The emergence of renewable energy sources to meet society’s energy demands while being more environmentally sustainable has created new challenges for utilities. It’s becoming more common that electricity is generated by renewable energy sources located far away from load centers and requires advanced transmission technologies to deliver the power efficiently and reliably. HVDC is perfectly suited for these situations of integrating bulk power renewable energy over long distances.
To elevate the intermittency of new generation sources, interconnection between adjacent power systems with HVDC systems is becoming more critical.
HVDC allows asynchronous power systems to be coupled with ease, and gives the operator fine control of power flow between the two. This allows integration of otherwise separate markets, bringing benefits such as reduced spinning reserve, lower intermittency, higher resilience, and the option to take advantage of price differentials. Where the power systems are in the same vicinity a back-to-back configuration cab be used. In this case, the two converters can be co-located in the same site and building, with no cable of over-head line required.
Power flows are increasing in areas of high demand, such as densely populated urban centers; as well as rural areas, where new, often renewable, generation is being connected . However, right-of-way permits for construction of new over-head line are taking longer and longer. Reinforcement through HVDC is typically a faster solution. This has added benefits, such as precise control over power flows, elevating existing stability limitations and ancillary benefits, such as black-start capability.
New sources of power generation, such as renewables, are typically located at large distances from load centers. In this case, connection through HVDC is the economical solution, when considering reactive power compensation requirements and overall system stability with an ac-based alternative. In the case of off-shore wind-farms, where very long sections of cable are required, transmission through HVDC is the optimum choice.
VSC Ancillary Functions
VSC-based HVDC has a number of benefits over traditional Line Commutation Converter (LCC) HVDC. A number of ancillary control functions are possible, thanks to the ability to arbitrarily control the output voltage such as: