Phase Adapter

Abstract

A device is disclosed for converting single-phase power to three-phase power. The device includes an autotransformer and a variable impedance device for adjusting the magnitude and phase of the autotransformer output. A first regulator circuit, including comparison, amplifier, phase shifting and SCR stages, is provided to regulate the impedance of the variable impedance device. A second regulator circuit, including comparison, control and power output stages, is also included to provide the device with the capability of compensating for changing power factors in three-phase loads coupled to it.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to phase adapted circuits, and more particularly to circuits for converting single-phase power to three-phase power.

2. Description of the Prior Art

In many instances a need exists for converting ordinary commercially available single-phase power to three-phase power. For example, many remote areas, such as farms and small shops are serviced by conventional single-phase power lines. However, in these locations it is often desirable to operate machine tools, water pumps, elevating equipment and other devices which are driven by three-phase electric motors. From an economic point of view it is much more desirable to convert a fraction of the single-phase power available at these locations to three-phase power than to attempt to build three-phase power lines to service these remote areas. Accordingly, a need exists for a phase adapter suitable for converting available single-phase power to three-phase power.

Devices for power phase conversion have been designed in the past. However, known devices have generally been deficient in one or more areas. For example, some conventional devices have been too expensive to manufacture commercially, and those that have been capable of commercial manufacture at a reasonable cost have often proven to be unreliable. Similarly, other known devices, while relatively inexpensive and generally reliable have lacked versatility in that they were incapable of providing large variations in phase and power factor. In addition, some known devices are capable of use with only one type of electric motor, and therefore do not provide a sufficient range of utility to be commercially successful. Thus a need exists for a novel phase adapter which is reliable, capable of being manufactured at a reasonable cost, and capable of efficient operation with various electric motors and other similar loads over a wide range of phase angles and power factors.

SUMMARY OF THE INVENTION

Accordingly, one object of this invention is to provide a novel phase adapter for converting single-phase power to three-phase power.

Another object of this invention is to provide a novel circuit for converting single-phase power to three-phase power which is suitable for use with a variety of electrical motor loads.

Yet another object of this invention is the provision of a novel phase adapter circuit which is highly reliable, and reasonably economical to manufacture.

A still further object of this invention is the provision of a novel phase adapter circuit which is capable of efficient operation with a wide variety of electrical loads including multiple motor loads.

Another object of this invention is the provision of a phase adapter which is capable of reliable and efficient operation with a variety of loads over a substantial range of power factors.

A still further object of this invention is the provision of a novel phase adapter circuit including a pair of automatic regulator circuits.

Another object of this invention is to provide a unique regulator circuit for use with a novel phase adapter circuit.

Another object of this invention is the provision of two unique regulator circuits for use with a novel phase adapter circuit.

Briefly, these and other objects of the invention are achieved by providing a phase adapter circuit including a main autotransformer having a fixed capacitor coupled in series therewith, and having a variable inductor coupled in parallel with the fixed capacitor. A saturable-core reactor is used in the circuit to provide quick response, and a wide range of reactance values. First and second regulator circuits are utilized to provide accurate phase and power factor control.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

FIG. 1 is a phasor diagram of induction motor operation;

FIG. 2 is a phasor diagram of a phase adapter;

FIG. 3 is a phasor diagram for an induction motor supplied from a phase adapter at 0.866 power factor;

FIG. 4 is a circuit diagram of a simplified phase adapter for supplying a three-phase motor with a single current at one value of power factor;

FIG. 5 is a circuit diagram of a variable reactance unit;

FIG. 6 is a circuit diagram of a saturable-core reactor coil arrangement;

FIG. 7 is a circuit diagram of a basic phase adapter unit;

FIG. 8 is a phasor diagram of a complete phase adapter circuit;

FIG. 9 is a phasor diagram for a 0.50 power factor load;

FIG. 10 is a circuit diagram of the complete phase adapter circuit of the present invention;

FIG. 11 is a V-curve for a synchronous motor at no load;

FIG. 12 is a circuit diagram of a phase adapter circuit employing power factor correction, according to the present invention, for use with a synchronous motor;

