The replacement of conventional generation sources by DER creates the need to carefully manage the reactive power maintaining the power system safe operation. The principal trend is to increase the DER volume connected to the distribution network in the coming years. Therefore, the microgrid represents an alternative to offer reactive power management due to excellent controllability features embedded in the DER, which enable effective interaction between the microgrid and the distribution network. This paper proposes a microgrid−iterative reactive power management approach of power-electronic converter based renewable technologies for day-ahead operation. It is designed to be a centralised control based on local measurements, which provides the optimal reactive power dispatch and minimise the total energy losses inside the microgrid and maintain the voltage profile within operational limits. The proposed optimal-centralised control is contrasted against seven local reactive power controls using a techno-economic approach considering the steady−state voltage profile, the energy losses, and the reactive power costs as performance metrics. Three different reactive power pricing are proposed. The numerical results demonstrate the optimal microgrid−interactive reactive power management is the most suitable techno-economic reactive power control for the day−ahead operation.
The integration of renewable resources is quickly growing in the Nordic power system (NPS), and it has led to increasing challenges for the operation and control of the NPS. Nordic countries require that the first-generation power plants have a more flexible operation regime to overcomes power imbalances coming from fluctuations of the demand and supply. This paper assesses optimal frequency support of variable-speed hydropower plants installed in Telemark and Vestfold, Norway, considering future scenarios of NPS. The total kinetic energy of the NPS is expected to be significantly reduced in the future. This paper looks into the implementation of hydropower units with a variable-speed operation regime and battery energy storage systems (BESS), equipped with fast-active power controller (FAPC) technology, to provide fast frequency response after a system frequency disturbance. The frequency support was formulated as an optimization process; therefore, the parameter of the FAPC was optimally calculated for future scenarios of low inertia in NPS. Three main futures scenarios were developed for technology penetration in the Vestfold and Telemark area in Norway. The simulation results showed that the integration variable-speed hydropower units and BESS technologies improved the frequency response even in low-kinetic energy scenarios.
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