FR2545292A1 - Self starting reversible synchronous miniature motor - Google Patents

Abstract

A self-starting reversible miniature synchronous motor has a permanent magnet rotor and a stator with a main and an auxiliary phase winding of the same electrical resistance. The auxiliary winding lies in parallel or in series to a capacitor. The rotor consists of high-energy low-remanence magnetic material. At the stalling torque with nominal supply voltage, the ohmic resistance of each stator winding equals max. 80% of its reactive resistance.

Description

 The present invention relates to a small synchronous electric motor reversible b automatic start, comprising a rotor with permanent magnetization and a stator whose winding consists of a main strand and an auxiliary strand both having electrical resistive values appronimetrically equal, the auxiliary strand being connected in parallel or in series with a service capacitor.

 According to the Valvo manual entitled "Motoren", November 1976, pages 23 to 29, we know the electrical design and the operating mode of a small reversible synchronous motor provided with a rotor with permanent magnetization consisting of a weak magnetic material. energy.

This small synchronous motor always turns in the same direction regardless of the value of the supply voltage and the load. Its yield is however limited to a maximum of 509 and it also cannot exceed this value by strengthening the excitation. On the other hand, the variations in angular velocity increase as the excitation increases.

 The object of the invention is therefore to dimension a small reversible synchronous motor, so that the efficiency always increases when the excitation increases and that the variations in angular speed decrease at least when this small synchronous motor is loaded.

 In accordance with the invention, this object is achieved by the fact that the rotor consists of a magnetic material of high energy and of low remanence and that, in the event of an inversion load and in the presence of the nominal supply voltage, the effective resistance of each stator strand is at most equal d> 80% of the inductance of this strand.

The invention will now be described in more detail by way of non-limiting examples, with reference to the appended drawings in which
Figure 1 is a schematic representation of a small reversible synchronous motor
Figure 2 is an equivalent electrical diagram of this small synchronous motor
FIG. 3 is a vector diagram of the voltages and intensities inside dF-a small synchronous motor whose rotor consists of a magnetic material of low energy
FIG. 4 illustrates characteristic curves of the efficiency, variations of angular speed and of the effective resistance / inductance ratio of a stator strand of the small synchronous motor whose rotor consists of a low energy magnetic material
FIG. 5 is a vector diagram of the voltages and intensities in a small synchronous motor whose rotor consists of a magnetic material of high energy and
Fig. 6 shows characteristic curves of the efficiency, variations in angular speed and the effective resistance-inductance ratio of a stator strand of the small synchronous motor whose rotor consists of a high-energy magnetic material
In all the figures of the drawings, the same reference numerals designate identical elements.

 In accordance with FIG. 1, the small reversible synchronous motor consists of a stator 1, the winding of which comprises two stator strands (a main strand 2 and an auxiliary strand 3), as well as a rotor 4 with permanent magnetization. In order to simplify the drawing, it has been admitted that the rotor 4 has only N and S polishes. The following considerations naturally also apply to a rotor 4 comprising several pairs of blades.

 We know that such a small synchronous motor can be used with a parallel connection or a series connection of the two strands of its stator.

In FIG. 1, the case of a parallel assembly has been considered, that is to say a service capacitor
C is connected in series with the auxiliary strand 3, then this series connection is then mounted in parallel with the main strand 2. The parallel mounting thus constituted is supplied, via an engagement contact 5, by a power source 6 delivering an alternating voltage UN
In the series connection, not shown, the service condenser C would be connected in parallel to the auxiliary strand 3 by means of the contact to, engagement 5 and this parallel connection would be connected in series to the main strand 2. The series connection thus formed would be directly supplied by the power source 6
In all the figures of the drawings examined below, it will always be a parallel assembly.

 The two stator strands 2 and 3 are massive windings and are in two identical stator groups electrically offset by 90. The main and auxiliary strands generate alternating magnetic fields which show a phase shift in time and an angle shift in space, and the effects of which they exert on the rotor combine to form a rotating field. Thus, the rotor 4 starts automatically and rotates in a predetermined direction.

 The closing contact 5 is made in the form of a switch. It only serves to invert the roles played by the main strand 2 and the auxiliary strand 3, and therefore to reverse the direction of rotation of the small synchronous motor, since the one and the other of the blades of the capacitor C are alternately connected directly to the power source 6.

 FIG. 2 illustrates the equivalent diagram of the small synchronous motor according to FIG. 1. The index 2 designates all the electrical quantities of the main strand 2 and the index 3 applies to those of the auxiliary strand 3. The main inductive reactance X '2 or X'3 of each of the respective stator strands is connected in series with its excitation voltage UE2 or UE3', then the series connection thus obtained is connected in parallel with the respective resistance RFe2 or RFe3 with losses in the iron of the stator strand considered. The parallel circuit thus obtained is in turn connected in series with the circuit in series of the effective resistance R2 or R3 and of the inductive dispersion reactance X "2 or X" 3 of the stator strand considered.

