US3697856A

US3697856A - Voltage regulating circuit

Info

Publication number: US3697856A
Application number: US97861A
Authority: US
Inventors: Kwang-Ta Huang
Original assignee: US Department of Navy
Current assignee: US Department of Navy
Priority date: 1970-12-14
Filing date: 1970-12-14
Publication date: 1972-10-10
Anticipated expiration: 1989-10-10

Abstract

An arrangement for desensitizing dc power supplies to momentary ac power interruptions by incorporating therein an energy-storage network which is charged rapidly to its peak capacity, and then remains on ''''stand-by'''' status until an ac power loss occurs. It then supplements the output of the conventional capacitor to maintain steady dc power for a longer period of time than would be otherwise possible.

Description

Umted States Patent 1151 3,697,856 Huang 1451 Oct. 10, 1972 [54] VOLTAGE REGULATING CIRCUIT 3,090,017 5/1963 Novic ..323/DlG. l Inventor: g g, Oxnard Benjamin X [73] Assignee: The United States of America as FOREIGN PATENTS OR APPLICATIONS rNepresenled by the Secretary of the 980,631 l/l965 Great Britain ..323/17 avy [22] Filed, 14 1970 Primary Examiner-Gerald Goldberg AttorneyRichard S. Sciascia, Howard J. Murray, Jr. [2l] Appl. NO-I 9 ,861 and Q. Baxter Warner [52] US. 01 ..321/10,323/17,323/1)1o. 1 [57] ABSTRACT [51] Int. Cl....'. ..H02m l/ 14, H02m 7/12 An arrangement for desensitizing dc power supplies to [58] Field of Search ,.323/17, DIG, 1, 22 SC, 22 T, momentary ac power interruptions by incorporating 323 93; 32 2017 0 1 307 23 45 4 therein an energy-storage network which is charged rapidly to its peak capacity, and then remains on I 56] References Cited stand-by status until an ac power loss occurs. It then supplements the output of the conventional capacitor UNITED STATES PATENTS to maintain steady dc power for a longer period of l b th 'bl 3,217,233 11/1965 Drusch ..321/27 R erw'se POSS 6 3,327,202 6/l967 Mills ..'.....323/22 T 3 Claims, 13 Drawing Figures RECTIFIER FILTER V x BRIDGE 4 REGULATOR OUTPUT ENERGY RESERVOIR CIRCUIT PATENTEDncT 10 I972

SHEET

1 or 4 PRIOR ART LOAD

INSTANT OF SOURCE INTERRUPTION t A Fig. la

INSTANT OF SOURCE INTERRUPTION 5 T N m 4 G U A HR m w w m m I 6V C n N U m w E K M FT 8 TE R .L mw IS m TIMI E CE mm U 0 CV A N N PATENTEDUCI 10 I972 3 6 97 856 ENERGY RESERVOIR CIRCUIT IOOFFIG.5

1 l 33 msec I* 33 msec Fig. 6b 'Q- VOLTAGE REGULATING CIRCUIT STATEMENT OF GOVERNMENT INTEREST BACKGROUND OF THE INVENTION The rudimentary function of a dc power supply is to receive energy from an ac source, store that energy, and then release it as required by the load. If the ac source fails abruptly, the dc output will drop-not suddenly, but exponentially-as the quantity of stored energy'is gradually siphoned by the load. The time that it takes for the energy todeplete obviously depends on the size of the capacitor storing the energy, the amount consumed by the load, and the minimum voltage required by the load.

It is not unusual for momentary ac power disruptions to occuras they might during a lightning storm or during frequency adjustments at the power station. If the disruption is brief enough, the stored energy in the power supply may be ample to smooth over any effect on the dc voltage to the load. When the power supply incorporates a basic bridge rectifier-capacitor circuit, it is possible to improve dc output stability in the event of an ac disruption by increasing the size of the output capacitor. This expedient is not practicable, however, for more sophisticated dc power supplies, such as those that make use of variable-phase-angle-firing SCRs.

SUMMARY OF THE INVENTION At the present time, dcpower supplies generally are not designed to maintain continuous and steady voltages during momentary disturbances in their ac powertransmission-supply .line. Yet, during lightning storms, or through some line fault, electrical disturbances can occur within transmission lines that tend to depress dc power-supply voltages. There are known methods for desensitizing the dc power supplies to these ,ac

disturbances. One way-if the power supply does not make use of SCRs-is to use larger capacitors in the rectifier circuit. However, this is often unfeasible economically. The present concept makes use of an auxiliary energy-reservoir network for sustaining the output power for relatively long periods even when SCRs are employed.

