Grid Distribution System Research Articles

High Brightness and High Voltage Dimmable LED Driver for Advanced Lighting System

In energy efficient system designs, LED lighting leads to reduction in global energy demand. This paper proposes a high brightness, high efficiency, dimmable LED driver based on linear current regulator technology for DC grid distribution systems. The proposed driver has excellent characteristics like highest lumen per watt, long lifetime, high reliability, compact, low cost, both environmental and user friendly which makes it suitable for lighting applications. Steady state and small signal model of the proposed driver are performed which helps in minimizing ground current and accurate compensator design, respectively. These two modelling approaches result in the optimization of both footprint and cost of the driver. The performance of the proposed 20W driver is modeled using real-time simulation in spice software. Experimental prototype is developed to validate the performance of the proposed driver for different dimming levels and achieves a maximum efficiency of 97%.

Vehicle-to-grid service development logic and management formulation

Vehicle-to-grid (V2G) is regarded as the effective way to reconcile contradictions between an electric power system and electric vehicles (EVs). A lot of research has been carried out to affect this, often based on different technical and trading model assumptions. The value of the research is dependent on how reasonable the assumptions it makes are. This paper presents a framework for analyzing V2G service development from a coevolutionary perspective in which the interactive relation between the diffusion of EVs and the upgrade of the distribution grid system is considered. A V2G service development logic and its management formulation are put forward. First, the motivations and contradictions of developing V2G services are analyzed. Then a development phase division of the V2G services is proposed in view of the coevolution relation between the grid upgrade and the development of the EV. Next, taking into account the characteristics of each phase, the physical trade structures and corresponding management hierarchies, management relations as well as management measures, are proposed. This paper provides a new perspective of V2G service development, answers the core question on how to make the V2G vision come true in synergy with the development of EVs, and gives some advice on future V2G management paradigms.

Storage Valuation in Congested Grids

This paper proposes an aggregated approach for the technical and economic assessment of battery energy storage systems (BESSs) in congested distribution grids (low voltage and medium voltage). For this purpose, the usage of BESS to avoid or temporally shift grid extensions is analyzed and compared with other technical measures such as grid extensions, innovative grid equipment, and feed-in curtailment. A combined optimization approach is used to identify jointly optimal economic decision of grid and storage operators. The investigations highlight the economic competitiveness of BESS, compared to other measures, when additional participation of BESS in wholesale market is allowed. It is shown that optimal decisions for grid development are strongly dependent on key grid parameters like line length and level of excess photovoltaic-feed-in. Moreover, the applied regulations, e.g., renewable curtailment rules, are found to impact considerably on the optimal decisions. The proposed methodology is, in contrast to existing approaches, suitable for the investigation of large varieties of grid configurations and grid utilizations with limited efforts. It thus allows identifying situations, in which the application of BESS in distribution grids is most effective. Moreover, it enables a thorough assessment of the impact of regulatory changes given large heterogeneity of existing distribution grids.

Heterogeneous Wireless Networks for Smart Grid Distribution Systems: Advantages and Limitations.

Supporting a conventional power grid with advanced communication capabilities is a cornerstone to transferring it to a smart grid. A reliable communication infrastructure with a high throughput can lay the foundation towards the ultimate objective of a fully automated power grid with self-healing capabilities. In order to realize this objective, the communication infrastructure of a power distribution network needs to be extended to cover all substations including medium/low voltage ones. This shall enable information exchange among substations for a variety of system automation purposes with a low latency that suits time critical applications. This paper proposes the integration of two heterogeneous wireless technologies (such as WiFi and cellular 3G/4G) to provide reliable and fast communication among primary and secondary distribution substations. This integration allows the transmission of different data packets (not packet replicas) over two radio interfaces, making these interfaces act like a one data pipe. Thus, the paper investigates the applicability and effectiveness of employing heterogeneous wireless networks (HWNs) in achieving the desired reliability and timeliness requirements of future smart grids. We study the performance of HWNs in a realistic scenario under different data transfer loads and packet loss ratios. Our findings reveal that HWNs can be a viable data transfer option for smart grids.

