Low-voltage Power Grid Research Articles

Effect of Reactive Power Generation in Photovoltaic Installations on the Voltage Value at the Inverter Connection Point

Worldwide, photovoltaic installations are making an increasing contribution to electric energy generation. These are power-unstable sources due to the rapid and frequent change in insolation. As a result, a common problem noted in low-voltage power grids is that the permitted voltage values at the source connection point are exceeded. There are several methods of limiting the voltage values present at the inverter. One of them is the generation of reactive power in a photovoltaic installation. In the literature, one can find many relationships that allow one to determine the increase in voltage caused by the change in reactive power, where the imaginary part of the voltage loss is omitted as insignificant. The authors’ research has shown that this can lead to significant errors. Omitting the imaginary value causes the determined values to be even more than 4.5 times smaller—these differences increase with the length of the line. The analyses carried out by the authors show that the determination of voltage increments with and without taking into account the imaginary part of the voltage loss in the calculations differs from the values determined via computer simulation (failure to take into account the imaginary part results in calculated values of voltage increase being lower than the values determined via a computer by about 40% on average).

Low-delay low-voltage load aggregator demand response communication transmission architecture based on 5g edge computing

Abstract Participation of low-voltage users in demand response is one of the most important ways to mitigate the mismatch between power supply and demand. However, existing smart metering devices cannot support the low-delay and high-reliability transmission of massive power data. 5G communication technology provides a new communication transmission structure for load aggregators to communicate with low-voltage users and power grid companies. This paper combines 5G communication slicing technology and edge computing technology to rationally allocate computing and communication resources through deep Q-learning algorithms. The scheme proposed in this paper has a lower delay than the equal resource allocation scheme and is suitable for high-speed transmission of massive interactive response data from low-voltage users.

Multi-point method using effective demodulation and decomposition techniques allowing identification of disturbing loads in power grids

The paper presents an innovative approach to identifying voltage fluctuation sources in power networks, also considering the localization understood as the indication of supply points of disturbing loads. The presented approach considers disturbance sources that change their operating state with a frequency higher than the power frequency. The implementation of the proposed solution is also proposed in such a way that its implementation in the smart meter infrastructure allows automatic localization of disturbance sources without additional expert knowledge. In the proposed approach, the modulation signal is estimated using a carrier signal estimator, which allows the estimation of a modulation signal with a frequency higher than the power frequency. The estimated modulating signal is decomposed into component signals associated with individual disturbing loads by decomposition by approximation using pulse waves. The decomposition process allows for the estimation of selected parameters associated with disturbing loads, on the basis of which the assessment of propagation of voltage fluctuations associated with the impact of individual disturbance sources is performed, which allows for the indication of their supply point. The proposed approach was verified in numerical simulation studies using MATLAB/SIMULINK and in experimental studies carried out in a real low-voltage power grid.

Role of Voltage Control Devices in Low Voltage State Estimation Process

Megatrends, such as the proliferation of distributed generation, electrification, and the appearance of aggregator companies, put the low voltage power grids under intense pressure. Since the network infrastructure developments cannot keep up with the trends, distribution system operators turned to alternative solutions. Smart grid assets, such as on-load tap-changing distribution transformers or serial low voltage regulators, are promising solutions. However, the energy transition cannot be handled with the network expansive on the distribution level. Control centers are predicted to expand to this voltage level in the near future, and distribution system state estimation could be an enabler of all functionalities. On the low voltage level, data scarcity is a great challenge in observability; therefore, research must focus on the creation of pseudomeasurements and integration of available data sources. This paper examines the inclusion of smart assets from the conceptual point to the application on two sites, based on data from operational environments, both with a pseudomeasurement and an integrated metering point approach. The results showed that integrating smart assets could considerably mitigate voltage fluctuations, and reduce estimation errors by two magnitudes on the low voltage network.

