GB2047485A - Frequency multiplication - Google Patents

Abstract

A circuit arrangement whereby semiconductor elements are combined with single or multiple phase electric machines, for instance transformers, whereby to obtain an alternating magnetic 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 could be for instance 6, 5, 4, 3, 2, 1, 5, 1, 3/4, 3/5, 1/2 etc. depending on the circuit arrangement and what semiconductor elements (e.g. thyristors) and their firing angles are employed. Various possibilities are described. In the Fig. 4 example a transformer is connected to a three phase AC mains (R,S,T) via separate primary windings (A,B,C) and respective pairs of anti- parallel thyristors with a firing angle of 120 DEG . If the input line frequency is f the frequency in the single phase load winding (D) is 3f. <IMAGE>

Description

SPECIFICATION Frequency multiplication This invention relates to circuit arrangements comprising semiconductor elements combined with single or multiple phase wound electrical machines for frequency multiplication purposes.

By means of semiconductor elements, such as diodes, thyristors, triacs, transistors etc., there are a number of known circuit arranged ments for the control and supervision of current or voltage and for obtaining another frequency than that of the A.C. mains. The ability of these components to, subject to a control impulse, utilize the whole or a part of the period of the alternating current, is then used. Examples of this include whole wave rectifiers with controlled valves or triacs and antiparallel connected thyristors for controlling light or soft starters for motors. These circuit arrangements are described in various books and publications.

It is 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 depends on the current in the primary circuit and a factor comprising the number of turns in the primary winding divided by the number of turns in the secondary winding. The frequency on the secondary side is the same as that of the primary side.

It is also known that if a m,-phase A.C.

mains is connected to a m,-phase electric machine a MMF wave is obtained with rotates with the synchronous speed uS which is determined by the frequency of the connected frequency fand the pole number p of the winding according to the formula:

Depending on the type, the rotor or the machine can be forced to rotate with the same speed (synchronous) or with a load depending slip (asynchronous).

According to the present invention there is provided a circuit arrangement comprising semiconductor elements combined with a single or multiple phase wound electrical machine for frequency multiplication purposes, wherein a primary winding of the machine is divided into a predetermined number of parts, each of which is isolated from one another, which parts are via the semiconductor elements supplied with impulses from an A.C.

mains phase or A.C. mains voltages in use of the circuit in such a way that an alternating magnetic flux occurs in the magnetic circuit of the machine at a frequency which is changed by a factor K with regard to the A.C. mains, which flux may be utilized for a load connected to the secondary windings of the machine, and wherein the factor K is related to the ignition angles of the semiconductor elements.

Preferably the impulses from the A.C.

means are brought essentially directly without any C.C. connection. Preferably also disconnections of the semiconductor elements take place without forced self commutator circuits (self commutation).

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figures 1, 2 and 3 illustrate a first example of the invention; Figures 4 and 5 illustrate a second example; Figures 6, 7, 8 and 9 illustrate a third example; Figures 10 and 11 illustrate a fourth example; Figures 12, 13 and 14 illustrate a fifth example; Figures 15 and 16 illustrate a sixth example; Figures 17, 18 and 19 illustrate a seventh example, and Figure 20 illustrates an eighth example.

By connecting impulses from a system of semi-conductor elements connected to A.C.

mains, for example, to a respective primary circuit of a transformer, a voltage is obtained in the secondary circuit having a frequency which is decided 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 mulitplying with a factor K, up to 6, could be obtained in the secondary circuit.

By alotting a suitable number of such impulses to the same or different phases in a multiple phase system (transformer, motor) it is possible to build up a voltage of a 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 1 (one). This means that also fractions of the A.C. mains frequency could be obtained. If in an mphase 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 emphases are fed with suitably chosen impulses, a 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 impulses. It is then important that the impulses are brought in such a way that a symmetrical alternating flux occurs.The result is that the synchronous speed of the machine is K times that corresponding to pole number and A.C. mains frequency.

Possible values for the factor K, defined as the relationship between the secondary voltage frequency and the A.C. mains frequency for transformers, or the relationship between actual motor r.p.m. which could be obtained by means of the principles of the invention and the synchronous r.p.m. obtained by the pole number of the motor and the A.C. mains frequency, are 6,5,4,3,1,5,3/4,3/5,1/2 etc For the highest K-values the ignition angle must be chosen high (150 ) and the possibilities of obtaining multiple phased secondary voltages are limited.

