Abstract:
A device for detecting the angular position of a rotor of a polyphase rotary electrical machine contains a stator and a plurality of magnetic field sensors ( 200 ) delivering first signals ( 2001 - 2003 ) representing a magnetic field. The device includes means ( 201 ) for generating, from linear combinations of the first signals, first ( 2010 ) and second ( 2011 ) sinusoidal signals, phase-shifted by a determined value φ representing an angular position of the rotor, referred to as real. The device includes means for detecting a value for an angular position of the rotor referred to as estimated ( 221 ) by locking between the real and the estimated angular positions using a feedback loop known as a “tracking” loop ( 214 - 216, 215 - 207 ). The device may relate to a polyphase rotary electrical machine containing such a device.

Description:
This application claims foreign priority benefit under 35 U.S.C. §119 of French patent application no. 08/53359, filed on May 23, 2008, which application is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention concerns a device for detecting the angular position of a rotor of a polyphase rotary electrical machine containing a stator. 
     The invention also concerns a rotary electrical machine containing such a device. 
     It is especially suitable for reversible machines, known as alternator-starters, which are used in the vehicle industry, both in alternator mode and in starter mode, or as an aid to moving off (boost mode), typically from 500 rpm. 
     2. Description of Related Art 
     Within the context of the invention, the term “polyphase” concerns more specifically three-phase or hexaphase rotary electrical machines, but may also concern biphase rotary electrical machines or those which operate at a higher number of phases. 
     For the sake of clarity, the following scenario relates to the preferred application of the invention, i.e. the case of a reversible three-phase rotary electrical machine of the alternator-starter type, without this in any way limiting the scope of the invention. 
     As is well known, a reversible rotary electrical machine contains an alternator comprising:
         a rotor constituting an inductor, traditionally combined with two collector rings and two brushes to supply an excitation current; and   a polyphase stator, bearing several coils or windings, three in the embodiment in question, constituting an armature, which are star-connected, or most often as a triangle in the case of a three-phase structure, and which deliver converted electrical power to a bridge rectifier when operating as an alternator. The machine includes two bearings, a front and a rear, to fix it to the thermal engine and to fix the stator. The stator surrounds the rotor. The rotor is carried by a shaft supported by the front and rear bearings. The brushes of an excitation circuit of the rotor are powered by a regulator of the alternator to maintain the output voltage of the alternator at a desired voltage to supply an electrical supply network containing a battery. The alternator enables any rotation movement of the inductor rotor driven by the thermal engine of the vehicle to be transformed into an electrical current induced in the coils of the stator.       

