CA2814864A1

CA2814864A1 - Method and system facilitating control strategy for power electronics interface of distributed generation resources

Info

Publication number: CA2814864A1
Application number: CA2814864A
Authority: CA
Inventors: Hussam Alatrash; Nasser Kutkut
Original assignee: Petra Solar Inc
Current assignee: Petra Solar Inc
Priority date: 2010-10-22
Filing date: 2011-10-21
Publication date: 2012-05-03
Also published as: CN103229380A; WO2012058114A2; EP2630715A2; AU2011320685A1; WO2012058114A3; BR112013009482A2; JP2013544063A; MX2013004553A

Abstract

The invention discloses a method and a system for implementing a control strategy for Distributed Generation (DG) units. The control strategy is implemented in such a fashion so that a DG unit behaves similar to a synchronous generator. The method also describes grouping of multiple DG units to form a micro grid by using a supervisory control agent. The micro girds may further be arranged in a hierarchy.

Description

METHOD AND SYSTEM FACILITATING CONTROL STRATEGY FOR
POWER ELECTRONICS INTERFACE OF DISTRIBUTED GENERATION
RESOURCES
This application is being filed on 21 October 2011, as a PCT international patent application in the name of PETRA SOLAR, INC., a U.S. national corporation, applicant for the designation of all countries except the US, and Hussam Alatrash, a citizen of Jordan and Nasser Kutkut, a citizen of the U.S., applicants for the designation of the US only, and claims priority to U.S.
Provisional Application Serial Number 61/455,556 filed October 22, 2010, the subject matter of which is incorporated by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates, in general, to the domain of the generation of electrical energy. More specifically, the present invention relates to a method and system facilitating control strategy for power electronics interfaces (PEI) of distributed generation resources.
BACKGROUND
A large amount of today's electric power is generated by large-scale, centralized power plants using fossil fuels, hydropower or nuclear power, and is transported over long distances to end-users. In these systems, power flows from the central power stations in one direction through the distribution networks to consumers. Yet, the centralized power generation paradigm has many disadvantages, including the environmental impact of greenhouse gases and other pollutants, transmission losses and inefficiency, growing security of supply concerns, system sustainability issues, over-consumption, and the high cost of ongoing upgrades and replacement of transmission and distribution infrastructure.
Over the past few years, technological innovations, changing economic and regulatory environments, and shifting environmental and social priorities have spurred interest in Distributed Generation (DG) systems. Distributed Generation is a new model for the power system that is based on the integration of small and medium-sized generators based on new and renewable energy technologies, such as solar, wind, and fuel cells, into the utility grid. All these generators are interconnected through a fully interactive intelligent electricity network.
This revolution will require sophisticated control and communication technologies.
Most DG resources are primarily used to supplement the traditional electric power systems. For example, these resources can be combined to supply nearby loads in specific areas with continuous power during disturbances and interruptions of the main utility grid. Such a grouping of DG resources with the nearby loads is referred to as a micro grid. Micro grids are, generally, self-contained electrical ecosystems. In these systems, power is produced, transmitted, consumed, monitored, and managed on a local scale. In many cases, they can be integrated into larger, central grids, but their defining characteristic proves that they can operate independently if disconnected from the whole.
Most of the current DG resources developed cannot be employed as a part of micro grids since these resources are designed as current sources. The output produced by such power systems is significantly unstable. Further, such a power system is not capable of operating in isolation from the main grid to power a specific area. The process of using a micro grid in isolation from the main grid to power a specific area or a location is known as islanding. Further, the DG resources cannot be employed as a part of a micro grid if they are designed as voltage sources.
This is due to minute differences in instantaneous output voltages that may result in large amounts of circulating currents and may damage the DG resources. Micro grids used in recent times employ synchronous generators that have moderate output impedance characteristics that allow them to operate in parallel, tied to the grid, or isolated from it.
In light of the aforementioned challenges, there lies a need for a system in which a plurality of the DG resources can be controlled to exhibit improved characteristics by utilizing a power electronics interface. Further, there exists a need for a system in which multiple DG resources are integrated to form a micro grid. In this way, multiple DG resources can be controlled in an appropriate manner to maintain a stable AC power system. Moreover, the system should be able to work when connected with a larger utility grid (known as grid-tie mode) as well as separately from a utility grid (known as islanding mode). In addition, the system should provide a smooth transition between the grid-tie mode and islanding mode of operation.

