CA2214370A1 - Method and apparatus for coupling power generator to utility power grid - Google Patents
Method and apparatus for coupling power generator to utility power grid Download PDFInfo
- Publication number
- CA2214370A1 CA2214370A1 CA 2214370 CA2214370A CA2214370A1 CA 2214370 A1 CA2214370 A1 CA 2214370A1 CA 2214370 CA2214370 CA 2214370 CA 2214370 A CA2214370 A CA 2214370A CA 2214370 A1 CA2214370 A1 CA 2214370A1
- Authority
- CA
- Canada
- Prior art keywords
- power grid
- generator
- utility power
- utility
- amplitude
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Supply And Distribution Of Alternating Current (AREA)
- Control Of Eletrric Generators (AREA)
Abstract
A switching circuit to reduce flashing in a switching circuit, when coupling a power generator to utility power grid. The reduction, in flash, is achieved by monitoring AC sine waves of utility power grid and power generator for compatibility in frequency, amplitude and phase. The switching occurs when all monitored signals are, momentarily, equal in time.
Description
Field of Invention This invention relates to a switching circuit suitable for power generators and particularly to an ~llxili~ry generating system for coupling an induction motor type generator to an AC power line for ~d(lin3~ power to that line.
Back~round of the Invention Various methods have been proposed, to couple a power generator and in particular, windmill generated power using an induction type motor, to a 0 utility power grid.
Mechanical relays, used to couple high culrellls, have a limited operating life due to excessive wear caused by fl~shing between the relay contacts when they make or break.
Wind velocity is random, unpredictable and subject to rapid changes and therefor complicates the controller in which the generator is connected to utility power grid.
Back~round of the Invention Various methods have been proposed, to couple a power generator and in particular, windmill generated power using an induction type motor, to a 0 utility power grid.
Mechanical relays, used to couple high culrellls, have a limited operating life due to excessive wear caused by fl~shing between the relay contacts when they make or break.
Wind velocity is random, unpredictable and subject to rapid changes and therefor complicates the controller in which the generator is connected to utility power grid.
2 o The problem is further complicated, by the fact that utility power grid is not stable either. In North America, the amplitude changes by as much as 7% and the frequency by 0.5Hz, while in other parts of the world the changes are a lot higher.
25 Naran Kanti (Patent number PCT WO 95/19659) teaches us a method of using a solid state relay and a mechanical relay in parallel to reduce heat within the solid state relay.
Frank J. Bourbeau ~'atent number US 4,656,413) teaches us a method of 5 using SCR, two per phase, to couple a power generator to a utility grid. The algolilhlll used is complex and not suitable for unstable utility power grid.
Frank J. Nola ~atent number US 4,473,792) teaches us a method of controlling a triac to connect the generator to utility power grid. The triac is10 turned on at a relatively late point in each half cycle to reduce power supplied by the utility power grid to the induction motor type generator and the net power delivered to the line is increased. This method does not monitor the changes in the power grid before connecting the generator to the power grid.
Summary of the Invention There remains a need to couple a power generator to utility power grid which is not stable (frequency and amplitude), as seen in non-industrialized countries to elimin~te in-rush cullell~ and fl~hing It is the object of this invention to effectively reduce fl~.~hing when couplingto utility power grid by monitoring AC sine waves of utility power grid and power generator, for compatibility in frequency, amplitude and phase.
2 5 Another object of this invention is to isolate the generator from the utility power grid when generator is de-coupled.
A further object of this invention is to effectively reduce in-rush current whena generator, which has induction type motor, is coupled to utility grid.
Brief Description of the Dr~.will~s In drawings which illustrate by way of example only a preferred embodiment of the present invention, Figure 1 is a block diagram of one embodiment of the present invention showing connection between utility power grid and windmill power generator;
5 Figure 2A is illustrating the frequency and ~mplitude of power utility grid;
and Figure 2B is illustrating the frequency and amplitude of generator.
