RELUCTANCE MOTOR

Abstract: A reluctance motor comprises a stator (11) with poles (1, 1'; 2, 2'; 3, 3') which are co-operating in pairs, and a rotor (12) made from soft magnetic material and having poles (13) which are disposed diametrically opposite each other in pairs. The stator poles have magnetizing windings (14, 15) which for each pair of stator poles are connectable to a DC source (18) under the control of a control device (26) in dependence on a signal from a sensor device (20) which is arranged during the movement of the rotor (12) to indicate the position of the rotor poles (13). The sensor device comprises a sensor (21) which co-operates with a disc (23) rotating with the rotor (12) and having wings (22) the number of which corresponds to the number of stator poles or to the said number multiplied by two. At start of the motor the control device (26) is arranged to connect in proper order a predetermined pair (1, 1') of stator poles to the DC source (18) and then the next pair of poles (2, 2') in the desired direction of rotation and thereafter the next following pair (3, 3') of poles in the said direction etc.

Description: Reluctance Motor The present invention relates to a reluctance motor of the kind indicated in the preamble of appending claim 1. In reluctance motors it is common to provide stator poles which are co-opera¬ ting in pairs and which are equally disposed along the way of movement of the rotor poles. Like the stator the rotor has a shape such that its poles are co-operating in pairs. Hence, during the turning of the rotor, at the same time the two poles of a stator pole pair co-operate with the corresponding poles of a rotor pole pair. In operation the stator pole pairs are connected to a source of DC voltage in proper order and in principle a selected stator pole pair is connected upon a rotor pole being about to turn in over the stator pole. The voltage remains until the rotor pole has been fully turned in over the stator pole. For the control of the motor speed the moments of connecting and disconnecting, respectively, of the supply voltage can be varied. Detailed information about reluctance motors of the kind indicated has been published under the heading "Variable-speed Switched Reluctance Motors" in IEE PROC., Vol. 127, Pt. B, No. 4, July 1980. The moments of connection and disconnection of the stator pole pairs are controlled by sensors indicating those positions in which a rotor pole begins to overlap a stator pole. In order for the rotor at start to turn in the desired direction, up to now one sensor has been required for each stator pole pair. The object of the invention is to simplify a reluctance motor of the kind indi¬ cated so that irrespective of the number of poles only one sensor be required for start of the motor in the desired one of the two possible directions of rotation. The object will be achieved in a motor having the features indicated in the appending claims. A reluctance motor according to the invention will now be described in detail with reference to the enclosed drawings. Fig. 1 schematically shows the construction of a reluctance motor having six stator poles and four rotor poles. Fig. 2 shows in perspective the rotor shaft of the motor of Fig. 1 completed by a sensor device. Fig. 3 shows the three sensor prior art arrangement. ' • Figs. 4 and 5 show two different sensor discs to be used in a single sensor arrangement according to the invention. San/ih 50- 10 Fig. 6 is a diagram of sensor signal waveforms of a motor constructed in accordance with Fig. 1 and including three sensors according to prior art. Figs. 7 and 8 are diagrams of sensor signal waveforms relating to the singl sensor embodiments of Fig. 4 and Fig. 5, respectively. Finally, Fig. 9 is a block diagram of a control device for a reluctance moto of the invention. In the paper referred to above formulas have been given for the calculatio of optimum combinations of pole numbers of the stator and the rotor. The embodi ment chosen is one such optimum combination wherein a reluctance motor 10, whic is schematically shown in Fig. 1, comprises a stator 11 having six poles and a rotor 1 having four poles. The stator poles are disposed so as to form pairs of poles in eac of which the poles are diametrically opposite each other and three pole pairs 1, l r 2, 2'; 3, 3' are evenly distributed along the way of movement of the rotor poles gene rally designated by 13. The pole surface of each stator pole has an extension alon the way of movement of the rotor poles which equals the pole gap between tw stator poles. The four rotor poles 13 are situated so as to form a cross and the pol surfaces have an extension along the way of movement of the rotor causing a roto pole which is just in front of a stator pole to completely match the said pole. The rotor is made from soft magnetic material and the stator poles are bein magnetized by means of windings 14, 15 which via terminals 16, 17, schematicall indicated, connect the poles of a pole pair in series to a DC source such that th poles co-operate to drive the motor in the direction chosen. Between the