Influence of the Type of Receiver on Electrical Energy Losses in Power Grids

The development of power electronics, including high-efficiency power supply systems, changes the structure of perception of the types of electrical energy receivers connected to the power grid at each supply voltage level. In the past, the dominant type of receivers were constant impedance devices. Currently, more and more devices have power supplies, which are most often constant power receivers. The construction and technological diversity of receivers allows mixed receivers, which are a combination of constant power and constant impedance receivers, to be distinguished. Therefore, there is a need to determine the impact of the type of electrical energy receivers on the power grid, both in the context of the operation of a single receiver and in the case of a branched power grid with a high penetration of distributed generation. This article will discuss the impact of the type of electrical energy receivers on the operation of the power grid, with particular emphasis on the issue of electrical energy losses at changing voltages. To determine the impact of receivers, simulation studies were performed based on two case stages: the first is a fragment of a low-voltage power grid in a household that supplies a heating device, which is analyzed as a different type of receiver; the second is a fragment of a low-voltage power grid with various types of consumers and photovoltaic installations. The research was carried out on the basis of the mathematical model of the low-voltage power network developed by the authors using the electric multipole method and Newton’s method. The obtained results show that the type of receiver may have an impact on electrical energy losses.

Resilience basins of complex systems: An application to prosumer impacts on power grids.

Comparable to the traditional notion of stability in system dynamics, resilience is typically measured in a way that assesses the quality of a system's response, for example, the speed of its recovery. We present a broadly applicable complementary measurement framework that quantifies resilience similarly to basin stability by estimating a resilience basin, which reflects the extent of adverse influences that the system can recover from in a sufficient manner. In contrast to basin stability, the adverse influences considered here are not necessarily displacements in state space, but arbitrarily complex impacts to the system, quantified by adequate parameters. As a proof of concept, we present two applications: (i) the well-studied single-node power system as an easy-to-follow example and (ii) a stochastic model of a low-voltage DC power grid undergoing an unregulated energy transition consisting in the random appearance of prosumers. These act as decentral suppliers of photovoltaic power and alter the flow patterns while the grid topology remains unchanged. The resilience measurement framework is applied to evaluate the effect and efficiency of two response options: (i) upgrading the capacity of existing power lines and (ii) installing batteries in the prosumer households. The framework demonstrates that line upgrades can provide potentially unlimited resilience against energy decentralization, while household batteries are inherently limited (achieving ≤70% of the resilience of line upgrades). Further, the framework aids in optimizing budget efficiency by pointing toward threshold budget values as well as budget-dependent ideal strategies for the allocation of line upgrades and for the battery charging algorithm.

A New Approach to the Use of Energy from Renewable Sources in Low-Voltage Power Distribution Networks

Currently, in rural networks with a large amount of distributed generation, PV installations are often disconnected due to the excessively high voltage in the network, which often exceeds the limit value, in accordance with the PN-EN 50160 standard. Disconnecting such an installation extends the return on investment costs by preventing the generation of electricity for the owner’s needs and results in the consumption of this energy from the grid. In such a case, the recipient has to bear the costs related to the purchase of this energy. In order to solve the problem of excessively high voltage in a low-voltage distribution network with a large amount of distributed generation, the authors of this article proposed a new approach to the use of electricity from these sources. In order to present the benefits of the proposed solution, a computer simulation was used. In order to carry it out, a mathematical model of a low-voltage power grid with distributed generation was developed using the electric multipole method and Newton’s method, which is discussed in the paper. To determine the advantages of the proposed solution, nine variants of the operation of an exemplary low-voltage power grid over one day were analyzed. The main conclusion based on the analysis of the results is that the proposed approach improves the operation of the power system by maintaining the voltage values within the standard range for the entire tested part of the network. In addition, the proposed approach does not increase the power or electricity when generating electricity from a PV installation. The proposed solution can also serve as a very attractive stimulus for the creation of energy cooperatives.