It will be admitted below that the losses in the iron of the two stator strands are negligently small, that is to say that RFe2 = RFe3 = @, In this case, the resistances at losses in the iron can be removed from the representation according to Figure 2, this is why they are only illustrated by dotted lines in this figure. The main inductive reactance X'2 or X'3 and the inductive dispersion reactance X "2 or X" 3 of each of the respective stator strands are then directly connected in series, which gives
X2 = X'2 + X "2 and
X3 = X'3 + X "3 '
Where X2 or X3 respectively denotes the total inductance of the stator strand considered.

Since the two stator strands are generally of identical realizations, they both have approximately equal resistive values, which gives in addition
X2 X3
R2 = R3 = R and
UE2 = UE3 Us
The effective resistance / inductance ratio of a stator strand is then R / X. The vector diagrams in Figures 3 and 5 apply in these cases.

 Figures 3 to 6 will now be discussed in more detail by describing the operation. The characteristic curves of FIGS. 4 and 6 have been plotted as a function of the relative excitation EU / UN.

 Small synchronous motors are dimensioned so that the reactive power they absorb is negligently small. This is the case when in the two stator strands 2 and 3, the phase shift between the currents is O '.

Consequently, in the parallel mounting of the two stator strands, the inductance of main strand 2 must, in known manner, be dimensioned such that the angle of phase shift between the supply voltage and the current is + 45 in this main strand 2, while the value of the service capacitor C must be chosen such that the angle of phase shift between the supply voltage and the current is -45 in the auxiliary strand 3. As is easily seen from the corresponding vector diagram of FIG. 3, this is reflected, in small synchronous motors provided with rotors 4 made of low energy magnetic material, by the double dimensioning condition according to which - the effective resistance R and the inductance X of each
stator strands must be chosen approximately
equal and - the inductance XC of the capacitor C must be chosen
equal to twice the inductance X of each of the strands
statorics.

Indeed, with rotors 4 made of a low energy magnetic material, we obtain
UE2 = UE2 = UE = O.

On this assumption and by neglecting the losses in iron, we obtain for figure 2 the following equations
IN = I2 + I3 '(1)
UN = R2I2 + jX2I2 = X 2 + UX2 (2) and
UN = jXCI3 + R3I3 + jX313
= UC + UR3 + UX3 '(3)
In complex representation, the above-mentioned values are the following 12 or I3 represents the electric current flowing through the main strand 2 or the auxiliary strand 3, respectively,
IN designates the supply current delivered by the source 6,
XC $ designates the inductance 1 / wC of the service capacitor C,
UC corresponds to the drop in electrical voltage at capacitor C,
UX2 or UX3 represents the drop in electrical voltage in the inductance of the main strand 2 or of the auxiliary strand 3, respectively, and
XR2 or UR3 designates the voltage drop in the effective resistance of said respective main 2 or auxiliary 3 strand.

In Figure 3, the triangle ABM, in which AB = I3 '
BM = I2 and AM = IN, represents the vector diagram of equation (1). The triangle AED corresponds to equation (2), with AE UR2 'ED = i2 and AD = UN. In this case, AE is parallel to BM and, because of the inductance, ED is phase shifted 900 ahead of AE. The vector suite
AFGD corresponds to equation (3), with AF = UR3 'FG = Ux3 and GD = UC' AD being always equal to UN. AF extends in the same direction as AB and, due to the inductance, FG is phase shifted by 900 in front of AF, while, due to the capacitance, GD is shifted by 1800 in relation to FG, neglecting the effective resistance of the service capacitor C.

It emerges directly from FIG. 3 that the reactive power absorbed by the stator winding is zero when the vectors UN = AD and IN = M4 are in phase, that is to say when the point M is on the right
AD. As mentioned above, this is the case when the angle ABM is equal to 90C, that is to say when BM (and therefore also AE) is parallel to CD and AF is parallel to ED. When the angle EAD is also equal to 45, AEDF is a square and there is an absolute identity between the values of AE, AF, FD and ED, on the one hand, and of AB and BM, on the other hand. This implies the two aforementioned design conditions.

Then, because the two stator strands are identical, we obtain
R2 = R3 = R and
X2 = X3 =
The identity AE = ED gives: UR2 = UX2 ', that is to say that
R2 12 = X2 12 or that R2 = X2 so that R3 = X3.

the equation AF = FD = GD - FG gives: UR3 = UC - UX3 ', that is to say:
R3. I3 = XC. I3 - X3. I3 'or R3 = XC - X3' and the identity R3 = X3 gives: X3 = XC - X3 or
X3 = XC / 2, and therefore X2 = XC / 2.

When the small synchronous motor is connected in series, the following two dimensioning conditions are obtained in the same way
R2 = R3 = R = X2 = X3 = X and
X2 = X3 = X =
Thus, the first of these two conditions is identical to the first dimensioning condition of the parallel connection.