Detailed Descrintion of the Invention As shown in Figure 1, in one embodiment the present invention comprises an AC induction motor/generator 24 which is mechanically driven by propeller 26 of a win~lmill (not shown).
Capacitors 42 and 44, are excitation or power factor correction capacitors, which are brought on line by solid state relays 20 & 22 under the control of controller 12.
Voltage sensors 30, 34 and 38 sense the voltage output of the generators while sensors 32, 36 and 40 sense the cullelll ofthe generator.
Transformer 28 converts three phase output of generator 24 into a single phase for connection to utility power grid 50 through solid state relay 14, 0 mechanical relay 16 and manual disconnect switch 18 which is required for maintenance purposes.
Although, three phase output of the generator can be connected to the utility power grid, for simplicity, only a single phase connection is shown in the example.
In the initial state, all relays 14, 16, 20 and 22 are opened to isolate all sections from each other and from power utility grid 50.
20 Wind velocity will start to turn propeller 26 which in turn, drives the induction motor 24. The output of generator 24 is monitored by controller 12 via sensors 30 to 40 for frequency, amplitude and phase.
The presence of frequency and amplitude at sensors 30 to 40, indicates that there is enough wind velocity to start the generator, in which case, capacitors 42 and 44 are brought on-line to start the excitation process.
At a pre-programmed generator output value, mechanical relay 16 is brought on-line while solid state relay 14 is still left open.
At this time, controller 12 starts to monitor utility power grid via sensors 46 and 48 and power generator via sensors 30 to 40 for compatibility in frequency, amplitude and phase.
0 The acceleration of generator 24 is also monitored, via the frequency of the output, to predict the time when the frequency output of the generator 24 will equal the utility power grid 50.
Solid state relay 14 is enabled at zero-crossing, when all monitored signals (frequency, amplitude and phase) between utility power grid 50 and power generator 24 are momentarily equal in time.
As the connection between utility power grid 50 and generator 24 is made only when both frequency and amplitude are equal, the variations in 20 frequency and amplitude within the utility power grid 50 and generator 24 are taken into account before connection is made.
As the speed of solid state relay is extremely fast, in the order of micro seconds, the connection between utility power grid 50 and generator 24 is 25 made while frequency and amplitude are still equal and thus effectually reducing flash and in-rush cull~nl problems.
Current sensors 32, 36, 40 and 48 are mollilored by controller 12 during operation, for flow of power. The flow of power lis from utility power grid 50 to generator 24 (generator acting as a motor) when the wind velocity is low and from the generator 24 to utility power grid 50 when there is sufficient wind velocity.
Generator 24 is disconnected from utility power grid 50, when the wind 10 velocity is low for a pre-programmed period of time or when the power re~-lin~ from sensors 30 to 40 are out of sync with each other indicating a problem or unbalancing of phases within generator 24.
Over heating of generator 24 (sensor not shown) will also disconnect the generator 24 from utility power grid 50.
During disconnect phase, the solid state relay 14 is turned off first and then mechanical relay 16 is disabled to isolate generator 24 from utility power grid 50.
Figure 2A shows the waveform of utility power grid 50 and Figure 2B shows the output of generator 24 at start up. As shown in Figure 2A, the utility power grid 50 is stable for the period of time, while the output of generator 24, as shown in Figure 2B, is ch~n~ing.
As indicated in Figure 2A and 2B, solid state relay 14 is enabled at zero-crossing 52, when all monitored signals (frequency, amplitude and phase) between utility power grid 50 and power generator 24 are momentarily equal m time.
A prerelled embodiment of the invention having thus been described by way of example only, it will be apparent to those skilled in the art that modifications and adaptations may be made without departing from the scope of invention, as set out in the appended claims.
25 Naran Kanti (Patent number PCT WO 95/19659) teaches us a method of using a solid state relay and a mechanical relay in parallel to reduce heat within the solid state relay.
