CA1051517A - Controlled ferroresonant transformer regulated power supply - Google Patents

Abstract

Abstract of the Disclosure Standard configuration a.c. power transformer core sections are combined with standard configuration solenoid winding sections to provide a saturable core transformer which is arranged according to the invention for being driven into saturation by applied alternating and direct current energy with the control of variations in flux changes up to saturation exercised by the direct current flow. A center tapped primary winding is arranged, on an I-shaped stack of transformer iron laminations for full-wave excitation. A C-shaped stack of laminations is arranged adjacent to the I-shaped stack and separated by an air gap whereby the primary winding also serves as an input filter choke.
The core structure is completed by an E-shaped stack of laminations arranged adjacent to the I-shaped stack and separated by another air gap. Two solenoid windings are arranged on the outer legs of the E-shaped stack and connected to a capacitor for resonating the overall ferroresonant transformer circuit arrangement. Secondary windings are also arranged on the outer legs and connected to a rectifying circuit for supplying direct potential to a load. A control winding is arranged on the central leg of the E-shaped stack of laminations. With this arrangement, the control winding is unaffected by variations in the a.c. voltage as they affect the ? ?hanges in the transformer or in the frequency of the a.c. Regulation of the power supply is executed by direct current flow in the control winding. An adjustable resistor connecting the control winding across the output of the rectifier circuit is often all that is required to complete the circuit. In some applications, an amplifying circuit is used to provide a desired gain in the control winding circuitry.

Description

~S~S~7 1 The lnvention relates to electric powcr supply arranye-ments and it particular]y pertains to such arrangements having 3 the output regulated by driving an a.c. power supply transformer 4 toward saturation under controlled condi-tions.
Controlled ferroresonant transformer regula-ted power 6 supplies have been known for about four decades. Much promise 7 has been shown but heretofor the control has been lacking even wlth the more complex control arrangements devised. Examples of g such power supplies are described in the following U.S. patents:
1,953,773 4/1934 P~ichhart 171/119 11 1,967,108 7/1934 Werner 171/119 12 2,143,745 1/1939 Sola 171/119 13 2,706,271 4/1955 Fletcher 323/48 14 2,777,987 1/1957 Deal 323/56 3,148,326 9/1964 Baycura et al 323/56 16 3,253,212 5/1966 Wentworth 323/56 17 3,316,481 4/1967 Owen 323/6 ; !
18 3,341,766 9/1967 Rhyne, Jr. 321/9 19 And in the technical literature: ~ :
E. W. Manteuffel and R. O. McCary; "The D-C Controlled A-C
21 Voltage Source, A New Magnetic Amplifier;" Preceedings of the 22 AIEE; November 1957, pp 562-6.
23 R. N. Basu; "A New Approach in the Analysis and Design 24 of a Ferroresonant Transformer;" IEEE Transactions on Magnetics;
March 1967, pp 43-9.
26 R. J. Kakalec; "A Feedback-Controlled Ferroresonant Voltage ~
27 Regulator"; IEEE Transactions on Magnetics; March 1970, pp 4-8. -28 P. L. Hunter; "Variable Flux-Reset Ferroresonant Voltage 29 Regulator"; IEEE Transactions on Magnetics; September 1971, pp 564-7.
' ~ , SA97~031 -2-:'' : .

lOS~L5~7 1 R. H. Ran~all, W. R. Archer, and R. M. Lewis; "A New Con-~ 2 trolled Constant~Vol-tage Transformer;" IEEE Transactions on ; 3 Magnetics; September 1971, pp 567-71.
H. P. Hart and R. J. Kakalec; "A New Feedback-Controlled Ferroresonant Regulator Employing a Unique Magnetic Component;"
6 IEEE Transactions on Magnetics;`September 1971, pp 571 4.
` 7 R. Walk, R. J. Kakalec and J. Rootenberg; "An Analytical 8 and Computer Study of the Jump Phenomenon in Ferroresonant g Regulators;" IEEE Transactions on Magnetics; September 1971, PP 574-7.
11 The patents to Richart, Werner and Sola and the articles 12 of Manteuffel et al, Basu and Kakalec are directed to basic 13 ferroresonant transformer power supply regulating circuit 14 arrangements. These teachings apply in general to the embodi-ment of the invention and the patents are considered to be , 16 closer prior art in this respect than the others listed.
17 However, these reference patent arrangements require critically ~; 18 tapped windings, additional core structure or specially cut ~-19 core laminations although not critical in stamping and the regulation in each core is sensitive to variations in the

