Patent Publication Number: US-9847648-B2

Title: Hybrid electric generating power plant that uses a combination of real-time generation facilities and energy storage system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. application Ser. No. 13/527,290 filed on Jun. 19, 2012, which claims the benefit of U.S. Provisional Appl. No. 61/499,065 entitled “Hybrid Electric Generating Power Plant That Uses a Combination of Real-Time Generation Facilities and Energy Storage System,” filed Jun. 20, 2011. The entire contents of these applications are hereby incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to systems and methods for providing generation services on a power grid and, more particularly, a hybrid electric generating power plant that uses an energy storage system. 
     BACKGROUND OF THE INVENTION 
     Typically, a utility obtains electric power from one or more primary power generation sources, such as gas-fired, coal-fired, nuclear and/or hydroelectric power plants, for delivery to customers via a distribution grid. The power supplied by these sources can vary moment-to-moment. Generally, the sources can be regulated to meet the demands of customers while at the same time conforming to the standards for such power, such as nominal voltage and frequency levels. 
     To supplement the power supplied by these primary sources, it is becoming more common to connect secondary sources of power, such as solar panels and windmills, to the electric distribution grid. Among other advantages, these secondary forms of energy are renewable, in contrast to the primary sources. 
     BRIEF SUMMARY 
     The present disclosure is directed to apparatus, systems, computer readable media and methods for controlling power supplied to an electric grid using energy storage devices to store energy. One exemplary method includes receiving an indication of power to be supplied to the electric grid, generating power from at least one power generator, and adjusting, using the generated power from the power generator, an energy level of the energy storage device to control the power supplied to the electric grid in accordance with the received indication. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING/FIGURES 
       Exemplary embodiments are best understood from the following detailed description when read in conjunction with the accompanying drawings. It is emphasized that, according to common practice, the various features of the drawings are not to scale. On the contrary, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. Included in the drawings are the following figures: 
         FIG. 1A  is a schematic diagram illustrating an exemplary power plant connected to an electric grid, according to embodiments of the invention; 
         FIG. 1B  is a schematic diagram illustrating another exemplary power plant connected to an electric grid, according to embodiments of the invention; 
         FIG. 2  is a more detailed schematic diagram illustrating a power plant connected to an electric grid, according to embodiments of the invention; 
         FIG. 3  is a flowchart illustrating a method of controlling power supplied to an electric grid, according to embodiments of the invention; 
         FIG. 4  is flowchart illustrating an adjustment or optimization of power contribution by generation and/or storage, according to embodiments of the invention; 
         FIG. 5  is a plot illustrating a demand curve being matched by the combined response curve of a thermal electrical generation plant and a grid stability electrical storage system, according to embodiments of the invention; and 
         FIG. 6  is a diagram of an example computer system in which embodiments can be implemented. 
     
    
    
     DETAILED DESCRIPTION 
     Unlike the relatively stable output of primary sources, the amount of energy produced by secondary sources can vary over a wide range within relatively short intervals, e.g., measured in seconds or minutes. For example, the output of a solar panel may vary not only in accordance with the time of day, but also as a result of meteorological events such as the sudden appearance and passing of clouds that block direct sunlight. Likewise, the output of a windmill farm may be subject to instantaneous gusts and/or lulls in the velocity of the wind. 
     A sudden upward spike (e.g., increase) in the output of a secondary source may be absorbed by the electric grid, and may be accommodated by: (1) decreasing the output of, for example, one or more of the primary sources and/or the other secondary sources; (2) storing power by the energy storage devices; and/or (3) increasing the load on the electric utility grid. 
     A sudden decrease in the output of the secondary source may be absorbed by the electric grid, and may be accommodated by: (1) increasing the output of, for example, one or more of the primary sources, and/or other secondary sources; (2) discharging power stored by energy storage devices; and/or (3) decreasing the load on the electric grid. In certain exemplary embodiments, a sudden spike or a sudden decrease may exceed a transmission capability of equipment on site and may result, for example, in a loss of generated power or possibly a blackout condition. These sudden changes may trip off the primary sources of power causing such blackouts or may induce additional costs at the primary sources of power, such as reduced operating capacity, increased maintenance and/or additional fuel costs associated with operation at a non-optimal operating set point. 
     Large swings in frequency may also exceed the distribution system&#39;s response capabilities for normal operations. For example, if a generator were suddenly to go offline or if a transmission line were to fail, a drop in frequency and/or voltage level may occur, which may create a cascading effect as more generators go offline due to the frequency and/or voltage deviation from normal operating set points (e.g., a blackout may occur). Traditional power generation equipment may not always respond swiftly enough to such changes. Grid frequency may fluctuate with load swings because power generators may slow down due to increased load or may speed up due to reduced load, thereby changing the frequency of the alternating current (AC) generated. 
     When managing variations in conditions on the power grid, the Electrical System Operator (ESO) may vary the output of selected power generating stations in order to accommodate the variations (e.g., stabilize the electric utility grid by operating the electric grid such that the loss of any one component of the electric utility grid may not cause the cascading effect (e.g., to prevent such blackouts). Existing electric power generating units may have constraints regarding the rapidity of progression from one level of output to another level of output (also referred to herein as “ramp rate”). Ramp rate may vary depending on the type of electric power generating unit (e.g., coal, or natural gas, among others) and the operating level (e.g., set point) of the electric generating unit. Although limits may be placed on total system capacity to satisfy ramping, the existing ramp rate for electrical power systems are generally sufficient to meet the ramping associated with primary sources of power. Small power systems, however, may have difficulty maintaining a supply/demand balance and sufficient ramping capabilities. With the advent of the secondary sources of power, there is a need for improved ramping capabilities. 
