Abstract:
A network topology for powering and communicating with groups of heliostats in a concentrated solar power plant. Heliostats are arranged in rows and wired together with inter-drive cables that distribute power and data from a field electrical system and plant network. Data is transmitted to and from heliostat drive control boards via network switches connected to intelligent power distribution units. Power is transmitted from battery banks to said intelligent power distribution units. Communication interface modules supply a connection between intelligent power distribution units and the heliostat control boards of non-adjacent heliostat rows to create communication and data loops having improved redundancy and robustness in the event of single point component failures.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to and the benefit of U.S. Provisional Patent Application No. 61/976,906, filed on Apr. 8, 2014, the entire disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    This disclosure relates generally to the power and communication delivery system for heliostats having reflectors for use in redirecting sun light to a target or receiver. In particular, the invention relates to a heliostat field having wiring loops and network topology to facilitate a system with multiple stages of redundancy. 
         [0003]    In Concentrating Solar Power (CSP) plants, arrangements of heliostats reflect sunlight toward a receiver mounted atop a tower containing a working fluid. One type of receiver transfers incident radiant energy to the working fluid to produce high-pressure, high-temperature steam through the means of a heat exchanger or a phase change of the working fluid itself. The working fluid can be water, air, or a salt material heated to a molten state. The output steam can facilitate a variety of applications, such as electrical power generation, enhanced oil recovery, and desalination. Heliostats are generally mounted on the ground in an area about the tower. Each heliostat has a rigid reflective surface, such as a mirror, capable of sun-tracking, wherein the reflective surface takes on orientations throughout the day so as to optimally redirect sun light from the sun toward the receiver. Arrays of heliostats may be arranged into a plurality of subgroups comprising a field. The subgroups may be configured to provide a preferred orientation that facilitates efficient land usage, optimizes the amount of flux delivered to the receiver, and minimizes the blocking of outer heliostats by inner heliostats. 
         [0004]    One approach to constructing a heliostat field is to utilize a small amount of comparatively large heliostats (e.g., greater than between about 50 and 150 m 2 ). In such a power plant, the fewer number of heliostats can make it economical to manufacture very precise, and thus very expensive, components for the positioning of the reflective surfaces. Another approach, however, is to use a large amount of comparatively small heliostats (e.g., between about 1 and 10 m 2 ), such as with reflective surfaces that measure between about 1 meter and 3 meters on each side. Such an approach may be more efficient at redirecting sun light because there are more individually adjustable reflective surfaces. In addition, smaller heliostats are easier to assemble, thereby decreasing installation time and the amount of requisite labor 
         [0005]    Heliostats may be controlled by a drive comprising a one or two-axis tracker that tracks the sun and reflects sunlight onto a target. Heliostats may comprise drive control boards that accept commands from a controller and operate one or more actuators, such as motors. A heliostat may have a data and a power connection in order to direct the drive to a desired orientation. The power connection provides an energy path to the actuators and control boards of the heliostat drive. The data connection provides a communication pathway to the heliostat drive from a central or distributed controller. Power and communication connections may be provided using field cabling wired from central power distribution units and networking hubs, respectively, to individual heliostats in the field. 
         [0006]    The routing of field cabling to thousands of actuating devices presents unique challenges and opportunities for improvement. Rows or subgroups of heliostats may receive power from a single bus while drive control boards may be connected in series to establish a communications network. Heliostats may have their data and communication delivery cables chained together, such that the same transmission line supplies power and facilitates data throughput to multiple units in a single subgroup. Such a configuration presents the possibility of cutting power and communication to an entire subgroup or a substantial portion thereof in the event a single component in the chain malfunctions. Components that could fail during the lifetime of the plant include, but are not limited to: connector wires, data and power transmission cables, power supplies, transceivers, and network switches. There exists a need to reduce the vulnerability of heliostat electronics topology to single point failures by incorporating redundant data and communication transmission pathways. 
       SUMMARY OF THE INVENTION 
       [0007]    A system for powering and controlling a heliostat field is described herein, wherein the system comprises a power and communication network topology having multiple transmission pathways looped between adjacent heliostat subgroups. The system is thereby configured to advantageously reduce the impact of single point failures on plant operation. 
         [0008]    The power and communication distribution network comprises both electronics hardware and controller software configured to operate said hardware. Heliostats in a field may be positioned into subgroups oriented to reflect sunlight onto one of a plurality of solar receivers and may be deployed in rows or other suitable arrangements. Each heliostat comprises a reflector and a controller. The controllers in adjacent heliostats in a row may be connected to each other via inter-drive cable, wherein an inter-drive cable facilitates both communication and power-delivery via constituent wiring. 
