Curtailment Scheme Research Articles

Administrative congestion management meets electricity network regulation: Aligning incentives between the renewable generators and network operator

Administrative congestion management mechanisms are commonly used to integrate renewable generation (RES) into capacity-constrained distribution networks. We study the compensation of RES curtailment as an efficient design element. Compensating curtailment allows for efficient network expansion while distorting the RES investment. Leaving curtailment without compensation improves RES investment incentives while reducing the network expansion efficiency. An economic regulation dilemma results. We propose aligning incentives with the help of a congestion-payments fund that mediates financial flows between the network and generation. A curtailment scheme capable of efficiently managing network congestion becomes possible.

Development of an Optimized Curtailment Scheme through Real-Time Simulation

When a lot of surplus power occurs in wind power system, an output limit is implemented to directly or indirectly curtail the output to maintain a balance between the supply and demand of the power system. The curtailment process of a large-scale wind farm causes loss of power and mechanical loads. Resultantly, imbalanced curtailments often occur, resulting in unilateral burdens for the owners of wind farms. Considering the curtailment issue, the study for minimizing system loss of power plants is required in terms of operational efficiency. This paper proposes an algorithm to achieve flexible control during the actual power curtailment process in a wind farm, considering the wake effect. Here, the Monte Carlo method was adopted to calculate the curtailment weight in wind farms by using power loss terms. In addition, an equivalent model of a real wind farm was implemented and simulated through real simulation computer-aided design (RSCAD) software. This paper verified the effectiveness of the proposed method by applying the curtailment communication signal to a real-time digital simulator (RTDS). The results showed a reduction in the computational loading of individual wind turbine curtailment values with the decline of the total effective power loss.

PV Inverter Reliability-Constrained Volt/Var Control of Distribution Networks

The increasing penetration of photovoltaic (PV) systems promotes utilization of PV inverters for volt/var control (VVC) in distribution networks. However, PV inverters are vulnerable and their reliability is one of the most critical concerns for sustainable PV energy utilization. To enhance PV inverter reliability, this paper proposes a PV inverter reliability-constrained VVC method of distribution networks under uncertainties. Firstly, a full reliability analysis procedure for PV inverters is developed to estimate the lifetimes of core devices inside inverters. Secondly, considering the impacts of VVC on PV inverter reliability, reliability constraints are proposed based on regulation of inverter apparent power and application of a PV curtailment scheme. Thirdly, a multi-objective PV inverter reliability-constrained VVC optimization model is proposed, which aims to minimize network power loss and PV curtailed power, simultaneously. Accordingly, the nonconvex model is relaxed by a second-order cone programming method, and the uncertainties such as PV power generation and loads are addressed by a scenario-based stochastic optimization method. The proposed VVC method is tested on the 33-bus and 69-bus distribution networks, and the simulation results verify high efficiency of the proposed method in energy loss reduction and inverter reliability enhancement.

Load Shedding in Microgrids with Consideration of Voltage Quality Improvement

Microgrids have become more and more popular their usefulness as a renewable energy resource has been recognized. The core ability and promise of microgrids is addressing the environmental concerns due to climate change that have been growing during recent years. The innovation of microgrids is that they are designed to operate either in island mode or interconnected with the main grid system. However, when the microgrid operates in islanded mode, faults may occur which can cause system collapse or even blackout. Load curtailment schemes can be utilized to decrease the quantity of associated load to a level that can be securely supported by accessible generation in isolated mode. The main goal of this research is to evaluate the optimal amount of shedding power considering sustainable power sources, with the help of primary and secondary adjustments of the generator to restore the frequency to the allowed range. Particle Swarm Optimization algorithm is applied in this paper to determine the distributed shedding power on each demand load bus which can improve the voltage quality of the isolated microgrid system. The effectiveness of the proposed method is demonstrated through the simulation of IEEE 16- bus microgrid.

On the Fairness of PV Curtailment Schemes in Residential Distribution Networks

Active power curtailment of residential PV systems is an effective way to mitigate technical issues in distribution networks. However, existing curtailment schemes can treat households unfairly; e.g., Volt-Watt schemes increasingly being adopted worldwide inherently penalize PV systems at remote locations in radial feeders. Nonetheless, whether fairness is improved or not by alternative curtailment schemes depends on how the impacts on households are considered. In this context, household-centric metrics that quantify PV harvesting, energy export and financial benefit are used along with the Jain’s fairness index to assess fairness from different perspectives. To explore the trade-offs brought by schemes that consider fairness differently, four linearized, three-phase Optimal Power Flow (OPF)-based schemes are proposed to determine, periodically, short-term curtailment settings. Using a real Australian 22kV feeder and realistically modelled LV networks with 4,500+ households, a detailed comparison is carried out considering also a Volt-Watt scheme. Results demonstrate tha tall the schemes that consider fairness are effective in removing locational penalizations. However, in terms of fairness, their performance across the adopted metrics reveals noticeable trade-offs. This highlights the need for decision-makers to determine the metric from which fairness can be based upon in a way that aligns with their respective policies.