A simulation framework for assessing the market and grid driven value of flexibility options in distribution grids

The increasing share of renewable distributed energy resources (DERs) entails a rising number of congestions in the German distribution grids, such as voltage band violations and overloading of network assets. Consequently the need for grid expansion increases [1]. A politically promoted alternative to grid expansion is managing congestions by the preventive use of flexibility options, such as flexible generation, load management and storage systems [2]. However, preventive congestion management is not yet established in distribution grids. Thus, various measures are under discussion to stimulate the provision of flexibility options by its owners for concerns of congestion management. Assessing the suitability of solutions among these congestion management measures (CMMs) requires a realistic modeling of grid operation, energy system structures and the behavior of the owners of DER and flexibility options.The intended application of the presented simulation framework is consequently the assessment of the macro- and micro-economic effects of preventative CMMs in distribution grids. Supporting that goal, the design of an agent-based simulation framework, which incorporates detailed optimization models for simulating the behavior of grid users (owners of DER and flexibility options) and Distribution System Operators (DSO) is presented. Exemplarily it is applied on a realistic distribution grid use case. The simulation framework enables analyzing the consequences of the grid users’ interaction with the DSO following defined CMMs. Within the framework, the grid users are modeled as individually or market driven oriented users, who both aim at improving their micro-economic situation. The DSO’s operational target is the minimization of congestion management costs under application of several CMMs.The exemplary application focuses on four congestion management concepts, such as flexible tariffs and a market-based flexibility provision. The chosen use case comprises a congested distribution grid with high PV penetration and grid users at the medium and low voltage level. In the use case, the alternatively necessary curtailment of renewable energy can be reduced from 15% to 35% depending on the considered CMM. The most promising CMM (a market-based flexibility provision) reduces the DSO’s congestion management costs by 33%, without degrading the grid users’ economic situation. Future work will advance the analyses based on a comprehensive database of realistic distribution grid scenarios.

An Impedance-Based Method for Distribution System Monitoring

This paper presents a new approach in monitoring of a power distribution system. It uses the bus voltage and injected current to extract the apparent impedance seen from the measuring unit location. Then the apparent impedance variation is used for the monitoring of different electrical quantities of the feeder such as feeder power factor, and the minimum and maximum of active and reactive power flow. This paper also presents the mathematics for defining the monitoring zone on the R-X plane to detect those parameters variations. The proposed method was tested with the unbalanced distribution system feeder loading, distributed and lumped model of solar, and wind power generations. OpenDSS and MATLAB are used to test the effectiveness of the method with the IEEE 8500 node test feeder. The dynamic performance of the proposed method is studied for online monitoring of the reactive power capability requirement of a Canadian utility for a wind farm integrated to the system. The results show that the monitoring method based on the apparent impedance has a good capability to detect different operation conditions. In addition, the simplicity of the proposed method allows easy application of it in smart grid and traditional distribution system.

Research on Publishing CIM Model Change Events through OPC UA

This paper studies how to publish the change events of CIM model using OPC UA, and proposes a method to publish CIM model change events using OPC UA based on mapping CIM model to OPC UA address space. By comparing with the CIS GDA model change notification service function in the legacy CIS interface, it is confirmed that the OPC UA service completely covers the original CIS GDA model change notification service function. Base-Model-Change-Event-Type and the more detailed General-Model-Change-Event-Type, Semantic-Change-Event-Type are used to provide appropriate model change information for clients through OPC UA Event service. CIM model change events in data platform of distribution grid and utilization system are published using OPC UA, the research results have been verified.

Modeling Coordination Between Renewables and Grid: Policies to Mitigate Distribution Grid Constraints Using Residential PV-Battery Systems

Distributed photo-voltaic (PV) generation is one of the pillars of energy transitions around the world, but its deployment in the distribution grid requires costly reinforcements and expansions. Prosumage - consisting of a household-level PV unit coupled with a battery storage system - has been proposed as an effective means to facilitate the integration of renewable energy sources and reduce distribution grid stress. However, tapping its full potential requires regulatory interventions; otherwise, system costs could rise despite increasing flexibility. We analyze the effectiveness of different policy schemes to mitigate the need for distribution capacity expansion by incentivizing beneficial storage operation. Our novel top-down modeling approach allows analyzing effects on market prices, storage dispatch, induced distribution grid requirements, system costs, and distributional implications. Numerical results for German power system data indicate that required distribution grid requirements can be reduced through simple feed-in policies. A uniform limit on maximum grid feed-in can leave distribution system operators better off, even if they fully compensate prosumage households for foregone revenue. Policies imposing more differentiated limits at the regional level result in only marginal efficiency improvements. Complete self-sufficiency (autarky) is socially undesirable, as it confines important balancing potential and can increase system costs despite adding storage.