         [0009]    A single heliostat in each row may be connected to a Communication Interface Module (CIM), the CIM being capable of interfacing in this manner with up to four heliostat rows simultaneously. This single heliostat may be the heliostat in the row that is closest to the CIM or closest to the end of the row. Each communication interface module is configured to pass along power and data communication to each connected heliostat in a row. The CIM may be further connected by way of field-routed cables to an Intelligent Power Distribution Unit (IPDU) housed in a Field Electrical Cabinet (FEC). Each IPDU may comprise a plurality of Intelligent Power Distribution Cards (IPDCs). Each CIM may be connected to a plurality of IPDCs; in this manner a single IPDU can deliver data and power to multiple CIMs. In a particular embodiment of the present invention, a CIM may be connected to adjacent IPDCs housed in the same IPDU. In an alternative embodiment, a CIM may be connected to IPDCs in different IPDUs. IPDCs in an IPDU may have network connections to each other, for instance adjacent IPDCs in an IPDU may be connected. Each IPDC in an IPDU may have a further connection by way of data-transmission cabling to a port of one of a plurality of network switches, the network switches being connected to each other in series via auxiliary data connectors and also to a plant network. The plant network may comprise additional communication pathways to a master power plant controller as well as monitoring systems. Commands issued to individual heliostats may originate from a control system within the plant network and may be delivered via the communication distribution topology described herein. 
         [0010]    As described previously, a centralized power and data distribution network for controlling thousands of individual heliostats is vulnerable to single point component failures. In order to increase the reliability of the system, power and communication loops may be created to provide redundant pathways for distribution in the event of aberrant breakdowns or power loss. One such redundancy may be created with the provision that no two adjacent IPDCs in an IPDU will be connected to the same network switch. If a connection between network switches fails, the IPDCs in an IPDU can still access the Plant Network through an auxiliary switch. 
         [0011]    As described above, each CIM may supply power and data communication to up to four rows of heliostats by interfacing with the inter-drive cable from the heliostat at the proximate end of each row. DC power may be delivered from a DC power source in the plant electrical network to an IPDU, where it is then transmitted to the CIM and the Drive Control Boards (DCBs) in the heliostats. Heliostats in a pair of adjacent rows may be connected in parallel to form a power transmission loop. Data may be delivered to and from the plant network through the network switches to an IPDU, where it is then transmitted between the IPDCs and CIM and finally between the CIM and the DCBs in the heliostats. 
         [0012]    In a preferred embodiment, the CIM may have one microcontroller per row to provide data communication (four microcontrollers in total). Each CIM microcontroller may provide a data communication pathway between a communication port on the IPDC (via field cable) and the first heliostat in a row (via inter-drive cable). The cables may be connected such that heliostats in adjacent rows connect to communication ports on different IPDCs. Additionally the outermost DCBs (furthest from the CIM) of two adjacent heliostat rows may be connected to each other via inter-drive cabling to create a power and communication transmission loop. In this manner data communication pathways are never interrupted by the failure of single component. In the event of a microcontroller failure, malfunctioning transceiver, or damaged microcontroller power supply, data may still be transmitted to the heliostats of all four rows. The result is an added element of redundancy to the system to mitigate the effects of component failures. In an alternative embodiment a single CIM may be used to facilitate data transfer to less than four heliostat rows. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIGS. 1A-1B  are isometric and side views, respectively, of heliostats comprising reflectors mounted to two-axis drive assemblies. 
           [0014]      FIG. 2  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in a concentrated solar power plant during normal operation. 
           [0015]      FIG. 3  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of an inter-drive communication link failure. 
           [0016]      FIG. 4  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of a CIM microcontroller failure. 
           [0017]      FIG. 5  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of a failure of at least one DCB. 
           [0018]      FIG. 6  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of an inter-drive power link failure. 
           [0019]      FIG. 7  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of a network switch failure. 
           [0020]      FIG. 8  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event a connection between network switches fails. 
           [0021]      FIG. 9  is a systems-level view of the communication and power distribution topology and delivery pathways for a heliostat field in the event of an IPDC to CIM communication link failure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]      FIGS. 1A and 1B  display examples of heliostats operated under the present network and power distribution topology.  FIG. 1A  is a perspective view of a subgroup of three heliostats, while  FIG. 1B  is a side view of the same subgroup. Each heliostat  10  may comprise a reflector module  11  attached to a reflector module channel  12  of drive  13 . The reflector module may have a planar shape, such as a flat quadrilateral, or a non-planar shape such as a concave parabolic dish. The reflector module may also comprise a plurality of segmented reflectors arranged in a planar or non-planar shape. The drive  103  may comprise two gear boxes and motors that actuate the drive about two axes. The axes may be in the azimuth (orthogonal to the ground) and elevation (orthogonal to the azimuth axis along the length of the reflector module channel) directions, or they may be linearly independent axes as, for example, in a Tilt-Tilt configuration. The drive  102  may interface with a post  104  of a heliostat structure assembly  105 . Heliostat structure assemblies may be arranged in triangles or other suitable shapes. Heliostats may further comprise drive control boards (“DCBs”, not shown) internal to the drive that receive power, actuate the motors, and facilitate data communication to and from a plant network. Actuation commands may be issued to the heliostats over the plant network from a control system. 
