Low Voltage Grid Research Articles

Island grid operation of a modified mobile generator - test and optimization in a living lab with high PV penetration

In the research project LINDA, a concept for local island grids with decentralized energy resources was developed. In the follow-up project LINDA 2.0 this concept is supposed to be transferred to mobile generators, used for auxiliary supply applications in the low voltage grid. A mobile generator cannot absorb reverse power flows. Therefore, the mobile generator was equipped with a load bank in order to allow the infeed of renewable sources during the island grid operation. Before the use in the real low voltage grid, this modified mobile generator was tested and optimized in a living lab. The tests in the living lab showed that the island grid operation of the modified mobile generator with the infeed of decentralized energy resources is possible and the power quality standards can be fulfilled. In some situations, during the tests, oscillations in the system frequency and voltage occurred. Measures to prevent the oscillations were tested and their influence observed.

Analysis and systematic comparison of concepts for voltage control with inverted-based prosumer devices

The German energy transition resulting in increased penetration of renewable energy generation and electrification raises the load on the electrical power grid. Especially the low voltage grid with rising shares of prosumer devices like photovoltaic systems and electric vehicles is affected by severe deviations of the bus voltage from nominal values potentially violating the limits of the voltage band. In this paper several voltage control concepts are analysed with a focus on supply quality, additional grid load, and losses. The concepts presented are implemented and analysed within simulative investigations. Main results are a positive effect of all concepts on bus voltages with no concept being superior in all key figures. The reactive power feed-in based on the current grid status using the Q(U) method presents the best trade-off for photovoltaic systems with regard to impact on critical voltage values and negative effect on the grid and prosumer devices. While a combination of Q(U) and P(U) is the most appropriate option for consumption devices, voltage control concepts for battery storage systems do not seem to have any significant impact. Adjusting the installation specifications of grid operators based on these results could mitigate critical grid situations in congested grids.

Analyses of the effects of customer flexibility on the distribution grid

The paper describes the implementation of a linear programming (LP) optimization method for distribution of household appliances aiming to minimize hourly load and consider the comfort preferences of the customers. The described method is envisaged to be implemented to allow customers to examine the use of their flexibility for various services. Namely, the paper shows how the method is applied for shifting the load to off-peak hours. To examine the effects of the implementation of such solutions, the LP based optimization method is simulated using a low voltage grid and typical households. In addition, the paper analyses how the optimization of the operation of household appliances contributes to improvement in the voltage conditions in the distribution grid.

A co-simulation environment to evaluate cyber resilience in active distribution grids utilising behind-the-meter assets

The increasing utilisation of behind-the-meter assets in an active distribution grid leads to an ever more complex cyber-physical system, producing a greater dependency on active communication and increasing vulnerability to cyber attacks. Consequently, there is a need to simulate relevant cyber-physical systems and incidents and their impact to assess the overall system's cyber resilience. This paper aims to present a simulation environment that can be used to analyse the cyber resilience of different system designs. This simulation environment incorporates all relevant domains, including the energy grid, the information and communication infrastructure and the used operational technology. Furthermore, we propose a new way to abstract the communication infrastructure inside the co-simulation, including the simulation of incidents like cyber attacks and communication failures. The basis of this work is a requirements analysis that considers the events to be simulated in the form of threat modelling based on the STRIDE framework. The functioning of the entire environment is demonstrated using an example concept for voltage control in the low-voltage grid, for which a cyber attack and its effects are simulated, and finally, a more resilient alternative is presented.

Integration of renewal planning results in an automated strategic power grid planning

This paper presents a concept for automated conventional strategic grid planning and the modelling of innovative technologies. An evolutionary algorithm is used for optimization. Based on this automated strategic grid planning, an approach to the integration and consideration of renewal planning results in the automated strategic grid planning is presented. The simulations are carried out on a real low-voltage grid. For this purpose, simulations are conducted with and without taking into account the renewal planning. The aim of this paper is to present the impact of taking into account renewal plannings in the strategic grid planning and the resulting planning measures. In the simulated low-voltage grid, the consideration of the renewal planning leads to a high cost decrease in the conventional strategic grid planning. As a result, the costs are at the same level than the innovative planning strategies.

