Patent Publication Number: US-2022231485-A1

Title: Scalable reconfigurable apparatus and methods for electric power system emulation

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention was made with government support under Award Number EEC-1041877 awarded by the National Science Foundation. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     The inventive subject matter relates to apparatus and methods for analysis of electrical power systems and, more particularly, to apparatus and methods for emulating electrical power systems. 
     The design and operation of electrical power systems (e.g., utility grids) commonly involves simulation and/or emulation using tools such as digital simulators, analog hardware emulators, or mixed digital-analog signal emulators. Computer-implemented simulation can provide advantages, such as relatively low cost and reconfigurability, but software-based simulators may have difficulty dealing with multi-timescale models and may suffer from numerical stability and convergence issues. Analog hardware-based emulators can provide advantages such as realism, actual communication and sensors, and that ability to reveal the impact of the aspects that may be overlooked by digital simulation, such as delay, measurement errors, and electro-magnetic interference. However, such emulators can be bulky and inflexible and may exhibit model fidelity issues when scaled. Mixed digital-analog signal emulators, such as described in U.S. Patent Application Publication No. 2010/0332211, are more flexible compared to scaled analog hardware-based emulators. However, they also may exhibit model fidelity issues especially with their unscalable line emulation method. 
     Emulators that utilize power electronics-based converters have been proposed in, for example, U.S. Pat. No. 10,873,184 to Wang et al. Such systems can provide more realistic behavior comparison to digital simulation and may be more flexible than other hardware-based platforms. However, these emulators may have limited flexibility and scalability. 
     SUMMARY 
     In some embodiments, an electric power system emulator apparatus includes a plurality of nodes arrayed in first and second dimensions and a plurality of transmission path emulator circuits, respective ones of which are configured to be connected between adjacent ones of the nodes in the first and second dimensions. The apparatus further includes a control circuit configured to control the transmission path emulator circuits to emulate transmission paths of an electric power system. The control circuit may be configured to control the transmission path emulator circuits to emulate transmission lines and/or transformers, sources and/or loads. The transmission path emulator circuits may include respective power electronics converter circuits. In some embodiments, each of the power electronics converter circuits may include first, second and third power electronics converter circuits and a DC bus coupling DC ports of the first, second and third power electronics converter circuits. 
     In further embodiments, the apparatus may further include switches configured to couple and decouple the emulator circuits to and from the nodes of the array. Respective bypass circuits may be configured to bypass respective ones of the transmission path emulator circuits. The switches and/or the bypass circuits may be incorporated into the emulator circuits. 
     The apparatus may further include a plurality of source/load emulator circuits, respective ones of which are configured to be coupled to respective ones of the nodes. The control circuit may be configured to operate the source/load emulator circuits to emulate loads and/or sources of the electric power system. The source/load emulator circuits may include respective power electronics converter circuits. 
     In still further embodiments, the transmission path emulator circuits may include DC transmission path emulator circuits including first, second, third, and fourth power electronics converter circuits. 
     According to some aspects, the nodes and transmission path emulator circuits may be implemented in a plurality of interconnected modules, each module comprising one or more of the transmission path emulator circuits. The modules may be contained in respective circuit cards configured to be installed in a chassis. The modules may each include at least one source/load emulator circuit. 
     Some embodiments provide an electric power system emulator apparatus including a chassis, a plurality of emulator modules in the chassis. Each of the emulator modules includes first and second transmission path emulator circuits, each having first ports configured to be connected to one another and second ports configured to be connected to another of the emulator modules, a source/load emulator circuit configured to be connected to the first ports of the first and second transmission path emulator circuits, and a control circuit configured to control the first and second transmission path emulator circuits and the source/load emulator circuit. 
     Methods of emulating an electric power system include selectively interconnecting nodes of an array of nodes having first and second dimensions using a plurality of emulator circuits, respective ones of which are configured to be connected between adjacent nodes of the array in the first and second dimensions and controlling the emulator circuits to emulate transmission paths of the electric power system. The methods may further include coupling second emulator circuits to respective nodes of the array and controlling the second emulator circuits to emulate loads and/or sources of the electric power system. The second emulator circuit may include respective power electronics converter circuits. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic diagram illustrating a reconfigurable and scalable electric power system emulator architecture according to some embodiments. 
         FIG. 2  is a detailed view of a portion of the electric power system emulator of  FIG. 1 . 
