Patent Publication Number: US-11641114-B2

Title: Use of the unused duration injection units in an array to reduce oscillations during impedance injection for corrections of problems

Description:
RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/893,673 filed Jun. 5, 2020, which claims benefit of priority from U.S. Provisional Application No. 62/939,413 filed Nov. 22, 2019, the disclosures of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to using available resources of transformerless flexible alternating current transmission system (TL-FACTS) based impedance injection units to manage disturbances on a high voltage (HV) transmission line. 
     BACKGROUND 
     The current move in the industry is to use modular transformerless flexible alternating current system (TL-FACTS) based impedance injection units (IIUs) for distributed and localized line balancing and localized control of disturbances in the high voltage (HV) transmission lines  108  of the grid, as shown in  FIG.  1   . This local control is in addition to utility-based control of power flow over the HV transmission lines. The local control of the HV transmission lines is achieved by use of intelligent impedance injection modules (IIMS)  300  connected in series with the transmission lines and comprise a number of IIUs typically connected in a series-parallel configuration. The parallel connected IIUs switched in synchronized fashion are used to provide increased current carrying capacity for the transmission lines while the series connected IIUs can be used to increase the injected impedance voltage in a cumulative fashion. The IIMs  300  are coupled to the HV transmission line  108 , typically in a distributed fashion as shown in  FIG.  1    to enable the local control. Since the IIMs  300  are connected in series with the HV transmission line  108 , their injected impedance voltages are also cumulative over the HV transmission line  108 . There is a need in the art for ongoing improvements. 
     SUMMARY 
     A method of operating impedance injection units (IIUs), an impedance injection unit system, and a computer-readable media are described in various embodiments. 
     One embodiment is a method of operating impedance injection units. The method includes controlling, by a control module, a plurality of IIUs to form multiple connection configurations in sequence. Each connection configuration includes one IIU, or multiple IIUs in series, parallel or combination thereof. Each connection configuration is coupled to a high voltage transmission line. The method includes generating a plurality of rectangular impedance injection waveforms. The generating is by the control module through the multiple connection configurations of IIUs in sequence. When the rectangular impedance injection waveforms are combined and injected to the high voltage transmission line, this produces a pseudo-sinusoidal waveform. 
     One embodiment is an impedance injection unit system. The system has a plurality of IIUs and a control module. The control module is to direct the plurality of IIUs to form connection configurations in sequence. Each connection configuration has one IIU or multiple IIUs in series, parallel or combination thereof, coupled to a high-voltage transmission line. The control module is to generate, through the connection configurations of IIUs in the sequence, rectangular impedance injection waveforms. The rectangular impedance injection waveforms are to combine and inject to the high voltage transmission line, to produce a pseudo-sinusoidal waveform on the high-voltage transmission line. 
     One embodiment is instructions on a tangible, non-transitory computer readable media. When the instructions are executed by a processor, this causes the processor to perform various actions. The processor is to direct a plurality of IIUs to form connection configurations in sequence, when the IIUs are coupled to a high-voltage transmission line. Each connection configuration includes one IIU or multiple IIUs in series, parallel or combination thereof. The processor is to generate, through the connection configurations of IIUs in the sequence, rectangular impedance injection waveforms. The rectangular impedance injection waveforms are to combine and inject to the high voltage transmission line, to produce a pseudo-sinusoidal waveform on the high-voltage transmission line. 
     Other aspects and advantages of the embodiments will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings in which like references indicate similar elements. 
         FIG.  1    is a diagram illustrating a conventional power grid system with a distributed and hierarchical intelligent control system. (prior art) 
         FIG.  2    is a block diagram illustrating a conventional dynamic intelligent impedance injection module with local and global time synchronization capability. (prior art) 
         FIG.  3 A  is a circuit diagram illustrating a local master control module of a TL-FACTS based IIU having an associated local clock according to one embodiment. 
         FIG.  3 B  is a circuit diagram illustrating a local master control module of a TL-FACTS based IIU having an associated local clock that can be synchronized to a global clock according to one embodiment. 
         FIG.  4    is a circuit diagram illustrating an example of a transformer-less flexible alternating current (AC) transmission system (TL-FACTS) based impedance injection unit (IIU), where one or more IIUs may constitute an impedance injection module IIM  300 . 
         FIG.  5    is an example block diagram illustrating an IIM having a 2×2 series-parallel connection comprising four TL-FACTS based ITUs according to one embodiment. 
         FIG.  6    is an example illustrative diagram of the IIM having two sets of parallel connected TL-FACTS based IIUs interconnected in series. A 2×2 Matrix of  FIG.  5    providing two rectangular waveforms from the two sets of series connected IIUs  400  in a synchronized fashion that when combined, generate a pseudo-sinusoidal wave for injection on to the HV transmission line. 
         FIG.  6 A  shows the synchronously-generated and injected rectangular waves from each of the two series connected groups of two parallel connected ITUs of the IIM  300  of  FIG.  5   . 
         FIG.  7    shows an 8 IIUs configured in four parallel groups, each group having two IIUs in parallel and the four groups connected in series to form an IIM. 
         FIG.  7 A  shows the injected output from the four groups of dual IIUs of  FIG.  7    with their injection start and end times adjusted in a synchronized fashion to generate a pseudo-sinusoidal waveform that smooths to a sinusoidal waveform  701  when injected on the HV transmission line. 
         FIG.  8    shows the synchronously injected waveforms from each of the four IIUs of the IIM that enable the modified injected waveform of  FIG.  7   . 
         FIG.  8 A  is an example illustrative diagram  800  of the use of the un-utilized capability of the IIUs of the IIM in  FIG.  7   . Diagram  800  shows injecting additional rectangular waveforms to modify the pseudo- sinusoidal waveform  701  of  FIG.  7 A . This injection results in a modified waveform which is smoothed to waveform  801 . The smoothed waveform addresses managing unexpected problems on the HV transmission line. 
       
