Reverse Power Flow Research Articles

An overvoltage adjustment strategy Based on Integrated Voltage Sensitivity in the Active Distribution Network

With the growing proportion of renewable energy resources represented by distributed photovoltaics in the distribution network, the overvoltage problem is becoming more and more serious owing to the photovoltaic reverse power flow in the active distribution network. This paper begins with the quantification and analysis of node voltage sensitivity, and the influence calculation formula of photovoltaic injection on the voltage sensitivity of the target node and other nodes is deduced; next, a general conclusion on the change of voltage sensitivity caused by active and reactive power of Photovoltaic is given. To solve the possible low control efficiency of control strategy simply depends on voltage sensitivity, a definition of so-called Integrated voltage sensitivity is proposed, and an optimized overvoltage control scheme is utilized under the distribution network structure. The effectiveness of the proposed control strategy is validated by a simulation example, namely, on the premise of not affecting the active power output of the photovoltaic as much as possible, the same overvoltage regulation effect can be obtained with smaller adjustments in reactive power output, further, rapid overvoltage regulation is achieved.

Assessing the Impacts of Solar PV Plants on Distribution Systems using DigSilent

The purpose of this paper is to evaluate the effects of integrating solar PV plants on distribution systems using Botswana Power Corporation greater Gaborone distribution system as a case. The study compares and analyses the system baseline to solar integrated system using DIgSILENT Powerfactory software. The system studies conducted in this paper include short circuit and effects on active and reactive power losses at different penetration factors. This research found out that integrating solar PV plants to the distribution network caused a decrease in grid losses and the extent of power losses decrease vary. Fault level contribution from the PV systems is generally low. In conclusion, the effects of these interconnections on line losses and fault level contribution differs in all circuits under study, therefore network assessment must first be thoroughly conducted before interconnecting solar PV plants with distribution systems as some areas indicated some reverse power flow that could affect the protection systems because initially the distribution system was designed to operate on a single source voltage.

Research on control strategy of distributed photovoltaic cluster based on improved particle swarm-gray wolf coupling algorithm

Conducting research on cluster control strategies for distributed photovoltaic systems to address voltage fluctuations and reverse power flow caused by large-scale distributed photovoltaic integration is crucial foundational work in establishing a new power system and ensuring its safe and stable operation. Based on the division of distributed photovoltaic cluster, this paper takes distributed photovoltaic cluster as the intermediate layer of control, and researches the two-layer control strategy of inter-cluster coordination and intra-cluster autonomy. The inter-cluster coordination strategy is located at the upper layer, and this strategy based on the power grid structure of the controlled area, comprehensively considering the observability, controllability, degree and betweenness centrality of each node, the latter two characterize the spatial location of the nodes. The dominant nodes of each cluster are selected by the above multiple indicators. The multi-objective inter-cluster coordination control model respectively focusing on the minimum voltage deviation of the dominant node or the minimum network loss of the system is constructed according to whether the voltage of the dominant node crosses the limit or not, and the improved particle swarm-gray wolf coupling algorithm (PSO-GWO) is used to generate the output indicators of each cluster. The intra-cluster autonomy strategy is at the lower layer. In the shortage of adjustable PV resources connected to the dominant node, the intra-cluster autonomy strategy adopting the control sequence of dominant node-downstream node-upstream node to distribute the output indicators of inter-cluster coordination within the cluster; In addition, in view of the situation that the cluster cannot receive the output indicators due to communication failure, The intra-cluster autonomy control model is constructed with the goal of minimum voltage deviation and minimum network loss of the dominant node in the cluster. The distributed photovoltaic inter-cluster coordination + intra-cluster autonomy two-layer regulation strategy is used to simulate the improved IEEE33-nodes system under multiple scenarios. The results show that the proposed control strategy can effectively solve the voltage overlimit, power flow back and other problems, and play an important role in ensuring the safe and economic operation of the system.