SUMMARY OF THE INVENTION
An objective of the present invention is to provide a stable AC power generation and distribution system based on Distributed Generation (DG) resources.
In an embodiment of the present invention, a system is provided to facilitate control of a DG resource by using a Power Electronic Interface (PEI) such that the DG resource exhibits predetermined electrical characteristics. The predetermined electrical characteristics exhibited by the system are similar to these of a synchronous generator.
In another embodiment of the present invention, a method is disclosed for grouping multiple DG units into a micro grid. The multiple DG units of the micro grid may be grouped by using a supervisory control agent. The supervisory control agent communicates with multiple DG units over a Low Bandwidth Communication Network (LBCN). Further, the micro grid operates when connected to a main grid and can also work in an island mode.
In yet another embodiment of the present invention, a method is provided to create a micro grid hierarchy by integrating multiple DG resources. The micro grid hierarchy can be implemented by arranging the multiple micro grids into a predefined hierarchical architecture.
BRIEF DESCRIPTION OF THE DRAWINGS
Various embodiments of the invention will, hereinafter, be described in conjunction with the appended drawings provided to illustrate and not to limit the invention, wherein like designations denote like elements, and in which FIG. 1 is an exemplary environment in which various embodiments of the present invention can be practiced;
FIG. 2 shows a block diagram illustrating system elements implementing control strategy for a Distributed Generation (DG) unit;
FIG. 3 is a circuit diagram representing a Virtual Electrical Network (VEN), in accordance with an embodiment of the present invention;
FIG. 4 is an exemplary circuit diagram of a Virtual Electrical Network (VEN), in accordance with another embodiment of the present invention;
FIG. 5 depicts another exemplary circuit diagram of a Virtual Electrical Network (VEN), in accordance with yet another embodiment of the present invention;

FIG. 6 depicts a block diagram illustrating grouping of DG systems, loads, and associated controllers into a micro grid, in accordance with an embodiment of the present invention; and FIG. 7 represents an exemplary micro grid hierarchy, in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
The present invention discloses a system and a method for facilitating a control strategy for Power Electronic Interfaces (PEIs) of Distributed Generation (DG) resources. Various examples of the DG resources may include, but are not limited to, Photovoltaic (PV) systems, wind turbines, battery storage, and fuel cells.
In particular, the present invention focuses on the interaction of one or more PEIs with Alternating Current (AC) power distribution systems.
FIG. 1 is an exemplary environment in which various embodiments of the present invention can be practiced. FIG. 1 is shown to include a generation station 102, one or more transmission units 104a, 104b, and 104c (collectively referred to as transmission units 104), one or more distribution units 106a and 106b (collectively referred to as distribution units 106), a micro grid 108, one or more loads 110a and 110b (collectively referred to as loads 110), and a distribution network 112.
Additionally, micro grid 108 further includes one or more PEIs 114a, 114b, and 114c (collectively referred to as PEIs 114), one or more DG resources 116a, 116b, and 116c (collectively referred to as DG resources 116), and one or more DG
units 118a, 118b, and 118c (collectively referred to as DG units 118). As shown in FIG.
1, PEI units 114 when combined with DG resources 116 form DG units 118.
In accordance with an embodiment of the present invention, FIG. 1 may include one or more grid control centers (not shown in FIG. 1). Additionally, the grid control center provides supervision and control of generation, transmission, and distribution.
As described above, the generation station 102 depends on traditional and renewable sources, which include, but are not limited to, fossil fuels, nuclear, hydro, wind, photovoltaic, and geo-thermal. In addition to the above, the generation station 102 generates a large-scale power to be distributed to the loads 110 via the distribution network 112.