Frank J. Bourbeau ~'atent number US 4,656,413) teaches us a method of 5 using SCR, two per phase, to couple a power generator to a utility grid. The algolilhlll used is complex and not suitable for unstable utility power grid.
Frank J. Nola ~atent number US 4,473,792) teaches us a method of controlling a triac to connect the generator to utility power grid. The triac is10 turned on at a relatively late point in each half cycle to reduce power supplied by the utility power grid to the induction motor type generator and the net power delivered to the line is increased. This method does not monitor the changes in the power grid before connecting the generator to the power grid.
Summary of the Invention There remains a need to couple a power generator to utility power grid which is not stable (frequency and amplitude), as seen in non-industrialized countries to elimin~te in-rush cullell~ and fl~hing It is the object of this invention to effectively reduce fl~.~hing when couplingto utility power grid by monitoring AC sine waves of utility power grid and power generator, for compatibility in frequency, amplitude and phase.
2 5 Another object of this invention is to isolate the generator from the utility power grid when generator is de-coupled.
A further object of this invention is to effectively reduce in-rush current whena generator, which has induction type motor, is coupled to utility grid.
Brief Description of the Dr~.will~s In drawings which illustrate by way of example only a preferred embodiment of the present invention, Figure 1 is a block diagram of one embodiment of the present invention showing connection between utility power grid and windmill power generator;
5 Figure 2A is illustrating the frequency and ~mplitude of power utility grid;
and Figure 2B is illustrating the frequency and amplitude of generator.
Detailed Descrintion of the Invention As shown in Figure 1, in one embodiment the present invention comprises an AC induction motor/generator 24 which is mechanically driven by propeller 26 of a win~lmill (not shown).
Capacitors 42 and 44, are excitation or power factor correction capacitors, which are brought on line by solid state relays 20 & 22 under the control of controller 12.
Voltage sensors 30, 34 and 38 sense the voltage output of the generators while sensors 32, 36 and 40 sense the cullelll ofthe generator.
Transformer 28 converts three phase output of generator 24 into a single phase for connection to utility power grid 50 through solid state relay 14, 0 mechanical relay 16 and manual disconnect switch 18 which is required for maintenance purposes.
Although, three phase output of the generator can be connected to the utility power grid, for simplicity, only a single phase connection is shown in the example.
In the initial state, all relays 14, 16, 20 and 22 are opened to isolate all sections from each other and from power utility grid 50.
20 Wind velocity will start to turn propeller 26 which in turn, drives the induction motor 24. The output of generator 24 is monitored by controller 12 via sensors 30 to 40 for frequency, amplitude and phase.
The presence of frequency and amplitude at sensors 30 to 40, indicates that there is enough wind velocity to start the generator, in which case, capacitors 42 and 44 are brought on-line to start the excitation process.
At a pre-programmed generator output value, mechanical relay 16 is brought on-line while solid state relay 14 is still left open.
At this time, controller 12 starts to monitor utility power grid via sensors 46 and 48 and power generator via sensors 30 to 40 for compatibility in frequency, amplitude and phase.
0 The acceleration of generator 24 is also monitored, via the frequency of the output, to predict the time when the frequency output of the generator 24 will equal the utility power grid 50.
Solid state relay 14 is enabled at zero-crossing, when all monitored signals (frequency, amplitude and phase) between utility power grid 50 and power generator 24 are momentarily equal in time.
As the connection between utility power grid 50 and generator 24 is made only when both frequency and amplitude are equal, the variations in 20 frequency and amplitude within the utility power grid 50 and generator 24 are taken into account before connection is made.
As the speed of solid state relay is extremely fast, in the order of micro seconds, the connection between utility power grid 50 and generator 24 is 25 made while frequency and amplitude are still equal and thus effectually reducing flash and in-rush cull~nl problems.
