WO2016207166A1

WO2016207166A1 - Electric motor comprising isolated auxiliary winding

Info

Publication number: WO2016207166A1
Application number: PCT/EP2016/064319
Authority: WO
Inventors: Bertrand Cassoret; Raphaël ROMARY
Original assignee: Universite D'artois
Priority date: 2015-06-23
Filing date: 2016-06-21
Publication date: 2016-12-29
Also published as: FR3038161B1; EP3314730A1; FR3038161A1

Abstract

The invention relates to an electric motor comprising a stator (10) having a laminated core defining notches (15) receiving conductors of a main winding (11), characterised by the fact that the electric motor comprises an isolated passive circuit comprising an auxiliary winding (13) wound in said notches, and capacitors (Cu, Cv, Cw) associated with the phase windings (14u, 14v, 14w) of said auxiliary winding. The invention also relates to a method for optimising such an electric motor.

Description

Electric motor with auxiliary winding isolated

The present invention relates to electric motors, including synchronous or asynchronous electric motors.

Electric motors, in particular synchronous and asynchronous electric motors, are conventionally manufactured with a package of magnetic sheets defining notches receiving the electrical conductors of the stator winding. The induction in the air gap is not perfectly sinusoidal due in particular to the notches, the magnetic saturation, the possible eccentricity of the rotor and, often, the supply by an electronic speed controller (inverter) delivering non-sinusoidal voltages. The operation of the motor then gives rise to vibrations of magnetic origin and to harmonics of couples, induced by variable electromagnetic fields of different frequencies, which cause deformations of the stator. These vibrations can in particular, when their frequency coincides with mechanical resonance frequencies, be of relatively large amplitude and generate a harmful noise.

It is known to act on noise and vibrations actively by injecting current harmonics, which creates electromagnetic forces opposing those at the origin of the vibrations. This technique, however, requires a high performance electronics and relatively difficult to implement.

There remains a need to reduce this noise of magnetic origin, in a simple and economical way.

Furthermore, it is obviously desirable to improve as much as possible the energy efficiency of the engines to meet the standards of more demanding in this area.

There is still interest in reducing the harmonics of current absorbed on the network, to meet the most stringent electromagnetic pollution standards. The existing solution of placing a passive filter on the electrical network upstream of the motor requires inductances which can be bulky and generate losses in order to effectively filter the harmonics. Active filters that adapt permanently exist, but they use complex and expensive electronics.

The invention aims to meet all or part of the above needs. To this end, the invention proposes an electric motor comprising a stator having a bundle of plates defining notches receiving conductors of a main winding, the motor electrical further comprising an insulated passive circuit having an auxiliary winding wound in said notches, and capacitors associated with phase windings of said auxiliary winding.

By "electrically isolated passive circuit" is meant a circuit which is not connected to the mains supplying the electric motor.

By "main winding" must be understood that which is connected to the source of electrical energy, for example the three-phase network or a speed controller itself powered by the network.

The invention has many advantages.

First, it avoids an expensive electronic circuit solution. The engine thus gains in reliability and can be manufactured at a reduced cost.

The invention makes it possible, if desired, to attenuate the noises and variations of magnetic origin by reducing the intensity of the harmonic induction waves and their consequences. Among these consequences, one can cite the vibrations of the engine and the noise that they generate, the harmonics of torque, the harmonic losses, the electromagnetic emissions.

In addition, the capacitors bring a part of the reactive power required by the motor, which can lead to a drop in the reactive power supplied by the network, thus an improvement in the power factor and also makes it possible to reduce Joule losses to the stator as well as a part of the iron losses, due to the induction harmonics.

It is remarkable that the invention offers a simple, reliable and inexpensive solution for simultaneously combating a set of problems encountered during operation of the motors, in particular synchronous or asynchronous motors, such as noise, current harmonics, the consumption and performance of the machine.

Depending on the value given to the capacity of the capacitors, however, it is possible to focus on optimizing the machine either to try to fight as effectively as possible against noise and vibrations of magnetic origin, or to seek to improve at best energy efficiency, as detailed below.

The isolated passive circuit may consist of an auxiliary winding wound in said notches, and capacitors associated with the phase windings of this auxiliary winding. The phase windings of the auxiliary winding can in particular be coupled in a star or in a triangle. It should be noted here that the phase windings of the auxiliary winding can be connected in a star or in a triangle, independently of the star or delta coupling of the phase windings of the main winding.

In the same way, the coupling of the capacitors can be star or triangle independently of the coupling of the auxiliary winding.

