GB2553872A

GB2553872A - Systems and methods for rapid activation of dispatchable power sources

Info

Publication number: GB2553872A
Application number: GB1706636.6A
Authority: GB
Inventors: William Johnson Robert
Original assignee: Flexgen Power Systems Inc
Current assignee: Flexgen Power Systems Inc
Priority date: 2016-09-19
Filing date: 2017-04-26
Publication date: 2018-03-21
Anticipated expiration: 2037-04-26
Also published as: GB2553872B; GB201706636D0; WO2018053429A1

Abstract

A system includes a switch CBI configured to couple a generator 10 to a utility grid 20, a first converter 210 having a first port coupled to the generator, a second converter 220 having a first port coupled to a second port of the first converter and a second port coupled to the utility grid, and a controller 240 configured to control the switch and the first and second converters. The controller may be configured to cause the first and second converters to provide power to the utility grid from the generator after the generator starts and before a state of the generator meets a predetermined criterion (which may be synchronisation of the generator to the power grid). The system may also include an energy store 30 (such as a battery or capacitor) which can provide power to the power network 30 until the generator has started and is providing a predetermined amount of power.

Description

(71) Applicant(s):

Flexgen Power systems Inc.

10607 Haddington Dr.Suite#150, Houston 77043, Texas, United States of America (56) Documents Cited:

EP 2341607 A2 EP 2325970 A2 US 20150145251 A1 US 20140103886 A1 US 20130184884 A1 US 20110140438 A1 US 20090218820 A1

EP 2339714 A2 EP 2161443 A2 US 20140204630 A1 US 20140070535 A1 US 20120217824 A2 US 20110140430 A1 US 20050200337 A1 (72) Inventor(s):

Robert William Johnson (58) Field of Search:

INT CL H02J Other: WPI, EPODOC (74) Agent and/or Address for Service:

Boult Wade Tennant

Verulam Gardens, 70 Gray's Inn Road, LONDON, WC1X 8BT, United Kingdom (54) Title of the Invention: Systems and methods for rapid activation of dispatchable power sources Abstract Title: Rapid activation of dispatchable power sources (57) A system includes a switch CBI configured to couple a generator 10 to a utility grid 20, a first converter 210 having a first port coupled to the generator, a second converter 220 having a first port coupled to a second port of the first converter and a second port coupled to the utility grid, and a controller 240 configured to control the switch and the first and second converters. The controller may be configured to cause the first and second converters to provide power to the utility grid from the generator after the generator starts and before a state of the generator meets a predetermined criterion (which may be synchronisation of the generator to the power grid). The system may also include an energy store 30 (such as a battery or capacitor) which can provide power to the power network 30 until the generator has started and is providing a predetermined amount of power.

FIG. 2

1/3

CRANK TIME I—I

RAMP SPEED I-1

SYNCHRONIZED I-1

RAMP LOAD |FIC.1

FIG. 2

2/3

' SYNCHRONIZING '

FIG. 3

3/3

CM

SYSTEMS AND METHODS FOR RAPID ACTIVATION OF DISPATCHABLE POWER SOURCES

BACKGROUND [001] Power shortages have become commonplace throughout the world. As renewable energy sources have become an increasing percentage of the total utility grid power, the variability of the power output of these renewable sources can have a destabilizing effect on the utility grid. As the percentage of traditional rotational generation decreases, there is some concern for the utility grid's ability to clear faults and support high inrush loads. To avoid power interruptions, dispatchable generation sources that are available in short notice and deliver required power have become more desirable.

[002] Power plants that can be dispatched within minutes to overcome power shortages are important assets for balancing electrical system loads and maintaining utility grid stability. It typically takes several minutes to start one of these dispatchable resources and for it to be connected to the utility grid. The choice of generating technology affects the time required for a power plant to startup and reach full load. Current state-of-the-art combustion engine power plants typically can start and reach full load in less than 10 minutes.

[003] Types of engines that can power a rapid-starting dispatchable source include diesel, spark-ignited gas and gas turbine engines. The process to bring a generation asset on line typically begins with starting the engine. Once started, the engine speed is increased to synchronous speed and voltage is increased to match the utility grid voltage. Once the generator is synchronized with the utility grid, a contactor is closed to connect the generator to the utility grid and the generator load is ramped up to 100%. FIG. 1 is an example of an aggressive starting of a gas generator. Several of the aggressive methods may include advanced throttle control and preheating of engine.