     The alternator may also be reversible and constitute an electric motor, or rotary electrical machine, enabling the thermal engine of the vehicle to be driven in rotation via the rotor shaft. This reversible alternator is known as an alternator-starter, or alterno-starter. It enables mechanical energy to be transformed into electrical energy, and vice versa. 
     Thus, in alternator mode, the alternator-starter specifically charges the vehicle battery, while in starter mode, the alternator-starter turns the motor vehicle&#39;s thermal engine, also known as internal combustion engine, in order to start it. 
     In reversible machines from the automotive industry, for example, operating in motor or starter modes, the stator must be current-controlled in such a way that at any moment the necessary torque can be applied to the rotor to impel the required rotation for the operation of the engine. The torque applied to the rotor, and hence the current supplied to the phases of the stator, is a sinusoidal function of the angular position of the rotor in relation to the stator, represented by an angle θ. 
       FIG. 1 , placed at the end of this description, illustrates in diagram form a complete system  1  for detecting the angular position θ(t) of the rotor of a three-phase alternator-starter and for controlling said organ, either in alternator mode or in engine (starter) mode. 
     The system  1  consists of four principal sub-systems: an alternator-starter  10 , a reversible AC-DC power converter  11 , a control module  13  for this converter and a module  12  for detecting the angular position ƒ of the rotor  100  (symbolised by an arrow turning about its axis of rotation Δ). 
     The converter  11  generally consists of a bridge of electronic rectifiers, comprising three banks of MOSFET power transistors, under the single reference  110 , one for each phase. A structure of this type is well known to the person skilled in the art and there is no need to describe it in further detail. 
     In alternator mode, the alternator-starter  10  supplies the converter  11  with three-phase AC current via its three outputs,  101  to  103 , which correspond to the junctions between the three coils (not shown in  FIG. 1 ) constituting the stator  104  of the alternator-starter  10 . The latter converts the three-phase AC current into DC current so as to (re)charge the battery Bat with which the vehicle is equipped (not shown in  FIG. 1 ). This, in turn, supplies various organs of this vehicle: on-board electronics, air conditioning, headlights, etc. 
     In engine mode, i.e. in starter mode, the alternator-starter  10  is supplied with three-phase electrical energy by the reversible converter  11 , which is operating in three-phase current generator mode. 
     Whichever mode is considered, the MOSFET transistors  110  are controlled according to an appropriate sequence of six control signals, SC 1  to SC 6 , generated by the control module  13 . As is also well known, these signals SC 1  to SC 6  must be generated synchronously with the angular position θ of the rotor  100  which detects the relative phases of the currents supplied by the outputs  101  to  103  of the alternator-starter  10 . 
     For this reason, it is necessary to detect this angular position θ with great precision, in order to achieve correct functioning of the bridge rectifiers, in particular to avoid any risk of deterioration of the semiconductor components, but also and above all, in engine or starter mode, to optimise the torque supplied by the alternator-starter  10 . 
     This is the function which is devolved to the module  12  for detecting the angular position θ of the rotor  100  so as to generate a signal θ(t) representing the instantaneous variation of the measured angular position and to transmit it as an input to the control module  13 . 
     In prior art, various methods have been proposed for this purpose. 
     Certain reversible electrical machines, especially those used in the automotive industry, are now equipped with a device known as a resolver, which is positioned at the end of the rotor shaft of the machine. Such a resolver is described, by way of non-exhaustive example, in the patent application US 2002/0063491 A1. The resolver itself contains a stator and a rotor which are fixed in relation to the respective stator and rotor of the reversible machine. The resolver measures the magnetic field produced by its own rotor. As this magnetic field is fixed in relation to said rotor, which is itself fixed in relation to the rotor of the machine, it represents the position of the actual rotor of the machine. 
     However, this type of equipment presents a certain number of disadvantages, in particular the following:
         resolvers are quite expensive, and, to render them operational, their implementation is complex, due to the coupling to be effected between the resolver and the actual reversible machine, which necessitates the presence of an electronic calculation component to provide the correct position of the rotor of the reversible machine based on the coupling parameters.   Secondly, resolvers are sensitive to the magnetic interference caused by the stray magnetic field produced by the rotor, which causes malfunctioning of the system, thus errors of measurement and poor control of the machine. To limit this disadvantage, it is necessary to use magnetic protection, such as a stainless steel tube placed between the rotor and the resolver at the shaft end. Moreover, the mechanical strength of these devices is imperfect, since they are especially sensitive to vibrations from the machine due to being mounted on the shaft end of the rotor. Moreover, their size is a problem and is unlikely to enable greater compactness of the electrical machine.   Finally, their resistance to salt spray and dust is not completely satisfactory.       

