Engine-driven generator

• US 5,376,877 A
• Filed: 06/11/1992
• Issued: 12/27/1994
• Est. Priority Date: 06/11/1992
• Status: Expired due to Term

• Current Assignee: Generac Power Systems Incorporated (Generac Holdings Incorporated)
• Original Assignee: Generac Corporation
• Inventors: Wheeley, Michael, Kern, Robert, Kastner, Mark, McLean, Graham, Ruehlow, Gerald, Wedel, Frank
• Primary Examiner(s): Hickey, R. J.
• Application Number:
  US07/897,380
• Time in Patent Office: 929 Days
• Field of Search: 322/32, 363/160
• US Class Current: 322/32
• CPC Class Codes: F02B 63/04 for electric generators
• CPC Class Codes: F02B 63/042 Rotating electric generators
• CPC Class Codes: H02P 9/04 Control effected upon non-electric prime mover and dependent upon electric output value of the generator

Abstract

An engine-driven generator includes an internal combustion engine, a permanent magnet alternator and an AC to AC converter. The output frequency and voltage of the permanent magnet alternator are largely dependent on engine speed and the alternator load. The AC to AC converter converts the speed-dependent alternating current developed by the alternator to another alternating current whose frequency and voltage are largely independent of engine speed. Voltage regulation is provided by varying the engine speed in accordance with the load current. Frequency regulation is provided by frequency dividing the alternator output by an integer divisor that varies in accordance with engine speed. Additional voltage regulation is provided by deleting selected cycles of the alternator output current as needed to maintain the RMS output voltage within predetermined limits.

Claims

1. An engine-driven generator comprising:

an internal combustion engine;

an alternator coupled to said engine and operable to develop a first alternating potential having a frequency and no-load voltage dependent on the speed of said engine;

means for converting said first alternating potential into a second alternating potential wherein said second alternating potential is of a lower frequency than said first alternating potential and wherein said second alternating potential comprises an integral number of positive polarity half-cycles of said first alternating potential followed by an equal integral number of negative polarity half-cycles of said first alternating potential; and

means for increasing or decreasing said integral number in accordance with the frequency of said first alternating potential so as to maintain the frequency of said second alternating potential between pre-established upper and lower frequency limits.

2. An engine-driven generator as defined in claim 1 further comprising speed control means for changing the speed of said internal combustion engine so as to maintain the RMS voltage of said second alternating potential above a pre-established lower voltage limit.

3. An engine-driven generator as defined in claim 2 wherein said speed control means functions to increase engine speed when the RMS voltage of said second alternating potential would not otherwise exceed said pre-established lower voltage limit and said integral number cannot be incremented without the frequency of said second alternating potential falling below said lower frequency limit.

4. An engine-driven generator as defined in claim 1 further comprising means for deleting from said second alternating potential selected ones of said positive and negative polarity half-cycles of said first alternating current so as to maintain the RMS voltage of said second alternating potential between pre-established upper and lower voltage limits.

5. A method of operating an engine-driven generator so as to generate an alternating potential having a frequency and voltage that remain within predetermined limits despite varying loads, said methods comprising the steps of;

turning an alternator with an engine to develop a first alternating potential having a frequency and no-load voltage related directly to the engine speed;

converting said first alternating potential into a second alternating potential of lower frequency than said first alternating potential wherein each positive polarity half-cycle of said second alternating potential consists essentially of an integral number of positive polarity half-cycles of said first alternating potential, and wherein each negative polarity half-cycle of said second alternating potential consists essentially of an equal number of negative polarity half-cycles of said first alternating current; and

increasing said integral number with increasing frequency of said second alternating potential so that the frequency of said first alternating potential remains within predetermined upper and lower frequency limits.

6. A method as defined in claim 5 further comprising the step of varying the engine speed so as to maintain the RMS voltage of said second alternating potential between said predetermined upper and lower voltage limits.

7. A method as defined in claim 6 wherein integral numbers of said half cycles of said first alternating potential are eliminated so as to maintain the RMS voltage of said second alternating potential substantially between said predetermined upper and lower voltage limits.

8. A method as defined in claim 7 further comprising the step of converting said first alternating potential into a series of unipolar pulses.

9. A method as defined in claim 8 further comprising the step of periodically reversing the polarity of said unipolar pulses at a cyclical rate determined by the desired frequency of said second alternating potential.

10. A method as defined in claim 9 wherein said cyclical rate is independent of the number of said positive and negative polarity half cycles included in said positive and negative polarity half cycles of said second alternating potential.

11. A method as defined in claim 5 further comprising the step of eliminating selected ones of said positive and negative polarity half cycles of said first alternating potential from said positive and negative polarity half cycles of said second alternating potential so that the RMS voltage of said second alternating potential remains substantially between predetermined upper and lower voltage limits.

12. An engine-driven generator comprising:

an internal combustion engine;

an alternator coupled to said engine and operable to develop a first alternating potential having a frequency and no-load voltage dependent on the speed of said engine;

means for converting said first alternating potential into a second alternating potential wherein said second alternating potential is of a lower frequency than said first alternating potential and wherein said second alternating potential comprises a predetermined number of positive polarity half-cycles of said first alternating potential followed by an equal number of negative polarity half-cycles of said first alternating potential;

means for increasing or decreasing said predetermined number in accordance with the frequency of said first alternating potential so as to maintain the frequency of said second alternating potential between pre-established upper and lower frequency limits; and

means for deleting from said second alternating current selected ones of said positive and negative polarity half-cycles of said first alternating current so as to maintain the RMS voltage of said second alternating current between pre-established upper and lower voltage limits.

13. A method of operating an engine-driven generator so as to generate an alternating potential having a frequency and voltage that remain within predetermined limits despite varying loads, said method comprising the steps of:

turning an alternator with an engine to develop a first alternating potential having a frequency and no-load voltage related directly to the engine speed;

converting said first alternating potential into a second alternating potential of lower frequency than said first alternating potential wherein each positive polarity half-cycle of said alternating potential comprises a predetermined number of positive polarity half-cycles of said first alternating potential, and wherein each negative polarity half-cycle of said second alternating potential comprises an equal number of negative polarity half-cycles of said first alternating current;

increasing said predetermined number with increasing frequency of said second alternating potential so that the frequency of said first alternating potential remains within predetermined upper and lower frequency limits; and

varying the engine speed so as to maintain an integral number of said half-cycles of said first alternating potential in each of said half-cycles of said second alternating potential and to maintain the RMS voltage of said second alternating potential between said predetermined upper and lower voltage limits.

14. An engine-driven generator comprising:

an internal combustion engine;

an alternator coupled to said engine, said alternator developing an alternator current having a frequency and no-load voltage dependent on the speed of said engine;

a controlled bridge coupled to said alternator operable to convert said alternator current to a series of pulses of selectable polarity, each of said pulses comprising substantially one half-cycle of said alternator current; and

a system control coupled to said controlled bridge operable to control the polarity of said pulses and thereby arrange said pulses into alternating sequences of opposite polarity, each of said sequences containing substantially exactly an integral number of said pulses;

said system control being further operable to vary said integral number so as to maintain the cyclical alternating rate of said alternating sequences substantially between pre-established upper and lower frequency limits.