WO2003084046A1

WO2003084046A1 - A control device for an electric motor, in particular a single-phase brushless synchronous motor with permanent magnets

Info

Publication number: WO2003084046A1
Application number: PCT/IB2003/001114
Authority: WO
Inventors: Paolo Pettenon
Original assignee: Sicce S.P.A.
Priority date: 2002-03-28
Filing date: 2003-03-24
Publication date: 2003-10-09
Also published as: ITBO20020163A0; ITBO20020163A1; AU2003215799A1

Abstract

A control device for an electric motor (10), in particular a brushless single-phase synchronous motor with permanent magnets, the motor comprising an induced circuit (20) and an inductor circuit (30) having a core (31), a primary magnetic flux (cp) passing through the core (31), the flux generated by an energising current (100). The control device (1) comprises an electromagnetic element (2) designed to be linked to the magnetic flux (cp). A detector circuit (40) is used for reading a paramater (3) characteristic of the electromagnetic element (2), and supplying at output the BEMF (110) induced in the electromagnetic element (2). This reading is taken when the electromagnetic element (2) is connected to the primary magnetic flux (cp). A controller (60) is designed to regulate the energising current (100) according to the BEM F.

Description

A CONTROL DEVICE FOR AN ELECTRIC MOTOR, IN PARTICULAR A SINGLE-PHASE BRUSHLESS SYNCHRONOUS MOTOR WITH PERMANENT MAGNETS

Technical Field

The present invention relates to a control device for an electric motor, in particular for a brushless synchronous motor with permanent magnets.

Background Art

As is known, in general, an electric motor basically consists of an inductor circuit and an induced circuit.

The first is designed to be energised by an electric current flowing through it so as to create a corresponding magnetic flux. This magnetic flux, operatively connecting to the induced circuit, allows the reciprocal movement of the inductor circuit and the induced circuit.

Depending on the types of motor and the requirements to be satisfied, the inductor circuit may remain stationary, whilst the induced circuit is moved. Alternatively, the induced circuit remains stationary whilst the inductor circuit is moved.

The portion of the motor which remains stationary is called the stator. The mobile portion is called the rotor. In greater detail, relative to one of the specific fields of application of the present invention, brushless synchronous motors with permanent magnets basically consist of a rotor, designed to rotate about its longitudinal axis, and a stator, connected to the rotor and able to activate rotor movement. The rotor has at least two magnetic poles, with opposite polarity and preferably in opposite positions on the rotor.

The stator normally has a plurality of energising windings, each positioned around a corresponding core made of ferromagnetic material. Suitable control means pass an energising current through the above-mentioned windings, generating a magnetic induction flux in the cores .

This flux, acting on the magnetic poles of the rotor, moves the rotor, using the forces of attraction and repulsion created between the rotor poles and the cores of the windings.

The energising current is supplied to the windings in such a way that the magnetic induction flux periodically changes its direction of propagation. Thanks to its magnetic polarisation, the rotor tends to be positioned in a preferential direction relative to the field. In other words, the rotor follows the variations in the direction of flux propagation, rotating at a predetermined synchronous speed. In this way, by suitably synchronising the variations in the energising current with the rotor angular position, the rotor rotates at the required speed.

To achieve this synchronisation, the several types of control techniques are known from prior art.

A first technique is the use of a sensor designed to detect the instantaneous angular position of the rotor. In brushless synchronous motors with permanent magnets, use of a Hall effect sensor positioned close to the rotor may be used to good advantage.

Suitable processing means, connected to the sensor element, are used for generating control signals applied to the control means, according to the angular position of the rotor, so as to create variations in the direction of magnetic flux propagation synchronised with the rotation of the rotor.

Control techniques of this type have obvious operating disadvantages if considered relative to the production complexity and high cost of the hardware needed for transfer of the rotor angular position parameter.

Therefore, the technical sector in question has seen the development of sensorless control techniques, that is to say, control techniques which do not involve the use of a sensor to detect the angular position of the rotor.

