Integration of Renewable Energy With Embedded High-Voltage dc Links in Brazil: A Time-Synchronized Angle Difference Controller

The continental-size Brazilian interconnected power system is divided into four geo-electric regions with different seasonal wet and dry conditions, all synchronously connected by extra high voltage ac lines. This natural characteristic emphasizes the importance of the transmission system among the regions. Bottlenecks in those connections may reflect in local energy shortage in one region and water spillage in another region, since Brazil is still a hydroelectricity powerhouse. Recently, the high share of hydro generation is being reduced, as wind and solar generation have significantly increased. Due to the fast-paced growth of wind and solar generation, Brazil has decided to increase the participation of HVdc transmission between the geo-electric regions, to transfer the surplus of wind and solar generation from one region to another. The growth of renewable energy with its intermittent characteristics, paired with market-based generation dispatch, has put new demands on the control systems of embedded HVdc links. Those uncertainties demand an adaptable HVdc power flow control to avoid adverse effects such as loop power flows and increased transmission losses. Through computer simulation the paper presents a time-synchronized controller that modulates the HVdc power flow setpoints according to the difference of the rectifier and inverter voltage phasor angles. The ongoing installation of phasor measurement units at the HVdc converter stations sets the ground for the planning of a wide-area monitoring, protection and control system able to coordinate the present and future embedded HVdc links.