DC sourc designated by 18 in Fig. 9, and the respective pair 14, 15 of stator windings an elec tronic switch 19 is connected which controls the connection of the stator winding to the DC source an the disconnection thereof. In Fig. 1 only the poles of one o the three stator pole pairs have been provided with windings 14, 15 but the remainin pole pairs are correspondingly equipped. In Fig. 9 the windings of the respectiv pair of windings have been designated 14, 15j 14', 15' and 14", 15". Correspondingl the electronic switches have received the reference numerals 19, 19' and 19". T make possible at the opening of the switches 19, 19', 19" the taking care of the energ magnetically stored in the windings each pair of windings is bridged by a diode i series with a resistor. The diodes have been designated 29, 29', 29" while the resisto have got the reference numerals 30, 30', 30". Below, the three pole pairs 1, 1'; 2, and 3, 3' will represent three phases analogous to what is common in connectio with AC motors. However, it should be pointed out that the three phases do n relate to the voltage phases in three phase operation. Instead, the motor is drive by DC voltage supplied to the windings during predetermined periods of time and the motor can be referred to as pulse operated. In order for the reluctance motor to work, in principle it is required that the windings in a selected stator pole pair be connected to the voltage source 18 at the moment when a rotor pole pair is about to turn in over the stator poles. Dis¬ connection takes place when the rotor poles completely match with the stator poles. At this later moment, for the continued turning of the rotor the windings of the next following stator pole pair, as seen in the direction of rotation, is to be con¬ nected. For the control of the motor, obviously, a sensor device must be provided to indicate the position of the rotor poles with respect to the stator poles. This sensor device is shown schematically in Fig. 9 and has got the reference numeral 20. As appears in Fig. 2 the sensor device comprises a Hall sensor 21 which co-operates with a disc 23 having six wings 22 and being fixed on a shaft 24 which also carries the rotor 12. A Hall type sensor is particularly suitable in the present case where it is desired that the indication remains during the whole period of time in which at least part of a rotor pole overlaps a stator pole. However, also other kind of sensors can be used, for example optical sensors. Via a line 25 the Hall sensor is connected to a control device 26, Fig. 9, intended for the control of the electronic switches 19. The control device 26, Fig. 9, can be constructed in different ways and in the example a microprocessor has been chosen which controls the switches 19 in dependence on signals from the sensor device 20. However, the control device ma just as well be made with the use of TTL logics. The technique for this as well as for microprocessors is commonly known and will not be discussed in detail. However, it can be mentioned that in the usual way the microprocessor is time-controlled by an oscillator 27 and in addition the microprocessor has an input 28 on which a starting pulse can be applied the appearance of which appears in Figs. 6-8. In starting a reluctance motor of Fig. 1 information is needed as to the rota¬ tional position of the rotor. It is known to provide the disc on the rotor shaft with four wings corresponding to the number of rotor poles and, in addition, to provide three sensors which are disposed 120° with respect to one another. In this way, by study of the signals from the three sensors it will be possible to determine which one of the three stator pole pairs is to be magnetized first in order for the rotor to start rotate in the desired direction. The four wing disc is shown in Fig. 3 and has got the reference numeral 34. Sensors, for example of the kind shown in Fig. 2, are situated in positions indicated by the reference numerals 31, 32 and 33. The function of a reluctance motor having three sensors will be best under¬ stood by study of Fig. 6 which shows the waveforms of actual stator voltages and sensor signals. The stator voltages have been designated "sensor 1", "sensor 2", and "sensor 3", respectively, corresponding to the sensor positions 31, 32 and 33 indicated in Fig. 3. The sensor 1 refers to phase 1, the sensor 2 refers to phase 2 and the sensor 3 refers to phase 3. In addition a starting pulse has been indicated having the shape of a ramp. When the starting pulse is applied the microprocessor 26 de¬ termines which one of the sensor signals that is positive corresponding to the stator and rotor in the corresponding phase matching each other in a position that creates a positive torque in the direction of rotation chosen. In the example the sensor 1 has a positive signal which causes the switch 19 of phase 1 to be activated to connec the stator windings of phase 1 to the voltage source. Upon the signal of sensor 1 changing level the switch of phase 1 will be inactivated. As appears from th diagram, in that moment the sensor signal 2 will be