A very widespread sensorless technique consists of reading the BEMF (Back electro-motive force) , that is to say, the electro-motive force induced by the rotor' s rotating magnetic field in one of the stator windings through which the energising current is not passing at that moment .

For example, the case of a three-phase motor may be considered. It will have three star-connected windings, and the energising current will periodically cross them.

In particular, at any moment, the energising current flows through two of the three windings (and, therefore, they are linked with the magnetic induction flux) , whilst the energising current does not flow through the remaining winding. The above-mentioned BEMF can be detected at this winding.

The BEMF detected in this way normally has a sinusoidal form over time and crosses the voltage at the centre of the star at regular intervals .

The switching points for the energising current are conventionally selected at the moment when the BEMF crosses the above-mentioned voltage at the centre of the star.

Therefore, the control circuits in the prior art synchronise rotor rotation and the energising currents, switching the latter at the moments in time defined when the BEMF detected as described above crosses the voltage at the centre of the star.

An evident disadvantage relative to the control techniques described up to now is the fact that they cannot be applied to single-phase electric motors, that is to say, motors which only have one energising winding, or, similarly, two half-coils connected to one another in series.

Disclosure of the Invention

The aim of the present invention is, therefore, to overcome the disadvantages indicated in the prior art described above. In particular, the aim of the present invention is to provide a control device for an electric motor, which takes a BEMF reading and which, at the same time, can be applied to single-phase motors.

An auxiliary aim of the present invention is to provide a control device for electric motors, in particular applicable to single-phase electric motors, characterised by simple circuitry and low production costs .

These and other aims are substantially achieved by a control device for an electric motor as described in the claims herein. Brief Description of the Drawings

Further features and advantages are more clearly illustrated in the detailed description which follows, with reference to the accompanying drawings, which illustrate a preferred embodiment of a control device for an electric motor without limiting the scope of its application, and in which:

Figure 1 is a block diagram of a device made according to the present invention, connected to a single-phase motor; Figures 2, 3 and 4 are block diagrams of alternative embodiments of the device illustrated in Figure 1.

Detailed Description of the Preferred Embodiments of the Invention

The control device for an electric motor disclosed is labelled 1 as a whole in the accompanying drawings.

Firstly, it must be said that the control device disclosed may be applied to various types of electric motors, irrespective of the characteristics of the motors themselves.

It is sufficient to create a BEMF induced at an electromagnetic element of the motor, by the electromagnetic interaction between the inductor circuit and the induced circuit, for the device 1 to be able to detect this BEMF and suitably synchronise the reciprocal movements of the inductor circuit and the induced circuit and the energising current. In particular, the device 1, as illustrated in Figures 1 and 2, may be applied to an single-phase, brushless synchronous electric motor 10 with permanent magnets.

This motor 10 comprises a stator 70, which basically constitutes the motor 10 inductor circuit 30, and a rotor 80, which forms the induced circuit 20.

The stator 70 has at least one winding 200, wound around a core 31 and designed to be energised by the current 100 flowing through it.

The winding 200 preferably consists of a first half-coil 4 and a second half-coil 5 which are connected to one another.

When the energising current 100 passes through the winding 200, a primary magnetic flux φ is generated in the core 31. The direction of propagation of the primary magnetic flux φ is varied by appropriate switching of the energising current 100. The winding 200 is designed to be driven between a first operating condition and a second operating condition according to the energising current 100, .

In the first operating condition, the primary magnetic flux φ has a direction of propagation which goes from a first end 4a of the first half-coil 4 to a second end 4b of the first half-coil 4. In the second operating condition, the direction of propagation of the primary magnetic flux φ goes from the second end 4b to the first end 4a of the first half-coil 4.

As indicated above, the motor 10 also comprises the rotor 80, electromagnetically connected to the stator 70 and having a first magnetic pole 81 and a second magnetic pole 82, with opposite polarity to the first pole 81. Since it is positioned close to the core 31, the rotor 80 is affected by the presence of the primary magnetic flux φ. In particular, as a result of interaction with the primary magnetic flux φ, the rotor 80 rotates about its longitudinal axis . Advantageously, to achieve optimum propagation of the primary magnetic flux cp, the core 31 is basically U-shaped. The core 31 basically consists of a first extended portion 32, a second extended portion 33, arranged parallel with the first portion 32, and a connecting portion 34, inserted between the first and the second portions 32, 33.

