CA1149456A

CA1149456A - Frequency multiplication

Info

Publication number: CA1149456A
Application number: CA000349649A
Authority: CA
Inventors: Hans Landhult
Original assignee: ITT Industries Inc
Current assignee: ITT Inc
Priority date: 1979-04-20
Filing date: 1980-04-11
Publication date: 1983-07-05
Also published as: ES8101341A1; DE3014352A1; ES490692A0; ZA801936B; SE7903474L; AU5741980A; BE882846A; GB2047485A; NL8002170A; JPS5668269A; FR2454725A1; BR8002409A

Abstract

H. Landhult-2 (Revision) Abstract of the Disclosure The invention relates to a combination of semi-conductor elements and single or multiple phase elec-tric machines, for instance transformers, to provide a magnetic alternative flux in the magnetic circuit of the machine. This gives a frequency in the secondary winding of the machine which is changed by a factor K
with reference to the frequency of the A.C. mains where the factor K may be predetermined and selected for design criteria.

Description

H. Landhult-2 ~ 56 ~Revision) FREQUENCY MULTIPLICATION
Background of the Invention Through the use of semiconductor elements such as diodes, thyristors, triacs, transistors, etc., there are a number of known circui~ configurations for control and supervision of current or voltage and for obtaining frequencies other than that of the A.C. mains. The ability of these components, subject to a control impulse, to utilize the whole or a part of the period of the alternating current, may be used, for example, in connections like whole wave rectifiers with controlled values or triacs and antiparallel con-nected thyristors for controlling of lights or soft starters for motors. Circuits of this type are well known.
It is also known that if windings are arranged around a magnetic circuit such as in a single phase or a multiple phase transformer, a current is obtained in the secondary windings, the strength of which de-pends on the current in the primary circuit and the ratio between the number of windings in the secondary and primary circuits respectively. The frequency on the secondary side is the same as that of the primary side.
Additionally, if an ml-phase A.C. mains is con-nected toan ml-phase electric machine, an MMF wave is obtained which rotates with the synchronous speed US
¦ which is determined by the frequency of the connected frequency f and the pole number of the winding accord-~L
ing to the formula: q~P
,..

., H. Landhult-2 1~9~56 (Revision) u = 120 . f s Depending on the type, the rotor or the machine can be forced to rotate with the same speed (synchronous) or with a load dependent slip (asynchronous).
Objects of the Invention It is an object of the invention to obtain an integrated combination of semiconductor connections with a transformer or an electric machine which is provided with a special winding arrangement which uses a minimum of semiconductor elements and a special wound machine and provides in an efficient manner, another frequency, another r.p.m. or another number of phases than those of the A.C. mains.
Brief Description of the Invention This is achieved according to the invention in that the operation of an electric machine having at least one primary winding including a plurality of separate primary winding parts to which electric current is supplied from A.C. mains to induce an alternating magnetic field in the electric machine is controlled by selecting portions of the A.C. mains voltages; and applying the selected portions of the A.C. mains voltages to the primary winding parts at such intervals and in such a sequence that the magnetic field induced in the electric machine by the resultant electric current flow through the primary winding parts has a frequency differing by a pre-determined factor from that of the A.C. mains. Advantageously, at least one switchable element which can be rendered con-ductive by the application of external control signals thereto is interposed between the A.C. mains and the respective primary winding part; and the selection is achieved by supply-ing the external control signals to the switchable elements of the primary winding parts at the above intervals and in the above sequence to render the switchable elements conductive to the resultant electric current flow during the occurrence of the selected portions of the A.C. mains voltages.

~,' H. Landhult-2 ll'~9~S6 ( Revision) - 2a -By connecting the impulses from a system of semi-conductor elements as described above to each respective primary circuit of a transformer, a voltage is obtained in the secondary circuit having a frequency which is determined by the number of primary circuits and the directions of the connected impulses. If for instance, the positive part and the corresponding part of the negative half period in each phase voltage and each main voltage in a three phase system are used, a frequency multiplying with the factor K, up to 6, could be obtained in the secondary circuit. By alotting a suitable number of such impulses to the same phase (or different phases in a multiple phase system, i.e., a transformer or motor) it is possible to build up a voltage at any desired frequency which is a multiple of the frequency of the A.C. mains. The factor K could be bigger or smaller or equal to one. This also permits fractions of the A.C. mains frequency to be obtained. If, in an m-phase wound machine (m -1, 2, 3, etc.), each winding phase is arranged with n parallel circuits which are magnetically equal and electrically isolated and the n circuits and the m-phases are fed with suitably chosen impulses, ;~
~ . .