[004] For power to be transferred from a generator to the utility grid, the generator should produce a line voltage, frequency, phase sequence, phase angle and waveform matching the utility grid, as any significant mismatch at the time connection to the utility grid may result in extremely high currents and generator damage. As shown in FIG. 1, a first interval is a crank time for starting the engine. If the engine fails to start, this interval may be extended by one or more additional retries. A crank cycle may include an initial 15 second crank interval followed by a 7 second rest period, followed by 5 cycles of 7 second crank intervals interspersed with 7 second rest periods. If the engine fails to start on the first crank cycle, significant time can be lost waiting for the engine to start.

[005] Once the engine starts, the engine may be ramped up to synchronous speed over the next 10 seconds. Matching the generator output to the utility grid in voltage, frequency and phase may require 15 seconds. Once the generator is matched to the utility grid, the generator output is connected directly to the utility grid. As shown, the generator loading may be gradually increased to 100% over the next 30 seconds. Thus, the illustrated process to bring the generator on line may take approximately 60 seconds if the engine starts on the first attempt.

SUMMARY OF THE INVENTION [006] According to some embodiments of the inventive subject matter, a system includes a switch configured to couple a generator to a utility grid, a first converter having a first port coupled to the generator, a second converter having a first port coupled to a second port of the first converter and a second port coupled to the utility grid, and a controller configured to control the switch and the first and second converters. The controller may be configured to cause the first and second converters to provide power to the utility grid from the generator before a state of the generator meets a predetermined criterion.

[007] In some embodiments, the controller may be configured to close the switch to directly connect the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion. The predetermined criterion may include a synchronization of the generator to the utility grid. According to further aspects, the controller may be configured to start the generator responsive to a command and to cause the first and second converters to provide power to the utility grid from the generator responsive to the command.

[008] In some embodiments, the second port of the first converter may be coupled to the first port of the second converter by a DC bus and the controller may be configured to cause the second converter to provide power to the utility grid from an energy storage device coupled to the DC bus until the generator has started and provides a predetermined amount of power. In further embodiments, the controller may be further configured to maintain substantially zero current transfer between the energy storage device and the DC bus after the generator is providing the predetermined amount of power.

[009] According to further embodiments, methods include coupling a generator to a utility grid via a series combination of a first converter coupled to the generator and a second converter coupled between the first converter and the utility grid. The methods further include providing power to the utility grid from the generator before a state of a generator meets a predetermined criterion. The methods may also include closing a switch to directly connect the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion. The methods may further include starting the generator responsive to a command and causing the first and second converters to provide power to the utility grid from the generator responsive to the command.

BRIEF DESCRIPTION OF THE DRAWINGS [0010] FIG. 1 is a graph illustrating a conventional starting sequence for bringing a generator on line.

[0011] FIG. 2 is a block diagram illustrating apparatus and operations for interfacing a generator to a utility grid according to some embodiments of the inventive subject matter.

[0012] FIG. 3 is a graph illustrating operations for coupling a generator to a utility grid according to some embodiments of the inventive subject matter.

[0013] FIG. 4 is a block diagram illustrating apparatus and operations for interfacing a generator to a utility grid according to further embodiments of the inventive subject matter.

DETAILED DESCRIPTION [0014] Specific exemplary embodiments of the inventive subject matter now will be described with reference to the accompanying drawings. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. In the drawings, like numbers refer to like items. It will be understood that when an item is referred to as being connected or coupled to another item, it can he directly connected or coupled to the other item or intervening items may he present. As used herein the term and/or includes any and all combinations of one or more of the associated listed items.

[0015] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms a, an and the are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms includes, comprises, including and/or comprising, when used in this specification, specify the presence of stated features, integers, steps, operations, items, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, items, components, and/or groups thereof.