STATEMENT OF THE OBJECTS OF THE INVENTION One object of the present invention, therefore, is to provide a dc power supply network having decreased sensitivity to momentary, interruptions in the ac source.

Another object of the invention is to provide a dc power supply having an auxiliary energy-reservoir network incorporated therein.

A further object of the invention is to provide means for sustaining output power from a dc supply circuit which includes SCRs therein.

An additional object of the invention is to eliminate the need for utilizing excessively large capacitors in order to maintain output power from a dc supply circuit in the face of momentary disturbances in the ac input thereto.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 (A) is a schematic circuit diagram of a basic dc power supply network as now known in the art;

FIGS. 1 (B) and (C) are graphs useful in explaining the operation of the network of FIGS. 1 (A);

FIG. 2 is a graph illustrating the effect of using a larger-valued capacitor in the network of FIG. 1 (A);

FIG. 3 (A) is a schematic circuit diagram of a conventional dc power supply network using SCRs;

FIGS. 3 (B) and (C) are graphs useful in explaining the operation of the network of FIG. 3 (A);

FIG. 4 is a block diagram of a dc power supply network designed in accordance with a preferred embodiment of the present invention;

FIG. 5 is a schematic diagram of the energy reservoir network of FIG. 4;

FIG. 6 (A) is a schematic circuit diagram of a conventional dc power supply network modified to add an auxiliary capacitor;

FIG. 7 (A) is similar to the circuit of FIG. 6 (A) but with the invention energy-reservoir network in place of the auxiliary capacitor; and

FIGS. 6 (B) and 7 (B) are graphs useful in explaining the operation of the networks of FIGS. 6 (A) and 7 (A), respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT A bridge rectifier and a capacitor connected as shown in FIG. 1 form the conventional configuration for converting ac voltage to dc voltage. The energystoring capacitor, C stores and supplies energy to the load. If the ac source is interrupted, the dc output voltage decays exponentially to zero. To illustrate, choose an arbitrary voltage, V,, as the minimum value required where V, is the instantaneous voltage across capacitor C at the time the ac source is interrupted. The time duration, t is given by EQEM E-m do Lin where I, is the dc load current. The shortest 1,. results if the ac source is interrupted when the instantaneous voltage across capacitor C is V,,,,-,, [FIG. 1(C)]; than Eq. (2) becomes o( min r) da emin Equation (3) shows that when I is fixed, r is exraises V,,,,,, and, therefore, the quantity V,,,,,, V,, the increase in C is dominant in increasing Q hence, t

FIG. 2 shows the increase in e obtained by using a larger C Curve 1 is for the large-valued capacitor C Even though a simple method of extending r is to increase C there are factors that limit the size of the energy-storing capacitance.

When selecting a larger-valued capacitance, it becomes necessary to examine the rise in rectifier cost against the extension of I, obtained. Also, with increasing capacitance, the ratio of initial turn-on current to rated load current increases. This necessitates opera tion of larger rectifiers at increasingly derated condition, which is inefficient. Also, a larger-valued capacitance increases the response time of the dc power supply thereby lengthening the flow duration of the turn-on current. Longer flow duration contributes to rectifier failure from heating.

FIG. 3 (A) is a circuit diagram of a basic silicon controlled rectifier (SCR) dc power supply. The dc output voltage level is controlled by the variable-phase angle-firing technique, which provides a partial fullwave rectified waveform and requires a very large capacitance to obtain a smoothed-out, limited-ripple waveform; therefore, unlike the transistor-regulated dc supply circuit, the SCR circuit is not amenable to significant increase in t,. by the mere increase of capacitance. This fact is displayed in FIG. 3 (B) which illustrates the limited-ripple voltage obtained by using a (large) capacitor, C,,. It also shows the extended duration r obtained with the loss of the ac power source. Increasing the capacitance reduces the ripple, as shown in FIG. 3 (C), but V,,,,-,, V, is essentially unchanged and duration t increases slightly. The limitations on extending 1,. in a basic dc power-supply circuit are therefore more severe in a power circuit using SCRs instead of transistors.

With either circuit, however, it is possible to supplement the Q available in the basic powersupply circuit-and thus t,.with an energy-reservoir circuit, designed in accordance with the principles of the present invention. One preferred embodiment is illustrated in FIGS. 4 and 5 of the drawings.

