Inductor apparatus for application to ferroresonant regulators

Abstract: An inductor structure is combined with a ferroresonant regulator as a filter inductor in one instance, and as a regulat­ ing inductor in another. In one example, a ferroresonant volt­ age regulator includes a pair of shunt filters at its output to re­ duce the low order odd harmonic content of the AC output. The filtering arrangement includes two LC shunt filters having their independent inductor windings wound on a single magnet­ ic core unit. Auxiliary windings coupled to each of the inductor windings are placed in series with the output to buck any re­ maining harmonics. In a second instance, independent regulating inductors in a multiphase ferroresonant regulator are also realized on a single magnetic structure.

Description: This invention relates to a ferroresonant regulator according to the introductory portion of the single claim. The energy storage requirements of most inductor applications has generally dictated that each inductor winding be wound on a separate and independent magnetic core. In applications requiring a plurality of inductors, this requirement of a separate core for each inductor considerably increases the physical dimensions and overall weight of electrical equipment compared with those values if the same inductive effect could be achieved with fewer magnetic cores than inductors. One such instance is the output filter for a ferroresonant regulator. An arrangement disclosed in US-A-2,694,177 avoids the need for a separate magnetic structure for the inductor by providing a separate magnetic path on the basic ferroresonant magnetic structure of the transformer. This arrangement, however, requires an extra set of shunts for the ferroresonant transformer core and complicates the design of the ferroresonant transformer. This becomes even less desirable when a particular transformer design must be capable of accommodating a wide range of output loads. Additionally, in some instances, the shunts may not be sufficient to achieve the desired inductance. In connection with alternating current machines a transformer is prior known (The Performance and Design of AC Machines. M.G. Say. Pitman Paperbacks. London. 1958. pages 9, 99, 161) having a magnetic core with a three leg magnetic path arrangement having two outer legs and a center leg, all legs being coupled by yokes and the center leg having a cross-section area at least twice that of each of the outer legs. From US-A-2,825,024 an AC voltage stabilizer is prior known which uses a saturated resonance transformer and a compensation of the generated harmonics by means of a linear transformer and a saturated reactor. A further AC current supply apparatus for providing a substantially harmonic free and constant output voltage is known from US-A-3,286,159. The apparatus uses a transformer with a high reluctance magnetic shund placed between the primary and secondary windings and a further high reluctance path as a return path for magnetic flux linking only the secondary winding. The present invention starts from that prior art. The invention is directed to the problem of providing a magnetic inductor structure combined with a multi-phase regulating transformer where the function of several inductors is realized by a single magnetic core. The solution of the problem is characterized in the single claim. Brief Description of the Drawings An understanding of the invention may be readily attained by reference to the following specification and the accompanying drawings in which: Fig. 1 is a schematic of a ferroresonant regulator utilized in an uninterruptible power supply arrangement and including harmonic filtering in the output, Fig. 2 is a perspective view of an embodiment of an inductor; Fig. 3 is a schematic of a multiphase ferroresonant regulator arrangement in which the regulating inductors for each phase are wound on a single magnetic structure according to the principles of the invention. Detailed Description In order to make clear the environment of the invention an uninterruptible power supply (UPS) including a ferroresonant regulating transformer is shown in Fig. 1. It has two independent input power sources; one an AC line source 10; the other a battery powered inverter circuit 20. Normally when the AC 1 line signal is acceptable, it supplied power through a ferroresonant regulating transformer 30 to the output terminals 41 and 42. If it is unacceptable, it is disconnected from the regulating transformer 30 by opening line switch 14, and the inverter 20 subsequently supplies all the power to the output. The uninterruptible power supply (UPS) operates under the direction of a central control unit 50, which determines the particular mode of operation of the ups. The normal mode of operation is one in which power applied to the output is derived solely from the AC line. The control circuit 50 continuously monitors the line signal for proper frequency and amplitude. During this normal mode of operation, the inverter 20 is operated in an idling mode. Its switching devices 21 and 22 are continuously operating, but the signal phase of the inverter signal relative to the output signal is controlled by the control unit 50 and the inverter drive 24 so that it delivers no power to the output. The control unit 50 accomplishes this by monitoring the phase of the output signal through winding 31 and controlling through the inverter drive 24 to have the inverter output signal substantially in phase with the output signal. If the AC signal is deemed unacceptable, the AC line 10 is disconnected from the regulating transformer 30 by the control unit 50 by opening a line switch 14, and the inverter 20 runs freely under inverter switch drive 24 and now supplies all the power from its battery 23 to the output terminals 41 and 42. An uninterruptible power supply utilizing a two input single output ferroresonant regulator and this particular mode of operation has been disclosed in US-A-4,010,381, The AC output of the secondary winding 32 includes harmonic components which comprise a significant part of the output power. These harmonics may damage or unduly stress electrical components coupled to the output, and hence, an output filter arrangement is included to suppress selected low order odd components of these harmonics. The overall filter circuit includes two inductor windings 61 and 62; each connected in series with a capacitor 71 and 72. The two capacitors 71 and 72 represent in addition the conventional ferroresonant resonating capacitor which is now divided into two separate capacitor devices 71 