FIG. 13 is a circuit diagram of the regulator circuit shown in block form in FIGS. 7, 10 and 12 as the first regulator unit; and,

FIG. 14 is a circuit diagram of the regulator circuit illustrated in block diagram form in FIGS. 10 and 12 as the second regulator unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Before discussing the specific embodiments of the present invention, a consideration of the range of induction motor loads and the power factors at which motors must operate under these loads is believed to be in order. In general, for a given horsepower rating, the higher the synchronous speed of a motor, the higher the power factor at full load. The normal range of power factors is from approximately 0.90 for 3,600 rpm motors to approximately 0.65 for 900 rpm motors. This range in power factors is equivalent to a range of from approximately 25.83.degree. (lagging) to approximately 49.53.degree. (lagging). As is familiar to those skilled in the art, the power factor at which a given motor operates varies as the load on its shaft changes. Thus, the power factor for a particular motor will be highest at full load, and will drop to its lowest value when no load is applied to the motor. In practice, the range of power-factors due to loading extends from approximately 0.90 to approximately 0.50 (lagging). This means a range in phase-angles from approximately 25.83.degree. (lagging) to approximately 60.00.degree. (lagging). Accordingly, it is necessary for a phase adapter of practical utility to operate reliably throughout these ranges of power factors and phase angles.

In developing a phase adapter, or single-phase to three-phase converter, an energy storage element is required to absorb energy from the single-phase power supply, and to deliver this energy at a subsequent phase to an appropriate load. The most common energy storage elements are, of course, the capacitor and the inductor. In the case of a capacitor, a phase shift will be created such that the current leads the voltage applied to the unit by nearly 90.degree.. Very low losses are possible with oil-filled capacitors, so that these devices deviate only slightly from the ideal phase shift of 90.degree.. Similarly, the current in a well designed inductor will lag the applied voltage by a large angle, which may approach 90.degree. in optimum situations. These basic aspects of energy storage devices must also be taken into consideration in constructing phase adapter circuits.

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, and more particularly to FIG. 1 thereof, a phasor diagram for a conventional induction motor operating from a balanced three-phase power source is shown. Voltage phasors V.sub.12, V.sub.23 and V.sub.31 represent the line voltages supplied to motor terminals 1, 2 and 3 from a three-phase source. If the induction motor stator is connected in a Y configuration, as is generally the case, the respective motor phase voltages radiate from a central or neutral position designated N. In this case the motor phase voltages are represented by the phasors V.sub.N1, V.sub.N2, and V.sub.N3. These voltages may be referred to as the line-to-neutral voltages. The corresponding motor currents designated by the phasors I.sub.1, I.sub.2 and I.sub.3 are shown lagging the phase voltages by appropriate phase angles .phi..sub.1, .phi..sub.2 and .phi..sub.3, respectively. For completely balanced conditions, the magnitudes of all respective phasors and phase angles are equal, respectively.

As was pointed out above, the symmetrical phasor diagram of FIG. 1 represents a situation in which a balanced three-phase power source is available. In the environment of the present invention, it is assumed that no source of three-phase power is available. Instead, only one voltage, represented by the phasor V.sub.12, for example, is supplied by the available power source, such as a public utility company. In this case, the voltages represented by the phasors V.sub.23 and V.sub.31 must be derived by means of an auxiliary apparatus.

FIG. 2 is a phasor diagram representing the voltages which are desirably supplied by a suitable phase adapter. The precise relationships among the phasors illustrated in FIG. 2 are set forth in Table 1 below.

TABLE 1

V.sub.1a = 2 V.sub.12

.theta..sub.1a = 0

V.sub.03 = (0.866) v 90.degree.

v.sub.10 = 0.5 v 0.degree.

v.sub.02 = 0.5 v 0.degree.

v.sub.0a = 1.5 V 0.degree.

V.sub.3a = 1.732 V -30.degree.