l~. L.lndhult-2 (Revision) .~ S6 an M.M.F. wave is obtained which rotates with a synchronous speed decided by the pole number of the winding and the frequency generated by the im-pulses. It is then important that the impulses are supplied in such a way that a symmetrical alternative flux occurs. The result is that the synchronous speed of the machine is the factor K times that corre-sponding to pole number and A.C. mains frequency.
The list below shows possible values for the factor K defined as the relationship of the secondary voltage frequency to the A.C. mains frequency in a transformer or the relationship between actual,motor r.p.m. which could be obtained by help of the princi-ples of the invention and the synchronous r.p.m. ob-lS tained by the pole number of the motor and the A.C.mains frequency. For the highest X-values the igni-tion angle must be chosen high, e.g.,(150), and the possibilities to obtain multiple phased secondary voltage are limited, i.e., K = 6, 5, 4, 3, 1,5,'3/4, 3/5, 1/2 etc.
Brief Description of the Drawings ~ .... ~
Figure 1 illustrates a transformer connected in accordance with the invention.
Figures 2 and 3 illustrate current flow in the primary,windings of the transformer of Figure 1.
Figure 4 illustrates a 3-phase transformer.
Figure 5 illustrates the current in the trans-former of Fig. 4.
Figures 6a and 6b illustrate circuitry for conversion of a 3-phase signal to a 3-phase signal having a higher frequency.
' Figure 7 illustrates the location and intercon-nection of primary and secondary windings in the , circuit shown in Figures 6a and 6b.
Figure 8 illustrates the line voltages in the circuit of Figures 6a, 6b and 7.
Figure 9 illustrates an alternative circuit , arrangement to that of Figure 6a.
.

H. Landhult-2 ~Revision) 3L1'~ 56 Figure 10 illustrates the interconnection of primary and secondary windings in the circuit of Figure 9.
Fig. 11 illustrates the pulses existing in S the circuit of Fig. 10.
Fig. 12 illustrates the order of windings in an electric motor.
Fig. 13 illustrates the interconnection of the windings of Figure 12.
Fig. 14 illustrates the pulses in the windings of Figure 13.
Fig. 15 illustrates a circuit arrangement for converting a 3-phase signal to a single phase signal.
Fig. 16 illustrates the line voltages in the circuit of ~ig. 15.
Figures 17aand 17b illustrate a circuit and its interconnections for obtaining a number of different frequency alterations.
Figures 18 and 19 illustrate various pulses contained in the circuit of Figs. 17a and 17b.
Figure 20 illustrates a circuit for varyinq the frequency.
Dbscription of the Preferred Embodiments ..
In order to appreciate the present invention, examination of the following exa~ples will be most illustrative.
Example 1 The principle according to this invention is to achieve an alternating flux by letting current pulses flow in different windings in such a direction that one pulse in one winding and the other pulse in another winding gives a flux of the same magni-tude but in opposite directions.
In Figure 1, the positive half-cycle gives a positive flux in winding A and the negative half-cycle gives a negative flux in winding B. This principle will ~e put to use in this invention.
Fig. 2 shows how the current i + flows in wind-ing A from 0 to T/2 inducting the positive flux ~ +

._~ . ~ t . .

~ `
~ S6 H. Landhult-2 (Revision) which is directed upwards. In Fig. 3 is shown how the current i - flows in winding B from T/2 to 1 inducting the flux ~ -. The average value of the ~lux during the whole period equals 0.
Example 2 , Fig. 4 shows a coupling where the primary winding on a transformer is split into three separate windings which are connected between the phases on a three phase A.C. mains. In each part there is a pair of anti-parallel thyristors with a firing angle of 120 degrees. This thyristor pair may be replaced by one triac. That means that the impulses 1 and 4 shown in Figure 5 from the line voltage UR S are fed to winding A. Impulses 3 and 6 come from line voltage Us T and are fed to winding B, while impulses 2 and 5 from line ~oltage UT R are fed to winding C. As shown in Figure 5, the impulses 1, 2, 3, 4, 5, 6 are directed in respective order to the windings A, C, B, A, C, B, where every second pulse is negative and alternate pulses are positive. As seen in Figure 6, the frequency of the impulses is three times that of the applied frequency. The frequency in the load winding will therefore be 150 Hz if the line frequency is 50 Hz.
With a circuit arranged as in Figure 5, a three-phase voltage with the frequency f, yieIds a single-phase voltage with the frequency 3 x f or a ~lux in the magnetic circuit with the frequency 3 x f, Example 3 In the connection shown in Figs. 6a, 6b and 7 a three-phase voltage having the frequency f is trans-; ferred to a three-phase voltage having the frequency

2 x f. Firing angles for the thyristors are 120 degrees.
A, B and C are 3 SCR bridges with the AC-mains connected to 1 and 2 and the DC terminais, 3 and 4, con-nected to the windings. The AC-mains, R, S, and T are connected as shown in Figure 6a. Each primary winding of the phase transformer is split into two separate parts. Windings Xl and X2, Yl and Y2 al g . . . .