and 72, included in the two LC filters, respectively. Each series connection of an inductor winding and a capacitor forming individual shunt filters 1 and 2 is connected across the output terminal 41 and terminal 33 of the regulator's secondary winding 32. Each inductor winding 71 and 72 is further coupled to an auxiliary or a secondary winding 91 and 92 are further connected in series with each other and with the output terminal 41 and are operative to block the harmonics supplied by the regulator's secondary winding 32 and complement the action of the shunt filters to further suppress these harmonics. The first and second shunt filter circuits 1 and 2 are tuned to the third and sixth harmonics of the fundamental of the output signal, respectively. The combined effect of these two shunt filters has a combined bandwidth wide enough to effectively suppress the third, fifth and seventh harmonics of the output signal. The added harmonic content of the voltage of the secondary winding 32 of the regulator appears mostly across the inductor windings 61, 62, 91 and 92, and very little appears at the output terminals 41 and 42. The two inductor windings 61 and 62 must be substantially independent of each other and yet be wound on a single magnetic structure. The magnetic core structure assembly for the inductor winding, as shown in FIG. 2, comprises a stacked array of EI laminations forming a three leg core structure 200. In order to operate effectively as a shunt filter, the two inductor windings 261 and 262, and their associated secondary windings 291 and 292, must be substantially effectively isolated magnetically from one another. Hence, inductor windings 261 and 262 and associated secondary windings 291 and 292 are wound on the outer legs 210 and 220 of the core structure. To minimize the coupling between the two windings, a cross sectional area of the center leg 230 of the core is dimensioned to at least exceed a cross sectional area of each of the outer legs 210 and 220 in area by a factor of at least two. This increase in area of the central core leg in the illustrative embodiment is achieved by making a width W of the center leg 230 twice a corresponding width w of the outer legs while the depth d of all legs is equal. This has been found to provide an inductive coupling of less than 0.3, which is sufficient to allow the two filters to operate in a stable mode and substantially independently of each other. It is apparent that this unique core structure arrangement providing considerable reduction in cost weight and volume of the overall power supply unit. The above description pertains to a magnetic core structure for a filter arrangement of a ferroresonant regulator. According to the invention the magnetic core structure is utilized in a multiphase controlled ferroresonant regulator such as shown in FIG. 3 wherein a regulating inductor must be switched into and out of the circuit in each phase. In this instance, the regulating inductors for each individual phase all share a common magnetic core. The example shown in Fig. 3 is a Scott T connection of two single phase controlled ferroresonant regulators to convert a three phase input into a regulated two phase output. The two regulating inductors for each output phase are constructed on the same core structure. The particular embodiment shown in Fig. 3 shows the main core 310 and auxiliary core 320 of a Scott T transformer connection and the two associated input windings 311 and 321. The three phase input is applied to the center tapped main winding 311. One phase of the input and the center tap of winding 311 is applied to winding 321, which in Scott T terminology is known as the teaser winding. It converts the three phase input of terminals 301, 302 and 303 into a two phase output on output windings 312 and 322. These two outputs are rectified in parallel and supplied as a DC voltage at output terminals 304 and 305. Regulation is controlled by using the controlled ferroresonant techniques such as disclosed in U.S. Patent Re. 27,916 issued to R.J. Kakalec, February 12, 1974, and assigned to the same assignee as this application. As disclosed therein, output voltages are regulated by simulating saturation of the transformer by switching an inductor device into a connection with the ferro-capacitor and regulating winding in response to a voltage error detection circuit. Accordingly as shown in Fig. 3, each output phase includes first and second control windings 314 and 324 respectively and first and second resonant capacitors 318 and 328 respectively. The first and second control windings 314, 324 are selectively coupled by triac switches 316 and 326 respectively to an inductor strcture 300 including first and second inductor windings 315 and 325 respectively. The triac switches 316 and 326 are controlled by a voltage error detection circuit which is not disclosed. In accordance with the principles of the invention, the two regulating inductors 315 and 325 share a single magnetic core 330 according to the core structure 230 of Fig. 2 and inductor windings 261 and 262 wound on outer legs 210 and 220 respectively. The secondary windings 291 and 292, however, are not required. This arangement significantly reduces the size and weight of the overal circuit.

Claims: A ferroresonant regulator comprising a three phase input (301, 302, 303), a two phase output (312, 322) and a Scott T transformer structure (310, 320) coupling the input to the output; at least a first and second control winding (314, 324) for resonance control and a first and second resonating capacitor (318, 328) connected to the first and second control windings respectively, characterized by an inductor structure (L1, L2) including first and second inductor windings (315, 325) and a further transformer structure (330) comprising two outer legs (210, 220) having an identical cross sectional area and a central leg (230) having a cross sectional area twice that of the identical cross sectional area, the first and second inductor windings (315, 325) being wound on the first and second outer legs (210, 220) respectively, and first and second controllable switches (316, 326) for selectively coupling the first and second inductor windings (315, 325) to the first and second control windings (314, 324) respectively.

Inventors: FOUAD FAKHRY AHMED, KAKALEC ROBERT JOHN, MENKES HENRY EDWARD, FOUAD, FAKHRY AHMED, KAKALEC, ROBERT JOHN, MENKES, HENRY EDWARD
Applicants: AMERICAN TELEPHONE & TELEGRAPH, AMERICAN TELEPHONE AND TELEGRAPH COMPANY
Application year: 1986
Main classification: G05F3
IPC codes: G05F3, H02J9, H01F37, H01F30