US 3239750 A Description (OCR text may contain errors) March 8, 1966 P. WEBER 3,239,750 MAGNETIC VOLTAGE STABILIZER Filed Oct. 4, 1962 2 Sheets-Sheet l 12 ,1 j, ww c O'\1.Q.U.LULUIJ 1 llllllllllllll & % Canr/an/ March 8, 1966 P. WEBER MAGNETIC VOLTAGE STABILIZER 2 Sheets-Sheet 2 Filed Oct. 4, 1962 United States Patent 3,239,750 MAGNETIC VOLTAGE STABILIZER Paul Weber, Freiburg im Breisgau, Germany, assignor t0 Fritz Hellige &'Co., G.m.b.H., Freiburg, Germany Filed Oct. 4, 1962, Ser. No. 228,793 Claims priority, application Germany, Oct. 5, 1961, 2 Claims. 61. 323-61) tional to employ a line voltage stabilizer to supply a' substantially constant operating voltage to the equipment. One class of devices of this type frequently used and well known in the art are the so-called magnetic voltage'stabilizers, which depend on the properties of a saturable reactor or transformer to achieve the desired regulating response. Generally, such arrangements are capable of providing a stabilized output voltage in the face of line voltage fluctuations of i%. Where operation of a particular regulator at a number of different nominal line voltages is anticipated, taps or switches are usually included to adapt the circuit to different supply voltages. It is, however, clear that such arrangements add to the cost of the unit, and actually do not extendthe range of voltage regulation once a particular nominal voltage is selected. In order to avoid the use of switches and taps and provide stabilization in the presence of extreme line variations, such as, for example, from 90 to 240 volts, magnetic wide range stabilizers have been developed. Such devices permit operation from either 110 or 220 volt sources without switching as an additional advantage. The knownvarieties of wide range stabilizers are, however,-cumbersome and heavy. In-addition, the apparent power input increases approximately as the square of the line voltage, so that the power factor decreases to a value of less than 0.5 in the vicinity of the upper regulation limit. While the poor power factor may be compensated by connecting an additional capacitor across the input, the device itself still draws heavy currents at higher input voltages. These heavy currents introduce additional significant losses which may result in overheating, unless a corresponding significant increase in the size of the regulator elements has been made. It is, therefore, an object of the present invention to provide a magnetic voltage stabilizer for producinga constant output voltage over a wide range of applied line voltages. A further object of the present invention is to provide amagnetic voltage regulator which operates at substantially unity power factor and high efliciency while providing a stabilized output voltage over a wide range of applied line voltage fluctuations. Yet another object of the present invention is to provide a magnetic voltage regulator which is comparatively light and compact, and easily fabricated from relatively inexpensive, non-critical components. The novel features which are believed to'be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description considered in connection with the accompanying drawings in which an embodiment of the "ice invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not intended as a definition of the limits of the invention. FIG. 1 is a schematic diagram of an embodiment of a magnetic voltage stabilizer according to the present invention; FIG. 2 is a vector diagram of currents and voltages in a voltage stabilizer typical of the prior art; and FIG. 3 is a vector diagram of currents and voltages in a voltage stabilizer according to the embodiment of the invention shown in FIG. 1. Referring now to FIG. 1, there is shown a schematic diagram of an embodiment of a magnetic voltage stabilizer according to the present invention; As shown in the figure, the embodiment comprises a pair of input terminals 1, 2 for applying line voltage through a series choke 3 to a shunt circuit generally designated 12. The shunt circuit includes the primary 5 of a transformer generally designated 4, across which the seriescombination of a capacitor 9 and choke 10 are connected. The secondary 6 of transformer 4 is connected to a pair of output terminals 7,, 8, from which the stabilized output voltage may be supplied to a load 11. More particularly, according to the present invention, series choke 3 is a saturable reactor, while transformer 4 is a saturable transformer. Capacitor 9 and choke 10 form a series circuit which'is tuned to the third harmonic of the line frequency, and operate to improve the output waveshape of the stabilizer by removing third harmonic distortion introduced by'the non-linear magnetic elements of the circuit. The improved voltage waveshape is accompanied by a significant decrease in copper losses in' the inductive elements of the circuit. The tuned series circuit also suppresses self-oscillations or jump phenomena