Renewable energy sources are expected to have a considerable share in the global energy mix over the next years and consequently further research is required to enhance the planning strategies, modify prudently the existing standards and set quality levels on delivered power in order to accommodate the penetration of these technologies. Depending on the distribution grid dynamics and the load demand, the amplitude of voltage may vary significantly, and therefore proper simulation models are required for performing dedicated studies. In this study, a simplified and accurate model representing the distribution grid dynamics is introduced for power quality studies in the presence of distributed photovoltaic (PV) generators. The proposed simplified distribution grid model (SDGM) is validated using measurements and it is then used along with a verified PV system model to estimate the voltage variation and PV capacity of the distribution grid under investigation. Moreover, a sensitivity analysis is performed by varying the parameters of the SDGM to assess how the PV capacity is altered. As a last step, common voltage regulation schemes are analysed through the use of the proposed model, validating operational modes that can accommodate high distributed PV capacities.

The high penetration of the Renewable Energy Sources and other emerging technologies likely to be installed in future power grids will pose new operational challenges to grid operators. One of the main issues expected to affect the operation of the power grid is the impact of inverter-based technologies to the power system inertia and, hence, to system stability. Consequently, the main challenge of the future grid is the evaluation of the frequency stability in the presence of inverter-based systems and how the aforementioned technology can support frequency stability without the help of the rotating masses of the traditional power grid systems. To assess the above problem, this paper proposes a methodology to evaluate the frequency stability in a projection of the real distribution grid in Cyprus with the time horizon to be the year 2030. The power grid under investigation is evaluated with and without the presence of smart hierarchical controllers for providing support to the power system under disturbance conditions. The advanced controllers were applied to manage the available power resource in a fast and effective manner to maintain frequency within nominal levels. The controllers have been implemented in two hierarchical levels revealing useful responses for managing low-inertia networks. The first is set to act locally within a preselected area and the second level effectively supporting the different areas for optimal operation. After undertaking a significant number of simulations for time-series of one year, it was concluded from the results that the local control approach manages to minimize the frequency excursion effectively and influence all related attributes including the rate of change of frequency (RoCoF), frequency nadir and frequency zenith.

The distributed and stochastic nature of Renewable Power Sources is certainly forming considerable challenges for the operation of the power system. Specifically, the stability of the system can be jeopardized when the penetration of inverter-based systems is high. Storage and the proper design of controllers is seen as part of the solution for supporting the future expansion of distributed systems. Thus, control strategies need to be designed to provide the appropriate support to the system and be capable of keeping the variation of the frequency within limits to keep the reliability of the system as high as possible. The main challenge is the appropriate parameterization of these distributed controllers and their coordination under the integrated grid approach in securing the stability of the system at all times. In this paper, a smart energy controller is utilized and incorporated into the projection case study for Cyprus’ real distribution grid for the year 2050 to evaluate its behavior and identify possible weaknesses in its usage. It was found that the parameterization and not only the architecture of such controllers is crucial in coping with the frequency variation and stability problem. From the simulation work and recorded results, it was observed that the smart energy controllers can maintain frequency variation within the desirable range when the parametrization of the controllers is chosen appropriately. This specific observation highlights the need to evaluate and configure the smart controllers while operating in the field, and possibly further research is required to provide the advanced capability to such systems to adjust dynamically during field operation, thereby achieving better response during abnormal conditions.

The distribution grid structure is expected to change in the upcoming years with the further penetration of renewable energy sources (RES). Most of the energy needs will be covered by local distributed generators (DG) responsible also for maintaining good levels of power quality and grid stability. As a consequence, measures for regulating the voltage within acceptable levels will be required as well as storage to allow proper utilization of produced energy and to ensure that the distribution grid operates in an uninterruptable and healthy way. In this work, a new voltage regulation scheme inspired by Thevenin's Theorem is developed and presented. The well-known dynamic power factor method is modified accordingly to provide a variable lower limit, which is defined by the Thevenin equivalent impedance (TEI) measured at the point of common coupling with the electricity grid. The new voltage regulation scheme is incorporated into the control circuit of a verified Photovoltaic (PV) system model for its further evaluation via computer simulations.