The invention will now be further described with reference to various examples.

EXAMPLE 1.

A basic feature of the present 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 in another winding gives a flux of the same magnitude but in opposite directions.

Fig. 1 shows that the positive half-cycle gives a positive flux in winding A and the negative half-cycle gives a negative flux in winding B.

In Fig. 2 is shown how a current i+ flows in winding A from 0 to T/2 inducing the positive flux f + which is directed upwards.

In Fig. 3 is shown how the current i- flows in winding B from T/2 to T inducing the flow (p - which is directed downwards.

The average value of the flux 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 antiparallel thyristors with a firing angle of 1 20 degrees. This thyristor pair may be replaced by one triac. That means that the impulses 1 and 4 from the line voltage URNS 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 voltage UT~R are fed to winding C. As shown in Fig. 5 the impulses come in the order, 1,2,3,4,5,6 to the windings A,C,B,A,C,B, the pulses being alternately positive and negative. As seen in Fig. 5, the frequency of the impulses is three times that of the applied frequency. The frequency in the load winding will therefore be 1 50 Hz if the line frequency is 50 Hz.With a circuit arranged as in Fig. 4, a three-phase voltage with frequency f, gives a single-phase voltage with frequency 3for a flux in the magnetic circuit with frequency 3f.

EXAMPLE 3.

In the circuit arrangement shown in Figs. 6 and 7 a three phase voltage having frequency fis transferred to a three phase voltage having frequency 2f. Firing angles for the thyristors are 1 20 degrees A, B and C are 3 SCR bridges with the AC-mains connected to 1 and 2 and DC terminals, 3 and 4, connected to the windings. The AC-mains R,S, and T are connected as shown in Fig. 6. Each primary winding of the phase transformer is plit into two separate parts. Windings X, and X2, Y, and Y2 along with Z1 and Z2 are the two circuits in each phase X, Y, and Z. W1, W2, and W3 are the secondary windings.

As shown in Fig. 7, the A3 terminal of the SCR A is connected to the input terminal of X,. The output terminal of X1 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 Y whose output terminal is connected to the output of Z2 The output of Y1 is connected to the output of Z2 whose input is connected to B4.

The SCR bridge C is connected in the same fashion to Z1 which is connected to X2.

The diagram in Fig. 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 displaced 1 20 electrical degrees from each other.

It should be noticed that all the positive pulses come from X1, Y1, and Z1 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 in Fig. 9, while the connection of the DC terminals is the same as in Fig. 7. The elementary diagram in Fig. 8 remains the same except that the line voltage UR is changed into UR O, US-T into U,~,, and UT R into UT O EXAMPLE 4.

Conversion of a 3-phase system of frequency finto a 2-phase system of frequency 3f.

In Fig. 10 one transformer is connected via anti-parallel thyristors (or triacs) to the line voltages and another 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.

The firing angle should be approx. 1 20 degrees. As shown in Fig. 11, the pulses in Y are 30 degrees 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 3 x 30 degrees. The advantage of this connection is obvious 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 X1, X2, X3 and Y1, Y2, Y3 respectively geographically displaced 90 eiec- trical degrees. Accordingly to electro machine theory a rotating flux will occur which has a synchronous speed depending on the A.C.

mains frequency and the pole number of the stator winding. This means that the motor obtains normal starting conditions like all three phase motors.

EXAMPLE 5.

To obtain a motor for 9000 rpm (2 poles 50 Hz) which is connected to all phase and line voltages. 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 X1, X2, and X3 and the other Y1, Y2, and Y3.

The diagram in Fig. 1 2 shows how the motor is wound. In Fig. 1 2 X = Motor-phase X, 0 = Motor-phase Y, there is one slot per phase and pole, 2 poles, 2 phases, and b = beginning of phase, and s = end of phase.

A pair of anti-parallel thyristors are connected in each phase. The flux in each phase is then displaced 90 electrical 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 Fig. 13.

The thyristors are turned on at 1 20 degrees.

Fig. 14 shows how the impulses in the phase X 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.

EXAMPLE 6.

Symmetric load on a three phase A.C.

mains by a single phase load.

