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A new d.c. machine arrangement for an electronically assisted commutation
G. Quichaud, A. Ihaddadene, M. Poloujadoff, H. Benalla, R. Goyet
To cite this version:
G. Quichaud, A. Ihaddadene, M. Poloujadoff, H. Benalla, R. Goyet. A new d.c. machine arrangement for an electronically assisted commutation. Journal de Physique III, EDP Sciences, 1993, 3 (11), pp.2065-2070. �10.1051/jp3:1993260�. �jpa-00249066�
Classification Physics Abstracts
41.90 86.90
Short Communication
A new d.c. machine arrangement for an electronically assisted commutation
G. Quichaud, A. Ihaddadene, M. Poloujadofl, H. Benalla and R. Goyet
Laboratoire d'Electrotechuique des Universitds Paris VI et XI, B£timent 214, Uuiversitd Paris XI, 91405 Orsay, France
(Received 8 July1993, accepted lo September1993)
R4sumd. La machine h couraut continu est le moyeu le plus dconomique pour rdaliser des entrainements h vitesse variable. La machine classique voit ndanmoins ses performances limi- tdes par la prdsence du collecteur. En elfet, ce dernier, sibge d'dtincelles voire d'arcs d'origiue dlectromagndtique s'use vite et coustitue de ce fait le point faible de la machine h courant
coutinu. Depuis quelques auudes, notre laboratoire a mis l'accent sur la recherche de disposi-
tifs externes d'aide h la commutation de ces machines qui remplaceraient avantageusement les p61es auxiliaires. Mars c'est la premibre fois qu'il expdrimente uue machine I courant coutinu
de techuologie classique mais sons p6Ies auxiiiaires avec
uu systbme d'aide h la commutation
dlectronique externe.
Abstract The d-c- machine is the cheapest way to realize variable speed drives. However its
performances are limited by the commutator operation. Indeed, the latter wears out very rapidly because of the sparks, even krciugs, which appear between the segments and )he brushes, in
spite of use of commutating poles. Over the last fifteen years, our laboratory has implemented external circuits to assist commutation and alleviate, or even suppress, the main difficulties.
This paper presents a new arrangement which seems very promising.
1 Introduction.
The most classical solution to the problems of d.c. machines commutation is the use of auxiliary poles. Auxiliary emfs are generated to help the inversion of current in rotor coils at the proper
time. However, generation of sparks between brushes and segments of the commutator remains the main limit to the performances of d-c- machines. At the beginning of the sixties, Bates [3]
suggested the addition of an external 50 Hz emf of constant amplitude to those generated by
the commutating poles. Fifteen years later, our laboratory proposed the use of other additional
emfs, whose nature had been inspired by our researchs ill on pulsed power devices. We have
2066 JOURNAL DE PHYSIQUE III N°11
tried several schemes which allow the frequency and amplitude of the additional emf to be varied according to the load and speed of the machine.
To introduce an external emf, it is necessary to open the usually short circuited commutating
coil. This is made by the use of special commutator segment arrangements.
In what follows, we review some of the previous works; then we describe an entirely new
scheme.
2 Previous works.
2. I USE OF A SYMMETRICAL COMMUTATING DEVICE (3, 5, il. Let us consider the clas-
sical commutator arrangement shown in figure la where the number of coils and segments is
even. Each brush as B which carries current Im is connected to the power d.c. network. In
figure 16, two new commutators are shown. Each one is analogous to the commutator in figure la, but every second bar has been replaced by an insulating segment and two brushes Bl and 82 replace B. If Bl and 82 are short circuited, and connected to the d-c- network, then figures
1a and 16 are essentially identical. A "chequered commutator" is thus obtained.
El
82 lm
lmi+lm2= lm
(ml 1m2
a) b)
Fig. I. Modification of the commutator in order to access the two extremities of the commutating
coil.
The general principle of using such a device is shown in figure 2. A single phase transformer with a three tap secondary allows to create an auxiliary emf in the commutating coil. The d.c. current enters the machine through the middle tap, and is forced through the appropriate thyristor.
In [3] was used a constant 50 Hz frequency and constant amplitude voltage at the terminals of the transformer's primary. The auxiliary emf was only a complement to the emf generated by the commutating pole.
2.2 USE OF AN ASYMMETRICAL COMMUTATING DEVICE II, 4-6j. The commutator is
a sequence of conducting and non conducting segments. There are two brushes per sliding
El
82
Thl Th2
1m
~
/s/
f
Fig. 2. Symmetrical commutating device.
rotor speed
Thl
Im
L Th3
a)
~ ~
rotor speed
rotor speed
Th2 Thi Th2
bn
L Th3
b) c)
Fig. 3. Asymmetrical assistance to commutation.