[0016] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent, with their meaning in the context of the specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

[0017] Embodiments of the inventive subject matter include systems and methods that allow for more rapid provision of power to a utility grid from a generator. An exemplary system is illustrated in FIG. 2. A generator 10 is driven and by an engine 12 and a contactor CB1 couples and decouples the generator 10 to and from a utility grid 20. The utility grid 20 may generally be fed from a plurality of different generation resources, including nondispatchable resources (e.g., wind generators, solar arrays and like) and/or dispatchable resources (e.g., diesel powered generators, microturbine generators and the like), and the engine 12 and generator 10 may be used as a dispatchable resource, e.g., commanded by a system administrator to provide power to the utility grid 20 to provide additional capacity in response to fluctuations in demand of users coupled to the utility grid 20 and/or fluctuations in capacity of other resources feeding the utility grid 20.

[0018 [ The system further includes a DC/AC converter 220 configured to be coupled to the utility grid 20 and to support transfer of power between an energy storage device 30 (e.g., a battery, capacitor bank or combination thereof) and the utility grid 20. The energy storage device 30 may have relatively limited capacity, e.g., may store an amount of energy that is only sufficient to provide a desired amount of power to the utility grid 20 for an amount of time sufficient to achieve the rapid generator activation described herein. The energy storage device 30 may be coupled to the DC/AC converter 220 with a DC/DC converter 230 to facilitate the interface between the energy storage device 30 and a DC bus 215 coupled to an input of the DC/AC converter 220 and maximize availability of the energy stored in the energy storage device 30, which may exhibit a significant drop in output voltage as it is discharged. The system further includes an AC/DC converter 210 configured to be coupled to the generator output and to support transfer of power between the generator 10 and the energy storage device 30.

[0019] In a first mode of operation, a controller 240 of the system may receive an administrative command to start the engine 12 and to provide a certain amount of power.

The engine 12 is cranked and, once the engine 12 starts, the controller 240 causes the DC/AC converter 220 to begin to provide the requested amount of power to the utility grid 20 using the energy stored in the energy storage device 30. The controller 240 may delay providing power from the DC/AC converter 220 because, if the engine 12 fails to start, the relatively small amount of energy stored in the energy storage device 30 may be quickly depleted and may further destabilize the utility grid 20 with its sudden removal.

[0020] The AC/DC converter 210 coupled to the generator 10 starts loading the generator 10 as it is ramping up its speed and synchronizing with the utility grid 20. The loading of the generator 10 continues until the current delivered from the energy storage device 30 is approximately zero. The AC/DC converter 210 maintains the loading of the generator 10 through this path (i.e., through the AC/DC converter 210 and the DC/AC converter 220) such that the current from the energy storage device 30 is zero. Thus, the required power output is being supported by the generator 10 even while the generator 10 is coming up to speed and synchronizing with the utility grid. This can reduce or minimize the amount of stored energy required to support the requested power output before contactor CB1 connects the generator 10 directly to the utility grid 20.

[0021 ] After the controller 240 causes the contactor CB 1 to close, the DC/AC converter 220 can reduce its power delivered as the generator 10 takes on the load. The system can thus provide the output power requested starting at the time the generator 10 begins to run to the time that the generator 10 completely takes over the load. Overloading of the generator 10 can be avoided because the AC/DC converter 210 may be operated to maintain zero current in the energy storage device 30. As the DC/AC converter 220 reduces the amount of power it delivers to the utility grid 20, the AC/DC converter 210 can implement a corresponding reduction in power it transfers from the generator 10 such that the energy store current remains zero.

[0022] FIG. 3 illustrates an example process, showing loading of the generator 10 and transfer currents of the DC/AC converter 220, the AC/DC converter 210 and the DC/DC converter 230 during the engine start, synchronization and load transfer phases. Once the generator has taken on 100% of the output power requirement, the controller 240 can cause the system to transition to a second mode of operation in which both the DC/AC converter 220 and the AC/DC converter 210 can be used provide support to the utility grid 20 from the energy storage device 30 in response to frequency and voltage deviations in a manner along the lines described in U.S. Patent No. 9,312,699 to Taimela et al. In particular, referring to FIG. 4, this mode may involve operating the AC/DC converter 210 and/or the DC/AC converter 220 to source and sink current to and from the utility grid 20, using the energy storage device 30 to help address step increases and decreases in load by bidirectionally transferring power between the utility grid 20 from the energy storage device 30 via the AC/DC converter 210 and/or the DC/AC converter 220.

