Distributed Energy Resources Units Research Articles

Consensus-Based Model Predictive Control for Active Power and Voltage Regulation in Active Distribution Networks

In this paper, a consensus-based model predictive control (Cb-MPC) scheme is proposed to control the active power and voltage at all nodes in grid-connected active distribution networks (ADNs) with multiple distributed energy resources (DERs). The proposed design methodology is based on a multiple-input multiple-output (MIMO) model of an ADN which accounts for both the internal and external interactions among the control loops of the DERs. To achieve the control objective, each DER unit is equipped with a controller–observer system. In particular, the observer implements the consensus algorithm to estimate the collective system state by exchanging data only with its neighbors. The scope of the controller is to solve the MPC optimal problem based on its collective state estimate, and, due to the presence of an integral term in the control action, it is robust against any unknown scenarios of the ADN, which are represented by uncertainty in the model parameters. The results of numerical simulations validate the effectiveness of the proposed method in the presence of unknown changes in the operating conditions of the ADN and of communication using a sample and hold function.

A Complex-Valued Stationary Kalman Filter for Positive and Negative Sequence Estimation in DER Systems

In medium- and low-voltage three-phase distribution networks, the load imbalance among the phases may compromise the network voltage symmetry. Inverter-interfaced distributed energy resources (DERs) can contribute to compensating for such imbalances by sharing the required negative sequence current while providing active power synchronized with the positive sequence voltage. However, positive and negative sequences are conventionally defined in a steady state and are not directly observed from the instantaneous voltage and current measurements at the DER unit’s point of connection. In this article, an estimation algorithm for sequence separation based on the Kalman filter is proposed. Furthermore, the proposed filter uses a complex vector representation of the asymmetric three-phase signals in synchronous coordinates to allow for the implementation of the Kalman filter in its stationary form, resulting in a simple dynamic filter able to estimate positive and negative sequences even during transient operation. The proposed stationary complex Kalman filter performs better than state-of-the-art techniques like DSOGI and very similarly to other Kalman filter implementations found in the literature but at a fraction of its computational cost (23.5%).

Distributed Energy Resources Based Two-Layer Delay-Independent Voltage Coordinated Control in Active Distribution Network

In order to solve serious voltage problem in active distribution networks and improve the utilization rate of renew-able energy resources, a distributed energy resources (DERs) based two-layer delay-independent voltage coordinated con-trol method is proposed. First, an upper-layer sensitivity-based voltage coordinated control strategy is designed by maximiz-ing the use of residual reactive power and minimizing active power reduction, where reactive power compensation and ac-tive power regulation from the most sensitive DERs are per-formed in a high priority. Then, a lower-layer delay-independ-ent coordinated controller is designed to dynamically regulate the reactive/active power of each DER unit, when communica-tion transmission delays are within allowable range estimated. A robust controller is designed with the local states of DER and the states of other coupling DERs with time delay, thereby overcoming the effects of coupling characteristics among DERs and parameter uncertainties. Finally, simulation results demonstrate the effectiveness of the proposed method.

Optimal planning of Microgrids using portfolio optimization with considering uncertainty

In this paper, the candidate points for distribution and substation transformers, low and medium voltage feeders, and the Distributed Energy Resources (DERs) are considered as a construction stock portfolio. The main goal of this research is to present a design method with the availability of smart grid infrastructure, which a main network is divided into several Microgrids (MGs). The design is done from the point of view of long-term operation (30 years), and all technical and economic constraints are taken into account for the optimal design of the MG. The most optimal portfolio is selected using the Imperialistic Competitive Optimization (ICA) algorithm and constituted the network design. Moreover, the uncertainty of load values is considered and the costs deviance as well as the expected value are obtained. The simulation is performed on a green field network with known geographical characteristics, and the load information is obtained using the regional load forecasting strategy. Using random values generated for the decision variable of substations, some candidate locations of DTs are selected. The low voltage feeders are connected to the not-selected substations. In the next step, the loads are considered to the selected substations based on the load allocation algorithm. Next, the assigned load points are classified into various groups by the K-means clustering algorithm. With applying the Prim method, the minimum spanning tree, with the grid graph, is calculated. The resilience of the designed grid is examined in a robust manner and in the presence of MGs. In order to study the resilience, the considered MG is divided into 4 zones based on the wind speed. The studied network is divided into 4 states as main network without dividing to several MGs, with 20 % more robustness, with 20 % less robustness, and with several MGs. The simulations are implemented with MATLAB in 11 scenarios that 3 scenarios include the controllable DERs and the remained scenarios are rendered for various uncertainty factors of loads related to the first scenario. The results show that the total cost of MG and operation cost of DER units in the third scenario are decreased about 16 % and 18 %, respectively. The results also show that the network with 20 % more robustness has better results and lower outage of loads in comparison with other states. Moreover, the connected MGs outperformed in comparison with the wide network.