V.sub.12 = v

although other relationships are usable with the present invention, the relationship set forth in the table above is considered optimum. Similarly, the phasor diagram for an induction motor supplied from a suitable phase adapter at 0.866 power factor is shown in FIG. 3. Concerning the phasor diagrams, it is pointed out that when a three-phase motor receives a balanced set of input voltages, the motor winding neutral will be located at the center of the phasor triangle. The voltage from the motor terminal 3 (the numerals at the corners of the phasor triangles designate motor input terminals) to the center point of the triangle base 0, that is V.sub.03, will be at right angles to the base which is the neutral point of the single-phase supply. Thus, it is clear that the purpose of a suitable phase adapter is to supply a current to the third terminal of the motor which is compatible with the currents supplied by the single-phase source to the remaining two terminals of the motor. Referring now to FIG. 3, the phasor I.sub.c represents current supplied from a phase adapter, and adjusted in phase by means of a suitable capacitor. It will be apparent that the direction or phase of the current phasor I.sub.c resulting from the voltage V.sub.3a is parallel to the required motor current for the illustrated condition. Thus, it is only necessary to adjust the magnitude of the current phasor I.sub.c to an appropriate magnitude to properly drive the motor when its power factor is 0.866.

A basic phase adapter circuit for developing the appropriately related current and voltage signals briefly described above is illustrated in FIG. 4. This circuit includes a pair of input terminals 10 and 12 which are adapted to be coupled to a suitable source of single-phase power. The input terminal 10 is coupled through a main autotransformer 14 and a capacitor 16 to one terminal (designated terminal No. 3) of a stator winding 18 of an induction motor 20. The input terminal 10 is also directly coupled to another terminal of the stator winding 18 (designated terminal No. 1) through a line 22. Similarly, the input terminal 12 is directly coupled to the remaining terminal of the stator winding (designated as motor terminal No. 2) through a line 24. A center tap 26 of the main autotransformer 14 is also coupled to the line 24, and thus to the motor terminal 2.

In order to control the current delivered to the motor in the circuit of FIG. 4, a variable capacitor could be used. However at low frequencies, such as 60 Hz, an extremely large and impractical capacitor would be required. However, a suitable circuit arrangement which provides the same effect as a large variable capacitor is illustrated in FIG. 5. This circuit includes a variable inductor 28 coupled in parallel with the fixed capacitor 16. The net output response of this circuit is substantially identical with that of a large variable capacitor. The variable inductor 28 preferably consists of a saturable core reactor 30 coupled in series with a linear inductor 32 to form a variable inductance unit.

The details of the saturable core reactor 30 are illustrated in FIG. 6. Since it is highly desirable to have a saturable core reactor designed for wide range reactance variations with quick response, a coil 34 wound on a center leg 36 of a reactor core 38 is used as the "gate" or A.C. winding. A pair of "control" or D. C. windings 40 and 42 are wound about the outer legs 44 and 46, respectively, of the reactor core 38. The control windings 40 and 42 are connected in series opposition so that no A. C. voltage appears across their free terminals. The A. C. winding is designed so that the peak value of flux density in the core is well below the saturation value. As a result, a wide range of current variation is possible. Since there are no short circuited loops in the A. C. current paths, as there are in saturable core reactors which have the outer leg coils in parallel as the A. C. winding, the response of this reactor is much more rapid than conventional saturable core reactors.

FIG. 7 illustrates a composite circuit wherein the circuits illustrated in FIGS. 4 and 5 have been combined. In addition, a first regulator unit 48 is shown coupled to the composite circuit. The first regulator unit 48, which will be described in more detail hereinafter, includes a first input terminal 50 coupled to the input terminal 10, a second input terminal 52 coupled to the input terminal 12, and a third input terminal 54 coupled to the third input terminal 3 of the stator winding 18. The first regulator unit 48 also includes a pair of output terminals 56 and 58 which are coupled across the D.C. input terminal of the saturable core reactor 30, as illustrated in FIG. 6. The first regulator unit 48 senses the differences between the magnitude of the input voltage applied across the terminals 10 and 12 and the quadrature voltage generated in the induction motor 20, and generates a proper D. C. voltage across its output terminals 56 and 58 in order to maintain the relationship illustrated in FIG. 2 and set forth in Table 1. Under these circumstances, if the motor operates at 0.866 power factor, the voltages at the motor inputs will be balanced, as will the motor input currents. At other values of power factor sufficiently near the 0.866 value, the voltages and currents will be approximately balanced.