         FIGS. 3 and 4  are schematic diagrams illustrating architectures that may be used for converters of the electric power system emulator of  FIG. 1  according to some embodiments. 
         FIGS. 5A and 5B  illustrate, respectively, an electrical power system and a configuration of the emulator of  FIG. 1  for emulating the electrical power system according to some embodiments. 
         FIG. 6  is schematic diagram illustrating a DC transmission line path emulator and DC stations circuits. 
         FIGS. 7A and 7B  illustrate, respectively, an electrical power system with DC transmission lines and stations, and a configuration of the emulator of  FIG. 1  for emulating the electrical power system according to some embodiments. 
         FIG. 8  is a schematic diagram illustrating a modular emulator assembly according to further embodiments. 
         FIG. 9  is a schematic diagram illustrating an emulator module for the assembly of  FIG. 8  according to further embodiments. 
         FIG. 10  is a view of a chassis configured for installation of multiple emulator modules along the lines illustrated in  FIG. 9 . 
         FIG. 11  is a schematic diagram illustrating a scalable emulator apparatus having a rack/chassis architecture employing multiple chassis along the lines of  FIG. 10  according to further embodiments. 
         FIGS. 12 and 13  are schematic diagrams illustrating potential interconnections of modular emulator chassis according to further embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Specific exemplary embodiments of the inventive subject matter now will be described with reference to the accompanying drawings. This inventive subject matter may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive subject matter to those skilled in the art. In the drawings, like numbers refer to like items. It will be understood that when an item is referred to as being “connected” or “coupled” to another item, it can be directly connected or coupled to the other item or intervening items may be present. As used herein the term “and/or” includes any and all combinations of one or more of the associated listed items. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive subject matter. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless expressly stated otherwise. It will be further understood that the terms “includes,” “comprises,” “including” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, items, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, items, components, and/or groups thereof. 
     Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this inventive subject matter belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein. 
     Some embodiments of the inventive subject matter can provide software configurable and scalable power electronics converter based electric power system emulation platforms that are also cost effective and size-efficient. Compared with digital simulation, electric power system emulation platforms according to some embodiments can provide greater test fidelity with little or no numerical stability and convergence issues. Compared to conventional scaled analog hardware-based emulators, power electronics converter based electric power system emulation platforms according to some embodiments can provide more accurate emulation results. Compared to prior power electronics converter based emulators, software configurable and scalable electric power system emulation platform according to some embodiments can provide easier system topology configuration, better scalability, and larger-scale system emulation capability. Compared to mixed digital-analog signal power system emulation platform, software configurable and scalable power electronics converter based electric power system emulation platform according to some embodiments can provide more accurate emulation results. 
     Some embodiments provide software configurable and scalable electric power system emulation platform that use a matrix structure for relatively easy implementation of various electrical power systems topologies. In particular, such a matrix structure may include an array of nodes selectively interconnectable by AC/AC converter circuits that can emulate AC transmission lines and/or transformers, along with DC/AC converter circuits that are selectively connectable to the nodes to emulate sources and loads. It may also include a plurality of DC/AC and AC/DC converter circuits that can emulate DC transmission lines, along with AC/DC converter circuits that are selectively connectable to the DC transmission lines to emulate DC stations. The converters can be organized as interconnectable modules that can be interconnected in, for example, a rack/chassis arrangement that supports easy scalability. Thus, this architecture can support emulation of small-scale and/or low power or voltage systems (e.g., microgrids and autonomous electrical systems), and large-scale and/or high power or voltage systems (e.g., utility transmission grids or large portions thereof). 
       FIG. 1  illustrates an electrical power system emulator apparatus according to some embodiments of the inventive subject matter, while  FIG. 2  provides a detailed view of a portion of the emulator apparatus of  FIG. 1 . Referring to  FIGS. 1 and 2 , the emulator apparatus includes a plurality of nodes  110  that are arrayed as a rectangular matrix along first and second dimensions. For conceptual purposes, the nodes  110  are illustrated shown in  FIG. 1  as arrayed in a common plane, but it will be appreciated that the first and second dimensions are not limited to this particular spatial arrangement. Rather, the “first dimension” and the “second dimension” described herein refer to topological relationships, i.e., the nodes are arranged in first and second dimensions in terms of the manner in which they are electrically interconnected, and such interconnection is not limited to the planar arrangement shown in  FIG. 1 . For example, non-planar but topologically two-dimensional arrangements are discussed below with reference to  FIGS. 7-9 . It will be further appreciated that the concepts shown herein may be extended to further dimensions. For example, a three-dimensional arrangement could be provided that includes one or more planar matrices of the type shown in  FIG. 1  oriented perpendicular to the matrix shown in  FIG. 1  (e.g., plural parallel matrices coinciding with respective columns of the matrix of  FIG. 1 ) and interconnected with the nodes  110  thereof. 