New Passive Loss of Mains Detection Scheme Using Characteristics of Differential Impedance of Series Inductor

Nowadays, renewable energy sources (RESs) are widely used as distributed generation sources, leading to issues such as unintentional islanding, protection concerns, and reverse power flow. Unintentional islanding is dangerous because it can endanger utility workers, damage DG units, and jeopardize grid stability. To overcome these issues, Researchers are developing islanding detection schemes. This article proposes a novel passive technique for islanding detection of multi-bust test systems, based on the differential impedance of a series inductor. The differential impedance changes during islanding and non-islanding events. However, in grid-connected mode, the voltage and frequency of the microgrid are handled by the utility grid. Therefore, no significant changes in differential impedance occur. The voltage and frequency of the microgrid are not handled by the power grid while in islanded mode. Therefore, the differential impedance varies significantly. The islanding is detected if the value of differential impedance is greater than the predefined threshold. This scheme detects islanding in 24 ms at zero mismatch power, has no impact on power quality, and is computationally simple. The proposed approach easily discriminates between islanding and non-islanding events. The distribution test system is simulated in MATLAB/Simulink environment. Additionally, the novel passive technique has been validated on an OPAL-RT real-time platform.

Balancing DSO interests and PV system economics with alternative tariffs

Distributed rooftop photovoltaics (PV) is one of the pillars of the energy transition yet their widespread integration strains grids, leading to over-voltage, reverse power flow, and infrastructure strain. Furthermore, increased PV self-consumption reduces imported electricity, posing challenges for cost recovery by Transmission System Operators (TSOs) and Distribution System Operators (DSOs), whose grid costs were traditionally tied to volumetric tariffs. To investigate whether alternative tariffs could mitigate PV impacts at the distribution level without hampering PV development, we assess five electricity tariffs that could help the DSOs to recover the costs of maintaining the distribution grid. We also analyze their effects on private storage investment and their implications for urban, semi-urban, and rural low-voltage networks. We found that tariffs with a capacity-based component promote further adoption of PV and storage. At the same time, they allow the DSOs to recover the grid cost without incurring relevant economic differences for the customer. Our study found that alternative tariffs like dynamic and capacity-based tariffs promote the adoption of storage and PV systems. While no single tariff alone can fully mitigate PV impacts at the distribution level, our results point towards the need of managing PV export through solutions like PV curtailment.

Consider Carbon Emission Flow Analysis of Power System with Regards to Power Loss and Wind Power Uncertainty

A method for analyzing the impact of wind power uncertainty and active power loss on carbon emission flow in power systems is proposed. Based on the stochastic power flow calculation of wind power injection, the correlation function between wind power output and the total carbon injection rate into the system is determined. Meanwhile, the reverse power flow method is used to analyze the contribution of each unit to the active power flow in different parts of the system and calculate the corresponding carbon emissions. Under the assumption that wind power fluctuations are borne by balancing units, this method combines a conventional unit and a system node, branch, load, and active network loss correlation matrix calculation model to solve the average impact factor of wind power injection on other nodes and branches, thereby determining the uncertain characteristics of carbon emission flow in power systems under stochastic and intermittent wind power injection. The correctness and effectiveness of the method are proved by analyzing the IEEE 14-node standard example, providing new theoretical support and ideas for quantitatively evaluating the low-carbon contribution of wind power generation to the system.

CHALLENGES AND DESIGN ASPECTS OF MICROGRID CLUSTERING

With the growing penetration of distributed energy resources, the traditional microgrid concept is evolving into microgrid clustering, which decomposes the distribution system into interconnected microgrids to improve stability, reliability, and efficiency. Microgrid clusters coordinate power-sharing between microgrids and the main grid, effectively reducing problems such as voltage rise, harmonics, poor power factor, reverse power flow, and conventional protection scheme failures. However, there are challenges to overcome before adopting microgrid clustering, particularly in the design aspects. This paper critically reviews the challenges in the design of microgrid clustering, categorizing multi-microgrids into different architectures based on the interconnections' layout, evaluating reported control techniques in microgrid clustering, and presenting aspects of multi-microgrid protection. Possible areas of future research are highlighted to improve the operational aspects of microgrid clusters. Ref. 3, fig. 6, tables 2. Keywords: energy management; microgrid cluster; ring connection; power converter; protection; synchronization.

