GB2110437A - A broadband saturable reactor regulated power supply - Google Patents

Abstract

A saturable reactor regulated power supply utilizes a power oscillator to convert line voltage to a higher frequency voltage which is passed through the gate windings of a saturable reactor to an output AC or DC circuit. A feedback circuit inter- connected between the output circuit and control windings of the saturable reactor controls the control winding current to pulse modulate the voltage applied to the output circuit. The feedback circuit synthesizes a series control winding resistance which enables broad bandwidth operation of the power supply and less power dissipation therein. The feedback circuit includes a voltage or current sensor 96 supplying a signal by way of a comparator amplifier circuit 98 to a driver circuit 100 connected to the reactor control windings over lines 78, 80. Resistors R1, R2, R3 and an amplifier controlling transistors 118, 124 synthesise an effective resistance in series with the control windings to reduce the time constant of the circuit without increasing power dissipation. Multiple output channels may be provided. <IMAGE>

Description

SPECIFICATION A broadband saturable reactor regulated power supply The present invention relates to electrical power supplies and more particularly to power supplies regulated by a saturable reactor, or magnetic amplifier.

Many types of electric and electronic equipment require closely regulated, stable power supplies. Such power supplies are capable of providing a constant output voltage to the equipment, or load, despite line voltage transients and variable current or power demands by the load.

Examples of equipment needing closely regulated power supplies are traveling wave tubes, radar systems and some electric motor driven servo systems. In some equipment the power demand is for various different voltages, each requiring close regulation, in other equipment the need is for a variable output voltage.

While a conventional linear power supply may be utilized to power such equipment, a power supply utilizing a saturable reactor, or magnetic amplifier, for regulation purposes, may be more efficient, economical and lighter in weight.

A saturable reactor regulated power supply typically utilizes a power oscillator to convert incoming line voltage to a high frequency voltage and an output power transformer for converting the high frequency voltage to a desired output voltage, the latter being passed through a rectifier and filter circuit if a D.C. output is desired. The output of such a power supply may be regulated by modulating the high frequency voltage from the power oscillator before it enters the power transformer. This modulation is accomplished with the use of a saturable reactor, or a magnetic amplifier, having a pair of gate windings connected in series with each other and the power oscillator and high voltage transformer.

Regulation of the power supply output is commonly done by use of a feedback circuit which varies current through control windings of the saturable reactor in order to pulse modulate the voltage applied to the output power transformer. The saturable reactor functions as a switch with the gate windings presenting little resistance between the power oscillator and the output power transformer when the saturable reactor is firing, and presenting a high resistance therebetween when the saturable reactor is not firing, the time of firing being regulated by the current in the control winding.

As hereinabove mentioned, this type of power supply design has the advantage of using both lighter and lesser expensive components than, for example, a conventional linear power supply, and further, it has a relatively high transform efficiency.

However, such power supplies may be subject to instability, with regard to output voltage, because of line voltage transients and/or variable load demands. The response time of such power supplies is typically about 0.5 milliseconds, corresponding to a first break co of 2 KRADS or, in terms of bandwidth, about 2 KHz.

It should be appreciated that in order for a power supply to adequately regulate, or hold output voltage constant, the power supply bandwidth must be substantially greater than the rate of change, or bandwidth, of both line voltage transients and load demand variations.

Hence, a conventional saturable reactor regulated power supply may not have sufficient bandwidth, when connected to a 400 Hz supply line, to accommodate line voltage transients of approximately 800 Hz (twice the nominal line frequency). That is, such line voltage transients may cause variations in the power supply output voltage.

Similarly, when such a conventional power supply is used as a driver for an electric motor in a high frequency servo system, wherein the varying current demands by the motor may correspond to a bandwidth as high as 2 KHz, the power supply output voltage may not be sufficiently regulated.

Conventional saturable reactor regulated power supplies typically have fixed voltage outputs which can not be varied over a range exceeding a maximum voltage to minimum voltage ratio of approximately 1 and a half. Hence, a separate power supply must be designed and configured for each load voltage requirement.

