Microprocessor controlled voltage regulating transformer

• US 4,419,619 A
• Filed: 09/18/1981
• Issued: 12/06/1983
• Est. Priority Date: 09/18/1981
• Status: Expired due to Term

• Current Assignee: Cooper Industries, Inc. (Eaton Corporation PLC.)
• Original Assignee: Mcgraw-Edison Company (Eaton Corporation PLC.)
• Inventors: Hurley, James R., Gilker, Clyde, Jindrick, James A., Dolnik, Thomas G., Nohria, Naresh K., Baranowski, James A.
• Primary Examiner(s): BEHA JR, WILLIAM
• Application Number:
  US06/303,608
• Time in Patent Office: 809 Days
• Field of Search: 323/256, 323/216, 323/257, 323/260, 323/263, 340/646, 340/659, 340/661, 361/82, 364/483, 307/31, 307/32
• US Class Current: 323/257
• CPC Class Codes: H02M 3/33515 with digital control
• CPC Class Codes: H02M 5/22 using discharge tubes with control electrode or semiconductor devices with control electrode
• CPC Class Codes: H02M 7/1626 with automatic control of the output voltage or current

Abstract

A voltage regulating transformer utilizing a microprocessor and a versatile multipurpose set of hardware modules and software modules it is described. A standard tap changing mechanism is driven in response to an analog control signal to change the output voltage of the transformer in response to digitally sampled values of voltage and current which have been transformed from the time domain to the frequency domain through a software program using Fourier transform techniques. The output current is also transformed and digitally processed to determine the power factor and the direction of power flow through the transformer. By inserting the digital values of the line characteristics to the load, line drop compensation is provided for. The difference in voltage across the input and output transformers is transformed to a digital signal and internally processed to provide an indication of the position of the tap changing mechanism without relying upon mechanical devices. The various software and hardware modules are designed so as to be readily utilizable in other electrical distribution controls.

Claims

1. A voltage regulating transformer, comprising:

a. a first winding defining a first plurality of turns and having an associated input terminal adapted to be connected to a source of A.C. voltage;

b. a second winding, electromagnetically coupled to said first winding, defining a second plurality of turns and having an associated output terminal;

c. changer means, operated in response to an analog control signal supplied thereto, for changing the ratio of turns through which current flows through said first winding and said second winding, whereby the voltage at said output terminal varies in response to said analog control signal when A.C. voltage is applied to said input terminal;

d. voltage output signaling means, operatively connected to said output terminal, for producing a plurality of digital voltage signals representative of the instantaneous A.C. voltage at said output terminal;

e. digital input means for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage;

f. digital computer means having a single microprocessor for Fast Fourier Transforming said plurality of digital voltage signals from the time domain into the frequency domain to obtain a measured digital voltage signal representative of the RMS voltage at said output terminal over the period of said A.C. voltage and for generating a digital control signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal; and

g. converter means for converting said digital control signals to an analog control signal to operate said changer means,

whereby said changer means is operated in response to the RMS voltage at said output terminal over the period of the A.C. voltage applied to said input terminal.

2. The voltage regulating transformer set forth in claim 1, further including:

a. current output signaling means, operatively connected to said output terminal, for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal, said digital current signals being separated in time from said digital voltage signals;

b. means, included within said digital computer means, for Fast Fourier Transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said measured digital voltage signal; and

c. means, included within said digital computer means, for processing said measured digital signals of current and voltage to produce a digital signal representative of the phase angle relationship of said instantaneous A.C. voltage and said instantaneous current at said output terminal over said period, whereby the power factor relationship between said instantaneous current and voltage is established.

3. The voltage regulating transformer set forth in claim 1, further including:

a. current output signaling means, operatively connected to said output terminal, for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal, said digital current signals being separated in time from said digital voltage signals;

b. means, included within said digital computer means, for Fast Fourier Transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said measured digital voltage signal; and

c. means, included within said digital computer means, for processing said measured digital signals of current and voltage to produce a digital signal representative of the product of;

1. said instantaneous A.C. voltage;

2. said instantaneous current; and

3. the cosine of the phase angle relationship of said instantaneous A.C. voltage and said instantaneous current, whereby the direction of power flow across said first winding and said second winding is established.

4. The voltage regulating transformer set forth in claim 2, wherein:

said single microprocessor has a plurality of digital registers for storing digital signals including said measured digital current and voltage signals and the power factor relationship between said current and voltage, and a digital I/O means for addressing and displaying the contents of said registers scaled to read RMS current and RMS voltage at said output terminal and said power factor.