Sliding Sector-Based Controller for Regulating Voltage/Frequency in Autonomous Microgrid

The application of microgrids (MG) has a vital role in grid modernization. However, a larger number of installations of electronically coupled distributed energy resources (DER) units in MGs have created opportunities and threats for grid operations. Therefore, efficient and reliable control strategies for MG operation are essential. This article introduces the concept of sector design to show the stabilization of voltage source converter-interfaced DER units in MG applications. The sliding sector design is advanced sliding mode control to obtain a region of attraction such that the state space is divided into attractive and nonattractive regions. In addition, a variable structure-based controlling method has been introduced to drive the trajectories of a plant from the exterior to the interior of the sector and strictly inside throughout the process. In autonomous MG operation, the proposed controller focuses on stabilizing the electronically coupled DER unit’s voltage and frequency response. Besides, it confirms the safety of the power conversion system from external disturbances. The system stability is proven using the Lyapunov candidate function. The proposed strategy has been effectively validated through PSCAD/EMTDC. The simulation results have examined the impact of balanced, unbalanced, nonlinear, and dynamic loading patterns in islanded MG.

Virtual Power Plant with Renewable Energy Sources and Energy Storage Systems for Sustainable Power Grid-Formation, Control Techniques and Demand Response

As the climate crisis worsens, power grids are gradually transforming into a more sustainable state through renewable energy sources (RESs), energy storage systems (ESSs), and smart loads. Virtual power plants (VPP) are an emerging concept that can flexibly integrate distributed energy resources (DERs), managing manage the power output of each DER unit, as well as the power consumption of loads, to balance electricity supply and demand in real time. VPPs can participate in energy markets, enable self-scheduling of RESs, facilitate energy trading and sharing, and provide demand-side frequency control ancillary services (D-FCAS) to enhance the stability of the system frequency. As a result, studies considering VPPs have become the focus of recent energy research, with the purpose of reducing the uncertainty resulting from RESs distributed in the power grid and improving technology related to energy management system (EMS). However, comprehensive reviews of VPPs considering their formation, control techniques, and D-FCAS are still lacking in the literature. Therefore, this paper aims to provide a thorough overview of state-of-the-art VPP technologies for building sustainable power grids in the future. The review mainly considers the development of VPPs, the information transmission and control methods among DERs and loads in VPPs, as well as the relevant technologies for providing D-FCAS from VPPs. This review paper describes the significant economic, social, and environmental benefits of VPPs, as well as the technological advancements, challenges, and possible future research directions in VPP research.

DER Participation in Ancillary Services Market: An Analysis of Current Trends and Future Opportunities

In an effort to push for low-carbon transition, national governments and regulatory authorities are working to define market structures and legislative frameworks able to effectively support the spreading of electricity production from renewables. To this purpose, the opening of national Ancillary Services Markets (ASMs) to Distributed Energy Resources (DERs) plays a key role. However, pricing schemes and rules in place (e.g., incentives) can act as a barrier to the supply of regulation services by small-sized and renewable-based power plants. In this context, the present work evaluates the economic opportunities for DERs provided by the provision of tertiary reserve and balancing control in the Italian ASM. The research is carried out through the collection and processing of price data from the Italian electricity and gas markets over 4 years (2019–2022). Considering a reference architecture where DER units bid on the market through a Balancing Service Provider, the potential revenues on the ASM of a non-programmable or partially programmable DER unit are compared to the earnings expected of a conventional power plant in order to highlight whether unfair competition can represent a barrier. Then, possible evolutions in the current remuneration schemes are analyzed, to evaluate whether they can be able to support a better DER integration. From the analysis, it emerges that, even if negative prices could be useful to increase the competitiveness of RES-based power plants for downward regulation, the loss of the incentives can act as a deterrent to the offering of services on the market by DERs. Therefore, other regulatory options, such as the incentives retention in case of downward regulation, could also be needed.