         
           
             
                 
               
                 
                     
                 
                 
                   NUMBERING AND LETTERS IN FIGURES 
                 
                 
                     
                 
               
              
                 
                     
                 
              
             
             
                 
                 
              
                 
                   100- an example grid 
                   300- Impedance injection 
                 
                 
                     
                   module (IIM) 
                 
                 
                   108- High voltage (HV) 
                   301-Sensor and power supply 
                 
                 
                   transmission line 
                 
                 
                   201- HV transmission 
                   302-Local Intelligence centers 
                 
                 
                   towers 
                   (LINC)s 
                 
                 
                   203-Generators 
                   303-High-speed communication 
                 
                 
                     
                   link 
                 
                 
                   204- Substations 
                   304- Power supply &amp; sensing 
                 
                 
                     
                   Transformer 
                 
                 
                   205- Connected loads 
                   305- Communication link 
                 
                 
                   206- System utility 
                   400 A-v or B-v -square wave 
                 
                 
                     
                   injection from IIU 400A 
                 
                 
                     
                   or 400B 
                 
                 
                   207- Communication link 
                   401- Impedance injection unit 
                 
                 
                   408B-IGBT Switch 
                   402- Master Control--Intelligent 
                 
                 
                     
                   with clock 
                 
                 
                   409- DC Capacitor 
                   403- Intelligent controller 
                 
                 
                   410- Highspeed wireless 
                   404A - Clock, synched to local 
                 
                 
                   communication 
                   clock 
                 
                 
                   500 - Generation of sinusoidal 
                   404B- Clock, synched to global 
                 
                 
                   impedance injection 
                   clock 
                 
                 
                   501 &amp; 701- Smoothed injected 
                   405- FACTS switch 
                 
                 
                   waveform 
                 
                 
                   800- modifying the injected 
                   406A &amp; B- Injection terminals 
                 
                 
                   waveform 
                 
                 
                   801-x-nv nth additional 
                   407- GPS satellite 
                 
                 
                   njection from IIU at free time. 
                 
                 
                   801- Modified impedance waveform 
                   408A-IGBT switch control 
                 
                 
                   400A &amp; B series connected dual 
                   400A-v to 400B-v &amp; injection 
                 
                 
                   parallel switches 400-A1 &amp; 
                   from the series groups 
                 
                 
                   A2 and 400-B1 &amp; B2 
                 
                 
                   700-1 to 4 group of four dual 
                   700-1v to 700-4v injected 
                 
                 
                   parallel connected switched 
                   cumulative impedance voltages. 
                 