2~ fre~uency of the line voltage.
~2 The patents to Fletcher, to Baycura et al, and to Rhyne 23 and the articles to Basu, to Hunter, and to Hart are directed 24 to ferroresonant transformers having non-standard core lamina-` tions and tapped winding sections among other features obviated 26 by the arrangement according to the invention. The patents 27 to Deal and to Owen show core laminations of some complexity 28 in punching and in assembly with the winding sections. Also, ' !
29 the patent to Owen shows a moveable transformer core section that is obviated by the arrangement according to the invention.
, '~ ,': ' '7 The patent to Wentworth and the a~ticle to flunter are 2 directed to ferroresonant transformer a.c. voltage reyulating

3 arrangements having a control winding divided into two sections

4 and arranyed on separate outer legs of the transformer in compensating for the effect of a.c. voltage from the primary 6 windings on the control winding.
7 The arrangements of Hunter and Kakalec simulate saturation ~ by firing a thyristor (or a triac or an SCR) across a winding.
9 This arrangement requires complex synchronizing circui~ry for maintaining synchronism with the a.c. input voltage.
11 Control windings as such are absent from the arrangements ~ -12 of Richhart, Werner, Sola, Fletcher, Rhyne, Jr., Basu, and of Walk 13 et al. The arrangements of Baycura et al have a single or 14 dou~le section control winding which is wound through an aperture in the core lamination stack. Two section windings 16 are used by Wentworth as described hereinbefore, while Deal 17 uses one control winding section and one "bias" winding 18 section with separate control current supplies of two 19 different current characteristics. The article of Walk et al ~0 discusses a complex feedback arrangement as does the article 21 to Randall et al which also includes a tapped control winding.
22 The objects of the invention indirectly referred to 23 hereinbefore and those that will appear as this specification 24 progresses are attained in a controlled ferroresonant transformer regulated power supply of simple form and improved performance.
26 The electric energy transformer according to the invention 27 comprises stacks of electric transformer iron core laminations 28 in I, C, and E configurations and a number of solenoid winding 29 sections arranged on legs of the core lamination stacks. In one exemplary embodiment of the invention, two solenoid winding ~S~S~7 1 sections are arranyed on the I-shaped s-tack of laminatlons as a 2 full wave primary winding whereby the direction of magnetic 3 flux lines alternates each half cycle. The C-shaped stack of 4 laminations is arranged adjacent the I~shaped stack of lamina-tions and separated b~ an air gap to realize a Eilter choke for 6 providing the effect of a smoothing choke in the primary winding 7 circuit of the power supply. The remaining E-shaped stack of 8 laminations is arranged adjacent to the I-shaped stack with an 9 air gap separating the two. This air gap stabilizes the gain of the regulating circuit. Two secondary winding sections are 11 individually arranged on the two outer legs of the E-shaped 12 laminations and connected to a full-wave rectifier circuit for 13 supplying direct current to a load. Somewhat similarly, 14 another pair of windings are arranged on the legs of the E-shaped laminations and connected to a capacitor for pro-16 viding a circuit resonant to a predetermined frequency related ~-17 to the frequency of the input a,c. energy much as in the con-18 ventional ferroresonant power supply. Further according to 19 the invention, a control winding section is arranged on the central let of the E-shaped laminations, in predetermined 21 flux pattern relationship whereby the current in the control 22 winding at any time is independent of the a.c. input and the induced a.c. voltages. Direct current for the control winding 24 is obtained from the output of the rectifier circuit by a simple series resistor of adjusted value or a simple potentio-26 meter whereby the current varies directly proportionally to 27 the direct potential at the output of the rectifier circuit 28 and across the load circuit. The transformer core is driven 29 toward saturation by the a.c. input energy and the d.c. through the control winding. The latter current varies directly as .