Modeling Coordination between Renewables and Grid: Policies to Mitigate Distribution Grid Constraints Using Residential PV-Battery Systems

Distributed photo-voltaic (PV) generation is one of the pillars of energy transitions around the world, but its deployment in the distribution grid requires costly reinforcements and expansions. Prosumage - consisting of a household-level PV unit coupled with a battery storage system - has been proposed as an effective means to facilitate the integration of renewable energy sources and reduce distribution grid stress. However, tapping its full potential requires regulatory interventions; otherwise, system costs could rise despite increasing flexibility. We analyze the effectiveness of different policy schemes to mitigate the need for distribution capacity expansion by incentivizing beneficial storage operation. Our novel top-down modeling approach allows analyzing effects on market prices, storage dispatch, induced distribution grid requirements, system costs, and distributional implications. Numerical results for German power system data indicate that required distribution grid requirements can be reduced through simple feed-in policies. A uniform limit on maximum grid feed-in can leave distribution system operators better off, even if they fully compensate prosumage households for foregone revenue. Policies imposing more differentiated limits at the regional level result in only marginal efficiency improvements. Complete self-sufficiency (autarky) is socially undesirable, as it confines important balancing potential and can increase system costs despite adding storage.

The German experience with integrating photovoltaic systems into the low-voltage grids

Abstract The integration of rooftop photovoltaic systems in the low-voltage distribution grids has become a major international trend, helped by the sinking prices for photovoltaics. One of the key questions revolves around the technical challenges brought about by the grid integration of these decentralized systems. This paper therefore analyzes the substantial practical experiences of ten representative German distribution system operators, who play a leading role in this field. Our findings show that grid expansion measures are primarily undertaken to ensure compliance with the permissible limits for voltage and current. Grid optimization measures represent the most economical initial step and include, for instance, changes in grid structure and wide-area control. Once their potential is maximized, classic grid expansion measures such as laying parallel cables are implemented. In individual cases, the low-voltage grid is reinforced by so-called intelligent operating equipment such as voltage regulators or voltage-regulated local distribution transformers. Moreover, improved grid planning measures lead to a better use of the available low-voltage grid capacity. The practical solutions successfully implemented by German distribution system operators should also prove relevant for other countries that are currently planning the deployment of decentralized renewable energies.

Modelling and control of vanadium redox flow battery for profile based charging applications

Abstract Batteries are the crucial link in accelerating the penetration of renewables in distributed grid systems. With multiple sources (most of which are intermittent), there is a need to optimize the usage of these energy storage systems. It is vital to have a charging algorithm to intelligently charge the battery, considering the losses and state of health. Several battery charging techniques exist for most of the mainstream batteries such as lithium ion and lead acid batteries. These charging algorithms are developed for specific battery chemistries to optimize the charging operation by controlling the charging current. There has been no specific charging methodology proposed, considering the uniqueness of flow batteries. In this paper a flow battery model is developed to accommodate the implementation of charging protocols by controlling the current and flow rate in real time. The aim is to demonstrate a methodology where different user requirements can be programmed for efficient operation of the battery to perform a given task. The control is established by an intuitive fuzzy logic controller for changing the input variables based on the intrinsic losses, pump power loss and the capacity decay due to the aging of the battery. The need for such a controller to handle different scenarios of operation arises from the vast applicability of large scale energy storage. A simple example of such a system is proposed with demonstrating three operator selectable modes namely Autonomous (A), Energy bias (E) and Time bias (T). In each case, a specific current value and flow rate value is selected by the controller and is fine-tuned during the charging process. The values are tuned for specific modes of operation and different aspects of the battery performance are studied for these modes. This work demonstrates a method to leverage the use of a physical model based system in a high level user interface for controlling flow batteries.

