Distribution system operators in rural areas of Germany are frequently facing imminent equipment overloading caused by the feed-in of local renewable Distributed Generation (DG). A grid operator's last resort to maintain system stability and avoid protection tripping is to temporarily curtail local feed-in until hosting capacity in the network has caught up with the demand. Due to technological limitations in today's networks the volume of curtailed energy can be greater than what would strictly be necessary. This paper presents a case study of a 110 kV overhead line in Avacon´s network and demonstrates the limitations of today's approach to DG curtailments, especially the relative coarse granularity of control steps. The authors develop a novel control algorithm for emergency curtailments that takes advantage of technological improvements and describes the architecture for a successful deployment at the example of Avacon´s network and SCADA. The authors compare the amount of curtailed energy under today´s best practice with the theoretical optimum and the novel approach.
Microgrids (MGs) are considered one of the key enabling factors of future electric power systems. Their limited size allows optimal control, as the solution space of optimization problems increases exponentially with the number of assets, if significant model simplifications are not undertaken. Additionally, the capability to disconnect from the main grid and autonomously supply loads can serve to increase the resilience to failures in the main grid and be provided as a service to the Distribution System Operator (DSO). An energy management system (EMS) is responsible to facilitate the optimal use of resources; however, optimality can refer to a multitude of target objectives. This paper builds up on previous research, implementing a Model Predictive Control (MPC) based EMS that is used to show the trade-off between four different objectives in MG operation. The different objective functions are the minimization of operational cost, minimization of the energy exchanged with the main grid, minimization of resistive losses and maximization of potential islanding time (PIT) for a possible future islanding event.
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