Systems and methods for black starting a power grid using a self-starting synchronous condenser

Systems and methods for black starting a power grid are described. A battery-powered configuration including, but not limited to, a motor, drive, and batteries can be coupled to a condenser which is coupled to a power grid. The drive can draw power from the batteries and use the power to accelerate the motor. As the motor accelerates, the condenser can accelerate by virtue of a shaft coupling the motor to the condenser. Upon the condenser reaching a certain speed or operational capacity, an inverter can de-block from a power distribution line and allow power to enter the power grid. In certain embodiments, a control device such as a circuit or computing device can be used to facilitate the black start of the power grid.

TECHNICAL FIELD

Embodiments of the invention relate generally to electrical power distribution and more particularly to using a battery-powered condenser to black start a power grid.

BACKGROUND OF THE INVENTION

Various planned or unplanned events can cause a power grid to lose power. In many situations, a synchronous condenser can be used to help black start the power grid or restore power to it after an outage. Providing power to the condenser, however, can be problematic, particularly when a direct current (DC) inverter is connected to the power grid. The inverter can supply power (watts) but because it can require reactive power (vars), it may be unable by itself to assist with black starting the power grid. For example, the power grid itself cannot be used to power the condenser in an outage situation. Instead, turbines, engines, or other prime movers may be used to power the condenser. Such devices, however, are oftentimes dedicated solely to the purpose of powering the condenser, which can add inefficiency, complexity, and cost to existing electrical power systems.

BRIEF DESCRIPTION OF THE INVENTION

Some or all of the above needs and/or problems may be addressed by certain embodiments of the invention. Certain embodiments may include systems and methods for starting a power grid. According to one embodiment, there is disclosed a system for starting a grid coupled to a condenser. The system includes an alternating current (AC) motor coupled to the condenser, a battery configured to power the motor, and a circuit operable to receive a signal to start the grid, initiate operation of the condenser coupled to the grid via the AC motor when the start is requested, and facilitate charging the battery via the AC motor when the start is complete.

According to another embodiment, there is disclosed a method for starting a grid coupled to a condenser. The method includes coupling an AC motor to the condenser, coupling, to the AC motor, a battery configured to power the AC motor, powering the motor by the battery, and initiating operation of the condenser coupled to the grid via the AC motor when a start is requested.

According to a further embodiment, there is disclosed a method for starting a grid. The method includes determining whether a start is requested, powering an AC motor by a battery, initiating operation of a condenser coupled to the grid via the AC motor when the start is requested, and charging the battery via the AC motor when the start is complete.

Other embodiments, systems, methods, aspects, and features of the invention will become apparent to those skilled in the art from the following detailed description, the accompanying drawings, and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION

Illustrative embodiments of the invention are directed to, among other things, black starting a power grid. “Black starting” can be referred to as the process of restoring a power grid to operation without relying on an external electric power transmission network, such as that which can rely on a power plant generator. “Black starting” may also be referred to herein more generally as “starting” the power grid. In the absence of an external power source, certain devices can be coupled to the power grid to black start the power grid. Such devices can be coupled to a condenser to assist the condenser in black starting the power grid. For example, battery power can be supplied via a coupling of batteries, a drive, and a motor to the condenser. The drive can draw power from a battery and use the power to accelerate the motor, which can in turn accelerate the condenser by virtue of the motor being connected to the condenser via a shaft. Upon the condenser reaching a certain speed, such as half-speed, an inverter coupled to a direct current, high-voltage (HVDC) power distribution system can de-block and allow power to begin moving into the power grid. The HVDC system can begin to accelerate the condenser and stabilize the power grid to a steady state condition, for example, such that loads can be added to the power grid. The configuration used to provide power to the condenser can also be used to charge the batteries so that they can provide power on subsequent black starts. In one embodiment, recharging the batteries can occur after the power grid has been restored to a steady state condition. In certain embodiments, a control device can be used to facilitate black starting the power grid. For example, the control device can receive a signal to start the power grid, initiate operation of the condenser via the motor when the start is requested, and charge the batteries.

The technical effects of certain embodiments herein can include lower maintenance and operating costs in the way that dedicated, expensive equipment such as a diesel engine or gas turbine may not be required to provide power to black start a power grid. Another technical effect can include economical use of energy in the way that a battery can be used for relatively brief periods of time, e.g., less than five minutes in certain embodiments, to assist in black starting a power grid. Furthermore, the described battery-powered configuration can provide a simpler solution than that provided by a dedicated diesel or gas turbine, for example.

