EP0470143A1

EP0470143A1 - Self-synchronous electric machine with controlled flow

Info

Publication number: EP0470143A1
Application number: EP90907148A
Authority: EP
Inventors: Guy Friedrich; Jean-Paul Vilain
Original assignee: Societe Generale pour les Techniques Nouvelles SA SGN
Current assignee: Societe Generale pour les Techniques Nouvelles SA SGN
Priority date: 1989-04-28
Filing date: 1990-04-26
Publication date: 1992-02-12
Also published as: WO1990013454A1; FR2646572A1; FR2646572B1; JPH04504948A; CA2054704A1

Abstract

L'invention concerne un ensemble de conversion électro-mécanique comportant une machine électrique susceptible de transformer de l'énergie électrique en énergie mécanique, constituée d'un stator (1), ou induit, dont les bobinages sont alimentés en courants polyphasés, d'un rotor (2) créant un champ inducteur et comportant un bobinage (5) alimenté en courant continu (IR) variable, et d'un capteur (11) de vitesse (n) ou de position () couplé au rotor, dans lequel le champ inducteur créé par le rotor (2) varie en fonction d'au moins un paramètre de fonctionnement du moteur suivant une loi de commande (phiIR) établissant une relation de dépendance entre une consigne (CIR) d'intensité du courant (IR) dans le rotor et ledit paramètre de fonctionnement, ce qui permet d'obtenir un très fort couple à basse vitesse et un couple plus faible à grande vitesse, la machine étant alimentée sous une tension continue faible, par exemple par une batterie d'accumulateurs.The invention relates to an electro-mechanical conversion assembly comprising an electric machine capable of transforming electrical energy into mechanical energy, consisting of a stator (1), or armature, the windings of which are supplied with polyphase currents, of a rotor (2) creating an inductive field and comprising a winding (5) supplied with variable direct current (IR), and a speed (n) or position () sensor (11) coupled to the rotor, in which the field inductor created by the rotor (2) varies as a function of at least one operating parameter of the motor according to a control law (phiIR) establishing a dependency relationship between a setpoint (CIR) of current intensity (IR) in the rotor and said operating parameter, which makes it possible to obtain a very high torque at low speed and a lower torque at high speed, the machine being supplied under a low direct voltage, for example by an accumulator battery.

Description

Self-synchronous flow-controlled electric machine

The invention relates to an electric machine capable of transforming electrical energy into mechanical energy, consisting of a stator, or armature, the windings of which are supplied with polyphase currents, a rotor creating an inductive field and a sensor. speed or position coupled to the rotor.

The problem posed consists in obtaining with a single machine a high speed at low torque and a high torque at low speed, the machine being supplied with a low direct voltage (<100 V). In addition, a precise position control must be achieved.

The electric machine must make it possible to obtain a precise torque / speed characteristic, essentially turned towards the motorization of mobile machines with on-board energy source.

In other words, this electric machine must be able to:

- to move autonomous mobile vehicles of small or medium dimensions on all types of terrain: on flat terrain - where a relatively high speed is required - or on stairs for example where a high torque is required for a low speed;

- perform a positioning function, for example positioning a robot arm.

The machines concerned are for example wheelchairs for the disabled, handling carts, mobile robots, etc .; this list is obviously not exhaustive.

Direct current machines and permanent magnets are known in which the stator is provided with permanent magnets, the rotor rotating in the stator field consists of a wound armature and the direct current (supplied by batteries for example) is brought to the rotor by a set of collecting brushes (forming a so-called mechanical collector). However, these machines pose problems in terms of position control. • The electromotive force E in these machines is proportional to the rotational speed n of the rotor: E = K.n and the

Φ torque C is proportional to the intensity I of the current in the machine: C = KI with the same proportionality constant K,.

Another well-known problem exists when there is only a low voltage which appears during a phase of operation in propulsion mode, that is to say when there is a relatively high speed with a low couple. To increase the torque, it would be necessary to increase the intensity of the current, which would produce an unacceptable heating by Joule effect (the machine not being able to dissipate the heat), or a too large size and weight. This is the case with forklifts for example, which run flat without problems but cannot tolerate uphill slopes of more than 3%. Usually, this problem is solved by adding a second motor or a gearbox. There are cases where such a solution is not suitable, for example when one does not want to increase the weight of the vehicle.