Auxiliary windings can alternatively be isolated from each other, each winding being connected to a capacitor.

The phase windings of the auxiliary winding are preferably wound in said notches with the same number of poles and phase as the main winding. However, it is possible to wind the auxiliary winding with a spatial offset from the main winding or to use only some notches.

As indicated above, the capacitance value of the capacitors may be chosen to decrease the induction harmonics. In particular, this capacitance value can be chosen such that the passive circuit has a resonant frequency greater than 20 Hz, preferably greater than 100 Hz, and / or less than 100 kHz, preferably less than 20 kHz, the frequency of induction harmonics whose attenuation is sought to be attenuated, being most often in this frequency range. The induction harmonic whose frequency is chosen may be that whose presence is estimated to be the most harmful to the operation of the machine, for example due to a mechanical resonance. A study of the vibration spectra of the machine can make it possible to identify the most judicious frequency or frequencies to be eliminated.

The capacitance value of the capacitors may be chosen to reduce the harmonic induction waves and / or their consequences and / or the motor efficiency and / or the motor power factor.

Thus, the capacitance value of the capacitors can be chosen to provide reactive power, so as to increase the efficiency of the motor. This value is chosen according to the characteristics of the machine, in particular the magnetizing impedance, the resistances and the leakage inductances of the windings. The number of turns of the auxiliary winding is also a parameter to choose. This number influences the value of the phase inductance of the auxiliary winding, and therefore the value of the capacitors to be chosen. In case the capacity value of the capacitors is chosen to reduce the consequences of high frequency induction harmonics, the resulting high impedance at the fundamental frequency causes the current in the auxiliary winding to be relatively low, and in particular may be less than a few percent of the nominal current flowing through the main winding.

In the case where it is sought to increase the efficiency of the motor, the current flowing through the auxiliary winding can be of the same order of magnitude as the nominal current.

The solution proposed here is a priori applicable regardless of the power range of the electric motor concerned.

However, in the case where it is sought to decrease mainly the induction harmonics, the auxiliary winding may be constituted by conductors of relatively small section, in particular less than or equal to that of the conductors of the main winding. When a reactive power supply is sought, the section of the conductors is sized to withstand the intensities involved. Thus, in exemplary embodiments of the invention, the conductors of the auxiliary winding may be of equal cross-sectional area. those of the main winding. In general, the necessary section of the conductors of the auxiliary winding will be even higher than the number of turns is low. The choice is a function of that of the capacitors.

The conductors of the auxiliary winding may preferably be arranged at the bottom of the notches, the conductors of the main winding being arranged radially between the gap and the conductors of the auxiliary winding.

The motor can in particular be a synchronous motor or an asynchronous motor.

The subject of the invention is also a method for optimizing an electric motor according to the invention, in particular for reducing the noise of magnetic origin of such an electric motor, in which the capacitance value of the capacitors of the capacitor is selected. passive circuit isolated so that the resonant frequency of this circuit is less than or substantially equal to the frequency of a harmonic induction wave contributing to phenomena that are to be eliminated, which may be in particular at the origin noise and / or vibration. The resonant frequency of the isolated passive circuit may for example be greater than 50%, preferably greater than 75%, more preferably greater than 90% of the frequency of the harmonic induction wave. By "substantially equal", it is necessary to understand that the resonant frequency of the isolated passive circuit differs by less than 10%, preferably less than 5%, from the frequency of the harmonic induction wave.

The invention will be better understood on reading the following detailed description, non-limiting examples of implementation thereof, and on examining the appended drawing in which:

FIG. 1 diagrammatically represents an example of an asynchronous electric motor according to the invention,

FIG. 2 is a partial section of an example of a stator according to the invention,

FIG. 3 illustrates an example of spatial distribution of the phase windings in the notches,

FIG. 4 is an equivalent electrical diagram of the motor valid at the supply frequency of the network, and at harmonic frequencies when the harmonic phenomena originate from a non-sinusoidal power supply, by an electronic speed variator,

FIG. 5 is a view similar to FIG. 4 that is valid at the frequency of an induction harmonic when this harmonic originates from a phenomenon internal to the machine (in particular a phenomenon due to the notches, to the saturation or to the eccentricity) and not a non-sinusoidal power supply,

FIG. 6 is a sound pressure spectrum of a tested motor, without capacitors connected to the phase windings of the auxiliary winding,

FIG. 7 is a view similar to FIG. 6 for the engine under test, after connection of the capacitors to the phase windings of the auxiliary winding,

