MULTIPOLAR EXCITATION SYSTEMS

Abstract: A D.C. excited rotor winding arrangement for a dynamoelectric machine comprises at least one closed loop (1, 2, 3) of three or more series-connected winding sections (10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23) with at least three current-supply terminals (ABCD) at their interconnections. At least one pair of adjacent winding sections (10, 13; 11, 12) generate opposite magnetic poles when fed in parallel with current from their common supply terminal (such terminals are designated "odd", as opposed to "even" terminals which are each associated with two poles of the same sense) and the pole number is varied by switching the current supply from "odd" to "even" terminals or vice versa. Preferably the winding arrangement comprises a plurality of series-connected closed loops (1) of four winding sections interconnected at two odd (B5, D5) and two even (A5, C5) terminals. Preferably the winding arrangement is fed with current from one of a plurality of rotating rectifiers (4, 6, 7) according to the pole number required.

Description: Multipolar excitation systems. The present invention relates to D.C. excitation systems for A.C. multipolar dynamoelectric machines and is particularly concerned with brushless excitation systems arranged to produce variable pole numbers in the rotor windings of such machines. In many cases it is desirable to vary the pole number in a winding of a dynamoelectric * machine in order to vary its speed (if it is a motor) or its output frequency (if it is an alternator). However, known arrangements for generating variable pole numbers require relatively complicates switching arrangements and/ or require large numbers of slip ring connection. O PI _! i ..-. ••>.-, i- -; ~-_ V" 3 y ' " An object of the present invention is to alleviate such disadvantages. According to the present invention a variable pole number D.C. - excited winding arrangement for a dynamoelectric machine comprises at least one closed loop (1, 2, 3) of three or more series - connected winding sections- (10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23) and current supply means (5, 6, 7, 8, 9) for energising said winding sections with D.C, characterised in that said winding sections are provided with three or more current-supply terminals (A, B, C, D) at their inter¬ connections and are so disposed that the pole number of the winding arrangement can be varied by energising said loop (1, 2, 3) at different pairs (AC, BD) of said terminals. The pair of winding sections common to a first one of said current supply terminal may be wound so as to generate magnetic poles of opposite senses when fed in parallel and the pair of winding sections common to a second, one of said current supply terminals may be wound so as to generate magnetic poles of opposite senses when fed in series, the current supply means being arranged to energise said winding sections via either said first or said second current supply terminal so as to reverse the current through at least one of said winding sections and thereby vary the pole number. O ^ I In the case of three series-connected winding sections in the loop, one output (say, the positive out¬ put) of the current supply means will always be connected to said third current supply terminal and the other output (say, the negative output) may be switched from said first to said second current supply terminal to vary the pole number. In the case of four or more series-connected winding sections in the loop, both outputs of the current supply means may be switched, as long as one is switched from the first to the second terminal. The or each loop may incorporate four or more winding sections defining at least one pair of odd term¬ inals , current supply means being arranged to feed the or each said loop via either the pair of odd terminals or the pair of even terminals according to the pole number required. Preferably the or each loop incorporates four winding sections defining two odd and two even terminals. Two or more winding sections may be wound on a common core so as -to generate a single magnetic pale. Said two or more winding sections may be incorporated in the same or in different loops. Additional groups of series or parallel- connected winding sections may be connected in series with the or each loop of winding sections. Preferably the or each loop of winding sections is incorporated in a rotor winding, separate pairs of said current supply terminals being connected via rectifying means to respective exciting windings , which exciting windings are individually excitable according to the pole number required. Preferably the terminal_s._Qf the winding sections of the rotor winding are directly connected to the exciting windings via rotating rectifiers. Alternat¬ ively the rectifying means may incorporate slip-ring connections. The winding arrangement may comprise a plurality of closed loops of winding sections, at least two of said loops being connected in series, and current supply means, wherein said current supply means is adapted to energise different pairs of current supply terminals of the winding sections according to the pole number required. Said current supply.