Medium Voltage Distribution Network Research Articles

An SDP relaxation in the complex domain for the efficient coordination of BESS and DGs in single-phase distribution grids while considering reactive power capabilities

This research proposes an efficient energy management system design for medium-voltage distribution networks from a perspective of convex optimization. The exact nonlinear programming problem that represents the operation of distributed energy resources (DERs), such as batteries and photovoltaic sources, is approximated as an equivalent semi-definite programming (SDP) problem. This SDP approximation is achieved in the complex domain using Hermitian matrices, which are the equivalent of positive semi-definite matrices in the real number domain. Two test feeders, one with 27 nodes and the other with 33 nodes, are modified to match the characteristics of Colombian rural and urban networks. The 27-bus grid is adapted to accommodate the average demand and solar generation conditions of the municipality of Capurganá, while those of the city of Medellín are used for the 33-bus grid. One of the main contributions of this research is that it considers a DER operation with variable power factors, which allows for significant improvements compared to the traditional use of a unitary power factor scheme. Numerical comparisons are conducted using metaheuristic optimizers, including parallel versions of the particle swarm optimizer, the vortex search algorithm, and the continuous version of the genetic algorithm. These comparisons demonstrate the effectiveness of the proposed SDP approximation. All simulations are carried out in the MATLAB software (version 2022b), using the disciplined convex optimizer (CVX) and the SDPT3 and SEDUMI solvers.

Analytical target cascading based real-time distributed voltage control for MV and LV active distribution networks

This paper proposes a new real-time distributed voltage control (RTDVC) scheme for medium and low voltage (MV&LV) distribution networks (DNs) based on the analytical target cascading (ATC) method. In this scheme, photovoltaic (PV) units at the LV level, on-load tap changer (OLTC) and distributed generation (DG) clusters at the MV level are optimally coordinated to regulate the bus voltages in MV&LV DNs to be close to the nominal value while minimizing the number of operations of OLTC and smoothing the reactive power outputs of DGs. Based on the ATC method, the large-scale strongly coupled voltage control problem of MV&LV DNs is decomposed into several subproblems while guaranteeing the optimality of the primal voltage optimization problem. The decomposed subproblems are iteratively solved in parallel in the MV and LV controllers, which achieves optimal voltage control in a distributed manner and effectively reduces the computation burden. An MV&LV test system with two 20 kV feeders and 39 0.4 kV LV grids was simulated to demonstrate the control performance of the proposed distributed voltage control scheme.

Key technologies and applications of cloud-edge collaborative integrated low and medium voltage distributed photovoltaic coordination control

The large-scale distributed photovoltaic access leads to overvoltage, equipment overload, and difficulty in on-site consumption, which causes power to be sent back to the high voltage level, posing hidden dangers to the safe operation of the distribution network. This article proposes optimizing the medium-voltage distribution network at the cloud side with the goal of maximum consumption and operating cost, forming a rolling strategy adjustment based on load forecasting within the day. At the edge side, the distributed photovoltaic control in the low-voltage distribution network within the jurisdiction is adjusted based on the daily adjustment strategy issued by the cloud side, completing the optimization and regulation of distributed photovoltaics on a distribution substation unit basis to achieve the control and integration of distributed power sources and consumption, coordination between operation and side, and coordinated control in the integrated medium and low-voltage zoning, achieving autonomous distribution substations and feeder lines. Field applications have proven that this solution solves problems such as line and transformer overload, and voltage quality caused by distributed photovoltaic power generation.

Low-voltage characteristic voltage based fault distance estimation method of distribution network

The traditional medium-voltage distribution network fault location method uses mainly the voltage and current measurements of the medium-voltage side, which results in problems such as high installation costs at the measuring points and complicated postoperation and maintenance work. Therefore, a fault location idea based on the distributed measurement of low-voltage side voltage is proposed in this paper. First, the characteristic voltage is adaptively selected according to the fault type. Second, the suspected fault section is determined by comparing the characteristic voltage amplitude of each measuring point. Third, the fault section is located using the section unit characteristic voltage drop defined for each suspected fault section. Finally, fault distance estimation is achieved based on the voltage difference matrix and characteristic voltage analysis. This method achieves accurate fault distance identification based on the distribution difference of the characteristic voltage of the low-voltage side under the fault state. This work provides a new economical and practical idea for determining the fault locations of distribution networks. The effectiveness of this method is evaluated by considering a 10 kV distribution network in Guangdong Province built in PSCAD/EMTDC.

