Scope of this paper is to investigate the effect of different load and distributed generation (photovoltaic systems and wind generators) modelling approaches for the steady-state analysis of ...distribution networks and the development of ancillary services by system operators. Specifically, five different modelling approaches are considered, based on different assumptions. The power flow problem is solved by applying the examined models to the 33-bus benchmark distribution network and the derived results are statistically analyzed. The accuracy, reliability and performance of the models is evaluated in terms of the calculated voltages, power losses and computational burden.
The evolution of distribution networks to active systems as a consequence of the increased penetration of distributed energy resources and the electrification of traditionally fuel-based activities ...have changed drastically the landscape of power systems operation promoting the necessity of benchmarking tools for planning studies. Nevertheless, there is a scarcity of such tools that enable the holistic analysis of modern power systems according to the new grid standards. In this paper, a multi-purpose benchmarking testbed for low-voltage active distribution networks is introduced. The testbed comprises a granular residential appliance-level dataset, a benchmarking framework based on quasi-static simulations, a set of technical indices and a non-intrusive load monitoring tool. A suite of benchmark case studies including overvoltage, undervoltage and line congestion is presented, supported by ancillary trouble-shooting services, such as voltage control and demand response. The proposed testbed can be a useful tool for distribution system operators to evaluate the operating conditions of the grid without violating technical limitations, test new technologies, identify operational challenges, and foresee grid investments.
This paper presents a methodology for the steady-state analysis, i.e., power flow analysis, of islanded AC microgrids (MGs), operated under the droop control scheme. In the proposed framework, the ...power flow is computed using conventional power flow methods. For this purpose, a slack bus is considered to be connected to a random node of the examined MG. Subsequently, an iterative procedure is applied to determine the operational conditions, i.e., voltage level, frequency, active and reactive power absorption/injection, of this slack bus as well as of the rest MG nodes. The objective of the proposed iterative procedure is to force active and reactive power, flowing through the slack bus, to zero, emulating this way the islanded operation of the MG. To evaluate the performance of the proposed methodology, time-domain simulations are conducted on a low-voltage MG, using detailed models for all system components. The corresponding results are compared with those derived using the proposed methodology. In all cases, trivial differences are observed, validating the accuracy and the robustness of the proposed approach.
The increasing penetration of renewable energy sources is strongly linked to the development of voltage source converters used in their connection to the grid. As a result, in the near future of an ...inverter-dominated power system it will be a requirement for renewable generation to provide ancillary services in order to compensate for the absence of synchronous generation. In this scenario, the use of energy storage systems along with advanced control algorithms mimicking the dynamic behaviour of the traditional generators will be of utmost importance. This paper deals with a renewable energy source interfaced with a voltage source converter and comprising an energy storage system in the DC bus. Particularly, a new energy management algorithm for the DC-bus based on a three levels hierarchical control is proposed, which is able to simultaneously provide ancillary services, maintain the state of charge of the storage system within the permissible limits and use it to control the DC bus voltage. The control strategy is validated experimentally using a prototype with results evidencing a reliable and stable operation.
This paper deals with the recently emerging technology of solid-state transformers (SSTs), focusing on the technical benefits provided towards the optimal network operation. More specifically, the ...contribution of the SST to the well-known Volt/Var optimization problem is examined in terms of voltage regulation, minimization of network losses, and reduction of the computational burden. For this purpose, the mathematical formulation of the optimization problem is properly modified to incorporate the distinctive characteristics of SST. Deterministic and probabilistic simulations are performed on an extended radial medium-voltage network with high penetration of distributed generation to demonstrate the improved performance of SST against conventional transformer.
The main objective of this paper is to investigate the maximum penetration level of distributed renewable energy sources (DRESs) in a real radial low-voltage network. For this purpose, the business ...as usual (BAU) scenario, where no control scheme is applied to the installed DRESs, is compared with two conventional droop control techniques, namely the active power curtailment and the uniform power curtailment. Appropriate key performance indicators are introduced to evaluate the long-term performance of the examined control strategies. Simulation results show that, compared to the BAU scenario, a higher penetration level can be attained by exploiting the above-mentioned droop control schemes.
The extensive integration of distributed renewable energy resources (DRES) can lead to several issues in power grids, particularly in distribution grids, due to their inherent intermittency. This ...paper presents a stochastic simulation-based approach to estimate the maximum permissible penetration level of DRES and to determine the optimal capacity of centralized battery energy storage systems (BESS) in distribution networks while adhering to technical constraints. The stochastic method creates a wide range of scenarios under various conditions. For each scenario, our proposed approach calculates the maximum allowable penetration level of DRES and the required BESS capacity with different DRES control logics. The maximum allowable penetration level of DRES and the requirements of the BESS capacity are determined by an analysis of various simulation results. This paper’s unique contribution lies in equipping distribution system operators (DSOs) with the ability to compare results and select the most appropriate voltage control and power smoothing methods. This aids in mitigating challenges associated with overvoltage and intermittency issues arising from DRES-generated power, thereby enhancing the overall resilience and reliability of the power grid. Case studies that include four voltage control algorithms and three power smoothing methods demonstrate the universality and effectiveness of the proposed approach.
•A stochastic simulation-based approach is proposed to estimate the maximum allowable renewable energy sources penetration level and to determine the optimal capacity of centralized battery energy storage systems.•This paper empowers distribution system operators with the ability to compare results and select the most appropriate voltage control and power smoothing methods.•The impact of different voltage control and power smoothing methods on the stability of the power grid are evaluated.
In this paper, a decentralized control scheme is proposed that achieves two objectives: To mitigate overvoltages and to reduce the frequency of tap changes in the high/medium-voltage transformer. The ...proposed control is based on the reactive power capability of the distributed generation units, while actions are individually taken by each unit based only on local measurements. The validity of this method is examined through time-domain and time-series simulations. The former highlights the quick response and the robustness of the proposed control, whereas in the latter the performance and effectiveness of the proposed method in the long term is presented, focusing on the reduction of the transformer tap changes.
The increased penetration of distributed renewable energy sources (DRESs) in the existing low-voltage (LV) distribution networks poses a series of technical challenges for distribution system ...operators (DSOs). Among them, the voltage rise is considered as the most important obstacle that limits the further penetration of DRESs. To increase the installed DRES capacity and to prevent overvoltage issues, active power curtailment (APC) techniques can be applied by the DSOs. A significant drawback of these methods is the nonuniform power curtailment among the installed DRESs. A number of coordinated APC (CAPC) methods have been proposed in the literature to overcome this issue. However, the majority of these techniques model the network loads as constant power loads, thus usually leading to conservative values regarding the power injection of the installed DRESs. In this paper, an enhanced CAPC strategy is presented. Contrary to the conventional approaches, the proposed control scheme employs a more generalized, accurate and realistic representation of power system loads, taking fully into account their voltage-dependent nature. The validity of the developed control strategy is thoroughly investigated using time-series simulations on a radial LV residential network, while its performance is evaluated using appropriate key performance indicators.
In this paper, a phase-based control algorithm is proposed to effectively address the voltage regulation problem in unbalanced low-voltage (LV) networks with high photovoltaic (PV) penetration. The ...proposed method is based on a single-phase droop characteristic of the injected power with respect to the phase-to-neutral voltage at the point of common coupling for each PV unit. The main objective is to regulate efficiently the grid phase voltages, as well as to ensure a uniform active power curtailment among the PV units connected in the same phase. Simulations of a highly unbalanced LV network justify the validity of the proposed method and its enhanced performance over the conventional droop control in terms of overvoltage and unbalance mitigation.
PDF