     As further shown in  FIGS. 1 and 2 , transmission path emulator circuits  120  are configured to selectively interconnect adjacent ones of the nodes  110  along the first and second dimensions of the array of nodes  110 . The transmission path emulator circuits  120  may be configured to emulate behavior of power system transmission elements, such as transmission lines and transformers. 
     The transmission path emulators  120  may take any of a variety of forms. For example, the transmission path emulators  120  could take the form of transmission line emulators described in the aforementioned U.S. Pat. No. 10,873,184 to Wang et al., the disclosure of which is incorporated by reference herein in its entirety. In some embodiments, the transmission path emulators  120  may also take the form illustrated in  FIG. 3 , which includes a combination of power electronics converter circuits, including a first converter circuit  322  having an AC port  322   a  configured to be connected to a first one of the nodes  110  and DC port  322   b  connected to a DC bus  325 , a second converter circuit  324  having an AC port  324   a  configured to be connected to a second one of the nodes  110  and a DC port  324   b  connected to the DC bus  325 , and a third converter circuit  326  having a DC port  326   a  coupled to the DC bus  325 . As illustrated, the first and second converter circuits  322 ,  324  may be three-phase converter circuits, but it will be appreciated that, in some embodiments, single-phase or any number of phases converter circuits may be used. The converter circuits  322 ,  324  may take the form of any of a variety of different types of converter circuits including, but not limited to, two-level or multi-level converter circuits. 
     As explained in a co-pending U.S. patent application Ser. No. ______ entitled “POWER CONVERTER BASED TRANSFORMER EMULATOR” (Attorney Docket No. 190725-00008), filed concurrently herewith and incorporated herein by reference in its entirety, the circuit arrangement shown in  FIG. 3  can be used to emulate a transmission line, transformer and/or other transmission path elements of an electrical power system. In particular, the first and second converter circuits  322 ,  324  may be used to emulate a voltage and/or current conversion function of the transmission path, while the third converter circuit  326  may be used to emulate losses associated with such a path. 
     As shown in  FIG. 2 , switches  122  may be used to selectively couple the transmission path emulator circuits  120  to the nodes  110 . In some embodiments, such interconnect switching functions may be integrated or incorporated in the emulator circuits  120  themselves, without requiring use of the switches  122 . For example, such selectively coupling and decoupling could be performed by the first and second converter circuits  322 ,  324  shown in  FIG. 3 . 
     Referring to  FIGS. 1 and 2 , source/load emulator circuits  130  are configured to be selectively coupled to the nodes  110 . The source/load emulator circuits  130  may be configured to emulate the behavior of power system sources (e.g., generators, energy storage devices and the like) and/or loads (e.g., consumer loads, energy storage devices, and the like). Referring to  FIG. 4 , the source/load emulator circuits  130  may take the form of DC/AC converter circuits  430 , which include an AC port  430   a  that is configured to be connected to a node  110  of the emulator apparatus and a DC port  430   b  that is coupled to a load and/or source (e.g., an energy storage device). Examples of such source/load emulator circuits are described, for example, in the aforementioned U.S. Pat. No. 10,873,184 to Wang et al. 
     Switches  134  may be provided to selectively couple the source/load emulator circuits  130  to the nodes. In some embodiments, such interconnect switching functions may be integrated within the source/load emulator circuits  130  themselves, without requiring separate switches. For example, such selective interconnection may be provided by converter circuits  430  as shown in  FIG. 4 . As further shown, bypass circuits  124  may be provided to bypass the transmission path emulator circuits  120  to allow direct interconnection of adjacent ones of the nodes  110 . Such bypass capability may be used, for example, to allow common connection of multiple ones of the source/load emulator circuits  130  to one of the nodes  110 . In some embodiments, such bypass circuits function may be integrated within the transmission path emulator circuits  120  themselves, without requiring separate bypass circuits. For example, such bypass circuits could be implemented by the first and second converter circuits  322 ,  324  shown in  FIG. 3 . 