Grid Planning Method of Medium Voltage Distribution Network Including Distributed Power Sources based on Timing Characteristics

Aiming at the problems of unbalanced load distribution of feeders and low utilization rate of system resources in existing medium voltage(MV) distribution network planning, it is difficult to meet the requirements of future grid construction, Propose a grid planning method of MV distribution network including distributed generator(DG) based on timing characteristics. Firstly, based on the existing grid planning achievements and temporal characteristics analysis, the grid structure and planning strategy of the MV distribution network are formed. Secondly, based on the network planning strategy, establish a dual level planning model for both internal and external distribution networks. The inner model uses comprehensive performance indicators as fitness functions to solve the optimal division of the distribution network grid, while the outer model calculates the distributed power capacity configuration of each grid with the goal of maximizing the consumption of DG. Then, based on the established dual layer planning model for the distribution network, genetic algorithms and self programming algorithms are used to solve the model by interconnecting the internal and external layers. Finally, the practicality and effectiveness of the proposed model and method were verified through practical examples combined with evaluation indicators.

A Novel Control Strategy for Soft Open Point to Address Terminal Voltage Violations and Load Rate Imbalance in Low-Voltage Power Distribution Station Areas.

In low-voltage power distribution station areas (DSAs), sensor devices and communication networks are often inadequate. Therefore, the control strategies mainly used for soft open points (SOPs) based on global information in medium-voltage distribution networks are difficult to be directly applied to low-voltage DSAs. This paper proposes a novel control strategy for SOP that only requires collecting the local information of SOP and the load rate of transformers. It aims to address the issues faced of voltage violations at the end of feeders and the load rate imbalance among adjacent DSAs under the current high penetration of renewable energy sources. In this paper, first, a sensor network consisting of sensor devices located at the transformers and each port of the SOP is introduced for information collection. Then, based on the sensitivity relationship between the node voltage and the injected power, considering capacity and voltage safety constraints, the adjustable range of the active power output for each port of the SOP is derived. According to this range, the operating states of the DSAs are categorized into four scenarios. For each scenario, the adjustment amount of SOP output power is determined to achieve comprehensive regulation of terminal voltage and load rate of all DSAs interconnected by SOP. Finally, the effectiveness of the proposed strategy is verified based on a simulation model of three flexible interconnected DSAs established in MATLAB/Simulink.

Construction of Measurement Model for Ultimate Carrying Capacity of Medium Voltage Distribution Network Based on Genetic Neural Network

Construction of Measurement Model for Ultimate Carrying Capacity of Medium Voltage Distribution Network Based on Genetic Neural Network

Decentralised Voltage Regulation through Optimal Reactive Power Flow in Distribution Networks with Dispersed Generation

The global capacity for renewable electricity generation has surged, with distributed photovoltaic generation being the primary driver. The increasing penetration of non-programmable renewable Distributed Energy Resources (DERs) presents challenges for properly managing distribution networks, requiring advanced voltage regulation techniques. This paper proposes an innovative decentralised voltage strategy that considers DERs, particularly inverter-based ones, as autonomous regulators in compliance with the state-of-the-art European technical standards and grid codes. The proposed method uses an optimal reactive power flow that minimises voltage deviations along all the medium voltage nodes; to check the algorithm’s performance, it has been applied to a small-scale test network and on a real Italian medium-voltage distribution network, and compared with a fully centralised ORPF. The results show that the proposed decentralised autonomous strategy effectively improves voltage profiles in both case studies, reducing voltage deviation by a few percentage points; these results are further confirmed through an analysis conducted over several days to observe how seasons affect the results.

Intelligent Control of the Dynamic Voltage Restorer for Fault Ride Through Capability Enhancement of a Grid-Connected Photovoltaic Power Plant in accordance with Recent Moroccan Grid Code

Background: The recent development of small-scale, decentralized generation from renewable sources and the fall in the price of the equipment needed for this operation have given a new role to the distribution networks, which is to collect the energy produced by the smallest generation plants and deliver it to the end customers. However, the national Grid Codes present technical requirements in terms of FRT and particularly LVRT and HVRT which are imposed on PV plants connected to medium voltage distribution networks, to ensure the energy needed by the loads connected to the network at the time of the failure and especially sensitive ones. Methods: In this paper, an intelligent neural network approach is applied to the DVR control circuit to enable the requirements of the sensitive load connected near the PCC, and the system is tested in the presence of a non-linear load to demonstrate its efficiency for all situations. The proposed strategy is based on the implementation of an improved ANFIS and ANN control which are compared to a tuned PI controller, the approach intends to meet the technical requirement of the recently approved Grid Code in Morocco. The simulation is performed using MATLAB Simulink. Results: The proposed approach brings great improvement to the load side voltage waveforms, and numerical experiment findings demonstrate that it can successfully guarantee the technical requirements of the electrical grid code. Conclusion: The results obtained show better behavior of the system using ANFIS and ANN control strategy in the presence of a nonlinear load and a significant improvement of the voltage THD.

Distribution network planning method: Integration of a recurrent neural network model for the prediction of scenarios

The integration of new types of consumers and prosumers into distribution networks presents significant challenges for network planners, especially given the uncertainties of future expansions. This paper introduces a method for distribution network planning that integrates a Long-Short Term Memory (LSTM) model with a confidence interval threshold for long-term scenario predictions. The proposed forecasting model considers datasets collected from monitoring systems which include aggregated demand and self-consumption from photovoltaic sources. The use of the LSTM model enables a more accurate prediction of expansions, as it captures nonlinear patterns in time series data while taking into account the inherent characteristics of non-stationary time series data. The proposed method was tested on an existing radial medium voltage distribution network in Spain, taking into account the operational thermal limits for lines and substation time series measurements. The proposed planning approach also considers asset costs, active planning solutions, and time-series load flow analysis. The results obtained indicate that the use of time-based forecasts from aggregated generation and demand is a more realistic solution for flexible planning solutions when they are compared to traditional strategies.

A new method for estimating fault location in radial medium voltage distribution network only using measurements at feeder beginning

A new method for estimating fault location in radial medium voltage distribution network only using measurements at feeder beginning

Passive filters allocation in unbalanced distribution network with high penetration of distributed generation

The purpose of this paper is the allocation of passive filters in an unbalanced power network with high penetration of distributed generation to minimize the costs of power losses in the distribution lines, including power losses caused by harmonic components and neutral conductor power losses due to unbalanced loads. The harmonic components and the fundamental current generated by the distributed generation cause a voltage increase in the generation bus, and the voltages in the network above the limit allowed by standard are reduced by allocating passive filters without cutting the active power in the distributed generation. The unbalance and reactive power compensation is performed by the ideal compensation method applied to the distribution network. The tests are for the IEEE 34 bus network, with the fourth wire in the simulation being the isolated neutral. The scatter search metaheuristic applied in the simulation tends to minimize the costs of power losses in the lines and the costs of the passive filters allocated in the medium voltage distribution network, meeting the operational constraints of the network.

Analisis Ketidakstabilan Beban Arus Netral dan Rugi-Rugi Daya Pada Trafo Distribusi Penyulang Pas 21 PT. PLN UPB Banda Aceh

This research focuses on analyzing power losses due to load imbalance in the medium-voltage distribution network in Pasar Aceh. The aim is to determine the magnitude of power losses that occur at the distribution substation in Pasar Aceh. The research method involves analysis, calculations, and simulations using the ETAP 12.6 software. The results of the analysis indicate that load imbalance in the Pasar Aceh substation leads to power losses. The Trafo Samping Pasar Aceh experiences power losses of 0.77% with a load imbalance of 16.33%. The second transformer in the BNI 46 area incurs power losses of 0.98% with a load imbalance of 30.33%, and the transformer in the BLKG KOTTY area has power losses of 1.17% with a load imbalance of 50.33%. These findings affirm that the greater the load imbalance, the higher the resulting power losses in the electrical distribution network.

A Stackelberg Game-Based Model of Distribution Network-Distributed Energy Storage Systems Considering Demand Response

In the context of national efforts to promote country-wide distributed photovoltaics (DPVs), the installation of distributed energy storage systems (DESSs) can solve the current problems of DPV consumption, peak shaving, and valley filling, as well as operation optimization faced by medium-voltage distribution networks (DN). In this paper, firstly, a price elasticity matrix based on the peak and valley tariff mechanism is introduced to establish a master–slave game framework for DN-DESSs under the DPV multi-point access environment. Secondly, the main model optimizes the pricing strategy of peak and valley tariffs with the objective of the lowest annual operating cost of the DN, and the slave model establishes a two-layer optimization model of DESSs with the objective of the maximum investment return of the DESSs and the lowest daily operating costs and call the CPLEX solver and particle swarm optimization algorithm for solving. Finally, the IEEE33 node system is used as a prototype for simulation verification. The results show that the proposed model can not only effectively reduce the operating cost of the distribution network but also play a role in improving the energy storage revenue and DPV consumption capacity, which has a certain degree of rationality and practicality.