Multi-Stage Volt/VAR Support in Distribution Grids: Risk-Aware Scheduling With Real-Time Reinforcement Learning Control

The ever-increasing penetration of intermittent renewable resources in low-voltage power grids necessitates efficient operational strategies for voltage regulation as well as power scheduling of the available resources. In this paper, a risk-aware Volt/VAR support framework followed by a real-time reinforcement learning controller is presented for three-phase distribution systems. In the risk-aware stochastic scheduling stage, the legacy voltage regulating assets along with inverter-based photovoltaics (PVs) and energy storage system (ESS) are optimized considering day-ahead and intra-day markets. Moreover, demand response (DR) and voltage reduction plans are included in the proposed scheduling framework. By incorporating voltage-dependent load modeling in this study, the implementation of the voltage reduction plan reduces energy consumption in feeders by running the network at lower permissible voltage limits. The shiftable loads under the DR program are employed for peak shaving and to reduce operational costs. The result shows that DR implementation also reduces dependencies on the operation of traditional devices. The stochasticity of abrupt changes in PV generations is represented as the Gaussian Mixture Model (GMM), indicating a non-unimodal probability distribution in day-ahead PV forecasting errors. The scenario sets for uncertain variables are then reduced using a fuzzy clustering technique. Decisions made in the scheduling, associated with PV inverters and ESS operation, are revised with a real-time controller, i.e., Deep Deterministic Policy Gradient (DDPG) reinforcement learning. The DDPG is adopted in the control stage of the framework considering the detailed modeling of unbalanced three-phase distribution grids to minimize the voltage deviation and power ramping of ESS. The performance of the proposed multi-stage scheme is verified using a three-phase active distribution grid under different scenarios.

A Notch Filter-Based Coupling Circuit for UNB and NB PLC Systems

This paper introduces an analog notch filtering-based coupling circuit for receivers in ultra-narrowband and narrowband power line communication systems, which are connected to low-voltage electric power grids. It is composed of a twin-T notch analog filter, which is responsible for imposing a significant attenuation on the main frequency (i.e., f0∈{50,60} Hz) in cascade with an elliptic low-pass analog filter, designed with a 3 dB cut-off frequency of fc≫f0. For f0=60 Hz and fc=2 MHz, the prototype of the analog notch filtering-based coupling circuit attains attenuation values of 22 dB and less than 2 dB at the main frequency and in the rest of the frequency bandwidth, respectively, when practical scenarios are considered. Lastly, it shows that the analog notch filtering-based coupling circuit is more effective than a typical capacitive coupling circuit when frequencies lower than 3 kHz are considered for data communication and sensing purposes.

Improved transient stability of virtual synchronous generators for grid voltage cascading faults

• The basis of the investigation is a cascading fault of a grid-connected inverter in both low and high voltage power grids. • Pay attention to the fault with equilibrium point and the fault without equilibrium point while dealing with low-voltage faults, and utilize the phase portrait to assess stability. Finally, a control technique is given to ensure that the two defects are well controlled. • The equal area method is utilized to assess the fault in high voltage faults, and it is inferred that there must be an equilibrium point in high voltage faults. Finally, a control technique for active power transient overshoot mitigation and PCC voltage support during faults is provided. The topic of VSG grid voltage fault ride through has drawn increasing attention as virtual synchronous generator (VSG) technology has been widely applied in the field of renewable energy power generation. Due to the delay of the reactive power compensation device after the low-voltage fault recovery, the high-voltage fault will happen immediately after the grid's low-voltage fault is resolved. This phenomenon is known as low and high voltage cascading faults. There is not enough research on this specific voltage fault right now. For specific investigation, the low and high voltage cascading faults in this paper are separated into low-voltage fault stages and high-voltage fault stages. The equal area criterion (EAC) is used to analyze the specific process at the low-voltage fault stage. In addition, the dynamic damping control (DDC) is utilized to resolve the problem of low-voltage fault stability. Under low voltage fault, the phase portrait studies the single-period stability with an equilibrium point in a single-period and the multi-period stability without an equilibrium point in a single-period, respectively. Using a phase portrait to analyze system performance during a high voltage fault, and a virtual capacitor feedback control (VCFC) is offered to effectively reduce active power overshoot due to high voltage fault. The EAC is used to analyze the specific process of the high voltage stage, it is concluded that there is always an equilibrium point in the high-voltage fault where IGBT limitations are ignored. Finally, the correctness and feasibility of the theory are verified by simulation, and the specific analysis results are given.