5. The voltage regulating transformer set forth in claim 4,

further including asynchronous communications interface means for addressing and displaying the contents of said registers and for serially transmitting the data therein to locations remote from the voltage regulating transformer.

6. The voltage regulating transformer set forth in claim 2, wherein said plurality of digital current signals and said plurality of digital voltage signals are cyclically and sequentially produced by said current output means and said voltage output means, each digital current signal having an associated digital voltage signal displaced in time by the amount of the phase angle relationship between the voltage and the current and by the interval between successive measurements of voltage and current by said current output means and said voltage output means.

7. The voltage regulating transformer set forth in claim 1, wherein said digital computer means includes accumulator means for adding a plurality of said measured digital voltage signals over a plurality of periods of said A.C. voltage to obtain a digital control signal suitable for driving said converter means, whereby said changer means operates in response to the RMS voltage at said output terminals over a long period of time relative to the period of said A.C. voltage.

8. The voltage regulating transformer set forth in claim 2, further including:

differential voltage signaling means, operatively connected to said input and output terminals, for producing a plurality of digital differential voltage signals representative of the instantaneous voltage difference across said input and output terminals over the period of said A.C. voltage, said digital differential voltage signals being separated in time from said digital voltage signals and said digital current signals; and

wherein one of said windings defines a plurality of voltage taps,

wherein said changer means includes a positionable tap changing means movable between successive voltage taps; and

wherein said digital computer means includes;

a. means for Fast Fourier Transforming said plurality of digital differential voltage signals from the time domain into the frequency domain to obtain a measured digital differential voltage signal representative of the RMS voltage difference between input and output terminals; and

b. means for processing said measured differential digital signal to produce a digital control signal representative of the relative position of said tap changing means.

9. The voltage regulating transformer set forth in claim 1, wherein said output terminal is adapted to be connected to an A.C. load using power transmission lines characterized by a predetermined value of electrical impedance;

and further including;

a. current output signaling means, operatively connected to said output terminal, for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal, said digital current signals being separated in time from said digital voltage signals;

b. means, included within said digital computer means, for Fast Fourier Transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said measured digital voltage signal;

c. means, includes within said digital input means, for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said load; and

d. means, included within said digital computer means, for processing said measured digital signals of current and voltage, said RMS load voltage, and said impedance to produce a digital control signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage and suitable for operating said changer means through said convertor means,

whereby said changer means operates to control the voltage at said load while compensating for the line drop induced by said impedance.

10. The voltage regulating transformer set forth in claim 2, further including:

a. voltage differential signaling means, operatively connected to said input and output terminals, for producing a plurality of digital differential voltage signals representative of the instantaneous A.C. voltage difference between said input terminal and said output terminal, said digital differential voltage signals being separated in time from said digital voltage signals and said digital current signals; and

b. means, included within said digital computer means, for Fast Fourier Transforming said plurality of digital differential voltage signals from the time domain into the frequency domain to obtain a measured digital differential voltage signal representative of the RMS voltage difference between said input terminal and said output terminal; and

wherein said changer means includes a multiposition electrical switch;

wherein one of said first winding and second winding defines a plurality of voltage taps adapted to be connected in sequence to said switch and the associated one of said input and output terminals, whereby the voltage at said output terminal varies in response to the position of said switch when A.C. voltage is applied to said input terminal; and

wherein said digital computer means includes means for storing a plurality of reference digital differential voltage signals representative of the instantaneous A.C. voltage difference between said input terminal and output terminals corresponding to the positions of said switch,

whereby the position of said switch is correlated to said digital differential digital voltage signals.

11. The voltage regulating transformer set forth in claim 10, wherein said switch is positioned by an electrical motor, the direction of rotation of which is controled by the direction of current flow through said motor;

further including;

a. motor current signaling means for producing a plurality of measured digital motor current signals representative of the current flowing through said motor;

b. timing means for producing a plurality of digital time signals representative of the time interval through which said current flows through said motor;

c. table means, within said digital computer means, for storing a table of reference digital motor current signals corresponding the current flowing through said motor in the time interval during which said motor moves said switch between said taps; and

d. comparison means, included within said digital computer means, for comparing said table of reference digital motor current signals to said measured digital motor current signal and said digital time signals and for producing a digital error signal representative of the deviation between said measured signals and said table of signals, whereby the operating characteristics of said motor in moving said switch is monitored by said digital computer means.

12. The voltage regulating transformer set forth in claim 1, further including:

isolation means, electrically interposed between said output terminal and said voltage output signaling means, for electrically isolating said second winding from said voltage output signaling means.