which might otherwise occur. At line frequency, the series combination of capacitor 9 and choke 10 appears as a capacitor which should be proportioned to resonate with transformer 4 in its satu Operation of the magnetic voltage stabilizer of the present invention and its improved characteristics may be most readily illustrated by a direct comparison of a vector diagram of the currents and voltages in a voltage stabilizer typical of the prior art with a similar vector diagramof' a voltage stabilizer according to the present invention. Referring now to FIG. 2, there is shown a vector diagram of currents and voltages in a voltage stabilizer typical of the prior art, thelengthsof each vector'repre'-' senting'amplitude, while the directions or angles indicate the mutual phase relationship of the various voltage andcurrents depicted. Such a prior art regulator, generally known as a similar to that of the present invention, as shown in FIG. 1, except that series choke 3 is a conventional, nonsaturable reactor, andshunt resonant circuit 12 is tuned to resonate at the supply frequency when the mean or nominal value of line voltage is applied to the regulator. In order to simplify the analysis and comparison, certain assumptions will be made, and certain magnitudes will be considered of negligible value. In practice, such assumptions have been found to be consistent with actual performance to an acceptable approximation. Thus, series choke 3, transformer 4 and capacitor 9 are regardedas lossless; transformer 4 has a turns'ratio and ierro-resonant regulator, has a structure coupling factor of unity, load 11 has a unity power factor, and choke 10 is regarded as short circuited. It has also been assumed that saturable transformer 4 is operated in its saturated range, and that the voltage V across the transformer is constant over the range of currents under consideration by virtue of the well known regulating properties of such a transformer, although such ideal performance cannot be achieved in practice. Under such assumptions, the amplitude of the real current I flowing in transformer 4, and the amplitude of the current I through capacitor 9 will also remain constant. The current 1,, leads the voltage V, by 90". Accordingly, the following vectorial equations may be written: V V,+V,, I I +I in L+ r+ c I =constant (4) I =constant (5 where V is the line supply voltage, V is the voltage drop across choke 3, I is the vector sum of the real current I and reactive current 1;, through transformer 4, 1 is the input current, and the remaining symbols have the significance heretofore noted. The input current I through series choke 3 is the vectorial sum of I I, and I Since the load current I is constant, the geometric locus of supply current 1 and transformer current I for various applied voltages V may be represented by line A-A' which is perpendicular to the vector 1,. Since all correlated current and voltage triangles are mutually similar (under the assumption that circuit values are constant), the line B-B similarly represents the geometric locus of supply voltage V for various values of V Line B-B is rotated 90 with respect to line AA', since the voltage V across series choke 3 has a constant ratio to current I and leads the current by 90, so that its vector must always be perpendicular to current vector 1 It has also been assumed that shunt circuit 12 resonates at a nominal supply voltage V and the related vectors are also designated by the subindex 0. Similarly, vectors corresponding to the minimum input supply voltage within the regulating range are designated by the subindex 1, while vectors corresponding to the maximum input supply voltage within the regulating range are designated by the subindex 2. At nominal input voltage, with shunt circuit 12 resonating, I =I and I is in phase with Vpo! i.e., the directions of the vetcors coincide. The impedance of shunt circuit 12 is real, and I is equal to I The voltage V across series choke 3 leads the current l through it by 90. As the supply voltage decreases, I decreases, and, in accordance with Equation 3, 1 increases in magnitude and shifts phase in a positive direction. Similarly, as the supply voltage increases, I increases, and 1 increases in magnitude and shifts in a negative direction. It will readily be seen from the diagram that the input current is a minimum at nominal line voltage, and increases with either increased or decreased line voltage. It will also be seen that the supply voltage and current, represented by vectors V and 11 respectively, are almost in phase when the supply voltage is at its minimum and shunt circuit 12 and series choke 3 move toward series resonance. Under these conditions, the power factor of the stabilizer approaches unity. However, when the supply voltage rises to its maximum V the power factor becomes substantially smaller and inductive, with li g substantially lagging V The different conditions prevailing for the