Topology Optimization of Regional Power Grid Under Large-Scale Access of Distributed Photovoltaic Power Generation

In order to avoid the impact of large-scale access of distributed photovoltaic power generation on regional power grid and minimize power grid line loss, a regional power grid topology optimization method under large-scale access of distributed photovoltaic power generation is proposed. Obtain the factors related to the line loss consumption of regional power grid and the access location and capacity of large-scale distributed photovoltaic power generation, as well as the power grid network structure and load. Take the minimum bus loss after large-scale access to distributed photovoltaic power generation as the objective function, and take the continuity, network structure, line relationship, node voltage, etc. as constraints, build the topology model of low-voltage power grid, Using k-means clustering algorithm, the power supply range of regional power grid after large-scale access of distributed photovoltaic power generation is divided into several regions. In each divided small region, KPSO algorithm is used to optimize the network topology, so as to realize the topology optimization of the whole regional power grid. The experimental results show that when the number of clustering centers is 4, the clustering effect of this method is the best and can effectively reduce the power supply line loss.

Effect of Power Quality on Production Reliability and Stability of Water Treatment Plant at Vodovod-Osijek

Power quality issues are pervasive in most industries. The system operator and the network user are responsible for the power quality at the point of common coupling (PCC). Since a water treatment plant must operate continuously, a reliable and continuous power supply of satisfactory quality is necessary in accordance with HRN EN 50160:2012. Additionally, the electromagnetic feedback of load consumption on the power grid must be within the permitted values prescribed by the Distribution System Grid Code (Official Gazzete nos. 74/18, 52/20). The low-voltage power grid of the “Nebo Pustara” water treatment plant contains sensitive electric and electronic loads. As such, the loads require a power supply of satisfactory quality. Moreover, these loads have non-linear voltage/current characteristics and as such negatively affect power quality. In order to prevent the effects of poor power quality on the water treatment plan operation and to reduce the impermissible effect of non-linear loads on the power grid, the “Nebo Pustara” power sub-station was outfitted with a PQube3 power quality analyzer. This paper presents the results of the power quality analysis. Additionally, the paper details the actions taken in the user and distribution power grid to increase effect production reliability and stability of the water treatment plant and water supply, with the aim of reducing the negative effect on plant operation and equipment and also reducing the impermissible feedback of non-linear loads. Key words: power quality, water for human consumption, production reliability and stability of water treatment plant and water supply, Nebo Pustara, PQube3

Estimation of Grid Reinforcement Costs Triggered by Future Grid Customers: Influence of the Quantification Method (Scaling vs. Large-Scale Simulation) and Coincidence Factors (Single vs. Multiple Application)

The integration of future grid customers, e.g., electric vehicles, heat pumps, or photovoltaic modules, will challenge existing low-voltage power grids in the upcoming years. Hence, distribution system operators must quantify future grid reinforcement measures and resulting costs early. On this account, this work initially evaluates different methods to quantify future grid reinforcement needs, applied by the current state of research. Thereby, it indicates the significance of large-scale grid simulations, i.e., simulating several thousand low-voltage grids, to quantify grid reinforcements accurately. Otherwise, a selected area’s total grid reinforcement costs might be misjudged significantly. Due to its fast application, deterministic grid simulations based on coincidence factors are most commonly used in the current state of research to simulate several thousand grids. Hence, in the second step, recent studies’ approaches to applying grid customers’ coincidence factors are evaluated: While simplified approaches allow fast simulation of numerous grids, they underestimate potential grid congestion and grid reinforcement costs. Therefore, a fully automated large-scale grid simulation tool is developed in this work to allow the simulation of multiple grids applying grid customers’ coincidence factors appropriately. As a drawback, the applied deterministic framework only allows an estimation of future grid reinforcement costs. Detailed determination of each grid’s grid reinforcement costs requires time-resolved grid simulations.