         [0023]      FIG. 2  displays a systems-level view of a heliostat field power and communication distribution network. Commands to actuate the heliostat field originate from control systems on the Plant Network  101  and are transmitted over network data transmission cables  107 . The network data transmission cables  107  connect the Plant Network  101  to at least one network switch  104 . Network switches may comprise a plurality of ports and may be connected to each other via auxiliary data connectors  105 . IPDCs  103  are housed in IPDUs  102  and connect to the network switches via IPDC data transmission cables  106 . The network data transmission cables  107 , the auxiliary data connectors  105 , and the IPDC data transmission cables  106  may all comprise different types of cable or cables of the same type, for example ethernet cable. 
         [0024]    Each IPDU  102  is a chassis for housing a plurality of modular IPDCs  103 , wherein each IPDC comprises an electronics board for delivering power and data communication to four microcontrollers  110  in a CIM  109 . Adjacent IPDCs within an IPDU may have network connections  120  to each other. The CIM acts as a “pass-through”, passing power and data to the DCBs  108  of heliostats in the heliostat field. Heliostats are mounted on structures  114  having an alternating tripod pattern, wherein the tripod configuration comprises members of two adjacent heliostat rows. 
         [0025]    Power and data connections between the CIMs and the IPDCs are made via field cables  118 . Power and data connections between the CIMs and heliostats, between adjacent heliostats in a heliostat row, and between heliostats in adjacent rows are made via inter-drive cables. Both field cables and inter-drive cables comprise communication delivery wires  111  and power delivery wires  112 . The field cables comprise one set of power delivery wires and two sets of communication delivery wires. The inter-drive cables comprise one set of power delivery wires and one set of communication wires. Field cables and inter-drive cables may comprise different gauge wires. For instance, the field cables may have a higher gauge wire than the inter-drive cables. In field cables and inter-drive cables both types of wire may be sheathed to form a single cable. Inter-drive cables may comprise coupling connectors on at least one end that can attach to compatible coupling connectors connected to DCBs  108  installed in the heliostats. Communication delivery wires  111  may be twisted pair wires or single-ended wires and may be shielded, for example with plastic material. All data communication pathways are bi-directional, for example the DCBs may send data up to the Plant Network via the CIM and IPDCs. 
         [0026]    As described previously, field cables  118  connect the IPDCs  103  to a plurality of CIMs  109 . Each IPDC comprises an electronics board, a microcontroller, two data communication ports, and PCB connectors for connecting to power delivery wires and communication delivery wires in a field cable. An IPDC may have the additional functions of converting data communication signals to and from the plant network and of monitoring power distribution. Each data communication port on an IPDC connects to one of two sets of communication delivery wires in a field cable. Each CIM comprises an electronics board, microcontrollers  110 , and PCB connectors  119  for passing through power and data communications from the IPDCs  103  to the DCBs  108 . The CIMs facilitate the field termination of field cables from the IPDC and the inter-drive cables from the heliostats and may comprise resistors for minimizing signal reflection over long transmission distances. In a preferred embodiment, each CIM interfaces with four rows of heliostats by connecting to four separate DCBs via inter-drive cables. Communication delivery wires  111  in the inter-drive cables connect a microcontroller  110  in a CIM to the first heliostat of a row, wherein the first heliostat is the closest heliostat to the CIM of the heliostats in the row. The communication delivery wires  111  in the first field cable connect to the CIM microcontrollers for rows N and N+2. The communication delivery wires  111  in the second field cable connect to the CIM microcontrollers for rows N+1 and N+3. 
         [0027]    In a preferred embodiment, the outermost DCBs  108  of two adjacent heliostat rows may be connected via inter-drive cabling to create a communication transmission loop  113  or  117 . Adjacent DCBs in a heliostat row or between heliostat rows are connected to each other in a “daisy chain” for the purposes of data transmission. As visible in  FIG. 2 , Communication Loop  113  comprises the first data communication port on each IP DC, two CIM microcontrollers, and all the heliostats in Row N and Row N+1. Communication Loop  117  comprises the second data communication port on each IPDC, two CIM microcontrollers, and all the heliostats in Row N+2 and Row N+3. In this manner data communication pathways are never interrupted by the failure of a single component in the communication loop. In the event of a microcontroller failure, malfunctioning transceiver, damaged microcontroller power supply, or communication delivery wire failure, data can still be transmitted from the plant network to the heliostats of all four rows by routing through the communication loop in the opposite direction. In an alternative embodiment a single CIM may be used to facilitate data transfer to less than four heliostat rows. 