lower and upper range of fluctuations cause quite differeh t power losses within the stabilizer depending upon whether the supply voltage deviates in one or the other direction from the nominal value. Since the elements of the circuit must in any event be designed to operate under the most unfavorable conditions, conventional stabilizers are almost of necessity large and bulky. In accordance with the present invention, the above and other disadvantages of the prior art stabilizer may be overcome by utilizing a saturable reactor as series choke 3, and adjusting shunt circuit 12 to resonate with transformer 5 in its saturated state in the upper range of input voltage fluctuations. Series choke 3, on the other hand, should be selected to be unsaturated when shunt circuit 12 is in resonance, and to saturate at a level of line input voltage somewhat less than that at which shunt circuit resonance occurs with maximum load connected. Referring now to FIG. 3, there is shown a vector diagram of current and voltages in a voltage stabilizer according to the embodiment of the invention shown in FIG. 1. The vector diagram is similar to FIG. 2, and may be derived therefrom by appropriate scale and other changes. Shunt resonance conditions represented by the fact that V and V, are mutually perpendicular, occur at a comparatively high level input supply voltage V which, for purposes of illustration, has been taken to be a value of supply voltage which would produce a primary voltage V which is 1.6 times its value as shown in FIG. 2. In order to produce the same secondary voltage, the number of turns of primary 5 must be increased, but the value of capacitor 9 may be reduced. The inductance of series choke 3 should be significantly higher than in prior art designs, and the choke should be selected so as to operate slightly below saturation when the shunt circuit in resonance, and to have a substantially constant voltage drop despite current changes when in a state of saturation. A significant advantage resulting from these conditions is that transformer 4 need not operate at its upper saturation level, and accordingly, excessive magnetizing currents with consequent high copper losses within primary 5 may be avoided. In order to permit a clear comparison of FIGS. 2 and 3, all currents have been referred to the secondary circuit assuming the same load conditions and output voltage. Since a transformer ratio of 1.6:1 has been assumed, all of the primary currents I I I and I have been multiplied by the factor 1.6, and are now shown and designated as primed letters. It can easily be seen from FIG. 3 that the maximum primary current 1 which occurs at maximum supply voltage V is about 25% smaller than the corresponding current 1 of FIG. 2, and therefore an approximately 45% reduction in power losses is achieved. When the supply voltage decreases from its upper limit V the current I through series choke 3 increases, and the choke becomes saturated. Under these conditions, the voltage V across the choke becomes substantially constant, and the inductance of choke 3 decreases, since, at saturation, it is a reciprocal function of the current I,,,'. Accordingly, current I increases with decreasing line voltage V and reaches its maximum value I with minimum supply voltage V As a result of the non-linear characteristic of series choke 3, the geometric locus BBB" of supply voltage vectors V is a straight line only in the vicinity of V and below this value it becomes the arc of a circle centered at V and having a radius equal to the substantially constant voltage across the series choke when satu rated. Accordingly, limit vectors of choke voltage V and V as well as input currents I and 1 and primary currents 1 and 1 form smaller phase angles with respect to each other as compared to FIG. 2. Current 1 will also be seen to be smaller than its value in FIG. 2. As a further result, the range of saturation of the iron core of the transformer is significantly reduced, as may be seen by comparing current vectors 1 and 1 of FIG. 3 with the corresponding vectors of FIG. 2. Accordingly, V will in practice have a smaller change of voltage over the stabilizing range, and enhanced stabilization will be achieved. Alternatively, if the maximum saturation of the transformer core is not to be reduced in order to reduce cooper losses, the maximum reactive current I of FIG. 2 may be maintained as a design parameter. Under these conditions, transformer 5 may be made significantly smaller, or, with the same size transformer, a correspondingly higher level of power may be transferred and stabilized. As a further possibility under such conditions, the range of stabilization may be significantly extended without changing the size of the transformer. Since the input current I through series choke 3 is a minimum when the supply voltage approaches the upper regulating limit, losses in the choke will be small when transformer losses are at a