Enabling a Robust Future HVDC Grid

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High Voltage Direct Current Transmission (HVDC) Systems are seeing increasing use for the transport of energy. Compared with ac transmission, dc transmission has lower power loss and can perform the role of a firewall, thereby preventing the cascading propagation of dangerous disturbances across a large network. This feature facilitates the interfacing of renewable energy resources. HVDC Systems are undergoing a revolutionary transformation due to recent advances in semiconductor technology and new circuit topologies such as the multilevel modular converter (MMC), which overcome the deficiencies of line commutated converters (LCC) used in the past. The increased HVDC penetration is resulting in multi-infeed configurations where several HVDC converters feed into the same ac system, with the potential for adverse interactions. The long-term objective of the research is to investigate new control methods and configurations for HVDC Transmission Systems to make the future HVDC grid more effective and resilient. In order to do this, the Discovery Grant will investigate three broad directions. Firstly, the research will attempt to improve converter behavior by co-ordinated control of the multiple converters, either in a multi-infeed or dc grid configuration. One area of interest will be to reduce the risk of commutation failure in LCC converters by coordinating the controls of nearby converters. As the phenomena are highly-non-linear, the primary study approach will be to use electromagnetic-transient simulation supervised by Monte Carlo simulation and non-linear optimization algorithms. Secondly, the research will investigate the ability of HVDC converters to damp dangerous oscillations in the network and prevent instability. Wide-area control methods will be investigated which use information transmission between remote converters. However, it is important to ensure that the system is robust to operating point changes, signal transmission latency and loss of communication. Small signal modeling coupled with recent robust control approaches will be used. Novel ways of controlling the MMCs such as using the stored energy in the MMC's capacitors appear promising. Thirdly the research will investigate new control methods for HVDC has been used for evacuating power from remote offshore power plants and for providing energy to remote locations such as oil platforms. Proposed approaches would include autonomous control algorithms that impart inertia-like behavior to the converters to operate them with a frequency droop characteristic. Other approaches include direct control where the phase locked loops of the converters are properly synchronized. The research will result in lower loses and resilient energy transmission networks in Canada and elsewhere. It be carried out in collaboration with several Canadian utilities and consulting companies, thereby improving their competitiveness.