In addition, the mechanical collector is bulky and is poorly suited to devices of reduced size and high torque.

Autosynchronous permanent magnet machines avoid some of these drawbacks: they allow precise positioning, avoid the use of collecting brushes, but they also do not offer the torque / speed characteristics suitable for moving mobile vehicles on varied terrain when the supply voltage is low and when the power source is on board.

Such machines include:

- a wound stator supplied with polyphase currents,

a rotor consisting of a permanent magnet, sensors of the speed n and of the position 6 of the rotor, and

- a control system associated with an electronic power converter to obtain the polyphase currents from the direct current supplied by the batteries. The frequency f of these currents imposes the speed of rotation of the rotor, and the intensity IS of the stator current depends on the state of charge of the machine, which corresponds to the torque required to perform the operation.

The polyphase current setpoints are calculated so as to maintain a constant angle between the stator field and the rotor field (internal angle '). Current embodiments make it necessary to maintain these two fields in quadrature in order to recreate an operation of the "DC motor" type.

In practice, at least one sensor is placed at the level of the machine to measure the speed n and / or the position θ of the rotor. When only one measurement is made, the other is deducted by calculation. It is however preferable to obtain both measures.

The control system produces CISi setpoints for the intensity of the stator current, the amplitude of which is calculated from the speed error En (difference between the speed setpoint CN and the measured speed n), and the phase of which is calculated so as to maintain the field created by these currents generally in quadrature with the rotor field.

The CISi instructions (i designating the respective phases of the polyphase currents) are supplied to the electronic power converter which then delivers the polyphase currents corresponding to the stator.

The object of the invention is an electric machine supplied with direct voltage comprising a rotor supplied with direct current. Typically, the field of induction created by the rotor is variable as a function of at least one operating parameter of the motor and of a control law establishing a dependence relationship between a current intensity setpoint in the rotor and said operating parameter, said law being able to be determined by the operator according to the chosen application.

Advantageously, the operating parameter is a setpoint for the rotational speed of the rotor and / or a measure of the intensity of the stator current. It is necessary to associate with the machine thus defined a control system intended to vary the rotor flux by slaving the intensity of the rotor current to the torque / speed characteristic, according to said control law. In addition, an electronic power converter is preferably associated with the control system, in order to produce the rotor current as a function of the current intensity setpoint delivered by the control system.

Finally, the rotor current intensity setpoint is advantageously developed as a function of at least one of the following parameters: the speed setpoint or the rotor speed, the stator current setpoint or the stator current , the torque setpoint or the torque and the position setpoint or the position of the rotor relative to the stator. Other features and advantages of the invention will emerge from the description which follows, with reference to the appended drawings, of nonlimiting exemplary embodiments.

Figure 1 shows in schematic perspective a machine according to the invention. Figure 2 is a cross section through the machine of Figure 1.

Figure 3 shows, in cross section, the rotor of a machine in an alternative embodiment.

FIGS. 4A, 4B and 4C schematically represent the control system of a machine according to the invention in three variant embodiments.

FIGS. 5a to 5e are graphical representations of laws controlling the intensity of the rotor current creating the variable inducing field. We see in Figures 1 and 2 a machine for motorizing a mobile machine. It comprises a stator 1 provided with windings in which polyphase currents IS pass, the number of these windings being equal to the number i of phases, and a rotor 2 mounted on a shaft 3 and comprising an inductive winding traversed by a direct current IR . In the present example, the rotor has a single winding 5 to a pair of poles and the stator 1 is composed of three windings 1.1, 1.2, 1.3 arranged at 60 ° and supplied with three-phase current. As shown in Figure 3, the rotor may include a winding 5 'creating several pairs of poles, here two pairs crossed at right angles, the stator (not shown) then being equipped with a three-phase winding with two pairs of poles . Each pole of the rotor can be provided with a permanent magnet 4 whose magnetic field combines with that created by the winding 5, so that the overall inducing field has a non-zero minimum value in the absence of excitation current in the rotor winding.