Novel Hybrid Modified Modal Analysis and Continuation Power Flow Method for Unity Power Factor DER Placement

Distributed energy resource (DER) has become an effective attempt in promoting use of renewable energy resources for electricity generation. The core intention of this study is to expand an approach for optimally placing several DER units to attain the most stable performance of the system and the greatest power losses decrease. The recommended technique is established on two analytical methods for analyzing voltage stability: the new modified modal analysis (MMA) and the continuation power flow (CPF) or MMA–CPF methods. The MMA evaluates voltage stability by considering incremental connection relating voltage and active power, which includes the eigenvalue and the related eigenvectors computed from the reduced modified Jacobian matrix. Furthermore, an active participation factor (APF) is computed from the eigenvectors of the reduced modified Jacobian matrix. The CPF method uses a predictor–corrector stepping pattern to reach the solution track and compute the tangent vector sensitivity (TVS). Both APF and TVS indicate each load bus sensitivity in the network. In addition, an objective function regarding losses decrease and eigenvalue is expressed to calculate the best bus position for DER allocation. The proposed MMA–CPF technique has been assessed on a 34-bus RDN and the outcomes demonstrate the effectiveness of the proposed scheme.

Embedded control system for reactive power control in distributed energy resources for voltage regulation in the distributed power system

Since more distributed energy resources (DER) are being linked to the electrical grid, the current distributed power system (DPS) is encountering additional voltage regulation challenges. Traditionally, on-load tap changers, step voltage regulators, and switched capacitor banks have been used for voltage regulation in DPS. However, these sources are insufficient for voltage regulation in current DPS. As a result, reactive power assistance from a DER unit based on power electronics is intended to adjust the voltage in the DPS. In terms of flexibility, security, reliability, and availability, embedded control systems are now being investigated by researchers for use in power converter-fed DER units. This paper presents a method for constructing an embedded controller unit based on XynergyXS for the power converter controller, which includes reactive power regulation in the DER unit. Furthermore, it proposes dynamic reactive power control in the DER unit for enhanced DPS voltage regulation. The suggested voltage control approach is tested in a MATLAB/Simulink model of a practical 85-bus distributed power system located in the northern Tamilnadu region, India as well as a modified IEEE 33-bus system. The new control approach investigates all potential power grid disruptions. The results reveal that the proposed reactive power control method in DER units enhances network voltage regulation while reducing the number of switching operations performed by static voltage regulating units such as on load tap changers and switched capacitor banks.

A novel dynamic planning mechanism for allocating electric vehicle charging stations considering distributed generation and electronic units

Achieving a sustainable and efficient power systems network and decarbonized environment involves the optimal allocation of multiple distributed energy resource (DERs) unit types and flexible alternating current transmission systems (FACTS) to distribution networks. However, while the most focus is on optimization algorithms and multi-objective techniques, little to no attention is paid to the underlying mechanisms in planning frameworks. This paper goes beyond existing literature by investigating the impact of planning mechanisms in smart grid planning frameworks when considering the allocation of PV distributed generation units, battery energy storage systems, capacitor banks, and electric vehicle charging station facilities. First, a single- and multi-objective planning problem is formulated. Then, we propose a novel adaptive-dynamic planning mechanism that uses a recombination technique to find optimal allocation variables of multiple DER and FACTS types. To cope with the additional complexity resulting from the expanded solution space, we develop a hybrid stochastic optimizer, named cooperative spiral genetic algorithm with differential evolution (CoSGADE) optimization scheme, to produce optimal allocation solution variables. Through numerical simulations, it is seen that the proposed adaptive planning mechanism improves achieves a 12% and 14% improvement to the conventional sequential (multi-stage) and simultaneous mechanisms, on small to large scale distribution networks.

Distributed economic nonlinear MPC for DC Micro-Grids with inherent bounded dynamics and coupled constraints

This paper proposes a hierarchical control scheme for DC Micro-Grids (MGs) composed of distributed energy resource (DER) units, active loads, and coupled constraints, that incorporates different control levels to achieve economic operation and coupled constraint satisfaction at all times. All loads are considered as constant power loads (CPLs), which are known to lead to instability due to the negative impedance characteristics. To this end, firstly an improved version of the recently developed sl-PI controller is introduced in the primary level to provide boundedness and local stability of the dynamics. The supervisory controller solves an economic optimisation problem to compute voltage setpoints and at a lower control layer the system is driven to those setpoints, by utilising a distributed nonlinear MPC setup with non-iterative, neighbour-to-neighbour communication framework. A rigorous analysis on the system robustness to uncertainties in the exchanged information and bounded load variations is provided, and recursive feasibility and stability of each subsystem is analytically proven for the first time, according to the authors’ knowledge. Finally, we demonstrate the proposed controller with the aid of simulated scenarios for a DC MG with multiple DER units and CPLs.

