Abstract:
A microgrid is a portion of an electric grid configured for separate management and control as compared with the rest of the grid and having attributes that can be tailored to meet specified needs including the needs of electric power consumers served by the microgrid.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an electrical apparatus. In particular, an electrical grid including a network of electrical conductors is a part of a larger grid. 
         [0003]    2. Discussion of the Related Art 
         [0004]    One of the earliest electrical grids in the United States was established in 1886 in Detroit when the Edison Illuminating Company began serving its first customers by distributing electricity for street lamps and factories in and around Detroit. Edison was a proponent of direct current electrical generation and distribution but this technology was quickly replaced by alternating current and its ability to be transformed to supply different voltage appliances and to be boosted to recover voltage lost during transmission over long distances. 
         [0005]    Modern day electric grids tend to have very high AC transmission voltages for traversing long distances and intermediate AC distribution voltages for supplying power to smaller areas. Grid development has been largely driven by sites of power generation, areas of dense population, and more recently by interconnection of disparate grids to increase grid reliability. 
         [0006]    Given that grids are designed and built by utility companies scattered across this and other countries, standardized grid designs are virtually unknown. Grid development is therefore a complex process that enlarges what has become, at least in the United States, an increasingly uncoordinated electric supply system. 
         [0007]    There is a need for better coordination of the electric supply system in the United States including standardization of grid design that provides for more straightforward interconnection and coordination of disparate grids and improves grid reliability and control. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides a microgrid for use with one or more power sources such as grid interconnections. In various embodiments, the microgrid is designed to receive power from at least two power sources such as independent power sources. When a microgrid power source experiences an outage, the microgrid is designed to operate on the remaining power source(s). 
         [0009]    In an embodiment an electric grid comprises a plurality of grid sections and at least one of the grid sections is a microgrid; the microgrid is configured to receive electric power at first and second microgrid interconnections; a first edge substation interconnects the microgrid first interconnection with a first source of electric power; a second edge substation interconnects the microgrid second interconnection with a second source of electric power; and, the microgrid is separable from one or more other sections of the grid. 
         [0010]    In some embodiments, the electric grid further comprises a plurality of distribution circuits extending between the substations of the microgrid; one or more sectionalization switches are operative to interrupt the flow of electric power in one or more distribution circuits; and, upon the occurrence of a fault in a sectionalized distribution circuit, the sectionalization switches operative to interrupt the flow of electric power to the fault. 
         [0011]    Further information about protective devices and systems together with explanations of electrical system faults is provided in U.S. Pat. App. No. 2004/0027748 A1 which is now incorporated herein in its entirety and for all purposes. In particular, the discussion of faults, protective devices, and protective device functions found in the abstract, summary,  FIGS. 18-23 , and the text relating to  FIGS. 18-23  is included. 
         [0012]    In an embodiment, an electric grid comprises a plurality of grid sections; at least one of the grid sections is a microgrid; an edge substation of the microgrid selectively interconnects a substation bus to an electric supply grid or a local generator; for each of a plurality of distribution circuits, a first switch connects one end of the circuit to the bus and a second switch connects another end of the circuit to the bus; for each of the plurality of distribution circuits, one of the first and second switches being closed and the other of the first and second switches being open; one or more sectionalization switches is operative to bifurcate one of the plurality of distribution circuits; and, upon the occurrence of a fault in a sectionalized distribution circuit, one or more of the sectionalization switches operative to interrupt the flow of electric power to the fault. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention is described with reference to the accompanying figures. These figures, incorporated herein and forming part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the relevant art to make and use the invention. 
           [0014]      FIG. 1  shows a block diagram of a microgrid in accordance with the present invention. 
           [0015]      FIG. 2  illustrates a microgrid with two external power sources and two substations in accordance with the microgrid of  FIG. 1 . 
           [0016]      FIG. 3  illustrates a microgrid with sectionalizing switches in accordance with the microgrid of  FIG. 1 . 
           [0017]      FIG. 4  illustrates a microgrid with distribution line looping in accordance with the microgrid of  FIG. 1 . 
           [0018]      FIG. 5  illustrates a microgrid with distributed generation in accordance with the microgrid of  FIG. 1 . 
