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Title:
METHOD FOR BRAKING A SINGLE-PHASE ELECTRIC MOTOR, AS WELL AS A SINGLE-PHASE ELECTRIC MOTOR IMPLEMENTING SUCH METHOD
Document Type and Number:
WIPO Patent Application WO/2012/080813
Kind Code:
A1
Abstract:
The present invention relates to an optimized braking method of a single-phase electric motor, as well as to a single-phase electric motor implementing such method. The method for braking a single-phase electric motor (10) comprising a rotor (11) and a stator, the stator having at least a main winding (12') and at least an auxiliary winding (12''), being supplied, in a drive condition, each with an alternate supply signal, where the alternate supply signals are mutually out of phase, and is characterized in that it comprises the step consisting in the supplying by a time interval (T1-T2), the main and auxiliary windings (12', 12'') of the stator each with a supply signal, where the supply signals are mutually in phase.

Inventors:
MICHIELA, Gianni (Via Delle Industrie, 89/C, Dosson Di Casier, I-31030, IT)
Application Number:
IB2011/003022
Publication Date:
June 21, 2012
Filing Date:
December 13, 2011
Export Citation:
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Assignee:
CAME GROUP S.P.A. (Via Delle Industrie, 89/C, Dosson Di Casier, I-31030, IT)
MICHIELA, Gianni (Via Delle Industrie, 89/C, Dosson Di Casier, I-31030, IT)
International Classes:
H02P3/22; H02P25/04
Foreign References:
EP0562673A2
JPS60131084A
Other References:
None
Attorney, Agent or Firm:
DI GENNARO, Sergio (Barzan├▓ & Zanardo Milano S.p.A, Corso Vittorio Emanuele II 61, Torino, I-10128, IT)
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Claims:
CLAIMS

1) Method for braking a single-phase electric motor (10) comprising a rotor (11) and a stator, said stator having at least a main winding (12') and at least an auxiliary winding (12''), said main winding (12') and said auxiliary winding (12'') being supplied, in a drive condition, each with an alternate supply signal, said alternate supply signal being mutually out of phase, characterized in that it comprises the stage consisting in the supplying for a time interval (Tl- T2) , said main and auxiliary windings (12', 12'') of said stator each with a supply signal, said supply signal being mutually in phase.

2) Method for braking a single-phase electric motor (10) according to claim 1, characterized in that said stage of phase supplying consists in a directly connection of said windings (12', 12'') of said stator to a same alternate supply source.

3) Method for braking a single-phase electric motor (10) according to claim 1 or 2 , characterized in that it comprises a subsequent stage of inversion of phase between the supply signal of said main winding (12') and the supply signal of said auxiliary winding (12'') with respect to said drive condition.

4) Method for braking a single-phase electric motor (10) according to claim 3, characterized in that said inversion stage consists in the interruption of the connection of said main winding (12') with said alternate supply source.

5) Method for braking a single-phase electric motor (10) according to one of claims 1 to 4 , characterized in that it actuates a static brake (14) of said single- phase electric motor (10) once the rotation of said rotor (11) is substantially stopped.

6) Method for braking a single-phase electric motor

(10) according to any of the preceding claims, characterized in that it comprises a stage consisting in the estimation of said time interval (T1-T2) according to the properties of said motor (10) and of a load driven by the same (10) .

7) Single-phase electric motor (10) comprising a rotor

(11) and a stator, said stator having at least two windings (12', 12'') which can be linked to an alternate supply source characterized in that it comprises a pair of electronic switches (22', 22'') each of them being interposed between a winding (12', 12'') and said alternate supply source and electronic processing means (21) for driving the opening and the closure of said pair of electronic switches (22) for interrupting the connection of said windings (12', 12'') to said alternate current source, in order to realize a drive condition in which a first switch (22') linked to a first winding (12') is in a close configuration and a second winding (22'') linked to a second winding (12'') is in an open configuration and a braking condition in which both switches (22', 22') are in a closed configuration.