As illustrated in Figures 1 to 4, the winding 200 is wound around two or more portions of the core 31.

As indicated above, in a preferred embodiment, the stator 70 winding 200 is divided into two half-coils, 4 and 5, the first wound around the portion 32 of the core 31, the second wound around the portion 33 of the core 31.

Both half-coils are designed to be energised by the current 100 flowing through them so as to generate the primary magnetic flux cp. In the same way as the first half-coil 4 described above, the second half-coil 5 is designed to be driven between a first and a second operating condition, according to the above-mentioned energising current 100 and the direction of propagation of the primary magnetic flux cp. In the first operating condition, the direction of propagation of the primary magnetic flux <p is from the first end 5a to the second end 5b of the second half-coil 5, whilst in the second operating condition, the direction of propagation of the primary magnetic flux φ is from the second end 5b to the first end 5a of the second half-coil 5.

Advantageously, the first half-coil 4 and/or the second half- coil 5 may be made with layered winding, to limit the amount of copper used and minimise the flux dispersed. Conveniently, the first half-coil 4 and the second half-coil 5 are connected to one another in series, and wound in such a way that the fluxes generated are concordant .

In this particular case, it is important that the first half- coil 4 and the second half-coil 5 are connected so that the first operating condition of the first half-coil 4 corresponds with the first operating condition of the second half-coil 5, and the second operating condition of the first half-coil 4 corresponds with the second operating condition of the second half-coil 5.

In light of the above description, it is clear that the primary magnetic flux φ is the magnetic flux generated in the stator 70 core 31 by all of the half-coils in the winding 200 when the energising current 100 flows through the winding.

Otherwise, the BEMF induced in the winding 200 is caused by the magnetic action exerted on the core 31 by the rotating magnetic field created by the rotor 80 as it moves.

The following formula applies to a generic winding around the core 31:

x = Ri + —φ_s ⁽i⁾

3( where φs is the magnetic flux resulting from the composition of the primary magnetic flux (cp) generated by the winding 200 when the energising current 100 passes through it, and the magnetic flux φm generated by the rotor's permanent magnet. The terms v, i and R represent the voltage, current and resistance of the generic winding. As indicated above, the device 1 is used to synchronise switching of the energising current 100 with the angular position of the rotor 80.

The device 1 comprises an electromagnetic element 2 designed to have the primary magnetic flux φ passing through it.

A detector circuit 40, connected to the electromagnetic element

2, is used for reading an electric or magnetic parameter 3 characteristic of the above-mentioned electromagnetic element 2 and generating at its output the BEMF 110 induced in the electromagnetic element 2.

The BEMF 110 supplied at output in this way is generated according to the characteristic parameter 3.

Depending on requirements and the specific applications for which the present invention is intended, the characteristic parameter 3 may be the voltage read at the ends of the electromagnetic element 2, or the current flowing in the electromagnetic element 2.

If the characteristic parameter 3 is the voltage read at the ends of the electromagnetic element 2, the formula (1) is conveniently expressed as follows:

v = Ri + —φ + e(θ) ⁽2⁾ dt showing the term e (θ) which represents the BEMF induced in the electromagnetic element 2 by the magnetic action exerted on the core 31 by the rotating magnetic field created by the rotor 80 as it moves. The term θ represents the angular position of the rotor, contained in the BEMF induced in the electromagnetic element 2.

However, in both cases, a possible algorithm for calculation of the BEMF induced in the electromagnetic element 2 requires a subtraction between the characteristic parameter 3 detected and a predetermined reference value, representative of the primary magnetic flux cp through the core 31.

If the characteristic parameter 3 is the voltage at the ends of the electromagnetic element 2, assuming that the current i in the electromagnetic element 2 is zero, the reference value is identified by the term d in formula (2), where cp is the primary magnetic flux.