           [0019]      FIG. 6  illustrates a microgrid with a single external feed in accordance with the microgrid of  FIG. 1 . 
           [0020]      FIG. 7  illustrates a microgrid utilizing a stored energy power source in accordance with the microgrid of  FIG. 1 . 
           [0021]      FIG. 8  illustrates a microgrid with a grid connected converter in accordance with the microgrid of  FIG. 1 . 
           [0022]      FIG. 9  illustrates a microgrid with a generator connected converter in accordance with the microgrid of  FIG. 1 . 
           [0023]      FIG. 10  illustrates a microgrid with distributed converters in accordance with the microgrid of  FIG. 1 . 
           [0024]      FIG. 11  illustrates a microgrid with power conditioning devices in accordance with the microgrid of  FIG. 1 . 
           [0025]      FIG. 12  illustrates a microgrid utilizing DC power in accordance with the microgrid of  FIG. 1 . 
           [0026]      FIG. 13  illustrates a microgrid with a master controller in accordance with the microgrid of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0027]    A microgrid is a subsection of the grid that can be separated either temporarily or permanently from the rest of the grid, the grid subsection being configured for interconnection with at least two sources of electric power. Power sources includes one or more of grid feeds from distribution or transmission circuits, generation sources such as solar/photovoltaics or natured gas fired engines, and a combination of local generation and grid feeds. 
         [0028]      FIG. 1  illustrates a block diagram of a microgrid  100 . The microgrid includes one or more of switches, distribution lines, loads, converters, local power sources, and grid power sources. For example, some microgrids include switches, distribution lines, loads, a Pt external power source and a 2 nd  external power source. This and other embodiments of microgrids in accordance with the present invention are disclosed below. 
         [0029]      FIG. 2  illustrates a single line diagram of a first microgrid  200 . The single line diagram includes grid feeds  1 A,  1 B, substations  2 A,  2 B, distribution conductors  3 , and loads  4 . A dashed line indicates a boundary  6  surrounding the microgrid. 
         [0030]    In various embodiments, grid feeds  1 A,  1 B are interconnected grids such as distribution lines from a utility company or another provider connected to the bulk grid. 
         [0031]    Substations  2 A,  2 B typically distribute power from transmission or distribution sources and include one or more of conductors, transformers such as transformers to step-down voltages from high voltage lines and circuit interrupters such as circuit breakers, fuses, or switches for protecting the distribution lines within the microgrid. In some embodiments, a substation may consist primarily of distribution buses or circuit breaker panels to distribute the power. Notably, in this patent application, the words connect, couple, and similar words such as interconnect, connected, and coupled refer, unless otherwise noted, to direct and indirect linkages, with or without intervening elements or parts. For example, “a substation connected to a grid” may be directly or indirectly linked, such as with or without an interposed transformer. 
         [0032]    As shown, the substations  2 A,  2 B are configured to provide power from two independent power sources  1 A,  1 B in case feeds to one of the substations fails. In various embodiments, only one substation  2 A,  2 B powers the microgrid while the other is in a standby mode. For example, the first substation  2 A breakers  5 A are closed to supply microgrid power while the second substation  2 B breakers  5 B are open so that a short circuit is not created. 
         [0033]    In this and other embodiments disclosed herein, one or more substations of a microgrid may be bi-directional. For example, in an embodiment a microgrid interposed between two grids transfers power from one grid to the other grid when a substation that normally imports power to the microgrid is used to export power from the microgrid. In another example, a microgrid interposed between a grid and a local power source exports power to the grid when a substation that normally imports power to the microgrid is used to export power from the microgrid. 
         [0034]    The distribution conductors or distribution lines  3  provide power from the substations  2 A,  2 B to the loads  4 . These loads can be homes, buildings, buildings with smaller loads contained within them, or a large load such as a chiller plant that supplies chilled water to a building(s) or campus. In the embodiment shown  200 , the power flow and the power flow direction are controlled by the switches or breakers in the substations. Notably, control of power flow and power flow direction in more complex embodiments described below may differ. 