SA974031 _5_ 1 the ou~p~l-t vol~age to main-tain it substant.ially constclnt. Thi.s arrangement is insensitive to variations i.n output voltaye 3 that otherwise would be present due to changes in the frequency 4 of the a.c. supply.

In order that the practical advantages obtain in -the 6 practice of -the invention, a preferred embodiment thereof 7 will be described in greater detail with reference to the accompanying drawing forming part of the specification and g in which:
FIG. 1 is a perspective view oE a transformer for a 11 power supply according to the invention;
12 FIG. 2 is a schematic diagram of a power supply according to the invention using that transformer;
14 FIG. 3 is a diagram illustrating the ~-H characteristics of the transformer according to the invention; and 16 FIG. 4 is a schematic diagram of an alternate circuit 17 according to the invention.
18 A perspective view of an a.c. transformer 10 as arranged 19 according to the invention is given in FIG. 1. The core of the transformer comprises a multiple of transformer iron laminations 21 clamped tightly in four L-shaped and/or mounting members 11-14.
22 A case (not shown) is shaped to slip over the transformer and 23 firmly clamp the mounting membe.rs. The core laminations are 24 further divided into three discrete I-, C-, and E-shaped stacks :

16,18,20. The central stack 16 is of I-shaped configuration .:
26 and two solenoid winding sections 22,24 are arranged thereon.
27 The C-shaped stack 18 carries no winding. It is arranged . :
2~ adjacent the stack 16 with air gaps 26,26 in the magnetic .~ .
29 circuit. In this manner a filter choke structure is effected ;; `:- -for a purpose more completely described hereinafter. The -: -, S~974031 -6 : ~.. . .. . . .
,: ::: . . . .
: : .

5 ~ 7~
I remaining E-shaped stack 20 of laminations is arranged adja-cent to the central stack 16 with an air gap 32 in the mag-netic circuit of the transformer. Secondary winding sec-tions 27,28 are arranged on the outer legs of the transformer structure. A control winding 30 is arranged on the central leg of the E-shaped stack 20. The air gap 32 arranged between the stack 30 and the stack 16 is smaller than the air gap 26. From this view it is readily seen that rela-tively standard configurations of laminations are used. No apertures of any kind are necessary in any of the lamina-tions, and no special shaping is necessary. Of course, L-shaped, I-shaped and T-shaped laminations can be used to make up stacks of E-shaped laminations and so on. Likewise, ~ the winding sections are relatively standard solenoids and - are readily slipped ;nto the laminations without any neces-sity for winding in place or for torroidal and like winding machinery.
The transformer is shown schematically in FIG. 2.
Primed reference numerals correspond to the reference numerals 1n the previously described view. Alternating potential is applied at input terminals 33,34. One terminal 33 is connected to the primary winding section 22',24' by isolating diodes 36,38 respectively. The other terminal 34 - is connected to the common central terminal of the windings 22',24'. The resonating windings 27',28' are connected to a capacitor 40 as shown. Secondary windings 27'',28'' are connected to a full wave rectifier circuit having rectifying diodes 42,44 for delivering direct potential to a pair of output terminals 46,48. The control winding 30' is connected between the cathode electrodes of the rectifying diodes 42,44 and the terminal 48 by an ..~

.`,; , ', ,,, :

'7 1 adjustable resistor 50. Alternatively, a poten-tiome-ter (not 2 shown) is connected as shown in FIG. 8 of the above-listed 3 U.S. Patellt 3,148,326. Preferably, a smoothing capacitor 52 4 is connected across the terminals ~6,68. A bleeder resistor 54 is optional. Alternatively, in some applications, the resonating