As will be apparent from the preceeding discussion, the circuit illustrated in FIG. 7 is not a completely satisfactory phase adapter, since additional circuits are required to correct for power factor variations in the motor as seen by the basic phase adapter. Referring again briefly to FIG. 2, it will be apparent that a reactive element, which may change its impedance characteristics from capacitive to inductive, may be connected between motor terminals 1 and 3, so that a current is supplied to terminal 3 which is represented by a phasor lying along the locus of the voltage phasor V.sub.3a. Since the phasor V.sub.31 is 90.degree. in phase from the phasor V.sub.3a, inductive reactance will produce a current component into terminal 3 which is opposite in phase to the phasor V.sub.3a. Similarly, capacitive reactance will produce a current component at terminal 3 which is in phase with the phasor V.sub.3a. Thus an auxiliary circuit can be added to the basic phase adapter illustrated in FIG. 7 which produces a regulated voltage so that the magnitude of the phasor V.sub.03 is equal to 0.866 V.sub.12, and the current component produced by the auxiliary circuit may be used to cause the motor load to appear to the basic phase adapter as if its power factor is maintained at a constant value of 0.866. The phasor diagram for this situation is illustrated in FIG. 8.

Referring now to FIG. 8, when a motor is operating at a power factor of 0.50, the motor current is represented by a phasor I.sub.Nc. As can be seen from FIG. 8, the motor current I.sub.Nc can be attained by adding together the basic phase adapter current, represented by the phasor I.sub.Nb and an additional current, represented by the phasor I.sub.bc, which leads the voltage phasor V.sub.31 by 90.degree.. On the other hand, if the motor is operating at a power factor of 0.90, the motor current is represented by the phasor I.sub.Nc.sub.'. In this case, a current represented by the phasor I.sub.b.sub.'c.sub.', which lags the voltage phasor V.sub.31 by 90.degree., must be added to the basic phase adapter current, represented by the phasor I.sub.Nb.sub.', to produce satisfactory motor operation. Naturally, this same analysis can be applied to any desired motor current value and its associated power factor by means of observing the appropriate current circle and associated current phasors. Concerning the various phasor diagrams, it is pointed out that these diagrams do not constitute a portion of the present invention, but are intended to aid in the explanation of the present invention. Further information pertaining to phasor diagrams of the type set forth herein may be obtained by reference to one or more of the following texts:

"Principles of Alternating Current Machinery" by: Ralph R. Lawrence 2nd ed. New York, McGraw-Hill 1921 4 ed. -- revised by Henry E. Richards New York, McGraw-Hill 1953.

"A Course in Electrical Engineering" by: Chester L. Dawes, Vol. II McGraw-Hill, New York, 4th ed. -- 1947-1952.

"Alternating Current Machines" Puchstein, Lloyd & Conrad New York, Wiley, 1954.

"Alternating Current Machines" by: Thomas Clair McFarland New York, D. Von Nostrand Co. 1948.

FIG. 9 represents a phasor diagram analysis which is an alternative to that illustrated in FIG. 8. The triangular phasor diagram of FIG. 9 may be obtained from that of FIG. 8 by making the point a in FIG. 8 correspond with the point 2. If it becomes desirable to operate a motor having a power factor of 0.866 from the phase adapter arrangement illustrated in the diagram of FIG. 9, the required motor current represented by the phasor I.sub.Nc is obtained by adding the component phasors I.sub.Nb and I.sub.bc, in essentially the same manner as described with reference to FIG. 8. However, it should be noted that in FIG. 9 the line of correction current from the second regulator, which will presently be described in detail, is 60.degree. from the basic phase adapter current represented by the phasor I.sub.Nb. This means that the correction is most favorable when the motor power factor is 0.866, or a 30.degree. lagging current, since the correction current is at right angles to the required motor current. For all values of power factor above 0.50 lagging, the required correction will be in the same direction. Similarly, for all values of power factor less than 0.50, the correction current required will be in the opposite direction.