         [0035]    Other equipment may be installed to stabilize voltages, power factors, and manage power quality within the microgrid  200 . In various embodiments, microgrids utilize different sources of electric power that may include or exclude a grid. For example, microgrids may be designed to operate a) on single phase AC, b) on multiple phase AC, c) at frequencies other than 60 Hz (standard utility transmission and distribution frequency in the United States), or on direct current (DC). 
         [0036]    Notably, the microgrid  200  can be electrically isolated from other sections of the grid. For example, opening the substation switches  5 A isolates the microgrid from the grid section associated with the first external power supply  1 A. In a similar fashion, opening the substation switches  5 B isolates the microgrid from the grid associated with the second external power supply  1 B. As a person of ordinary skill in the art will appreciate, similar switching arrangements present in other embodiments of the invention provide similar electrical isolation. 
         [0037]      FIG. 3  shows a microgrid with section isolation fault protection  300 . In this embodiment, sectionalizing switches  12  are included in one or more of the distribution lines  3 . If a fault  10  should occur in a protected distribution line, the sectionalizing switches allow the faulted section of the distribution line to be isolated and at the same time allow power to flow to the sections that are not faulted. In this example, two sectionalizing switches  12  surrounding a fault  10  are opened to isolate the faulted section carrying loads L 1 , L 2 . Before the fault, all of the power on the faulted distribution line came from Substation  2 A. After the fault, the faulted distribution line is feed from substations  2 A and  2 B as indicated by the position of the substation breakers  5 A,  5 B. 
         [0038]      FIG. 4  shows a microgrid with distribution line looping  400 . Here, a single substation  16  is interconnected with two power sources  1 A,  17  via switches  20 ,  21  and the distribution lines  3  loop back to substation feeder breakers  19 . Looping back refers to each end of a distribution line being connected to a respective feeder breaker in the same substation. 
         [0039]    In the loop back configuration, power can flow into either end of a distribution line  3 , i.e., from two directions. However, irrespective of the power flow direction, the power is supplied from the same substation  16  rather than from two separate substations. In an embodiment, local generation  17  supplies power to the substation during grid feed  1 A outages illustrating the utility of two independent sources of power. Substation interconnection switches  20 ,  21  allow the power source for the main substation to be switched between the grid  1 A and local generation  17 . In order to avoid a short circuit, the source that is not used should be disconnected from the microgrid. 
         [0040]    In the event of a fault  10 , sectionalizing switches  12  are operative to isolate the faulted section of the distribution line and its loads L 1 , L 2 . When the faulted distribution line is cleared by isolating the fault, loads to either side of the faulted section of the distribution line can be fed by closing the feeder breakers  19  at each end of the faulted distribution line. 
         [0041]    The local generation  17  can also be replaced by a feed from another power source such as a different grid source so that the microgrid maintains redundant power supplies. Another suitable power source is a feed from another substation in the same microgrid that is feed by an independent supply. In the latter instance, an enlarged microgrid can be constructed by chaining together substations with looped distribution circuits, the microgrid being maintained as long as the microgrid as a whole has two independent sources of power. 
         [0042]      FIG. 5  shows a microgrid with distributed generation  500 . Distributed generation power sources include renewable and fossil fueled power sources such as solar photovoltaic and natural gas fired engines. In various embodiments, generation is installed at one of the distribution lines  3  or at one of the substations  2 A,  2 B. An advantage of installing generation on a distribution line is that it can provide voltage support along the line. The generation can also be isolated with circuit breakers  5 A,  5 B or sectionalizing switches  12  (See  FIG. 4 ) to provide power to critical loads during a grid outage. For generation installed on distribution lines, generation capacity can be limited by the size of the distribution conductor and one generator may not be able to supply power to the entire microgrid. For this reason, in some embodiments it is advantageous to install generation on a substation bus. When installed on the substation bus, the generated power can be distributed through the substation. 
         [0043]    There are several reasons for installing generation within a microgrid. One reason is to increase power security and reliability, so that when the grid supply is interrupted, the generation or local power source can act as a back-up power supply to the microgrid by electrically isolating the microgrid from the bulk grid and supplying power from the local generation. 
         [0044]    Another reason is to reduce costs. If power can be generated locally on the microgrid at a lesser cost than a grid supply, then the microgrid operator can save money by utilizing generation from within the microgrid. 