8) Single-phase electric motor (10) according to claim 7, characterized in that said electronic processing means (21) are adapted to pilot said pair of switches (22', 22'') in order to realize an inverted condition in which said first switch (22') associated with said first winding (12') is in an open configuration and said second switch (22'') associated with said second winding (12'') is in a closed configuration.

9) Single-phase electric motor (10) according to claim 7 or 8, characterized in that said at least two windings (12', 12'') are electrically coupled by means of an interposition of a driving capacitor (13) .

10) Single-phase electric motor (10) according to one or claims 7 to 9, characterized in that said electronic switches (22) are devices at the solid state, for controlling the current flow in both directions.

11) Single-phase electric motor (10) according to claim 10, characterized in that said electronic switches (22) are any of the electronic components chosen from a group formed by:

- TRIAC (TRIode for Alternating Current) ;

- SCR (Silicon Controlled Rectifier) ;

- IGBT (Insulated Gate Bipolar Transistor) ; and

- MOSFET (Metal-Oxide- Semiconductor Field-Effect Transistor) .

12) Single-phase electric motor (10) according to any of claims 7 to 11, characterized in that said electronic switches (22) are provided with insulating means towards said electronic processing means (21) .

13) Single-phase electric motor (10) according to anyone of claims 7 to 12, characterized in that it comprises a static brake (14) .

14) Single-phase electric motor (10) according to anyone of claims 7 to 13, characterized in that it is of a non-synchronic type.

Description:
METHOD FOR BRAKING A SINGLE-PHASE ELECTRIC MOTOR, AS WELL AS A SINGLE-PHASE ELECTRIC MOTOR IMPLEMENTING SUCH METHOD

The present invention relates to an optimized braking method of a single-phase electric motor, as well as to a single-phase electric motor implementing such method. By single-phase electric motor it is meant electric motors that require the use of an electric line with an electric phase and a neutral wire for the operation thereof, therefore comprising also those that, through the use of a capacitor, obtain a second phase required for an autonomous start of the same.

In particular, two types of single-phase electric motors are known: the asynchronous motor, characterized by a rotation of the induced magnetic field not synchronized with the magnetic field of the stator, which therefore rotate at different frequencies, and the synchronous motor, characterized by a rotation of the induced magnetic field synchronized with the magnetic field of the stator, which therefore rotate at the same frequency.

Nowadays, single-phase electric motors are used in various types of applications such as for example the automation of suction and ventilation machines, household appliances, shutters, blinds, gates or rolling shutters of a different type.

To this end, the single-phase electric motor is coupled to the object to be driven through a motor reducer that adapts the speed and the torque thereof.

In movement applications, single-phase electric motors are normally provided with static braking systems, that is, of the type that with no power supply the motor is blocked and released when they are supplied again, such as for example an electric brake.

An example of electric brake is a spring pressure brake provided with a solenoid that, when supplied, pulls back a movable anchor, opposing the spring return force and thus allowing the free rotation of the driving shaft . In the lack of power supply, the solenoid does not exert the magnetic force required for retaining the movable anchor, which is then pushed by the springs to compress against a brake gasket associated to the driving shaft, thus exerting a braking action.

A further example of electric brake that exhibits a similar behaviour is a flow deviation brake wherein the force opposing the springs that retracts the anchor is generated not by an independent solenoid, but by the same stator winding.

Static braking systems exhibit several drawbacks due in particular to the fact that they impose a sudden mechanical block to the moving motor and to the element driven thereby.

In this way it is not possible to gradually dissipate the kinetic energy accumulated by the motor-element system.

A strong noise may therefore be heard upon the electric brake triggering due to the impact and to the friction between the moving parts of the motor and the static parts of the brake. Such friction also causes a quick wear of the parts that come into contact in the braking step .