In accordance with an embodiment of the present invention, the power generated by the generation station 102 is provided to the transmission units 104 to further transmit the power to the distribution units 106.
In accordance with an embodiment of the invention, the micro grid 108 includes DG units 118 as depicted in FIG. 1. The DG units 118 may depend on sources such as photovoltaic systems, wind turbines, battery storage, and full cells.
In accordance with an embodiment of the present invention, the micro grid 108 is connected to operate in parallel with a utility grid. In accordance with another embodiment of the invention, the micro grid 108 may operate in isolation with the utility grid.
In accordance with an embodiment of the present invention, the generation station 102, the transmission units 104, the distribution units 106, the loads 110, and the distribution network 112 may collectively be referred to as the utility grid.
FIG. 2 shows a block diagram illustrating system elements implementing control strategy for a Distributed Generation (DG) unit. As depicted in FIG.
2, the block diagram illustrates a Distributed Generation unit 202. The DG unit 202 includes a Distributed Generation (DG) resource 204, a Power Electronics Interface (PEI) unit 206, an AC current sensor 208, a behavioral controller 210, a current feedback controller 212, a power flow controller 214, and short-term energy storage 216.
The DG resource 204 utilizes one or more sources such as photovoltaic systems, wind turbines, battery storage, and/or fuel cells for generating power. In accordance with an embodiment of the present invention, a control scheme is implemented using the PEI unit 206 to control the DG resource 204 to obtain a preferred behavior. The architecture of the PEI unit 206 may vary in accordance with specific characteristics of the DG resource 204 connected to it.
In accordance with an embodiment of the present invention, the PEI unit 206 may be programmed to exhibit electrical characteristics similar to a synchronous generator. The PEI unit is typically a combination of hardware and software.
The characteristics are emulated using a Virtual Electrical Network (VEN), which is represented as a combination of an AC voltage source (Vs) and a pre-defined impedance network. Further, various parameters of the AC voltage source (Vs) such as amplitude, frequency, and phase may vary in real time to control the reactive/active power output of the DG unit 202. This process will be described in greater detail in subsequent paragraphs.
A control strategy implemented by the PEI unit 206 is built around a current feedback loop. The current feedback loop is implemented through the current sensor 208 and the current feedback controller 212. The output current of the PEI
unit 206 is controlled based on the comparison between current sensed using the current sensor 208 and a current reference (Iac). The behavioral controller 210 utilizes an instantaneous measurement of the AC system voltage (Vac) in addition to the mathematical model of the VEN for calculating instantaneous values for the output current reference (Iac). The behavioral controller 210 manipulates the current reference (Iac) to reproduce the behavior of the VEN, and thereby the behavior of a synchronous generator is emulated. The VEN, as described above, will be explained in detail in conjunction with FIG. 3.
The power flow controller 214 manages energy flow between the DG
resource 204 and the short-term energy storage 216 by continuously modulating a power angle to achieve specific power management objectives. One of the power management objectives may be to create a pre-determined droop relationship between average active power output of the DG unit 202 and the frequency of the AC system voltage (Vac). The power angle is determined by utilizing the phase difference between the AC system voltage (Vac) and a voltage Vs of the VEN, which will be discussed later. In addition, the power flow controller 214 is responsible for ensuring that short-term energy storage 216 maintains a satisfactory level of energy that allows proper PEI operation and response to system transients.
FIG. 3 is a circuit diagram representing a Virtual Electrical Network (VEN), in accordance with an embodiment of the present invention. As depicted in FIG.
3, the circuit diagram includes an AC voltage source (Vs) 302 and impedances 304 and 306 (collectively referred to as impedances). Impedances 304 and 306 may be referred to as an impedance network.
In accordance with an embodiment of the present invention, the virtual circuit as shown in FIG. 3 may be implemented through the behavioral controller 210.
An imaginary circuit such as VEN is designed to include the AC voltage source (Vs) 302 in combination with the impedance network. Further, the impedances forming the impedance network are designed in accordance with desired characteristics and the value of the AC voltage source (Vs) 302. The value of the AC voltage source (Vs) 302 is determined by the power flow controller 214.
It may be appreciated by a person ordinarily skilled in art that the impedance network is designed to fulfill one or more objectives. The design should maintain an acceptable output voltage quality from the DG unit when supporting a dedicated load. This includes minimizing voltage distortion in the presence of load current harmonics, providing appropriate damping in response to load transients and minimizing voltage drop at heavy loads. Another objective of the impedance network relates to creating preferred droop characteristics based on amplitude and phase of the voltage (Vac). The preferred droop characteristics result in increased reactive power output of the DG unit when the amplitude of the AC system voltage (Vac) is decreased. The preferred droop characteristics also result in increased active power output of the DG unit when the phase angle of Vs is increased relative to the AC system voltage (Vac).
In accordance with an embodiment of the invention, the value of the impedances is kept constant for the VEN, and the values are determined based on the desired characteristics of the output. Further, the value of Vs is kept dynamic as the amplitude and phase of Vs with respect to the system voltage Vac will affect the active/reactive power output of the DG unit. Also, as discussed above, the instantaneous value of Vs is determined by the power flow controller 214.
FIGS. 4 and 5 represent exemplary circuit diagrams of Virtual Electrical Networks (VENs). The diagrams illustrate practical VEN configurations in accordance with respective embodiments.
In accordance with an embodiment of the present invention, an exemplary circuit diagram representing a VEN configuration, as shown in FIG. 4, will be described herein. For a person ordinarily skilled in art, it is understood that the implementation details of the circuit as shown in FIG. 4 are similar to that shown in the circuit of FIG. 3.
The VEN circuit diagram as illustrated in FIG. 4 includes an AC voltage source (Vs) in combination with an impedance network. The impedance network includes a combination of impedances Z1 and Z2 as described in accordance with FIG. 3. In this embodiment, the VEN circuit diagram, according to FIG. 4, includes a series combination of inductance Ls and resistance Ric (similar to Z1 defined in = CA 02814864 2013-04-09 FIG. 3). Further, FIG. 4 may include a capacitance Cs (similar to Z2 defined in FIG.
3).