FIG. 1depicts an illustration of a power distribution system100, such as an HVDC power distribution system. In one aspect of an embodiment, the HVDC system can be a thyristor-based HVDC system. The power distribution system100can include, but is not limited to, a bus110for distributing electric power to the power grid requiring a black start via one or more leads112a,112b, and112c. In one embodiment, the bus110can be AC bus. The power distribution system100can also include an inverter116, (e.g., an HVDC inverter). The inverter116can be coupled to DC line114and can de-block from DC line114to allow power to enter into the power grid upon the occurrence of certain events, such as a condenser108reaching at least half-speed.

The condenser108can be coupled to the power grid. In one aspect of an embodiment, the condenser108can be a synchronous condenser. As shown inFIG. 1, the synchronous condenser108can be in communication with bus110, DC lines114, one or more transformers111, or other electrical power equipment that can be used to provide power in an electrical power network. The synchronous condenser108can provide reactive power needs by acting either as a synchronization or source of reactive power to support the power grid's voltage requirements or provide a certain voltage to enable black starting of the grid. In one embodiment, the HVDC system can supply real power (MW) to the synchronous condenser108while the synchronous condenser108can supply reactive power (MVAR), short circuit strength, and voltage support to the HVDC system. In one embodiment, the synchronous condenser108can provide power commensurate with about at least half-speed, or 40-50% of its operational capacity. Upon reaching this speed or capacity in one embodiment, the power distribution system100can begin accelerating the condenser108to stabilize the power grid. Various types and sizes of synchronous condensers can be used in various embodiments. Such condensers can also be sized appropriately for use with a motor106and a drive104, for example, to enable a successful black start of a power grid.

The HVDC power distribution network100can also include various devices configured to black start the power grid. Such devices can include, but are not limited to, batteries102, a drive104, a motor106, and a control device115. In one embodiment, the motor106and the batteries102can be coupled to the drive104. The batteries102can be configured to power the motor106via the drive104when the black start is requested, in one embodiment. For example, the drive104can draw power from the batteries102to accelerate the motor106, which can in turn accelerate the condenser108via a connection to the condenser108via shaft107. Thus, as the drive104accelerates the motor106around the shaft107, the condenser108can subsequently accelerate. In one embodiment, the motor106can accelerate the condenser108to at least when the black start request occurs. In one aspect of the embodiment, half-speed can represent at least 40-50% of operational capacity of the condenser. Such a speed or capacity of the condenser108can be considered the point at which the condenser108generates sufficient reactive power to enable the HVDC power distribution network100to begin accelerating the condenser108and complete the black start of the power grid. Various other speeds and percentages of operational capacity can accomplish a successful black start in other embodiments.

In addition to accelerating the condenser108, the motor106can also act as an induction generator which the drive104can use to recharge the batteries102. In a particular aspect of an embodiment, the motor106can be configured to recharge batteries102via the drive104when the black start is complete. The configuration shown inFIG. 1can also include a clutch that can be used to decouple or disconnect the AC motor106from the shaft107. In some embodiments, however, the motor106can remain coupled to the shaft107and freewheel in instances where relatively high inertia may be desired, for example.

The motor106can be coupled to the condenser108to accelerate the condenser108. Certain embodiments herein can include a motor106that is an AC motor. In one embodiment, the motor106can be a three-phase AC pony motor rated for variable frequency duty. Such a rating can correspond to the drive104which the motor106can use to draw power from batteries102. The motor106may also be sized in accordance with the condenser108in some embodiments. In other embodiments, the motor106can be a direct current (DC) motor that draws power from a DC power source.

The motor106can be coupled to various types of the drives104to draw power from batteries102. In one embodiment, the drive104can include a four-quadrant AC drive. In one aspect of the embodiment, the four-quadrant AC drive can include a variable frequency drive. In another aspect, the four-quadrant AC drive can include an insulated-gate, bipolar transistor (IGBT) four-quadrant AC drive. Each of these drives can control the rotational speed of the motor106by controlling the frequency of the electrical power supplied to the motor106. In this way, the drives104can facilitate control of the power supply from batteries102to the motor106, as well as facilitate control of the power supply from the motor106to the batteries102to recharge the batteries102.