An improved Newton-Raphson based linear power flow method for DC grids with dispatchable DGs and ZIP loads

PurposeThis study aims to provide a solution of the power flow calculation for the low-voltage ditrect current power grid. The direct current (DC) power grid is becoming a reliable and economic alternative to millions of residential loads. The power flow (PF) in the DC network has some similarities with the alternative current case, but there are important differences that deserve to be further concerned. Moreover, the dispatchable distributed generators (DGs) in DC network can realize the flexible voltage control based on droop-control or virtual impedance-based methods. Thus, DC PF problems are still required to further study, such as hosting all load types and different DGs.Design/methodology/approachThe DC power analysis was explored in this paper, and an improved Newton–Raphson based linear PF method has been proposed. Considering that constant impedance (CR), constant current (CI) and constant power (CP) (ZIP) loads can get close to the practical load level, ZIP load has been merged into the linear PF method. Moreover, DGs are much common and can be easily connected to the DC grid, so V nodes and the dispatchable DG units with droop control have been further taken into account in the proposed method.FindingsThe performance and advantages of the proposed method are investigated based on the results of the various test systems. The two existing linear models were used to compare with the proposed linear method. The numerical results demonstrate enough accuracy, strong robustness and high computational efficiency of the proposed linear method even in the heavily-loaded conditions and with 10 times the line resistances.Originality/valueThe conductance corresponding to each constant resistance load and the equivalent conductance for the dispatchable unit can be directly merged into the self-conductance (diagonal component) of the conductance matrix. The constant current loads and the injection powers from dispatchable DG units can be treated as the current sources in the proposed method. All of those make the PF model much clear and simple. It is capable of offering enough accuracy level, and it is suitable for applications in DC networks that require a large number of repeated PF calculations to optimize the energy flows under different scenarios.

Research on online monitoring and cause identification system of building electrical fire

Frequent building electrical fire accidents have brought great harm to life and property. In order to prevent the occurrence of accidents and reduce the losses to the greatest extent, it is necessary to take effective measures for building electrical fires. Based on the Internet of things (IoT) technology, a system for online monitoring and cause identification of building electrical fire is proposed in this paper. For both hardware and software, this paper introduces the overall structure, component units and system functions in detail. According to the characteristics of arc fault and fire, the complete scheme of online monitoring is given, and the system workflow is also described to realize the cause identification. Finally, the effectiveness of this system is verified by practical testing. The results show that the proposed system is helpful to solve the problems in monitoring and cause identification of building electrical fire, which can not only provide decision-making basis for firefighting, but also provide strong technical support for improving the safety of low-voltage power grid.

Assessment of power quality parameters and indicators at the point of common coupling in a low voltage power grid with photovoltaic generation emulated

Increased photovoltaic (PV) integration can affect the quality of both voltage and current in low-voltage (LV) power-grid operations. This work evaluates the influence of emulated PV power injection on several power-quality parameters and indicators (P&I) at the point of common coupling in an LV network. The assessed steady-state P&I values are the RMS voltage (VRMS), non-active power (Q), total and harmonic components of voltage (THDv, Vh) and current (THDi, Ih), voltage imbalance (Desbv), and total rated-current distortion (TRD). Fifteen scenarios are emulated, considering the active power derating, shading percentage over the PV panel surface, and number of shaded PV panels. A PQube3 smart meter is used to measure 256 samples/cycle and store 16 cycles of both voltage and current, for each emulated scenario. The results indicate that the Q, Desbv, and TRD meet the reference values in each emulated scenario. However, the following P&I do not comply with the reference values of 66.67% VRMS, 26.67% THDv, and 100% THDi. Moreover, in all scenarios, Vh and Ih do not satisfy at least one harmonic component requirement, mostly the fifth and/or seventh harmonic components.

Application of Augmented Reality (AR) Technology in Low-Voltage Line Interruption Training and Power Grid Emergency Training

Augmented reality technology uses computer performance to create a virtual scene and accurately integrate the virtual scene with the real world, and finally uses a video projector to present the virtual and real scene to the user, thereby significantly improving the user’s visual experience and Feeling knowledge. Therefore, augmented reality technology can be well applied to training companies. The use of virtual reality and augmented reality technology in the aerospace, construction and shipbuilding industries has achieved remarkable results, and the era of augmented reality applications in the power grid has also arrived. With the development of mobile terminals such as mobile phones, it has become an excellent platform for augmented reality applications. This article focuses on the application of augmented reality (AR) technology in low-voltage line interruption training and network emergency training. First, the basic technology of augmented reality (AR) and the application of augmented reality (AR) in power grid emergency training are introduced using bibliographic research methods. Then design a network emergency training system for low-voltage disconnection training, and finally test the algorithm used in this article. The detection result shows that the detection of feature points using AGAST takes less than 3ms, while the Shi-Tomasi operator is about 20ms. It can be seen that the use of AGAST operator to detect feature points has a great improvement in speed.

