Research Projects
Interaction between AC and HVDC system
Introduction
In recent years there has been an increased interest in HVDC networks due to a number of reasons. Many existing bulk transmission systems, e.g. in Europe and North America, have reached their capability limits and a significant increase of the transmission capacities is foreseen within the next decades. There are several reasons calling for this upgrade, where the most significant are the expected increase in new renewable energy sources that are located far away for the load centers and an expected overall increase in consumption of electric energy. Furthermore, the fluctuation nature of many renewable energy sources requires higher transmission capacities in order to provide the regulating power from other power plants. Another important driving force is the latest development in HVDC technology such as high power ratings of semiconductors devices and the introduction of Voltage Source Converters (VSC) for power transmission, which are deemed to make HVDC network a viable option for future transmission systems.
Even if the general conception is old there are numerous technical issues that need to be solved or further elaborated before actual planning, design, and implementation of an actual HVDC network can commence. The aim of this research project is to address some of the most salient questions in order to establish a more solid basis of knowledge and results on which system planners, manufacturers, regulators, and others can base their future decisions and planning activities.
Goal of project
The overall goal of the project is to contribute to answer the question: “Under which conditions is a true HVDC network of advantage and what would be the preferred scheme?”
Key aspects are to determine the layout and operational characteristics of the HVDC network so that the overall benefits and performance of the combined AC and HVDC system is optimal. The most important criteria consider are economy, reliability and stability.
As a basis an optimal power flow (OPF) simulation of the combined AC and DC grid is programmed. This is important to know the changes in power flows in the AC network if a HVDC network is installed. Later the optimal topology of the HVDC network is investigated.
The cost of the HVDC network is another point to investigate. The investment costs to build different topologies are estimated and a cost/benefit analysis is done. The losses in long HVDC lines are smaller than in similar AC lines, therefore loss evaluation is also an issue in this project.
The operation of a true HVDC network needs an appropriate control strategy in steady state and emergency state of the combined AC and HVDC system. If a fault occurs in the AC or DC network the control has to handle the damping for power oscillations after a restart.