     In addition, a hybrid power plant that includes an energy storage device, such as batteries, may allow for a more efficient use of existing power generators. Typically, power plants withhold a portion of output to serve as spinning reserve for fast ramp-up and/or for regulation services. Spinning reserve typically refers to generators that are already online, synchronized, and generating a portion (i.e., a subset) of their total output capability. The use of such spinning reserve generation may be costly because: (1) a portion of the power generators&#39; output cannot be used for base load capacity, (2) additional wear and tear may occur on the spinning power generators; and/or (3) additional energy may be lost and additional fuel costs may be incurred and additional emissions may be emitted due to the operation of the spinning power generators. 
     By including a fast ramp rate energy storage device with the power generators, the power generators may be used for base load capacity and the energy storage devices may provide regulation and fast ramp rate control allowing the power generators additional time to adjust their outputs, or to forgo changes to output altogether. 
     A power generating system that provides prompt rapid adjustment (e.g., decrease or increase) in power output while maintaining a high operating rate (e.g., efficiency) of an electric power generating station may better serve the present requirements of the electric grid. 
     In certain exemplary embodiments, systems, apparatus, and methods may maintain a stable electric grid frequency and/or voltage levels by combining responses to grid frequency and/or voltage fluctuations by one or more power generators and one or more energy storage devices. The combined response may be governed (e.g., controlled) by Power Contribution Control Equipment (PCCE). It may be noted that the present system may be used in conjunction with the system disclosed in U.S. Patent Application Publication No. 2010/0090532 entitled “Frequency Responsive Charge Sustaining Control of Electricity Storage Systems for Ancillary Services on an Electrical Power Grid,” which issued as U.S. Pat. No. 7,839,027 on Nov. 23, 2010. 
     In certain exemplary embodiments, a controller, based on information (e.g., an indication) received, may adjust energy stored by an energy storage device (e.g., a battery, capacitor, chemical storage unit, and/or mechanical storage unit, among others) using the generated power from the power generator, and may control the power supplied to the electric grid in accordance with the received information. 
     Methods and apparatus for responding to changes in grid frequency or grid voltage level are described herein to enable a power plant to operate at a fixed operating rate. The apparatus may include: (1) at least one power generator configured to generate alternating current for distribution across the electric grid (e.g., power grid); and (2) at least one power storage device connected to the power grid either through the same connection as the power generator or separately. The power generator and the power storage device may be co-located in a single plant or generation site or may be distributed at different locations and coupled to the power grid. The apparatus may include a grid frequency detector and the PCCE. The grid frequency detector may be configured to detect the grid frequency for frequency changes in alternating current distributed on the power grid. The PCCE may be configured to control power contribution to the power grid by controlling the (1) discharge in storage of power with respect to at least one power storage device and (2) increasing or decreasing the power generation from at least one power generator. The PCCE may be configured to provide a response to received input such as the detected fluctuations in frequency on the power grid or voltage fluctuations on the power grid. The PCCE may, for example, provide stability by discharging stored power during changes in power generation (e.g., during ramp-up) by at least one power generator and/or storing power to prevent transmission of the power on the grid during changes in power generation (e.g., during ramp-down) by at least one power generator. The combined response of discharging store power and storing power may follow instantaneous (e.g., real-time or near real time) demand information supplied to the PCCE. 
     Certain exemplary embodiments may advantageously reduce wear and tear, reduce fuel costs, increase operation efficiency and/or reduce environmental impact of the primary sources of power, and may provide faster response contingencies for large load swings, shortages, and equipment failures, among others, that may otherwise lead to fluctuations in voltage and/or grid frequency. Generally, power plants are overbuilt and include excess capacity. For example, a hydroelectric plant may have a spinning but disengaged generator (e.g., a reserve generator) for grid regulation such that the reserve generator may be available (e.g., may come on line) when a variation (e.g., a rapid variation) in grid frequency or voltage level occurs, which may increase wear and tear on the reserve generator and may require overbuilding of the power plant and underutilization of the same. 
       FIG. 1A  is a schematic diagram illustrating an exemplary power plant  100  connected to an electric grid  150  in accordance with exemplary embodiments. 
     Referring to  FIG. 1 , a power plant  100  may be connected to a power grid  150  (e.g., utility electric grid. The illustration has been simplified for clarity to show a typical tri-phase electrical power system, but one skilled in the relevant art(s) understands that other configurations are possible. The power plant  100  may include power generators  110 , power (or energy) storage devices  120 , a grid indication receiver  130 , power bus bar  101 , and Power Contribution Control Equipment (PCCE)  140 . 
     The power generators  110  may be connected or coupled to the PCCE  140  and to the power bus bar  101  and may be configured to generate (i.e., convert) one form of energy to electrical energy. The power generators  110  can be formed as a discrete power generator, or as a bank of individual power generators that may be connected or selectively interconnected to generate power. The power generators  110  can be hydroelectric generators, fossil fuel generators (e.g., coal generators, gas generators, oil generators, diesel generators or any other form of fossil fuel generators), nuclear power generators, and/or renewable energy sources such as wind harnessing power generators, tidal power generators, geothermal power generators, and/or solar power generators and other form of power generation that may be controlled by the PCCE  140 . 
     The power storage devices  120  may be connected or coupled to the PCCE  140  and to the power bus bar  101  and may be configured to selectively provide energy to the power grid  150  or to selectively receive energy from the electric grid  150 . 
     The power storage devices  120  may be, for example, batteries or capacitors in combination with batteries to provide bursts of energy (e.g., short term bursts of energy of less than a threshold duration). The power storage devices  120 , in the alternative or in addition, may be, for example, inertial power systems such as flywheels, pneumatic systems that compress a gas to be released in mechanical system to rotate an electrical generator, or suspended mass systems such as water pump systems that deliver water to a higher level near a hydro-electric plant for later use in the generation of electricity. By no means, however, is the power storage devices  120  limited to these examples. 
