Process Improvement CSP internal bus communications are also a challenge.
About 150,000 tags are communicated through the system buses, which are typically Modbus TCP or Profibus DP. Com- munication from the solar field to the central power plant database has to provide a complete solar field update in less than five seconds. Te distributed control system (DCS) has to be highly
reliable (with 99.99% availability). For this reason, redundancy has to be provided for the control processors, the I/O cards for all analog I/Os for critical control loops, the communication and interface processors, the data storage devices, communi- cation networks and power supplies—so that single compo- nent failures will have minimal effect. The software communication system (SCS) is respon-
sible for managing the huge volume of data traffic and for controlling some of the solar field functions related to the overall behavior of the plant—such as the emergency modes, start-up modes, etc.—and it is fully integrated with the plant (DCS) hardware. Depending on customer specifications, the SCS can be equipped with the same hardware pro- cessor as the DCS or with an industrial PC. This subsystem is critical for secur- ing any kind of point-to-point, event- driven or broadcast communication.
Local Automation Controllers In the case of CSP technologies, the
solar field of each solar thermal plant consists of a system of long pipes in which the fluid is heated by the reflec- tion of the sun’s rays and concentrated by an optical mirror system onto the pipes. The average number of local automation controllers (LOCs) per 50 MW is around 450–640 units, depending on the solar field design and whether the plant has thermal storage. These several hundred devices are connected to a communication bus system that is managed by the SCS in order to avoid communication collapse and to secure data integrity and the time cycle. Te LOCs should accurately calculate the expected posi-
Typical control parameters of a CSP parabolic trough managed by an LOC from an installation in Spain.
Each component and system part should be of proven
reliability. Te minimum reliability of each item of equip- ment—such as the electronic modules/cards, power supply and peripherals—should be such that the availability of the complete system is assured for 99.7% or higher. Te design of the LOC and related equipment should adhere
tion of the sun, as per the National Renewable Energy Labora- tory (NREL) model, and drive the mirror system to track the sun for closed-loop control. Control of the solar field and its coordination with the bal-
ance of plant processes and electrical systems is provided by the LOC, in order to ensure that the temperature and pressure are optimal for each moment of the day and that safety condi- tions like high winds, hail and overpressure conditions are taken into account.
42 Energy Manufacturing 2013
to the principle of fail-safe operation wherever the safety of personnel and plant equipment is involved. Fail-safe operation means that the loss of a signal or the loss of excitation or failure of any component should not cause a hazardous condition. It also means that the occurrence of false trips is avoided.
Control Functionality As pointed out earlier, the control part of the LOC should
be performed by proven standard industrial microprocessor- based PLCs, not by a low-cost dedicated electronic board that is likely to create operational problems for maintenance.
LOC Design Principles Te control part of the LOC is performed by proven
standard industrial microprocessor-based programmable logic controllers (PLCs). Te LOC should have a modular design to facilitate easy
system adaptation to future requirements and achieve an operating life of at least 20 years. Te system should have the capability and facility for expansion through the addition of controller modules, I/O communication cards, etc., as well as for future soſtware modifications. Te LOC should be easy to maintain. Each hardware part
of the LOC should be supplied by an industrial standards manufacturer and be able to be replaced within a reasonable time anywhere in the world.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194