The detector circuit 40 can process a possible estimate of the term from a mathematical model of the stator circuits, starting with the energising current 100 and the voltage applied to the winding 200.

The dependence of the induced voltage BEMF on the angular position of the rotor θ is indicated by the formula

e{θ) = Kωf_(θ) (3)

10 where fs (θ) represents a function with form characteristic of the construction of the motor 10, K is a constant and ω is the speed of the rotor 80. For the forms of construction of the motor indicated here, the normalised form function fs (θ) has a sinusoidal trend with a certain degree of distortion.

The BEMF 110 generated in this way is then processed by a processing block 50, connected downstream of the detector circuit 40 and designed to receive the BEMF 110 at input.

According to the BEMF 110, the processing block 50 can define the angular position θ and the speed ω of the rotor 80 using mathematical functions applied to the form function fs (θ) contained in the BEMF 110, and generate a corresponding command signal 120 at output, which is an expression of the angular position θ and the speed co, for controlling the energising current 100. In particular, the energising current 100 is regulated in such a way as to correctly synchronise it with the angular position of the rotor 80 and to allow it to be switched at predetermined angular positions of the rotor 80.

To regulate the energising current 100 in this way, the device 1 also has a controller 60, connected to the processing block 50 and designed to receive the command signal 120 at input.

Using this command signal 120, the controller 60 can regulate the energising current 100 as described above.

In particular, a regulating algorithm implemented by the processing unit 50 requires the calculation of a difference between the angular position θ and the instantaneous speed ω of the rotor

80, estimated by the processing unit 50 according to the characteristic parameter 3, and suitable reference values θsp and ωsp. This algorithm also minimises the value resulting from the difference calculation, acting on the energising current 100.

It is important to emphasise how the characteristic parameter 3 of the electromagnetic element 2 is read when the electromagnetic element 2 is connected to the primary magnetic flux φ.

In other words, the reading is taken by the circuit 40 when the electromagnetic element 2 is linked to the primary magnetic flux cp.

Advantageously, the electromagnetic element 2 consists of a winding 2a, connected to the core 31 and designed to be linked to the primary flux φ, when the characteristic parameter 3 is read by the detector circuit 40.

In particular, the winding 2a is wound around the core 31 in such a way as to minimise the flux dispersed and to obtain optimum linking with primary magnetic flux φ. In the embodiment illustrated in Figure 1, the electromagnetic element 2 is designed to be energised by the current 100 flowing through it at least periodically in order to generate the primary magnetic flux φ.

The electromagnetic element 2 consists of part of the first half-coil 4 or, alternatively, the whole of the first half-coil 4.

In other words, the electromagnetic element 2 may coincide with the first half-coil 4, the characteristic parameter 3 being read on the first half-coil 4.

The embodiment illustrated in Figure 3 generalises the above so that the electromagnetic element 2 may coincide with the whole of the winding 200, the characteristic parameter 3 being read on the whole winding 200.

In another embodiment illustrated in Figure 4 the electromagnetic element 2 coincides with the first half-coil 4, the characteristic parameter 3 being read on the first half-coil 4, or the electromagnetic element coincides with the second half-coil 5, the characteristic parameter 3 being read on the second half-coil 5, depending on two operating conditions which involve control of the two half-coils by a controller 60 alternately and in such a way as to create opposite directions of propagation of the primary magnetic flux (p.

In other words, the controller 60, receiving a suitable command from the processing unit 50, selectively supplies current to the first and second half-coils 4, 5, according to a predetermined time pattern. When the first half-coil 4 is supplied with power, the detector block 40 detects the voltage and/or the current of the second half-coil 5, to obtain the BEMF 110. When the second half- coil 5 is supplied with power, the electrical measurements (voltage and/or current) needed to obtain the BEMF 110 are taken on the first half-coil 4.

