Minas Patsalides

Assessing the power quality behaviour of high photovoltaic (PV) penetration levels inside the distribution network

In recent years, increasing concerns about climate change and the liberalisation of energy market have provided the necessary impetus for a revolutionary restructuring of the electricity network at every level, namely production, transmission and distribution. Increased electricity production from renewable energy sources (RES) coupled with energy efficiency lie at the heart of the ambitious targets set by Europe in the quest to curb greenhouse gas emissions and to reach energy sustainability. Therefore the security and stability of the power system should be considered carefully to identify possible impacts due to uncontrolled deployment of RES. This paper focuses on the study of varying concentrations of photovoltaic (PV) systems on a proposed electricity grid in an attempt to assess the power quality response of the power system. The study has been performed using a detailed PV system model. The model is initially validated using data from the output of PV systems and then this is used for the study of varying PV penetrations on common distribution system topologies. The results are compared to international power quality standards.

Thevenin equivalent circuit for the study of high photovoltaic penetration in distribution grids

The electricity grid is unidirectional operating in a passive way and consequently it is not yet ready to accept high penetration of renewable energy sources (RES). Further research is required to assess the impact of distributed Photovoltaic (PV) generation on power quality and establish the necessary measures for the restructuring of the electricity grid to ensure its optimum operation. In this paper, appropriate models are developed in order to assess the effects of PV generation. Thevenins theorem is used to develop the equivalent circuit representing the exact distribution grid behaviour. The Thevenin equivalent circuit in combination with a verified PV system model are employed to study the power quality response of the distribution grid in the presence of PV via simulation and the results are compared to actual measurements yielding good agreement.

The impact of simulation studies on the distribution grid operation and planning in Cyprus

Simulation tools offer a wide range of prospective advantages that give utilities and system operators the ability to improve power quality and operational costs. The use of such tools can make the analysis/study of complex power networks simpler, giving valuable answers about the power quality behaviour of electricity networks in the presence of intermittent renewable energy generation and can help in reducing undesirable energy losses. In this work, steady-state simulations are performed by undertaking measurement investigations and model development in order to assess the impact of such studies on system planning and operation. By using DigSILENT PowerFactory, typical feeders of Nicosia district, Cyprus are realized into circuit form and simulated while considering demand and renewable energy production time series measurement data. The aim of the paper is to reveal the operational benefit of using design and analysis tools for proactive or corrective actions. From the simulations, it has been shown that network reconfiguration tasks lead to the reduction of power losses which can inevitably create an economic benefit for electricity utilities. In addition, simulation tools can help utilities meet challenging voltage regulation requirements/issues. One example of eliminating voltage violations through transformer tap optimization is also provided.

New voltage regulation scheme for photovoltaic systems based on Thevenin's Theorem

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 Thevenins 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.