     Although the power storage devices  120 , as shown in  FIG. 1  and described above, are co-located in the power plant  100  with the power generators  110 , it is contemplated that other configurations are possible. For example, in some exemplary embodiments, the power storage devices can be distributed along the electric grid  150 . In other exemplary embodiments, the power storage devices may be co-located in the power plant with the power generators as well as being distributed along the electric grid  150 . These configurations may be advantageous insofar as power storage devices tend to be discrete and compact and can be placed in distributed locations without significant costs. The power generators  110  may be dependent upon the location of hydropower, water supplies and/or fuel supplies, among others. In this way, the power storage devices  120  may be located closer to the loads or distributed for load balancing within the electric grid  150 . Other synergies for collocating energy storage devices  120  with the power generators  110  include, but are not limited to, sharing of: control and monitoring systems, operations and maintenance personnel, substations, electrical switch gear, and transformers between energy storage devices  120  and power generators  110 . Additionally, provision of Volt-Amperes Reactive (VAR) support required by local power generators  110  is possible when they are collocated with energy storage devices  120 . 
     The output of the power generators  110  and the output of the power storage devices  120  may be coupled to power bus bar  101  which may be coupled via a station transformer (not shown) to the electric grid  150 . The power bus bar  101  may be connected to the power generators  110 , the power storage devices  120 , and the electric grid  150  and may be configured to transfer electricity from the power plant  100  to the electric grid  150  for distribution. 
     Although the power bus bar  101  and the power storage devices  120  are shown in  FIG. 1  and described above as being electrically connected, in some exemplary embodiments, the power storage devices  120  may be coupled directly to the electric grid  150 . In certain exemplary embodiments, the energy stored in the energy storage devices  120  may be DC power and an AC/DC bidirectional converter may be included between the energy storage devices  120  and the power bus bar  101  to convert between AC power on the power bus bar  101  and the DC power of the energy storage devices  120 . 
     The grid indication receiver  130  may be operatively coupled to (e.g., wired or wireless connected to) the PCCE  140  for receiving an indication of power to be supplied to the electric grid  150 . The grid indication receiver  130  may receive: (1) a signal that indicates a current (e.g., present) power supply level to be supplied to the electric grid; (2) a signal indicating a grid frequency for determining a current adjustment to the power to be supplied to the electric grid  150 ; and/or (3) one or more operating parameters indicating one or more operating set points for a combination of the power generators  110  and the power (energy) storage device  120 . 
     Responsive to receiving the one or more parameters indicating one or more operating set points, the PCCE  140  (e.g., controller) may determine one or more other operating set points for each of the power storage devices  120  and the power generators  110  such that the combination of the set points of the at least one power generator  110  and the energy storage device  120  satisfies the set points associated with the received one or more operating parameters. 
     The PCCE  140  may control (e.g., adjust) the generated power from the power generators  110  simultaneously with the adjustment of the energy (or power) stored by (or in) the energy storage devices  120  to meet or satisfy the power to be supplied to the electric grid  150 . For example, the PCCE  140  may control the adjustment of the generated power from the power generator  110  by simultaneously: (1) discharging the energy storage devices  120  and increasing the power supplied from the power generators  110 ; (2) discharging the energy storage devices  120  and decreasing the power supplied from the power generators  110 ; (3) charging the energy storage devices  120  and decreasing the power supplied from the power generators  110 ; and/or (4) charging the energy storage devices  120  and increasing the power supplied from the power generators  110 . 
     As would be understood by those skilled in the relevant art(s), control of charging and/or discharging of an energy storage device may be accomplished by, for example, a bidirectional inverter for AC-to-DC power conversion or a bidirectional DC-to-DC converter for DC-to-DC conversion and that the charging mode and discharging mode of such a bidirectional device may be controlled based on external signals such as various set points and/or voltage/frequency indicators. One skilled in relevant art would also understand that control of the power generators may be independent of control of the energy storage device. The net output from the power generators and the energy storage device may be controlled, for example: (1) to optimize ramp rate for the combination of the power generators and the energy storage device; (2) to reduce maintenance of the energy storage device and/or the power generators; and/or (3) to reduce spinning reserve services of the power generators, among others. 
     The PCCE  140  may determine power contribution from the power generators  110  (e.g., each generator) and power contribution from the power storage device  120  to satisfy the indicated current power supply level for the electric grid  150 , in response to receiving a signal that indicates the current combined power supply level to be supplied to the electric grid from the power plant  100 . 
     For example, the PCCE  140  may control discharging of stored energy (or power) by the power storage devices during initial ramp-up in power generation by the power generators  110  and/or may control storage of power by the power storage devices  120  for later transmission on the electric grid  150  during ramp-down in power generation by the power generators  110 . 
     The set point for energy storage in the power storage devices  120  may be varied based on expected power demands on the electric grid  150 . For example, energy may be stored in the power storage devices  120  at a lower level, below capacity, during periods in which the power demands on the electric grid  150  may be expected to decrease, and at a higher level during periods in which the power demands on the electric grid  150  may be expected to increase. 
     The PCCE  140  may control or adjust the storage of energy by the power storage devices  120  according to an optimum or predetermined profile (e.g., a power discharge and storage profile) of the power storage devices  120  and may control or adjust, based on the optimum or predetermined profile of the power storage devices  120 , the power generation by the power generators  110  to satisfy the indication received by the grid indication receiver  130 . 
     The PCCE  140  may control or adjust the power generation from the power generators  110  according to an optimum or a predetermined ramp profile of the power generators  110  and may control or adjust, based on the optimum or predetermined ramp profile, the energy level of the energy storage devices  120  to satisfy the indication received by the grid indication receiver  130 . 