Capacity assessment for wind power integration considering transmission line electro-thermal inertia

Considering differences in planning and construction period, there may exist a mismatch of between effective wind farms capacity and dedicated transmission line ampacity. Then, conflict appears while increasing wind power integrates into main system through limited transmission utilities. Once excessive wind power integration (WPI) causes transmission overload, wind power generation is preferably curtailed with certain scheme. However, transmission conductor electro-thermal characteristic in case of wind power fluctuation makes static thermal rating inaccurate for overload confirmation. Then this study centers on analyzing WPI considering wind power curtailment scheme which allows for overhead conductor dynamic electro-thermal inertia involving various time-varying ambient factors. Accordingly, this study presents a WPI capacity assessment method, which captures the dynamic features of WPI by synchronously simulating wind power generation as well as curtailment regulation, transmission line electro-thermal behaviors and ambient changes. The sequences of wind power and ambient factors with fixed time span given in advance are approximately treated as piecewise linear functions of time and incorporated into differential-algebra equations for WPI. Performances of power curtailment and network loss are explored by taking either static or dynamic thermal rating as transmission overload standard to adjust wind farm output.

Energy management in commercial building microgrids

Energy systems face problems such as increasing energy cost, greenhouse (GHG) emissions, and network load deviations. A wide range of load variations may cause network instability. Large commercial buildings with a heavy load, treated as microgrids (μGs), may contribute meaningfully to demand response and network stability. Therefore, a strategy for optimal energy consumption and bidirectional power trade between the building and the utility grid is required for this class of customers. The objective of this paper is to develop a linear bi-level macro energy hub (MEH) control for a group of large commercial building μGs, to minimize the network load deviation, while satisfying the customer specified total μG energy cost and the GHG emission constraints. The resulting constrained optimization problem is mapped in a flower pollination algorithm environment under deterministic and uncertain conditions such as the random presence of solar irradiance and electric and natural gas networks. The μG considers the solar photovoltaic panel, internal combustion engine, fuel cell, microturbine, and electric vehicle lot and battery. Using the results obtained under deterministic conditions, customer-utility relationship is developed by applying the multi-linear regression analysis technique, between the network load deviation, operation and maintenance cost of distributed generators, μG's spinning reserve value, and total μG energy cost. Analysis proves that under an MEH, customer-utility interest is non-linearly related. Building owned micro energy hub control reduces the energy cost and the GHG emissions; however, the load deviation inflates and vice versa for utility owned MEH control. To address this nonlinearity, biogas is integrated with the MEH, using a method termed as integrated demand response (IDR), which successfully brings the energy cost down at a low load deviation. The results show that if uncertainties are not severe, the IDR alone will be adequate to bring the cost down for simultaneous achievement of end-to-end stakes. However, if the cost is high, due to adverse conditions, in addition to the IDR, the proposed load curtailment scheme is applied. Simulations demonstrate that the cost, GHG emission, and load deviation drop by 22.448%, 11.716%, and 36.410%, respectively, for biogas integrated MEH compared to building owned micro EH control.

Integrating Direct and Indirect Load Control for Congestion Management in LV Networks

With the energy transition, capacity challenges are expected to occur more frequently in low-voltage (LV) distribution networks. In the literature, several direct and indirect load control methods have been suggested as solutions to alleviate network congestion. Direct methods involve the network operator directly controlling appliances at the households, while indirect methods aim to motivate end-users to shift their consumption through price changes. In this paper, the direct and indirect methods are combined into an integrated approach, making use of the advantages of both methods. An agent-based architecture is adopted so that distributed and computational intelligence can be combined to ensure a smooth coordination among the actors. A sensitivity-based curtailment scheme is used to incorporate the unbalanced loading condition of the LV networks. The efficiency of the proposed integrated approach is investigated through simulations in the unbalanced IEEE European LV test feeder. Simulation results reveal up to 94% reduction in congestion by the integrated approach, while maintaining the required levels of supply in the network.

Efficient Algorithm for Scalable Event-Based Demand Response Management in Microgrids

Demand response management has become one of the key enabling technologies for smart grids. Motivated by the increasing demand response incentives offered by service operators, more customers are subscribing to various demand response programs. However, with growing customer participation, the problem of determining the optimal loads to be curtailed in a microgrid during contingencies within a feasible time frame becomes computationally hard. This paper proposes an efficient approximation algorithm for event-based demand response management in microgrids. In event-based management, it is important to curtail loads as fast as possible to maintain the stability of a microgrid during the islanded mode in a scalable manner. A simple greedy approach is presented that can rapidly determine a close-to-optimal load curtailment scheme to maximize the aggregate customer utility in milliseconds for a large number of customers. This paper further derives a novel theoretical guarantee of the gap between the proposed efficient algorithm and the optimal solution (that may be computationally hard to obtain). The performance of algorithm is corroborated extensively by simulations with up to thousands of customers. For the sake of practicality, the proposed event-based demand response management algorithm is applied to a feeder from the Canadian benchmark distribution system. The simulation results demonstrate that the proposed approach efficiently optimizes microgrid operation during islanded mode while maintaining appropriate voltage levels and network constrains.