         [0045]    There may also be environmental reasons for generating within the microgrid. For instance, if electricity on the grid is primarily generated from coal fired plants, engines such as local natural gas engines might have a lower emissions and carbon footprint than the grid. 
         [0046]    Local generation may also be beneficial when there is an abundant supply of a local fuel source. For instance, if a particular industrial, commercial, or biological process generates methane, the methane can be collected, stored, and burned in a gas fired engine. Depending on the quantity and the steadiness of the methane flow, the generation may only be operated periodically. 
         [0047]    Local generation sources  25 ,  26  may also produce thermal energy that can also be utilized within a microgrid service area or sold outside this area. An example would be a combined heat and power system including a natural gas fired turbine, and a heat recovery system  27  on the exhaust of the turbine. The recovered heat can be used to create hot water, steam, or to heat another thermal transfer fluid. The recovered heat can be used to heat a building or to provide heat to other processes. One such process could be to provide heat to an absorption chiller  28  which can create chilled water from a high temperature heat source such as hot water. In various embodiments, the buildings are heated or cooled through thermal paths  29 . 
         [0048]      FIG. 6  shows a microgrid having a single utility feed  600 . Here, only one substation  2 A is supplied by a grid power source  1 A. The other substation  2 B is supplied by a local generator power source  35 . In various embodiments, the distribution lines are supplied with power from one or more local generators  36 . Some microgrids may be completely independent from the grid. For example, one embodiment replaces the grid feed  1 A with a generator such as a local generator. 
         [0049]    In other embodiments, stored energy can be used to supply power to the microgrid as an alternative to a grid feed  1 A or generation  35 ,  36 . In some such embodiments, generators are replaced with batteries and DC to AC converters for supplying AC power to the microgrid. 
         [0050]    In this and other embodiments disclosed herein, one or more converters of a microgrid may be bi-directional. For example, in an embodiment a microgrid interposed between two grids transfers power from one grid to the other grid when a converter that normally imports power to the microgrid is used to export power from the microgrid. In another example, a microgrid interposed between a grid and a local power source exports power to the grid when a converter that normally imports power to the microgrid is used to export power from the microgrid. 
         [0051]    As used in the patent application, the term “converter” refers to a device for converting between alternating and direct current. The term includes AC to DC devices, DC to AC devices, AC to AC devices, and DC to DC devices. As indicated by context of use, the term may refer to inverters (DC to AC), to rectifiers (AC to DC), and to switched semiconductor devices that construct particular waveforms including sinusoidal waveforms. 
         [0052]      FIG. 7  shows a microgrid utilizing a stored energy power source  700 . Energy storage devices include batteries, super capacitors, flywheels, and other such devices known to persons of ordinary skill in the art. In the embodiment shown, energy is stored in a battery  45  and a power converter  46  is interposed between the battery and a substation  2 A. Notably, the power converter may be a unidirectional device converting DC to AC to feed the substation or it may be a bidirectional device capable of feeding the substation (converting DC to AC) and capable of charging the batteries from the substation (converting AC to DC). 
         [0053]    In the embodiment shown, the power converter  46  is a bi-directional converter that converts electric power from AC to DC to charge the batteries and DC to AC to supply the microgrid with power from the batteries. The bi-directional converter  46  can be used to charge the batteries from a generation or grid source. At other times of the day, power can be supplied from the batteries. 
         [0054]    The benefits of charging the batteries at particular times of day include the possibility of taking advantage of electric power pricing differences throughout the day. For instance, if the microgrid has access to dynamic or time of use electric rates from the grid, the batteries can be charged when the prices are low (typically at night) and discharged when the prices are generally the highest throughout the day. Another circumstance where this approach would be beneficial is when solar photovoltaic arrays can be used to charge the batteries during the day, and the batteries are discharged during the night or when electricity prices are expected to peak during the day. Another reason for adding energy storage is for microgrid reliability and energy security. The energy storage can be used to supply power while backup generation is being started. 
         [0055]    Up to this point, only basic elements of the invention have been discussed. However, other components may need to be added to make these concepts work together. For instance, up to this point, this description has not included a discussion on synchronization between power sources or power conditioning. If the microgrid distributes alternating current (AC), then generation sources, DC to AC converters, and other AC power sources must be synchronized. 