Scenario generation of residential electricity consumption through sampling of historical data

The low-voltage grid (LVG) needs to be reinforced to handle the increased load due to the transition towards renewable energy. Doing this optimally requires knowledge of typical currents and voltages throughout the grid, which are unknown. They can be calculated from the grid layout and electricity consumption time series of each consumer, but for many consumers this time series is unknown. To alleviate this problem, we have developed two techniques to generate accurate and realistic daylong electricity consumption time series (scenarios) for a given consumer. Both techniques generate scenarios by sampling from historical consumption measurements of a limited set of consumers, considering available information about consumers (e.g., total yearly consumption) and days (e.g., weather). The first technique uses expert knowledge to define this sampling procedure, whereas the second learns it automatically using machine learning. The quality of the generated scenarios is evaluated by estimating how well the distributions of predicted and observed time series match, conditional on the available information. The data-driven technique performs better than the expert-based technique and, contrary to the latter, can easily be applied to datasets with different attributes without requiring any domain knowledge. Both proposed techniques outperform random sampling (the prevalent approach in existing LVG studies) and standard load profiles (commonly used by distribution system operators (DSOs)). Most of the improvement is obtained by including consumer attributes, whereas daily attributes lead to little or no performance improvement. The proposed techniques can help DSOs estimate the state of the LVG more accurately, thereby reducing investment costs.

Modern Use of Prosumer Energy Regulation Capabilities for the Provision of Microgrid Flexibility Services

Due to the prospect of climate change and the challenges posed by the European Union to the modern power grid, a decentralized system based on distributed energy sources is being created from a centralized system based on utility power. It also involves new ideas on the operation and management of power grids, especially at the level of low-voltage distribution networks, where prosumers play a special role. In addition to the transformation of sources to renewables, the aim is to increase the flexibility of power grids by exploiting the regulatory potential of flexible grid components. The issue of grid flexibility assumes particular importance in the case of microgrids and local grids covered by the energy communities. Many posts describe the realization of the task of flexibility through energy storage, e.g., storing storage resources in electric vehicles or the use of energy transformation through conversion to heat, air compression air, or process cooling. However, there seems to be a lack of exploration of the topic, where the photovoltaic inverter could provide a flexible energy source while maintaining the rigor of power quality. This article presents current developments in low-voltage grids and the prospect of using prosumer installations to provide grid flexibility and stability.

Power flow control system and its effectiveness evaluation in low-voltage grid with many interconnected PV systems

Power flow control system and its effectiveness evaluation in low-voltage grid with many interconnected PV systems

Voltage Support and Selective Harmonic Current Compensation in Advanced AC Microgrids

The high penetration of distributed energy resources (DERs) and non-linear loads in low-voltage (LV) grids may cause overvoltage and voltage harmonic distortion. This paper proposes an automatic control strategy to flexibly steer dispatchable DERs in AC microgrids (MGs) while simultaneously mitigating harmonic voltage distortion and over- and undervoltage at the MG nodes. Voltage support is performed through integrated local and coordinated volt-var and volt-watt functionalities, with a well-defined coordinated sequence of actions to avoid active power curtailment. A voltage detection-based decentralized selective harmonic current compensation (HCC) is enabled when the voltage total harmonic distortion exceeds the established threshold at the MG point of common coupling (PCC). The proposed scheme consists of a model-free control that provides power flow controllability at the MG PCC. It does not require computationally intensive algorithms, does not require extra grid-side and/or load-side current measurements, and effectively regulates the internal MG node voltages regardless of the line impedance X/R feature. The strategy is evaluated based on multiple simulations and experimental results, considering a LV MG model with several DERs as well as unbalanced, non-linear loads and non-dispatchable photovoltaic inverters. The simulations and experimental results showed an improved overall voltage profile throughout the MG nodes in terms of magnitude and distortion, which certifies the feasibility of the proposed scheme in real-field applications.