2068 JOURNAL DE PHYSIQUE III N°11
contact, as shown in figure 3a. The gap between the two brushes of the same set is less wide than one conducting segment. At a given time la, when relative positions are as shown in
figure 3a, Thl is on, Th2 and Th3 are off. The current Im charges C positively. A little later,
when 52 touches both 81 and 82 (Fig. 3b), firing on Th2 turns off Thl; currents in the rotor are not modified. It is then possible to reverse the charge of capacitor C by firing on Th3. At time t~ when Bl touches Sl and 82 touches 52 (Fig. 3c), firing Thl establishes conduction
through Sl and produces a short circuit current icc which cancels the current through 52. The situation is then the same as in figure 3a, but 52 and 53 have been replaced by Sl and 52
respectively. Such a principle allows to replace the commutating emf created by commutating poles by a voltage across the capacitor.
3. The new scheme [2],
The object of the present paper is to propose a new scheme. We use a wave winding with only
two parallel circuits (2a
= 2) and at least two pole pairs (p > 2). In addition, p must be, in
preference, even. We assume that there are two coil sides in each slot. The commutator is
a conventional one and the number of segments is twice the number of slots. Every second segment is connected to the winding, the other segments are not connected. In figure 4, these
segments which are not connected are represented by a black rectangle. The 2p brushes are placed on the neutral lines as in a classical machine. The segments are little wider than the
brushes. A simplified example (4 poles, 9 slots) is shown in figure 4.
~, d,
~ e
~ rotor speed
a c b
b a
El Al 82 A2
lAl+iA2=lm
'~~ lB2 lA2 iBl+iB2=lm
Fig. 4. The new arrangement.
The commutating emf will be provided by generator G connected between two successive brushes of same polarity. Only one of those generators is shown in figure 5a, and it will be
enough to explain its operation.
We first consider a time la when current Im enters the machine through brush Bl and segment I, as shown in figure 5a. A time 16, when brushes Bl and 82 touch segments I and 6 respectively, generator G will be controlled to a positive pulse voltage I-Vi which will cancel
and reverse the current in conductors lo and 5 (Fig. 5b). A convenient control of G makes
possible to ensure that current is zero through brush Bl when it leaves segment I. Then, as long as Bl is in contact with the unconnected segment, the current enters the machine through
brush 82 and segment 6 (Fig. 5c). A little latter, when brushes Bl and 82 touch segments
~ d
,
~ d
', d d
e
~_
~
rotor speed
rotor speed
6
~, C
b ~ b
a b a
al 11 82
iAi jBimj~ j~i ~~~
'~~ lB2=0 lBl+iB2=lm
lAl+lA2=lm
i~im~
iA2-lm
a) bj
d d
e, d .,
', d
e e
_
~°~°~ ~~~~~
rotor speed '~~
0 4 iB~ a
C b
a, b
a b a
Al al ~~
iAi lA2
~~~=o
lB2-lm iBl+lB2.lm
lAl+lA2=1m
lAl~lm iA2m0
C) d)
Fig. 5. Operation of the new arrangement.
2 and 6 respectively, generator G will be controlled to produce a negative pulse voltage V6-V2
to force the current into the machine through brush 81 (Fig. 5d). Then when brush 82 will touch only an insulating segment (between 6 and 7), the situation will be described by a figure
similar to figure 5a, where segment I will be replaced by segment 2.
It is seen that it is not possible to use this principle with a two poles machine, because in this case the two extremities of a coil are connected to two adjoining segments.
4. Conclusion.
The new structure is more favourable than the previous ones, because it allows the use of a
classical technology for the commutator and the brush sets. To test it, two different experiments have been conducted on a machine which has been specially built for our laboratory. Its nominal power is 8 kW (135 V, Go A). It has no commutating poles; there are two pole pairs, and 31
slots; the commutator has 62 segments (31 are connected, 31 are not). We have reached II kW without a spark. The description of the generators G which have been used, and the detailed results will be published latter.
2070 JOURNAL DE PHYSIQUE III N°11
References
[II Roux C., Sultauem F., Guillet R., Bleijs C. et Clade J., Brevet d'invention intituld Dispositif
d'alimentatiou h frdqueuce variable h commutation dlectromdcanique, N° FR 2589647, ddposd
le 4 novembre 1985.
[2] Quichaud G. et Goyet R., Demande de brevet d'invention intituld : machine h courant coutinu
dquipde d'un collecteur et dotde de moyeus de commutation assistde, N° 9306195, d6posd le 25 mar 1993.
[3] Bates J-J-, Thyristor-assisted commutation in electrical machines, Proc. I.E.E. 115 n° 6 (1968).
[4j Gouiaa R., Etude thdorique et expdrimeutale de deux types de collecteurs assistds dlectronique- meat, Thbse de Doctorat de l'Universitd de Paris VI (1986).
[5j Namiraniau H., Alimeutation I frdquence variable par collecteur mdcauique assistd par dlectro-
nique, Thbse de Doctorat de l'Universitd Paris VI (1989).
[6j Goyet R., Benalla H., Roux C. et Poloujadolf M., A new concept: the electronically assisted commutation collector, I-C-E-M 90, Boston (M.I.T., August 1990).
[7jPham-Coug-Suu M-C-, Etude des machines sans p61es auxiliaires et h collecteur assistd par dlectronique, Thbse de Doctorat de l'Universitd de Paris VI (1993).