         [0056]    Power sources need to be synchronized with one another in order to work properly and prevent damage to interconnected equipment. If an AC generator is to be interconnected with an AC network, the generator must have its line voltage, frequency, phase sequence, phase angle, and waveform equal to that of the network. Suitable interconnecting networks include the grid and electric generators. 
         [0057]    When the microgrid operates in parallel with the grid, the grid will provide a stable frequency. When the microgrid is operated independent of the grid (island mode), the generation source and DC to AC power converters must be synchronized. In various embodiments, a relatively large interconnected generator acts as a master and logic controlling interconnected smaller generators is able to interpret information from the microgrid phase waveforms and adjust the related small generator frequencies so they remain synchronized with the larger generator. Another approach uses communications between the inverters, power converters, and generators to maintain synchronization. Here, one generation source, power conditioner, or DC to AC power converter acts as a master and the other generation sources, power conditioners, or DC to AC power converters will follow synchronization commands to remain synchronized with the master. 
         [0058]    Synchronization communication may take several forms. In various embodiments, synchronization communications include one or more of direct interpretation of the sinusoidal waveforms from the master generator or grid, communication of synchronization commands over wires, fiber optics, infrared, and radio frequency. 
         [0059]      FIG. 8  shows a microgrid with a grid connected AC/AC converter  800 . Here, a DC bridge  52  interconnects an AC/DC converter  59  coupled to a grid  1 A and a DC/AC converter  58  coupled to a microgrid substation  2 A. The interconnected converters  56  provide an AC/AC converter. 
         [0060]    In an embodiment the AC/AC converter  56  is connected to the bus in one of the substations. In other embodiments, separate AC/AC converters are connected to the grid  1 A and the distribution lines  3 . In an embodiment, the AC/AC converter provides for bi-directional power flow. In one operating embodiment, while power flows from the grid to the microgrid  57 , the first converter  58  converts the AC power from the grid to DC power. The second converter  59  receives DC power from the first converter  58  and converts it back to AC. One advantage of this approach is that the microgrid need not be synchronized with the grid  1 A because the DC bus  52  eliminates the need for synchronization. In addition, the bus voltage and frequency can be different than the grid voltage and frequency. Yet another advantage of the AC/AC converter is that synchronization of the grid and microgrid, if needed, can be coordinated through the converter  56  which is often easier to control than a generator. For the purpose of synchronizing the microgrid to the grid, the generator or local power source  35  in various embodiments communicates with the converter  56  to coordinate their respective frequencies until they are synchronized. 
         [0061]    It should be noted that in this, and in other embodiments utilizing converters interposed between a grid section and the microgrid, the converter provides a means of isolating the microgrid from the grid section. 
         [0062]      FIG. 9  shows a microgrid with a generator connected converter  900 . In various embodiments a converter  67  is an AC/DC converter and in various embodiments the converter is an AC/AC converter. For example, an AC/AC converter connects a source  35  such as an AC generator to a microgrid substation  2 B. In other embodiments, an AC/DC converter connects DC power sources such as a battery or solar photovoltaic cells, to a microgrid substation  2 B. 
         [0063]    The converter  67  can also be used to decouple certain aspects of the generator from the rest of the microgrid. Through this decoupling, the generator can operate at a different frequency and different voltage from the microgrid. For example, gas fired generators can be designed to operate more efficiently as variable speed machines and this decoupling allows for their use. In various embodiments a communications line  68  enables communications between the converters  56 ,  67 . 
         [0064]      FIG. 10  shows a microgrid with distributed converters  1000 . Here, distributed converters  78  are interposed in each distribution line  3  between the corresponding loads  4  and a microgrid substation  2 B. In various embodiments, a DC power source  35  provides power to the substation  2 B and the converters  78  are AC/DC converters for converting the supplied DC power to AC power for supplying the loads. And, in various embodiments, an AC power source  35  provides power to the substation  2 B and the converters  78  are AC/AC converters for supplying AC power to the loads. 
         [0065]    An advantage of this arrangement is that some of the functions of the substation  2 B, such as current limiting and short circuit protection, can be replaced by the inverters  78 . In some embodiments, the inverters are designed to control the power flow to the distribution lines  3  and to provide protective controls, such as short circuit protection, normally contained in a substation. Various embodiments utilizing the inverters to provide protection typically found in the substation enable the use of less expensive substation breakers and relays. 