The present invention provides a saturable reactor regulated power supply which has a variable output over a wide range, for example, a maximum voltage to minimum voltage ratio of up to 5, while at the same time having a bandwidth of over 5 KHz. Further, the present invention provides a power supply having a number of separately regulated output voltages from a single line source.

Such performance is enabled by a saturable reactor control winding feedback circuit configuration which synthesizes a series control winding resistance Rc. This synthesized, or phantom, resistance is an apparent resistance in the control winding circuit having a very high value, thus enabling rapid response of the saturable reactor and a power supply having a large bandwidth as will be hereinafter discussed.

A power supply in accordance with the present invention is adapted for connecting to a line voltage and provides a selected regulated output voltage to a load having variable power demand.

The power supply includes a power oscillator circuit means for inverting the line voltage to higher frequency voltage, and output means adapted for connecting to the load, for providing output voltage thereto.

A saturable reactor is provided for modulating the higher frequency voltage from the power oscillator and includes a gate winding, interconnected between the power oscillator means and the output means, and a control winding.

A feedback circuit means is interconnected between the output means and the saturable reactor control winding for controlling, in response to varying power demands of load, the control winding current to regulate the output power voltage. The feedback circuit means includes load current sensing means for determining load current.

Importantly, the feedback circuit is configured for controlling the current through the control winding of the saturable reactor without adding significant fixed resistance in series with the control winding, thus enabling rapid accommodation of line voltage transience and variable load demands without substantial change in the selected output voltage.

More particularly, a power supply in accordance with the present invention is adapted for connection to line voltage for providing separate output voltages to a plurality of loads, each load having variable power demands.

A common power oscillator circuit means provides high frequency voltage to a plurality of separate output channels. Each of the separate output channels is associated with one of the loads and includes output means, adapted for connecting to the associated load, for providing output voltage thereto, and saturable reactor means for modulating the higher frequency voltage from the common power oscillator circuit means. Each of the reactors has a gate winding interconnected between the power oscillator circuit means and the associated output means, and a control winding.

Feedback circuit means included in each channel is interconnected between the associated output means and the associated saturable reactor control winding for controlling, in response to varying power demands of the associated load, the control winding current to regulate the output power voltage.

Each feedback circuit means includes sensing means for determining associated load current, and is configured for controlling the current through the associated reactor control winding without adding significant fixed resistance in series with said control winding to enable rapid accommodation of line voltage transients and variable load power demands without substantial change in the selected output voltage.

Voltage selection means is included in each feedback circuit means to enable selection of associated output voltages from a minimum to a maximum voltage, the ratio of maximum to minimum voltage having a ratio of up to five.

These features provide a number of advantages, such as, for example, a saturable reactor regulated power supply having a broad bandwidth, or rapid response time, while additionally being more efficient because less power is dissipated in the control winding circuit of the reactor. Further voltage regulation can be provided for each of separate output channels.

The foregoing and other features and advantages will be apparent from the following specification describing an exemplary embodiment of the invention, taken in conjunction with the accompanying drawings, in which: Figure 1 is a block diagram of a power supply in accordance with the present invention showing generally a power oscillator circuit and two exemplary voltage output channels, each including a modulator, output circuitry and a feedback circuit; Figure 2 is a schematic representation of a saturable reactor for use as the modulator shown in Figure 1; Figure 3 is a schematic circuit diagram of the feedback circuit shown in Figure 1; and, Figure 4 is a representation of a motor load with an associated series resistor which may be drawn and controlled by the power supply shown in Figure 1.

Referring now to the drawings, Figure 1 shows, in block diagram form, a power supply 10, in accordance with the present invention, which generally includes a power oscillator circuit 12, a plurality of output channels 14, an auxiliary power circuit 1 6 and a reference voltage circuit 1 8. It is to be appreciated that since each of the output channels 14 are identicai, only one of the channels is detailed for clarity of presentation.