-means may comprise-- two 'or more exciter output windings magnetically linked to two or more independent exciter field windings so disposed that each exciting winding is exclusively energisable by a respective one of said field windings. Preferably the terminals of the winding sections are connected to the exciter output windings of the exciter via rotating " Rectifiers . Alternatively, slip-ring connections may be employed. Each loop may incorporate four winding sections. Two or more winding sections may be wound on a common core so as to generate a single magnetic pole at the rotor-stator interface. Said two or more winding sections may be incorporated in the same or in different loops. The invention includes within its scope dynamo- electric machines incorporating winding arrangements as set out hereinabove. The invention will become clearer on consideration of Figures 1 to 3 of the accompanying drawings, of which: Figure 1 is a schematic diagram of three loops of winding sections for use in one arrangement in accordance with the invention; Figure 2 is a schematic circuit diagram showing by way of example a variable pole number rotor winding arrangement in accordance with the invention,and —Figure 3 is a schematic diagram representing the disposition of the winding sections of Figure 2 about the rotor circumference. Referring to Figure 1, three types of closed loops, namely a) and b); c) and d), and e) and f) are shown. Each loop consists of four serially interconnected winding sections distributed about a rotor or stator circumference which are interconnected at four terminals A, B, C, and D. OMPI Each winding section is labelled + or - according to whether it generates a north pole or a south pole when the current flows clockwise between the adjacent terminals (i.e. A to B, B to C, C to D or D to A). Reading clockwise from terminal A, the three types of loop may thus be denoted +—+. -+-+, and ++++. Each type of loop is shown fed from alternative pairs of terminals, namely A to C (diagrams a) c) and e)) and A to B (diagrams b), d) and f)). The resulting N or S magnetic poles at the rotor-stator interface are indicated. It will be appreciated that each loop of winding sections will in general additionally generate a set of magnetic poles of opposite senses to those indicated, since each winding section will generate two opposite poles. For the sake of simplicity, only one set of poles, namely the set of adjacent poles at the rotor-stator interface, has been indicated in each of parts a) to f) of Figure 1. The (omitted) poles of the other set may either combine with poles produced by other loops of winding sections or will cancel out in the rotor or stator laminations. In 'either case they will not affect the pole number. It will be seen that the common terminal of adjacent winding sections will be "odd" (as defined above) if they are both positive or both negative but will otherwise be "even" (as defined above). The change in pole number and distribution resulting from the change in current feed will now be examined for each of the three types of loop, adjacent N or adjacent S poles being considered as single N or S poles. Between diagrams a) and b) the current exit rail is shifted from terminal C(odd) to terminal .E(even) , giving a change from four poles to two poles. Between diagram c) and diagram d) there is no change in pole number (two poles in each case) but the poles are rotated clockwise. Between diagram e) and diagram f) there is similarly no change in pole number (two poles) but the poles are rotated anti- clockwise. The fourth type of loop, namely +++-, is not considered here but can similarly be shown to generate two poles which are rotated anticlockwise when the current feed is changed from AC to AB. In general it can be shown that for any number. _ of winding sections greater than three, no change in pole number is achieved by shifting a current supply or current exit rail from an odd to an odd or from an even to an even terminal, and that two extra poles will be created by shifting a current supply or current exit from an even to an odd terminal (compare diagrams a) and b)). In a loop of five or more winding sections the changes in pole number achievable by successively shifting a current supply or current exit rail from an odd to an even terminal (or vice versa) are additive - hence the maximum change in pole number obtainable by shifting two current supply rails be¬ tween terminals of such a loop of interconnected winding sections is 2 + 2 = 4. This applies irrespective of the configuration of the winding sections. For example the axes of the winding sections may be tangential to the rotor circumference or they may be radial. A closed loop of four windings with means for feeding current to either one or other of the pairs of opposite terminals Is particularly advantageous for use In accordance with the invention because a variety of symmetrical pole distributions with balanced current in the windings may be obtained if the windings have equal resistances. More elaborate pole distributions than those shown in Figure 1 na be obtained by employing a number of loops and suitably positioning the windings of each loop on the rotor circum¬ ference and by combining the magnetic fields of two or more windings from the same or different loops. It will be under¬ stood that the invention includes within its scope winding arrangements utilising loops of five, six or more winding sections since the pole number contribution of each such loop can be changed by up to four poles, as noted above. Figures 2 and 3 show a , 6 , 8 or 10 pole rotor winding arrangement in accordance with the Invention for an alternator. The rotor winding consists of three groups of windings 1, 2 and 3. Group 1 consists of a loop of four winding sections 10, 11, 12 and 13 connected between terminals A5, B5 , C5 and D5, and two parallel-connected winding sections 14 and 15 connected in series with the loop between terminals E4 and F4; group 2 consists of a loop of four winding sections 16, 17, 18 and 19 connected between terminals A7, B7, C7 and D7, and group 3 consists of a loop of four winding sections 20, 2 ' 1 , 22 and 23 connected between terminals A9 , B9 , C9 and D9 and two groups of three winding sections 24, 25 and 26 and 27, 28 and 29 connected in parallel between terminals E10 and F10. The windings between terminals E4, F4 and E10, F10 are arranged to have appropriate resistances to equalise the electrical loads on rotating rectifiers 4, 5, 6 and J . The distribution of the three groups of winding sections (all of whose axes are radial) round the rotor circumference is shown schematically in Figure 3, the horizontal axis representing distance round the rotor circumference and the vertical axis representing distance in the radial direction. The layers of winding sections are shown separated for the sake of clarity. Groups of winding sections 1, 2 and 3 are each arranged to be D.C. excited at either of two pairs of terminals from shaft- mounted three-phase bridge rectifiers 4, 5, 6 and 7- The winding sections in each loop are of equal resistance so that none of the e.m.f. generated at the D.C. terminals of any one bridge rectifier is distributed across the D.C. terminals of any of the other bridge rectifiers. A similar effect may be achieved by making one pair of ad¬ jacent windings each of resistance r and the other pair of adjacent windings in the loop of resistance R, where r i R. Field winding F1 produces 12 stator poles and field winding F2 produces 24 stator poles in the exciter— these exciter stator pole options all result in D.C. at the bridge reftifiers and are not to be confused with the basic pole number options of the invention. The exciter field and rotor windings are arranged in a known manner so that each exciter rotor winding is energisable by one field winding exclusively. Exciter 8 is provided with two sets O PI of three phase rotor windings 30 and 32 for generating _ four and 8 poles respectively in the rotor winding of the ' alternator according to whether its field winding F1 or F2 is energised, winding 30 being fully pitched to 12 poles and winding 32 being fully pitched to 24 poles. Similarly exciter 9 is provided with two sets of rotor windings 31 and 33 energisable by its field windings F1 and F2 respect¬ ively for generating six and ten poles respectively in the alternator rotor winding. Windings 31 and 33 are pitched to 12 and 24 poles respectively. Each exciter winding 30, 31 , 32 and 33 is independently excitable according to the particular exciter field winding which is energised, so that four, six, eight or ten poles may be generated in the rotor winding of the alternator. The above mentioned four, six, eight or ten poles are generated in a symmetrical fashion around the rotor circumference of the alternator, as can be seen from Figure 3- The N and S poles in Figure 3 (which are the poles at the outer ends of the winding sections) are marked 0 in Figure 2. The -+■ and - notation of Figure 1 is used in Figure 2, and it will be seen that loop (10, 11 . , 12, 13) is similar to that shown in Figure 1 a) and b) and that loops (16, 17, 18, 19) and (20, 21, 22, 23) correspond to those shown in Figure 1 c) and d) and Figure 1 e) and f) respectively, except that- the D.C. supply can be transfer¬ red from terminal A to terminal D, as well as from terminal C to terminal B. Winding sections 10 and 12 are combined on a common yoke so as to produce a common pole at the rotor stator interface (N in the case of 6 poles and S in the case of 4 poles) and winding sections 11 and 13 are also combined to produce a common S pole (Figure 3). In accordance with the invention, winding sections 16, 18, 20 and 22 generate either N or S poles according to the pair of terminals at which the rotor winding is excited (and hence according to which exciter winding 30, 31, 32, 33 is excited). It can be seen that excitation at terminals E4 and C5 generates four poles at winding sect¬ ions (10 and 12), 14, (11 and 13) and 15; excitation at terminals B5 and D7 generates 6 poles at winding sections (10 and 12), 17, 19, (11 and 13) 16 and 18; excitation at terminals A7 and C9 -generates eight poles at winding sections 21, 17, 19, 20, 22, 16, 18 and 23; and that excitation at terminals B9 and F10 generates ten poles at windings 21, 24, 25, 26, 20, 22, 27, 28, 29 and 23- The winding".:; sections may have their axes radially aligned as on conventional alternator rotors, or other orientations (e.g. tangential axes) may be used. It will be appreciated that the two aspects of the invention illustrated in the