In contrast, in the embodiment illustrated in Figure 2, the electromagnetic element 2 is physically separated from the winding 200. However, since it is wound around the core 31, it still allows the primary magnetic flux φ to pass through it, so that the characteristic parameter 3 can be read by the detector circuit 40 when the primary magnetic flux φ is linked to the electromagnetic element 2. To summarise, from the operating viewpoint, the following steps are basically performed: firstly, the characteristic parameter 3 of the electromagnetic element 2 is detected during linking of the primary magnetic flux φ to the electromagnetic element 2; - then, according to the characteristic parameter 3 detected, the BEMF 110 induced in the electromagnetic element 2 is calculated. A preferred algorithm calculates the difference between the characteristic parameter 3 and a predetermined reference value, representing the primary magnetic flux p; - finally, according to the BEMF 110 calculated as described above, the energising current 100 is regulated so as to synchronise the reciprocal movement of the rotor 80 and the stator 70.

As indicated above, the characteristic parameter 3 may be the voltage read at the ends of the electromagnetic element 2, or the current made to flow in the electromagnetic element 2.

In the first case, the step of detecting the characteristic parameter 3 comprises a sub-step of detecting the voltage at the ends of the electromagnetic element 2.

In contrast, in the second case, the step of detecting the characteristic parameter 3 comprises a sub-step of detecting the current flowing in the electromagnetic element 2.

The present invention brings important advantages. Firstly, it allows the application of a sensorless control system which makes use of BEMF reading to single-phase electric motors .

Moreover, the control device disclosed has very simple hardware and very low production costs .

Claims

1. A control device for an electric motor (10), in particular a brushless synchronous motor with permanent magnets, of the type comprising an induced circuit (20) and an inductor circuit (30) with a core (31), a primary magnetic flux (Φ) generated by an energising current (100) passing through said core (31), to establish an electromagnetic connection to the induced circuit (20) and generate relative motion between the inductor circuit (30) and the induced circuit (20), the control device (1) comprising:

- an electromagnetic element (2), which can be connected to the primary magnetic flux (Φ) ;

- a detector circuit (40) for reading a magnetic or electric parameter (3) characteristic of the electromagnetic element (2) and generating the BEMF (110) induced in the electromagnetic element (2) at output, according to the parameter (3) ; - a processing block (50), connected to the detector circuit (40) and used for receiving the BEMF (110) generated by the detector circuit (40) at input, the processing block (50) also being able to generate a command signal (120) at output, according to the BEMF (110) received at input, so as to control the energising current (100);

- a controller (60), connected to the processing block (50) and used for receiving the command signal (120) at input, the controller (60) also being able to regulate the energising current (100) according to the command signal (120), the control device (1) being characterised in that the detector circuit (40) is used for reading the characteristic parameter (3) of the electromagnetic element (2) when the electromagnetic element (2) is connected to the primary magnetic flux (Φ) .

2. The device according to claim 1, characterised in that the electromagnetic element (2) is a winding (2a), connected to the core (31) and designed to be linked to the primary flux (Φ) when the characteristic parameter (3) is read by the detector circuit (40) .

3. The device according to claim 2, characterised in that the winding (2a) is wound around the core (31), to achieve a link with the primary flux (Φ) at least when the characteristic parameter (3) is read.

4. The device according to claim 3 characterised in that the energising current (100) periodically passes through the winding (2a) to generate the primary magnetic flux (Φ) in the core (31) .

5. The device according to any of the foregoing claims, characterised in that the BEMF (110) generated at output by the detector circuit (40) is calculated as the difference between the characteristic parameter (3) and a predetermined reference value.

6. The device according to any of the foregoing claims, characterised in that the characteristic parameter (3) is the voltage at the ends of the electromagnetic element (2) .

7. The device according to any of the foregoing claims, characterised in that the characteristic parameter (3) is the current flowing in the electromagnetic element (2) .