The direct current necessary to supply the machine is supplied for example by a battery mounted on board the mobile machine. It is advantageously brought to the rotor by known sliding contacts, but any other means of transmitting energy to the rotor may be suitable (rotary transformer, optical power link, etc.).

FIGS. 4A to 4C represent the control system, in three variants, of the assembly 9 composed of the stator 1 and the rotor 2 as described above. The measurement of the rotor current MIR is provided by a sensor 10 and the measurement of the stator current MIS by a sensor 12, while a sensor 11 measures the angular position θ or the speed of rotation n of the rotor 2. The polyphase stator current ISi is supplied to stator 1 by an electronic power converter 15 from the measured current MIS and from a current setpoint CISi delivered by a control circuit 13. The DC rotor current IR is supplied to rotor 2 by an electronic power converter 16 from the measured current MIR and from a current setpoint CIR delivered by a control circuit 14. The electronic power converter 15, which is a source of switching sinusoidal currents using a natural sampling technique, and the converter 16, which uses a device called "fork regulator", thus receive the current setpoints CISi and CIR from a control assembly 7 composed of the circuits s 13 and 14.

The control system processes the information delivered by sensors according to control laws to supply electronic power converters with setpoint signals CIR, CISi indicative of the intensity of the current to be injected into the rotor and the stator, respectively. Electronic power converters supply the desired current to the machine windings.

More precisely, the information necessary for controlling the stator current (θ and n) is obtained from the sensor 11 placed at the level of the rotor to measure at least one of the following mechanical quantities: the position θ of the rotor, its speed n , its couple C. The measurement of a single quantity is sufficient, the others being able to be deduced therefrom by calculation.

The simplest realization consists in measuring θ and in calculating n and C if necessary. The control circuit 13 determines the phase of the polyphase currents of the stator from the signals delivered by the sensor 11 and, possibly, from the sensor 12, this latter arrangement making it possible to vary the internal angle ψ between the stator and rotor fields (see on this subject the French patent n ° 79 15 809). In the latter case, the internal angle is controlled not only to the position of the rotor (conventional autosyπchrone machine) but also to the torque and the speed of the machine.

The control circuit 13 also determines the amplitude of said stator currents from the difference between the speed n of the rotor and the speed reference CN. Finally, it delivers a setpoint signal CISi comprising the phase and amplitude information necessary for the production by the converter 15 of suitable stator currents ISi.

The control circuit 14 supplies the rotor current setpoint CIR in accordance with one or more predefined fe-IR laws, the setpoint CIR depending on

- the CN speed reference or the rotor speed n,

- the stator intensity setpoint CISi or the measured stator intensity MIS,

- of the torque CC or torque C setpoint, - the angular position setpoint Cθ or the angular position θ of the rotor.

In the examples shown, the CIR reference is a function of the CN speed reference (FIG. 4A), of the stator current measured MIS (FIG. 4B) or of these two optional parameters (FIG. 4C), according to a predetermined TIR control law. FIGS. 5a to 5e give examples of such control laws, which have the effect of varying the coefficient K, of proportionality between the speed n of the rotor and the electromotive force E, by variation of the intensity of the rotor current, in order to honor the various operating points imposed. These laws are chosen essentially according to the technological constraints of which the machine is the object and, consequently, of the chosen application. In the case of the laws represented in FIGS. 5a and 5b, the intensity of the direct current injected into the rotor (controlled by the CIR reference) is a function of the speed reference CN of the rotor. Either to honor, under a given continuous supply voltage U, two operating points M ,, and _? corresponding to respective values n ^, C _* , P., and n ₂ , C ₂ , P-, of the speed of rotation n, of the torque C and of the power P. The point M., corresponds to a significant torque for low speed and point ₂ at high speed for low torque. The coefficients K ,,. and K. corresponding can be deduced therefrom by calculation, which makes it possible to impose intensity setpoints in the rotor CIR ,, and CIR ₂ corresponding respectively to said coefficients. We also deduce by calculation the speed setpoints CN ,, and CN „setting the speeds where the rotor flux must vary. In the particular case of FIG. 5b, three operating zones are thus defined:

- from 0 to CN ^: the rotor flux is constant, the coefficient K, is maximum and the speed control is ensured by the stator current under the control of circuit 13; it is for example a phase of positioning or climbing stairs for the machine, corresponding to a high torque and a low speed; - from CN ^ to CN: the rotor flux and the coefficient K. vary; piloting is obtained by controlling the rotor current using circuit 14;

- beyond CN „: the rotor flux is constant and the coefficient K, minimum; the piloting is again ensured by the control of the stator current; it is for example a phase of progression of the machine on flat ground, corresponding to a high speed and a low torque.

A similar analysis could be made for the control law illustrated in FIG. 5a, with the difference that the variation of the rotor flux is here abrupt at the level of the reference values CN ₁ , CNp, instead of being carried out gradually along a segment. linear of finished slope.

FIGS. 5c, 5d and 5e show control laws IR according to which the rotor current setpoint CIR is a function of the measured current MIS in the stator. The law of FIG. 5c, where the rotor current setpoint CIR varies proportionally to the measured stator current MIS, corresponds to the classic characteristic of a series machine. It is interesting with regard to the propulsion of the machine, but unfavorable relative to the positioning function. The laws of FIGS. 5d and 5e remedy this drawback, by creating a horizontal plateau below an MIS value. and above a value MISp> MIS ,, of the stator current MIS, the lower level corresponds to a high speed regime with low torque and the upper level corresponds to a low speed regime with high torque. In the case of FIG. 5e, the lower stage is interrupted at a value MIS „<MIS ,, of the stator intensity MIS, below which another stage is created corresponding to an increased rotor current, which favors a phase positioning with low stator current.

Those skilled in the art can imagine other control laws <_ClR, taking care, however, that they do not lead to an excessive rotor current liable to damage the machine. The control laws chosen can be obtained by analog and / or digital means.

It goes without saying that any other instruction or additional law can be introduced into the control system to act on the machine; for example, stop at such a time, at such a place, etc.

Claims

claims

1. Electro-mechanical conversion assembly comprising an electric machine capable of transforming electrical energy into mechanical energy, consisting of a stator (1), or armature, the windings of which are supplied with polyphase currents, of a rotor ( 2) creating an inducing field and comprising a winding (5) supplied with variable direct current (IR), and a speed (n) or position (θ) sensor (11) coupled to the rotor, characterized by the fact that the inductor field created by the rotor (2) varies as a function of at least one motor operating parameter according to an OβER control law) establishing a dependency relationship between a current intensity (IR) setpoint (CIR) in the rotor and said operating parameter, which makes it possible to obtain a very high torque at low speed and a lower torque at high speed, the machine being supplied under a low direct voltage, for example by an accumulator battery.

2. Electro-mechanical conversion assembly according to claim 1, characterized in that said motor operating parameter is a speed reference (CN) of rotation of the rotor.

3. Electro-mechanical conversion assembly according to claim 1, characterized in that said motor operating parameter is the intensity of the stator current (MIS) measured by a sensor (12) associated with the stator (1).

4. Electro-mechanical conversion assembly according to claim 1, characterized in that said operating parameter is a speed setpoint (CN) and / or the intensity of the stator current (MIS) measured by an associated sensor (12) stator (1).

5. Electro-mechanical conversion assembly according to one of the preceding claims, characterized in that it comprises a control circuit (14) intended to vary the rotor flux according to said control law CβlR), which delivers a setpoint (CIR) to an electronic power converter (16), which produces the rotor current (IR) from said setpoint (CIR).

6. Electro-mechanical conversion assembly according to one of the preceding claims, characterized in that the instruction (CIR) is produced as a function of at least one of the following parameters:

- the speed reference (CN) or the speed (n) of the rotor (2),

- the stator intensity setpoint (CIS) or the measured stator intensity (MIS),

- the torque setpoint (CC) or the torque (C), and

- the position setpoint (CG) or the position (θ) of the rotor (2) relative to the stator (1).