Advanced HVDC Converter Applications in the Modern Power Grid

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High Voltage Direct Current (HVDC) transmission is growing in importance. Power generators are usually ac (alternating current) generators, and most loads are also ac. The HVDC transmission system connects these together by transforming the ac voltage to dc and then back to ac. In comparison with ac transmission, HVDC has reduced losses and does not require the sending and receiving end ac networks to be synchronized. Consequently it is seen as a preferred means to transport renewable energy from remote locations such as remote wind farms, to distant load centres. **Conventionally, the Line Commutated Converter (LCC) has been the only type of ac-dc converting equipment to handle large power ratings. Its drawback is that it works poorly under distortion or under-voltage conditions. However, two other types of converter, the Voltage Sourced Converter (VSC) and the Capacitor Commutated Converter (CCC) have recently been introduced and are not susceptible to this problem. As HVDC penetration in the network grows, it is more and more likely that HVDC converters of different types (i.e. LCC, VSC, etc.) will terminate in close proximity and interfere adversely with each other. The resulting system is referred to as a multi-infeed HVDC system. Using advanced computer simulation tools, I intend to investigate the sensitivity of such inter-converter interactions to various network parameters, with a view to establishing guidelines for converter placement. My team and I hope to develop improved control algorithms that would minimize such interaction. Another objective of our research is to develop techniques to estimate the losses in VSC converters, with a view to determining the operating conditions under which these are minimized. **The significant outcome of this research will be the development of study methods, modelling tools and improved designs for multi-infeed HVDC systems and dc grids. This will hopefully result in more robust power transmission schemes that can operate securely, efficiently and reliably.**********