From consideration of the phasor diagrams of FIGS. 8 and 9, it is apparent that a second regulator must be added to the basic phase adapter circuit illustrated in FIG. 7 to provide the necessary power factor correction current. Thus, in FIG. 10, a second regulator unit 60 is shown coupled to the basic phase regulator circuit of FIG. 7. More particularly, the second regulator unit 60 includes first, second and third input terminals 62, 64 and 66, respectively, which are coupled to the first, second and third input terminals 50, 52 and 54, respectively of the first regulator unit 48. Similarly, the second regulator unit 60 includes two output terminals 68 and 70 which are coupled to the D. C. input terminals of a second saturable core reactor 72. The second saturable core reactor 72 forms a portion of a second variable inductor 74 which is coupled in parallel with a second fixed capacitor 76. The second variable inductor 74 may be identical to the variable inductor 28, previously described, and the second fixed capacitor 76 may be identical with the fixed capacitor 16. However, one A. C. input terminal of the second variable inductor 74 is coupled to the input terminal 10 and to the first motor input terminal 1, while the other A. C. input terminal is coupled to the third motor input terminal 3. It should be noted that the second variable inductor 74 includes a second linear inductor 78 in addition to the second saturable core reactor 72.

In operation, the second regulator unit 60, which will be described in detail hereinafter, senses the differences between the magnitudes of the voltage phasors V.sub.23 and V.sub.31, and produces an output signal at terminals 68 and 70 for controlling the second variable inductor 74 and producing appropriate correction currents. The regulator preferably includes an integrating circuit so that when the error voltage is zero, there will be a proper D.C. current through the second saturable core reactor to provide the desired correction current.

From the discussion above it is apparent that proper three-phase motor operating current is obtained by adding an out-of-phase current component to the output current of the basic phase adapter shown in FIG. 7.

A second circuit for power factor correction can be developed from the well-known phenomenon that a synchronous motor with a D.C. field supply operates at various values of power factor providing its field excitation is suitably adjusted. This concept may be more clearly understood by reference to the synchronous motor curve of FIG. 11. This curve, which is known as a V curve, is clearly described in the various publications referenced above. The V curve illustrated in FIG. 11 is the no-load curve for a synchronous motor, and includes a minimum point 80 at which the motor operates at a unity power factor. For values of field current lower than that corresponding to a unity power factor, the motor is magnetized from the line and the input current will be lagging. Similarly, for values of field current greater than that required for unity power factor, the generated voltage of the motor will be greater than the applied voltage, and the current to the motor will lead the applied voltage, so that the power factor will be leading. This ability of the synchronous motor to produce both lagging and leading power factors may be used to correct the power factor of a total load, for example induction motors and synchronous motors coupled in parallel in a manner similar to that described above with reference to the circuit of FIG. 10. In this case, the second regulator unit 60 merely adjusts the field current of the synchronous motor until the power factor of the combined load matches the natural power factor of the basic phase adapter circuit. A circuit of this type is shown in FIG. 12. The circuit of FIG. 12 is generally similar to that of FIG. 10, except that the second variable inductor 74 and second fixed capacitors 76 have been removed, and the induction motor 20 has been replaced by a synchronous motor 82. The output signal generated by the second regulator unit 60 is applied over a pair of lines 84 and 86 to the field windings of the synchronous motor 82. The control or correction signals generated by the first and second regulator units 48 and 60, respectively are substantially the same as those generated in the embodiment illustrated in FIG. 10. However, as pointed out above, the synchronous motor provides the necessary correction in power factor which was performed by the additional variable inductor and fixed capacitor circuitry shown in FIG. 10. In the embodiment of FIG. 12 properly converted three-phase power is available at the output terminals of the circuit, designated by the reference numerals 88, 90 and 92.