     To alleviate these disadvantages, in international patent application WO 2006/010864 A2, the claimant proposed a device for detecting the position of a rotor of a rotary electrical machine containing a stator, which makes it possible to obtain the precise angular position sought, while at the same time being cheap, simple to operate and having low sensitivity to magnetic interference. 
     SUMMARY OF THE INVENTION 
     The device taught in this patent application contains a plurality of magnetic field sensors, fixed in relation to the stator of the rotary electrical machine and able to deliver first signals representing a rotating magnetic field detected by these sensors, and means for processing these first signals by an operator able to supply second signals depending on the angular position attained by the rotor. 
     In one embodiment, illustrated by  FIG. 1 , three linear Hall effect sensors CA 1  to CA 3  placed at 120° electric on the rotary electrical machine, in this case the alternator-starter  10 , facing a target (not shown in  FIG. 1 ) integral with the rotor  100  and magnetised alternately North/South for each pole of the machine. For a more detailed description, it would be advantageous to refer to the description in the previously cited international patent application WO 2006/010864 A2.  FIG. 1  also shows an angular reference marker RRef θ physically connected to the rotor  100  of the alternator-starter  10 . 
       FIG. 2 , which is at the end of this description, illustrates in diagram form an example of a series of three signals, CH 1  to CH 3 , delivered by the sensors, CA 1  to CA 3 , with the alternator-starter  10  rotating at a fixed speed. 
     The ordinates axis is graduated in amplitudes, by way of example, for the sake of clarity, between 0 and 4.5V, and the abscissa axis in angles (degrees). 
     It has been found experimentally that the signals CH 1  to CH 3 , which are referred to as “raw”, usually contain a high level of harmonics, in particular a high level of harmonic  3  and their relative amplitudes are different. Hence, it is difficult to construct, from these far from perfect raw signals CH 1  to CH 3 , signals which approach an ideal sinusoidal function (i.e. free from harmonics), with identical amplitudes, zero offsets and mutually phase-shifted in a non-obvious fashion (phase shift not a multiple of 180°). 
     The basic principle set out in international [application] WO 2006/010864 A2 is to find two distinct linear combinations which simultaneously enable the two sinusoids desired to be obtained, while at the same time finding the best possible solution to the problems raised above. 
     As a first approximation, it is possible to admit that the sensors CA 1  to CA 3  have identical, or at least very close, characteristics, that they are placed in an identical thermal and electromagnetic environment and thus that the signals delivered by these sensors retain some common characteristics. These hypotheses, as well as a fixed angular relation between these sensors, lead to the view that:
         their offsets develop simultaneously as a function of any interference field (such as, for example, magnetisation of the rotor);   their levels of order  3  harmonics are very similar and in phase with their fundamental harmonics; and   the electrical signals generated by these sensors are phase-shifted by about 120°.       

     These hypotheses make it possible to choose two linear combinations which partly cancel out the order  3  harmonic and the offsets. Simply by choosing, for linear combinations, the difference between two sensor output signals, one obtains two signals phase-shifted by 60° and which meet the selection criteria mentioned above. 
       FIG. 3 , which is at the end of this description, illustrates in diagram form the result obtained. The ordinates axis is graduated in amplitudes, by way of example for the sake of clarity between −2V and +2V, and the abscissa axis in degrees.  FIG. 3  also shows the phase shift φ between the two signals C 1  and C 2 . 
     It is easy to see, on inspecting  FIG. 3 , that the two curves C 1  and C 2  are close to ideal sinusoidal functions. The signals represented by these curves are recentred and contain fewer harmonics than the raw signals ( FIG. 2 : CH 1  to CH 3 ). 
     Nevertheless, the amplitudes of these signals are not completely identical and their offsets are not absolutely zero. This mean that a factory calibration stage, at the end of the manufacturing chain, is necessary. 
     To do so, one may subtract an adjustable value from each of the signals in order to cancel each offset. This signed value can be obtained in purely analogue fashion, for example using a potentiometer or an adjustable resistive bridge (for example by using a procedure known as laser trimming) or semi-analogue, by using a digital value converted into an analogue value. Finally, a completely digital solution is also possible, if the signals are converted into digital signals. 
     With respect to amplitude calibration, a single adjustment is necessary, because it is sufficient for the signal amplitudes to be equal. To do so, a variable gain amplifier can be used. This variable gain amplifier can be purely analogue, semi-analogue or completely digital. It should be noted that the amplitude calibration could have been carried out in advance on both raw signals delivered by the sensors CA 1  to CA 3  so that subsequent linear combinations are more effective in eliminating the order  3  harmonic. The disadvantage of this method lies in the fact that a supplementary adjustment is necessary and that it does not correct any disparities in amplification of the linear combinations themselves. 
     Once the two sinusoids have been obtained (curves C 1  and C 3 ), it becomes possible to extract directly the value of the angular position θ. To do this, by dividing the two signals represented by the curves C 1  and C 3 , one eliminates the amplitude, then, using a mathematical function or a table, one may invert the function and determine the angular quadrant using the signs of the signals. For the sake of clarity, by way of non-limiting example, if the phase shift between signals is φ=90°, for example, this is an arctangent function Again, for a more detailed description, it would be advantageous to refer back to the description in the previously cited international patent application WO 2006/010864 A2. The method according to WO 2006/010864 A2 gives good results and achieves the aims set by this patent application, at least if the signals really do approach a pure sinusoidal function (that is, presenting few harmonics and little noise). In practice, these operating conditions, which may be referred to as “ideal”, are rarely found. It follows that, again in practice, the method just mentioned often proves to be unsatisfactory. 
     The object of the invention is to propose a method, for detecting the angular position which obviates the disadvantages of prior art, firstly, some of which have just been recalled, and secondly, more robust, while not significantly increasing either the complexity or the cost. 
     To do so, according to an essential characteristic, the method used in the device according to the invention consists of estimating the real angular position of the rotor of the rotary electrical machine from sinusoidal signals obtained by linear combinations of the signals from sensors, as in WO 2006/010864 A2, but using locking between a real angular position and an estimated angular position. The device of the invention includes a feedback loop, which will be referred to as a “tracking loop”, the behaviour of which is similar to that of a phase lock loop or “PLL” according to the Anglo-Saxon terminology currently in use. 
     The circuits composing the device for detecting the angular position of the stator are configured such that the following relation (1) is satisfied:
 