It has been indicated earlier how a lower frequency can be obtained by sending current pulses through separate windings in the same phase.

Fig. 1 5 shows how three pairs of antiparallel thyristors (firing angle 1 20') connected to separate primary windings on a transformer, convert a three phase voltage to a single phase voltage. Figs. 4 and 5 describe the connections and the principle of multiplying the frequency by 3. In Fig. 15, one winding is connected in the opposite way compared to Fig. 4. This winding should have a smaller number of turns in order to give a stronger pulse. This will result in a voltage waveform of the secondary side that is closer to a sine wave. (X2 has less turns than X, and X3)W Fig. 1 6 shows this principle.

EXAMPLE 7.

General couplings with a possibility to chose or control the frequency (speed).

The principle is, as previously described, to supply the windings with a suitable number of phase and/or line voltages. It is required that the primary winding in the 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 example 3/2, 3/4, 3/5, 1/2 etc. The principle is explained with two examples.

One way of arranging the windings is shown in Fig. 1 7. Six SCR bridges are connected to separate windings. Three of the SCR bridges should be connected 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 shown.

In the examples two different firing angles are used 1 20 and 60 degrees (Figs. 1 8 and 19). The tables show the firing order of the SCR bridges used to obtain the desired value of K.

EXAMPLE 8.

Using SCR bridges and/or power transistors of a suitable kind, a continuous variable frequency can be obtained. The winding is split into two parts here also (Fig. 20). 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 noticed that a multiple phase system can be obtained by building up more phases.

Therefore, a circuit arrangement with semiconductor elements connected with a transformer or an electric machine, which is provided with a special winding arrangement, according to the invention results in obtaining with a minimum of semiconductor elements and a specially wound machine, another frequency, another r.p.m. or another number of phases than those of the A.C. mains, in a cheap way.

Claims (7)

1. A circuit arrangement comprising semiconductor elements combined with a single or multiple phase wound electrical machine for frequency multiplication purposes, wherein a primary winding of the machine is divided into a predetermined number of parts, each of which is isolated from one another, which parts are via the semiconductor elements sup plied with impulses from an A.C mains phase or A.C. mains voltage in use of the circuit in such a way that an alternating magnetic flux occurs in the magnetic circuit of the machine at a frequency which is changed by a factor K with regard to the A.C. mains, which flux may be utilized for a load connected to the second ary'windings of the machine, and wherein the factor K is related to the ignition angles of the semiconductor elements.

2. A circuit arrangement as claimed in claim 1, wherein the machine is a transformer and the same or another phase number and the same or another frequency than the A.C.

mains phases and frequency, respectively, are obtained on the-secondary side of the transformer.

3. A circuit arrangement as claimed in claim 1, wherein the machine is a single phase electrical machine, preferably an asynchronous or synchronous machine, and wherein suitably chosen impulses from the A.C. mains and obtaned via the semiconductor elements are brought to isolated~from each other, parts of the single phase winding of said machines, thus generating a pulsating alternating magnetic flux having a frequency K times the frequency of the A.C. mains in the magnetic circuit of the machine, whereby the generated r.p.m. is K times the synchronous r.p.m. which is determined by the pole number of the machine and the frequency of the A.C. mains.

4. A circuit arrangement as claimed in claim 1, wherein the machine is a multiple phase electrical machine, preferably an asynchronous or synchronous machine, and wherein suitably chosen impulses from the A.C. mains obtained via the semiconductor elements, are brought to isolated from each other, parts of the windings of said machine, thus generating a pulsating alternating magnetic flux having a synchronous speed which is changed by the factor K with reference to the speed that is determined by the A.C.

mains frequency and the pole number of the machine, the starting conditions being similar to those of a conventional multiple phase machine.

5. A circuit arrangement as claimed in claim 1, wherein the impulses from the A.C.

mains are brought essentially directly without any C.C. connection.

6. A circuit arrangement as claimed in claim 1, wherein disconnections of the semiconductor elements take place without forced self commutator circuits (self commutation).

7. A circuit arrangement comprising semiconductor elements combined with a single or multiple phase wound electrical machine for frequency multiplication purposes substantially as herein described with reference to any one of Examples 1 to 8 and as illustrated in the respective accompanying drawings.