When a synchronous motor is used for power factor correction, the rotor of the motor stores mechanical kinetic energy. Since the motor is synchronous, the energy is fed back into the power system by a generator action during disturbances to the input. This property can be very useful for starting induction motors when they are used as loads. Where extremely heavy starting currents are required, the synchronous motor may be equipped with a fly-wheel. Thus, the energy stored in the fly-wheel augments the energy stored in the rotor of the motor to generate larger starting currents, when needed.

No starting capacitors are shown in the phase adapter circuits described above. However, if additional capacitance is needed to provide higher starting torques, additional capacitors can be added to the circuit.

Referring now to FIG. 13, the circuit of the first regulator unit 48 is shown in detail. To facilitate description of the first regulator circuit 48, the circuit has been divided into separate functional stages, namely a comparison stage 94, and amplifier stage 96, a phase shifting stage 98 and a SCR stage 100.

Attention is first directed to the comparison stage 94, which serves to compare the voltage applied to the third motor terminal (v.sub.30) with the magnitude of the input voltage (V.sub.12), which is the voltage applied to the terminals 10 and 12 of the circuit shown in FIG. 10, and corresponds to the voltage applied to the terminals 50 and 52 of the first regulator unit. More particularly, the comparison stage 94 produces an error signal at a pair of terminals 102 and 104 according to the following equation:

V.sub.error = .vertline.V.sub.30 .vertline. - 0.866 .vertline.V.sub.12 .vertline. (1)

however since the voltages corresponding to the phasors V.sub.30 and V.sub.12 are 90.degree. apart in phase, they cannot be directly compared. It is therefore necessary to rectify and filter these voltages, and then compare their D.C. Components, which is the specific function of the comparison stage 94.

The comparison stage 94 includes a first transformer 106 for measuring the input voltage V.sub.12 applied across the terminals 50 and 52. The output of the first transformer 106 is fed through a padding resistor 108 and a potentiometer 110 to a full wave rectifier including four diodes 112, 114, 116, and 118. The output of the full wave rectifier is then applied to a filter capacitor 120 having a bleeder resistor 122 coupled in parallel therewith.

A second transformer 124 is coupled to the input terminal 54 and to a primary center tap 126 of the first transformer 106, setting up a Scott Connection. A loading resistor 128 is coupled across the output of the second transformer 124 so that the two input voltages, which are 90.degree. apart, will be balanced at the tranformer output. The transformer output is coupled to a second full wave rectifier including four diodes 130, 132, 134 and 136, which are in turn coupled to a second filter capacitor 138 having a bleeder resistor 140 coupled in parallel therewith. This combined circuit provides an output which is proportional to the voltage V.sub.30 between the terminal 104 and a terminal 142. It is pointed out that the terminal 142 is the common negative terminal of each of the above described rectifier circuits, which are connected in opposition. Thus, the voltage between the terminals 102 and 104 will be the difference between the respective rectifier output voltages. Accordingly, the voltage between the terminals 102 and 104 will be given by the following equation.

V.sub.102, 104 = k .vertline.V.sub.12 .vertline. - .vertline.V.sub.30 .vertline. (2)

variation of the constant k is made by adjusting the potentiometer 110. By appropriate adjustment of the potentiometer 110, the error voltage V.sub.102, 104 can be made equal to zero for desired values of V.sub.30.