Control of a Hybrid Modular Solid-State Transformer for Uninterrupted Power Supply Under MVdc Short-Circuit Fault

Modular multilevel converter (MMC)-based solid-state transformers (M-SSTs) show promise in hybrid ac/dc distribution grids where there is need for a medium-voltage dc (MVdc) interface. It can be used to interconnect several distribution networks with different voltage forms and levels and enable flexible power flow among them. In an M-SST, the MVdc short-circuit fault is a critical issue due to the rapidity of the fault current, which can cause device damage and power failure of the low-voltage (LV) grids. Aiming at addressing this issue, this article proposes a fault-mode control strategy applied to a hybrid M-SST topology for uninterrupted power supply of its LV ports. The topology consists of a hybrid MMC with both half- and full-bridge submodules and isolated bidirectional dc–dc converters. Through the proposed control, the fault current is eliminated when an MVdc short-circuit fault occurs. The hybrid M-SST can keep uninterrupted power interaction between the MVac port and the LVdc port during the fault, thereby improving power supply reliability. Moreover, an improved capacitor voltage balance control and an optimized modulation scheme are developed and included in the uninterrupted operation scheme to maintain the harmonic performance of the ac port. The feasibility and effectiveness of the proposed topology and control are verified by simulation and experimental results.

Power Conditioner Design and Control for a Grid-Connected Proton Exchange Membrane Fuel Cell

In this paper, the design, control and stability analysis of the inverter-based power conditioner - which is connected to the low voltage grid via an LCL filter - is presented to manage the power flow of the Proton Exchange Membrane Fuel Cell (PEMFC). Since the PEMFC-generated voltage is lower than the grid voltage, a DC-DC converter is utilized to increase the PEMFC output voltage. The LCL filter is employed to improve the injected current quality and to reduce the inverter output voltage distortions. This filter can cause resonance and system instability. The current double feedback control method, which uses inverter side and grid side currents as feedback current, is suggested to dampen the resonance and improve harmonic eliminations. The suggested power conditioner system is simulated in MATLAB/Simulink to verify the model performance and the suggested control method. The obtained results show i) good performance of the suggested system in managing PEMFC power flow into the grid, ii) high quality of the injected current and iii) system stability against the grid impedance change disturbances.

Impact of Electrical Vehicle Private Charging Stations on the Quality of the Low Voltage Network Supply

The appearance of new single-phase intensive and often coincident loads, such as the electric vehicle private charging stations (i.e., residential or private parking lots of shopping malls or workplaces), can affect the operation of low voltage (LV) distribution networks. Unbalances among the three-phase loading are extremely common, even if the end-users of a given LV network have similar behaviors. Due to the coincidence of such loads, excessive voltage drops may often appear, altering the quality of supply voltage provided to the LV end-users. This work evaluates the effects of residential and other charging stations located in parking lots of shopping malls or workplaces on the quality of supply voltage of LV grids. Then, a decentralized approach is proposed, based on the multi-agent system, which allows the different flexibility resources available on the grid to act together to improve the network quality. The agents cooperate to regulate the network nodal voltage, taking into account the characteristics of the resources they are controlling and the needs of their owners. A case study derived from a real portion of the Italian distribution system demonstrates the validity of the approach in solving the network operation criticalities.

State management of rural electricity in Phu Tho province

Electricity is an essential factor for the swift development of a country’s socio-economic status. For rural areas, electricity plays an even more important role in changing the face of rural areas, helping to gradually narrow the gap between rural and urban areas. This study uses both primary and secondary data collection methods. The primary data comes from a survey of 50 managers and employees of the Phu Tho Electricity company. The secondary data comes from a survey of 120 households in the province that use electricity. Research findings suggest that the management of rural electricity prices has been completed, including the establishment of a price bracket to control and limit abnormal price increases (the price bracket for the average retail electricity price ranges from 1,490 VND/Kwh to 1,582 VND/Kwh); gradually implementing advanced types of rural power management, such as rural cooperatives, etc. However, there are existing barriers to the state's management of rural electricity in Phu Tho province. These include the province's wide area, the traversal of power lines across hilly terrain with numerous trees and other obstacles, and the fact that the landscape shifts shape every time it rains, floods, or is hit by a tornado. In instance, the energy service cooperatives that oversee the rural low-voltage grid have not invested in upgrades in many years. As a result, electrical service continues to deteriorate. The purpose of this research is to examine the power structure of state management of rural power in the province. Therefore, this paper recommends and discusses potential options to strengthen the role of state management of rural power in Phu Tho province in the future.