Current sensors 32, 36, 40 and 48 are mollilored by controller 12 during operation, for flow of power. The flow of power lis from utility power grid 50 to generator 24 (generator acting as a motor) when the wind velocity is low and from the generator 24 to utility power grid 50 when there is sufficient wind velocity.
Generator 24 is disconnected from utility power grid 50, when the wind 10 velocity is low for a pre-programmed period of time or when the power re~-lin~ from sensors 30 to 40 are out of sync with each other indicating a problem or unbalancing of phases within generator 24.
Over heating of generator 24 (sensor not shown) will also disconnect the generator 24 from utility power grid 50.
During disconnect phase, the solid state relay 14 is turned off first and then mechanical relay 16 is disabled to isolate generator 24 from utility power grid 50.
Figure 2A shows the waveform of utility power grid 50 and Figure 2B shows the output of generator 24 at start up. As shown in Figure 2A, the utility power grid 50 is stable for the period of time, while the output of generator 24, as shown in Figure 2B, is ch~n~ing.
As indicated in Figure 2A and 2B, solid state relay 14 is enabled at zero-crossing 52, when all monitored signals (frequency, amplitude and phase) between utility power grid 50 and power generator 24 are momentarily equal m time.
A prerelled embodiment of the invention having thus been described by way of example only, it will be apparent to those skilled in the art that modifications and adaptations may be made without departing from the scope of invention, as set out in the appended claims.
Claims (4)
1. A switching means for stabilized coupling of an induction generator to an alternating current (AC) utility power grid, comprising:
monitoring frequency, amplitude and phase of utility power grid, monitoring frequency, amplitude and phase of induction generator, and hybrid switching means for coupling induction generator to utility power grid when the monitored frequency, amplitude and phase are equal in time between the induction generator and utility power grid.
monitoring frequency, amplitude and phase of utility power grid, monitoring frequency, amplitude and phase of induction generator, and hybrid switching means for coupling induction generator to utility power grid when the monitored frequency, amplitude and phase are equal in time between the induction generator and utility power grid.
2. A switching means as claimed in claim 1, wherein the hybrid switching means comprises a solid state relay in series with a mechanical relay.
3. A switching means as claimed in claim 2, comprising delay means for delaying the closing of solid state relay relative to closing of mechanical relay.
4. A switching means as claimed in claim 2, comprising delay means for delaying the opening of mechanical relay relative to opening of solid state relay.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2214370 CA2214370A1 (en) | 1997-10-28 | 1997-10-28 | Method and apparatus for coupling power generator to utility power grid |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2214370 CA2214370A1 (en) | 1997-10-28 | 1997-10-28 | Method and apparatus for coupling power generator to utility power grid |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2214370A1 true CA2214370A1 (en) | 1999-04-28 |
Family
ID=29274986
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2214370 Abandoned CA2214370A1 (en) | 1997-10-28 | 1997-10-28 | Method and apparatus for coupling power generator to utility power grid |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2214370A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107228980A (en) * | 2017-06-06 | 2017-10-03 | 北京智芯微电子科技有限公司 | A kind of method and device for measuring mains frequency |
| WO2021122724A1 (en) * | 2019-12-16 | 2021-06-24 | Gerald Hehenberger | Method for connecting an electric asynchronous machine of a powertrain to an electric grid |
-
1997
- 1997-10-28 CA CA 2214370 patent/CA2214370A1/en not_active Abandoned
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN107228980A (en) * | 2017-06-06 | 2017-10-03 | 北京智芯微电子科技有限公司 | A kind of method and device for measuring mains frequency |
| CN107228980B (en) * | 2017-06-06 | 2020-09-08 | 北京智芯微电子科技有限公司 | Method and device for measuring power grid frequency |
| WO2021122724A1 (en) * | 2019-12-16 | 2021-06-24 | Gerald Hehenberger | Method for connecting an electric asynchronous machine of a powertrain to an electric grid |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Dead |