embodiment of Figures 2 and 3 involve the use of loops of winding sections in slightly different ways to achieve the two distinct advantages: a) by disposing * the winding sections of a loop so as to provide at least one "even" and at least one "odd" terminal in the loop, the pole number contribution- of that loop can be varied by transferring the D.C. ' excitation from an ' "even" to an " "odd" terminal whilst keeping all the winding sections energised, so that no winding sections in the loop are redundant, whatever the pole number; b) by utilising two or more series-connected closed loops • of winding sections and arranging for the resistances of the winding sections in each loop to be appropriate¬ ly balanced, separate independent D.C. supplies may be connected permanently to respective pairs of opposite terminals of the loops and energised individ- ually according to the required pole number, no high power switching arrangements being required. A compact efficient winding arrangement results, whose pole number can be varied simply be controlling low' power exciter field windings. ETO O PI ■

Claims: CLAIMS . 1. A variable pole number D.C. excited winding arrange¬ ment for a dynamoelectric machine comprising at least one closed loop (1, 2, 3) of three or more series-connected winding sections (10, 11, 12, 13, 16, 17, 18, 19, 20, 21, 22, 23) and current-supply means (5, 6, 7, 8, 9) for energising said winding sections with D.C, characterised in that said winding sections are provided with three or more current-supply terminals (A, B, C, D) at their inter¬ connections and are so disposed that the pole number of the winding arrangement can be varied by energising said loop (1, 2, 3) at different pairs (AC, BD) of said terminals. 2. A variable pole number DC excited winding arrangement as claimed in Claim 1 , wherein the pair of winding sections common to a first one (B5, D5; A9 , C9) of said current supply terminals are wound so as to generate magnetic poles of opposite senses when fed in parallel and the pair of winding sections common to said second current supply (A5 C5) are wound so as to generate magnetic poles of opposite senses when fed in series, current supply means being provided for energising said winding sections via either said first or said second current supply terminal so as to reverse the current through at least one of said winding sections and thereby vary the pole number. 3- A winding arrangement according to Claim 1 or Claim 2 wherein said current supply means (5, 6, 7, 8, 9) comprises one exciter winding (31, 32) connected via rectifying means (5, 6) to said first terminal (B5, D5; A9 , C9) , another exciter winding (30) connected via rectifying means (4) to said second terminal (A5, C5) and two exciter field windings (F1, F2) each said field wind- ing being magnetically linked to both exciter windings but arranged so that each said field winding can energise one respective exciter winding exclusively. _. 4. A winding arrangement according to any preceding claim comprising a plurality of interconnected closed loops (1, 2, 3) of three or more series-connected winding sections. 5. A winding arrangement according to any preceding claim wherein at least one said loop (1, 2, 3) incorporates • four or more of said series-connected winding sections (10-13, 16-19, 20-23). 6. A winding arrangement according to any preceding claim wherein the or each loop of winding sections (1, 2, 3) is incorporated in a rotor winding. 7- A winding arrangement according to Claim 6 wherein the terminals (A, B, C, D) of the winding sections of the rotor winding (1, 2, 3) are directly connected to exciting windings of an exciter via rotating rectifiers. 8. A variable pole number D.C excited winding arrange¬ ment as claimed in Claim 1 , comprising a plurality of closed loops (1, 2, 3; 24-29) of winding sections, at least two of said loops being connected in series, and current supply means (8, 9) wherein said current supply means is adapted to energise different pairs of current supply terminals (A, B, C, D, E10, F10) of the winding sections according to the pole number- required. 9- A winding arrangement according to Claim 8 wherein said current supply means is an exciter (8, 9)' and said current sapply terminals (A, B, C, D, E10, F10) are con¬ nected to the exciting windings (30 to 33) of said exciter via rotating rectifiers (4, 5, 6, 7). 10. A winding arrangement according to Claim 8 or Claim 9 wherein two or more of said loops (1, 2, 3) incorporate four winding sections (10 to 13, 16 to 19). 11. A winding arrangement according to any preceding Claim wherein two or more winding sections (10, 12, 11, 13) are wound on a common core so as to generate a single magnetic pole at the rotor-stator interface. 12. A winding arrangement according to Claim 11 wherein said two or more winding sections (10, 12, 11, 13) are incorporated in difference ones of said loops (1, 2, 3)- 13- A winding arrangement according to any preceding claim wherein the axes of said winding sections (10 to 13, 16 to 19, 20 to 23) are disposed radially on a rotor.

Inventors: QUAYLE GEORGE PHILIP, QUAYLE, GEORGE, PHILIP
Applicants: ASS ELECT IND, ASSOCIATED ELECTRICAL INDUSTRIES LIMITED
Application year: 1984
Main classification: H02K19
IPC codes: H02K19