The amplifier stage 96 includes a third transformer 144 having its output coupled to a third full-wave rectifier including four diodes 146, 148, 150 and 152. A pair of resistors 154 and 156, along with a filter capacitor 158 supply direct current to the amplifier circuit 160. The amplifier circuit 160 includes a pair of interconnected transistors 162 and 164. The transistor 162 is preferably of the NPN type, while the transistor 164 is preferably of the PNP type. The collector of the transistor 162 is coupled to the base of the transistor 164 to provide two stages of amplification. The input to the amplifier circuit 160 is the error voltage defined by equation (2) above, and is applied to the amplifier circuit 160 through a blocking diode 166 and a voltage divider consisting of resistors 168 and 170. The blocking diode 166 insures that no negative current reaches the base of transistor 162. Appropriate loading resistors 172 and 174 are coupled to the collectors of the transistors 162 and 164, respectively. A dropping resistor 176 and a zener diode 178 are coupled in series across the amplifier circuit 160. The zener diode 178 maintains a circuit point 180 at a constant positive reference potential with respect to a circuit point 182. Whenever the transistors 162 and 164 are not conducting, a circuit point 184 will be at the same potential as the point 182, and the point 180 will be positive with respect to either of the other two points. Thus, the voltage between point 184 and point 180 will be the negative of the value of the reference voltage across the zener diode 178. Accordingly, when transistors 162 and 164 are conductive, it is possible that the voltages between the circuit points 184 and 182, 180 and 182, and 184 and 180 are equal to zero. In addition, whenever conduction of the transistors 162 and 164 causes the voltage drop across the resistor 174 to be greater than the reference voltage across the zener diode 178, the voltage between the points 184 and 182 will be greater than the voltage between the points 180 and 182. Thus, the voltage between the points 184 and 180 will be equal to the difference between the voltages between the points 184 and 182 and 180 and 182. In addition, this difference will be positive. Accordingly it will be apparent that negative voltages do not affect the amplifier circuit 160.

The phase shifting stage 98 includes a pair of conventional phase shifting RC networks, including a pair of resistors 186 and 188, and a pair of capacitors 190 and 192. An isolation transformer 194 is coupled to the combined phase shifting networks to isolate the power circuit from the output circuit of the phase shifter. The isolation transformer is also preferably a step-down transformer to increase the output current. The output of the isolation transformer 194 is coupled through a pair of diodes 196 and 198 to a pair of protective resistors 200 and 202. A pair of anti-floating resistors 204 and 206 are coupled across the diode outputs.

Referring now to the SCR stage, it will be seen that this stage includes first and second silicon controlled rectifiers (SCR's) 208 and 210 having a free-wheeling diode 212 coupled between them. The SCR's 208 and 210 and the diode 212 are coupled to the D.C. winding of the saturable core reactor 30. The output of the amplifier circuit 160 is coupled to the cathode of both SCR's 208 and 210, and also to the cathode of the diode 212. The outputs of the phase shifting stage 96 are coupled to the gate electrodes of the SCR's 208 and 210. Thus, the amplifier and phase shifting stages control the phase and duration of the conductive period of each SCR. Consequently, the current fed to the D. C. winding of the saturable reactor 30 by the SCR stage 90 is controlled by the amplifier and phase shifting stages. Since the signal developed by the comparison stage 94 controls the output of the amplifier stage 96, the SCR stage 100 also operates under the control of the comparison stage 94. By proper selection of circuit parameters in conventional manners known to those skilled in the art, the current applied to the D. C. winding of the saturable core reactor 30 is accurately regulated in accordance with the requirements set forth hereinabove.

The purpose of the R-C networks is to produce voltages at diodes 196 and 198 which lag the anode voltages of the SCRs 208 and 210 by a suitable angle, usually 90.degree..

Attention is now directed to FIG. 14 wherein the circuit of the second regulator units 60 is shown in more detail. As in the case of the first regulator unit, the second regulator unit will be described in terms of three functional stages, namely a comparison stage 213, a control stage 215 and a power output stage 217.

The comparison stage 213 is substantially identical with the comparison stage 94 of the first regulator unit. More particularly, the comparison stage 213 includes first and second transformers 214 and 216. The input terminals of the transformer 214 are coupled to input terminals 62 and 66 of the second regulator 60, while the input terminals of the transformer 216 are coupled to terminals 64 and 66 of the second regulator unit. The output of the transformer 215 coupled to a full-wave rectifier, consisting of diodes 218, 220, 222 and 224, which are in turn coupled to a filter capacitor 226 shunted by a bleeder resistor 228. Similarly, the output of the transformer 216 is coupled to a full-wave rectifier comprised of diodes 230, 232, 234 and 236, which are coupled to a filter capacitor 238, which in turn is shunted by a bleeder resistor 240. The basic purpose and functioning of the comparison stage 213 is also substantially identical to that of the comparison stage 94 of the first regulator unit, with the exception that different input voltages are supplied to the comparison stage 213.