     As further shown in  FIG. 2 , the transmission path emulator circuits  120 , the source/load emulator circuits  130 , the interconnection switches  122  and the bypass circuits  124  may be controlled by at least one control circuit  140 . The control circuit  140  may comprise one or more control circuits which may be implemented in a number of different ways, such as in control circuits that are included in emulator modules that include groups of the transmission path emulator circuits  120 , the source/load emulator circuits  130 , the interconnection switches  122  and the bypass circuits  124 , as explained below with reference to  FIGS. 8 and 9 . The control circuit  140  may generally be implemented using any of a variety of different types of digital and/or analog circuitry, including, but not limited to microprocessor or microcontroller based circuitry that controls the transmission path emulator circuits  120 , the source/load emulator circuits  130 , the interconnection switches  122  and the bypass circuits  124  based on software instructions executed therein. The control circuit  140  can be configured to provide software configurability of the operations of the transmission path emulator circuits  120 , the source/load emulator circuits  130 , the interconnection switches  122  and the bypass circuits  124  as desired to implement different emulator configurations, such as the ones described below with reference to  FIGS. 5A, 5B, 7A and 7B . The control circuit  140  may also include, for example, user interface circuitry (e.g., circuitry to interface with devices such as displays, keyboards and other user interface devices) to facilitate such configurability and to support, for example, extraction, storage and processing of data, such as data relating to states (e.g., voltage and current) of the emulator apparatus, for analytical and other uses. 
       FIGS. 5A and 5B  illustrate an example of how the emulator apparatus illustrated in  FIG. 1  might be configured to emulate a particular power system arrangement by selectively coupling transmission path emulator circuits  120  and source/load emulator circuits  130  to the nodes  110  of the emulator apparatus. Referring to  FIG. 5A , an electrical power transmission system to be emulated may include generators G 1 , G 2 , G 3 , G 4 , G 5 , loads L 1 , L 2 , L 3 , L 4 , and interconnecting transmission lines  1 - 9 . Referring to  FIG. 5B , this system may be emulated by operating the transmission path emulator circuits  120  and load/source emulator circuits  130  to emulate corresponding components, i.e., the transmission lines  1 - 9 , generators G 1 , G 2 , G 3 , G 4 , G 5  and loads L 1 , L 2 , L 3 , L 4 . As shown in  FIG. 5B , transmission path emulator circuit  120  T_bypass is configured to be a low (e.g., near zero) impedance line for providing the bypass circuit function. It will be understood that a wide variety of different power systems may be emulated in a similar fashion by selectively operating the emulator circuits  120 ,  130  to form the desired system topology and mimic the operations of corresponding components (transmission lines, transformers, sources and loads) of the system being emulated. 
       FIG. 6  illustrates how the emulator apparatus in  FIG. 1  can emulate DC transmission line and DC station. Referring to  FIG. 6 , the DC transmission line may include a first converter circuit  622  having an AC port  622   a  configured to be connected to one of the nodes  110  and DC port  622   b  connected to a DC bus  625 , a second converter circuit  624  having a AC port  624   a  configured to be connected to the node  110  and DC port  624   b  connected to a DC bus  627 , a third converter circuit  626  having a DC port  626   a  coupled to the DC bus  625 , and a fourth converter circuit  628  having a DC port  628   a  coupled to the DC bus  627 . As illustrated, the first and second converter circuit  622 ,  624  may be three-phase converter circuits, but it will be appreciated that, in some embodiments, single-phase or any number of phases of converter circuits may be used. The converter circuits  622 ,  624  may take the form of any of a variety of different types of converter circuits including, but not limited to, two-level or multi-level converter circuits. As shown in  FIG. 6 , the AC/DC converter circuits  642 ,  644  can be configured to emulate DC stations in DC system. 
     Referring to  FIG. 6 , the first and second converter circuits  622 ,  624  may be used to emulate voltage and/or current conversion function of the DC transmission path, while the third and/or fourth converter circuits  626 ,  628  may be used to emulate losses associated with such a path. 