Il. L~ndhult:-2 (Revision) .ll~ S6 and Z2 are the two circuits in each phase X, Y, and Z. Wl, W2, and W3 are the secondary windings.
As illustrated in Figure 7, the A3 terminal of the SCR A is connected to the input terminal of Xl. The output terminal on Xl is connected to the output terminal of Y2. The input terminal of Y2 is connected to A4.
In the same fashion, the SCR bridge terminal B3 is connected to the input of terminal Yl whose out-put terminal is connected to the output of Z2 The output of Yl is connected to the output of Z2 whose input is connected to B4.
The SCR bridge C is connected in the same fashion to Zl which is connected to X2.
The diagram in Figure 8 shows how the three-phase secondary voltages are built up from pulses from the SCR bridges. The frequency of the secondary windings is twice that of the AC mains and the voltages are dis-placed 120 electrical degrees from each other.
It should be noticed that all the positive pulses come from Xl, Yl, and Zl and all the negative pulses come from X2, Y2, and Z2 The SCR bridges A, B and C can also be connected to the phase voltages as shown in Figure 9, while the connection of the DC terminals is the same as in Figure 7. The elementary diagram in Figure 8 remains the same except that the line voltage UR-S is changed into UR 0 Us_T into Us_O and UT_R T-0 Example 4 Conversion of a 3-phase system of the frequency f into a 2-phase system of the frequency 2 x p.
In figure 10, one transformer is connected via anti-parallel thyristors (or triacs) to the line voltages and the other transformer is connected in the same way but to the phase voltages. The reason for this arrangement is to obtain a higher frequency and also to get 90 degrees between the secondary voltages.
.-~ ~ ~I. Landhult-2 ~ 56 ( Revision) The firing angle should be approximately 120 de-grees. As shown in Figure 11, the pulses in Y are 30 de~rees ahead of the pulses in X, if 360 degrees is the period of the AC-mains. Since the frequency of the windings of the secondary side is three times higher, the angle between the voltages in Xs and Ys is in a motor application where the two transformers according to Fig. 10 are replaced by the stator of a two-phase motor where each winding phase has three parallel circuits Xl, X2, X3 and Yl, Y2, Y3 respectively geographically displaced 90 electrical degrees. According to electro machine theory, a rotating flux will occur which has asynchronous speed depending on the A.C. main8 frequency and the pole number of the stator winding.
lS This means that the motor obtains normal starting conditions like all three-phase motors.
Example 5 A motor for 9000 rpm (2 poles-50 Hz) and connected to all phase and line voltages may be made pursuant to this invention.
This motor is wound as a two-phase motor with the phases displaced 90 degrees. Each phase is split into three separate windings equally placed in the slot.
The windings in one phase are called Xl, X2, and X3 and the other Yl, Y2, and Y3.
The diagram in Figure 12 shows how the motor is wound.
By help of the principles according to the invention, a pair of anti-parallel thyristors are connected in each phase. The flux in each phase is then displaced 90 elec-trical degrees. The frequency of the flux is three times that of the AC-mains, which means that the flux will rotate with 9000 rpm at 50 Hz and 10800 rpm at 60 Hz.
Phase X is connected to the line voltages and phase Y is connected to the phase voltages.
The diagram of these connections is shown in Figure 13.
The thyristors are turned on at 120 degrees.
Figure 14 shows how the impulses in the phase X

. __.. . .. \ ~ .... . . . . . .