FIG. 8 is a spectrum of the vibrations of the tested motor, without capacitors connected to the phase windings of the auxiliary winding,

FIG. 9 is a view similar to FIG. 8 with capacitors connected to the phase windings of the auxiliary winding,

FIG. 10 is a spectrum of the current absorbed by the motor without capacitors connected to the phase windings of the auxiliary winding, and

- Figure 11 is a view similar to Figure 10, with capacitors connected to the phase windings of the auxiliary winding. FIG. 1 shows schematically a three-phase asynchronous motor according to the invention, comprising a stator 10 and a rotor 20 rotating relative to the stator, both of which are separated by an air gap 30.

The rotor 20 is for example cage, with copper conductors or aluminum.

The stator 10 comprises a stator winding 11 comprising three phase windings 12u, 12v, 12w, coupled for example star-shaped as illustrated. As a variant, the three windings can in particular be coupled in a triangle.

It should be noted here that the number of windings is a function of the number of phases. In this case, the motor being three-phase, it has three coils.

As illustrated, the stator comprises an auxiliary winding 13 comprising three phase windings 14u, 14v, 14w. The phase windings 14u, 14v and 14w of the auxiliary winding 13 are here star-connected. In addition, as shown in FIG. 1, each phase winding 14u, 14v, 14w is connected in series with a capacitor Cu, Cv, Cw, the capacitors Cu, Cv, Cw being moreover connected in a star.

The passive circuit thus formed, an RLC circuit, is electrically isolated, that is to say that it is not connected to the electrical network supplying the motor or to the main winding.

The internal electrical resistance of the conductors of the phase windings corresponds to the resistance R of this passive circuit.

Preferably, the electrical conductors of the phase windings 12u, 12v, 12w are received in notches 15 of the stator laminations, those of the coils of the auxiliary winding 13 are received in the same notches, as illustrated in FIG. 2. Preferably, the windings of the main winding 11 are arranged radially outside the windings of the auxiliary winding 13. The main winding 11 is of the distributed type, with the conductors of each phase winding wound in several notches of the pack of sheets. An example of a winding with four notches per phase and per pole is illustrated in FIG. 3, it being understood that the invention is not limited to a particular way of winding the main windings 11 and the auxiliary windings 13. Preferably, the windings of phase 14u, 14v, 14w of the auxiliary winding 13 are wound identically phase windings 12u, 12v, 12w of the main winding 11. A simpler winding for the auxiliary winding is possible, however, which has the even number of phases and poles as the main winding but which is received in a smaller number of notches.

It is also possible for the windings of the main winding 11 to be arranged radially inside the coils of the auxiliary winding.

FIG. 4 shows the equivalent electrical diagram of a phase of the motor, with the consecrated notations, which will therefore not be explained. The passive circuit RLC constitutes in this diagram an additional branch connected in parallel, traversed by a current I ' ^a at the supply frequency.

FIG. 5 shows an equivalent electrical diagram for a fictitious harmonic current I with a harmonic pulse ο¾, which would create the same harmonic induction as that created by the fundamental current. This scheme is particularly valid in the case where this harmonic induction originates from a phenomenon internal to the machine and not a non-sinusoidal supply.

In the diagram of Figure 5, the network is seen as a short circuit for this harmonic and as the auxiliary winding adds a branch in parallel to the others, it decreases the overall impedance of the assembly and causes an electromotive force ( below fem) induced lower e.

This feme is proportional to the harmonic induction to be fought and will be weaker as the impedance of the auxiliary winding will be weak, so the frequency close to the resonance. The capacitance of the capacitor C ' ^a is thus advantageously adjusted in exemplary embodiments of the invention so that its association with the inductance L' ^a of the phase winding, minimizes the voltage of the capacitor.

In the case of a non-sinusoidal power supply, the diagram of FIG. 4 is valid at harmonic frequencies and the f.e.m. harmonic across L¾ is reduced for the same reasons.

Depending on the value of the pulsation ω of the phenomena to be controlled, the value of the capacitance can be chosen more or less, since it is also possible to play on the inductance of the phase winding of the auxiliary winding, according to its number of turns.

The higher the value of the capacitance, the higher the reactive power supplied, which can contribute to reducing the current absorbed and the losses. For a high puls pulsation of the phenomena to be fought, a low capacitance value is sufficient and the auxiliary winding can be traversed by a relatively weak current; its realization then requires only a small number of drivers. This allows a reduction in magnetic noise and vibration, but makes a relatively small contribution to improving efficiency and power factor.