positive and phase 2 will b connected. Then this phase is connected until the sensor signal goes low. At hi moment the sensor signal 3 will take a positive value connecting phase 3 which there after will be followed by phase 1 etc. The diagrams of Figs. 6 and 7 are both tim diagrams which means that at start of the motor the pulses are long while at ful speed the pulses stabilize at a shorter value. The simplified sensor device according to the invention including only on single sensor disposed in the position corresponding to the position 31 in Fig. 3 wil now be described. Here, the sensor is of the same type as described above, however the rotating discs have six and twelve wings, respectively. In Fig. 4 there is show a disc 44 having six wings and in Fig. 5 a disc 54 is shown having twelve wings. Fo both embodiments the wings have the shape of a sector of a circle the periphera extension of which coincide with the corresponding extension of the gap betwee two wings. The advantage with the twelve wing disc is that it makes possible th use of a simplified logic in the control device 26. In Fig. 7 the waveforms have been traced for, as counted from above, th starting signal, the stator voltages of phase I, phase 2, and phase 3 and, finall the single sensor signal. In this case it will not be possible to get any idea abou the position of the rotor from the sensor signal as was possible in the three senso case. Still, in order to be able to bring the motor into controlled rotation the ram of the starting signal is allowed to operate the microprocessor to activate th windings of phase 1 for so long time that the rotor with certainty is driven so lon that the rotor poles that are closest fully overlap the stator poles of phase 1. The depending on the desired direction of rotation the microprocessor activates eithe phase 2 or phase 3. In the example phase 2 is activated at the same time as phase is inactivated. Then, phase 3 is activated as soon as a negative flank appears in th sensor signal and at the same time phase 2 is inactivated. As appears in the diagram the sensor signal is neglected 'during the first part of the start procedure. The sensor signal is accepted after the activation of phase 2 and then first when the signal by a negative flank indicates that the stator and rotor poles of phase 2 fully match. This control of the sensor signal is carried out by the microprocessor. When the sensor signal is accepted phase 3 is activated and henceforth the sensor signal controls the activation and inactivation respectively, of the different phases. The diagram of Fig. 8 relates to a twelve wing disc according to Fig. 5, however, as far as waveforms are concerned having the same overall dispostion as Fig. 7. The same start procedure is valid as in Fig. 7. By arrows in Fig. 7 as well as in Fig. 8 interrelated points have been indicated in which a flank in the sensor signal causes either activation or inactivation of a phase. Hence, the arrows traced at the far left in Fig. 7 shows that a negative flank of the sensor signal causes the inactivation of phase 2 and the application of supply voltage to phase 3. The remai- ning arrows show that positive as well as negative flanks of the sensor signal operate the different phases. This means that the logic in the control device 26 has to be designed such that positive and negative flanks in the sensor signal can be identified. This will not be necessary in the embodiment of Fig. 5 wherein the sensor disc is provided with twelve wings. As appears from Fig. 8 twice as many pulses are gene- rated by this sensor and accordingly only the negative flanks of the sensor signal need to be noted. Hereby, the logic in the control device 26 will be considerably simplified. In certain applications it is desirable that the motor be kept ready for the next start and then at the starting moment that it moves in the correct direction. One such application is the washing machine in which the motor which drives the washing drum is intermittently started and stopped and reversed as well under the control of a programmer. Then a reluctance motor according to the invention can be so positioned at the start of the machine that the motor control device knows the position of the rotor and the start to be about will take place immediately in the correct direction. In intermittent operation of the motor no new positioning will take place between consecutive εtartings but the control device will receive from the sensor device information about the actual position of the rotor. In a modified embodiment the control device can be designed such that when the motor is to be stopped one of the stator pole pairs is permanently connected to the DC source causing a braking effect to develop and . in addition providing an automatic positioning for the next start. The said stator pole pair remains magne¬ tized until the motor is to be started again. Summarizing, the invention provides a control device for a reluctance motor which by use of only one sensor still operates the motor to start rotate in the desired one of the two possible directions of rotation.