         [0066]    Since generation is a voltage source, generation distributed on the microgrid can be used to stabilize voltages and power quality on the microgrid while the microgrid operates in parallel to the grid. Inverters also work to stabilize disturbances and improve power quality on the microgrid as their primary function is to create sinusoidal AC waveforms for the microgrid. Depending on the design of the microgrid and whether or not microgrid loads may cause power surges or add harmonics on the distribution lines, equipment may be required to enhance power quality on the microgrid. In various embodiments, a communication line  79  enables communications between the converters  56 ,  78 . 
         [0067]      FIG. 11  shows a microgrid including power conditioning devices  1100 . Here, the power conditioning devices  85  may include one or more of advanced power electronics, capacitor banks, inductive banks, and resistor banks to remove disturbances from the AC waveform. Disturbances may be from the grid  1 A,  1 B or they may be caused by particular loads  4  within the microgrid. As mentioned above, converters may also accomplish this function. 
         [0068]    As shown, one power conditioning device is dedicated to each distribution line. In various embodiments, power conditioners are placed between loads or between loads and the distribution lines. 
         [0069]      FIG. 12  shows a DC microgrid  1200 . Here, bi-directional converters  95 ,  96  convert AC power from the grid  1 A,  1 B to DC power that is supplied to the microgrid. Substations  2 A,  2 B provide protection for the distribution lines  3 . In various embodiments, DC microgrids provide efficiency benefits such as use, without conversion, of DC sources such as photovoltaics. 
         [0070]      FIG. 13  shows a microgrid including a master controller  1300 . Here, the master controller  109  maximizes the benefits of a microgrid by coordinating the control of devices in the microgrid with each other and with the external devices outside of the microgrid including power sources and data sources such as weather data sources and independent system operator data sources. In an embodiment, the master controller communicates through communication pathways  107  to devices on the microgrid. Such devices include the distribution system, local generation, building controls, home automation devices, converters, and other devices for managing the microgrid. 
         [0071]    In various embodiments, communications paths  107  within the microgrid interconnect the master controller with one or more of local power sources  35 ,  106 , building load controllers, home automation devices in the microgrid loads  4 , and the distribution system through the substations  2 A,  2 B. Communications path media includes one or more of wires, fiber options, and radio waves. 
         [0072]    In various embodiments, communication to other servers and data sources outside of the microgrid occurs. External data sources include price and demand response signals from the local utility  111 , the ISO  110 , or an aggregator  112 . In some embodiments, the master controller collects weather data and weather forecasts from an outside data source. The weather prediction is useful for predicting grid loads and the amount of generation produced locally from solar and wind generation sources. The local utility may sell the microgrid power using time of use pricing where the price depends on the hour of the day. The utility may also sell the microgrid power based on real time pricing which can change as often as every five minutes depending on transactions in the wholesale electricity markets and day ahead prices which typically change every hour and are determined the day before in a special day ahead electricity market. 
         [0073]    The ISO  110 , known as the Independent System Operator, refers to the entities that run the electricity markets in the United States. Not all states within the US are deregulated and as such they do not participate in an ISO. Currently, ten Independent System Operators and Regional Transmission Organizations (ISO/RTOs) in North America serve two-thirds of electricity consumers in the United States and more than 50 percent of Canada&#39;s population. Some ISOs only serve one particular state such as the NYISO which only servers the state of New York, while others such as the PJM server several states along the Atlantic Coast and the Midwest. Notably, some states are served by multiple ISOs. 
         [0074]    A microgrid can also strike a business deal with an ISO, either directly or through a third party to purchase blocks of power at a fixed price, to participate in real time markets set up by the ISO, and to participate in day-ahead markets. The ISOs also setup other markets, called ancillary services, which are intended to help stabilize the bulk grid in the ISO&#39;s territory. The microgrid may also be able to participate in these ancillary markets which tend to evolve over time. Some of the ancillary services that microgrids can potentially participate in are demand response where the participant agrees to reduce their load by a certain amount when called on to do so and capacity markets where the participant agrees to maintain generation sources and operate them to supply power to the grid when called to do so. Utilities may also offer ancillary services to the microgrid operator. 