6 windinq sections 27',28' are combined in effect with the secondary

7 winding sections 27'',28'' and a resonating capacitor is connected

8 across the secondary winding or a portion thereof. Such an g arrangement is shown in the above-mentioned U.S. Patent 3,148,326.
The basic theory of operation of ferroresonant transformers 11 (constant voltage stabilizers) is well established. The 2 invention utiliæes the same principles except that the net 13 change in magnetic flux density per half cycle of the saturating 1~ transformer core 15 controlled with a control winding.
The output voltage across the secondary windings of a 16 ferroresonant transformer is:
17 Eo = 2~ AcfNsX10 volts (1) :
1~ where ~ is the change in flux density per half cycle 19 Ac is the cross-sectional area of the outer legs of the core; i~
f is the operating frequency; and Ns is the number of turns of the secondary winding.
22 With the operating frequency substantially constant, the 23 output voltage is maintained substantially inversely proportional ~-24 to current flow in the control winding 30' according to the ~5 invention by the simple feedback arrangement shown. ;-26 The ~H characteristics of the outer legs of the core , i 27 stack 20 is shown by a curve 60 in FIG. 3 while the ~-H
28 characteristic for the central leg is depicted by another curve 70. The latter differs from the former because of the ; 30 effect of the air gap 32. With direct current applied to the '. ' ~' `' .... .. . . . . . . .
~ . : , . ~ - . ' : . ' ' ~!~35~S~7 1 control winding 30 a magnetomotive force ~11 as shown will be 2 imposed on the center leg of the core. A Elux density equal 3 to ~1 will then be established in the center leg. Assuminq that 4 the reluctance of both outer legs are equal, a flux density of 31 will be established in each outer leg. By connecting the 6 respective primary windings in the proper phase rela-tionship as shown in FIG. 2, the net ~ that will occur during each '~ 8 half cycle for each outer leg will be ~s-~l Hence, by increasing g the control current, Ic, ~ is reduced and thP output voltage Eo will decrease.
11 The gain equation is derived as follows:

12 ~ ~s ~1 (2) 13 ~1 ~d 1 (3) 14 where ~d is the effective core permeability with an lS air gap Q
16 ~d ~mQm (4) , 17 ~m+~mQg 18 where Qm is mean flux path of the center leg, and ~m is ~' 19 the core material permeability and Hl -- o-4~NCIC

m (S) 23 where Nc is the number of turns in the control winding c is the control current Substitution of (3), (4) and (5) into (2) yields:

s ~ 0.4~ N I

7 m ~m g (6) 28 Substituting equation (6) into equation (1):
29 Eo = 2AcfNs ~ s - 0.4~mNCIc] X 10 Qm+~mQg (7) .

, ..
.: , . . .

~ ()5~
erenticlting (7? with respect to control current Ic, 2 the desired gain equa tiOII iS:
3G = dEo = -0.8~r~lmNcN fA XlO 8 (8) dI Q +~ Q
4 c m m g 5if ~mQg<<Qm, then:
6G = -0.8~NcNsfAcxlO 8 (9) ` Q
7 g 8 Equation (9) shows that the gain is controlled by defining g the frequency of operation, judicious choice of control and secondary windings, and specifying appropriate core dimensions ~, 11 and gap length according to the invention.
12 The power supply functions in direct manner. The a.c. input 13 power source is applied to terminals 33 and 34. Assuming 14 terminal 33 is positive and terminal 34 negative, the a.c.
flux 0ac, set up by the winding 22' is in the left to right 16 direction. Control current, Ic flowing in winding 30 as 17 shown sets up flux 0dc in each of the outer legs of the 18 lower half of the core 20. The flux shown veering to the 19 left opposes 0ac, and the flux veering to the right adds ~ -to 0ac.
-: ~
` 21 Because of the air gap 26 separating the C-shaped stack 22 18 from the I-shaped stack 16 of the core, the magnetic ~`
23 reluctance path around the outer right leg of the E-shaped -24 stack 20 will present a lower reluctance to the flux 0ac + 0dc ,.,. ~
i~ 25 until the core leg saturates. Hence, as this flux flows, j 26 power will be applied to the load, across terminals 46 and `l 27 48, winding 28~ and diode 42. At the same time, since the ,. . . .
~l 28 resonating winding sections are in parallel, both the outer ~
: !
29 legs will experience the same flux change. As the right outer leg saturates and the reluctance increases, the ac .
. ' , ~ SA974031 -lO-: ~ :
:
.
:: ". :, .
, .. . ...

