Abstract:
Distributed static synchronous series compensators (DSSSCs) which may also be designated tower routers capable of injecting series inductive or capacitive impedances to enable distributed power-flow control. When a large number of these (a fleet of) DSSSCs are distributed over the grid for power-flow control, it is necessary to ensure that coordinated communication and control capabilities are also established, enabling fast reaction to changes that can exist across the grid. A system architecture and method for enabling localized high-speed low-latency intelligent control with communications between subsections (local network) of the grid along with communication to the central Grid operations center at the utility for supervisory control is disclosed herein. The architecture provides sub-cyclic (&lt; 1/60 of a second) response capability, using the local DSSSCs with high-speed communication at the local network level to power-system disturbances, such as power-oscillation damping (POD), sub-synchronous resonance (SSR) etc.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application No. 62/294,230 filed Feb. 11, 2016. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to systems for distributed control with hierarchical supervision of the power grid when using a plurality of self-aware distributed power flow controllers. 
         [0004]    2. Prior Art 
         [0005]    Most power utilities use centralized energy management systems (EMS) and supervisory control and data acquisition (SCADA) systems for control of the power grid systems. These control systems provide communication and control between any of the following at the various geographically-distributed sub-stations and the centrally-located EMS: 
         [0006]    remote terminal units; 
         [0007]    breakers; 
         [0008]    phase-shifting transformers; 
         [0009]    analog and digital sensing devices; 
         [0010]    FACTS (Flexible AC Transmission Systems and Sub-systems). 
         [0011]    One problem of this type of centralized control is the inherent delay to and from the EMS. This delay can easily reach three to five seconds, and may even be as long as a minute under certain cases. This limits the responsiveness of the EMS-based grid control system to disturbances in the system. The recent inclusion of plurality of distributed power generation, such as local solar generators and wind-farms, have increased the need for fast optimization of power transfer and fast response to disturbances on the grid, a basic necessity for smoother operation of the power grid. 
         [0012]    A fixed substation-based response and control system  200  has been proposed for Flexible AC Transmission System (FACTS) for improved control of the power grid. Such a system is shown in  FIG. 2 . This system provides a better response capability to the disturbances and perturbations of the high-voltage Transmission grid  202  using static synchronous series compensator (SSSC) at substations  204 . Though these SSSCs are able to provide fast response to disturbances recognized, it being a non-distributed system, with communication link  207  to central utility  206  for control inputs and data analysis. This limits the capability of the system by adding delays for detection of problem, delays in communication, and delays for decision, before action can be initiated. This reduces the capability for the system for really fast proactive and interactive responses to local-level perturbations and oscillations of the grid from distributed generators  203 , loads  205  or disturbances on the HV transmission lines  202  suspended on transmission towers  201  due to current in-balances, wind-related voltage perturbations due to rapid energy injections, or wind-turbine controls-related resonances etc. 
         [0013]    Of recent, distributed control of power flow over the high-voltage (HV) transmission lines using distributed impedance injection modules, has been proposed and is being implemented.  FIG. 1  is an exemplary block diagram  102  of such distributed control modules that are static inductive- or capacitive impedance-injection modules  100 , attached directly to the HV transmission line  108  transferring power from generator  104  to distribution point  106 . A safer and more reliable way to attach the modules has been shown to be to suspend the distributed static impedance-injection modules from the transmission towers. These self-aware static inductive or capacitive impedance-injection modules are then able to identify and react very fast to the changes in the power line characteristics of the individual HV transmission lines  108  to which these are attached at a local level. These intelligent devices, are capable of injecting inductive or capacitive impedances on to the HV transmission lines  108  and hence provide the capability to have localized control of line current, and therefore establish a level of power-flow control on the HV transmission lines. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The drawings are made to point out and distinguish the invention from the prior art. The objects, features and advantages of the invention are detailed in the description taken together with the drawings. 
           [0015]      FIG. 1  is an exemplary block diagram of the distributed control modules attached directly to the HV transmission lines. 
           [0016]      FIG. 2  is a schematic of an alternate non-distributed control system based in substations with customized Static Series Synchronous compensators (SSSC) for grid control. 