(sin(θ real +φ 1 )·sin(θ est +φ 2 )−sin(θ real +φ 2 )·sin(θ est +φ 1 )=sin(φ 2 −φ 1 )·sin(θ real −θ est ),
 
relation in which:
         θ real  represents the real angular position of the rotor;   θ est  represents the estimated angular position of the rotor; and   φ 1  and φ 2  represent the phase shifts of the signals corresponding to the angular offsets of the sensors in relation to an angular reference marker linked to the stator of the rotary electrical machine.       

     It follows that φ=(φ 1 −φ 2 ) is a constant (these two phase shifts being determined from a single angular reference marker), and represents the phase shift between the signals θ real  and θ est . 
     This relation makes it possible to obtain an error signal between the real angular position and the estimated angular position. 
     The loop known as the tracking loop makes it possible to minimise the error between θ real  and θ est . If this error becomes low, it is well known that sin(θ real −θ est ) is more or less equal to (θ real −θ est ). The second term of the relation (1) then becomes more or less equal to K(φ 1 −φ 2 ), with K constant equal to sin(φ). 
     Moreover, the inventive entity has demonstrated that phase shifts of 120° and more particularly 60° between the electrical signals generated by the sensors are particularly beneficial in suppressing harmonic  3 . 
     So the principal object of the invention is a device for detecting the angular position of a rotor of a polyphase rotary electrical machine containing a stator and a plurality of magnetic field sensors, fixed with respect to the stator and capable of delivering first signals representing a rotating magnetic field detected by said sensors. 
     According to the invention, the device for detecting the angular position includes means for generating, from linear combinations of said first signals, at least first and second sinusoidal signals, phase-shifted by a determined value φ different from zero and from 180°, representing an angular position of the rotor referred to as real, in that it includes means for detecting a value for the angular position of the rotor referred to as estimated by locking between said real and estimated angular positions by making use of a feedback loop referred to as “tracking”, reinjecting as input at least the third and fourth sinusoidal signals determined on the basis of said estimated angular position value and phase-shifted by said determined value φ, and in that said means for detecting the estimated value of the angular position of the rotor include first and second means of multiplication of said first and third signals, firstly, and said second and fourth sinusoidal signals, secondly, and of subtracting the results of these multiplications, such that the following relation is satisfied at any moment:
 
(sin(θ real +φ 1 )·sin(θ est +φ 2 )−sin(θ real +φ 2 )·sin(θ est +φ 1 )=sin(φ 2 −φ 1 )·sin(θ real −θ est ),
 
relation in which θ real  and θ est  are said real and estimated angular positions, φ 1  and φ 2  the phase shifts of said first and second sinusoidal signals in relation to a reference marker linked to said stator and said detected phase shift φ being equal to (φ 2 −φ 1 ).
 