     Although the power generators  110  are described in terms of plural generators, it is contemplated that in certain exemplary embodiments a single power generator  110  may be used. Although the energy storage devices  120  are described in terms of plural storage devices, it is also contemplated that a single energy storage device  120  may be used. 
     In certain exemplary embodiments, the received indication may be a sequence of indications indicating the power to be supplied to the electric grid over a period of time. For example, the received indication may be a sequence of communication messages including real-time indications of the power to be supplied to the electric grid  150 . 
     In various exemplary embodiments, the power storage devices  120  may have a ramp rate or a power transient response that is faster than the ramp rate or power transient response of the power generators  110  such that regulation (e.g., regulation services) may be supplied by the power storage devices  120 . 
     In various exemplary embodiments, the PCCE  140  may determine a low frequency component of the received sequence of indications associated with power supply fluctuations below a threshold frequency and a high frequency component of the received sequence of indications associated with the power fluctuations at or above the threshold frequency. The PCCE  140  may control or adjust the energy level of the power storage devices  120  in accordance with the determined high frequency component and may adjust generation power by the power generators  110  in accordance with the determined low frequency component. 
     As will be appreciated by persons skilled in the relevant art(s), PCCE  140  may include various switches and relays, a database and computer equipment including a non-transitory computer readable storage medium having stored therein computer software such as program code to control at least the power storage devices  120 . 
     In this document, the terms “computer program medium,” “non-transitory computer readable medium,” and “computer usable medium” are used to generally refer to storage media such as a hard disk, memories, which can be memory semiconductors (e.g. DRAMs, etc.). 
       FIG. 1B  is a schematic diagram illustrating another exemplary power plant  170  connected (or coupled) to the electric grid  150  in accordance with exemplary embodiments. 
     Referring to  FIG. 1B , a power plant  170  is similar to power plant  100  except that power plant  170  may not include the grid indication receiver  130  and may include a grid frequency detector  160 . 
     The grid frequency detector  160  may be coupled (e.g., connected) to the PCCE  140  and the power bus bar  101  (or directly to the electric grid  150 ) and may be configured to detect and report changes in grid frequency. Based on reports, signals or messages from the grid frequency detectors  160 , the PCCE  140  may control the power storage devices  120  for storing power generated by the power generators  110 , thus, effectively preventing energy from reaching the electric grid  150 . Conversely, the PCCE  140  may control the power storage devices  120  to actively remove energy from the electric grid  150 . 
     The PCCE  140  may determine the current adjustment to the power to be supplied to the electric grid  150 , responsive to receiving a signal indicating the grid frequency and/or a direction of the change in the grid frequency (e.g., in response to the grid frequency moving lower, the power to be supplied to the electric grid  150  may be increased and responsive the grid frequency moving higher, the power to be supplied to the electric grid  150  may be decreased). The power contribution control equipment may determine power contribution by the power generators  110  (e.g., each generator) and power contribution by the power storage devices  120  (e.g., each device) to satisfy (meet) the determined power adjustment. The respective power contributions may be based on, for example, the deviation in the grid frequency from a nominal frequency and the rate of change of the deviation in the grid frequency. For example, the power storage device  120  may be assigned to charge or discharge and the power generator  120  may provide the remaining capacity. 
       FIG. 2  is a more detailed schematic diagram illustrating an exemplary regulation unit  200  in accordance with exemplary embodiments. 
     Referring to  FIG. 2 , the regulation unit  200  (e.g., frequency or power regulation, among others) may provide energy (power) to and may receive energy from the electric grid  150 . For example, the energy may be provided through a local substation or transmission lines. In this manner, the electricity grid  150  may provide an appropriate amount of power for the current load, at a specified nominal frequency, (e.g., generally 60 Hz in the United States and/or 50 Hz in some other parts of the world). 
     The regulation unit  200  may include at least one power generator  205 , a database or storage device  207 , such as an optical storage unit or a magnetic storage unit, and a set of energy storage cells  210 . The power generator  205  may be configured to generate alternating current for distribution across a power grid and may be coupled to the database  207  such that the power generator  205  can have its own unique profile (individual profile). Profile generally refers to operational parameters for proper operation of the power generator  205  and may include: (1) operational limits for the power generator  205 ; (2) maximum, minimum and/or optimal operating set points for the power generator  205  and/or (3) ramp rates or power transient responses rates for the power generator  205 . 
     The energy storage devices or cells (e.g., batteries)  210  may be electrically and/or energetically coupled to the electric grid  150  and may be any device suitable for storing energy. For example, in some exemplary embodiments, advanced lithium ion batteries may be used. As used herein, the term “energetically coupled” generally refers to energy that may flow from one object to another. For example, electricity in the form of an AC or DC current may flow from one object to another in a bi-directional fashion. The batteries  210  may provide energy to the electric grid  150  or power generator  205 , or receive energy from the electric grid  150  or the power generator  205 , for regulation, e.g., services to regulate and/or stabilize the electric grid with regard to frequency, voltage level and/or power factor, among others. Such services may include regulation services, spinning reserve services, supplemental reserve services, replacement reserve services and/or voltage control services, among others. 
     When providing energy to the electric grid  150 , a DC current may travel from the batteries  210  to bidirectional AC/DC converters  215 , which convert the DC current to an AC current. In some exemplary embodiments, inverters are used for the DC to AC conversion. When storing energy from the electric grid  150 , rectifiers may be used for AC to DC conversion. Different types of inverters and rectifiers may be used, as would be apparent to one skilled in the relevant art(s). AC current flows between the bidirectional AC/DC converters  215  and the electric grid  150  via a transformer  220 . 
     A power conversion system (PCS)  225  may include a logical control system for the AC/DC bi-directional converters  215 . A programmable logic controller (PLC)  230  may instruct the PCS  225  to connect or disconnect the AC/DC converters  215  from the batteries  210  and/or the electric grid  150 . 
