Microprocessor controlled voltage regulating transformer

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.

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.

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.

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.

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.

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
• 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.