         [0028]    In a preferred embodiment, the outermost DCBs  108  of two adjacent heliostat rows may be connected via inter-drive cabling to create a power transmission loop  115  or  116 . Adjacent DCBs in a heliostat row or between heliostat rows may be connected to each other in a “daisy chain” for the purposes of power transmission. As visible in  FIG. 2 , Power Loop  115  comprises the CIM and heliostats in Row N and Row N+1. Power Loop  116  comprises the CIM and heliostats in Row N+2 and Row N+3. In this manner power transmission pathways are never interrupted by a single break in the power loop. DC power is ultimately delivered to a pair of heliostat rows from the DC power source for the IPDC via power delivery wires in the field cables that connect an IPDC to a CIM. The DC power source may have a battery bank backup for added reliability. 
         [0029]      FIG. 3  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event that a communication link failure occurs between two DCBs of adjacent heliostats in a row or between the DCBs of heliostats at the end of two adjacent rows (failure is shown to be occurring in row N+2). Possible failure modes may include a damaged or worn out connector, damage to the cable wires themselves, or damage to a communication transceiver. Under these conditions a communication pathway (shown as a bold line) is still maintained to all DCBs in Rows N+2 and N+3. The third CIM microcontroller  110  provides a data communication pathway for the first DCB of Row N+2. The fourth CIM microcontroller provides a data communication pathway for all DCBs in Row N+3 and the remaining DCBs in Row N+2 via the inter-drive cable that connects the outermost DCBs of Rows N+2 and N+3. 
         [0030]      FIG. 4  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event a CIM microcontroller fails (shown to be occurring in row N). Under these conditions a communication pathway (shown as a bold line) is still maintained to all DCBs in Rows N and N+1. The second CIM microcontroller  110  provides a data communication pathway for all DCBs in Row N+1 and all DCBs of Row N via the inter-drive cable that connects the outermost DCBs of Rows N and N+1. 
         [0031]      FIG. 5  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event of a DCB failure (shown to be occurring in row N+2). Possible failure modes include a malfunctioning DCB power supply or failure of the DCB microcontroller. Under these conditions a communication pathway (shown as a bold line) is still maintained to all functioning DCBs in Rows N+2 and N+3. The third CIM microcontroller  110  provides a data communication pathway for the DCBs in Row N+2 from the first DCB connected to the CIM to the DCB immediately before the failed DCB. The fourth CIM microcontroller provides a data communication pathway for all DCBs in Row N+3 and the outermost DCB in Row N+2 via the inter-drive cable that connects the outermost DCBs of Rows N+2 and N+3. 
         [0032]      FIG. 6  displays the same network topology as shown in  FIG. 2  as well as the power delivery pathway in the event of a power link failure between two adjacent DCBs within a power loop (the failure is shown to be occurring in power loop  116 ). Possible failure modes may include faulty connectors at either end of the power delivery wires  112  or damage to the power delivery wires themselves. The third CIM inter-drive cable provides a power delivery pathway for the first DCB of Row N+2. The fourth CIM inter-drive cable provides a power delivery pathway for all DCBs in Row N+3 and the remaining DCBs in Row N+2 via the inter-drive cable that connects the outermost DCBs of Rows N+2 and N+3. 
         [0033]      FIG. 7  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event of a network switch failure. Possible failure modes include damage to connectors, cables, and a malfunction of the network switch. Because all of the network switches have redundant access to the plant network by virtue of their connections to multiple switches, a communication pathway (shown as a bold line) can still be established from the IPDC in the IPDU to an active switch via the network connection  120  between IPDCs. 
         [0034]      FIG. 8  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event a connection between network switches fails. As described with reference to  FIG. 7 , a communication pathway (shown as a bold line) can still be established from the IPDC to an active switch with access to the plant network as a result of redundant connections between active switches. 
         [0035]      FIG. 9  displays the same network topology as shown in  FIG. 2  as well as the data communication pathway in the event of a communication link failure between an IPDC and a CIM. Possible failure modes include failure of the network switches, transceivers, local power supplies, microcontrollers, connectors, or the communication delivery wires. A communication pathway (shown as a bold line) can still be established from the still-functional IPDC to DCBs for all heliostats in the four rows of heliostats connected to the CIM.