The batteries102can be configured to power the motor106. The batteries102can include, but are not limited to, Li-Ion, Ni-Cad, Ni-MH, or other battery technologies that may be suitable for shorter durations of power. For example, in one embodiment, batteries102can bring the condenser108to at least half speed within about five minutes of the drive104drawing power from batteries102. Power can also be provided by various other bi-directional power sources such as capacitors or capacitor banks, in some embodiments.

An inverter116, such as an HVDC inverter, can be used to convert direct current to three-phase alternating current, and vice versa. In one embodiment, the inverter116can be configured to de-block the power grid from a direct current line, e.g., DC line114, and provide power to the grid after the condenser108reaches at least half-speed or at least 40-50% operational capacity. In this way, the HVDC inverter can control the flow of power into the power grid.

A control device115can facilitate a black start of the power grid, in one embodiment. The control device115can be coupled to the power distribution system100, for example to the batteries102, drive104, motor106, and condenser108as shown inFIG. 1. In one embodiment, facilitation of a black start by the control device115can include receiving a signal (i.e., a request) to black start the power grid, initiating operation of the condenser108coupled to the power grid via the AC motor106when the black start is requested, and facilitating the charging of the batteries via the AC motor106when the black start is complete.

Exemplary control devices115can include, but are not limited to, one or more circuits, computing devices, or generally processor-driven devices that are capable of communicating with a memory that stores computer-executable instructions to facilitate a black start as described in certain embodiments herein. A processor in a computing device may be implemented as appropriate in hardware, software, firmware, or combinations thereof. Software or firmware implementations of the processor may include computer-executable or machine-executable instructions written in any suitable programming language to facilitate black starting the power grid. Examples of computing devices may include a mainframe, personal computer, web server, mobile device, or any processor-based device capable of executing instructions to facilitate the black start.

A memory in a computing device may store program instructions that are loadable and executable on the processor, as well as data generated during the execution of these programs. Depending on the configuration and type of computing device, a memory may be volatile (such as random access memory (RAM)) and/or non-volatile (such as read-only memory (ROM), flash memory, etc.). The computing device may also include additional removable storage, and/or non-removable storage including, but not limited to, magnetic storage, optical disks, and/or tape storage. The disk drives and their associated computer-readable media may provide non-volatile storage of computer-readable instructions, data structures, program modules, and other data for the computing devices. In some implementations, the memory may include multiple different types of memory, such as static random access memory (SRAM), dynamic random access memory (DRAM), or ROM.

The computing device can also include one or more communication connections that can allow the computing device to communicate with various other devices, such as sensors that can be configured to collect measurement data regarding the operation of the condenser108. The connection between the computing device and other devices can be a wired or wireless connection, according to various embodiments.

The control device115can receive a signal to black start the power grid. In one embodiment, the signal can be received from one or more sensors that can be configured to monitor operation of the synchronous condenser108to, for example, identify an interruption in power supply to the power grid. Such an interruption can include a complete power outage which may require black starting the power grid to restore power. To determine whether an outage has occurred, the control device115can analyze measurement data collected by the one or more sensors. In some embodiments, the control device115can also receive an automated signal (e.g., via a software monitoring tool running on a computing device) or a manual signal (e.g., received from an operator who desires to issue an on-demand black start of the power grid).

The control device115can also initiate operation of the condenser108. For example, in one embodiment, the control device115can cause the AC motor106to accelerate using batteries102, which in turn can cause the condenser108to accelerate by virtue of the shaft connection107between the two devices. The control device115can determine or calculate an amount of power to supply to the motor106to attain a certain acceleration, e.g., at least half-speed in certain embodiments. The control device115can also facilitate charging the batteries102. In one embodiment, batteries102can be charged when the black start is complete. The circuit115can notify the control device115of such completion, at which time the drive104can use the AC motor106as an induction generator for recharging the batteries102. The control device115can also determine an amount of power to supply to the batteries102from the AC motor106acting as an induction generator.