13. The voltage regulating transformer set forth in claim 1, further including:

a. interval timer means, triggered into operation when said measured digital voltage signal differs from said reference digital voltage signal more than a predetermined difference, for measuring time in multiples of said AC voltage period; and

b. register means, included within said digital computer means, for storing a plurality of digital signals including a first digital signal representative of said predetermined voltage difference, and a second digital signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal after a time interval equal to a preset multiple of A.C. voltage periods, said second digital signal forming said digital control signal to drive said convertor means,

whereby said changer means operates in response to long-term variations in the RMS voltage at said output terminal over the RMS voltage represented by said reference digital voltage signal relative to the period of said AC voltage.

14. The voltage regulating transformer set forth in claim 11, further including indication means, operated in response to said comparison means, for indicating that said measured signals deviate from said table of digital signals.

15. The voltage regulating transformer set forth in claim 1, further including:

frequency monitoring means, included within said digital computer means, for monitoring the electrical frequency at said output terminal and for generating a digital signal representative of calendar time, whereby digital signals within said digital computer means are historically related to one another.

16. A voltage regulator, comprising:

a. a first winding, a second winding with one of said first and second windings having a plurality of voltage taps, a set of input terminals adapted to be connected to a source of A.C. voltage, and a set of output terminals adapted to be connected to a load impedance;

b. tap changing means, operated in response to a control signal supplied thereto, for electrically and selectively connecting one of said input and output terminals to one of said plurality of voltage taps, whereby the voltage across said output terminals varies in response to said control signal when A.C. voltage is supplied to said input terminals;

c. a plurality of response means, associated with said input and output terminals, for generating digital signals representative of the electrical conditions at said input and output terminals

d. a digital processor including a single microprocessor, memory means for storing digital signals, and program means for programming said processor and for Fast Fourier Transforming selected digital signals within said memory means to produce a first digital signal representative of the RMS voltage at said output terminals;

e. display means, for selectively presenting digitally processed information and for inserting reference digital signals into said memory means including a reference RMS digital voltage signal;

f. sequencing means, operatively connected to the processor, for cyclically and sequentially enabling each of said response means to signal said processor as to the electrical conditions at said input and output terminals;

g. non-volatile storage means, operatively connected to said processor, for storing digital signals from said memory means as enabled by said sequencing means;

h. means for producing a second digital central signal representative of the difference between said reference RMS digital voltage signal and said first digital signal; and

i. control means for converting said second digital control signal to a control signal suitable for operating said tap changing means, whereby said tap changing means is operated in response to digitally processed signals representative of the RMS voltage.

17. The voltage regulator set forth in claim 16, wherein:

said first winding and said second winding are submerged in a dielectric fluid;

said plurality of response means includes means for supplying digital signals to said processor representative of the thermodynamic state of said dielectric fluid, and

said display means includes means for inserting into said memory means reference dielectric digital signals representative of the thermodynamic state of said dielectric fluid when said voltage regulator is operating to produce a preselected RMS voltage and current at said output terminals; and

further including means for producing a third digital control signal representative of the difference between said reference dielectric digital signals and said digital signals representative of the thermodynamic state of said dielectric fluid, whereby said third digital control signal is a measure of the loading of said voltage regulator.

18. In a transformer producing at an output terminal an output voltage from an input A.C. voltage supplied to an input terminal by using a transformer winding which defines a plurality of voltage taps and by using a motor driven switch which electrically connects one of the input and output terminals and one of the plurality of voltage taps, a method of regulating the output voltage, comprising of steps of:

a. pre-selecting the RMS output voltage to be maintained at said output terminal;

b. initiating a timer for monitoring elapsed time over uniformly spaced apart time intervals;

c. digitally sampling the instantaneous output voltage at fixed intervals over a plurality of A.C. cycle periods of the current flowing out of said output terminal so as to obtain a plurality of instantaneous digital voltage samples;

d. Fast Fourier transforming said plurality of voltage samples to a digital signal which is a function of frequency of said A.C. current, whereby the RMS output voltage over a plurality of said A.C. cycle periods is determined;

e. digitally comparing said pre-selected voltage RMS output and the RMS output voltage over said plurality of A.C. cycle periods so as to obtain the sign and the magnitude of the difference between said pre-selected RMS output voltage and said RMS output voltage over said plurality of A.C. cycle periods; and

f. energizing said motor driven switch to change the position of said switch from the one voltage tap to another using the sign of the difference between said voltages so as to reduce the difference between said pre-selected RMS output voltage and said RMS output voltage over said plurality of A.C. cycle periods.