Reactive Power Control of a Converter in a Hardware-Based Environment Using Deep Reinforcement Learning

Due to the increasing penetration of the power grid with renewable, distributed energy resources, new strategies for voltage stabilization in low voltage distribution grids must be developed. One approach to autonomous voltage control is to apply reinforcement learning (RL) for reactive power injection by converters. In this work, to implement a secure test environment including real hardware influences for such intelligent algorithms, a power hardware-in-the-loop (PHIL) approach is used to combine a virtually simulated grid with real hardware devices to emulate as realistic grid states as possible. The PHIL environment is validated through the identification of system limits and analysis of deviations to a software model of the test grid. Finally, an adaptive volt–var control algorithm using RL is implemented to control reactive power injection of a real converter within the test environment. Despite facing more difficult conditions in the hardware than in the software environment, the algorithm is successfully integrated to control the voltage at a grid connection point in a low voltage grid. Thus, the proposed study underlines the potential to use RL in the voltage stabilization of future power grids.

Dynamic pricing and the flexible consumer – Investigating grid and financial implications: A case study for Germany

Due to the ongoing expansion of renewable energies and the increasing energy demand of household consumers, e.g., due to the electrification of the mobility and heating sectors, grid bottlenecks and voltage band violations in low-voltage grids in Germany are expected to occur more frequently in the future. Dynamic pricing, implemented through digitization, is seen as one option to incentivize flexible and responsive electricity use of household consumers. Flexible consumption of household consumers could make grid utilization more efficient. So far, most studies on the effects of dynamic pricing focus on only one tariff for all household consumers within one low-voltage grid, whereas, in reality, households are free to choose between many different static and dynamic electricity tariffs. As previous studies have shown, the choice of tariff plays a major role in how flexibility is used. To address this research gap, we developed a model which integrates households and their static and flexible consumption and generation units into a home energy management system (HEMS) and minimizes the households’ power purchase costs. The model considers a range of dynamic tariffs that are already available today and includes the decision-making of heterogeneous household customers regarding the choice of tariff. Load flow calculations are then used to determine and analyze the effects on a low-voltage grid area. With this methodology including the free choice of tariff we go beyond the state of the art and paint a more realistic picture of the effects of dynamic tariffs on low-voltage grids. Our results show that, even though dynamic tariffs lead to increased peak demand at the level of individual households, peak loads are spread more widely within a grid area as the result of households choosing different tariffs based on economic considerations. Due to these effects, dynamic pricing has positive effects on grid utilization and could reduce the need for grid expansion.

Performance Analysis and Energy Conservation of PV Based Hybrid Power System

The increase in energy consumption due to population expansion and scarcity of fossil fuels is happening simultaneously in developing countries like India. In this regard, commercial buildings are increasingly required to employ renewable energy sources (like PV) and conserve the energy for improving energy efficiency. This research article examines the performance of such PV-based hybrid power system, consists of 11 kV grid supply, 100 kWp PV plant & 200 kVA diesel generator. The results indicate that the addition of 68.34 kVAr shunt capacitor bank to Automatic Power Factor Compensation (APFC) panel, keeps the Power Factor (PF) unity and also eliminates the PF penalties in electricity bills. The maximum demand (MD) saving Rs 54528.00 (INR) on annual basis is achieved after the integration of PV with low voltage (433 V) distribution system and grid supply (11 kV). This integration has also reduced the average transformer loading to 64.73% and improved the transformer life. However the development of high current harmonics (average value 47.10%) must be reduced to ensure the life of the electrical load.

Secondary control with grid-forming inverters for an island grid restoration approach without communication

If a blackout occurs, self-starting units, like grid-forming inverters, are needed for a black start and a restoration in a low voltage grid. Reliable power supply of the grid by grid-forming inverters can be achieved by storage systems connected to the grid-forming inverters. The use of storage systems as a power source for the grid-forming inverters requires that the storage systems must not be completely discharged or charged, otherwise the functionality of balancing the power of the grid-forming inverters is not guaranteed and a restoration failure would result. This paper presents a concept for grid restoration and maintaining a reliable island operation using a secondary control structure in combination with the implementation of a state machine in smart meters to handle such critical cases of the storage systems. The secondary control can also restore the nominal frequency after load changes without any communication between grid elements. RMS simulations are carried out in DIgSILENT PowerFactory showing the restoration process and island operation in different scenarios.