FIG. 2depicts an exemplary flow diagram for configuring a power distribution network for black starting a power grid, according to one embodiment. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the process. At block202, the motor, e.g., motor106, can be coupled to the condenser, e.g., condenser108. As noted above, the motor can be coupled to the condenser via a shaft, e.g., shaft107. Such a coupling of the condenser and the motor can allow the condenser to accelerate as the motor accelerates. One or more batteries, e.g., batteries102, configured to power the motor can be coupled to the drive, e.g., drive104, at block206. The drive can be coupled to the motor at block204. Thus, in one aspect of an embodiment, the motor and the battery can be coupled to the drive. The drive can draw power from the batteries and use the power to accelerate the motor. At block208, the power grid can receive an inverter, e.g., inverter116, coupled to the power grid. The inverter can include an HVDC inverter that can de-block from a direct current line to allow power to enter the grid when, for example, the condenser accelerates to at least half-speed or 40-50% operational capacity. The acceleration can cause the condenser to spin and as a result provide reactive power and voltage regulation, thereby allowing the inverter to function according to certain embodiments herein.

FIG. 3is an exemplary flow diagram illustrating details of a method for black starting a power grid, according to one embodiment. In one example, a control device such as control device115can be used to manage or control the operations of process300. The process300is illustrated as a logical flow diagram, in which each operation represents a sequence of operations that can be implemented in hardware, software, or a combination thereof. In the context of software, the operations can represent computer-executable instructions stored on one or more computer-readable storage media that, when executed by one or more processors, perform the recited operations. Generally, computer-executable instructions can include routines, programs, objects, components, data structures, and the like that perform particular functions or implement particular abstract data types. The order in which the operations are described is not intended to be construed as a limitation, and any number of the described operations can be combined in any order and/or in parallel to implement the process.

In one particular implementation, a power grid requiring a black start can be configured as illustrated inFIGS. 1 and 2. The process300can begin at decision block302, where a determination can be made whether a black start has been requested or completed. Such a determination can be made in various ways. In one embodiment, a control device, e.g., control device115, can access and update an indicator in a memory of the control device, for example, to indicate whether a black start has been requested or completed. Such an indicator can be updated based on measurement data received from one or more sensors, in one embodiment. The indicator can also be updated based on an automated or manual request received from a computing device, for example. Whether a black start has been completed can be based on the occurrence of certain events, such as a reading of voltage levels in the power grid or the speed or operational capacity of the condenser after the power distribution system has accelerated the condenser, in one embodiment. Various other techniques or indicators implemented in hardware or software, for example, can be used to indicate that a black start has been requested or completed.

Upon a black start being requested, the motor can be powered via batteries at block304. Powering the motor in such a way can initiate operation of a condenser coupled to the power grid. In one embodiment, the motor can be configured to initiate operation of the condenser to at least half-speed. In one aspect of the embodiment, half-speed can mean that an operational capacity of at least 40-50% for the condenser has been reached. Such an operational capacity can be sufficient to start an HVDC power distribution system, in one embodiment. Various other speeds of the AC motor and capacities of the condenser can be used to start an HVDC power distribution system and subsequently black start a power grid in other embodiments.

At decision block306, a determination can be made whether at least half-speed of the condenser has been reached. If such a speed of the condenser has not been reached, the AC motor can continue to be powered via batteries at block304until the speed is reached. If the desired speed of the condenser has been reached, the HVDC power distribution system can be started with the condenser as a load, at block308. In one embodiment, the condenser can be the only load upon starting the HVDC power distribution system. In another embodiment, the condenser, motor, drive, and batteries can be the only loads upon starting the HVDC power distribution system. When at least half-speed of the condenser is reached, an HVDC inverter can de-block and allow power to begin moving into the power grid. At such a speed the HVDC power distribution system can accelerate the condenser, instead of or in addition to the motor. The condenser can provide reactive power and voltage support for the HVDC power distribution system to stabilize the power grid so that additional loads can be added to the power grid at block310. In one embodiment, the ability to successfully add loads in addition to the condenser can represent a successful black start of the power grid.

If it is determined that a black start has been completed at decision block304, a determination can be made whether the batteries from which power was drawn to accelerate the condenser have been charged, at block312. If the batteries have been charged, processing can return to decision block302where a determination can again be made to determine whether a black start has been requested or completed. If the batteries have not been charged, they can be charged via the motor at block314, in one embodiment. According to this embodiment, a drive, e.g., drive104, can recharge the batteries so that they can be used to black start the power grid on subsequent black start requests.