As far as three-phase electric motors are concerned, it is known to perform the braking step dynamically, through the supply of the motor with direct current. A progressive reduction of the kinetic energy accumulated by the elements it thus obtained, without it being dissipated by mechanical friction.

However, it is not convenient to apply such solution to single-phase electric motors since a direct current for braking generally is not available in the circuits commonly used for controlling such single-phase electric motors.

At the end of the braking, it would therefore be necessary to make a special rectification and levelling section as well as set up dedicated electronic switches .

The object of the present invention is to obviate the drawbacks mentioned above and in particular that of devising a method for braking a single-phase electric motor capable of gradually dissipating the kinetic energy accumulated by the moving parts.

Another object of the present invention is to provide a method for braking a single-phase electric motor which is capable of stopping such motor in substantial absence of noise.

A further object of the present invention is to provide a method for braking a single-phase electric motor which prevents a quick wear of an electric brake associated to the electric motor.

Last but not least, a further object of the present invention is to devise a single-phase electric motor which may be effectively braked in substantial absence of wear and noise.

These and other objects according to the present invention are achieved by providing a method for braking a single-phase electric motor as described in claim 1.

Further features of the method for braking a single- phase electric motor are defined in the dependent claims .

The features and the advantages of a method for braking a single-phase electric motor according to the present invention will appear more clear from the following description, made by way of an indicative non-limiting example with reference to the annexed schematic drawings, wherein:

- figure 1 shows a schematic view of a single-phase electric motor which may be driven by a braking method according to the present invention;

- figure 2 shows a first diagram of the voltages applied to the single-phase electric motor in the braking step;

- figure 3 shows a second diagram of the voltages applied to the single-phase electric motor in the braking step.

With reference to the figures, reference numeral 10 globally denotes a single-phase electric motor, preferably of the asynchronous type.

Single-phase electric motor 10 comprises a rotor 11 and a stator, wherein the stator exhibits two windings 12', 12'' : a first main drive winding 12' and a second auxiliary or start winding 12'', wherein the main winding 12' is the one directly connectable to the terminals of an alternate supply source.

In the embodiment shown, therefore, each winding may act as primary winding 12' or, as an alternative, as auxiliary winding 12'' according to the particular temporary connection configuration. In this way it is possible to define the direction of rotation of rotor 11. A driving capacitor 13 is preferably interconnected between the two windings 12', 12'' which, introducing a phase displacement between the currents in the two windings 12', 12'', generates a rotating magnetic field that allows motor 10 to start. Single-phase electric motor 10 is provided with control means 20 that drive the connection of the two windings 12 ',12'' to the power supply source, thus defining which winding acts as the main one 12' and which as the auxiliary one 12'' and thus the rotation direction of rotor 11.

Control means 20 comprise electronic processing means 21 adapted for driving the opening and closing of a pair of electronic switches 22', 22'', thus providing the direct connection of one and/or of the other winding 12 ',12'' to the alternate supply source.

Solid state devices are preferably used as electronic switches 22', 22'', capable of controlling the current flow in both directions. An example of devices of this type are TRIAC (TRIode for Alternating Current) or other combined single-pole devices, such as SCR {Silicon Controlled Rectifier) , IGBT (Insulated Gate Bipolar Transistor) or MOSFET {Metal-Oxide- Semiconductor Field-Effect Transistor) or equivalent ones .

Electronic switches 22', 22'' are preferably provided each with an activation control that allows the closing thereof only when the voltage at their ends is null . Electronic switches 22', 22'' are preferably provided with insulating means towards electronic processing means 21.

Moreover, electronic switches 22', 22'' are preferably provided with active or passive devices adapted for reducing the electric stress of the possibility of self-triggering, such as for example snubbers or other equivalent electronic elements .

According to the present invention, electronic processing means 21 are such as to drive, in the braking step, the opening and closing of electronic switches 22', 22'' so that both phases of motor 10 are supplied in phase by a predetermined time interval substantially coinciding with a plurality of half- cycles of an alternating current.

