Control system and circuits for distributed electrical-power generating stations

• US 5,731,688 A
• Filed: 03/13/1996
• Issued: 03/24/1998
• Est. Priority Date: 03/13/1996
• Status: Expired due to Fees

• Current Assignee: Alaska Science and Technology Foundation
• Original Assignee: Alaska Power Systems, Inc.
• Inventors: Thomson, William R.
• Primary Examiner(s): Laballe, Clayton E.
• Assistant Examiner(s): Ponomarenko, Nicholas
• Application Number:
  US08/614,637
• Time in Patent Office: 741 Days
• Field of Search: 322/25, 322/28, 322/22, 290/2, 290/40 C, 290/52
• US Class Current: 322/22
• CPC Class Codes: H02J 13/00024 by means of mobile telephony
• CPC Class Codes: H02J 3/38 Arrangements for parallely feeding a single network by two or more generators, converters or transformers
• CPC Class Codes: Y02E 40/70 Smart grids as climate change mitigation technology in the energy generation sector
• CPC Class Codes: Y02E 60/00 Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
• CPC Class Codes: Y04S 10/12 Monitoring or controlling equipment for energy generation units, e.g. distributed energy generation [DER] or load-side generation
• CPC Class Codes: Y04S 40/126 using wireless data transmission

Abstract

A system (30) for providing electrical-power to remote communities (34) widely distributed over an extended geographical area (38) includes a generating station (32) located proximate each of the communities, each generating station supplying only that community to which it is proximate. The generating stations are in electronic communication with a central computer (40). Each generating station includes a plurality of generators (54-56). Each of the generators is controlled by a microprocessor based controller (64). Each controller is arranged to operate the generating station cooperatively with the other controllers associated with other generators in the station, and to assume a supervisory role in doing so by a mutual arbitration procedure among the controllers. Each controller is also arranged to monitor important generator operating parameters and to communicate these parameters to the central computer. Any controller may be reprogrammed by instructions communicated from the central computer, and functions of any controller may be overridden by instructions communicated from the central computer. The controllers include novel signal processing circuits (90 and 85) and logic for improved voltage and frequency regulation. The controllers also include novel circuits (92) and logic for monitoring generator fuel consumption and calculating generator fuel-efficiency therefrom.

Claims

1. In a control system for an electrical power generator, the control system including a microprocessor and circuit elements driven by the microprocessor for maintaining generator output voltage at a preset level based on a measurement of the generator output voltage, an electrical circuit for providing the microprocessor with signals representative of the measurement comprising:

means for receiving a generally sinusoidal, positive and negative going, first analog signal representative of the output voltage of the generator;

means for converting said first analog signal into a second analog signal having only positive going cycles, alternate ones of which are representative of the magnitude of alternate positive and negative half-cycles of said first analog signal;

means for converting said first analog signal into a square-wave pulse representative of polarity of said alternate half-cycles of said first analog signal; and

wherein said square-wave pulse and said second analog signal are provided to the microprocessor for controlling the output voltage of the generator.

2. In a control system for a three phase electrical power generator, the control system including a microprocessor and circuit elements driven by the microprocessor for maintaining generator output voltage at a preset level based on a measurement of the generator output voltage, an electrical circuit for providing the microprocessor with signals representative of the measurement comprising:

means for receiving a generally sinusoidal, positive and negative going, first analog signal representative of a particular phase of the output voltage of the generator, and means for receiving a second analog signal representative of residual neutral voltage of the generator;

means for converting said generator voltage and generator neutral signals to respectively first and second current signals;

means for providing from said first and second current signals a third current signal representative of a said generator voltage corrected for said residual neutral voltage;

diode means for converting said third current signal into a third analog voltage signal having only positive going cycles, alternate ones thereof being representative of the magnitude of alternate positive and negative half-cycles of said first analog signal;

means for converting said third current signal into a square-wave pulse train representative of polarity of said half-cycles of said first analog signal and

wherein said square-wave pulse train and said third analog signal provided to the microprocessor for controlling the output voltage of the generator.

3. The circuit of claim 2, wherein said rectifier means is a current mode, precision full wave rectifier.

4. In a voltage regulation arrangement for an electrical power generator having a generator frequency, wherein a voltage regulator provides a generator field current signal to the generator for controlling output voltage thereof, the field current signal being generated by the voltage controller in response to a voltage error correction signal representative of a voltage error to be corrected, a method for providing the voltage error correction signal, comprising the steps of:

(a) sampling a first analog signal representative of generator output voltage and a second analog signal representative of residual neutral voltage of the generator;

(b) subtracting said second analog signal from said first analog signal to provide a third analog signal representative of said generator output voltage corrected for said residual neutral voltage

(c) digitizing said third analog signal and electronically storing the result as a first digital signal representative of said third analog signal;

(d) continuously repeating steps (a) through (c) at fixed time intervals;

(e) calculating a change in said first digital signal compared with a corresponding signal last previously generated in steps (a) through (c) and storing the result as a first differential term;

(f) subtracting said first digital signal from a stored setpoint voltage signal, thereby determining a voltage error value;

(g) adding said voltage error value to an accumulator defined as an integral term;

(h) multiplying said voltage error value by a first constant, thereby determining a proportional term;

(i) multiplying said differential term by a second constant, thereby determining a second differential term;

(j) adding said second differential term to said proportional term thereby determining a first running value;

(k) reducing said first running value by a first proportion if said first running value is less than a predetermined value, else reducing said first running value by a predetermined amount, thereby determining a second running value;

(l) reducing said second running value by said first proportion if said second running value is less than said predetermined value, else reducing said first running value by said predetermined amount, thereby determining a third running value;

(m) without affecting said integral term, multiplying the value of said integral term by a third constant and adding the result to said third running value, thereby determining a fourth running value;

(n) supplying said fourth running value to the voltage regulator as the voltage error correction signal; and

(o) continuously repeating steps (e) through (m) at a first time interval synchronized to the generator frequency, and a repeating step (n) at a second time interval synchronized to generator frequency.

5. The method of claim 4, further including, between steps (e) and (f), the step of (p) limiting changes to said setpoint to ten percent per second.

6. The method of claim 4 further including, between steps (g) and (h) the step of (q) limiting said integral term to a predetermined maximum value.

7. In a voltage regulation arrangement for an electrical power generator having a generator frequency, wherein a voltage regulator provides a generator field current signal to the generator for controlling output voltage thereof, the field current signal being generated by the voltage controller in response to a voltage error correction signal representative of a voltage error to be corrected, a method for providing the voltage error correction signal, comprising the steps of:

(a) repeatedly, at a fixed time interval, receiving an analog signal representative of generator output voltage and an analog signal representative of generator residual neutral voltage, correcting said generator voltage signal according to said generator residual neutral signal thereby providing a corrected generator output voltage signal, and digitizing and electronically storing said analog signal; and

(b) repeatedly, at a time interval synchronized to the generator frequency, sampling said stored, digitized corrected, generator output voltage signal, comparing said stored, digitized corrected, generator output voltage signal, with a predetermined setpoint value and with a last previously sampled one said digitized corrected, generator output voltage signals, and generating, based on said comparison, said voltage error correction signal.