In accordance with another embodiment of the present invention, an exemplary circuit diagram representing a VEN configuration as shown in FIG. 5 will be described herein. For a person ordinarily skilled in art, it is understood that the implementation details of the circuit diagram shown in FIG. 5 are similar that shown in the circuit diagram of FIG. 3.
The VEN circuit diagram as shown in FIG. 5 includes an AC voltage source (Vs) in combination with an impedance network. The impedance network includes a combination of impedances Z1 and Z2 as described in accordance with FIG. 3. In this embodiment, according to FIG. 5, the circuit diagram includes a series combination of inductance Ls1 and a parallel combination of resistance 114c and capacitance Cdc (similar to Z1 defined in FIG. 3). In addition to this, FIG. 5 may include a series combination of capacitance Cs and resistance Rklamp (similar to Z2 defined in FIG. 3).
In accordance with an embodiment of the present invention, the configuration of the VEN circuit may vary during operation to optimize the characteristics of the synchronous generator at various operating conditions.
To a person ordinary skilled in the art, it is understood that the VEN may vary according to requirements. Varying elements of the circuit may include, but are not limited to, one or more voltage sources, one or more current sources, linear or non- linear resistive components, capacitive components, and inductive components.
FIG. 6 depicts a block diagram illustrating grouping of DG systems, loads, and associated controllers into a micro grid, in accordance with an embodiment of the present invention.
A control scheme can be applied to a DG system such that it allows grouping of a number of DG units, loads, and associated controllers into a micro grid.
The block diagram as shown in FIG. 6 includes: a utility grid 622; a utility grid controller 628; and a micro grid 602. The micro grid 602 in turn includes: some combination of one or more DG units 604 controlled according to the control scheme presented herein; one or more additional DG units 606 controlled in accordance other control schemes,; synchronous machine systems 608; a Supervisory Control Agent (SCA) 610; a low bandwidth communication network (LBCN) 624; and a load 626. All components may be hardware only, software only, or combinations of hardware and software. The load 626 may include one or more of a smart load 630 and a conventional load 632. Further, the SCA 610 includes a smart switch 612 and an energy management controller 614. The SCA 610 may further include a load scheduling controller'. In an embodiment of the present invention, the load scheduling controller 616 may form a part of the smart load 630 or connected to the conventional load 632. The smart switch 612 further includes a smart controller 618 and sensors 620. In various embodiments of the present invention, the micro grid 602 and the utility grid 622 may be directly connected to the smart switch 612 such that the smart switch 612 provides a switching interface between the micro grid 602 and the utility grid 622.
In accordance with an embodiment of the present invention, all components as shown in FIG. 6 may be a combination of hardware and software. In accordance with another embodiment of the present invention, all components as shown in the figure may represent hardware components.
In accordance with an embodiment of the invention, the SCA 610 can exist as a single physical module. In accordance with another embodiment of the invention, the SCA 610 may exist as a collection of features built into a number of discrete systems or sub-systems.
In accordance with an embodiment of the invention, the load 626 may comprise, but is not limited to, adjustable load, schedule-able load, and fixed load.
The load 626 may further include one or more of smart loads 630 integrated with a load scheduling controller 616 and a conventional load 632. To operate with the conventional load 632, an external load controller may be desirable. The external load controller may be a part of the SCA 610 or may be a discrete component.
In accordance with an embodiment of the invention, the smart switch 612 functions as an AC connector to isolate the micro grid 602 from the utility grid 622.
The smart switch 612 may further include a smart controller 618 and sensors 620.
The smart controller 618 is responsible for analyzing measurements of the micro grid voltage, the utility grid voltage, and the current flow. The smart controller 618 further reports results of the analysis to the energy management controller 614 over the low bandwidth communication network (LBCN) 624. The smart controller 618 also assists in disconnection, synchronization, and interconnection of the micro grid 602 to the utility grid 622. Further, the smart controller 618 manages adherence to standards at the point of common coupling to the utility grid 622. This may include the limitation of reactive power and/or harmonic currents into the main grid and/or the prevention of non-intentional islanding (energizing the load outside the microgrid during a grid brownout/blackout period).
In accordance with an embodiment of the invention, the energy management controller 614 and the load scheduling controller 616 may perform one or more functions. The functions may include, but are not limited to: gathering and sharing information with individual DG units 604, 606, and the synchronous machine systems 608, smart switch 612, and the load scheduling controller 616;
gathering and sharing information with the utility grid controller 628; forecasting of the availability of DG resources and availability of the grid; and energy pricing.
The forecast is based on factors such as current/forecast load, weather conditions, and other data obtained locally or from external services. In addition to this, their functions may also include: making decisions about transition into and out of intentional islanding mode of operation, providing load shedding and prioritization schedule, prioritizing utilization and recharge of DG resources, responding to real-time pricing, and engaging in energy markets.
According to FIG. 6, all communication between the DG PEIs takes place over the LBCN 624. The low bandwidth communication is preferred over other modes because it is less expensive and easier to design. In accordance with one embodiment of the invention, the LBCN 624 may be implemented as a separate network which is dedicated towards the control of such systems. In accordance with another embodiment of the invention, the LBCN 624 may be implemented using one or more combinations of Local Area Network (LAN), Wi-Fi, WLAN, power line communications, and GPRS network.
In accordance with an embodiment of the invention, the system as described in FIG. 6 can be operated in an island mode by integrating multiple DG units and 606 in parallel with each other to support an AC load. The SCA 610 implements a process of operation in the island mode by controlling the DG
units 604 and 606. Initially, the SCA 610 facilitates disconnection of one or more micro grids from the utility grid 622. Thereafter, the DG units 604 and 606 collectively regulate the micro grid voltage within a tolerable limit. Further, in accordance with one embodiment of the invention, the SCA 610 may facilitate load sharing for the DG units 604 and 606. In accordance with another embodiment of the invention, the SCA 610 may also allow the exchange of energy based on a predefined loading priority schedule without necessitating the requirement of direct communication between at least two of the multiple DG units 604 and 606. Further, the SCA