         [0075]    Additionally, aggregators or third party energy service providers  112  may offer different combinations of dynamic pricing or ancillary services to the microgrid, though the power would ultimately be purchased from the ISO. Dynamic pricing is a term for electric rates that change over the course of the day and includes, time of use pricing, real time pricing, and day ahead pricing. 
         [0076]    In various embodiments, the microgrid controller  109  assists with coordination of the actions of the microgrid to a) maximize the economic benefits of participating in different electricity markets, b) improve the reliability and energy security of the microgrid, and c) reduce its environmental impact. The microgrid master controller operates in a mode suited to the external conditions. For example, when electric prices are relatively high, the master controller  109  requests that building loads be reduced or local generation be increased to reduce the amount of electricity purchased from the utility, ISO, and/or aggregator. In this example, the master controller determines the cost to produce the electricity locally and compares this with the cost of purchasing electricity from the grid; the microcontroller then selects the lowest cost option. 
         [0077]    The master controller  109  can also be used to facilitate bidding and purchasing of electric power from a seller. This facilitation can be for purchasing primary power or ancillary services. The master controller will have the ability to predict the aggregate load for the microgrid based on models constructed from historical data. In various embodiments, these forecasts are submitted electronically to sellers who may bid on selling power to the microgrid. In addition, embodiments of the master controller  109  will have the ability to model the load shedding capabilities of the microgrid, through either load control, generation, or a combination of both. This information can be used to offer bids for taking part in demand response events. 
         [0078]    In a weather watch mode, the master controller uses predicted weather information to predict generation available from solar and wind generation sources that is available to offset grid loads. Estimated grid power shortfalls are used in various embodiments to dispatch microgrid generation and to curtail microgrid loads. 
         [0079]    In another weather watch mode, the master controller  109  determines that there is a severe weather threat from a source of weather information  108 , such as a weather service, that could cause a grid outage. Weather and weather severity indicators include icing, wind speed, lightning, thunder storms, flooding, tornadoes, hurricanes, and microbursts. As indicated by the severity of the predicted weather, the master controller can choose to disconnect from the grid and dispatch local generation to meet at least some of the power supply needs of the micro grid. In this mode, the master controller also sends load reduction signals to the loads on the microgrid to balance power available to the microgrid with the total load on the microgrid. 
         [0080]    In a demand response mode, the master controller  109  uses a combination of reducing loads on the microgrid and dispatching local generation to meet the demand response request. Whether generation or load reduction is used depends on the load reduction capability under the control of the master controller, the capacity of the generation, and the amount of load reduction requested in the demand response event. It is generally less expensive to reduce loads using load controllers than it is to dispatch fueled generation, but reducing loads solely through load reduction requests may have secondary costs such as loss of comfort, inconvenience, or spoilage. 
         [0081]    In some embodiments, the master controller predicts the microgrid&#39;s response to load reduction command(s) with the prediction a) selecting loads to be curtailed with the associated KW curtailment and b) selecting local generation to be added with the associated KW addition. In various embodiments, the master controller selects loads/KW ratings and generation/KW ratings to achieve the commanded load reduction while meeting criteria set by a microgrid operator. In various embodiments, operating constraints include one or more of a) never curtail for certain loads, b) always run for certain generators, c) comfort level of building occupants, and d) preferences set by microgrid customers and/or consumers. 
         [0082]    Additionally, in a demand response mode, the master controller  109  uses load models to predict how the microgrid and the loads on the microgrid respond to the demand response event depending on the time of year, time of day, and weather conditions. These load response models can be based on prior historical data stored in the database  108 . Such load response models can also be built using data collected during times of testing. During tests, the master controller can perturb load or thermostat settings to learn the responses in different weather conditions, times of the day, and times of the year. These learned responses enable predictions of microgrid response which is useful for bidding into demand response markets and for determining what level of load reduction can be achieved. If a target load reduction level are not likely to be achieved, more drastic load reduction measures may be required. 
