Author: Systems Control Division / Wang Jian
I. MARK VI System Overview
As the first gas turbine manufacturing plant in the world today, GE has used its decades of experience in gas turbine manufacturing and control. The SPEEDTRONIC series of Mark VI control systems upgraded on the basis of the original Mark V has been widely used in GE's various types of combustion. On the machine control system. It has accumulated GE's successful turbine control, protection, and sequence control concepts that have been proven over a long period of time. It has features such as configuration honors, hardware building blocks, software modularization, control configuration, and humanized diagnosis. The three-redundant TRM (Triple Modular Redundant) structure of control modules (R, S, T) and protection modules (R8, S8, T8) and Software Implemented Fault Tolerant (SIFT) have obvious features. It is more reliable than the universal distributed control system (DCS).
Second, MARK VI system network structure
Mark VI control system network is divided into three levels of data communication network, namely PDH network, UDH network and IONET network.
Mark VI control system is based on the network hierarchy, he used to connect individual nodes, these networks according to individual functions to different communication information assigned to different levels. These levels include the enterprise level, supervisory level, control level, and IO level. Enterprise layer: DCS sends data from the plant data highway through the router or HMI data server to the LAN. The supervisory layer: Through the HMI operator in the management layer, remote data acquisition and operation can monitor the operation of the unit; Layer: consists of a controller, a device data highway, etc. The communication between the controller and the controller is implemented between the control layers; the IO layer implements communication between the controller and the module through the IONET network. The communication protocols of each layer are different. The MARK VI system connects the IO components, controllers, HMI, MIS, etc. through the communication network.
MARK VI system network structure diagram
For small systems, HMI Servers and HMI Viewer functions are combined, and PDH is often combined with UDH.
2.1 Plant Data Highway PDH (Plant Data Highway)
PDH adopts Transmission Control Protocol/Internet Protocol (TCP/IP), which is a communication protocol of transmission control protocol/Internet protocol. Its communication method is broadcast type, and it has carrier monitoring, multiple access/collision detection CSMA/CD (Carrier Sence Multiple Access/ The Collision Detection function allows multiple sites sharing a transmission line to randomly access transmission lines. Each site is equally competitive and uses 32-bit CRC (Cyclic Redundancy Check) error correction techniques.
The PDH network speed is 100Mb/s, and can connect up to 1024 contacts. When two twisted-pair cables are used between adjacent two nodes, the longest transmission distance is 100 meters. When using a fiber optic cable, the maximum transmission length is 2000 meters.
PDH is used by the system to network the HMI (Human Machine Interface) server with operator stations, printers, historical data stations, etc., to monitor the unit. PDH is also used for data communication with non-GE systems such as DCS or third-party control devices. PDH and DCS communication protocols include Ethernet TCP/IP GSM Ethernet, TCP/IP Modbus slave, and RS232/485 Modbus RTU.
2.2 Device Data High Speed ​​Network UDH (Unit Data Highway)
UDH is used for communication between controllers. It is not open to the outside world. It provides high-speed peer-to-peer peer-to-peer communication between the gas turbine controller, the turbine controller, the generator excitation controller EX2100, and the static starter LCI.
UDH is an Ethernet-based network that uses UDP/IP (User Datagram Protocol/Internet Protocol) or user datagram protocol/international protocol. The protocol standard is EGD (Ethernet Global Data) Ethernet global data protocol. Like PDH, UDH communication is also broadcast type, using CSMA/CD technology, and also uses 32-bit CRC cyclic redundancy check error checking technology. It can receive GPS (Global Positioning System Global Positioning System) signal to realize clock synchronization. The supported synchronization signals are: IRIG-A, IRIG-B, NASA-36, timing pulse, etc., with an accuracy of ±1ms.
UDH can support up to 10 nodes, and the network speed is 100Mb/s. When two twisted-pair cables are used between adjacent two nodes, they can transmit up to 100 meters. When using optical fibers, they can transmit up to 2000 meters.
Although the UDH supports control parameter communication between different controllers, each control loop is completed within its own controller. In addition, to ensure reliability, all trip instructions between the controller and from the DCS are hard-wired.
UDH and PDH are based on CIMPLICITY graphical interface and Windows operating system servers (HMI). These servers are used as local/remote operator stations or engineering stations for human-machine communication and control maintenance.
2.3 I/O bus (IONET)
IONET is an Ethernet-based network for communication between three control processors, three protection modules, and expansion modules in the Mark VI control cabinet. The network is also three-redundant.
IONET uses ADL (Asynchronous Drives Language) which is asynchronous device language to vote on controller data. It is a master/slave communication structure. The VCMI communication card acts as a master station to select which slave station to use for data transmission. The 32-bit CRC error check technology is used. The network rate is 10 Mb/s and can support up to 16 nodes. When using coaxial cable, the distance between two adjacent nodes can transmit up to 185 meters, while using optical fiber cable can transmit up to 2000 meters.
Third, the MARK VI system and NT6000 DCS system connection
Through the analysis of the three network characteristics and functions of the Mark VI control system, and the system security and reliability considerations, Mark VI can communicate with the DCS system through the PDH or the HMI itself. There are three ways to connect with other DCS systems.
From human-machine interface server RS-232 port or optional dedicated gateway controller to DCS serial Modbus slave connection, support MODBUS RTU and MODBUS ASCII mode;
High-speed 100MB Ethernet connection via Modbus slave using TCP/IP protocol;
High-speed 100MB Ethernet connections are implemented via the TCP/IP protocol via an application layer called GEDS Standard Messages (GSM).
GSM supports turbine control commands, MARK VI data and alarms, alarm mute functions, logic events, and contact input event records with 1ms accuracy. MODBUS is widely used in DCS connections, but the advantage of Ethernet GSM is its more compact integration.
For a small system, the PDH is generally not set. The MARK VI does not directly transfer data to the SIS or MIS. Instead, it communicates to the DCS first. The DCS integrates all the data and integrates the interface with the SIS.
3.1 Comparison of Three Communication Methods
Each of the three communication methods has its own advantages and disadvantages:
Serial MODBUS: The communication is slow to realize, can't integrate all data, the configuration is more troublesome, influenced by outside interference, reliability is bad, its advantage is that the communication protocol supports most distributed control systems;
Ethernet MODBUS: Poor integration, unable to integrate all data, configuration is cumbersome and has poor reliability, but it is widely used in distributed DCS systems like serial MODBUS.
Ethernet GSM: high degree of integration, can integrate all the data including event records, alarm records, SOE, easy configuration, communication speed, high efficiency, high reliability, the disadvantage is poor generality;
MARK VI System and DCS System Connection Diagram
Modbus-based communication simply transmits data. Because all aspects of Modbus communication cannot effectively achieve full control from DCS to MARK VI, thorough system connection must be made. DCS must communicate with MARK VI via GSM. .
3.2 Connection of MARK VI System and NT6000 System Based on Ethernet GSM Protocol
The application layer protocol of GSM (GE Industrial Systems Standard Messages) provided by GE is used by the GE Human Interface Server to transfer data with the DCS data server through the PDH or UDH platform. GE's Human Interface Server is the source of Ethernet GSM communications. GSM supports four types of application-level messages.
Management messages: From the human-machine interface to the DCS, which carries a support device information that describes the systems that can be used for the connection's communications and the availability of regular communication connections.
Event-driven messages: Naturally sent from the human-machine interface to the DCS when a system alarm or system log occurs or the contact input (SOE) is closed or turned on. The sending of each logical point is accomplished by a single header time stamp.
Periodic data message: A specific group of data points, defined by DCS, and sent by a set of time stamps. All 5,000 data points in the MARK VI control device can be sent to the DCS at a periodic rate of 1 s. DCS can define a list of multiple data by means of the controller's name and point name.
Public request messages: Includes turbine control commands and alarm queue commands. They are sent from the DCS to the human interface. Turbine control commands include instantaneous logic control commands (such as upgrade and start-stop commands) that have module setpoint target commands. Alarm queue commands include silence, device alarm horns, and reset command already alarm accumulation requests that enable the entire alarm queue to be sent from the MARK VI control device to the DCS.
Through GSM communication, DCS can monitor all operating conditions of the turbine, and can control it, and can monitor and intervene with the operating conditions of the MARK VI system, crew alarms, etc. However, Modbus communication cannot achieve all the functions of GSM. In most cases, GSM communication must be implemented.
The GE6000 interface software of the NT6000 system is responsible for implementing GSM communication with GE. Through the Ethernet TCI/IP GSM protocol, the GEGSM interface software obtains real-time data, events, alarms, and other data from the GE Mark VI control system. At the same time, it provides external OPC or DDE data services. In order to adapt the needs of the system such as engineering unit conversion, the interface software integrates general data computing functions such as addition, subtraction, multiplication, division, and square root. The data exchange diagram between DCS system and Mark VI control system is as follows:
GEGSM DDE/OPC Server program running interface
Through the GSGSM OPC/DDE Servers interface software, the difficulty of direct communication between DCS and non-standard protocol GSM is solved, which lays a foundation for the integration of monitoring information of combined cycle units. This program has been successfully applied to practical projects. The figure above shows the real-time interface of a project GEGSM communication. All GE Class 4 information is periodically exchanged through this software packet. The entire communication volume is over 1200 points, and the communication sampling period is 1s, and the communication is reliable and stable. The DCS monitors the gas turbine system and simultaneously uploads all data from the DCS to the plant level information monitoring system, achieving the goal of integration.
3.3 The significance of communication based on the GSM protocol
At present, natural gas power generation, as a kind of new energy, is increasingly receiving attention and advocacy, and the share of natural gas power generation is gradually increasing. As a leader in the gas turbine industry, GE's DCS system for natural gas combined cycle units is paying more and more attention to communication with the MARK VI system. At the same time, with the process of localization of DCS systems, whether to support GSM communication has become a rigid indicator of the performance of domestic DCS systems. The implementation of the NT6000 system based on GSM communication with the GE MARK VI system will surely lead the field in natural gas combined cycle units.
Ningbo Autrends International Trade Co.,Ltd. , https://www.supermosvape.com