Stability improvement of microgrids in the presence of constant power loads

Renewable energy sources, the most reasonable fuel-shift taken over the naturally limited conventional fuels, necessarily deal with the self-sustainable microgrid system rather than the traditional grid distribution system. In practice, the microgrid system experiences the challenge of instability due to the Constant Power Load (CPL) from many electronic devices. In this paper, AC microgrid stability, besides the stability analysis and pole zero movement, is thoroughly investigated for each and every considerable parameter of the system in order to improve the stability scenario. After demonstrating all cases regarding the instability problem, the storage based virtual impedance power compensation method is introduced to retain the system stability and extend the loading limit of the microgrid system. Here, in this proposed method, both the active and reactive power compensation techniques are suggested for a potential solution. Besides this, a PID controller is implemented to maintain the constant terminal voltage of CPL via current injection method from storage. All the cases and results are rigorously scrutinized in the virtual platform such as MATLAB/Simulink with appreciable aftermaths. Hardware implementation of the proposed method is also conducted to find out its effectiveness.

Optimized Measurement Allocation for Power Distribution Systems Using Mixed Integer SDP

This paper presents a method for placement of metering systems in distribution grids taking into account the aspects of observability and state estimation accuracy. The measurement placement problem is conceptualized as the optimized allocation of a prespecified number of measurements in order to minimize the error variances of the state estimates either for observable or nonobservable networks. The proposed approach exploits the M-optimal experimental design technique to formulate the problem as a mixed integer semidefinite programming model. We demonstrate the efficacy of the proposed approach in terms of optimality and convergence speed through simulations on a 95-bus distribution grid.

Optimal hybridisation and management of PV/batteries hybrid systems in residential distribution networks

This study presents a decentralised off-line strategy for optimal hybridisation and management of photovoltaic (PV)/batteries hybrid systems in residential distribution grids. The aim is to study the voltage plan of the network without/with this process for different penetration rates of PVs and also comparing with the initial grid without PV. The tool has been tested by using a real Swiss distribution network and real data of houses electricity consumption. In addition, a voltage assessment methodology has been proposed. Lot of study cases has been performed and the results show that the voltage plan of the grid is greatly improved, thanks to the tool proposed. For quantify the results, one performance index, which assesses the quality of the network voltage has been introduced.

Development Of An Agent-based Model For Assessing The Market And Grid Oriented Operation Of Distributed Energy Resources

The increasing share of renewable distributed energy resources (DERs) entails a rising number of congestions and consequently the need for grid expansion measures in distribution grids. Preventive congestion management measures using flexibility options are a frequently discussed alternative for grid expansion. The flexibility options in distribution grids comprise flexible generation and load management as well as storage systems. However, preventive congestion management is not yet established in distribution grids. Traffic light concepts and flexibility markets are among the congestion management concepts in discussion. In order to determine the optimal design option for the future, a model for the quantitative assessment and simulation of different congestion management measures (CMMs) is needed.This publication presents a newly developed agent-based model for the evaluation of different congestion management concepts considering the perspectives of electricity market-oriented grid users and distribution system operators (DSOs). The market-oriented grid users can be divided into two major categories: Smart Homes (SHs) and Virtual Power Plants (VPPs). Both concepts combine synergies from distributed energy technologies. Four different congestion management concepts are analyzed with the model for an exemplary test case. The analysis of the test case shows that the necessary amount of curtailment in distribution grids can be reduced, when actively using SHs as part of a preventive congestion management. Depending on the considered CMM, the reduction of curtailment in the examined distribution grid ranges from 15% to 35%. The most promising strategy, a market-based flexibility deployment, reduces the curtailment costs for the DSO by 33% compared to the curtailment needed without the use of flexibilities.