                 
                   connected in series 
                 
                 
                   t1 to t4 -start times of the 
                   t1′ to t4′ - end times 
                 
                 
                   synchronized generated 
                   of the synchronized generated 
                 
                 
                   impedance waveforms 
                   impedance waveforms 
                 
                 
                   d1 to d4-duration of the 
                   s - the duration of short 
                 
                 
                   synchronized generated 
                   pulse waveform generated 
                 
                 
                   impedance waveforms 
                   during unused period 
                 
                 
                     
                 
              
             
           
         
       
     
    
    
     DETAILED DESCRIPTION 
     Intelligent impedance injection modules (IIMs) comprising connected transformer-less FACTS (TL-FACTS) devices are used as impedance injection units (IIUs) for control of high-voltage (HV) transmission lines. The IIUs generate and inject rectangular impedance waveforms which if cumulatively large when injected create high-frequency oscillations that interfere with control systems on the HV transmission lines and user premises. By staggering and synchronizing the timing of the injection from the series connected IIUs or IIU groups, the injected waveform is converted to a pseudo-sinusoidal waveform to reduce generation of oscillations. This method of injection leaves some IIUs or groups of IIUs with very low utilization. The idle time of the IIUs are used to generate and inject impedance on to the HV power line and modify the injected waveform to overcome unexpected disturbances when need arises. 
     Definitions 
     1. LOCAL: belonging or relating to a particular area or neighborhood, typically exclusively so. In this case the term local is used to denote a segment of the HV transmission typically line under a single local control. 
     2. IMPEDANCE: is the measure of the opposition that a circuit presents to a current when a voltage is applied. The term complex impedance may be used interchangeably. Impedance extends the concept of resistance to AC circuits, and possesses both magnitude and phase, Impedance can be inductive, capacitive, resistive. 
       FIG.  1    shows the example system  100  that includes distributed impedance injection modules (IIMs)  300  distributed over HV transmission lines  108  between substations  204 . The IIMs  300  are directly attached to the HV transmission lines  108  of the power grid and are suspended insulated from ground on HV transmission lines suspended from HV towers  201 . Generators  203  and loads  205  are typically connected to the HV transmission lines  108  of the power grid at the substations  204 . The groups of local IIMs  300  are communicatively connected or coupled to a local intelligence center (LINC)  302  via high-speed communication links  303  that allow for communication and response by the IIMs  300  in the local area at sub-synchronous speeds when required. The plurality of LINCs  302  are also connected by high-speed communication links  303  to other neighboring LINCs  302  for coordination of activity of the local IIMs  300  groups. A supervisory utility  206  oversees the activity of the system  200 A using command and communication links  207  connecting to the LINCs  302  and substations  204 . The supervisory utility  206 A is able to have interactive control of the local IIMs  300  via the communication links connecting it to the LINCs  302 . The supervisory utility has superseding control of the LINCs  302  and the IIMs  300  at any time. 
       FIG.  2    is a block diagram showing the main components of an intelligent IIM  300 . Referring to  FIG.  2   , IIM  300  includes at least an impedance generation and injection module  401 , an intelligent control capability  402  with at least a clock with time synchronization capability, and a high-speed communication link  410 . 
       FIG.  3 A  shows use of a local clock  404 A coupled to an intelligent control module  403  within each IIM to synchronize the generation and injection of impedance on to the power line  108 . The  FIG.  3 B  shows use of a global clock  404 B controlled typically by the GPS  407 , coupled to an intelligent control module  403  to synchronize the generation and injection of impedance on to the power line  108 . The IIM  300  uses power extracted from the HV transmission line  108  using a power transformer  301 A coupled to a sensor and power supply module  301  to provide the power to the circuits of the IIM  300  including the intelligent control unit  403 , communication unit  410  and the IIUs  400 . 