           [0017]      FIGS. 3A and 3B  are exemplary schematic diagram of intelligent and self-aware DSSSCs with fast communication capability. 
           [0018]      FIG. 4  is an exemplary block diagram of an intelligent and self-aware DSSSC with fast communication capability. 
           [0019]      FIG. 5  is an exemplary schematic diagram of the distributed and hierarchical intelligent control system for the grid as per the current invention. 
           [0020]      FIG. 6  is an exemplary assessment of the response need and the capability of the current invention to respond to problems of the grid. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    It will be very useful to have the capability of the intelligent, self-aware impedance injection devices to be extended by using self-aware and intelligent distributed static synchronous series compensators (DSSSCs) attached to the individual transmission lines and suspended from the transmission towers as tower routers (TRs). These DSSSCs will be able to provide distributed capability for control of the power grid. By making the DSSSCs dynamic, intelligent and self-aware and linking these DSSSCs into an interconnected hierarchical system, the capability to react to changes in the power grid faster may be established. Such a system if implemented with capability for fast response at the local level, fast communication between system elements in the neighborhood, and information transfer capability from the local centers to the main control centers will be very advantageous for optimizing the power grid. Also having such a system with local response capability for computation and control of the distribution grid as well, will be useful in establishing a complete self-aware and self-healing grid system encompassing generation, transmission and distribution. Such a system if all the sub-system elements can be made self aware and intelligent, should be able to optimize the grid operation, speed-up recovery from problems and disturbances and improve overall grid operational efficiency. 
         [0022]    The invention disclosed is generally directed toward providing very high reliability distributed active control capabilities for sub-cyclic power grid control. The invention uses the capability of DSSSC or tower router (TR) technology that is being implemented by the applicant entity for fast localized power flow balancing across the multiple high-voltage lines used for power distribution on high-voltage transmission grids. Active power flow control modules that are intelligent, self-aware DSSSCs are placed in a distributed fashion on segments of high-voltage lines to provide localized control of the segments of the power lines. The co-pending patent applications “Voltage or impedance-injection method using transformers with multiple secondary windings for dynamic power flow control” filed as U.S. Provisional Patent Application No. 62/264,744 on Dec. 7, 2015 and “Transformers with multi-turn primary windings for dynamic power flow control” filed as U.S. Provisional Patent Application No. 62/264,739 on Dec. 7, 2015 cover the functional aspects of distributed active impedance injection modules that are usable with the addition of dynamic sensing and control capability and high-speed communication capability as self-aware DSSSCs. These provisional applications assigned to the current entity, are herewith incorporated herein by reference. The present invention is focused on developing a closed-loop distributed sub-cyclic solution to address the monitoring and control need that exists for high-voltage transmission grids using these self-aware DSSSCs. In addition to steady-state power-flow control and responsive line-current balancing, the use of the distributed self-aware DSSSCs with the added high-speed communication capability implemented by the present invention, enable transient and small-signal stability, power-oscillation damping (POD) and sub-synchronous resonance (SSR) damping. These capabilities for fast responses to instabilities of the grid improve and optimize the efficiency, stability and power transfer capabilities of the transmission grid. 
         [0023]    The four main needs that have been defined to achieve the above include:
       1. The need to have distributed control modules, DSSSCs, attached to the transmission lines that are intelligent and self-aware, and can react independently to disturbances on the local transmission lines of the grid. The distributed DSSSCs developed by the inventors and assigned to the inventor&#39;s parent organization meets the above requirement with a few modifications.   2. The second need is to provide local high-speed interconnect and communication between the DSSSCs and a local supervising controller to enable coordination of action between the local DSSSCs to overcome/limit the disturbances within the local control area of the grid.   3. A high-speed inter-link between local supervisory controllers, for keeping the near local controllers apprised of the nature of the disturbances and responses in the local area enable proactive response from these neighboring regions if it becomes necessary.   4. A communication link inter-connecting the supervisory modules with the utility central supervisory control is used to enable power flow diversion, or other major remedial action.       