     In certain exemplary embodiments, the connection between the transformer  220  and grid  150  may include or may be by a manual switch, which may be normally closed during operation of the regulation unit  200 . 
     In certain exemplary embodiments, an AC power storage device such as a capacitor storage system or an inductive storage system may be charged or discharged for Volt-Amperes Reactive (VAR) support, for example, to adjust power factor on the electric grid. 
     In various exemplary embodiments, DC power storage devices such as battery storage units may be charged or discharged via a bidirectional inverter. The inverter may be controlled to provide VAR support, for example, to adjust power factor on the electric grid  150  by converting the DC power to AC power with a high power factor (e.g., above a threshold level) for supply to the electric grid  150 . The control of VAR support may include determining the power factor (e.g., the phase difference between the current and voltage on the electric grid  150 ) or receiving an external signal (e.g., from the electric grid operator) indicating the power factor of the electric grid  150  and supplying power at a power factor above a threshold level in response to the determined or indicated power factor being below a specified threshold. 
     In certain exemplary embodiments, the PLC  230  may use program ladder logic to produce real-time control. The PLC  230  may send data signals to the PCS  225  via a data interface and/or may receive data signals from the PCS  225  via the data interface. Exemplary inputs to the PLC  230  from the PCS  225  may include a state of readiness signal, and exemplary outputs from the PLC  230  may include a signal indicating the amount of energy to charge or discharge, and/or instructions to connect the AC/DC converters  215  to the electric grid  150  and/or batteries  210  or to disconnect the AC/DC converters  215  from the electric grid  150  and/or batteries  210 . A computer executing specific program code may also be used for this function. Such computer can be any type of computing device having one or more processors, a user input (for example, a mouse, QWERTY keyboard, touch-screen, microphone, or a T9 keyboard), and a communications infrastructure capable of receiving and transmitting data over a network. For example, the computer can include, but is not limited to, a desktop computer, a cluster of desktop computers, a server, a cluster of servers, a set-top box, or other similar type of device capable of processing instructions and receiving and transmitting data to and from the electric grid and other computing devices. 
     To maintain the batteries  210  in a state that enables the batteries  210  to respond to requests to add energy to or absorb energy from the electric grid  150 , the regulation unit  200  may include a battery management system (BMS)  235 . The BMS  235  balances the battery cells  210  and maintains knowledge of a state of charge (SOC) of the battery cells  210 . The SOC of the batteries  210  may be a measurement of the current ability of the batteries to send and to receive energy (e.g., discharge or charge the energy). Exemplary inputs to the PLC  230  from the BMS  235  may include the power capabilities of the batteries  210  (e.g. in MWsec), faults, the temperature of the batteries  210 , the current draw on the batteries  210  or the current drawn by the batteries  210  and the SOC, among others. 
     In certain exemplary embodiments, the SOC is a percentage that runs from 0% to 100%, where 100% indicates that no more energy may be stored in the batteries  210 . The SOC may be calculated from the open circuit and/or closed circuit voltage levels. The SOC, however, may be calculated in any number of ways, as would be apparent to one skilled in the relevant arts. 
     A remote terminal unit (RTU) (not shown) may be used to connect to a Supervisory Control and Data Acquisition (SCADA) system  255 . In certain exemplary embodiments, the SCADA system  255  may be associated with an operator (e.g., the ESO) that operates the electric grid  150 . Exemplary inputs from the SCADA system  255  to the PLC  230  may include a request to regulate the grid frequency, the voltage level or other regulation services. The request may include an energy amount (e.g. in MW) to charge or discharge, and may include, for example, the grid frequency or other operating parameters for the electric grid  150 . 
     Exemplary outputs from the PLC  230  may include a status and availability of the regulation unit  200 . In certain exemplary embodiments, the PLC  230  may send information to the SCADA system  255  about the SOC or its capabilities so that the SCADA system  255  understands whether the regulation unit  200  may be able to provide the services to be scheduled by the ESO (e.g., knows ahead of time whether or not the regulation unit  200  can provide such services). 
     The PLC  230  may receive data signals from a transducer  260 , which may be coupled to the electric grid  150 . The transducer  260  may be configured to sense the AC signal on the electric grid  150  to determine the frequency, voltage level or/and the power factor, among others of the electricity being delivered by the electric grid  150 . Although one transducer  260  is shown, it is contemplated that any number of such transducers may be used to reliably detect the appropriate grid parameters at disparate locations. 
     An uninterruptible power supply (not shown) may supply power to the PLC  230 . The PLC  230  may send to the HVAC unit and may receive signals from an HVAC unit (not illustrated) to maintain proper environmental conditions for the batteries  210  and other components. Exemplary inputs to the PLC  230  from the HVAC unit may include temperature, humidity and other operating parameters for the HVAC unit, and exemplary outputs from the HVAC unit may include one or more thermostat settings and other control set points. 
     In certain exemplary embodiments, a computer  245  may be coupled to (e.g., connected to) the PLC  230  for controlling, programming, or setting parameters of the PLC  230 . The computer  245  may be used to monitor the regulation unit  200 . Exemplary inputs from the computer  245  to the PLC  230  may include shut-down and start-up signals. Exemplary outputs to the computer  245  may include log events, log data, and reports of alerts, among others. 
     When frequency or voltage regulation is performed, a request may be received at the PLC  230  from the operator (or ESO) of the electric grid  150  through the SCADA system  255  and the RTU (or using any other communication network). The request may include instructions to absorb energy from or to add energy to the electricity grid  150 . In certain exemplary embodiments, the request may specify how much energy to transfer or a rate for the transfer. In response, energy may be transferred: (1) from the energy storage device to the electric grid  150  to increase the current grid frequency or to increase the grid voltage level; or (2) from the electric grid  150  to the energy storage device to decrease the current grid frequency or to decrease the grid voltage level. 
     The regulation may be stopped in response to another dispatch request from the ESO or operator (e.g., the operator may include an automated computer supervisory system and may occur without human intervention). For example, the operator or computer supervisory system may determine that the grid frequency and/or the voltage level may be at or near the desired nominal frequency and/or voltage level. In another example, the regulation may be stopped based on a measurement by the regulation unit  200  that the grid frequency or the grid voltage level measurement may be at or near the desired value. The regulation may be stopped for other reasons, such as the detection of a fault. 
     During the regulation, the SOC of the batteries  210  may rise or fall dramatically. For example, the batteries  210  may have transmitted a significant amount of energy to the electric grid  150 , thus leaving the batteries  210 , for example, with very little charge (e.g. an SOC in the range of about 10% to 30% and maybe around 20%). In another example, the batteries  210  may have received a lot of energy from the electric grid  150 , thus leaving the batteries  210  with a large amount of charge (e.g. an SOC in the range of about 75% to 95% and maybe 85%). The charging range, for example, the range from 10% to 85% for the SOC may be dependent on many factors including the battery chemistry used (e.g., lead acid, or lithium, among others). In both of the examples, the batteries  210  may be in a poor condition to continue to regulate the grid frequency or the grid voltage level if more energy needs to be respectively added or absorbed. To provide a more reliable service, the charge on the batteries may be modified in accordance with the principles of the presently disclosed system and/or in accordance with U.S. Patent Application Publication No. 2010/0090532 A1, to maintain the batteries within a desirable range for the greatest amount of time possible. The modification may be to selectively increase or decrease the energy level (charge), as appropriate. The modification may occur (e.g., may only occur) when it is beneficial to do so, to balance the need for an appropriate SOC with the overall needs of the power distribution system. 
     In accordance with one exemplary embodiment, the modification may be carried out while the grid frequency or grid voltage level is in a deadband that does not use regulation. During this time, energy (or charge) may be added or removed until the SOC value, which may be monitored at the PLC  230  based on information from the BMS  230 , is within a specified range. For example, the range may be centered around 50% of SOC so that the regulation unit  200  may equally provide or receive energy. In other embodiments, the target state may be higher or lower than about 50%, for example, when it is known that a large transfer of energy in a specific direction is likely. 
       FIG. 3  is a flowchart illustrating a method  300  of controlling power supplied to the electric grid  150  in accordance with exemplary embodiments. 
     Referring to  FIG. 3 , at block  310 , the grid indication receiver  130  may receive an indication of power to be supplied to the electric grid  150 . At block  320 , at least one power generator  110  may generate power. At block  330 , the PCCE  140  may adjust, using the generated power from the power generator  110 , the energy level of the energy storage device  120  to control the power supplied to the electric grid  150  in accordance with the received indication. 
     It is contemplated that the power may be stored as DC power and may be converted between AC power and DC power when storing power in the power storage device  120  and may be converted from DC power to AC power when distributing power to the electric grid  150  from the power storage device  120 . 
     In certain exemplary embodiments, the reception of the indication at block  310  may include (1) detecting, by a detector, grid frequency changes and the adjustment of the energy of the energy storage device  120  may include controlling power contribution by generating additional power from the power generators  110  and/or distributing stored power from the power storage devices  120 . The controlling of power contribution to the electric grid may be performed by controlling either the discharge of or storage of power from at least one power storage device  120  and increasing or decreasing power generation from at least one power generator  110 . The controlling of power contribution may be accomplished by controlling the discharge and storage of power from at least one power storage device using a system such as the SCADA system  255  to control the generation of power. 
     The present method and apparatus may thereby be an add-on to control power storage and distribution from a power storage device to a legacy system. Alternatively, the system may be optimized to permit the control of both the power storage device(s) and the power generator(s) by the PCCE  140 . The PCCE  140  may provide a response to detected voltage and/or frequency fluctuations on the electric grid  150  to ensure stability of the electric grid  150 . For example, an energy storage device  120  may provide additional power to the electric grid  150  when the power generators  110  may be ramping up and may absorb power from the electric grid  150  when the power generators may be ramping down. The combined response of the power generators  110  and the energy storage device  120  may achieve a faster transient response than the power generators  110  alone and may also achieve improved operating efficiency and lower maintenance costs due to the use of a smaller power generator capacity that may be designed to have a slower ramp rate (or transient response) relative to a standalone generator. 
     Changes in grid parameters (e.g., frequency) may be detected using, for example, the transducer  260  (shown, e.g., in  FIG. 2 ) that can measure instantaneous grid frequency changes, grid voltage changes or other grid operating parameter changes. The selection of the operating level (e.g., the SOC) of the batteries  120  may be based on the detected changes in grid frequency and/or the grid voltage. The SOC for the batteries may also be adjusted based on relatively short historical trends (e.g., in the range of about 15 seconds to about 10 minute trends) in the detected parameters. If the PCCE  140  determines that a reduction in power may be expected based on the historical trend, the batteries  120  may be operated at a reduced SOC in order to absorb additional power in the downward trending of the total power distribution. If the PCCE  140  determines that an increase in power may be expected based on the historical trend, the batteries  120  may be operated at an increased SOC in order to provide additional power in the upward trending of the total power distribution. Further, the SOC of the batteries may be controlled as disclosed in Patent Application Publication No. 2010/0090532. 
       FIG. 4  is flowchart illustrating an adjustment of power contribution by generation and/or storage in accordance with embodiments. 