Il. L.u~ lt-2 . ~l~cv ision . , ~ ' and Y are achieved. It also shows that the frequency of the applied voltage is three times greater than the frequency of the power supply and that the impulses in X and Y are displaced 90 electrical degrees.
S Example 6 Symmetric load on a three-phase A.C. mains by a single-phase load.
It has been indicated in the patent application how a lower frequency can be obtained by sending current pulses through separate windings in the same phase.
~igure 15 shows how three pairs of anti-parallel thyristors (firing angle 120) connected to separate primary windings on a transformer, convert a three-phase voltage to a single-phase voltage. Figures 4 lS and S illustrate the connections for multiplying the frequency by 3, and the principle has been previously explained. In Figure 15, one winding is connected in the opposite way compared to Figure 4. This winding should have a smaller number of turns in order to give a stronger pulse. This will result in a voltage wave-form of the secondary side,that is closer to a sine wave.
Figure 16 illustrates this principle.
Example 7 General couplings with a possibility to chose or control the frequency (speed).
The principle of the patent i8, as previously described, to supply the winaings with a suitable number of phase and/or line voltages. It is required that the primary winding in ~he transformer or motor is split into a suitable number of separate windings. This number depends on the desired frequency.
The following describes some examples where it is possible to obtain different frequencies, both higher and lower than the frequency of the AC-mains. The multiplication factor K described previously, can be an integer for example 1, 2, 3 etc., or a fraction, for examples 3/2, 3f4, 3/5, 1/2 etc. The principle is explained wi~h two examples.

.

H. Landhult-2 (Revision) ~ 9~S6 _g One way of arranging the windings is shown in Figure 17. Six SCR bridges are connected to separate windings. Three of the SCR bridges should be con-nected so that they give a positive flux and the other three so that they give a negative flux. To make it easier, a single phase transformer has been described.
As an example, two different firing angles are used ~20 and 60 degrees. The table shows the firing order of the SCR bridges used to obtain the desired value of K.
................ ,.... ............ . ...... ~
..: . ; ~ Firin an le 120 de rees Pactor K
+ g g _ _ g :
: Firing order R T S R T S : 3 `
_ . n _ R + S R T S 3/2 _ _ + T S R T S 13/4 etc. R T S R T+ S 3/5 i, ' ' ' ', . .. .................. .. .. . ... . .. .. .. ..
. ........ ..... . . ......... . ..... ,. ..
~iring angle 60 degrees ~ K
l _ Firing order R S T R S+ T 3/2 20. _ n _ R 5 T R S T 3/4 etc R S T R S T

Example 8 Using SCR bridges and power transistors of a suitable kind, a continuous variable frequency can be obtained. The winding is split into two parts here - also. One gives the positive flux and the other the negative flux. The transistor is switched by a control circuit which gives the desired frequency.
It should be noted that a multiple phase system can be obtained by building up more phases.
TNT:mmg March 5, 1980

Claims

H. Landhult-2 (Revision) THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A method of controlling the operation of an electric machine having at least one primary winding including a plurality of separate primary winding parts to which electric current is supplied from A.C. mains to induce an alternating magnetic field in the electric machine, comprising the steps of selecting portions of the A.C.mains voltages;
applying the selected portions of the A.C. mains voltages to the primary winding parts at such intervals and in such a sequence that the magnetic field induced in the electric machine by the resultant electric current flow through the primary winding parts has a frequency differing by a pre-determined factor from that of the A.C. mains.

2. The method as defined in claim 1, wherein said apply-ing step includes interposing at least one switchable element which can be rendered conductive by the application of external control signals thereto between the A.C. mains and the respec-tive primary winding part; and said selecting step includes supplying the external control signals to the switchable elements of the primary winding parts at said intervals and in said sequence to render the switchable elements conductive to the resultant electric current flow during the occurrence of the selected portions of the A.C. mains voltages.

3. The method as defined in claim 1, wherein said select-ing step includes so selecting the A.C. mains voltage portions as to obtain a mean flux of zero for the magnetic field as considered over the respective period.

4. An arrangement for controlling the operation of an electric machine having at least one primary winding including a plurality of separate primary winding parts to which electric current is supplied from A.C. mains to induce an alternating magnetic field in the electric machine, comprising H. Landhult-2 (Revision) means for selecting portions of the A.C.
mains voltages; and means for applying the selected portions of the A.C. mains voltages to said primary winding parts at such intervals and in such a sequence that the magnetic field induced in the electric machine by the resultant electric current flow through said primary winding parts has a frequency differing by a predetermined factor from that of the A.C. mains.

5. The arrangement as defined in claim 4, wherein said applying means includes a plurality of switchable elements which can be rendered conductive by the application of external control signals thereto, at least one of said switchable elements being interposed between the A.C. mains and each respective of said primary winding parts; and wherein said selecting means includes means for supplying the external control signals to said switchable elements at said intervals and in said sequence to render the respective switchable elements conductive to the resultant electric current flow during the occurrence of the selected portions of the A.C. mains voltages.

6. The arrangement as defined in claim 5, wherein said switchable elements are semiconductor elements.

7. The arrangement as defined in claim 5, wherein said switchable elements are inverse parallel thyristors.

8. The arrangement as defined in claim 5, wherein said switching elements are triacs.