[0023] According to further aspects, to support engine starting, the AC/DC converter 210 may also be operated to drive the generator 10, i.e., operate it as a motor, to assist starting of the engine 12 and/or aiding the engine 12 in more quickly causing the generator 10 to achieve synchronous speed. This technique can facilitate engine starting in cases where the engine starting battery fails. Starting battery failure due to inadequate maintenance is a common failure mode.

[0024] The system may be energy storage agnostic. For example, the energy storage device 30 may include electrochemical storage, such as lithium-ion batteries and/or ultracapacitors (electro-chemical double layer capacitors) and/or other types of storage systems, such as a flywheel-based or compressed air based storage system. The selection and sizing of the energy storage may be based on the application.

[0025] With increased capacity in the energy storage device 30, the system may also be used for peak shaving operations. As noted above, the AC/DC converter 210 and the DC/AC converter 220 may be bidirectional and provide power to and absorb power from the utility grid 20. Since the AC/DC converter 210, the DC/AC converter 220 and the generator 10 are capable of providing 100% rated power, the total system may provide on the order of 300% rated power (excluding overload ratings) of the generator 10. For example, in this mode, with the contactor CB1 closed, the energy storage device 30 may supply 200% of the power by simultaneously feeding the utility grid 20 through the AC/DC converter 210 and DC/AC converter 220 at 100% of their respective ratings, while the generator 10 provides 100% of its power rating to the utility grid 20.

[0026] In the drawings and specification, there have been disclosed exemplary embodiments of the inventive subject matter. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being defined by the following claims.

That which is claimed:

1. A system comprising:

a switch configured to couple a generator to a utility grid;

a first converter having a first port coupled to the generator;

a second converter having a first port coupled to a second port of the first converter and a second port coupled to the utility grid; and a controller configured to control the switch and the first and second converters.

2. The system of claim 1, wherein the controller is configured to cause the first and second converters to provide power to the utility grid from the generator before a state of the generator meets a predetermined criterion.

3. The system of claim 2, wherein the controller is configured to close the switch to directly connect the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion.

4. The system of claim 3, wherein the predetermined criterion comprises a synchronization of the generator to the utility grid.

5. The system of claim 2, wherein the controller is configured to start the generator responsive to a command and to cause the first and second converters to provide power to the utility grid from the generator responsive to the command.

6. The system of claim 5, wherein the second port of the first converter is coupled to the first port of the second converter by a DC bus and wherein the controller is configured to cause the second converter to provide power to the utility grid from an energy storage device coupled to the DC bus until the generator has started and provides a predetermined amount of power.

7. The system of claim 6, wherein the controller is further configured to maintain substantially zero current transfer between the energy storage device and the DC bus after the generator is providing the predetermined amount of power.

8. The system of claim 1, wherein the second port of the first converter is coupled to the first port of the second converter by a DC bus and wherein the controller is configured to operate the switch and the first and second converters in a first mode to provide power to the utility grid from the generator before the generator is synchronized to the utility grid and to operate the switch and the first and second converters in a second mode wherein an energy storage device coupled to the DC bus sources and sinks current to and from the utility grid via at least one of the first and second converter circuits in response to load changes on the utility grid while the generator is providing power to the utility grid.

9. The system of claim 8, wherein the switch is open in the first mode and wherein the switch is closed in the second mode.

10. A method comprising:

coupling a generator to a utility grid via a series combination of a first converter coupled to the generator and a second converter coupled between the first converter and the utility grid; and providing power to the utility grid from the generator before a state of a generator meets a predetermined criterion.

11. The method of claim 10, further comprising closing a switch to directly connect the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion.

12. The method of claim 11, wherein the predetermined criterion comprises a synchronization of the generator to the utility grid.

13. The method of claim 11, further comprising starting the generator responsive to a command and causing the first and second converters to provide power to the utility grid from the generator responsive to the command.

14. The method of claim 13, wherein the first converter is coupled to the second converter by a DC bus and wherein the method further comprises causing the second converter to provide power to the utility grid from an energy storage device coupled to the DC bus until the generator has started and provides a predetermined amount of power.

15. The method of claim 14, further comprising maintaining substantially zero current transfer between the energy storage device and the DC bus after the generator is providing the predetermined amount of power.