A Fault Location Method for Medium Voltage Distribution Network Based on Ground Fault Transfer Device

The arc suppression device based on ground fault transfer (GFT) has been preliminarily applied in the medium voltage distribution network (MVDN). An accurate travelling wave (TW) fault location method is proposed to extend the use of the ground fault transfer device. D-PMU is used as a travelling wave detection tool to record the transient voltage travelling waves of fault grounding and bus active grounding during arc suppression. Then, the faulty section is identified through the time difference of travelling wave arrival at the upstream and downstream measurement points. On this basis, the fault location equations of the arrival time and distance of the upstream travelling wave are established, and an accurate fault location method based on the arrival time difference of the travelling wave is proposed. The simulation model is established by PSCAD/EMTDC, and the results show that the method has high location accuracy, and the absolute error is less than 30 m. It is not affected by the TW velocity, the fault conditions, or the distributed power sources.

Study on the Change of Power Consumption Structure in Xumai Township, Nimu County, Lhasa, Xizang

The research on the evolution of rural power consumption structure in Xizang reflects the information on rural power development in Xizang, and the information on rural power development shows the people's living standards and demand trends. In order to understand the depth of changes in the power consumption structure of farmers and herdsmen households, the project team conducted a field survey of the changes in power supply sources, power consumption structure, power consumption equipment, and operation and management status of Sumai Township, a typical village in Nimu County, Lhasa City, Xizang over the years, and explored the history and trend of power development in remote villages in Xizang. Field research has found that before 2014, the township mainly relied on small-scale independent solar photovoltaic power supply, which was almost used for lighting; Since the implementation of the State Grid in 2014, electricity consumption has shifted from low voltage to wide voltage. In the past three years, the annual electricity consumption growth rate in Xumai Township has exceeded 6%, and the power supply stability has reached 90%. At the same time, the township utilizes solar photovoltaic street lights. The electrical appliances used have developed from a single lamp to power appliances such as household appliances, agricultural electric vehicles, tsamba machines and oil presses. The distribution line of the township is gradually being replaced with medium and low voltage, and is equipped with a 35kV Xumai substation. The 10kV medium and low voltage distribution network project of the rural power grid is gradually being put into operation and put into practice. However, research has found that villagers hope to use more clean energy such as solar energy for power supply and heating, in order to reduce the cost of electricity and gas bills.

OPTIMIZATION OF THE USE OF DISTRIBUTED ENERGY RESOURCES IN LOCAL ELECTRICAL POWER SYSTEMS ACCORDING TO THE CRITERION OF MINIMUM LOSS OF ELECTRICITY

The issue of optimizing the use of distributed energy resources in local electric power systems (LES) based on the criterion of minimum power loss is considered. It was determined that an important step in optimizing the use of distributed energy resources in the LES is the development of an energy router that allows devices that generate, store, and consume electricity to be combined into a single system at low voltage (without integration into medium voltage electrical networks). The energy router itself can be positioned as a basic device that ensures the operation of LES, the interaction of neighboring LES at the level of energy and information exchange, and the integration of specific LES to medium voltage distribution networks.
 It is shown that the basic component of the evaluation of the effective functioning of energy routers and the platform approach in the LES, in accordance with the requirements of the Energy Internet, is the analysis of the components of electricity losses, the influence on their level of various factors, as well as the formation of appropriate energy efficiency criteria and the assessment of the partial impact of LES elements. It is proposed to carry out a description of energy processes during the decomposition of Frize reactive power with the allocation of reactive and active current in the controlled intersections of the system. The decomposition of the QF power into components under the action of various causes (factors) of additional electricity losses in the LES, in particular, due to different modes of operation of generators and LES loads (voltage and current spectra), both during the period of system operation and for an arbitrary period of time, was considered. which is determined by technological factors of system operation.
 The use of Frize power made it possible to take into account the energy supply processes of LES loads on alternating and direct current from a single point of view, in particular, to assess the impact of a combination of various factors of the appearance of additional electricity losses; comparison of electricity losses for different time intervals through a selected controlled intersection, when the direction of the flow of electricity is constant or the direction of the flow of electricity changes during separate time intervals; analysis of electricity losses in direct and alternating current systems of LES or hybrid systems, where modified capacities are introduced, as integral estimates of the discrepancy, which determines the influence of distorting factors; assessment of the impact of changes in voltage and current in the intersection of LES of limited power on the components of additional losses; analysis of changes in load consumption of active power according to the first harmonic and higher harmonics as integral indicators.