Thus, it may be necessary to favor a more or less important capacity value according to whether one seeks to favor the improvement of the yield or the attenuation of the noise of the vibrations of magnetic origin. The number of turns of the winding of the auxiliary winding can be chosen accordingly, taking into account winding stresses, imposed for example by the size and the filling factor of the notches.

Trial

The machine tested is a three-phase 50 Hz motor with a nominal power of 11 kW, for which all stator windings are accessible, allowing only half of the conductors to be used as the main winding. The other half serves to form the auxiliary winding, each phase winding being connectable to a corresponding capacitor to form the passive RLC circuit.

In the machine tested, the conductors of the auxiliary winding are thus spatially offset from the conductors of the main winding; better results being obtained when the motor is by construction coiled so that conductors of the main winding and those of the auxiliary winding are received in the same notches. The main and auxiliary windings are here star-coupled.

The performance measured in this test is as follows:

Capacitorless With 3 capacitors

120 μΡ connected in star

Absorbed current 15.3 A 9.77 A

Active power absorbed 1725 W 1618 W

Reactive power absorbed 8455 VAR 5267 VAR

Power factor 0.2 0.3

Estimated yield (load 34.8% 37%

driven here requires little

power)

Current in the winding 0 A = 7.6 A

auxiliary

Overall noise 75 dB 70 dB

Noise at 850 Hz 69 dB 58 dB If we compare Figures 6 and 7, we see that the invention reduces the overall noise of 5 dB, the latter from 75 dB to 70 dB. The vibration spectrum given in FIGS. 8 and 9 shows that certain vibrations are suppressed, in particular between 800 and 1200 Hz. Referring to FIGS. 10 and 11, it can be seen that the intensity of certain spectrum lines.

Thus, the invention achieves a relatively high overall noise reduction in a simple manner. The invention also makes it possible to reduce the electrical losses significantly, in this example by more than 6%, and to improve the efficiency by more than 2 points.

Other tests carried out in load confirm these results, the improvement of the power factor being even more important.

Theoretical calculations on a machine with a nominal power of 15 kW, designed to operate on 50 Hz, with six poles, show that the machine generates an annoying noise at around 3600 Hz, due to electromagnetic phenomena, this noise being accompanied by vibrations and vibrations. harmonics of absorbed current and torque. Since the frequency of the harmonic phenomenon to be combated is relatively high, a choice can be made between on the one hand the priority to the reduction of the consequences of the harmonic induction waves, and on the other hand the priority to the reduction losses and reactive power consumed. The consequences of harmonic induction waves include vibrations, noise, harmonic harmonics, harmonic losses, electromagnetic emissions.

In the first case, it is possible to choose for the auxiliary winding a smaller number of turns than for the main winding, and for example equal to one tenth of the number of turns of the main winding. Capacitors with a capacitance of 11 μΡ can be used and are only traversed by a current of about 70 mA, which makes it possible to use conductors of small section. The auxiliary winding can thus easily be added to the existing notches, being for example arranged at the bottom of the notch, so as to reduce noise and vibrations. The impact on the power factor is, however, almost zero and the impact on the losses relatively low, only the iron losses being reduced thanks to a more sinusoidal induction, but not the Joules losses.

In the second case, capacitors with a capacitance of about 115 μΡ can be used, connected to phase windings of the auxiliary inductance winding more important than in the previous case, for example the same number of turns as those of the main stator winding.

A current of about 7.5 A flows in the conductors of the auxiliary winding, which imposes a relatively large section to the conductors, so that the auxiliary winding takes a significant place in the stator and can not always be added on a machine already wound and not provided for this purpose. The space available to accommodate the auxiliary winding must be sufficient, ideally anticipated from the manufacture of the machine, except to accept that the useful power of the latter is lower. In this example, the stator current for the same useful power increases from 19.6 to 15.2 A and the power factor from 0.73 to 0.92, the yield increasing from 81.7 to 83.3 %.

Many variations can be made to the implementation of the invention. In particular, the auxiliary winding may not be wound in all the notches of the stator, so as to simplify its implementation.

The motor can be powered not directly by the network, but via an electronic variable speed drive. This is very often the case for a synchronous or asynchronous electric motor. The invention is particularly interesting in this case, because the non-sinusoidal supply is causing significant noise and vibration that the system effectively fights.