Optimal Voltage Control Method for a Step Voltage Regulator Considering the Under-Load Tap Changer in a Distribution System Interconnected with a Renewable Energy Source

The voltage in distribution systems is controlled by the under-load tap changer of the substation and the pole transformer of the primary feeders. Recently, as one of the main countermeasures, a step voltage regulator is being introduced to solve voltage problems such as overvoltage phenomena in a distribution feeder interconnected with a renewable energy source and under voltage in a long-distance feeder. However, the tap of the step voltage regulator may be frequently operated due to its interdependent relationship with the under-load tap changer in the distribution system. Furthermore, given the existing operating characteristics of the step voltage regulator, it is difficult to perfectly maintain the customer voltage within an allowable limit using existing methods such as the line drop compensation method for a step voltage regulator. In addition, the existing line drop compensation method, considering the distributed generators, may be not able to control the proper voltage within an allowable limit. Therefore, in order to solve such voltage problems, this paper proposes a voltage control method for a step voltage regulator by considering the output voltage of an under-load tap changer that is operated via the line drop compensation method. In other words, to overcome the limitations of existing voltage control methods for step voltage regulators, this paper proposes an optimal control method to determine the optimal compensation rate for a step voltage regulator by considering the reverse power flow from a renewable energy source and the output voltage of the under-load tap changer of the main transformer.

Targeted demand response for flexible energy communities using clustering techniques

The present study proposes clustering techniques for designing demand response (DR) programs targeting commercial and residential prosumers. The goal is to alter the consumption behavior of the prosumers within a distributed energy community in Italy. This aggregation aims to: (a) minimize the reverse power flow at the primary substation, occurring when generation from solar panels in the local grid exceeds consumption, and (b) shift the system wide peak demand, that typically occurs during late afternoon. Regarding the clustering stage, we consider daily prosumer load profiles and divide them across the extracted clusters. Three popular machine learning algorithms are employed, namely k-means, k-medoids and agglomerative clustering. We evaluate the methods using multiple metrics including a novel metric proposed within this study, namely peak performance score (PPS). The k-means algorithm with dynamic time warping distance considering 14 clusters exhibits the highest performance with a PPS of 0.689. Subsequently, we analyze each extracted cluster with respect to load shape, entropy, and load types. These characteristics are used to distinguish the clusters that have the potential to serve the optimization objectives by matching them to proper DR schemes including time of use, critical peak pricing, and real-time pricing. Our results confirm the effectiveness of the proposed clustering algorithm in generating meaningful flexibility clusters, while the derived DR pricing policy encourages consumption during off-peak hours. The developed methodology is robust to the low availability and quality of training datasets and can be used by aggregator companies for segmenting energy communities and developing personalized DR policies.

PV Hosting Capacity in LV Networks by Combining Customer Voltage Sensitivity and Reliability Analysis

This paper investigates voltage regulation in low voltage (LV) networks under different loading conditions of a supply network, with increased levels of distributed generation, and in particular with a diverse range of locational solar photovoltaic (PV) penetration. This topic has been researched extensively, with beneficial impacts expected up to a certain point when reverse power flows begin to negatively impact customers connected to the distribution system. In this paper, a voltage-based approach that utilizes novel voltage-based reliability indices is proposed to analyse the risk and reliability of the LV supply feeder, as well as its PV hosting capacity. The proposed indices are directly comparable to results from a probabilistic reliability assessment. The operation of the network is simulated for different PV scenarios to investigate the impacts of increased PV penetration, the location of PV on the feeder, and loading conditions of the MV supply network on the reliability results. It can be seen that all reliability indices improve with increased PV penetration levels when the supply network is heavily loaded and conversely deteriorate when the supply network is lightly loaded. Moreover, bus voltages improve when an on-load tap changer is fitted at the secondary trans-former which leads to better reliability performance as the occurrence and duration of low voltage violations are reduced in all PV scenarios. The approach in this paper is opposed to the conventional reliability assessment, which considers sustained interruptions to customers caused by failure of network components, and thus contributes to a comprehensive analysis of quality of service by considering transient events (i.e., voltage related) in the LV distribution network.

A novel non-intrusive load monitoring method based on ResNet-seq2seq networks for energy disaggregation of distributed energy resources integrated with residential houses

The increasing effects of global warming and energy depletion have raised concerns about the pollution caused by traditional oil and fossil energy usage. Distributed energy resources (DERs) have emerged as promising techniques to address these issues. However, the growing proportion of power injection from DERs presents technical challenges such as power quality decline and power flow reversal, which may destabilize the grid. Non-intrusive load monitoring (NILM) is a promising and cost-effective approach that can provide residential power information to improve grid scheduling, dispatching, and optimize residential power consumption behavior. This paper proposes a novel NILM method that can decompose the power of both household appliances and DERs integrated with residential houses. The proposed approach employs a data segment method that utilizes adaptive window lengths to identify the behavior of DERs based on the operating periods and characteristics of different equipment. A non-intrusive load monitoring method is proposed based on the ResNet-seq2seq framework to address the problem of model degradation and gradient vanishing. Post-processing techniques are applied to the output results using a feature list of the target equipment. Experiments are conducted on a dataset organized based on the REDD and Pecan Street datasets to demonstrate the accuracy and effectiveness of the proposed method. The results show that compared to the start-of-the-art CNN-seq2seq model, the proposed method achieved 54.95%, 69.18%, 56.95%, and 84.98% reduction in MAE for PV, EV, refrigerators, and microwaves, respectively.