influences loading priority and loading distribution by issuing appropriate commands over the LBCN 624. In accordance with another embodiment of the invention, the load sharing and exchange of energy based on predefined loading priority schedule may be performed by the DG units without any involvement of the SCA 610.
In accordance with another embodiment of the invention, the system as described in FIG. 6 may be operated in a grid-connected mode by connecting the DG units 604 and 606 in parallel to the utility grid 622. The system illustrated in FIG. 6 implements the process of operation in grid-connected mode as described below. The SCA 610 first facilitates the connection of the micro grid 602, including the DG units 604 and 606, to the utility grid 622. The DG units 604 and 606 supply active/reactive power based on predefined default settings. Further, the SCA

influences the active/reactive power supplied by each of the DG units 604 and in the micro grid by issuing appropriate commands over the LBCN 624.
In accordance with another embodiment of the invention, the DG units 604 and 606 may be able to achieve seamless transition between the grid-connected mode and the island mode. Further, the process of achieving seamless transition from the island mode to the grid-connected mode may influence voltage amplitude, frequency, and phase of the DG units 604 and 606 by issuing commands from the SCA 610 to the PEIs of each of the DG units 604 and 606 over the LBCN 624.
Accordingly, the SCA 610 connects the micro grid 602 to the utility grid 622 when voltage, amplitude, frequency, and phase of the output of the DG units 604 and are satisfactorily synchronized.
FIG. 7 represents a micro grid hierarchy, in accordance with an embodiment of the present invention. FIG. 7 includes a system 702, one or more child micro grids 704 and 706 (collectively referred to as child micro grids), and a parent micro grid 708.
A micro grid hierarchy represents an arrangement of multiple micro grids into a predefined hierarchical architecture. The micro grid hierarchy is created by assigning pre-determined parent-child relationships between the SCAs of different micro grids, as discussed above. The predetermined parent-child relationships are based on various factors which may include, but not limited to, the size of micro grids, topology, and geographical location within the system. Further, the relationships may be pre-assigned or dynamically modified in real time to adapt to varying operating conditions.
In accordance with an embodiment of the invention, different micro grids in the micro grid hierarchy may be enlisted as a child micro gird or a parent micro grid.
Each of the child micro grids may be enlisted as a member of a parent micro grid, thereby creating a parent-child relationship between the SCAs of these micro grids.
It is understood by a person ordinarily skilled in art that a parent micro grid may further behave as a child of even larger micro grids, as illustrated in conjunction with an example below.
As depicted in FIG. 7, the system 702 behaves as a parent micro grid for the child micro grids 704 and 706. However, at the same time, the system 702 behaves as a child micro grid for the parent micro grid 708. The parent-child relationship as discussed above allows the parent SCA to treat the child micro grid as a generic DG
resource. The parent SCA may use DG communication protocols and data models to gather data from the child micro-grid, and subsequently issue commands to supervise its operation. Further, the child SCA is responsible for collecting data from its member systems, presenting aggregated data to the parent SCA. The child SCA also analyzes commands issued by respective parent SCA, and may issue commands to its member systems ensuring a proper response to the parent micro-grid.
The formation of the micro grid hierarchy allows the distribution of intelligence throughout the utility grid that includes a main grid and the hierarchy of micro grids. The distribution helps in avoiding reliance on a centralized energy management controller that requires massive data collection, processing, decision-making, and communication resources. Further, avoiding reliance oti the centralized energy management controller also eliminates the possibility of a single point of failure. The formation of a micro grid hierarchy further allows sectioning of the system and assists in the formation of intentional islands at different levels of the hierarchy.
The method and the system facilitating control strategy for power electronics interface of distributed generation resources, or any of its components, as described in the present invention, may be embodied in the form of an embedded controller.