The example described is an asynchronous electric motor, such a motor being very widespread. In this case, the invention notably makes it possible to improve the efficiency of the engine. But as discussed above, the invention applies to different types of electric motors, including synchronous electric motors.

The example described above is also a three-phase electric motor, but the invention applies to other types of polyphase electric motors, including electric motors comprising more than three phases. In this case, the motor according to the invention may have fewer notches per poles and per phase for the auxiliary windings.

Several passive circuits may be used with different resonance frequencies or different capacitance and inductance values. These circuits are then electrically isolated from the main winding and also electrically isolated from each other. This can further improve the performance of the machine, choosing different resonance frequencies for the passive circuits used, corresponding to different phenomena to fight.

Also, the phase windings can also each be connected to a capacitor, without being coupled to each other. Alternatively, the three phase windings 14u, 14v and 14w, and the capacitors Cu, Cv and Cw can still be connected in triangle-triangle, triangle-star, star-triangle.

The expression "comprising one" shall be understood as being synonymous with "comprising at least one" unless the contrary is specified.

Claims

Electric motor comprising a stator (10) having a bundle of plates defining notches (15) receiving conductors of a main winding (11), characterized in that it comprises an isolated passive circuit comprising an auxiliary winding ( 13) wound in said notches, and capacitors (Cu, Cv, Cw) associated with phase windings (14u, 14v, 14w) of this auxiliary winding (13).

2. Electric motor according to claim 1, wherein the isolated passive circuit consists of an auxiliary winding (13) wound in said notches, and capacitors (Cu, Cv, Cw) associated with the phase windings (14u, 14v, 14w). of this auxiliary winding (13).

3. Motor according to claim 1 or 2, wherein the phase windings of the auxiliary winding (13) are coupled in a star or in a triangle.

4. Motor according to one of the preceding claims, wherein the capacitors (Cu, Cv, Cw) associated with the phase windings (14u, 14v, 14w) of the auxiliary winding (13) are coupled star or triangle.

5. Motor according to claim 1 or 2, wherein the phase windings (14u, 14v, 14w) of the auxiliary winding (13) are isolated from each other, each phase winding (14u, 14v, 14w) being connected to a capacitor (Cu, Cv, Cw).

6. Motor according to any one of the preceding claims, wherein the auxiliary winding (13) is wound in said notches (15) with the same number of poles and phases (14u, 14v, 14w) as the main winding. (11).

7. Motor according to any one of the preceding claims, wherein the capacitance value of the capacitors (Cu, Cv, Cw) is chosen so that the isolated passive circuit has a resonant frequency greater than 20 Hz, preferably greater than 20 Hz. 100 Hz, and / or less than 100 kHz, preferably less than 20 kHz.

8. Motor according to any one of claims 1 to 7, wherein the capacitance value of the capacitors (Cu, Cv, Cw) is chosen to reduce the harmonic induction waves and / or their consequences.

9. Motor according to any one of claims 1 to 8, wherein the capacitance value of the capacitors (Cu, Cv, Cw) is chosen to increase the efficiency and / or the power factor of the engine.

10. Motor according to any one of claims 1 to 8, wherein the value of the capacitance of the capacitors (Cu, Cv, Cw) is chosen such that the resonant frequency of the isolated passive circuit is less than or substantially equal to the frequency of a harmonic induction wave contributing to phenomena that we seek to eliminate, which are notably the source of noise and / or vibrations.

11. Motor according to any one of the preceding claims, wherein the current flowing through the conductors of the auxiliary winding (13) is less than or equal to the nominal current flowing through the main winding (11).

12. Motor according to any one of the preceding claims, the auxiliary winding (13) being constituted by electrical conductors of section less than or equal to the section of the electrical conductors constituting the main winding (11), these conductors being preferably arranged in the same notches as those receiving the main winding (11).

13. Motor according to claim 12, wherein the conductors of the main winding (11) are arranged at the bottom of the notches, the conductors of the auxiliary winding (13) being arranged radially between the air gap (30) and the conductors. of the main winding (11).

14. Motor according to any one of the preceding claims, the motor being asynchronous.

15. Motor according to any one of claims 1 to 13, the motor being synchronous.

16. A method for optimizing an electric motor according to any one of the preceding claims, in particular a method for reducing the noise of magnetic origin of such an electric motor, characterized in that the value of the electric motor is selected. capacitance of the capacitors of the isolated passive circuit so that the resonant frequency of this circuit is less than or substantially equal to the frequency of a harmonic induction wave contributing to phenomena that are to be eliminated, which may notably be causing noise and / or vibrations.