The power oscillator circuit 1 2 may include a conventional bridge rectifier circuit 26 for providing D.C. input to a power oscillator 28 from an A.C. line voltage source 30, or the power oscillator may be supplied direct current from an alternate D.C. line voltage source 32.

By switching the inputted D.C. voltage, the power oscillator, which may be of conventional design, operates to generate a higher frequency voltage to a pair of bus lines 34, 36. This high frequency voltage may have, for example, a peak to peak value of 56 volts and a frequency of approximately 20 KHz.

Each output power channel 14 is connected to the bus 34, 36 along with the auxiliary power circuit 1 6 which includes a conventional transformer rectifier and filter circuit, not shown, for providing appropriate bias voltages +A, -A, and power as needed to each output channel.

Additionally, the auxiliary power circuit provides +A voltage to a conventional reference voltage circuit which in turn provides an appropriate reference voltage, REF, to the output channels 14.

The output channel 14 includes a modulator 42 interconnected between power oscillator circuit 12 and an output means of circuit 44 via the bus line 36, channel input line 46, and line 48.

A second line 50 connects the output circuit 44 to the bus line 34. Being of usual design, the output circuit may include a high frequency power transformer 54 for stepping the power oscillator voltage to a desired channel output voltage level, and providing isolation between the output circuit and other positions of the power supply 10. A full wave rectifier 56 and an output choke and filter circuit 58 may be provided if the desired channel output is D.C. voltage.

Alternatively, and in accordance with well known design principles, the output circuit may not include the high frequency power transformer, or the full wave rectifier 56 and choke and filter circuit 58 depending upon the desired output voltage and type, ie, A.C. or D.C.

A feedback circuit 60 is interconnected between channel output lines 62, 64 and the modulator 42 via lines 74, 76 and 78, 80 respectively. The modulator may be a conventional type saturable reactor, or magnetic amplifier 82 as represented in Figure 2, having gate windings 88 interconnected between the power oscillator circuit 12 and the output circuit 44 via lines 46 and 48 respectively, and control windings 90 interconnected with the feedback circuit 60 via lines 78, 80 respectively.

As hereinbelow discussed, the saturable reactor 82 operates as a switch to modulate the high frequency voltage from the power oscillator circuit 12 to the output circuit 44.

Turning now to Figure 3, the feedback circuit 60 generally includes a sensing means or circuit 96, an amplifier circuit 98 and a reactor control winding and impedance, or driver circuit 100. It is to be appreciated that the resistor and capacitor values and component identification numbers are typical values, and that any component substitution which may occur to those skilled in the art, should be considered to be within the scope of the present invention. The sensing circuit includes a pair of resistors 102, 104 and a potentiometer 106, connected to the output lines 62, 64 via lines 74, 76 respectively, the output voltage being determined by the voltage drop across the sensing circuit 96.

Alternatively, if the power supply is used to drive a motor 112, Figure 4, the sensing circuit may be connected across a resistor 114 appropriately connected with the motor windings, not shown, in order to determine the current therein, and enable the power supply to regulate motor torque.

Referring again to Figure 3, the amplifier circuit 98 may be of typical design for providing an amplified signal, generated by the sensing circuit 96, to the driver 100.

The driver circuit 100 operates in response to varying power demands from a load, not shown in Figure 3, as determined by the sensing means, to control the current through the reactor control winding 90 provided by the auxiliary power circuit 1 6 through +A and lines 78, 80.

In accordance with well known design principles the saturable reactor, Figure 2, configuration is dependent upon the desired power output of the power supply. For example, for an output of 15 volts and 2 amps D.C. into a load, not shown the gate winding Ng, may be approximately 45 turns of 25 gauge wire, and the control winding, Nc, may be 270 turns of 30 gauge wire, giving a ratio of Nc Ng equal to approximately 6. The ratio corresponds to the gain of the saturable reactor.

As described in Magnetic Amplifiers by H. F.

Storm, published by John Wiley, New York, 1955, the gate voltage change necessary to accommodate transient load demand is in part limited by the time constant Tc of the control winding circuit, and

where Lc is the effective inductance of the control winding, and Rc is the resistance of the control winding and resistance in series therewith in the driver circuit 100.