 
         [0028]    Sub-cyclic dynamic control has been identified as an essential need to have a stable and dynamic power grid. The grid system should be able to handle issues of stability, intermittency and transients that are inherent in the new distributed, localized renewable power generation and distribution that is becoming part of the power grid. In order for the grid to be stable under these conditions it is necessary for the response actions to disturbances on the grid to be within milliseconds to prevent these from growing into major issues that can take the grid down. Centralized control of the grid using high-level algorithms and modeling used for grid control is not efficient in this regard due to the time delays inherently associated with the detection, communication, decision and action. The solution to this problem is intelligent distributed power-flow controllers such as the distributed intelligent dynamic impedance injection modules with fast intercommunication capability with sufficient intelligence and computing capability, such as implemented in the DSSSCs, to locally respond to any sensed disturbance in a sub-cyclic time frame. The capability for local data collection analysis and coordination between a plurality of such dynamic impedance injection modules are implemented by local intelligent controllers having high-speed communication links to the distributed dynamic intelligent impedance injection modules. These local intelligent controllers are used to enhance the capability of the distributed intelligent dynamic impedance injection modules. These local intelligent controllers are also enabled to communicate and coordinate with each other to enhance the overall capability of grid control and analysis of problems in a sub-cyclic time frame. The local intelligent controllers also coordinate with the system utility control center (housing the EMS) to provide the system utility with consolidated data and status information and receive commands and responses for implementation by the distributed intelligent dynamic impedance injection modules in case of system-level problems on the grid. 
         [0029]      FIG. 3A  and  FIG. 3B  are exemplary block schematic diagrams of exemplary distributed intelligent impedance-injection modules or DSSSCs as per the present invention. The exemplary intelligent impedance-injection modules of the previously mentioned U.S. Provisional Patent Applications Nos. 62/264,739 and 62/264,744, are modified into DSSSCs by adding dynamic control capabilities and high-speed local communication capabilities.  FIG. 4  is an exemplary block diagram of such a DSSSC. The impedance injection module  401  with built-in dynamic intelligent local HV transmission line monitoring and control capabilities is modified by the addition of high-speed local communication capabilities  410  to convert these to computation-and-dynamic-response capable DSSSCs  300 A and  300 B of  FIGS. 3A and 3B . 
         [0030]      FIG. 3A  is the block schematic of an implementation of intelligent distributed DSSSC  300 A that has a multi-turn primary  303  connected in series with the high-voltage (HV) transmission line  202  by cutting and splicing  301 . A secondary winding  304  couples to the primary and has electronic impedance generation circuits comprising a converter  307 . The converter  307  is capable of generating either leading or lagging voltages to be impressed on the HV transmission line  202 . The decision of which voltage type is needed is controlled by an intelligent local controller  308  that senses inputs from the secondary winding via a transformer connected to the HV transmission line and also obtains commands from either the EMS or the localized controller, as proposed here. The controller  308  also has a transceiver that enables high-speed communication  310  with neighboring DSSSCs by connecting to their controllers for intelligently coordinating the responses to identified local disturbances. It is also enabled for receiving control inputs, data collection and feedback to central or local control units that enable coordinated response for the grid segment or the grid system in case of problems. A transformer  302  with the power supply unit  305  is enabled to extract power from the line for driving the electronic components in the secondary  304  circuit of the injection transformer. The DSSSC  300 A is enabled to intelligently generate and inject inductive or capacitive impedances of appropriate magnitude on to the HV transmission line via the injection transformer. 
         [0031]      FIG. 3B  is an alternate exemplary embodiment of the DSSSC  300 B having a plurality of secondary windings  304 - 1  and  304 - 2  coupled directly to the HV transmission line used as a single-turn or multi-turn primary. A converter  307 - x  that is capable of producing dynamic impedance of inductive or capacitive voltages is attached to each of the secondary windings. A second transformer that has a secondary winding  302  coupled to the HV transmission line  202  is connected to a power supply unit  305 . The power supply unit extracts power from the HV transmission line and supplies the power to the circuits connected on the secondary side of the injection transformers  304 - 1  and  304 - 2 . The DSSSC senses the current and the grid disturbances over the transmission line through ancillary sensing equipment and generates appropriate responses as voltages that are orthogonal to the line currents as impedances to be injected onto the transmission line. The master controller  308  coordinates the generation of the injected impedances by the plurality of converters  307 - x  of the tower router module. The master controller  308  also incorporates a transceiver with high-speed communication capability, which transceiver enables communication with neighboring DSSSC controllers for intelligently coordinating the responses to disturbances. The transceiver is also enabled for receiving control inputs, and for data collection and feedback to central or local control units that enable coordinated responses for the grid system in case of problems. 