The control stage 215 includes a two-phase induction motor 242 having a permanent splitter capacitor 244 and a surge surpressing resistor 246 coupled thereto. A pair of gate controlled full-wave A.C. silicon switches, such as Triacs (TM) 248 and 250 are coupled to the two-phase induction motor for controlling the operation thereof. For example, if Triac 248 is conducting, the motor 242 will rotate clockwise, while if Triac 250 is conducting the motor will rotate counterclockwise. A diode and resistor network, including resistors 252, 254, 256 and 258 and diodes 260, 262, 264 and 266 is coupled to the gate electrodes of the Triacs 248 and 250 for controlling the operation thereof.

The power output stage 217 includes a rotatable transformer 268 which is mechanically coupled to and rotated by the output shaft of the two-phase induction motor 242. The output voltage of the rotatable transformer 268 is measured by shaft rotation from a reference position for a given maximum angle. If the transformer windings are coupled in series, the output voltage varies from 0 to twice the input voltage for a 180.degree. shaft rotation. A pair of limit switches 270 and 272 are interposed in the phase leads of the motor 242, and are mechanically actuated by cams (not shown) on the rotatable transformer shaft to limit rotation of this shaft to a predetermined maximum allowable angular range. The output of the rotatable transformer 268 is applied to a diode rectifier including diodes 274, 276, 278 and 280. This rectifier then applies power to the field of the synchronous motor 82 shown in FIG. 12, or the D. C. windings of the second saturable core reactor 72 shown in FIG. 10.

Naturally, the regulator circuits illustrated herein are considered to represent exemplary circuits for performing the necessary regulative functions required according to the present invention. It will be apparent to those skilled in the art that other types of circuits for performing the same functions may be constructed.

Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

What is claimed as new and desired to be secured by letters patent of the

1. A device for converting single-phase power to three-phase power comprising:

input means for coupling said device to a suitable source of single-phase power,

transformer means coupled to said input means,

variable impedance means coupled to said transformer means for adjusting the phase of output current from said transformer means said variable impedance means including a saturable core reactor coupled in series with a linear inductor,

first regulator means coupled to said input means and to said variable impedance means for controlling the impedance of said variable impedance means in accordance with the magnitude of the three-phase power demand, and

second regulator means coupled to said first regulator means for providing

2. A device for converting single-phase power to three-phase power as in claim 1, wherein:

a first capacitor is coupled in parallel with said series connected

3. A device for converting single-phase power to three-phase power as in claim 1, wherein:

said saturable core reactor includes a core having a center leg and two outer legs, a gate winding wound on said center leg, and a pair of control windings wound on said outer legs and connected in series opposition whereby a wide range of reactance variations with rapid response is

4. A device for converting single-phase power to three-phase power comprising:

input means for coupling said device to a suitable source of single-phase power,

transformer means coupled to said input means,

variable impedance means coupled to said transformer means for adjusting the phase of output current from said transformer means,

first regulator means coupled to said input means and to said variable impedance means for controlling the impedance of said variable impedance means in accordance with the magnitude of the three-phase power demand and including comparison means for developing an output error signal representing the difference between two input signals, amplifying means and for amplifying said error signal, output means for supplying an output signal, electronic switching means coupled to said output means for controlling said output signal, and phase shifting means coupled to said electronic switching means for controlling the switching phase thereof, and

second regulator means coupled to said first regulator means for providing

5. A device for converting single-phase power to three-phase power comprising:

input means for coupling said device to a suitable source of single-phase power,

transformer means coupled to said input means,

variable impedance means coupled to said transformer means for adjusting the phase of output current from said transformer means,

first regulator means coupled to said input means and to said variable impedance means for controlling the impedance of said variable impedance means in accordance with the magnitude of the three-phase power demand, and

second regulator means coupled to said first regulator means and including comparison means for developing an output error signal representing the difference between two input signals for providing said device with load

6. A device for converting single-phase power to three-phase power as in claim 5, wherein:

said second regulator means further includes control means comprising a servo motor and output means including a rotatable transformer coupled to said servo motor.