Microinverter Curtailment Strategy for Increasing Photovoltaic Penetration in Low-Voltage Networks

Transition toward smart distribution networks with high penetration of photovoltaics (PVs) will involve incidental generation curtailment as an alternative to grid reinforcements. Microinverters are taking over popularity of string inverters in residential and some commercial areas mainly due to increased energy harvest. This paper demonstrates how microinverters with a modified overvoltage protection scheme could provide a reliable curtailment solution and accommodate additional PV capacity. Two wide-area curtailment schemes were proposed for a typical Dutch residential feeder with densely clustered PV. First, a single worst-case scenario was used to demonstrate the capabilities of the proposed curtailment schemes: the distribution network operators can optimize between various priorities such as total feeder output, economic equality between connected parties, voltage levels, voltage unbalance, and curtailment execution time. Second, a yearly comparison was made against conventional overvoltage protection and the results show 62%-100% reduction in overvoltage losses.

A review and analysis of renewable energy curtailment schemes and Principles of Access: Transitioning towards business as usual

In the last decade, the EU has driven forward the development and connection of renewable power sources across Europe. This has changed the way in which distribution networks operate, moving from a passive system, to a more active system where generation and demand are located closer together with system states being more complex and variable. Increased penetration of renewable generation into distribution networks is presenting a number of challenges to Distribution Network Operators (DNOs) including the provision of network access in capacity constrained networks. The introduction of Active Network Management (ANM) is enabling an increase in renewable generation connections through enhanced network access in otherwise ‘full’ networks.This paper presents a way in which DNOs might move towards Business as Usual (BAU) arrangements for ANM schemes. It is necessary to determine the curtailment arrangements, or Principles of Access (PoA), and from this estimate generation access under ANM and the flow of services and money for different scenarios. In this paper, a comprehensive literature review, detailed case study evaluation on early ANM schemes, quantitative curtailment assessment for different PoA and a qualitative analysis of business models for different ANM PoA is presented in turn with conclusions drawn from these three approaches.

The approach‐dependent, time‐dependent, label‐constrained shortest path problem

AbstractIn this article, we consider an approach‐dependent, time‐dependent, label‐constrained shortest path problem. This is a variant of the shortest path problem defined on a transportation network comprised of a set of nodes and a set of directed arcs such that each arc has an associated label designating a mode of transportation, and an associated travel‐time function that depends on the time of arrival at the tail node, as well as on the link via which this node was approached. A label constraint is specified that controls the admissible sequence of transportation modes, and the approach‐dependent travel‐time feature models turn‐penalties and prohibitions in transportation networks, whereby the time spent at an intersection before entering the next link depends on whether we travel straight through the intersection, or make a right turn at it, or make a left turn at it, as permissible. We propose two effective algorithms to solve this problem and present related theoretical complexity results. In addition, we also explore various heuristic delay estimation and network curtailment schemes that can be used to confine the search to only the more promising subsets of the network to reduce computational effort while preserving near‐optimality. Extensive empirical results using available data for the Portland, OR, and Blacksburg, VA, transportation networks are presented to demonstrate the efficacy of the developed procedures. © 2006 Wiley Periodicals, Inc. NETWORKS, Vol. 48(2), 57–67 2006

Trade curtailment schemes for the security control of the transmission network in a deregulated environment

Due to deregulation, the electrical power industry is undergoing deep changes, moving towards an open market. Two kinds of parties are active in the new environment: the economical agents (producers, consumers, brokers) and the power system operator, the former interested in power exchanges and their economic value, the latter in bus injections and their threat to the security of the transmission network. The variables used to model the transmission network operation have to be meaningful to the power system operator as well as to the economical parties; the action rules followed by the power system operator to enforce network security have to be carefully designed to be equitable and non-discriminatory. In this paper, a modeling of the power exchanges is proposed in the form of multilateral trades, and some rules for the action of the power system operator are proposed and discussed. The results obtained on a simple study case are discussed.

Cold load pick-up of residential load

Field studies have been performed in residential areas to determine the load restoration process after a disturbance. Similar measurements were also performed for individual houses with different heating supplies. Load aggregation for the different houses during the same outdoor conditions have been made for various durations of the outages, and a load model is presented. The cold load pick-up from individual houses is compared with field measurements from substations and with load models. Load curtailment schemes are analysed based on the collected data.