US2463540A - Frequency reducer - Google Patents

Description

March 8, 1949. H. M. HUGE FREQUENCY REDUCER Filed April 15, 1946 FIG. 2 28 w FIGS I N VEN TOR.

HENRY MARTIN HUGE BY 9% MW A RNEYS.

Patented Mal. 8, 1949 I 2,463,540 FREQUENCY REDUCER Henry Martin Huge, Lor

mesne assignments, to Lorain Products Corporatlon, Lorain, Ohio, a corporation of Ohio Application April 15, 1946,

ain, Ohio, assignor, by

Serial No. sears:

15 Claims. (Cl. 172-281) 7 pand the useful operating range of a magnetic frequency reducer.

A further object of my invention is to provide saturable magnetic coupling means in a frequency changer and to impress an asymmetrical current wave on the coupling means through a half-wave rectifier.

A still further object of my invention is to modify the ratio of forward to reverse current of the asymmetrical current wave to maintain suitable operating conditions under wide variations of supply voltage and load impedance.

An additional object of my invention is to introduce high order harmonics in the output voltage of a self-starting frequency changer without adversely affecting its self-starting characteristics.

Another object of this invention is to protect the rectifier producing the asymmetrical current wave for my frequency changer against excessive inverse voltage by shunting the rectifier with a non-linear resistive element.

Other objects and a better understanding of my .invention may be obtained from the following specification and claims together with the accompanying drawings, in which:

Figure 1 is a circuit diagram of a frequency changer made in accordance with my invention utilizing a three-legged saturable magnetic core having an input winding on its central member and output windings on its two outer members;

Figure 2 is a modification of the arrangement of Figure 1, with the input windings on the two outer core members and the output windings on the central core member; and

Figure 3 shows an embodiment of my invention utilizing two saturable cores instead of the threelegged core shown in Figures 1 and 2.

In general, my invention deals with a means for producing an output frequency which is a ierred from the input subharmonic of the input frequency. My frequency changer is particularly adapted to the production of an output frequency which is one-half the input frequency, but it is also applicable to the production of other even subharmonics of the input frequency. My invention makes use of saturable magnetic coupling means for coupling the input and output branches of the frequency changer in conjugate relationship, The circuits are said to be in coniugate relationship because the application of voltage to one branch produces practically no voltage in the other branch. This relationship is established by a substantial cancellation of voltages or fluxes in the coupling means. The coupling means includes two saturable magnetic fiux paths, and the cancellation of the voltages or fluxes is accomplished only when the degree of saturation is the same in both flux paths, since only under this condition are the permeabilities of the two paths equal.

If voltage is applied to the input branch of the conjugate circuit, while none is applied to the output branch, the substantially balanced condition is established and no appreciable power is transto the output branch. If now a small current is impressed on the output branch this current will, at any instant when current is flowing in the input branch, increase the saturation of one of the fiux paths and reduce the saturation of the other path. An unbalanced condition of saturation is therefore produced by the disturbance in the output branch, and the voltages or fluxes no longer cancel each other completely. A transfer of power thereby occurs from the input to the output branch upon the stimulus of the disturbance in the output branch. If the output branch includes an energy storage device, such as a capacitor, a regenerative condition may be established and an extremely small disturbance in the output branch will produce a transfer of power to increase the amplitude of the disturbance until oscillations are built up. It is not necessary to actively introduce the disturbance in the output branch, since the conjugate circuits will never be in absolutely perfect balance and some disturbance will normally be present in the output branch even though no source of energy is included therein.

The input branch of my frequency changer includes a rectifier for supplying a biasing current to the magnetic coupling means. The output branch includes a capacitor. When the input branch is energized by an alternating current source, the frequency changer produces subharmonic oscillations excited by the capacitor in the aeeasao This action is similar to that described in my prior U. S. patent applications, Serial No; 485,832, filed May 6, i943 and Serial No. 605,969, filed July 19, 1945. The oscillations are termed self-excited because it is the presence of the oscillations which unbalances the saturation of the magnetic coupling means and provides for the transfer of power from one to the other of the conjugate circuits.

As previously mentioned, the oscillations most readily produced are of one-half the energizing frequency, but it is also possible to produce oscillations of one-fourth theenergizing frequency and of other even subharmonics of the energizing frequency.