       FIG. 7A  and  FIG. 7B  illustrate an example of how the emulator apparatus illustrated in  FIG. 1  might be configured to emulate a particular power system arrangement by selectively operating DC transmission path emulator circuits, DC station emulator circuits, source/load emulator circuits, AC transmission path emulator circuits, and transformer emulator circuits. Referring to  FIG. 7A , an electrical power transmission system to be emulated may include generators G 1 , G 2 , loads L 1 , L 2 , transformers T 1 , T 2 , T 3 , DC transmission lines  3 ,  4 ,  5 , AC transmission lines  1 ,  2 , and DC stations  1 ,  2 ,  3 . As shown in  FIG. 7B , DC transmission path emulator circuit T_bypass  2 , T_bypass  3 , T_bypass  4  are configured to provide the bypass circuit function. It will be understood that a wide variety of different power systems may be emulated in a similar fashion by selectively operating the emulator circuits to form the desired system topology and mimic the operations of corresponding components (transmission lines, transformers, DC stations, sources and loads) of the system being emulated. 
     According to further embodiments, a software configurable emulator apparatus along the lines of that illustrated in  FIG. 1  may be implemented in a modular fashion that can provide a scalability that can facilitate emulation of systems of a variety of different sizes and levels of complexity. Referring to  FIGS. 8 and 9 , the emulator apparatus may be implemented as a plurality of interconnected modules  800 , each of which includes at least two transmission line emulator circuits  120  and at least one source/load emulator circuit  130 , along with a control circuit  810  that is configured to control the emulator circuits  120 ,  130  and the associated interconnection and bypass switches  122 ,  124 . The interconnection and bypass circuit functions of  122 ,  124  could be integrated into the emulator circuit  120 ,  130 . The modules  800  are configured to be interconnected at the nodes  110 . 
     Referring to  FIG. 10 , the modules  800  may be implemented as respective circuit cards or other circuit assemblies that are configured to be installed in a chassis  1000 . The chassis  1000  may include power interconnection circuitry  1010 , such as wiring that coincides with the nodes  110  of the emulator apparatus and that is configured to be coupled to the modules  800  such that the modules  800  are interconnected at the nodes  110 . Such wiring may, for example, take the form of traces provided on a backplane or similar structure in the chassis  1000 . The chassis  1000  may further include control circuitry  1020  that supports communications with the control circuits  810  of the modules. For example, the control circuits  810  may be configured to communicate using serial communications buses or similar arrangements, and the control circuitry  1020  may include wiring on a backplane and other circuitry that supports such communications. Such communications circuitry may be used, for example, by a system controller (not shown in  FIG. 10 ) installed in the chassis  1000  or elsewhere that controls the various modules  800  installed in the chassis  1000  to configure the modules  800  and operate the emulator circuitry thereof to emulate various electric power systems. 
     As shown in  FIG. 11 , the chassis  1000  may, in turn, serve as a modular component of a scalable system comprising racks  1100  that are configured to receive multiple ones of the chassis  1000 , enabling expansion to emulate more extensive and complex electrical power systems. Similar to the chassis  1000 , each of the racks  1100  may include power interconnection circuitry  1110  and control interconnection circuitry  1120  that may be used to interconnect the multiple chassis  1000  in the rack  1100 . The racks  1100  may, in turn, be interconnected using power interconnection circuitry  1130  and control interconnection circuitry  1140 , which may communicate with a system controller  1160  via a system control bus  1150 . The system controller  1160  may be operative to configure, control and monitor operations of the emulator modules  800  in the racks  1100 . 
     The modular, scalable arrangements illustrated in  FIGS. 8-11  may enable emulation of a variety of different system topologies. For example, as shown in  FIG. 12 , nodes, transmission path emulators and load/source emulators from first and second chassis  1000 - 1 ,  1000 - 2  may be interconnected to provide an expanded rectilinear matrix, which may be useful, for example, for emulating a relatively large electrical power system, such as a relatively large microgrid or a utility grid. However, the interconnection of chassis such as the chassis  1000 - 1 ,  1000 - 2  can be varied. For example, as shown in  FIG. 13 , the chassis  1000 - 1 ,  1000 - 2  may be connected in an offset manner, which might be useful, for example, in emulation of two grids that are coupled by a single intertie. Arrangements similar to those in  FIGS. 12 and 13  could also be implemented with multiple racks house multiple module-filled chassis, such as the racks  1100  of  FIG. 11 . 
     The drawings and specification, there have been disclosed exemplary embodiments of the inventive subject matter. Although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the inventive subject matter being defined by the following claims.