8. An electric motor comprising:

- an induced circuit (20);

- an inductor circuit (30) , with a core (31) through which a primary magnetic flux (Φ) passes, generated by an energising current (100) , to establish an electromagnetic connection with the induced circuit (20) and generate relative motion between the inductor circuit (30) and the induced circuit (20) ;

- a control device (1), connected to the inductor circuit (30) and the induced circuit (20) and equipped with:

- a detector circuit (40) , used for reading an electric or magnetic parameter (3) characteristic of the electromagnetic element (2) and generating at output the BEMF (110) induced in the electromagnetic element (2), according to the parameter (3); - a processing block (50) , connected to the detector circuit (40) and used for receiving at input the BEMF (110) generated by the detector circuit (40) , the processing block (50) also being able to

75 generate a corresponding command signal (120) at output, according to the BEMF (110) received at input, in order to control the energising current (100);

- a controller (60), connected to the processing block (50) and used for receiving the command signal (120) at input, the controller (60)

80 also being able to regulate the energising current (100) according to the command signal (120) , the electric motor being characterised in that the detector circuit (40) is designed to read the characteristic parameter (3) of the electromagnetic element (2) when the electromagnetic element (2) is

85 linked to the primary magnetic flux (Φ) .

9. The motor according to claim 8 characterised in that the electromagnetic element (2) is a winding (2a) connected to the core (31) .

90

10. The motor according to claim 9, characterised in that the winding (2a) is wound around the core (31), to create the link with the primary flux (Φ) at least when the characteristic parameter (3) is read.

95

11. The motor according to claim 10, characterised in that the energising current (100) passes through the winding (2a), generating the primary magnetic flux (Φ) in the core (31) .

100 12. The motor according to any of the foregoing claims, characterised in that the BEMF (110) generated at output by the detector circuit (40) is obtained from the difference between the characteristic parameter (3) and a predetermined reference value.

105 13. The motor according to any of the foregoing claims, characterised in that the characteristic parameter (3) is the voltage at the ends of the electromagnetic element (2) .

14. The motor according to any of the foregoing claims 110 characterised in that the characteristic parameter (3) is the current flowing in the electromagnetic element (2).

15. The motor according to claim 1, characterised in that the relative motion between the inductor circuit (30) and the induced

115 circuit (20) is of the rotary type.

16. The motor according to claim 15 characterised in that the inductor circuit (30) is a motor (10) stator (70), the induced circuit (20) being a motor (10) rotor (80) .

120

17. The motor according to claim 16 characterised in that the core (31), preferably U-shaped, has a first portion (32) and a second portion (33) , arranged in opposite positions relative to the rotor (80) .

125

18. The motor according to claim 8 characterised in that the inductor circuit (30) also comprises a winding (200), designed to be energised by the current (100) flowing through it so as to generate the primary magnetic flux (Φ) .

130

19. The motor according to claim 18 characterised in that the electromagnetic element (2) is part of the winding (200).

20. The motor according to claim 18 characterised in that the 135 electromagnetic element (2) coincides with the winding (200).

21. The motor according to claim 18 characterised in that the electromagnetic element (2) is physically separated from the winding (200) and is designed to have the primary magnetic flux (Φ) passing

140 through it when the characteristic parameter (3) is read by the detector circuit (40) .

22. A single-phase brushless synchronous electric motor, of the bipolar type with permanent magnets, comprising:

145 a stator (70), with a winding (200) wound around a core (31) and designed to be energised by an electric current (100) flowing through it so as to generate a primary magnetic flux (Φ) , the winding (200) preferably being divided into at least one first half- coil (4) and one second half-coil (5), the first half-coil (4)

150 having a first end (4a) and a second end (4b) opposite the first, which can be driven at least between a first operating condition, in which the direction of propagation of the primary magnetic flux (Φ) generated by the energising current (100) is from the first end (4a) to the second end (4b) of the first half-coil (4), and a second

155 operating condition, in which the direction of propagation of the primary magnetic flux (Φ) is from the second end (4b) to the first end (4a) of the first half-coil (4);

- a rotor (80) , connected to the stator (70) and equipped with a first magnetic pole (81) and a second magnetic pole (82) with

160 opposite polarity to the first pole (81) , the rotor (80) being subjected to the action of the primary magnetic flux (Φ) so that it rotates about its longitudinal axis, the motor being characterised in that it also comprises a control device (1), connected to the stator (70) and to the rotor (80), and

165 having:

- a detector circuit (40), connected to the winding (200) and able to read the voltage at the ends of the winding or the current flowing in the winding, the detector circuit (40) also being designed to generate at output the BEMF (110) induced in the winding

170 (200);

- a processing block (50), connected to the detector circuit (40), and used for receiving at input the BEMF (110) generated by the detector circuit (40), the processing block (50) also being able to generate at output a command signal (120) , according to the BEMF

175 (110), to drive the winding (200) between the operating conditions;

- a control circuit (60), connected to the processing block (50) and to the winding (200) and used for receiving at input the command signal (120) from the processing block (50), the control circuit (60) also being able to regulate the energising current (100)

180 according to the command signal (120) to drive the winding (200) between the first and the second operating conditions.

23. The electric motor according to claim 22, characterised in that the core (31) has a first extended portion (32), a second 185 extended portion (33) arranged substantially parallel with the first portion (32), and a connecting portion (34), inserted between the first and second portions (32, 33), the first half-coil (4) being wound around the first portion (32) .

190 24. The electric motor according to claim 23, characterised in that the stator (70) also comprises a second half-coil (5), wound around the second portion (33) of the core (31) and designed to be energised by a current (100) flowing through it so as to generate the primary magnetic flux (Φ) , the second half-coil (5) having a

195 first end (5a) and a second end (5b) opposite the first end, it being possible to drive the second half-coil at least between a first operating condition, in which the direction of propagation of the primary magnetic flux (Φ) is from the first end (5a) to the second end (5b) of the second half-coil (5) , and a second operating

200 condition, in which the direction of propagation of the primary flux (Φ) is from the second end (5b) to the first end (5a) of the second half-coil (5) .

25. The electric motor according to claim 24 characterised in that 205 the first half-coil (4) and the second half-coil (5) are connected to one another in series, the second half-coil (5) being designed to be energised by the current (100) flowing through it.

26. The electric motor according to claim 25, characterised in 210 that the first end (5a) of the second half-coil (5) is connected to the second end (4b) of the first half-coil (4), so that the first operating condition of the second half-coil (5) corresponds to the first operating condition of the first half-coil (4), and the second operating condition of the second half-coil (5) corresponds to the 215 second operating condition of the first half-coil (4).

27. The electric motor according to claim 22, characterised in that the detector block (40) is connected to the first and second ends (4a, 4b) of the first half-coil (4) for detecting a voltage

220 between the first and second ends (4a, 4b) and/or for detecting a current flowing in the first half-coil (4), and for generating at output the BEMF (110) induced in the first half-coil (4).

28. A method for controlling an electric motor, in particular a 225 brushless synchronous motor with permanent magnets, of the type comprising an induced circuit (20) and an inductor circuit (30) having a core (31), a primary magnetic flux (Φ) passing through the core (31), said flux generated by an energising current (100), for establishing an electromagnetic connection with the induced circuit 230 (20) and for generating relative motion between the inductor circuit (30) and the induced circuit (20), the method comprising the following steps:

- detecting a parameter (3) characteristic of an electromagnetic element (2) which can be connected to the primary flux (Φ) ;

235 - calculating the BEMF (110) induced in the electromagnetic element (2) according to the characteristic parameter (3);

- adjusting the energising current (100), according to the BEMF (110) calculated, so as to synchronise the reciprocal movement of the inductor circuit (30) and the induced circuit (20),

240 the method being characterised in that the step of detecting the characteristic parameter (3) at the electromagnetic element (2) is carried out during linking of the electromagnetic element (2) to the main magnetic flux (Φ) .

245 29. The method according to claim 28, characterised in that the step of calculating the BEMF (110) induced in the electromagnetic element (2) comprises a sub-step of identifying the difference between the characteristic parameter (3) detected and a predetermined reference value.

250

30. The method according to claim 28 or 29, characterised in that the step of detecting the characteristic parameter (3) comprises a sub-step of detecting the voltage at the ends of the electromagnetic element (2) .

255

31. The method according to claim 28 or 29, characterised in that the step of detecting the characteristic parameter (3) comprises a sub-step of detecting the current flowing in the electromagnetic element (2) .