In prior self-starting subharmonic generators or frequency reducers it has been necessary to protect the generator against overloads, as by providing a load-limiting impedance. This has in general been necessary because the overloading of the generator caused the oscillations to become intermittent or to fluctuate intermittently between a high level and a low level of output voltage. In the prior art, if the input current or the biasing current was increased to the point where overloads no longer produced intermittent oscillations, a point was reached where the oscillations would no longer be self-starting if they were stopped by overloads. This action was ordinarily associated with an excessive input current or biasing current which reduced the impedance of the saturable magnetic coupling means and thereby prevented the oscillations from restarting- According to this invention, these disadvantages are overcome, and, not only is the need for overload protection eliminated, but the operating range of the subharmonic generator is output branch.

of the operating conditions and to self-start the oscillations under equally difficult conditions.

The operation of my invention will be explained by referring to the examples shown in the accompanying drawings.

The circuit of Figure l is a preferred embodiment of my invention and utilizes a three-legged saturable magnetic core structure is having an input winding I4 on its central member and output windings l5 and IS on its two outer members. The input winding I4 is energized from the alternating current source It! through the half-wave rectifier II and the resistor l2.

The output windings I5 and 56 are substantially equal and are connected in series with each other,'polarlzed to substantially cancel voltages of the frequency of source Ill induced in the output branch from input winding l4 so the input and output branches are conjugate. The output circuit is completed through capacitor 20 and saturable inductance 2 I.

In some cases it may be desirable to unbalance the coupling means slightly to aid in starting of the oscillations as is done in my U. S. patent application Serial No. 605,969. Such circuits, although slightly unbalanced, will nevertheless be herein referred to as being in conjugate relationship.

When the input branch is energized as shown in Figure 1, the output circuit through capacitor 20 oscillates at a frequency which is one-half the frequency of source it. The oscillations are self-excited, since there is substantially no coupling from the input to the output circuit except that which results from the variations in saturation produced by the secondary or output current.

The self-excited oscillations are self-starting and require no shock or starting transient. Furthermore, I am able to produce frequency changers which may be heavily overloaded without stopping the oscillations, but merely reducing their amplitude.

In the circuit of Figure 1 the load is supplied from taps l1 and it; on output windings l5 and 86 respectively, so that the load may be supplied a lower voltage than that which appears across capacitor 20. If the higher load voltage is required, the taps ill and 88 may be omitted and the load connected across the entire windings i5 and it.

The half-wave rectifier ii in series with primary windings M provides direct current for biasing the saturable core. l9. Rectifier H has a further action in that it blocks one-half of the alternating input current cycle if the peak value of the alternating current wave exceeds the direct current in the circuit. The input winding it thus has an asymmetrical current wave impressed on it.

I prefer to use a dry-disc rectifier stack for the rectifier ll, not only to minimize the losses in the circuit, but also because its reverse resistance characteristic provides a regulating action as utilized in my invention.

l have found that the conditions which, as previously mentioned, may prevent the oscillations from starting. are associated with the rectifying ratio of the rectifier ii, the rectifying ratio being the effective reverse resistance divided by the effective forward resistance. In particular when the rectifying ratio is very high, optimum results may not be obtained. In this case, I have found that excellent results may be obtained by providing a dry-disc rectifier which will operate with a lower rectifying ratio. This is accomplished by operating the rectifier at an abnormally high reverse voltage to reduce its reverse resistance, or by inserting resistor l2 to increase the forward resistance of the input branch. Resistor l2 also tends to increase the reverse voltage across the rectifier, thus producing a double effect.

As an example of the effectiveness of resistor 62, I have found that the extent of the useful input voltage range of a typical model of my frequency changer is more than doubled by the insertion of resistor l2 having a resistance approximately equal to that of the input winding I4.

The asymmetrical current wave impressed on winding M is limited by the impedance of the winding. The

rent, particularly the direct current, which flows through it. The rectifier ll thus produces a regenerative action and relatively small changes in flow, the impedance of the winding has a tendency to fall below its optimum value. By controlling the ratio of forward to reverse current as is done by my invention, optimum impedance may be automatically maintained in spite of wide variations in the voltage of source l0.