~)5~ 7 1 flux will be forced to flow upwards through -the air yap 26 2 and the upper lamination stack 18. The flux change through 3 outer legs of the E-shaped core goes to zero and no more 4 energy is transferred to the load for the remainder of that half cycle. The voltage across the resonating winding section 6 collapses and the voltage across the resonating capacitor 40 7 is discharged.
8 As the polarity across terminals 33 and 34 reverses on g the next half cycle, the same explanation is valid for the left side of the magnetic circuit.
11 With the proper choice of values for the resonating 12 capacitor 40, the resonating winding sections 27,28 for 13 resonance at the a.c. line frequency and the air gap 32 for a 14 given core geometry, the ferroresonant phenomenon obtains and the output waveform will be trapezoidal with the net rectified 16 dc voltage across the terminal 46 and 48.
17 Because the saturation flux level of the outer legs 18 can be varied as a function of current in the winding 30, 19 the net result is a ferroresonant regulator with closed l.oop control in a single unique magnetic structure.
21 An alternate embodiment of the invention is shown schematically .22 in FIG. 4. The arrangement is similar in many respects to that 23 previously described. The core of the transformer is denoted 2 by the reference numbers 16' and 20', while the magnetic shunt 18' is depicted in conventional form for that structure in -~
26 ferroresonant transformer diagrams. The power available across 27 the d.c. output terminals 46,48 is frequently used for maintaining , 28 the control current but a separate supply is prefereably used 29 as shown here. This auxiliary supply comprises rectifying :, diodes 82,~84, secondary winding sections 87,88, and a smoothing .

,::

5~ 7 1 capacitor 89. A bleeder resistor is optional.
The voltage across the remotely located load 90 is applied to input terminals 92,9~ of a control current trans-lating circuit arrangement. This voltage is divided by resistors 96,98 and the resultant error signal applied to one input terminal of a differential amplifying circuit 100 at the output of which an "actuating signal" is generated.
The other input terminal is connected to the arm of a command potentiometer 102 connected in a stable potential network.
This network is a part of the amplifier circuit 100 as readily available commercially. Alternatively, this network circuit is external to the amplifier circuit 100 as shown. A dropping ~
resistor 103 and a Zener diode 104 are optional. The control -current flowing through the control winding 30'' is obtained ~
from the collector-emitter electrode circuit of a final cur- --rent controlling transistor 105 having a resistor 106. Another -~
Zener diode 108 is connected between the base electrode of ~: ~
the transistor 104 and the amplifying circuit 100 for level shifting purposes. Leakage current flows through a resistor 109. The control current through the winding 30'' is varied by adjustment of the potentiometer 102 in the reference poten-tial and actuating signal generating circuity.
The regulation of the supply output voltage is obtained by a d.c. control current obtained from a d.c. monitoring point, whereby the circuit is not sensitive to changes in the frequency of the a.c. input source in any way. -~
While the invention has been described and illustrated in terms of a preferred embodiment, and alternate structure has been suggested, it is to be clearly understood that those skilled in the art will make additional changes without departing from the spirit and scope of the invention as .~
defined in the appended claims.

,-,

Claims (11)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A controlled ferroresonant transformer for a regulated power supply circuit arrangement comprising a ferromagnetic electric transformer core comprising an E-shaped stack of laminations, an I-shaped stack of laminations and a C-shaped stack of laminations, a primary winding arranged on said I-shaped stack with said C-shaped stack adjacent and spaced by an air gap for imparting the effect of a filter choke, a secondary winding comprising two coils arranged on the outer legs of said E-shaped stack with the E-shaped stack adjacent said I-shaped stack and spaced by an air gap, a resonating winding comprising two coils arranged on the outer legs of said E-shaped stack, and a control winding arranged on the central leg of said E-shaped stack.

2. A controlled ferroresonant transformer assembly for a regulated power supply circuit arrangement comprising a ferromagnetic electric transformer core comprising an E-shaped stack of laminations, an I-shaped stack of laminations and a C-shaped stack of laminations, a primary winding arranged on said I-shaped stack with said C-shaped stack adjacent and spaced by an air gap for imparting the effect of a filter choke, a secondary winding comprising two coils arranged on the outer legs of said E-shaped stack with the E-shaped stack adjacent said I-shaped stack with an air gap, a resonating winding comprising two coils arranged on the outer legs of said E-shaped stack, a capacitor connected across said resonating winding, and a control winding arranged on the central leg of said E-shaped stack.

