represented in Fig. 3 makes possible the performance of several functions:
- detection of rotor position by means of electromotor windings;
- current limitation in the case of overload or starting and blocking of the rotor;

- processing and transmission of the signals from position sensors;
- pulse-width modulation of windings excitation by transforming
control voltage into a pulse-width modulated signal assuring
unsteady or steady regulation of the electromotor rotational speed;
- control of power transistors in the output stage j by means of the matching
circuit i;
- switching of windings by means of switches made of output transistors or
modules;
- feeding the regulation circuit also performing the function of
starting and stopping the electromotor.

The proper operation of the electromotor depends on the proper distribution of the rotor position sensors 6; OD1, OD2, OD3 as it is represented in Fig. 2.

The signal originating from the rotor position sensors 6; OD1, OD2, OD3 is first processed and possibly pulse-width modulated and then conducted to individual transistors or modules in the output stage j. These transistors are directly connected to the winding terminals and to the supply source so that they act as switches and commutate the power supply of the windings between the supply source terminals -B and +B in the correct rhythm.

Therefore all three phase voltages have a rectangular shape like the output voltages of the rotor position sensors 6; OD1, OD2, OD3, their phase lag, however, being 120° due to the described arrangement of the rotor position sensors 6; OD1, OD2, OD3 as it is described and represented in Fig. 2. Therefore the electromotor supplied in this way operates in its basic mode as a three-phase synchronous motor, the excitation frequency being variable and always synchronous with rotor rotation.

At a given supply voltage the rotational speed is determined by two parameters, i.e. by a load on the electromotor shaft and by voltage at the analogue input of the pulse-width modulator. Proportionally to the input voltage, the latter provides for chopping the voltage across the stator windings k.