     A further object of the invention is a polyphase rotary electrical machine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described in more detail, making reference to the attached drawings, in which: 
         FIG. 1  illustrates in diagram form an embodiment of a device for detecting the angular position of a rotor of an alterno-starter according to prior art; 
         FIG. 2  is a diagram illustrating an example of signals delivered by three magnetic sensors for measuring the angular position of the rotor used in the device from  FIG. 1 ; 
         FIG. 3  is a diagram illustrating two phase-shifted sinusoidal signals obtained by a linear combination of the preceding signals, usable to determine the angular position of the rotor; 
         FIG. 4  illustrates an embodiment of a complete device for detecting the angular position of a rotor from an alterno-starter according to a preferred embodiment of the invention; and 
         FIG. 5  illustrates a block diagram of the functions of a supplementary module used in the device from  FIG. 4 , implementing a hysteretic filtering system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the following description, without in any way limiting its scope, the following scenario relates to the preferred application of the invention, unless otherwise stated, i.e. that of a device for detecting the angular position of the rotor of an alterno-starter using locking between a measured angular position and an estimated angular position. 
       FIG. 4  illustrates an example of a device  2  for detecting the angular position of the rotor of an alterno-starter according to a preferred embodiment of the invention. 
     The alterno-starter (not shown in this figure) may be of a type very similar to the prior art, even identical. It may, for example, be the alterno-starter  10  from  FIG. 1 . Again, the sensors from the block  200  have the same function as those from  FIG. 1 . In the particular form described here, for example, three Hall-effect sensors are used (CA 1  to CA 3 ) arranged at 120° electric. Of course, the invention is not limited to this number of sensors and to this particular angular relation of 120° between them. As indicated above, an angular relation of 60° between the sensors is very beneficial in suppressing harmonic  3 . According to particular applications of the invention, the person skilled in the art will select the number of sensors and the angular relation between them which is most appropriate to the application in question. 
     In this embodiment, the sensors CA 1  to CA 3  deliver at interfaces  2001  to  2003  three “raw” signals of the type illustrated by  FIG. 2 , which are sent to a module  201  of linear combinations and amplitude correction, generating at its outputs, interfaces  2010  and  2011 , two signals of the type of those illustrated by  FIG. 3 . 
     The modules,  204  and  205 , apply to these signals the offset values delivered by modules  202  and  203  respectively. The modules  202  and  203  can be constituted by memory circuits containing predetermined offset values. 
     At the outputs  2040  and  2050  of modules  204  and  205 , there are thus available two sinusoidal signals centred on an axis (i.e. without offset) and of the same amplitude, phase-shifted by a determined non-obvious value φ ( FIG. 3 : C 1  and C 2 ), i.e. different from 0° or 180°. 
     These two components, derived from the signals measured by the sensors  200  ( FIG. 2 : CH 1  to CH 3 ), and shaped to best approach sinusoidal functions, are each sent to the first inputs of analogue multipliers,  208  and  209 , respectively, via the interfaces  2020  and  2040 . So they represent two instances of the instantaneous value of the measured angular position of the rotor  100  ( FIG. 1 ). These analogue multipliers  208  and  209  receive at second inputs two components derived from the instantaneous value of the angular position estimated by two feedback branches which will be detailed below, in accordance with one of the essential characteristics of the invention, which has been named “tracking loop”. So at outputs  2080  and  2090  the results of the two multiplications of the first member of the relation (1) are obtained.
 
(sin(θ real +φ 1 )·sin(θ est +φ 2 )−sin(θ real +φ 2 )·sin(θ est +φ 1 )=sin(φ 2 −φ 1 )·sin(θ real −θ est )
 