3. A controlled ferroresonant transformer as defined in claim 2 and wherein said capacitor and said resonating winding have values of capacity and inductance at which the subcircuit thereby comprised is substantially resonant at the frequency of the alternating current for which the trans-former is designed.

4. A controlled ferroresonant transformer assembly as defined in claim 2 and further comprising a rectifier connected to said secondary winding, a resistor connected to the output of said rectifier, and said control winding arranged on the central leg of said E-shaped stack and connected in series with said resistor and said rectifier.

5. A controlled ferroresonant transformer assembly as defined in claim 4 and incorporating isolating diodes interposed at the terminals of said primary winding.

6. A controlled ferroresonant transformer assembly as defined in claim 4 and wherein a reference potential and actuating signal generating circuit is connected between said control winding and said resistor and arranged for adjusting current flow in said control winding.

7. A controlled ferroresonant transformer assembly as defined in claim 6 and wherein said reference potential and actuating signal generating circuit is adjustable.

8. A controlled ferroresonant transformer assembly as defined in claim 4 and incorporating a variable resistance device having a control terminal and having a resistance element interposed in series with said resistor, said control winding and said rectifier, a differential amplifying circuit having an output terminal coupled to said control terminal and two input terminals, electric circuitry connected across said rectifier for deriving an input signal reflecting any variation in potential and connected to one of said input terminals of said amplifying circuit, an electric circuit arranged for generating a reference input level substantially free from said variation and connected to the other input terminal of said amplifying circuit, other secondary winding sections arranged on the outer legs of said E-shaped core stack, and another rectifier circuit connected between said other secondary winding sections and said amplifying circuit for energizing the latter circuit.

9. A controlled ferroresonant transformer assembly as defined in claim 8 and incorporating a potentiometer connected in the reference input level generating circuit of said interconnected amplifying circuit and said rectifying circuit and having a tapping connected to the other input terminal of said amplifying circuit.

10. A controlled ferroresonant transformer assembly as defined in claim 8 and wherein said variable resistance device comprises a current controlling transistor connected to said amplifying circuit and having the collector-emitter electrode circuit connected in series with said control winding and said rectifier circuit independently of said connections for ener-gizing said amplifying circuit.

11. A controlled ferroresonant transformer regulated power supply cir-cuit arrangement comprising a ferromagnetic electric transformer core comprising an E-shaped stack of laminations, an I-shaped stack of laminations and a C-shaped stack of laminations, a primary winding arranged on said I-shaped stack with said C-shaped stack adjacent and spaced by an air gap for imparting the effect of a filter choke, a secondary winding comprising two coils arranged on the outer legs of said E-shaped stack with the E-shaped stack adjacent said I-shaped stack with air gap for stabilizing device gain, a resonating winding comprising two coils arranged on the outer legs of said E-shaped stack, a capacitor connected across said resonating winding, said capacitor and said resonating winding have values of capacity and inductance at which the subcircuit thereby comprised is substantially resonant at the frequency of the alternating current for which the trans-former is designed, a control winding arranged on the central leg of said E-shaped stack, a rectifier connected to said secondary winding, electric leads for connecting an electric load device to said rectifier, a differential amplifying circuit having two input terminals and an output terminal, other secondary winding sections arranged on the outer legs of said E-shaped core stack, and another rectifier circuit connected between said other secondary winding sections and said amplifying circuit for energizing the latter circuit, a current controlling transistor having a base electrode connected to said output terminal of said amplifying circuit and having the collector-emitter electrode circuit connected in series with said con-trol winding and said other rectifier circuit, a potentiometer connected in the direct current energizing circuit of said interconnected amplifying circuit and said other rectifying cir-cuit and having a tapping connected to one of the input terminals of said amplifying circuit, and a voltage divider connected between said electric leads for detecting any variation in potential at said electric leads and having a tapping connected to the other input terminal of said amplifying circuit.