Starting from a drive configuration of the motor wherein a first electronic switch 22' is closed, connecting then the corresponding first winding 12' directly to the alternate supply source, and a second electronic switch 22' is open, by the effect of driving capacitor 13 interconnected between windings 12', 12'', the phase of voltage 15 of the second winding 12'' is advanced by 90┬░ relative to the phase of voltage 16 of the first winding 12', as is shown in figures 2 and 3. To start the braking step, electronic processing means 21 drive the second electronic switch 22'' to close at a braking start time Tl, in order to directly connect also the second winding 12 1 to the alternate supply source and thus reduce to zero the phase displacement introduced by capacitor 13.

The phase displacement is held null by a time interval T1-T2 substantially corresponding to a multiple of half-cycles .

Contrary to a purely theoretical analysis, in the practical embodiment the time interval T1-T2 during which both switches 22', 22'' are active is not exactly a multiple of the mains half period.

In fact, the closing of electronic switches 22', 22'' takes place at null voltage at the ends thereof, whereas the reopening takes place when the current is null. Due to inductive loads and to the initial phase displacement introduced by capacitor 13, the phase between voltage and current is substantially non null, leading to activation intervals of switches 22', 22'' only approximately coinciding with an entire number of half cycles.

According to a preferred embodiment, subsequent to the step at null phase displacement between the voltages at the terminals of the two windings 12', 12'', there occurs an inversion step T2-T3 during which the first switch 22' connected to the first winding 12' is opened and only the second winding 12 ' ' responsible for the braking is left directly connected to the alternate supply source .

Such particular supply of the phases of motor 10 leads to a further braking action, thus reducing the speed of rotor 11 up to the stop.

In particular, during the main braking step, that is, when both main winding 12' and auxiliary winding 12'' are directly connected to the alternate supply source, a resistant torque develops substantially proportional to the rotation speed of rotor 11 up to a maximum value, beyond which it remains constant.

In the optional inversion step, the motor develops a so-called starting torque, adapted for completing the effect of the dynamic brake, which is minimal at speeds that are now low.

The duration of braking step T1-T2 required for the substantial completion of the kinetic energy dissipation, as well as of inversion step T2-T3, is estimated on the basis of the features of the motor and of the load driven by the same.

The number of half-cycles that needs to be injected in the single steps is thus determined. In alternative embodiments it is possible to introduce auxiliary measurement elements, such as for example an encoder, which facilitate the estimate of the braking time.

Single-phase electric motor 10 preferably comprises also a static brake 14, such as for example an electric brake .

Static brake 14 remains inactive up to the end of the braking periods performed through the controlled activation of electronic switches 22', 22'' described above, so as to operate when the kinetic energy of rotor 11 is substantially dissipated.

Such behaviour occurs automatically in the case of static brake 14 of the flow deviation or solenoid type if arranged in series with the common terminal of windings 12 , 12 ' ' .

A reduced wear of static brake 14 is thus obtained, which acts as a block in full accordance with the static nature thereof, without having to dissipate the kinetic energy of rotor 11 through mechanical friction. The features of the device object of the invention as well as the relevant advantages are clear from the above description. The braking piloting of the single- phase electric motor according to the present invention allows gradually dissipating the kinetic energy accumulated by the moving parts without the sudden operation of the static brake.

A braking is thus obtained in substantial lack of noise, also preserving the parts of the static brake that, not having to dissipate the kinetic energy of the rotor through mechanical friction, are subject to a lower wear.

Last but not least, the braking method of the single- phase electric motor according to the present invention is capable of performing a dynamic braking without damaging the electronic components making up the motor. Finally, it is clear that several changes and variations can be made to the device thus conceived, all falling within the invention; moreover, all details can be replaced with technically equivalent elements. In the practice, the materials used as well as the sizes, can be whatever, according to the technical requirements .