Claims: Claims 1. A reluctance motor comprising a stator (11) with poles (1, 1'; 2, 2'; 3, 3') co-operating in pairs and provided with windings (14,15), and a rotor (12) made from soft magnetic material and having poles (13) which are disposed diametrically opposite each other in pairs, the windings (14,15) in each stator pole pair (1, 1'; 2, 2'; 3, 3') being connectable to a DC source (18) under the control of a control device (26) in dependence on a signal from a sensor device (20) which during the movement of the rotor is arranged to indicate the position of the rotor poles, character¬ ized in that the sensor device (20) inludes a sensor (21) which co-operates with a part (23) rotating with the rotor, the sensor during one turn of the rotor (12) emitting to the control device (26) at least as many pulses as correspond to the number of stator poles, the control device (26) at start of the motor being arranged first with disabled sensor function to position the rotor (12) and then with enabled sensor function to connect the stator pole pairs (1, l'j 2, 2'; 3, 3') to the DC source (18) in the order corresponding to the desired direction of rotation of the rotor (12), the control device (26) being arranged during the course of positioning first the connect a .predetermined one of the stator pole pairs (1, 1'; 2, 2'; 3, 3') to the DC source (18) and thereafter a predetermined one of the remaining stator pole pairs, the connect time period for the respective pole pair being so long as to permit the completion of the transient period of the rotor movement. 2. A reluctance motor according to claim 1, characterized in that the rotating part co-operating with the sensor (21) is a disc (23) provided with wings (22) the number of which corresponds to the number of stator poles or to the said number multiplied by two. 3. A reluctance motor according to claim 2, characterized in that the signal from the sensor device (20) is a train of rectangular pulses, the wings (22) of the disc (23) rotating with the rotor (12) being so disposed with respect to the rotor poles (13) that a flank in the pulse train appears when a rotor pole is about to turn in over a stator pole. 4. A reluctance motor according to claim 3, characterized in that the stator (11) has three pairs of poles (1, l'j 2, 2'; 3, 3') while the rotor (12) has four poles, the disc (44, Fig.4) included in the sensor device (20) having six wings (22) equally disposed and each having the shape of a sector of circle the peripheral ex¬ tension of which corresponds with the corrsponding extension of the gap between two wings. 5. A reluctance motor according to claim 3, characterized in that the stator (11) has three pairs of poles (1, 1'; 2, 2'; 3, 3') while the rotor (1) has four poles, the disc (54, Fig.5) included in the sensor device (20) having twelve wings equally distributed and each having the shape of a sector of a circle the peripheral extension of which corresponds with the corresponding extension of the gap between two wings. 6. A reluctance motor according to any of the preceding claims, charac¬ terized in that the control device (26) is arranged at intermittent operation to carry out positioning of the rotor only at the first start, the sensor device being arranged between consecutive startings to provide to the control device (26) informa¬ tion about the position of the rotor. 7. A reluctance motor according to any of the preceding claims, charac¬ terized in that preferably in intermittent operation the control device (26) for the purpose of stopping the motor is arranged to permanently connect one of the stator pole pairs (1, 1'; 2, 2'; 3, 3') to the DC source (18) and to have the connec¬ tion remain until the next start of the motor.

Inventors: HEDLUND BENGT GUNNAR, MOREN LARS GUNNAR, HEDLUND, BENGT, GUNNAR, MOREN, LARS, GUNNAR
Applicants: ELECTROLUX MECATRONIK AB, ELECTROLUX MECATRONIK AKTIEBOLAG
Application year: 1989
Main classification: H02P6
IPC codes: H02K29, H02P25