     The output signals from the two multiplication modules  208  and  209  are sent to a module  210  which effects the analogue subtraction of these signals, more precisely the signal at the output interface  2080  of module  208  is sent to a “+” input and the signal at the output interface  2090  of module  209  to a “−” input of module  210 . So, one obtains the result of the subtraction of the first member of the aforementioned relation (1) as output  2100  of module  210 . 
     Where necessary, the output signal from module  210  is amplified by a fixed-gain G amplifier  211 , then converted into a digital signal by an analogue-digital converter  212 . 
     Up to this point, the circuits of the device  2  are of the analogue type. 
     The two following stages, before applying feedback, are constituted by a digital correction module  213 , of the proportional integral type referred to as “PI”, followed by a “pure” digital integrator module  216 , as previously indicated. 
     The output  2130  of module  213  gives the speed of the rotor  100  ( FIG. 1 ) and is sent to a module  217  to process this signal, for example a display device. 
     The output  2160  of the integrator  216  gives the estimated angular position and is looped, by two parallel branches, to the second inputs of the multipliers  208  and  209 . 
     The estimated position makes it possible to address two tables directly (or again, a single table used twice by multiplexing access, once for the estimated position and again by the sum of the estimated position and a constant digital offset representing a pre-calibrated phase shift) containing the desired sinuses. These tables may be constituted by memories, for example of the read-only memory (ROM) type. 
     In the embodiment described in  FIG. 4 , the branches, which will be referred to arbitrarily as the upper and lower respectively, each contain, in cascade, a table  214  and  215  respectively, (also referred to as “Table S” and “Table C”) addressed by the digital signal present at the output of module  216 , and a digital-analogue converter  206  and  207  (also referred to as “NA 1 ” and “NA 2 ”). This arrangement makes it possible to move from the digital part of the device  2  to the analogue part thereof constituted by input organs up to module  212 . 
     The upper branch (output of the digital-analogue converter  206 ) sends the following signal to the second input of the analogue multiplier  208 :
 
 S   s   =A   s (sin(θ est ), calculated by Table  S  214  (2)
 
     The lower branch (output of the digital-analogue converter  207 ) sends the following signal to the second input of the analogue multiplier  209 :
 
 S   c   =A   c (sin(θ est +φ), calculated by Table  S  215  (3),
 
φ representing the phase shift (φ 2 −φ 1 ) between the two sinusoidal signals looped as inputs of the device  2 . This phase shift φ depends on the positions of the sensors ( FIG. 1 ; CA 1  to CA 3 ), especially their positions in relation to the angular reference marker RRefθ ( FIG. 1 ), any offsets in the measurement signals and a certain number of physical parameters connected with the practical embodiment of the device  2 , in particular the real characteristics of the alterno-starter  10 , of the measurement sensors CA 1  to CA 3 , etc. The simplest solution is to determine a constant, pre-calibrated phase shift value φ theoretically, and to implement it in the table  215 .
 
     It should be noted that the operation of calibrating signals amplitudes C 1  and C 2  ( FIG. 3 ) resulting from the linear combinations may be done directly in the digital tables,  214  and  215 , by adjusting the amplitudes of the sinuses included in these tables, instead of processing this operation in the module  201 . In relations (2) and (3) this calibration is obtained by multiplying the sinuses by constants A s  and A c1  respectively. 
     It can be arranged that φ 1 =0 (in this case φ=φ 2 ) and that the amplitudes of all the sinusoidal signals are equal (this is the case if said calibration is done correctly). Taking account of said relations (2) and (3), and of the signals injected at the first inputs of the multiplier modules,  208  and  209 , one obtains, at output  2100  of the subtractor  210 , the following signal:
 
 V   2100 =sin(θ real )·sin(θ est +φ)−sin(θ real +θ)·sin(θ est )  (4)
 
     A classic trigonometric calculation allows the following relation (4a) to be found:
 
 V   2100 =sin(θ real)·sin(θ   est +φ)−sin(θ real +φ)·sin(θ est )=sin(θ 2 −θ 1 )·sin(θ real −θ est )
 
Or, again:
 
 V   2100 =sin(θ real )·sin(θ est +φ)−sin(θ real +φ)·sin(θ est )=sin(φ)·sin(θ real −θ est )  (4b)
 
since φ=(φ 2 −φ 1 )=φ 2  as indicated above.
 