A Comparative Study of the Influence of BESS and STATCOM on Post-Fault Voltage Recovery in Microgrid

Reliable and efficient power flow in the electrical grid is crucial given network expansion and the incorporation of numerous renewable sources. Microgrids are becoming more and more important in the global energy sector due to its numerous benefits. The variable nature of distributed energy resources (DER) in microgrid makes large-scale DER integration potentially unstable for system voltage. Grid regulations place restrictions on the voltage control of DER unit, which raises the need for reactive power support. Proper placement of flexible AC transmission system (FACTS) under post-fault conditions may enable faster voltage recovery. In this work, battery energy storage system (BESS) and static synchronous compensator (STATCOM) have been considered for improving the post-fault voltage in DER integrated weakly grid-connected microgrid system. Two operation scenarios have been considered for analyzing the behavior of BESS and STATCOM individually at post-fault situation. According to the results of the simulation, BESS requires lesser rating than STATCOM for faster recovery of post-fault voltage of the system.

An Enhanced Approach for Solar PV Hosting Capacity Analysis in Distribution Networks

With the falling cost of Distributed Energy Resources (DERs) and the shift from fossil fuel to renewable energy in many countries, the integration of DERs is expected to grow. This can lead to a wide range of problems in the power system, such as voltage violations, overloading of distribution lines, reverse power flow, etc. Therefore, it is imperative to account for these adverse effects of the integration of DERs on the distribution network and minimize their impact when calculating the Hosting Capacity (HC). Two algorithms are presented in this study derived from a novel modified iterative method and a novel Repeated Particle Swarm Optimization (RPSO) method for determining the HC for multiple DER units simultaneously or a single DER unit integrating into radial or mesh networks. These algorithms calculate the optimal HC based on six scenarios of annual load and DER generation profiles. The developed algorithms were tested on the IEEE 123 bus network, and their results were compared. For a large-scale DER case, the modified iterative method significantly outperforms both the PSO and the normal iterative method in terms of computation time (30 minutes versus 3 hours versus 6 hours, respectively). In the case of multiple DERs, the RPSO method is the only option, as the other two methods cannot simultaneously optimize multiple DERs. As a result, it has been concluded that it is necessary to select HC calculation methods carefully and in accordance with the application, as each method has its own strengths and weaknesses.

Placement analysis of combined renewable and conventional distributed energy resources within a radial distribution network

<abstract> <p>System islanding, relay tripping, and reverse power flow-like issues in the distribution network are all caused by randomly placed distributed energy resources. To minimize such problems, distributed energy resource (DER) optimal placement in the radial distribution network (RDN) is essential to reduce power loss and enhance the voltage profile. When placing DERs, consideration of constraints like size, location, number, type, and power factor (PF) should be considered. For optimal placement, renewable and nonrenewable DERs are considered. The effects of different types and PFs of DER placements have been tested on the IEEE 33 bus RDN to satisfy all limitations. Using various intelligent techniques, distributed energy resource units of optimal type, PF, size, quantity, and position were placed in the IEEE 33 bus RDN. These intelligent strategies for minimizing power loss, enhancing the voltage profile, and increasing the convergence rate are based on an adaptive neuro-fuzzy inference system, a genetic algorithm, and enhanced particle swarm optimization.</p> </abstract>

Sensor Fault-Resilient Control of Electronically Coupled Distributed Energy Resources in Islanded Microgrids

In this paper a sensor fault resilient control approach for electronically interfaced distributed energy resources (DERs) in islanded microgrids is proposed. The proposed control strategy consists of a sliding mode observer (SMO) and a H infinity output feedback controller that ensures resiliency of the DER units in an islanded microgrid against erroneous measurements due to sensor malfunctioning. Any error in the measurements due to malfunctioning of the associated sensors are modelled as sensor faults in this paper. The SMO in the proposed approach estimates the sensor faults, and the estimated faults are used to devise fault tolerant control strategy so that the H infinity output feedback control remains unperturbed by the erroneous measurements. In order to demonstrate the efficacy of the proposed control strategy, rigorous simulation studies are carried out on a test islanded microgrid system with single DER and multiple DERs. The efficacy of the proposed approach has been further validated through an experimental study carried out on a prototype islanded microgrid system

TPCPF: Three-Phase Continuation Power Flow Tool for Voltage Stability Assessment of Distribution Networks With Distributed Energy Resources