         [0032]      FIG. 5  is an exemplary block schematic of the grid control and optimization system  500  as per the disclosed invention. The system  500  comprise the dynamic response capable DSSSCs (DYRECTORs)  400  of  FIG. 4 , that are used as distributed injection modules for line balancing and steady-state power flow control. These DYRECTORs  400  are enabled to communicate using built-in high-speed links  410  between other DYRECTORs in the local area. A set of localized intelligent centers (LINC)s  502 , at least one each for each local area, are also enabled with high-speed communication capabilities to accept data and status inputs from and to provide intelligent coordinated control capability, via communication links  410 , for the activities of the DYRECTORs in the local area when necessary. The LINCs  502  of adjacent local areas are also able to communicate with each other using their high-speed communication links  504  to intelligently respond to disturbances on the high-voltage transmission lines at sub-cyclic speeds. The LINCs  502  are able to provide necessary local supervisory control and coordination to a plurality of transmission line groups  510  and  520 . The use of the DYRECTORs  400  and the LINCs  502  combination enables optimization of performance of the power grid system  500  by receiving their status information and coordinating the response at ultra-high speeds to optimize power transfer, line balancing and respond at sub-cyclic speeds to identified disturbances of the power grid. The LINCs  502  also function to aggregate the collected grid status and performance data for transmission to utility control. The LINCs  502  also provide the capability to run computationally intensive calculations locally to support the operation of the DYRECTORs  400 . The LINCs  502  use normal communication links  505  to system utility  506  for transferring aggregated status data and activity information and for receiving control instructions from the system utility  506  for the distributed components of the grid control and optimization system  500 . 
         [0033]    By having intelligence and computational capability built into the individual DYRECTORs  400  and LINCs  502  enable decisions to be taken by these devices, when a problem on the power grid system  500  is sensed and identified, without waiting for the data to be transmitted to the utility control  506  and instructions to arrive from the utility control  506  with concomitant delays. The system  500  disclosed is hence able to handle problems of distribution, including those related to other FACT devices  511  and storage systems  512  attached at the grid edge, and generation such as distributed generation by green energy systems as well as problems associated with transmission of power over the power grid very effectively locally when appropriate, and under utility control when needed. 
         [0034]      FIG. 6  shows the required response times, comprising time for detection, communication, decision and responsive action, applicable for typical problems on a modern power grid system  500 . Typical steady-state power-flow control is the only problem that can be optimally handled without a distributed control capability using normal communication speeds. In order for the power grid system to handle problems associated with wide-area control of the grid and power oscillation, it has been shown that high-speed communication capabilities are required. The problems of small-signal stability, transient stability and sub-synchronous oscillations, require the sub-cyclic local response capability provided by the DYRECTORs  400  and LINCs  502  that comprise localized intelligence incorporated in the units for detection, computation and controlled response, with high-speed communication to establish coordinated response with neighboring local area controllers. 
         [0035]    The disclosed power grid system  500  is hence able to respond optimally and at high-speed to any of the disturbances on the grid, as well as monitoring and controlling general operation of the grid, such as, but not limited to, line balancing, harmonic reduction or elimination and all the other characteristics to be monitored and controlled, all of which are collectively referred to a “conditions” or conditions on the high-voltage transmission lines of the power grid in the claims to follow. 
         [0036]    Even though the invention disclosed is described using specific implementations, circuits and components, it is intended only to be exemplary and non-limiting. The practitioners of the art will be able to understand and modify the same based on new innovations and concepts, as they are made available. The invention is intended to encompass these modifications.