HVDC Classic control system

The control system is the brain in an HVDC transmission system.

One major advantage of a HVDC transmission is its controllability. A modern HVDC station is equipped with a well integrated microprocessor based control and protection system.

The basic power control is achieved through a system where one of the converters controls its DC voltage and the other converter controls the current through the DC circuit. The control system acts through firing angle adjustments of the thyristor valves and through tap changer adjustments on the converter transformers. Each pole in a bipolar ABB HVDC link has its own control system and each control system is duplicated. In the normal mode, the control systems of the two stations of a two-terminal HVDC system communicate with each other through a telecommunication link between the stations. Most of the ABB HVDC transmissions are remotely controlled from a dispatch center for the grid.

The MACH2™ control and protection system developed by ABB is fully digital. All functions for control, supervision and protection of the stations are implemented in software running in a family of microprocessor circuit boards.

Highest performance and specifically developed for HVDC.

MACH2^TM, is designed specifically for converters in power applications, meaning that many compromises have been avoided and that both drastic volume reductions and substantial performance improvement have been achieved.

The MACH2 system is the highest performance HVDC control and protection system on the market. It has gradually evolved from an unequalled installed base of HVDC control systems around the world. MACH2 is today also used in conventional SVC, HVDC and SVC Light and a number of other applications. Integrated with the MACH 2 control and protection equipment is the Station Control and Monitoring (SCM) system. Work stations (PCs) are interconnected by a local area network. The distributed system for remote I/O, for control as well as for process interfacing with the SCM system, is built up by a field bus network.

Main computer in MACH2

The most important part of the control system, the converter firing control, is built around a host 1.3 GHz Pentium III dual-processor system and six high performance digital signal processors (SHARC). This gives an unequalled calculation capacity that is used to fine-tune the performance of the converter firing control system during various system disturbances.

The fact that high performance industrial computer components are used, assures that ABB can fully utilise the extremely fast development in the field of micro processors and always design the control and protection system for the highest possible performance.




MACH2 - Open systems strategy and redundant system for maximum security.



Open systems strategy
The development in the field of electronics is extremely fast and the best way to make sure that the designs can follow and benefit from this development is to build all systems based on open interfaces. This can be done by using international and industry standards wherever possible as these types of standards have a long life and assures that spare parts and enhancements are readily available. The open systems strategy in MACH2™ is reflected both in the use of industrial standard serial and parallel communication buses, as well as in the use of standard formats for all collected data (such as events, alarms and disturbance data).

Redundant system for maximum security

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All critical parts of the system are designed with inherent parallel redundancy in accordance with the principles used by ABB for HVDC since the early 80's. The redundant systems are designed as duplicated systems acting as active or hot standby. At any time only one of the two systems is active, controlling the converter and associated equipment.

The other system, the standby system, is running, but the outputs from that system are disabled. If a fault is detected in the active system, the standby system will take over the control, with no disturbance to the transmission.

HiDraw screen dump. Click to enlarge)

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Most application software for the MACH2TM system are produced using a fully graphical code generating tool called HiDraw. This facilitates the programming enormously and improves the quality of the software.

HiDraw can be run on any industry standard Windows compatible computer and is very easy to use, as it is based on the easiest possible pick, drag, place method. It is designed to produce code either in a high level language (ANSI standard C) or in assembly language. For functions not available in the comprehensive library (one for each type of processor board) it is very easy to design a new block and link to the schematic with a simple name reference.

	For debugging, a fully graphical debugger, called HiBug, operating under Windows is used. HiBug allows the operator to view several HiDraw pages at the same time and look at any internal software "signal" in real time by just double clicking on the line that represents the signal. Parameters can easily be changed by double clicking on their value.

Efficient tools for control, monitoring and analysis of HVDC transmission systems is of great importance.



The relevance of a well designed and flexible Human Machine Interface (HMI) is obvious when it comes to more demanding application areas such as HVDC power transmission. These systems must also in all parts be easy to use in order to avoid human errors. It must be able to announce alarms and perform operator controls in a safe and reliable way. Wrong operator actions due to a bad HMI is not acceptable and could be very costly.

The requirements on these types of tools are therefore high. It is for example necessary to handle several thousands of measured values, indications and alarms of different types. All changes of state of these signals must be recorded with high time resolution for accurate real time and post fault analysis. Time resolution down to one millisecond between the stations is often required.

The new generation of integrated HMI adopted by ABB in MACH2™, the Station Control and Monitoring (SCM) System, employs the most advanced software concepts with regard to system openness and flexibility as well as ergonomic aspects. A number of different power companies have given valuable contributions to this work.

Distributed over an Ethernet LAN, the SCM system comprises several operator workstations (OWS) and SQL servers. The Windows based OWSes are characterised by high performance and an open software architecture based on the latest trends in data engineering.

The SCM system integrates a large number of features such as:

• Control of the HVDC from process images
• Sequence of Event Recorder (SER)
• Archiving of events
• Powerful alarm handling via list windows
• Effective user defined data filtering
• Flexible handling of both on-line and historical trends
• On-line help functions and direct access to plant documentation
• TFR analysis
• Remote control
• Instant access to standard applications such as e-mail, word processing, spreadsheet, Internet
• Automatic performance report generation developed with the most versatile graphical package

Modern Man-Machine Interface for HVDC Systems


Quality is of paramount importance in MACH2.



To achieve high reliability in MACH2^TM, quality is built into every detail from the beginning. This is secured by careful component selection, strict design rules and finally by extensive testing of all systems.

The tests are finalized by an extensive factory system test where the function and performance of the complete control and protection system is tested during normal and disturbed operation. The factory system test is performed using a real time HVDC simulator, meaning that the complete system can be tested in a very realistic way. The extensive factory system test is a guarantor for fast and trouble free field commissioning of the HVDC system.