     Referring to  FIG. 4 , at block  410 , the PCCE  140  may determine the preferred or optimal power contribution profile of the power generator(s) or may use a predetermined generator profile. The profiles may be stored, for example, in the generation profile database  207 . The generation profile database  207  may be formed as part of the database connected to the PLC  230 , or may be connected directly to the power generators  205  (shown, for example, in  FIG. 2 ) such that each power generator  205  may have its own unique (e.g., individual) profile. 
     At block  420 , the PCCE  140  may determine the preferred or optimal power contribution profile of the energy storage device(s) or may use a predetermined energy storage profile. The profiles may be stored in the storage profile database  212  such that each energy storage device may have its own unique (e.g., individual) profile. Although a generation profile database  207  and a storage profile database  212  are shown, it is contemplated that one common database may include both sets of profiles. 
     At block  430 , the PLC  230 , or a computer connected thereto may optimize the power contributions of the generator(s)  110  and/or storage device(s)  120  based on the respective profiles such that various factors may be optimized. These factors include may include wear and tear, maximum rate of change of the power generator(s)  110 , optimum rate of change of the power generator(s)  110 , fuel consumption rate profiles of the power generator(s)  110 , state of charge (SOC) of at least one power storage device  120 , durability of the respective equipment  110  and  120 , cost of initial acquisition and depreciation and transmission losses over the power grid  150 , among many others. For example, the PCCE  140  may determine the preferred operating set points for the energy storage device(s)  120  and/or the power generator(s)  110  based on the determined or predetermined profiles and may adjust the current (present) operating set points to the preferred operating set points. 
       FIG. 5  is a plot  500  illustrating a demand curve  510  being matched by the combined response curve  520  of a thermal electrical generation plant response  530  and a grid stability electrical storage system response  540  in accordance with exemplary embodiments. The lines are not drawn to scale, and may be more exact, according to a particular implementation. 
     Referring to  FIG. 5 , by combining the battery based energy storage system  120  with a power plant  100  or  170  (i.e., the power plant  100  or  170  may operate in conjunction with the battery based storage system), the ramping capabilities of that power plant  100  or  170  may be increased relative to a standalone power generator. The power plant may ramp-up or ramp-down from a set point while the battery energy storage system  120  may regulate the power plant to satisfy the demand curve. 
     One skilled in the relevant art understands that the demand curve  510  is a plot of the load demand which may be provided sequentially in real-time from the ESO or operator via the grid indication receiver  130 , as a sequence of demand load levels. Because the electric grid  150  is controlled in real-time, the relatively short historical trends in the demand curve may be used by the PCCE  140  for establishment of the actual set points for the power generator(s)  110  and energy storage device(s)  120 . 
     In certain exemplary embodiments, the battery energy storage devices  120  may act as a buffer to the electricity grid  150  and may supply faster ramping than possible with the power plant alone. 
     The foregoing examples have been described in the context of frequency regulation, in which power is added to or absorbed from the electric grid  150  for purposes of load following. In this situation, the decision to add or absorb power is based upon the instantaneous value of the operating frequency or instantaneous operating voltage relative to ramp limits and optimal performances. The principles described herein are equally applicable to other ancillary services of the electric grid. For example, to respond to a rapid drop in the operating frequency, a parameter such as the rate of change of the frequency could be employed in addition to, or in lieu of, the instantaneous value of the operating frequency, as a trigger for an instruction to add power to the electric grid. Within different applications for ancillary services, the set points of the device may be modified for that service using the same control and logic structure described for frequency or voltage regulation. 
     Although a hybrid power plant is described as including one or more energy storage devices, it is contemplated that any generator or any generation sink having a ramp rate sufficient to stabilize the electric grid may be used in addition to or in lieu of the energy storage devices. Such generators or generation sinks may increase the efficiency of existing power generators by reducing or eliminating spinning reserve capacity. 
     It is to be understood that exemplary embodiments as described above can be implemented in the form of control logic using hardware and/or using computer software in a modular or integrated manner. Based on the disclosure and teachings provided herein, a person skilled in the relevant art(s) would know and appreciate other ways and/or methods to implement the exemplary embodiments using hardware such as the computer system  600  illustrated in  FIG. 6  and/or a combination of hardware and software. 
     Any of the software components or functions described in this application, may be implemented as software code to be executed by a computing device and/or processor using any suitable computer language such as, for example, Java, C++ or Perl using, for example, conventional or object-oriented techniques. The software code may be stored as a series of instructions, or commands on a computer readable medium for storage and/or transmission, suitable media include random access memory (RAM), a read only memory (ROM), a magnetic medium such as a hard-drive or a floppy disk, or an optical medium such as a compact disk (CD) or DVD (digital versatile disk), flash memory, and the like. The non-transitory computer readable medium may include storage devices, such as, but not limited to, magnetic or optical disks or tape, solid state memory devices, program cartridges and cartridge interfaces (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other computer readable media and interfaces which allow software and data to be transferred from storage to a computing device. 
     Aspects of the present invention shown in  FIGS. 1-5 , or any part(s) or function(s) thereof, may be implemented using hardware, software modules, firmware, tangible computer readable media having instructions stored thereon, or a combination thereof and may be implemented in one or more computer systems or other processing systems. 
       FIG. 6  illustrates an example computer system  600  in which embodiments of the present invention, or portions thereof, may be implemented as computer-readable code. For example, the power plant  100 , regulation unit  200 , and methods  300  and  400  of  FIGS. 1-4 , can be implemented in computer system  600  using hardware, software, firmware, non-transitory computer readable media having instructions stored thereon, or a combination thereof and may be implemented in one or more computer systems or other processing systems. Hardware, software, or any combination of such may embody any of the modules and components used to implement the components of  FIGS. 1-5 . For example, the display  630  and display interface  602  can be configured to render the plot  500  of a demand curve matched by a combined response curve of a thermal electrical generation plant response and a grid stability electrical storage system response illustrated in  FIG. 5 . 
     If programmable logic is used, such logic may execute on a commercially available processing platform or a special purpose device. One of ordinary skill in the art may appreciate that embodiments of the disclosed subject matter can be practiced with various computer system configurations, including multi-core multiprocessor systems, minicomputers, mainframe computers, computers linked or clustered with distributed functions, as well as pervasive or miniature computers that may be embedded into virtually any device. 
     For instance, at least one processor device and a memory may be used to implement the above described embodiments. A processor device may be a single processor, a plurality of processors, or combinations thereof. Processor devices may have one or more processor “cores.” 
     Various embodiments of the invention are described in terms of this example computer system  600 . After reading this description, it will become apparent to a person skilled in the relevant art how to implement the invention using other computer systems and/or computer architectures. Although operations may be described as a sequential process, some of the operations may in fact be performed in parallel, concurrently, and/or in a distributed environment, and with program code stored locally or remotely for access by single or multi-processor machines. In addition, in some embodiments the order of operations may be rearranged without departing from the spirit of the disclosed subject matter. 
     Processor device  604  may be a special purpose or a general purpose processor device. As will be appreciated by persons skilled in the relevant art, processor device  604  may also be a single processor in a multi-core/multiprocessor system, such system operating alone, or in a cluster of computing devices operating in a cluster or server farm. Processor device  604  is connected to a communication infrastructure  606 , for example, a bus, message queue, network, or multi-core message-passing scheme. 
     Computer system  600  also includes a main memory  608 , for example, random access memory (RAM), and may also include a secondary memory  610 . Secondary memory  610  may include, for example, a hard disk drive  612 , removable storage drive  614 . Removable storage drive  614  may comprise a floppy disk drive, a magnetic tape drive, an optical disk drive, a flash memory, or the like. 
     The removable storage drive  614  reads from and/or writes to a removable storage unit  618  in a well-known manner. Removable storage unit  618  may comprise a floppy disk, magnetic tape, optical disk, etc. which is read by and written to by removable storage drive  614 . As will be appreciated by persons skilled in the relevant art, removable storage unit  618  includes a non-transitory computer usable storage medium having stored therein computer software and/or data. 
     In alternative implementations, secondary memory  610  may include other similar means for allowing computer programs or other instructions to be loaded into computer system  600 . Such means may include, for example, a removable storage unit  622  and an interface  620 . Examples of such means may include a program cartridge and cartridge interface (such as that found in video game devices), a removable memory chip (such as an EPROM, or PROM) and associated socket, and other removable storage units  622  and interfaces  620  which allow software and data to be transferred from the removable storage unit  622  to computer system  600 . 
     Computer system  600  may also include a communications interface  624 . Communications interface  624  allows software and data to be transferred between computer system  600  and external devices. Communications interface  624  may include a modem, a network interface (such as an Ethernet card), a communications port, a PCMCIA slot and card, or the like. Software and data transferred via communications interface  624  may be in the form of signals, which may be electronic, electromagnetic, optical, or other signals capable of being received by communications interface  624 . These signals may be provided to communications interface  624  via a communications path  626 . Communications path  626  carries signals and may be implemented using wire or cable, fiber optics, a phone line, a cellular phone link, an RF link or other communications channels. 
     In this document, the terms “computer program medium,” “non-transitory computer readable medium,” and “computer usable medium” are used to generally refer to media such as removable storage unit  618 , removable storage unit  622 , and a hard disk installed in hard disk drive  612 . Signals carried over communications path  626  can also embody the logic described herein. Computer program medium and computer usable medium can also refer to memories, such as main memory  608  and secondary memory  610 , which can be memory semiconductors (e.g. DRAMs, etc.). These computer program products are means for providing software to computer system  600 . 
     Computer programs (also called computer control logic) are stored in main memory  608  and/or secondary memory  610 . Computer programs may also be received via communications interface  624 . Such computer programs, when executed, enable computer system  600  to implement the present invention as discussed herein. In particular, the computer programs, when executed, enable processor device  604  to implement the processes of the present invention, such as the steps in the methods illustrated by the flowcharts  300  and  400  of  FIGS. 3 and 4 , discussed above. Accordingly, such computer programs represent controllers of the computer system  600 . Where the invention is implemented using software, the software may be stored in a computer program product and loaded into computer system  600  using removable storage drive  614 , interface  620 , and hard disk drive  612 , or communications interface  624 . 
     Embodiments of the invention also may be directed to computer program products comprising software stored on any computer useable medium. Such software, when executed in one or more data processing device, causes a data processing device(s) to operate as described herein. Embodiments of the invention employ any computer useable or readable medium. Examples of computer useable mediums include, but are not limited to, primary storage devices (e.g., any type of random access memory), secondary storage devices (e.g., hard drives, floppy disks, CD ROMS, ZIP disks, tapes, magnetic storage devices, and optical storage devices, MEMS, nanotechnological storage device, etc.), and communication mediums (e.g., wired and wireless communications networks, local area networks, wide area networks, intranets, etc.). 
     It is to be appreciated that the Detailed Description section, and not the Summary and Abstract sections, is intended to be used to interpret the claims. The Summary and Abstract sections may set forth one or more but not all exemplary embodiments of the present invention as contemplated by the inventor(s), and thus, are not intended to limit the present invention and the appended claims in any way. 
     Embodiments of the present invention have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed. 
     The foregoing description of the specific embodiments will so fully reveal the general nature of the invention that others can, by applying knowledge within the skill of the art, readily modify and/or adapt for various applications such specific embodiments, without undue experimentation, without departing from the general concept of the present invention. Therefore, such adaptations and modifications are intended to be within the meaning and range of equivalents of the disclosed embodiments, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance. 
     The breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.