The capacitor I3 is highly effective in modifying the ratio of forward to reverse current of the asymmetrical current wave through winding l4. Because the capacitor I2 is in parallel with the input winding l4, it supplies a portion of the exciting current for winding H. The current wave through winding I4 is asymmetrical, so capacitor l2 supplies a negligible proportion of the forward half cycle of the current wave, but, since the reverse half cycle is so much smaller, the reverse current supplied by the capacitor may represent a considerable portion of the total reverse current. Capacitor I; therefore modifies the ratio of forward to reverse current in winding l4 and keeps the impedance of the winding from falling to an undesirably low level.

The action of capacitor [3 is most pronounced when the output circuit is not oscillating. Under this condition, the addition of capacitor i3 can reduce the biasing current through winding I4 considerably and insure the starting of the oscillations without appreciably reducing the input current when the output circuit is supplying load. This is true because when the circuit is oscillating the impedance of winding I4 is chiefly determined by reflected impedance from the output circuit, and the effect of capacitor I3 is masked. Capacitor l3 therefore has the effect of reducing the biasing current when a low value of biasing current is desired, without greatly reducing it under load conditions which require more biasing current.

Like resistor l2, capacitor i3 greatly extends the useful operating range of the frequency changer. I have found that it is not always necessary to include both resistor 12 and capacitor l3 in order to obtain satisfactory operation, as will be more fully explained in connection with Figure 2.

With my invention, I am able to maintain stability of operation without the use of a protective or load-limiting impedance. When the frequency changer is overloaded, the output voltage falls steadily as the load impedance is diminished, there being no unstable fluctuations between two values of output voltage. If the load is short-circuited, the subharmonic oscillations stop, but as the load resistance'is increased, the oscillations restart at a low value of load resistance, and increase in amplitude as the load resistance is increased to a normal value.

The elimination of a load-limiting impedance not only results in a saving of material but also improves the output voltage regulation of the frequency changer.

Saturable inductance 2! in series with capacitor 20 is provided in order to introduce high order harmonics in the load voltage. These harmonics having an audible frequency are often required when the frequency changer is used to supply telephone ringing voltage, in which case the audible frequencies supply the reverting ringing tone.

Capacitor 22 in parallel with saturable inductance 2i serves to accentuate the desired audible frequencies by increasing the circuit impedance at those frequencies.

I prefer to construct the saturable inductance 2| with a small air gap in its magnetic core. I have found that if saturable inductance 2| has a closed magnetic core, it may prevent the selfstarting of the oscillations. By providing the saturable core with a small air gap, as by buttjoint stacking of the laminations, I am able to maintain the necessary conditions for self-startings in Figure 2 may content is required, the

ing oscillations and still provide a high'audible harmonic content. If a relatively low harmonic inductance 2| may be small. In this case it may be constructed with a closed magnetic core without disturbing the starting of the oscillations.

When the required-frequency and amplitude limits on the audible components of the output voltage are not too narrow, the capacitor 22 may be omitted as is done in Figure 2. If the audible components are not required, both inductance 2| and capacitor 22 may be omitted.

In the circuit of Figure 2, the positions of the input and output windings on the saturable core l9 are reversed from the positions shown in ,Figure 1.

Substantially equal input windings 23 and 24 are on the two outer members of core I'D. They are connected in series, and are polarized to produce substantially cancelling voltages in output winding 25, which is on the central member of core IS. The fundamental properties and method of operation of this arrangement are substantially the same as those of Figure 1. The conjugate relationship between input and output branches in Figure 2, as in Figure 1, produces a condition in which a capacitive output circuit may produce self-excited oscillations. The fiow of secondary current affects the different members of the saturable core unequally, as a result of the primary or input energization. Hence, the flow of secondary current provides coupling between the primary and secondary circuits to produce selfexcited oscillations.

In Figure 2 the load is supplied across a separate output winding 26 to insulate the load from the circuit of capacitor 20. It will be seen that both output winding 25 and output winding 26 are in the output branch of the circuit and are in conjugate relationship to the input branch which includes windings 23 and 24, rectifier H and source III. The insulated lead type of windbe applied to Figures 1 and 3, if an insulated load circuit is required.

Capacitor l3 in Figure 2, connected in parallel with the input windings, modifies the ratio of forward to reverse current of the asymmetrical current wave impressed on the input windings as in Figure 1.

