Abstract
Frequency stability is an important issue for the operation of islanded microgrids. Since the upstream grid does not support the islanded microgrids, the power control and frequency regulation encounter serious problems. By increasing the penetration of the renewable energy sources in microgrids, optimizing the parameters of the load frequency controller plays a great role in frequency stability, which is currently being investigated by researchers. The status of loads and generation sources are received by the control center of a microgrid via a communication system and the control center can regulate the output power of renewable energy sources and/or power storage devices. An inherent delay in the communication system or other parts like sensors sampling rates may lead microgrids to have unstable operation states. Reducing the delay in the communication system, as one of the main delay origins, can play an important role in improving fluctuation mitigation, which on the other hand increases the cost of communication system operation. In addition, application of ultra-capacitor banks, as a virtual inertial tool, can be considered as an effective solution to damp frequency oscillations. However, when the ultra-capacitor size is increased, the virtual inertia also increases, which in turn increases the costs. Therefore, it is essential to use a suitable optimization algorithm to determine the optimum parameters. In this paper, the communication system delay and ultra-capacitor size along with the parameters of the secondary controller are obtained by using a Non-dominated Sorting Genetic Algorithm II (NSGA-II) algorithm as well as by considering the costs. To cover frequency oscillations and the cost of microgrid operation, two fitness functions are defined. The frequency oscillations of the case study are investigated considering the stochastic behavior of the load and the output of the renewable energy sources.
Highlights
Microgrids are small power networks that are composed of loads, distributed generations, energy storage resources, telecommunication facilities and other infrastructure [1,2]
The frequency oscillations of the case study are investigated considering the stochastic behavior of the load and the output of the renewable energy sources
Since the source is less than thesystem power for electric or the consumption of loads at their peak, the performance of this isrequired similar is to the voltage source inverter, transfer function offunction this power ultimate performance of this system similar toloads the voltage sourcethe inverter, the transfer of fuel cell begins to generate power by injecting hydrogen stored in its hydrogen tank
Summary
Microgrids are small power networks that are composed of loads, distributed generations, energy storage resources, telecommunication facilities and other infrastructure [1,2]. As discussed above, improving the inertia of microgrid and reducing the time delay of the communication system are effective methods to overcome frequency oscillations. This approach increases the operation cost of a microgrid. It is essential to select optimum values of time delay and Ultra capacitor size to have acceptable frequency oscillation of a microgrid and operation costs. With considering the challenges that discussed above, this paper aim is determining optimal virtual inertia, comunication delay time and frequency control parameters simultaneously that are not investigated in privious papers.
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