Selective Identification and Localization of Voltage Fluctuation Sources in Power Grids

The current study presents a novel approach to the selective identification and localization of voltage fluctuation sources in power grids, considering individual disturbing loads changing their state with a frequency of up to 150Hz. The implementation of the proposed approach in the existing infrastructure of smart metering allows for the identification and localization of the individual sources of disturbances in real time. The proposed approach first performs the estimation of the modulation signal using a carrier signal estimator, which allows for a modulation signal with a frequency greater than the power frequency to be estimated. In the next step, the estimated modulating signal is decomposed into component signals associated with individual sources of voltage fluctuations using an enhanced empirical wavelet transform. In the last step, a statistical evaluation of the propagation of component signals with a comparable fundamental frequency is performed, which allows for the supply point of a particular disturbing load to be determined. The proposed approach is verified in numerical simulation studies using MATLAB/SIMULINK and in experimental studies carried out in a real low-voltage power grid. The research carried out shows that the proposed approach allows for the selective identification and localization of voltage fluctuation sources changing their state with a frequency of up to 150Hz, unlike other methods currently used in practice.

Research on energy control of low voltage PV storage microgrid

Abstract Renewable energy sources cannot guarantee long-term and stable output supply when they are given energy consumption at the load end. At the same time, traditional solar and utility power supply systems cannot guarantee the priority of using solar energy to generate electricity, which has certain limitations. In this regard, an energy control strategy for achieving smooth and no backflow switching and prioritizing the use of clean energy solar energy under a joint power supply system of a solar power grid and a municipal power grid is proposed, which is used for a conventional combined power supply system of a contactor switching circuit. A topology of low voltage power grid is proposed, which effectively reduces the impact on the solar power grid and the municipal power grid during the system switching process combined control mode for controlling the current phase and repetitive control at the output end of the solar power grid in the combined power supply mode, and adding a feedforward control method for the grid voltage is adopted to ensure that the solar grid and the municipal power prioritize the use of clean energy solar energy and, at the same time, ensure the maximum utilization of solar energy. This paper chose the combined power supply system with the solar power grid and the municipal power grid as the object of this research. The topology structure and controlling strategy of the power supply system were comprehensively and deeply researched, and on this basis, the combined power supply system prototype was designed on the foundation of DSP28335 and CPLD. Moreover, hardware parameters are designed in the system, and an energy management optimization algorithm based on the system is developed on the corresponding experimental platform. The experimental results show that the proposed energy control strategy can effectively reduce the impact on the solar power grid and the municipal power grid during the system switching process, ensure that the solar power grid and the municipal power grid have no backflow combined power supply and give priority to the use of clean energy solar energy.

Resilience Assessment in a Low Voltage Power Grid with Photovoltaic Generation in a University Building

High integration of photovoltaic (PV) systems into the power systems causes negative or positive impacts. Typically, research considers the PV impacts on the RMS voltage, power losses, transformers and feeder stress, and power quality indicators. However, a generalising assessment of the electrical parameters and indicators (P&I) describes the power grid performance. It considers a complete holistic view of the real impacts that many events cause over the power grid operation. Therefore, this research proposes the resilience index in order to quantify and assess the impacts that the PV systems cause in low voltage. This scheme has four stages: i) P&I measurement, ii) P&I normalisation, iii) P&I weights assignment, and iv) resilience index quantification and assessment. The resilience scheme assessment has been applied in a low voltage university building with a PV system interconnected of 11.53 kWp. Monitoring has lasted for a month, with data acquisition every ten minutes. P&I monitored have been RMS voltage, RMS current, active, and non-active power, voltage imbalance, total harmonic distortion of voltage and current, and harmonic components of voltage and current. Results indicate that the PV system has positively affected the resilience index in the point of common coupling and floor four-node because the THDv, Vh, THDi, and Ih improved.