       FIG.  4    shows an example circuit diagram of a transformer-less flexible alternating current transmission system (TL-FACTS) based impedance injection unit (IIU)  400  connected in series on the HV transmission line. The IIU  400  is capable of generating inductive or capacitive impedance to be injected on to the power line  108 . The IIU  400  comprise two leads  406 A and  406 B that are connected in series with the HV Transmission line  108 . Four insulated-gate bipolar transistor (IGBT) switches  408 B are used to connect the input line, lead  406 A to the output line, lead  406 B. The switching of the four IGBT switches  408 B are controlled by switch controls  408 A- 1  to  408 A- 4  that are coupled to a master control  402 . The master control, for example intelligent control capability  402  of  FIG.  2   , is coupled to a sensor and power supply module  301 , which extracts power from the HV transmission line  108  for the operation of the ITU  400  via the transformer  304 . A DC capacitor develops a DC voltage across itself that is used as injected impedance into the HV power line  108 . Depending on the sequence of switching of the IGBT switches  408 B an inductive or capacitive impedance can be generated and injected on to the HV transmission line  108 . Typically, an IIM  300  comprise a number of IIUs  400  that are connected in a series-parallel configuration. 
       FIG.  5    shows an IIM  300  having a 2×2 configuration of IIUs  400 . The IGBT switches of the IIUs are enabled to switch to generate rectangular impedance waveforms which get injected on to the HV transmission line. IGBT switches  408 B have to be de-rated during application for their current carrying capacity to improve reliability, in some embodiments. IGBT paralleling within IIUs  400  and multiple IIU paralleling with switch synchronization in each IIM  300  are used to ensure adequate current capability through the IIMs  300  connected in series with the line. The paralleled groups of IIU  400  may be connected in series within each IIM  300  to increase the generated and injected impedance voltage from the IIM  300 . The result of such a connection configuration is to increase both the current carrying capacity and the generated injected impedance voltage from the IIM  300 . 
     The injected waveforms from the series connected IIUs  400  groups,  400 A and  400 B are additive and make up a rectangular impedance injection waveform of typically double the amplitude if the start and stop times are synchronized. Such a large amplitude rectangular injection on to the HV transmission line  108  may result in oscillations being initiated and harmonics being injected on the HV transmission line  108 . It will be ideal if such oscillations and harmonic injections are avoided on the HV transmission lines of the grid for improved stability and reliability of operation of the power grid. This can be accomplished by staggering the impedance injection from various series connected IIUs  400  or groups of parallel connected IIUs  400  where the groups are connected in series. 
     In some cases, individual capability of a single IIM  300  is insufficient to provide the impedance injection required. The resources from multiple distributed IIMs  300   s  which are connected in series on the HV power grid may be utilized to generate the total impedance injection needed. Staggering of start and stop times (or duration of injection) is needed in these cases to limit oscillations and injection of harmonics on the HV transmission line. Use of the synchronizable clock across IIMs  300  enables such staggering of injected waveforms within an IIM  300  and/or between IIMs  300  by modifying the start and end times of the series connected IIU  400  groups, the IIU  400  groups being IIUs  400   s  connected in parallel and switched simultaneously as previously discussed. 
     In certain instances, the HV transmission lines can experience sudden disturbances which may be local in nature. It will be ideal if responsive action can be initiated in the sensed local region to remedy such disturbances and limit their spread. 
     It is optimum if the generated waveforms from the IIUs  400  of the IIM  300  can be adjusted to represent a pseudo-sinusoidal impedance waveform when cumulatively injected on to the HV transmission line  108 . IIM  300  may comprise one or more IIUs  400  that are connected in series, parallel or series-parallel connections. A set of start-time-synchronized and duration-adjusted waveforms generated by four IIUs  400 s connected in a 2×2 array of  FIG.  5    is shown in  FIG.  6   . The 2×2-connected array of IIUs  400  of the example IIM  300  comprise four IIUs, the first two IIUs  400 -A 1  and  400 -A 2  forming a parallel-connected group  400 A and the second two IIUs  400 -B 1  and  400 -B 2  forming a second parallel-connected group  400 -B. The waveforms generated by each of the parallel connected IIUs of a group are synchronized to start, end and have same amplitude. The two parallel connected groups  400 A and  400 B are connected in series to form the example implementation of the IIM  300  of  FIG.  5   . The IIM  300  of  FIG.  5    is able to generate impedance injection waveforms  400 A- v  and  400 B- v  as shown in Fig. 6 A, the waveform  400 A- v  having a start at time t 1  and an end time t 1 ′ with a duration d 1 , and the waveform  400 B- v  having a start time at t 2  and an end time t 2 ′ wherein the duration is d 2  which is less than d 1 . The two waveforms are cumulative when injected onto the HV transmission line as the two parallel connected IIU groups  400 A and  400 B are in series and typically will smooth out to the sinusoidal waveform  501  shown in  FIG.  6   . 