The basic principle of this circuit is to charge an energy-storing capacitor at a high voltage and release this energy to the load during momentary ac power loss. The energy storing C is charged rapidly to its peak capacity during normal operations of the ac power source. The reservoir circuit of FIGS. 4 and 5 remains on standby status and consumes very little power. At the instant of ac power loss, the reservoir circuit 10 supplies Q to supplement Q, and maintain V throughout the outage. The capacitance C can be calculated by modifying Eq. (3):

aux"

where r,,,, is the extended duration of dc voltage without insertion of the energy reservoir circuit; and V,, is the peak value to which C can be charged.

The current limiter 12 in the auxiliary circuit is used to (I) prevent damage to the rectifier D by the initial charging current and (2) protect the active elements in the control circuit from the high current from the rectifier transformer during a malfunction of dc power supply.

During the initial charging, the' voltage of C usually is lower than the output voltage, V,,. Rectifier D is used to prevent damage to transistors Q, and Q: from the current flowing from point 3. The voltage difference, V V,), determines the selection of the maximum rating of V the voltage of the power transistor 0,. The comparison circuit 14 is present to sense the voltage drop and to fumish the actual signal to operate the control circuit 16. The sensing voltage should be adjusted in such a position that the energy-reservoir circuit 10 remains on standby status in normal operation. The control circuit 16 adjusts the flow rate of Q as required by the load to maintain the output voltage The energy-reservoir circuit is connected to the basic power supply as shown in FIG. 4. The reservoir circuit 10 offers considerable latitude in the selection of the value of the energy-storing capacitance and the operating voltage. This flexibility is not offered in the basic dc power-supply circuit because the required output voltage fixes the voltage across theenergy-storing capacitor, C the method of obtaining the larger Q, is limited to increasing C, and a larger C, is accompanied by undesirable effects, such as excessive inrushing of turn-on current.

The power ratings of the components in the reservoir circuit 16 can be modest because the average power is low, although the peak energy delivered momentarily may be appreciable. The auxiliary reservoir circuit,

even with the use of a large energy-storing capacitor C does not reduce the response time of the basic power supply because the one is independent of the other.

FIGS. 6 and 7 illustrate the advantages obtainable by utilizing a network embodying the principles of the present invention. Simply adding a capacitor C as in FIG. 6 (A) extends the dc output level by 12 msec (FIG. 6 (8)). However, utilizing the energy-reservoir network 10 of FIGS. 4 and 5 in the circuit of FIG. 7 (A) extends the dc output level to 38 msec (FIG. 7 (8)), using the same value of capacitor. This is an increase of over 200% as compared to the conventional technique of FIG. 6 (A).

Obviously many modifications and variations of the present invention are possible in the 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.

lclaim:

1. An energy reservoir circuit for desensitizing a dc. power supply to momentary ac. power interruptions comprising:

a charge storing network connected in parallel with the main rectifying and filtering network of a dc. power supply, and storing network comprising;

a transformer;

a current limiter connected in series with the secondary of said transformer;

a rectifier connected in series with said current limiter;

a capacitor connected in parallel with the transformer secondary, current limiter and rectifier;

discharge rate controlling means connected in se- 3. A circuit as recited in claim 2 wherein said actuatwlth said capacltori and ing means is comprised of a comparison circuit conactuating means connected to said discharge rate controlling means. 2. A circuit as recited in claim 1 wherein said 5 discharge rate controlling means comprises a power transistor in series withaprotective diode.

nected across the output of the energy reservoir for sensing a voltage drop in the output from the main rectifying and filtering network of a dc. power supply.

Claims

1. An energy reservoir circuit for desensitizing a d.c. power supply to momentary a.c. power interruptions comprising: a charge storing network connected in parallel with the main rectifying and filtering network of a d.c. power supply, and storing network comprising; a transformer; a current limiter connected in series with the secondary of said transformer; a rectifier connected in series with said current limiter; a capacitor connected in parallel with the transformer secondary, current limiter and rectifier; discharge rate controlling means connected in series with said capacitor; and actuating means connected to said discharge rate controlling means.

2. A circuit as recited in claim 1 wherein said discharge rate controlling means comprises a power transistor in series with a protective diode.

3. A circuit as recited in claim 2 wherein said actuating means is comprised of a comparison circuit connected across the output of the energy reservoir for sensing a voltage drop in the output from the main rectifying and filtering network of a d.c. power supply.