19. The method set forth in claim 18, further including the steps of:

a. digitally sampling the instantaneous output current at fixed intervals over a plurality A.C. cycle periods of the current flowing out of said output terminal so as to obtain a plurality of instantaneous digital current samples, said plurality of instantaneous digital current samples being obtained in sequence relative to said plurality of instantaneous digital voltage samples, such that for each voltage sample there is an associated current sample;

b. Fast Fourier transforming said plurality of digital current samples to a digital signal current which is a function of said A.C. cycle period, whereby the RMS output current over a plurality of A.C. cycle periods is determined;

c. using said timer to measure the difference in time between corresponding current samples and voltage samples;

d. using said time difference and the frequency of said A.C. voltage, digitally calculating the angular difference between corresponding current and voltage samples;

e. using said angular difference and said RMS values of voltage and current, digitally calculating the phase angle difference between the instantaneous output current over said A.C. cycle period and the instantaneous output voltage over said A.C. cycle period; and

f. digitally calculating the cosine of the phase angle between said instantaneous output voltage value and said instantaneous output current value, whereby a digital value is obtained representative of the power factor of the A.C. current flowing out of said output terminal.

20. A voltage regulating transformer, comprising:

a. A first winding defining a first plurality of turns and having an associated input terminal adapted to be connected to a source of A.C. voltage;

b. a second winding, electromagnetically coupled to said first winding, defining a second plurality of turns and having an associated output terminal, one of said first and second windings defining a plurality of voltage taps;

c. tap changer means, operated in response to an analog control signal supplied thereto, for changing the ratio of turns through which current flows through said one winding relative to said second winding, whereby the voltage at said output terminal varies in response to said analog control signal when A.C. voltage is applied to said input terminal;

d. voltage output signaling means, operatively connected to said output terminal, for producing a plurality of digital voltage signals representative of the instantaneous A.C. voltage at said output terminal;

e. digital input means for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage;

f. current output signaling means, operatively connected to said output terminal, for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal;

g. a digital computer;

h. means, within said digital computer, for transforming said plurality of digital voltage signals from the time domain into the frequency domain to obtain a measured digital voltage signal representative of the RMS voltage at said output terminal over the period of said A.C. voltage and for generating a digital control signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal;

i. means, included within said digital computer, for transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said measured digital voltage signal;

j. means, included within said digital computer, for processing said measured digital signals of current and voltage to produce a digital signal representative of the phase angle relationship of said instantaneous A.C. voltage and said instantaneous current at said output terminal over said period, whereby the power factor relationship between said instantaneous current and voltage is established;

k. converter means for converting said digital control signal to an analog control signal to operate said tap changer means,

whereby said tap changer means is operated in response to the RMS voltage at said output terminal over the period of the A.C. voltage applied to said input terminal;

l. differential voltage signaling means operatively connected to said input and output terminals, for producing a plurality of digital differential voltage signals representative of the instantaneous voltage difference across said input and output terminals over the period of said A.C. voltage;

m. means, included within said digital computer, for transforming said plurality of digital differential voltage signals from the time domain into the frequency domain to obtain a measured digital differential voltage signal representative of the RMS voltage difference between input and output terminals; and

n. means for processing said measured differential digital signal to produce a digital control signal representative of the relative position of said tap changing means.

21. A voltage regulating transformer, comprising:

a. a first winding defining a first plurality of turns and having an associated input terminal adapted to be connected to a source of A.C. voltage;

b. a second winding, electromagnetically coupled to said first winding, defining a second plurality of turns and having an associated output terminal;

c. multiple position switch means, operated in response to an analog control signal supplied thereto, for changing the ratio of turns through which current flows through said first winding and said second winding, one of said first winding and second winding defines a plurality of voltage taps adapted to be connected in sequence to said switch and the associated one of said input and output terminals, whereby the voltage at said output terminal varies in response to the position of said swtich when A.C. voltage is applied to said input terminal;

d. voltage output signaling means, operatively connected to said output terminal, for producing a plurality of digital voltage signals representative of the instantaneous A.C. voltage at said output terminal;

e. digital input means for producing reference digital voltage signals representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage;

f. current output signaling means, operatively connected to said output terminal, for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal;

g. voltage differential signaling means, operatively connected to said input and output terminals, for producing a plurality of digital differential voltage signals representative of the instantaneous A.C. voltage difference between said input terminal and said output terminal;

h. digital computer means for digital computation of digital signals supplied thereto;

i. means, within said digital computer means, for transforming said plurality of digital voltage signals from the time domain into the frequency domain to obtain a measured digital voltage signal representative of the RMS voltage at said output terminal over the period of said A.C. voltage and for generating a digital control signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal;

j. means, within said digital computer means, for transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said meansured digital voltage signal;

k. means, within said digital computer means, for processing said meansured digital signals of current and voltage to produce a digital signal representative of the phase angle relationship of said instantaneous A.C. voltage and said instantaneous current at said output terminal over said period, whereby the power factor relationship between said instantaneous current and voltage is established.