       FIG.  7    shows another example IIM  300 - 2 X comprising a 4×2 combination, four groups of two IIUs  400  in parallel, the four groups are connected in series to form an IIM  300 - 2 X. That is, each of the four groups  700 - 1  to  700 - 4  are formed by paralleling two IIUs  400 . Group  700 - 1  comprising IIUs  400 -A 1  and A 2 , group  700 - 2  comprising IIU  400 - 301 B 1  and B 2 ,  700 - 3  comprising IIUs  400 -C 1  and C 2 , the group  700 - 4  comprising IIU  400 -D 1  and D 2 . The four parallel-connected groups of IIUs  700 - 1  to  700 - 4  are connected in series to generate impedances  700 - 1   v  to  700 - 4   v  to be injected on to the HV transmission line  108 . The individually injected impedances  700 - 1   v  to  700 - 4   v  have start times staggered as t 1 , t 2 , t 3  and t 4  with end times staggered as t 1 ′, t 2 ′, t 3 ′ and t 4 ′ providing injection durations d 1 , d 2 , d 3  and d 4  respectively, as shown in  FIG.  7 A . These impedances, when injected onto the HV transmission line, cumulatively combine to provide a pseudo-sinusoidal waveform which gets smoothed to the sinusoidal waveform  701  due to the impedance of the line as shown in  FIG.  7 A . 
     Considering  FIGS.  7  and  7 A , it is clear that the impedance generation capabilities of all the groups of IIUs  700 - 1  to  700 - 4  of the IIM  300 - 2 X are not fully used in generating the impedance for injection on to the HV transmission line. In one embodiment, it is assumed that all of the IIUs groups  700 - 1  to  700 - 4  of the IIM  300 - 2 X have equal capabilities for generation of impedance waveforms, as shown in  FIG.  7 A . The IIU group  700 - 1  injects the rectangular waveform  700 - 1   v  having a start time t 1 , a duration d 1 , and an end time at t 1 ′. Furthermore, IIU  700 - 2  is constrained to inject a waveform  700 - 2   v  starting at a later time t 2  having a duration d 2  that ends at t 2 ′ before the  700 - 1   v  tl&#39; ends. Similar conditions are repeated for IIU group  700 - 3  and IIU group  700 - 4 , resulting in each of the IIU groups that start later ends earlier with smaller and smaller duration. Hence the later starting groups of IIUs have larger and larger unused capacity as clearly shown in  FIG.  7 A . 
     A sudden disturbance or a local disturbance that happens on the HV transmission line can require an injection of inductive or capacitive impedances as corrective action. This corrective action can be accomplished within the same injection cycle by generating short duration pulses by the IIU groups  700  with their available unutilized time. The sudden or local disturbance is sensed by the sensors coupled to the IIM  300 - 2 X or alternately sensors distributed over the HV transmission line. The IIM  300 - 2 X of the local area receives the sensed data, and using the intelligence built into it, develops an impedance injection response to the disturbance by taking into account the available resources including the unused capacity of the groups of IIUs  700  of the IIM  300 - 2 X. 
     The response defines the generation and injection of additional short duration pulses of duration ‘s’, shown in  FIG.  8   , during the unutilized IIU groups&#39;  700  available time. The additional short duration pulses are synchronized with the normally injected impedance pulses using the local or global clock used by the IIM  300 - 2 X generating the short pulses. These short-duration pulses are used to amend or modify the normally injected impedance injection waveform  701  to the example modified waveform  801  to address the sudden or local disturbance identified on the HV transmission line. 
       FIGS.  8  and  8 A  show the example short-pulse generation and injection of these short-duration pulses during the unused times of the groups of IIU  700 .  FIG.  8    shows the short-duration pulse  801 - 3 - 1   v  having a start time synchronized to t 1  and duration ‘s’ generated and injected by IIU group  700 - 3  and also the additional short pulses  801 - 4 - 1   v  having a start time at t 2  and duration ‘s’ and  801 - 4 - 2   v  having a start time t 3  and duration ‘s’ being generated by IIU group  700 - 4  which when cumulatively injected with the regular injected waveforms  700 - 1   v  to  700 - 4   v  modify the original injected and smoothed impedance waveform  701  to a modified smoothed waveform  801  to be injected on to the HV transmission line  108  to overcome the sudden or local disturbance that was sensed on the HV transmission line  108 . 
     As discussed previously, the additional pulses generated and injected can be either inductive or capacitive depending on the disturbance sensed and the response identified by the TIM  300 - 2 X. Though the short pulses are shown as having a fixed duration, it is not necessary to have it so. The short pulses can have any duration without encroaching on the existing impedance injection waveform from the group of IIUs  400 . Similarly, the amplitude of the short pulses and the injected impedance waveform are shown as being equal in magnitude from each of the groups of IIUs. The equal magnitude injection is not always necessary or optimum. The amplitudes of injected waveform can be different from different switch groups and the amplitudes and timing can be optimized to respond to any line balancing, flow control or disturbance correction needs within the injection capability of the group of IIUs. 
     Even though the invention disclosed is described using specific implementations as examples, it is intended only to be examples 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 and become available. The invention is intended to encompass these modifications that conform to the inventive ideas discussed.