European Green Deal Implications on Country Level Energy Consumption

Abstract Research background: The European Green deal set by the European Commission has launched new business models in sustainable development. Major contributions are expected in the road transport sector; as far as conventional internal combustion creates significant input in Green House Gas emission inventories. Each EU member state has an obligation to reduce GhG emission by accelerating Electric Vehicle development. In order to foster growth of EVs, there is the need of significant investment into charging infrastructures. The article propose the model of forecasting of investment based on the forecast of the growth of the amount of electric vehicles and their demand on energy. The model includes the behaviouristic approach based on the total cost of ownership model as well as calculations of efficient usage of EV charging points. The model takes into account all types of vehicles including personal and commercial, freight and passenger. Purpose: The aim of this article is to present a complex model for forecasting the required investments based on the fore-cast of the increase in the number of electric vehicles and their demand on energy and investments. Research methodology: The general algorithm of forecasting consists of several consecutive phases: (1) Forecasting the number of electric vehicles, (2) Forecasting the energy needed for electric vehicles, based on the forecast (1) and the predicted usage level of these vehicles. (3) Forecasting the charging station number with the expected technical capacities and characteristics of these charging stations based on the forecasts (1) and (2). (4) Forecasting the need to upgrade the low-voltage grid based on the forecast (3). (5) Calculating the total investment needed based on the results of the forecasts (3) and (4). The main limitations of the study are related to the statistics available for modelling and human behaviour uncertainty, especially in the evaluation impact of measures to foster use of electric vehicles. Results: The findings of the Lithuanian case analysis, which is expressed in three scenarios, focuses on two trends. The most promising scenario projects 319,470 electric vehicles by 2030 which will demand for 1.09 TWh of electricity, representing 8.4–9.9 percent of the total energy consumption in the country. It requires EUR 230, million in the low-voltage grid and EUR 209, million in the charging stations. Novelty: The scientific problem is that the current approach on the forecasting of electric vehicles is too abstract, forecast models cannot be transferred from country to country. This article proposes a model of forecasting investments based on the forecast of the increase in the number of electric vehicles and their demand on energy. The model includes the behaviouristic approach based on the total cost of ownership model as well as calculations of efficient usage of EV charging points. The model takes into account all types of vehicles including personal and commercial, freight and passenger. The article has proven that statistics-based forecasting gives very different results compared to the objective function and to the evaluation of the effects of measures. This has not been compared in previous studies.

Monitoring of low-voltage grids using artificial neural networks and its field test application based on the beeDIP-platform

Cost-effective operation of low-voltage (LV) grids with the increasing share of distributed generators, electric vehicles, and associated volatility and unpredictability requires novel operational management strategies from the distribution system operators. To reduce the cost for grid reinforcements, monitoring of the distribution grids is of crucial importance. However, reliable measurement of the entire LV grid is economically rather impractical since it would require a very high density of measuring instruments, of which there are only very few in LV grids today. Thus, we need suitable grid monitoring methods that provide sufficiently accurate results even with a relatively low density of direct measurements. For this paper, we applied artificial neural networks (ANN)-based grid state estimation method, which has already been successfully used for medium-voltage grid monitoring, to LV grids. The performance of the ANN-based method for different measurement configurations is investigated in simulations with SimBench LV grids and is currently researched in a field test based on the beeDIP-Platform within a German suburban grid.

Avoiding low-voltage grid overloads through curative grid operator intervention with focus on electric vehicles

The increasing market penetration of electric vehicles in Germany challenges the low-voltage grid in the upcoming years. Besides conventional grid expansion, emerging congestions can be cured by using demand-side flexibility. One approach is the model of peak smoothing. This paper investigates the effects of a realisation. Therefore, the electricity grid model GridSim is extended. The effect of peak smoothing is analysed based on load flow calculations of 1,206 low-voltage grids. Future developments such as tariff-optimized (dis-)charging of bidirectional electric vehicles, known as vehicle-to-grid (V2G), are considered. The results show that the model of peak smoothing postpones but mostly does not avoid the need for grid expansion. Until the year 2040, 386 out of 1,206 grids must be expanded despite the application of peak smoothing. In most cases, this happens due to transformer overloads and voltage band violations. However, on the other hand, the model results in minor restrictions for customers, as an implementation only leads to grid operator interventions for a few hours a year. In addition, almost all the curtailed energy (> 97,8%) is recharged by the customers later. Due to the infrequent interventions, there is also little impact on the power forecast.