The effective inductance Lc is:

Where f is the frequency of operation and R0 is the output resistance of the saturable reactor.

Hence, it is apparent that it is desirable to have the driver circuit 100 include a series resistance in order to reduce the time constance of the reactor 82, see equation (1), and hence, the power supply 10.

However, in as much as such a series resistance must carry considerable current in order to saturate the reactor, it dissipates considerable power and as a result lowers the efficiency of the power supply. For example, for the power supply 10, with the output channel providing an output of 1 5 volts at 2 amps, the current in the control winding may be up to 1/4 amperes.

Turning again to Figure 3, the driver circuit 100 connects the reactor control winding 90 to the power source +A via line 80 through a transistor 118, which may be mounted on a heat sink, represented by the dashed line 1 20. Line 80 connects the control winding 90 to -A through a low resistance R1 valve to complete a circuit through the control winding.

The driver circuit 100 configuration utilizes the transistor 11 8, an amplifying transistor 1 24 and resistors R1, R2 and R3 to provide a synthesized, or phantom resistance Rc* in series with the control winding 90 equal to RC*=R1(Av1), (3) where

For the resistance values shown in Figure 3, the synthesized resistance Rc* is 36 ohms.

Using the formula Tc=Lc/Rc, Tc, for Roc=36 ohms, is approximately .2 milliseconds, which corresponds to a power supply first break of approximately 5.3 KRADS.

The driver circuit 100 causes the saturable reactor to perform as if it had a resistance of 36 ohms in series with the control windings 90, without having any substantial fixed resistance in series therewith. The only other voltage drop in the control winding circuit between +A and -A is the drop across resistor Rr, and across the transistor 118.

The low value (1.5 ohms) of the resistor R1 does not cause significant voltage drop thereacross, and does not significantly reduce the efficiency of the power supply 10.

For comparison, a conventional saturable reactor modulator power supply, not shown, typically utilizes a 1 5 ohm fixed resistor in series with the reactor control winding, and a driving transistor. Hence, the bandwidth of such a conventional power supply utilizing the saturable reactor 82 would be only, in accordance with equation (1) approximately 2 KRAD. In addition to a much lower bandwidth, the conventional power supply is less efficient because of the power dissipated across the fixed series resistance of 1 5 ohms.

When the saturable reactor is firing and current is established in the control winding, the emitter voltage of the driving transistor 120 is low.

However, when the saturable reactor stops firing the voltage at the emitter of transistor 120 begins to rise. To limit the peak of this voltage excursion, a diode 130, 5.6 V zener diode 132 and resistor 134 are connected in parallel with R3. Hence, when the voltage at the emitter reaches approximately 5.6 V, the low resistor 134 clamps the high resistor R3 to reduce the emitter voltage.

It is well known that the stability of a saturable reactor power supply is related to the power supply bandwidth, the higher the bandwidth, the greater the stability.

The bandwidth, and hence stability, of the power supply is determined by the saturable reactor and control winding driver circuit as hereinabove discussed. A more stable reactor is operable for a greater range of modulation, without unwanted oscillation, than a less stable reactor. It follows that with a greater range of modulation, a power supply output voltage can be more widely varied.

It is to be appreciated that, the driver circuit 100 configuration in synthesizing a 36 ohm resistance in series the control winding, enables the saturable reactor, and the power supply, to have sufficient stability over a wider range than a conventional type saturable reactor power supply utilizing a large fixed series resistor.

Turning to the sensing circuit 96, it is apparent that the potentiometer 106 provides a means for enabling selection of the output voltage, by varying the voltage thereacross which in turn, through the amplifier circuit 98 and the driver circuit 100, adjusts the amount of current in the control winding. This in turn adjusts the amount of modulation of the high frequency voltage from the power oscillator 12 circuit to the output circuit 44, resulting in a higher or lower output voltage.