Flexible load control of new energy based on improved genetic algorithm

In the medium and low voltage distribution network, the load form of users is complex and changeable. There are a large number of single-phase and two-phase loads connected to the distribution network, resulting in a three-phase unbalanced operation of the distribution network. With the development of the new energy, the high proportion of distributed new energy will further aggravate the three-phase imbalance of the distribution network. Therefore, this paper proposes a coordinated optimization framework of droop parameters based on the multi-converter droop control, which takes the minimum loss of the distribution network as the optimization objective, and optimizes the reference point and the slope of the VSC droop hierarchically. A small-signal stability optimization dispatching method for the VSC droop slope in the DC distribution network is proposed. By adding small-signal stability constraints to the slope optimization model, the optimal slope command and slope stability region which can ensure the small-signal stable operation of the system are obtained. Experiments show that the optimization model of the VSC small-signal stability slope can make the droop control instruction significantly improve the small-signal stability of the system to adapt to the intra-day source load power fluctuations with a small economic cost. The slope stability region pre-optimization model can provide a reliable stability slope upper limit for the slope optimization problem based on ensuring the system operation economy. The research in this paper can make full use of the flexible control ability of power electronic equipment, and then suppress the three-phase imbalance, which is of great significance to improve the security and economy of the distribution system operation.

A New Control Strategy of Hybrid Reactive Power Compensation System in Distribution Network

Reactive power compensation is an important measure to improve the power quality of distribution networks, especially with the increasing connection of distribution transformers, heavy industrial electrical equipment, and asynchronous motors, which generate a large amount of reactive power demand. Traditional reactive power compensation devices, such as fixed capacitors (FC) and thyristor switched capacitors (TSC), have some drawbacks, such as low response speed, harmonic generation, and switching shock. A static synchronous compensator (STATCOM) is a flexible AC transmission system (FACTS) device that can provide fast and continuous reactive power compensation, but it also has some limitations, such as high cost, large capacity requirement, and low utilization rate. Therefore, hybrid reactive power compensation systems that combine FC or TSC with STATCOM have attracted much attention in recent years. Many researchers have proposed and studied different topologies and control methods of hybrid systems to overcome the disadvantages of single devices and achieve better performance. However, most of the existing hybrid systems are designed for low or medium-voltage distribution networks, and their performance under high-voltage distribution networks is still unclear. Moreover, the coordination control strategy of the hybrid system and its subsystems is also a key issue that affects the effectiveness and efficiency of reactive power compensation. In view of this, this paper aims to propose a TSC+STATCOM hybrid reactive power compensation system for high-voltage distribution networks, which optimizes the shortcomings of traditional reactive power compensation devices. The system uses the synergistic effect of TSC and STATCOM to achieve large-scale static reactive power and small-scale dynamic reactive power compensation and adopts a switching strategy based on an expert decision system. This paper introduces the working principle of each subsystem of the hybrid reactive power compensation system in detail and builds a simulation model of the hybrid reactive power compensation system under a high voltage distribution network on Matlab/Simulink platform. The simulation results verify the feasibility and excellent performance of the system control method in reactive power compensation and improving power quality.

The Impact of a 1.1 MWp PV Rooftop Integration in Medium Voltage Distribution Networks

A high penetrating the capacity of Rooftop PLTS has an impact on the performance of distribution network operations and the prior technical studies only using simulation. This paper examines the impact of integrating a 1.1 MWp PV Rooftop into the medium voltage distribution network, involves a comparison between simulation data obtained using the ETAP software, before and after integration, compared with direct measurements. The results indicate improvements in the distribution operating performance. Following the integration, there was a 0.05% increase in voltage levels, a 0.06% increase in short circuit current, a 1.25% reduction in network losses, up to 8.9% harmonics current, up to 0.14% harmonics voltage, and a 0.28% decrease in power factor, as observed at both the substation and the network, they are in accordance with the measurement results.