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.

No abstract

No abstract

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.

The Altai-Uliastai regional power system (AURPS) is a regional power system radially interconnected to the power system of Mongolia. The 110 kV interconnection is exceptionally long and susceptible to frequent trips because of weather conditions. The load-rich and low-inertia AURPS must be islanded during interconnection outages, and the under-frequency load shedding (UFLS) scheme must act to ensure secure operation. Traditional UFLS over-sheds local demand, negatively affecting the local population, especially during the cold Mongolian winter season. This research paper proposes a novel methodology to optimally calculate the settings of the UFLS scheme, where each parameter of the scheme is individually adjusted to minimise the total amount of disconnected load. This paper presents a computationally efficient methodology that is illustrated in a specially created co-simulation environment (DIgSILENT® PowerFactoryTM + Python). The results demonstrate an outstanding performance of the proposed approach when compared with the traditional one.

No abstract

The Nordic power system is continuously changing, and it has been experiencing a growing replacing of conventional power plants with renewable power plants, this together with other factors are causing reduction of the total inertia of the Nordic power system. The application of technologies that emulates the dynamic response of the synchronous generators has been a feasible solution. This paper focuses on finding the bests control adjustment of the fast-active power injection/absorption (FAPIA) model by using an optimization algorithm. The FAPIA model has two frequency sensible control actions: a proportional control (K-f) and a derivative control (K-df/dt). The optimization problem is defined using the gains of the proportional and derivative control together with the volume of FAPIA model contribution as decision variables. Two objective functions are determined based on two system frequency response indicators: minimum frequency, the and steady-state frequency. A simplified version of the Nordic power system is implemented for system frequency response studies.

Mongolia power system (MPS) is evolving quite fast, and the integration of renewable resources (mainly wind power and solar photovoltaic) reached 20% by 2019. The MPS is interconnected to Russia in order to cover local energy deficits, especially during freezing winters. However, the interconnection to Russia is a sensible element of the MPS, especially from the frequency control and stability point of view. This situation was evident during the sudden disconnection of the two interconnecting lines that provoked the major event of 29 th June 2018, disconnecting 112 MW by the action of the Under-Frequency Load Shedding (UFLS) and making more than 1.5 million without electricity that day. This paper is dedicated to using numerical time-domain simulations to assess the existing UFLS schemes installed in the MPS. As the MPS is especially sensitive to disconnection from the Russian grid, this event is used to assess the suitability of the UFLS considering two scenarios: Summer and Winter. Results of this research paper have demonstrated that the actual UFLS scheme is not enough to avoid frequency collapse in real-life conditions during the Summer lowdemand and low inertia scenario.