         [0083]    In a cost reduction mode, the master controller  109  can dispatch local generation to reduce costs when the cost to purchase electricity is higher than the cost to generate electricity. Price forecasting models built from data stored in the database or data from day ahead electricity markets is used to estimate times when the price of electricity on the gird is above the price to of electricity generated local to the microgrid so that local generators can be prepared to start before they are actually required which is important when using generating devices that require relatively long startup times. 
         [0084]    Similar to the demand response mode, load response modes can be used in the cost reduction mode to estimate the load reductions during periods of high prices and to estimate the electricity costs during an expected price increase. In some embodiments, this information is feed back into the system so that more aggressive measures can be taken if necessary. 
         [0085]    Further, price forecasts can be used to predict when electricity prices will be above certain price thresholds that are set to trigger when certain load reduction actions are required on the microgrid. In some embodiments, the price forecasting data is combined with weather data and weather forecasts to help predict when prices and loads may be high. In the case of reducing cooling loads, pre-cooling can be used to lower the temperature of a building before prices are expected to increase so that the building can operate its air conditioning system less frequently during periods of high prices. And in some embodiments, other conservation measures are taken such as periodically sweeping lights and curtailing non-essential loads. 
         [0086]    In various embodiments, depending on the capabilities of the distribution switches and breakers installed in the microgrid, the distribution system autonomously heals itself when a distribution outage occurs. In some embodiments, this function is handled by the master controller  109 . Here, the master controller  109  sends commands to the substation breakers in  5 A,  5 B and sectionalizing switches (see sectionalizing switches  12  of  FIG. 2 ) to re-direct and coordinate the flow of power when a breakage in a distribution power conductor occurs or when loss of power occurs from one the microgrid power sources such as the grid  1 A or local generation  35 . Current and voltage sensors within the breakers and sectionalizing switches are operative to report currents and voltages back to the master controller giving the master controller an indication of where faults may have occurred and which distribution lines have power and which have faults. This information can then be used to position the sectionalizing switches and substation breakers to isolate sections where faults have occurred and to redirect power to fault free sections in need of power. 
         [0087]    In an embodiment, the master controller includes a mode for reducing environmental impact. The actions taken in this mode will depend on the environmental characteristics of the local generation, the environmental characteristics of the grid, and the load reduction capabilities on the microgrid. Since they operate the electricity markets and know which generators in their system are running at any given time, each ISO can calculate the hourly environmental impact of the generators operating on its grid in real time. The environmental impact includes carbon production, air emissions, and can include water and other impacts. The environmental impact is retrieved by the master controller  109  which determines if it is better to operate its own generation sources to reduce the microgrid&#39;s external power demand given environmental preferences, comfort preferences, the cost to operate local generation, and the cost to purchase external power. 
         [0088]    Many of the energy systems associated with the microgrid may have autonomous control over their respective systems and these autonomous controllers (sometimes called “agents”) can independently control their respective system. In this case, the microgrid master controller feeds these controllers external data such as weather data, price data, and demand response communications so that these systems can determine optimal solution sets between themselves. 
         [0089]    In addition to providing supervisory control for the microgrid, various embodiments of the master controller collect data. For example, some embodiments of the master controller collect data that is useful for tracking microgrid events and microgrid performance. In particular, current and voltage data from the distribution system that is feed to the master controller enables tracking outage metrics such as SAIFI, SAIDI, and MAIFI, as well as power quality events. Power and emissions data can be stored and used to report the microgrids efficiency, the grids efficiency, power consumption, peak demand, fuel consumption, microgrid carbon and emissions production, grid carbon and emissions productions, the cost to generate power locally, and the cost to purchase power from the grid over different time periods such as daily, weekly, monthly, and annually. 
         [0090]    The microgrid of the present invention provides control capabilities and/or ease of control not available from traditional grids. In particular, embodiments of the microgrid utilizing a master controller enable multiple benefits to be realized including one or more of reliability enhancement, market based operating decisions, optimizations based on customer and cost criteria, secure operating modes, and modes optimizing the microgrid operation in the context of a larger grid. 
         [0091]    While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to those skilled in the art that various changes in the form and details can be made without departing from the spirit and scope of the invention. As such, the breadth and scope of the present invention should not be limited by the above-described exemplary embodiments, but should be defined only in accordance with the following claims and equivalents thereof.