A soft computing technique based on PSO algorithm and energy management strategy for optimal allocation and placement of PVDG-BES units

In the pursuit of achieving a harmonious equilibrium between electricity production and consumption, the integration of distribution generators (DG) has garnered substantial attention. Yet, the escalated integration of DG systems has given rise to the predicament of reverse power flow, instigating elevated system power losses and voltage profile distortions. Thus, an imperative emerges to judiciously apportion and dimension DG systems, complemented by the incorporation of battery energy storage (BES) systems, as a remedial measure against these challenges. In this scholarly work, we present an innovative approach rooted in a precise energy management strategy (EMS) aimed at the adept allocation and capacity optimization of (PVDG-BES) systems. The study employs a two-step optimization methodology, the former facet of which expounds on the influence of BES system integration on grid power losses and voltage profiles during stable operational conditions. Subsequently, a pioneering optimization technique is formulated in the latter facet to identify the optimal siting and capacity allocation of the aforementioned system based on an optimal EMS framework. The primary focal point of this investigation is the minimization of total power losses. Validation of our proposition is conducted on the IEEE 14-bus standard system, incorporating the particle swarm optimization (PSO) algorithm. Simulation outcomes incontrovertibly affirm the efficacy and robustness of the proposed EMS, yielding substantive reductions in power losses and noteworthy enhancements in voltage profile integrity. Notably, the implementation of EMS leads to a remarkable 31% reduction in total power losses as compared to the initial scenario, prior to the amalgamation of PVDG-BES components. In sum, this study epitomizes a comprehensive strategy for fortifying power grid efficiency by orchestrating the symbiotic interplay of distribution generators and battery energy storage systems through an adept energy management paradigm.

An Efficient Hybrid Particle Swarm and Gradient Descent Method for the Estimation of the Hosting Capacity of Photovoltaics by Distribution Networks

With many distribution networks adopting photovoltaic (PV) generation systems in their networks, there is a significant risk of over-voltages, reverse power flow, line congestion, and increased harmonics. Therefore, there is a need to estimate the amount of PV that can be injected into the distribution network without pushing the network towards these threats. The largest amount of PV a distribution system can accommodate is the PV hosting capacity (PVHC). The paper proposes an efficient method for estimating the PVHC of distribution networks that combines particle swarm optimization (PSO) and the gradient descent algorithm (GD). PSO has a powerful exploration of the solution space but poor exploitation of the local search. On the other hand, GD has great exploitation of local search to obtain local optima but needs better global search capabilities. The proposed method aims to harness the advantages of both PSO and GD while alleviating the ills of each. The numerical case studies show that the proposed method is more efficient, stable, and superior to the other meta-heuristic approaches.

Distribution network adaptability assessment considering distributed PV “reverse power flow” behavior - a case study in Beijing

Distribution network adaptability assessment considering distributed PV “reverse power flow” behavior - a case study in Beijing

Fairness-Aware Distributed Energy Coordination for Voltage Regulation in Power Distribution Systems

The accelerating deployment of solar photovoltaics into low-voltage distribution networks can cause reverse power flow and overvoltage problems. However, if coordinated properly, the real and reactive power flexibility of these resources enables distribution operators to manage their networks more efficiently. Existing literature is rich in droop-based control (Volt-Watt and Volt-VAr) and optimization-based distributed energy coordination for four-quadrant control of photovoltaics to prevent overvoltage issues. While optimal coordination can effectively mitigate overvoltage, it treats resources at sensitive parts of the grid unfairly. To address this concern, we propose a distributed optimal power flow formulation that incorporates fairness in curtailing photovoltaic generation and utilizes the reactive power capability of smart inverters. Fair curtailment of photovoltaic systems is studied with aggregation at each of two layers in a distribution network: 1) area-level fairness and 2) feeder-level fairness to demonstrate the flexibility of the proposed approach in resource aggregation. To explore the trade-off, the fairness-aware control actions are compared against the performance of a centralized controller that aims to maximize the aggregate PV generation without incorporating fairness. Simulation results show that introducing area-level fairness increased curtailment by 1.11 percentage points, and feeder-level fairness increased curtailment by 4.7 percentage points compared to a fairness-agnostic control.