maximum. The converse is also true, and the total heat losses in the stabilizer will always be less than those of the prior art, where, as shown in FIG. 2, for example, the maximum of loss for both series choke 3 and transformer 4 occur simultaneously at high level supply voltages. Advantage may be taken of this fact to reduce the cooling arrangements for the stabilizer. Ordinarily, series choke 3 will include an air gap in its core, but it is a particular feature of the present invention that the width of the air gap is comparatively noncritical. Only voltage V associated with the unsaturated state is a function of the air gap width, but voltage V corresponding to a state of saturation in the choke is comparatively unaffected by changes in air gap width which merely results in a change in the degree of saturation of choke 3 but has little effect on the reluctance of its magnetic circuit, since a change in reluctance of the air gap produces an equivalent reluctance change in the iron because of its saturation characteristic. In contrast, in the stabilizer of FIG. 2, fluctuations in line voltage V within the lower range result in significant, inverse changes in choke voltage V Changes in the air gap width can accordingly have an appreciable effect on the range of stabilization possible. The insignificant effect of variations of air gap width on the performance of the stabilizer of the present invention, on the other hand, considerably simplifies manufacture of the stabilizer. In a stabilizer according to the present invention, capacitor 9 handles a greater apparent power than in the prior art design, and if advantage is taken of the lower transformer saturation levels possible, less distortion of waveform will occur in the output waveshape. In the stabilizer of the present invention, the power factor presented to the line is always close to 1 over the full regulating range. It varies from capacitive values close to 1 With low line voltages, to inductive values close to 1 with high line voltages. This relationship is shown in FIG. 3 by the relatively small phase angle between corresponding values of V and 1 and results in enhanced efficiency for the stabilizer. While variations in load have not been considered in the present analysis, the stabilizer of the present invention operates independently from the load within predetermined limits. If desired, well known circuits may be included to compensate further for load fluctuations or variations. Although transformer 4 has been described as a saturable transformer, it will be appreciated that the transformer may be replaced by a saturable reactor, where voltage or current transformation is not required. On the other hand, advantage may be taken of the presence of the transformer to provide output voltages different from the line voltage where desired or required. What is claimed as new is: 1. A magnetic voltage stabilizer comprising: a reactor having a linear and a nonlinear operating region; a non-linear saturable transformer having a primary and a secondary winding; means for applying input voltage to the primary winding of said saturable transformer through said series reactor; a capacitor connected in shunt with the primary winding of said saturable transformer, said reactor, transformer and capacitor being selected to respond to applied input voltages to cause said saturable transformer to operate in its linear region at the maximum range of input voltages, and to cause said reactor to operate in its non-linear region in response to input voltages less than the maximum producing linear operation. 2. A voltage stabilizer for providing a substantially constant output voltage in response to widely varying applied input voltages comprising: a first saturable reactor; a parallel resonant circuit including a second saturable reactor and a capacitor; means for applying line voltage to said parallel resonant circuit through said first saturable reactor, said parallel resonant circuit being adjusted to resonance at a value of applied input voltage substantially cor responding to the upper limit of input voltage for which a stabilized output voltage is achieved, and said first saturable reactor being adjusted to saturate in response to applied input voltages less than the upper limit of input voltage with the stabilizer under load; and means for deriving an output voltage from said second saturable reactor. References Cited by the Examiner UNITED STATES PATENTS 1,948,704 2/1934 Fischer 32376 2,088,621 8/1937 Stocker 323--76 2,436,925 3/1948 Haug et al. 323-60 2,801,383 7/1957 Comins et al. 323-66 2,814,738 11/1957 Freeman et a1 323-56 X 2,858,455 10/1958 Trabut 323--56 X 2,983,862 5/1961 Montner et al. 323-61 2,997,644 8/1961 Weinberg 323-56 FOREIGN PATENTS 1,032,387 6/ 1958 Germany. 315,844 5/ 1930 Great Britain. 583,497 12/ 1946 Great Britain. LLOYD MCCOLLUM, Primary Examiner. Patent Citations
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