16. The method of claim 11, wherein the first converter is coupled to the second converter by a DC bus and wherein the method further comprises operating the switch and the first and second converters in a first mode to provide power to the utility grid from the generator before the generator is synchronized to the utility grid and operating the switch and the first and second converters in a second mode wherein an energy storage device coupled to the DC bus sources and sinks current to and from the utility grid via at least one of the first and second converter circuits in response to load changes on the utility grid while the generator is providing power to the utility grid.

17. The method of claim 16, wherein the switch is open in the first mode and wherein the switch is closed in the second mode.

11 17

Amendments to the claims have been made as follows;

Claims

1. A system comprising:

a first converter having a first port coupled to an output of a generator; a second converter having a first port coupled to a second port of the first converter and a second port coupled to a utility grid;

a switch configured to couple the output of the generator to the utility grid and thereby bypass the first and second converters; and a controller configured to cause the first and second converters to provide power to the utility grid from the generator responsive to a command to start the generator and to close the switch to directly connect the generator to the utility grid responsive to a state of the generator meeting a predetermined criterion.

2. The system of claim 1, wherein the predetermined criterion comprises a synchronization of the generator to the utility grid.

3. The system of claim 1, wherein the controller is configured to start the generator responsive to the command.

4. The system of claim 3, wherein the second port of the first converter is coupled to the first port of the second converter by a DC bus and wherein the controller is configured to cause the second converter to provide power to the utility grid from an energy storage device coupled to the DC bus until the generator has started and provides a predetermined amount of power.

5. The system of claim 4, wherein the controller is further configured to maintain substantially zero current transfer between the energy storage device and the DC bus after the generator is providing the predetermined amount of power.

30 11 17

6. The system of claim 1, wherein the second port of the first converter is coupled to the first port of the second converter by a DC bus and wherein the controller is configured to operate the switch and the first and second converters in a first mode to provide power to the utility grid from the generator before the generator is synchronized to the utility grid and to operate the switch and the first and second converters in a second mode wherein an energy storage device coupled to the DC bus sources and sinks current to and from the utility grid via at least one of the first and second converter circuits in response to load changes on the utility grid while the generator is providing power to the utility grid.

7. The system of claim 6, wherein the switch is open in the first mode and wherein the switch is closed in the second mode.

8. The system of claim 1, wherein the controller is configured to cause the first and second converters to provide a power output level to the utility grid from the generator before the state of the generator meets the predetermined criterion and to close the switch to directly connect the generator to the utility grid to continue to provide the power output level to the utility grid responsive to the state of the generator meeting the predetermined criterion.

9. A method comprising:

coupling an output of a generator to a utility grid via a series combination of a first converter coupled to the generator and a second converter coupled between the first converter and the utility grid;

responsive to a command to start the generator, providing power to the utility grid from the generator output via the first and second converters before a state of a generator meets a predetermined criterion; and closing a switch to directly connect the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion.

30 11 17

10. The method of claim 9, wherein the predetermined criterion comprises a synchronization of the generator to the utility grid.

11. The method of claim 9, further comprising starting the generator responsive to the command.

12. The method of claim 11, wherein the first converter is coupled to the second converter by a DC bus and wherein the method further comprises causing the second converter to provide power to the utility grid from an energy storage device coupled to the DC bus until the generator has started and provides a predetermined amount of power.

13. The method of claim 12, further comprising maintaining substantially zero current transfer between the energy storage device and the DC bus after the generator is providing the predetermined amount of power.

14. The method of claim 9, wherein the first converter is coupled to the second converter by a DC bus and wherein the method further comprises operating the switch and the first and second converters in a first mode to provide power to the utility grid from the generator before the generator is synchronized to the utility grid and operating the switch and the first and second converters in a second mode wherein an energy storage device coupled to the DC bus sources and sinks current to and from the utility grid via at least one of the first and second converter circuits in response to load changes on the utility grid while the generator is providing power to the utility grid.

15. The method of claim 14, wherein the switch is open in the first mode and wherein the switch is closed in the second mode.

16. The method of claim 9, wherein providing power to the utility grid from the generator output via the first and second converters before the state of the generator meets the predetermined criterion comprises providing a power output level to the utility grid and wherein closing the switch to directly correct the generator to the utility grid responsive to the state of the generator meeting the predetermined criterion is followed by providing the power output level to the utility grid from the generator.

30 11 17

Intellectual

Property

Office

Application No: GB1706636.6 Examiner: Jonathan Huws