     When the error tends towards zero, sin(θ real −θ est  may be confused with the error itself (θ real −θ est ). 
     Relation (4b) thus becomes identical to relation (1), according to the method of the invention. 
     Purely digital processing is also possible, as the signals C 1  and C 2  ( FIG. 3 ) originating from the linear combinations have been digitised by sampling. In this case, the multiplication may be done digitally, which simplifies processing. On the other hand, this method, while it can simplify certain operations, is not without difficulty. It is in fact necessary to ensure the instantaneity of the two samplings and especially the quality of the resolution, since the input error of the loop calculated by difference thus ends up under-sampled. 
     The output  2160  of the integrator  216  theoretically makes it possible to obtain the required “estimated angular position” θ( t ). However, it is generally necessary to apply an initial setting value, for example memorised in the module  218  and added to the signal present at the output of the integrator  216 . This initial setting value gives the true physical angular position of the rotor  100  ( FIG. 1 ) for an initial reference value θ=0. This operation is realised by a digital adder  218 , the output of which represents a corrected estimated angular position value. 
     Finally, in certain operating conditions (for example, due to noise or high frequency instability of the loop), arbitrary fluctuations of the estimated angular position value θ( t ) may arise which are detrimental to the proper operation of the reversible AC-DC power converter  11  and may even cause deterioration of the semi-conductor components  110 . Also, in one preferred embodiment, a “hysteretic” filtration is applied to the output signal  2190  of the digital adder  219 : module  220 . At the filtered output  2220  of the hysteretic system  220 , a signal is obtained which represents an estimated angular position θ( t ) which is fully usable by the control module  13  to generate six correctly phase-shifted signals to control the bridges  110  of the reversible AC-DC power converter  11 . 
       FIG. 5  is a block diagram illustrating one embodiment of a hysteretic filtering system  220  which can be used in the device  2  from  FIG. 4 . 
     The hysteretic filtering system functions, by analogy, like mechanical play in a gearing: when there is a change in direction of speed, a driven pinion does not reverse its position until any play between the teeth has been taken up, i.e. when the change in direction of speed has caused a displacement of the driving pinion equal to the play. It is possible to reproduce this behaviour by using the iterations described by the block diagram in  FIG. 5 . Hereafter “play” will be used to refer to the value of this play, a value which depends on a certain number of physical parameters linked to the organs used in a real system  1  as in  FIG. 1 . 
     In the block  2200 , the value of the difference is calculated, thus “Difference” between the position filtered at stage (n−1), thus “FilteredPosition (n−1)” and the position at stage n, thus “Position(n)”, n being an arbitrary whole number. In the block  2201 , the “Difference” value is compared to zero. If the result of the comparison is less than or equal to zero (“YES” branch), the “Difference” value is sent to block  2202 , if not, (“NO” branch), it is sent to block  2203 . In block  2203 , the value of the filtered position at stage n, i.e. “FilteredPosition(n)” is forced to the value of the position at stage n, i.e. “Position(n)”. In the block  2202 , the “Difference” value is compared to the “-play” value. If the result of the comparison is less than or equal to “-play” (“YES” branch), the “Difference” value is sent to block  2204 , if not, (“NO” branch), it is sent to block  2205 . In block  2204  the value “FilteredPosition(n)” is forced to the value “FilteredPosition(n)+jeu”. In block  2205  the value “FilteredPosition(n)” is forced to the value “FilteredPosition(n−1)”. The outputs of blocks  2204  and  2205  are added in a block  2206  and the output from this block  2206  is added to the output from block  2203 . Finally, the output from block  2207  is looped to the input of block  2200  to do a new iteration (stage n+1). 
     The hysteretic filtering system  220  according to the block diagram from  FIG. 5  makes it possible to apprehend the functioning of an electrical machine able to rotate in two directions, as is the case of the alterno-starter  10  from  FIG. 1 . 
     If the direction of control of the rotary electrical machine can only be unidirectional, it is sufficient to use an infinite “play” value, so that the position is only sent when it increases (anti-return type device equivalent to that of a wheel known as “ratcheted” in mechanics). 
     On reading the above, it can easily be seen that the invention certainly achieves the aims set by it, and there is no need to recapitulate all of it. 
     However, it will be recalled that the implementation of what has been referred to as a “tracking loop” makes it possible precisely to adjust the passband of the angular position θ(t) signal and the acceleration dynamics of a rotary machine (in engine mode). This characteristic allows the noise interfering with the angular position θ(t) signal to be eliminated more effectively. 
     However, the invention is not merely limited to the device according to the embodiment explicitly described with respect to  FIGS. 4 and 5 , nor merely to the preferred application relating to the detection of the angular position of the rotor of a three-phase alterno-starter with a view to controlling a reversible rectifier device arranged between this alterno-starter and a source of DC electrical energy, for example a rechargeable battery ( FIGS. 1 to 5 ). 
     Without exceeding the scope of the invention, the device can be applied to any polyphase rotary machine, for example biphase, triphase, hexaphase, etc., in engine (starter) mode, and/or alternator mode (current generator).