This work presents a three-phase unbalanced continuation power flow algorithm for voltage stability assessment of distribution systems with high penetration of distributed energy resources (DERs). Analyzing distribution system voltage stability with DER will allow high penetration of renewable energy necessary for the sustainability goals. The developed algorithm can analyze voltage stability for both the meshed and radial systems and the balanced and unbalanced three-phase distribution systems. The developed tool allows the voltage stability analysis to facilitate the planning, operation, control, and distribution system management. The impact of DER on the voltage stability of several test cases has been analyzed considering constant power (PQ) and regulated-voltage (PV) modes of operation for DER units. Moreover, different voltage stability case studies are presented to demonstrate the impact of unbalance, load increment, and network topology on the maximum loading capacity. Results using the IEEE 13-node feeder, the 18-bus balanced shipboard system, the 13-node CIGRE benchmark system, and the 136-bus redial distribution feeder demonstrate that the developed continuation power flow tool can efficiently perform voltage stability analysis for active distribution systems.

An adaptive decentralized economic dispatch method for virtual power plant

This paper introduces a decentralized economic dispatch method and an architecture suitable for the virtual power plant (VPP) aggregating massive distributed energy resources (DERs). The convergence condition is given for quadratic cost functions, and is extended to the case of general increasing function of incremental cost (IC). Further analysis shows that the step of this method is adaptive, which is generated from the bottom up according to the responsiveness of each DER unit (DERU). Combined with the decentralized architecture based on message queue (MQ), the algorithm design considers the hosting mechanism of the coordinator failure, which not only improves the efficiency of calculation and communication without losing privacy-protection, but also makes it more fault-tolerant. The correctness and effectiveness of the method are verified in the case studies. The iterative process can respond and converge quickly when DER units reach capacity limits or devices fail/join. Due to the adaptability of the step, the method has strong robustness to the quantity and parameters randomness of underlying units. Therefore, it can be applied to the VPP with a massive number of DERs in order to get consensus solution by rapid economic dispatch.

Reliability enhancement and voltage profile improvement of distribution network using optimal capacity allocation and placement of distributed energy resources

In the radial distribution system, reliability is the most critical performance criterion. Additionally, optimizing the voltage profile is critical. This work proposed the optimal placement of distributed energy resources (DERs) to enhance the reliability and improve the voltage profile of the distribution feeder. To perform this research, two practical feeders of the Debre Markos (D/M) city distribution network, Ethiopia were used, which were affected by the outages. A composite system adequacy assessment, which includes the two main components of the power grid, i.e. generation and distribution, is performed using Monte Carlo simulation. The computed results show that integrating DER units improved the overall system's reliability. Further, the effect of varying DER penetration on reliability and voltage profile is also analyzed. ETAP and DIgSILENT software environments are used to perform this research.

Model reduction and feedback design based on singular perturbation method applied to a lumped DER-microgrid model

In the context of microgrids, the distributed energy resources (DERs) are interfaced through an LCL output filter with the rest of the microgrid. The dynamic model of this filter and the lumped model of the microgrid constitute the set of differential equations employed to design the controller that allows the integration of DER units within the modern power systems. For those control strategies based on cascade structure; shunt capacitor voltage (inner) and droop (outer) controllers, it is important to specify under which conditions the model reduction is authorized. In this work, the singular perturbation method is used to derive the conditions that allow a model reduction of the output filter. In addition, two case studies are presented to illustrate the applicability and the possibility of model reduction.

Network constrained optimal performance of DER and CHP based micro-grids within an integrated active-reactive and heat powers scheduling

Nowadays, different types of dispatchable and non-dispatchable distributed energy resource (DER) units, combined heat and power (CHP) plants as well as heat only units are integrated into a micro-grid (MG) platform. These facilities can help MG operators to satisfy the required electricity and heat demands of controllable and non-controllable loads even with no power exchange between the external main grid and the MG. This paper introduces a network constrained optimal operation model based on an integrated active-reactive and heat powers scheduling in MG for both grid-connected and isolated modes. The DERs like fuel cell (FC) units, diesel generators (DGs) and micro turbines (MTs) are motivated to take part in providing reactive power to the MG based on a reactive power payment function. Meanwhile, the dependency of produced heat and active power by CHP units through feasible operating region as well as the dependency of produced active and reactive powers by DER units through capability curves are taken into account in the optimal economic dispatch of the MGs. The main goal of this paper is to find the optimal economic dispatch of active and reactive powers as well as heat energy for DER and CHP based micro-grids in which network constraints such as AC power flow limitations are taken into consideration. The proposed model is examined on a 33-bus test MG for grid-connected and isolated modes and the simulation results are presented to investigate and analyze the different features of the proposed method.