短時間フリッカ測定機能を備えたバンク逆潮流事故記録装置の配備とその計測事例

With the increase in the amount of interconnection of renewable energy, a transformer reverse power flow has occurred. In the past, transformer reverse power flow was restricted, but with the revision of the law in May 2013, it has permitted to operate the system on the premise of transformer reverse power flow by installing the necessary protection device. Along with this, the bank reverse power flow fault recorder is installed at the distribution substation for power system failure recording and analyzing at the time of transformer reverse power flow. On the other hand, the occurrence of voltage flicker phenomenon due to renewable energy has become a problem in recent years. This voltage flicker has the property of changing rapidly, and it is difficult to measure with the conventional ΔV10 flicker meter. Therefore, we implemented a short-time flicker measurement function that can measure voltage flicker with rapidly changing in the bank reverse power flow fault recorder. The outline and measurement examples are introduced.

Transition and Issues of Substation Protection Relay Systems for Power Distribution

In June 2023, the Protection Relay System Technical Committee planned a special issue labeled as “Protection Relay System Technology in Power Distribution Stations”. Protection relay systems play a vital role in the stable operation of power systems. In recent years, they have also been responsible for solving various problems in power systems, such as the realization of mass introduction of renewable energy, expansion of the operational capacity of power distribution facilities, and rationalization of facility configuration. The following topics were gathered and discussed as a result of the call for this special issue.: (1) Proposals for distribution line protection methods (short circuit protection, ground fault protection), (2) Case studies using IEDs (IEC 61850), N-1 inter trip scheme, bus bar protection relays, and comprehensive retrofits, (3) Optimizing accident recovery during distribution line accidents, (4) Voltage adjustment methods using storage battery capacity operation, (5) Bank Recorder and switchboard configuration when dealing with reverse power flow. A total of 10 papers were submitted. This commentary touches on the contents of the technical reports as an aid to understanding these papers. It also outlines the history of distribution substation protection relays and the latest technology in distribution substation protection relay systems.

再生可能エネルギーの系統連系拡大に伴う系統保護面の課題解決のためのIEDの活用

The interconnection of a large amount of renewable energies to the power system has created new problems in terms of supply and demand, system protection, and power quality. System protection issues include reverse power flow in transformers at distributing substations and overload of power distribution equipment.

Intensive Data-Driven Model for Real-Time Observability in Low-Voltage Radial DSO Grids

Increasing levels of distributed generation (DG), as well as changes in electricity consumption behavior, are reshaping power distribution systems. These changes might place particular stress on the secondary low-voltage (LV) distribution systems not originally designed for bi-directional power flows. Voltage violations, reverse power flow, and congestion are the main arising concerns for distribution system operators (DSOs), while observability in these grids is typically nonexistent or very low. The present paper addresses this issue by developing a method for nodal voltage estimation in unbalanced radial LV grids (at 0.4 kV). The workflow of the proposed method combines a data-driven grey-box modeling approach with generalized additive models (GAMs). Furthermore, the proposed method relies on experimental data from a real-world LV grid in Denmark and uses data input from only one measuring device per feeder. Predictions are evaluated by using a test data set of 31 days, which is more than twice the size of the training data set of 13 days. The prediction results show high accuracy at root mean squared errors (RMSEs) of 0.002–0.0004 p.u. The method also requires a short computation time (14 s for the first stage and 2 s for the second stage) that meets requirements for the practical, real-time monitoring of DSO grids.

A Soft-Switched Current-Fed Dual-Input Isolated DC–DC Converter Topology

A soft-switched current-fed dual-input isolated dc-dc converter topology is proposed in this article. This converter integrates two low-voltage dc sources with similar transferred characteristics such as two PV panels or two batteries into a dc bus using a simple circuit topology and a minimum number of active and passive components. The energy transfer between the input and output ports is controlled by modulating the pulse-width of the control signals. Moreover, the soft-switching operations are discussed, and the smooth connection between the input-side inductor and the transformer leakage inductance is achieved. Furthermore, the operation of the converter in reverse power flow direction is presented to demonstrate the bidirectional operational capability of the converter. Finally, different operation modes of the proposed dual-input converter are verified by the experimental results obtained from a 250 W hardware prototype.