Typical examples of embedded controllers include a general-purpose computer, a programmable microprocessor, a micro controller, a peripheral integrated circuit element, ASIC's (Application Specific Integrated Circuit), PLC's (Programmable Logic Controller), and other devices or arrangements of devices that are capable of implementing the steps that constitute the method for the present invention.
The embedded controller executes a set of instructions (or program instructions) that are stored in one or more storage elements to process the input data.
These storage elements can also hold data or other information, as desired, and may be in the form of an information source or a physical memory element present in the processing machine. The set of instructions may include various commands that instruct the processing machine to perform specific tasks such as the steps that constitute the method for the present invention. The set of instructions may be in the form of a software or firmware program. Further, the software or firmware may be in the form of a collection of separate programs, a program module with a large program, or a portion of a program module.
While various embodiments of the invention have been illustrated and described, it will be clear that the invention is not limited only to these embodiments.
Numerous modifications, changes, variations, substitutions, and equivalents will be apparent to those skilled in the art, without departing from the spirit and scope of the invention.

Claims

1. A system for controlling distributed generation, the system comprising:
a distributed generation (DG) resource;
a short-term energy storage;
an alternating current (AC) sensor;
a power flow controller configured to received status information from the DG resource and the short-term energy storage;
a behavioral controller in communications with the power flow controller and configured to sense a voltage (Vac) from an AC system;
a current feedback controller in communications with the behavioral controller and the AC sensor; and a power electronics interface (PEI) configured to cause the DG resource to behave similarly to a synchronous generator based on a signal received from the current feedback controller.