Although there has been described hereinabove a particular arrangement of fire control apparatus for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art, should be considered to be within the scope of the invention as defined in the appended

Claims (10)

claims. Claims

1. A power supply adapted for connecting to a line voltage, for providing a selected regulated output voltage to a load having variable power demand, comprising: power oscillator circuit means for converting the line voltage to a high frequency voltage; output means, adapted for connecting to the load, for providing output voltage thereto; saturable reactor means for modulating the higher frequency voltage from the power oscillator circuit means, said reactor having a gate winding interconnected between the power oscillator circuit means and the output means, and a control winding; and, feedback circuit means interconnected between said output means and the saturable reactor control winding for controlling, in response to varying power demands of the load, the control winding current to regulate the output power voltage, said feedback circuit means including sensing means for determining load current, said feedback circuit means being configured for controlling the current through the control winding without adding significant fixed resistance in series with said control winding to enable rapid accommodation of line voltage transients and variable load power demands without substantial change in the selected output voltage.

2. The power supply of Claim 1 wherein the output means includes a high frequency power transformer and rectifying and filtering means for providing D.C. output voltage to the load.

3. A power supply adapted for connecting to a low frequency A.C. line voltage, for providing a selected regulated D.C. output voltage to a load having variable power demands, comprising: power oscillator circuit means for converting the low frequency A.C. line voltage to a higher frequency A.C. voltage; output means adapted for connecting to the load, said output means including a high frequency power transformer and rectifying and filtering means for providing D.C. output voltage to the load; saturable reactor means for modulaing the high frequency voltage from the power oscillator circuit means, said reactor having a gate winding interconnected between the power oscillator circuit means and the power transformer, and a control winding; and, feedback circuit means interconnected between said output means and the saturable reactor control winding for controlling, in response to varying power demands of the load, the control winding current to regulate the output power voltage, said feedback circuit means including sensing means for determining load current, said feedback circuit means being configured for controlling the current through the control winding without adding significant fixed resistance in series with said control winding to enable rapid accommodation of line voltage transients and variable load power demands without substantial change in the selected output voltage.

4. The power supply of Claims 1 or 3 wherein the feedback circuit means includes means for enabling the selection of output voltage.

5. The power supply of Claim 4 wherein the voltage selection means is configured to enable selection of output voltages from a minimum voltage to a maximum voltage, said maximum and minimum voltages having a ratio of up to five.

6. The power supply of Claims 1 or 3 wherein the load is a motor, and the feedback circuit means includes means for sensing motor current thereby enabling the power supply to regulate the motor torque.

7. A power supply adapted for connecting to a line voltage, for providing separate selected output voltages to a plurality of loads, each load having variable power demands, each of said output voltages being separately regulated, said power supply comprising: (a) common power oscillator circuit means for converting the line voltage to a higher frequency voltage; and (b) a plurality of separate output channels, each of said channels being associated with one of said loads and each channel separately including: (1) output means, adapted for connecting to the associated load, for providing output voltage thereto; (2) saturable reactor means for modulating the higher frequency voltage from the common power oscillator circuit means, said reactor having a gate winding interconnected between the power oscillator circuit means and output means, and a control winding;; and, (3) feedback circuit means interconnected between said output means and the saturable reactor control winding for controlling, in response to varying power demands of the associated load, the control winding current to regulate the output power voltage, said feedback circuit means including sensing means for determining load current, said feedback circuit means being configured for controlling the current through the control winding without adding significant fixed resistance in series with said control winding to enable rapid accommodation of line voltage transients and variable load power demands without substantial change in the selected output voltage.

8. The power supply of Claim 7 where each output means includes a high frequency power transformer and rectifying and filtering means for providing D.C. output voltage to the associated load.

9. The power supply of Claims 7 or 8 wherein each feedback circuit means includes means for enabling the selection of output voltages for the associated load.

10. The power supply of Claim 9 wherein each voltage selection means is each configured to enable selection of output voltages, to the associated load, from a minimum voltage to a maximum voltage, said maximum and minimum voltage having a ratio of up to five.