' The rectifier II is shunted by the resistance element 21 in Figure 2. In the operation of my invention, the ratio of forward to reverse current is modified to meet the operating requirements of the oscillating circuit. As mentioned in connection with Figure l, the reverse resistance characteristic of a dry-disc rectifier may be utilized for this purpose, but I have found that this frequently requires that the rectifier be operated at an inverse voltage in excess of its normal inverse voltage. Thus by the use of a drydisc rectifier operating as a half wave rectifier and having the required characteristics, the required ratio of forward to reverse current may be maintained in the circuit of Figure 2 without the use of either capacitor l3 or element 21 and in Figure 1 without capacitor l2 or resistor H. For some types of dry-disc rectifier and for thermionic rectifiers, however, this type of operation might produce damage to the rectifier, resulting from the passage of the reverse current. In such cases, the resistive element 21 is included to provide a path for the reverse current.

The element 21 is preferably a non-linear element, having a lower resistance at high voltage than at low voltage. Thus element 21 may be made of a material such as "thyrite or it may comprise a gaseous discharge device.

I have found that when the proper ratio of I forward to reverse current is maintained, the peak inverse voltage across the rectifier I! is generally less than the root mean square value of the voltage of source Ill. The reduction in reverse voltage is brought about by the reverse resistance characteristic of the rectifier Ii or the shunting element 21.

The saturable three-legged core E8 of Figures 1 and 2 is replaced by the two saturable cores 28 and 29 in Figure 3. These cores are preferably substantially alike and have substantially equal primary windings 30 and 3t and substantially equal secondary windings 32 and 33 wound upon them. The primary windings 3t and ii are connected in series to the alternating current source l through the rectifier if] and resistor it. The secondary windings 32 and 33 areconnected in series, polarized to substantially cancel voltage from source I'B in the secondary circuit to establish a conjugate relationship between the primary and secondary circuits. The secondary windings are connected to capacitor it as in Figures l and 2, but with the harmonic producing inductance 2| omitted in Figure 3. The load is supplied in parallel with capacitor 20.

The essential features of the arrangement of Figure 3 are the same as those of Figures 1 and 2. The primary and secondary branches or the circuit are coupled in conjugate relationship by the saturable magnetic coupling means which in Figure 3 comprises the saturable cores 2B and 29. The saturable coupling means is energized with an asymmetrical input current wave through the rectifier ii. The capacitor in the secondary branch excites the subharmonic oscillations as previously described.

It will be apparent to those skilled in the art that other forms of saturable magnetic coupling means having a conjugate relationship between input and output branches may be applied to the practice of my invention. Several such combinations are shown and described in my prior patent application Serial No. 485,832 filed May 6, 1943.

Although I have described my invention with a certain degree of particularity, it is to be un-- derstood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the spirit and scope of the invention as hereinafter claimed.

I claim as my invention:

1. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, a halfwave dry-disc rectifier serially connected in said input branch, and means for energizing said input branch from an alternating current source.

2. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for ex citing subharmonic oscillations therein, a halfwave dry-disc rectifier serially connected in said input branch, a resistor connected in series with said rectifier for modifying the ratio of forward to reverse current in said input branch, and

means for energizing saidinput branch from an alternating current source.

3. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a first capacitor connected in a closed circuit in said output. branch for exciting subharmonic oscillations therein, a second capacitor connected in said input branch in parallel with said magnetic coupling means, a half-wave dry-disc rectifier serially connected in said input branch, first circuit means in said input branch for energizing said coupling means and said second capacitor from an alternating current source through said rectifier, and second circuit means in said output branch for supplying the subharmonic frequency to a load.

4. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, a halfwave dry-disc rectifier serially connected in said input branch, means for energizing said input branch from an alternating current source, said rectifier having a non-linear reverse resistance characteristic whereby reverse current in said input branch produces across said rectifier a peak voltage less than the root mean square voltage of said source.

5. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, means for energizing said input branch from an alternating current source, asymmetrical resistance means, and circuit means connecting said resistance means in said input branch in series with said coupling means for impressing on said coupling means an asymmetrical current wave.

6. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, means for energizing said input branch from an alternating current source, a half-wave rectifier, circuit means connecting said rectifier in said input branch in series with said coupling means for impressing an asymmetrical current wave on said coupling means, and a resistor connected in series with said rectifier for modifying the ratio of forward to reverse current in said input branch.

7. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillationstherein, means for energizing said input branch from an alternating current source, a half-wave rectifier, circuit means connecting said rectifier in said input branch in series with said coupling means for impressing an asymmetrical current wave on said coupling means, and means for modifying the ratio of forward to reverse current of said asymmetrical current wave.

8. A frequency changer comprising input and output branches, saturable magnetic coupling aaeauo means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, means for energizing said input branch from an alternating current source, a half-wave rectifier, circuit means connecting said rectifier in said input branch in series with said coupling means for impressing an asymmetrical current wave on said coupling means, and non-linear resistance means connected in parallel with said rectifier for modifying the ratio of forward to reverse current of said asymmetrical current wave.

9. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, a half-wave rectifier serially connected in said input branch, means for energizing said input branch from an alternating current source, load circuit means in said output branch, and an inductance connected in series with said capacitor for providing harmonics in said load circuit means, said inductance having a saturable magnetic core with a nonmagnetic gap therein.

10. In combination, a saturable magnetic core having first second, and third members with first, second, and third windings respectively thereon, said first and third windings being connected in series opposition with respect to said second winding, a first capacitor connected in a closed circuit with said first and third windings, a halfwave rectifier, means for energizing said second winding from an alternating current source through said rectifier, and a second capacitor substantially in parallel with said second winding, said first capacitor exciting oscillations of a frequency equal to one-half the frequency of said source when said second winding is energized from said source, said second capacitor cooperating with said rectifier in controlling the magnetizing current impressed on said second winding.

11. A frequency changer comprising in combination, a saturable magnetic core having first, second and third members, with first, second and third windings respectively thereon, said first and third windings being connected in series opposition with respect to said second winding, a capacitor connected in a closed circuit with said first and third windings for exciting subharmonic oscillations therein, a half-wave rectifier, a resistor connected in series with said rectifier, meansfor energizing said second winding from an alternating current source through said rectifier and resistor, and means for supplying subharmonic voltage to a load, said resistor and said rectifier cooperating to control the magnetizing current impressed on said second winding.

12. A frequency changer comprising in combination, a three-legged saturable magnetic core, an input winding on the central member of said core, two output windings, one on each outer member of said core, said output windings being connected in series, a capacitor, an output circuit including said output windings and said capacitor, a rectifier, means for impressing on said input winding an asymmetrical alternating current wave through said rectifier, and means for modifying the ratio of forward to reverse current of said asymmetrical current wave, said input and output circuits being conjugate, said capacitor being adapted to excite oscillations in said output circuit of a frequency which is a subharmonic of the frequency of said alternating current wave.

13. A frequency changer comprising in combination, a three-legged saturable magnetic core, two input windings, one on each outer member of said core, an output winding on the central member of said core, said input windings being connected in series and polarized to produce opposing fiuxes in said central member, a capacitor connected across said output winding, 9. rectifier, means for impressing on said input windings an asy metrical alternating current wave through said rectifier, and means for modifying the ratio of forward to reverse current of said asymmetrical current wave, said capacitor being adapted to excite oscillations in said output circuit of a frequency which is a subharmonic of the frequency of said alternating current wave.

14. A frequency changer comprising two substantially equal saturable transformers having primary and secondary windings, a capacitor, a rectifier, an output circuit including said secondary windings in series in a closed circuit with said capacitor, an input circuit including said primary windings and said rectifier in series, said input and output circuits being condugate, means for impressing on said primary windings an asymmetrical alternating current wave through said rectifier, and means for modifying the ratio of the forward to reverse current of said asymmetrical current wave, said capacitor being adapted to excite subharmonic oscillations in said output circuit.

15. A frequency changer comprising input and output branches, saturable magnetic coupling means coupling said input and output branches in conjugate relationship, a first capacitor connected in a closed circuit in said output branch for exciting subharmonic oscillations therein, a second capacitor connected in said input branch in parallel with said magnetic coupling means, a rectifier serially connected in said input branch, and means for energizing said coupling means and said second capacitor from an alternating source through said rectifier.

HENRY MARTIN HUGE.

No references cited.

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