2. The system of claim 1, wherein the PEI is a combination of hardware, firmware, and software.

3. The system of claim 1, wherein the PEI being configured to cause the DG resource to behave similarly to a synchronous generator comprises the PEI
being configured to cause the DG resource to behave similarly to a synchronous generator as a result of the behavioral controller supplying the current feedback controller with a current reference (I ac) produced by the behavioral controller using a virtual electrical network (VEN) comprising:
an AC voltage source (V s); and a pre-defined impedance network.

4. The system of claim 3, wherein parameters of the VEN comprising at least one of: amplitude of the AC voltage source (V s), frequency of the AC
voltage source (V s), and phase of the AC voltage source (V s), are varied in real time to control reactive and active power output of the DG resource.

5. The system of claim 3, wherein the behavioral controller is configured to use an instantaneous measurement of the voltage (V ac) from the AC
system and a mathematical model of the VEN to calculate instantaneous values for the current reference (I ac) to produce a desired behavior of the VEN, and thereby causing the PEI to cause the DG resource to behave similarly to a synchronous generator.

6. The system of claim 3, wherein the signal received from the current feedback controller is based on a comparison between a current sensed by the AC
sensor and the current reference (I ac).

7. The system of claim 3, wherein the power flow controller is configured to manage energy flow between the DG resource and the short-term energy storage by continuously modulating a power angle to achieve at least one power management objective.

8. The system of claim 7, wherein the at least one power management objective comprises creating a pre-determined droop relationship between average active power output of the DG resource and the frequency of the voltage (V ac) from the AC system wherein the power angle is determined by utilizing the phase difference between the voltage (V ac) from the AC system and the AC voltage source (V s) of the VEN.

9. The system of claim 7, wherein the at least one power management objective comprises ensuring that the short-term energy storage maintains a satisfactory level of energy to allow the PEI to response to system transients.

10. The system of claim 3, wherein the VEN is an imaginary circuit comprising wherein the value of the AC voltage source (V s) is determined by the power flow controller.

11. The system of claim 10, wherein the value of the AC voltage source (V s) is kept dynamic.

12. The system of claim 3, wherein the VEN is an imaginary circuit wherein the impedance network comprises impedance values designed in accordance with desired characteristics.

13. The system of claim 12, wherein the impedance values are kept constant and determined based on the desired characteristics of output.

14. The system of claim 3, wherein the configuration of the VEN being configured to vary during operation to optimize the behavior similar to the synchronous generator.

15. The system of claim 3, wherein the VEN comprises at least one of the following: at least one additional voltage source, at least one additional current source, at least one linear resistive component, at least one non-linear resistive component, at least one capacitive component, and at least one inductive component.

16. A method for controlling distributed generation, the method comprising:
receiving an instantaneous measurement of an alternating current system voltage (V ac);
calculating an instantaneous value of an output current reference (I ac) based on the received instantaneous measurement of the alternating current system voltage (V ac) from an AC system and a mathematical model of a virtual electrical network (VEN);
creating a control signal based on a comparison of the calculated instantaneous value of the output current reference (I ac) and an AC current sensed from the AC system; and regulating, based on the created control signal, output of a distributed generation resource to emulate characteristics of a synchronous generator.

17. The method of claim 16, wherein calculating the instantaneous value of the output current reference (I ac) based on the mathematical model of the virtual electrical network (VEN) comprises calculating the instantaneous value of the output current reference (I ac) based on the mathematical model of the virtual electrical network (VEN) comprising:
an AC voltage source (V s); and a pre-defined impedance network.

18. The method of claim 16, wherein regulating the output of the distributed generation resource comprises regulating the output of the distributed generation resource comprising one of the following: a photovoltaic systems, a wind turbine, a battery storage, and a fuel cell.

19. A system configured to allow the grouping of distributed generation (DG) resources, loads, and associated controllers, the system comprising:
a utility grid;
a utility grid controller; and a micro grid comprising:
a combination of one or more DG resources controlled either according to a control scheme, the one or more DG resources having include power electronics interface (PEI) units;
synchronous machine systems;
a smart switch;
a supervisory control agent (SCA);
a low bandwidth communication network (LBCN); and a load.

20. The system of claim 19, wherein the SCA comprises one of the following: a single physical module and as a collection of features built into a number of discrete systems or sub-systems.