## Research Output

Now showing 1 - 9 of 9
• Publication
An Analysis on PV Forecast Allocation for Distribution System Planning
(IEEE, 2019-09-02)
As the adoption of residential photovoltaic (PV) continues to increase, its influence on distribution feeder voltage and currents also increases. Effective allocation or modelling on the appearance of PV across the system as a function of an adoption forecast is an important consideration for future distribution planning. The spatial information required for the forecast/allocation process is expected to be available to utilities at a cost proportional to its level of detail. Naturally, there is a need to understand the potential trade-offs between different modelling approaches and options. This paper explores three allocation models that differ on the complexity of their allocation mechanism. Both the error due to ignoring customers' PV adoption mechanisms and due to the PV forecast uncertainty are explored and compared.
• Publication
Grid Impedance Characterization To Provide a Robust Phase-Locked Loop Design for PV Systems
(IEEE, 2021-10-21)
The operation of rooftop photovoltaic (PV) systems can be challenged by the electric characteristics of the low voltage (LV) feeders. On this subject, high-impedance LV feeders can result in PVs facing the loss of synchronization due to instability in the phase-locked loop (PLL) unit of their inverter, mainly because PLLs are commonly designed to operate under nominal grid conditions and their performance can be highly affected when the loading of the feeder deviates from the nominal one. One way to avoid such a problem is by characterizing the network impedance at the PV connection point, and use this characterization to provide a robust PLL design. This paper presents a methodology to construct a stochastic representation of the network impedance seen at the PV point of connection. To do so, the distribution of the grid resistance and inductance, under various operational scenarios, is extracted using a Monte Carlo simulation framework and then modeled via a Gaussian distribution. This distribution is employed to obtain an ellipse that embraces the values of the aforementioned resistance and inductance. This ellipse determines the range of the variations of the network impedance to be regarded in the robust design of the PLL.
• Publication
Coordinating Demand Response Aggregation with LV Network Operational Constraints
(IEEE, 2021-03)
High shares of renewable energy resources are increasing the value of using demand response (DR) mechanisms to enhance the resiliency and efficiency of power system operation. In this context, residential DR is expected to become an increasingly important asset. In order to exploit this resource, DR aggregators are expected to combine the capabilities of a large group of householders and participate, as a single provider, in the electricity market. In doing so, it is imperative for aggregators to consider the operational constraints of the local network. Otherwise, the quality of the electricity service can be jeopardized and the true DR potential overestimated. This paper presents a novel methodology that integrates DR aggregators with distribution network operators for a secure and efficient scheduling and real-time operation of DR in residential radial feeders. The method is evaluated on a real unbalanced feeder where DR provision (from a mix of technologies) is coordinated with the network steady-state thermal and voltage limits. In this study, with the corresponding data seasonality and controllable devices, it is shown that complying with network operational constraints can impose, at certain times, a significant limit to the allocation of DR.
• Publication
Remote voltage estimation in LV feeders with local monitoring at transformer level
(IEEE, 2017-07-20)
On-load tap changer-fitted transformers have been proposed to solve voltage problems in low voltage (LV) networks with rich penetration of distributed generation. However, knowledge of the voltage level at customers' point of connection is key for the performance of potential control strategies. This work proposes a generic methodology to estimate voltages in LV feeders without the need of remote monitoring. The methodology relies on local flow measurements at the transformer level and residential load models. Maximum Likelihood Estimation (MLE) is applied to obtain the most likely residential loads' power consumptions which are later used to calculate the associated nodal voltages. A novel formulation of power flow equations based on sensitivity analysis is used to simplify the MLE problem. The methodology is tested on a real unbalanced feeder with unique presence of residential loads. The high accuracy of results promotes it as a potential alternative to monitoring investments.
• Publication
Optimising Load Flexibility for the Day Ahead in Distribution Networks with Photovoltaics
(IEEE, 2019-06-27)
In this paper a methodology is proposed to calculate the load demand flexibility that could be activated within the next 24-hours for solving the technical impacts of contingencies that may come up in an unbalanced low voltage distribution networks with high penetration of intermittent DG sources. The methodology is formulated within a Demand Response program environment via load shifting as flexibility enabler mechanism. To achieve that, a non-linear optimisation problem is formulated based on an unbalanced optimal power flow, which allows the determination of the load flexibility that each Demand Response customer could provide at the request of the Distribution System Operator. The demand as well as weather conditions are forecasted for the day ahead. The optimisation problem is solved in a sequence fashion, within a daily framework, splitting the whole problem in optimisation blocks. In each block, the flexible load demand is obtained and the load demand forecasting its updated for the upcoming blocks based on the changes in the scheduled load demand. The methodology is applied to a real distribution network with the load data received from the smart metering infrastructure. The results obtained show the strength of the methodology in solving the technical problems of the network under high unbalanced operation.
• Publication
Real-Time Estimation of Support Provision Capability for Poor-Observable Distribution Networks
(IEEE, 2023-03)
An indispensable step towards coordinating the actions of distribution and transmission system operators (DSOs-TSO) is to estimate the range of flexibility that can be offered to the TSO by DSOs. Within this context, a data-driven probabilistic approach is proposed to evaluate the capability of a distribution network in providing active and reactive power support in real-time. To this end, in an offline phase, a linear discriminant analysis model, together with a piecewise linear model of the distribution network are trained to delineate the boundary of a region representing the adherence to distribution network operational constraints. In the implementation phase, this region comprises the feasible set of a series of optimization problems, formulated to determine the support provision capability. These optimization problems are of iterative linear programming type, which allows for real-time applicability. The evaluated support capability can be deemed as the available reserve in real-time transmission operation, which enables providing a coordinated response towards unexpected events, and facilitates the participation of distributed resources in the balancing market by granting an up-to-date estimation of available supports. This approach is tested on the IEEE 123-node system and verified through comparison with an AC optimal power flow technique.
• Publication
Estimation of voltage sensitivities in low voltage feeders with photovoltaics
(IEEE, 2018-10-25)
With increasing penetration levels of photovoltaic panels (PVs) in low voltage (LV) networks, voltage statutory limits are likely to be violated. To avoid this, most strategies rely on the capacity of inverters to modify power injections as needed. In cases for which the required set points are not obtained from a constrained formulation of the power flow problem, voltage sensitivities to power injections are required. Therefore, recent publications have proposed methods to estimate these sensitivities in residential LV feeders. However, as they rely on extensive monitoring and communication infrastructure, they may result impractical for operators to implement. This paper introduces a novel methodology that allows every PV to autonomously estimate voltage sensitivities based merely on the real-Time local voltage at the customer point of connection. A robust accuracy assessment under multiple system states is performed and benchmarked against a more traditional method.