The small synchronous motors thus dimensioned have, as a function of UE / UN 'the characteristic curves represented in FIG. 4 and concerning the efficiency, the variation S of angular speed and the ratio d = R / X = 1 between the effective resistance and l inductance of a stator strand. This last characteristic curve is thus a horizontal line drawn at 100%. The characteristic curve S croft continuously as EU / UN increases and, when
EU / UN = 70%, the characteristic curve n shows a maximum of 50%. This maximum value of ri is never reached in practice and, in any case, it can never be exceeded with small synchronous motors thus dimensioned.

 To obtain nevertheless an increased yield, it is necessary, on the one hand, to increase UE / Ug by the choice of a rotor 4 made of a magnetic material of high energy and of low remanence, for example a magnetic material of the rare earth metal-cobalt type. or of the manganese-aluminum minium-carbon type; on the other hand, it is necessary to modify at least one of the two design conditions. FIG. 5 is a vector diagram illustrating the small modified synchronous motor.

In this case, in addition to equation (1) above, we obtain the following equations
UN = R2I2 + jX2I2 + UE2 = UR2 + UX2 + Ue (4) and
UN = UC + R3I3 + JX3I3 + UE3 =
UC + UR3 + UX3 + UE '(5) because, since the rotor 4 consists of a high energy magnetic material, the value UE2 = UE3 = UE can no longer be neglected, but is at least equal to 20% of the value UX2 or UX3 in the presence of the nominal supply voltage and an inversion load. By: inversion load ", it is necessary to understand the load in the presence of which the small motor loses its synchronism.

The vector diagram in FIG. 5 presents a structure similar to that of FIG. 3, with the difference that the vectors EH = UE2 and
FK = UE3 and these two vectors certainly have the same value UE 'but, in the presence of the inversion charge,
EH = UE2 is approximately in phase with UR2 and
FK = UE3 is approximately in phase with UR3 '
The triangle AHD and the AFKGD vector sequence correspond respectively to equation (4) and equation (5) This time, AKDH is a square and, with
R2 = R3 = R and X2 = X3 = X, we obtain the two design conditions a) and b) below
a) AH = AE + EH = HD, i.e. UR2 + UEs = UX2 or
UR2 = UX2 - UE2 <UX2 - 20% UX2 with UE2 <20% UX2.

it follows that
UR2 # 80% UX2 or
R2 <80% X2 '
given that R2 = R3 = R and that X2 = X3 = we generally obtain
R <80% X, i.e. in the presence of the nominal supply voltage and the reversing load, the effective resistance R of each stator strand must not be chosen equal to the inductance X as before, but equal to a maximum of 80% of this inductance X of a stator strand.

b) AK = KD gives AF + FK = GD - KG
or
UR3 + UE3 = UC Ux3
or, respectively,
UC = UR3 + UE + Ux3.

Since UR3 = UR2 'UX2 = UX3' UR3 <80 ~
UX3 and
EU # 20% UX3 '
we obtain
UC = 2UX3 or XC = 2X3, or else X3 = X = Xc / 2.

On the other hand, in the case of the series connection of the small synchronous motor, the following two dimensioning conditions are obtained
R <80% X and
X = XC
The first of these two conditions is thus again identical in the two types of connections.

 Small synchronous motors having such a modified dimensioning have, as a function of UE / UN, the characteristic curves illustrated in FIG. 6 and concerning the efficiency n, the variations S of angular speed and the ratio d = R / X between the effective resistance and the inductance of a stator strand. In this case, the characteristic curve S is a horizontal line of value O ^, that is to say that these variations are practically zero.

On the other hand, the yield no longer has any maximum, but continuously increases up to the value 100% as the values of UE / UN increase, the latter value of 100% being however only reached when the value d = R / X = O, which is not achievable in. the practice.

 It goes without saying that numerous modifications can be made to the engine described and shown, without going beyond the ambit of the invention.

Claims (3)

 1. Small reversible synchronous motor with automatic start, comprising a rotor with permanent magnetization and a stator whose winding consists of a main strand and an auxiliary strand both having approximately equal electrical resistive values, the auxiliary strand being connected in parallel or in series with a service capacitor, motor characterized by the fact that said rotor (4) consists of a magnetic material of high energy and low remanence, and by the fact that, in the event of an inversion charge and in the presence of the nominal supply voltage, the effective resistance (R) of each stator strand (2; 3) is at most equal to 80% of the inductance (X) of this strand  2. Small synchronous motor according to claim 1, characterized in that the magnetic material of high energy and low remanence is a magnetic material of the rare earth metal-cobalt type.  3. Small synchronous motor according to claim 1, characterized in that the magnetic material of high energy and low remanence is a magnetic material of the mangandse-aluminum-carbon type.