1. means, withing said digital computer means, for transforming said plurality of digital differential voltage signals from the time domain into the frequency domain to obtain a measured digital differential voltage signal representative of the RMS voltage difference between said input terminal and said output terminal;

m. converter means for converting said digital control signals to an analog control signal to operate said changer means,

whereby said changer means is operated in response to the RMS voltage at said output terminal over the period of the A.C. voltage applied to said input terminal; and

n. means, within said digital computer means, for storing a plurality of reference digital differential voltage signals representative of the instantaneous A.C. voltage difference between said input terminal and output terminals corresponding to the positions of said swtich,

whereby the position of said switch is correlated to said digital differential digital voltage signals.

22. A voltage regulating transformer, comprising:

a. a first winding defining a first plurality of turns and having an associated input terminal adapted to be connected to a source of A.C. voltage;

b. a second winding, electromagnetically coupled to said first winding, defining a second plurality of turns and having an associated output terminal, said output terminal being adapted to be connected to an A.C. load using power transmission lines which are characterized by a predetermined value of electrical impedance;

c. current output signaling means, operatively connected to said output terminal for producing a plurality of digital current signals representative of the instantaneous A.C. current flowing through said output terminal;

d. changing means, operated in response to an analog control signal supplied thereto, for changing the ratio of turns through which current flows through said first winding and said second winding, whereby the voltage at said output terminal varies in response to said analog control signal when A.C. voltage is applied to said input terminal;

e. voltage output signaling means, operatively connected to said output terminal, for producing a plurality of digital voltage signals representative of the instantaneous A.C. voltage at said output terminal;

f. digital input means for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage and for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said load;

g. a digital computer;

h. means, within said computer, for transforming said plurality of digital voltage signals from the time domain into the frequency domain to obtain a measured digital voltage signal representative of the RMS voltage at said output terminal over the period of said A.C. voltage and for generating a digital control signal representative of the differnece between said meansured digital voltage signal and said reference digital voltage signal;

i. means, within said digital computer, for transforming said plurality of digital current signals from the time domain into the frequency domain to obtain a measured digital current signal representative of the RMS current flowing through said output terminal over said period and corresponding to said measured digital voltage signal;

j. processing means, within said digital computer, for processing said measured digital signals of current and voltage, said RMS load voltage, and said impedance to produce a digital control signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage and suitable for operating said changer means; and

k. converter means for converting said digital control signals to an analog control signal to operate said changer means,

whereby said changer means operates to control the voltage at said load while compensating for the line drop induced by said impedance.

23. A voltage regulating transformer, comprising:

a. a first winding defining a first plurality of turns and having an associated input terminal adapted to be connected to a source of A.C. voltage;

b. a second winding, to electromagnetically coupled to said first winding, defining a second plurality of turns and having an associated output terminal;

c. changer means, operated in response to an analog control signal supplied thereto, for changing the ratio of turns through which current flows through said first winding and said second winding, whereby the voltage at said output terminal varies in response to said analog control signal when A.C. voltage is applied to said input terminal;

d. voltage output signaling means, operatively connected to said output terminal, for producing a plurality of digital voltage signals representative of the instantaneous A.C. voltage at said output terminal;

e. digital input means for producing a reference digital voltage signal representative of the RMS voltage to be maintained at said output terminal over the period of said A.C. voltage;

f. digital computer means including means for transforming said plurality of digital voltage signals from the time domain into the frequency domain to obtain a measured digital voltage signal representative of the RMS voltage at said output terminal over the period of said A.C. voltage and for generating a digital control signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal;

g. interval timer means, triggered into operation when said measured digital voltage signal differes from said reference digital voltage signal more than a predetermined difference, for measuring time in multiples of said A.C. voltage period;

h. register means, included within said digital computer means, for storing a plurality of digital signals including a first digital signal representative of said predetermined voltage difference, and a second digital signal representative of the difference between said measured digital voltage signal and said reference digital voltage signal after a time interval equal to a preset multiple of A.C. voltage periods; and

24. i. converter means for converting said second digital control signal to an analog control signal to operate said changer means,

whereby said changer means operates in response to long-term variations in the RMS voltage at said output terminal over the RMS voltage represented by said reference digital voltage signal relative to the period of said A.C. voltage.