Electric field energy harvesting under actual three‐phase 765 kV power transmission lines for wireless sensor node

For the first time, under the actual three-phase 765 kV power transmission lines, electric field energy is harvested and Zigbee-based sensor node powered by the harvested energy is operated autonomously. A conductor tube is placed between power lines and the earth surface for electric field energy harvesting. The voltage difference between conductor tube and the earth surface is rectified and the harvested electric energy is stored in a storage capacitor. A self-sustaining power management circuit adopting low-power comparator with hysteresis is devised to monitor the stored energy and to operate the sensor node autonomously according to the stored energy. Experimental results under the actual three-phase 765 kV power lines show that the data transfer period is almost inversely proportional to the square of the height of the sensor module from the earth surface. The temperature data is transmitted in every 25 s when the conductor tube is located at 4 m from the earth surface. Since the presented non-contact energy harvesting apparatus is very simple, robust and low-cost, it is believed that the presented technology can be widely applied to power transmission, distribution and smart grid system.

Modeling and simulation of micro grid distribution system to reduce harmonics using active power filter and PI Controller

Modeling and simulation of micro grid distribution system to reduce harmonics using active power filter and PI Controller

Synchrophasor Sensor Networks for Grid Communication and Protection.

This paper focuses primarily on leveraging synchronized current/voltage amplitudes and phase angle measurements to foster new categories of applications, such as improving the effectiveness of grid protection and minimizing outage duration for distributed grid systems. The motivation for such an application arises from the fact that with the support of communication, synchronized measurements from multiple sites in a grid network can greatly enhance the accuracy and timeliness of identifying the source of instabilities. The paper first provides an overview of synchrophasor networks and then presents techniques for power quality assessment, including fault detection and protection. To achieve this we present a new synchrophasor data partitioning scheme that is based on the formation of a joint space and time observation vector. Since communication is an integral part of synchrophasor networks, the newly adopted wireless standard for machine-to-machine (M2M) communication, known as IEEE 802.11ah, has been investigated. The paper also presents a novel implementation of a hardware in the loop testbed for real-time performance evaluation. The purpose is to illustrate the use of both hardware and software tools to verify the performance of synchrophasor networks under more realistic environments. The testbed is a combination of grid network modeling, and an Emulab-based communication network. The combined grid and communication network is then used to assess power quality for fault detection and location using the IEEE 39-bus and 390-bus systems.

Fault Diagnosis of Smart Grid Distribution System by Using Smart Sensors and Symlet Wavelet Function

In today's era of smart grid system scenario, the fault diagnosis is of utmost important task. Present distribution networks change drastically due to expansion and inclusion of large number of distributed generation units into power system at distribution level. To face the challenges of modernized girds, conventional fault diagnosis methodologies require drastic change by making use of advanced infrastructure and technologies. This will be helpful to achieve automation in fault diagnosis tasks, improved power quality, reliability, resilience and self healing property of the power system. This paper proposes the use of smart sensors and advanced communication technology that will be available in future smart grids to carry out automated fault diagnosis tasks using signal processing techniques. Methods of using Standard deviation features of fault transient signal and a fault location factors are proposed. Performance of various scaling levels, features and components of fault transient current signals extracted using the latest non conventional Symlet mother wavelet function are evaluated and compared. The attempt is made to select optimal features and components of fault transient currents to improve the performance of present limited types of available fault locators. The tests are taken on standard model of smart grid distribution system but can be applied for fault diagnosis of any other power equipment. Results show adequate accuracy to extend the use of proposed method for real time applications.

Thermal Stress Analysis of Medium-Voltage Converters for Smart Transformers

A smart transformer (ST) can take over an important managing role in the future electrical distribution grid system and can provide many advanced grid services compared to the traditional transformer. However, the risk is that the advanced functionality is balanced out by a lower reliability. To address this concern, this work conducts thermal stress analysis for a modular multilevel converter (MMC), which is a promising solution for the medium voltage stage of the ST. The focus is put on the mission profiles of the transformer and the impact on the thermal stress of power semiconductor devices. Normal operation at different power levels and medium voltage grid faults in a feeder fed by a traditional transformer are considered as well as the electrical and the thermal stress of the disconnection and the reconnection procedures. For the validation, the thermal stress of one MMC cell is reproduced on a laboratory setup with high-speed temperature measurement. It is concluded that the investigated conditions, including inrush currents and power variations, do not cause a significant lifetime reduction.