DIgSILENT PowerFactory Research Articles

Online Estimation of Disturbance Size and Frequency Nadir Prediction in Renewable Energy Integrated Power Systems

The displacement of conventional synchronous generation by Inverter-Based Resources (IBRs) poses critical challenges to the frequency stability of Renewable Energy (RE) integrated power systems. An increased shift towards green energy by integrating RE sources that provide little or no inertia results in a high Rate of Change of Frequency (RoCoF) and deteriorated frequency nadir/zenith following a credible system disturbance. Prediction of frequency metrics, such as frequency nadir and RoCoF, immediately after disturbances will help grid operators to take preventive/corrective actions, such as the deployment of faster frequency control, to ensure secure and stable grid operation. This paper presents an easy-to-implement analytical method to estimate disturbance size in a power system immediately following a contingency which is then used for predicting frequency nadir. The proposed estimation method uses active power measurements from a limited number of monitoring nodes and an adaptive bus admittance matrix of the system for the disturbance size estimation. The estimated disturbance size is then used to predict frequency nadir using a Neural Network (NN) based method. The performance and accuracy of the presented approach are evaluated using a standard IEEE 39 bus system and a real-life Gujarat power system in India through extensive simulations in DIgSILENT PowerFactory, considering various cases of disturbance size, type, and location.

Performance Evaluation of Distribution System Interconnected with Solar PV Plants Using DIgSILENT

Many African countries, such as Botswana, receive high insolation that can be used to generate electricity. However, they still rely on thermal power generation and imports from neighbouring countries through various African power pools. Thermal generation methods result in an increase in carbon footprint. Therefore, in pursuance of the global climate change goals, the Government of Botswana has subscribed to allow all end users with the capacity to install solar rooftops and sell extra electricity to the power utility. These interconnections of solar PV plants to the grid are bound to bring challenges to the steady state system performance. This research, therefore, evaluates the performance of the integrated system focusing on the greater Gaborone distribution system (GGDS), where five government projects are being piloted. The study has adopted two scenarios by providing a performance comparative analysis between the system baselines to a solar integrated system using DIgSILENT Power Factory software. The system studies conducted include power flow, effects on voltage and line loading. This research found out that integrating PV plants to GGDS distribution network improves voltage profiles and a decrease in overall percentage loading of the feeders and interconnectors. However, some notes could only permit a limited loading. In conclusion, the implications of the effects of solar PV on the distribution system differ from one circuit to another; therefore, it calls for utilities to conduct an intensive network assessment for each particular feeder before interconnecting with solar.

Providing Reactive Power Support from Photovoltaics for Voltage Profile Improvement in Distribution Networks

The increasing prevalence of distributed generation, particularly photovoltaic (PV)-based sources, in electricity distribution networks underscores the need for comprehensive studies on their impact on network operation. This paper addresses the significance of leveraging PV inverters to provide both capacitive and inductive reactive power support, thereby reducing the necessity for additional investments. By incorporating PVs in this dual role, the distribution network gains enhanced flexibility in managing voltage profiles, reducing dependency on additional investments in infrastructure. This dual functionality addresses the dynamic needs of the grid, offering a sustainable solution to optimize the network's overall performance while harnessing the inherent capabilities of PV technology. In this investigation, Python-based Particle Swarm Optimization (PSO) and Firefly algorithms (FA) have been applied to ascertain the optimal amount of reactive power support for enhancing the voltage profile of the network, and the effectiveness of the algorithms are compared. The algorithms take into account the reactive power limits inherent in PV plants within the distribution network, and optimize the reactive power support that should be taken from each PV that won’t result in any curtailment in PVs’ active power generation, i.e., only the remaining capacity of the inverter is allowed for the reactive power support, if needed. The network is modeled, analyzed, and simulated using the DIgSILENT PowerFactory program, with seamless integration between the network model and the optimization algorithm facilitated through Python. The obtained results demonstrate that reactive power support from PV plants yields positive effects on the overall voltage profile of the network.

P-f Stability of 2030 Nordic Power System due to Non-Synchronous Generation

The Nordic Power System is undergoing significant transformation and development in the coming years. A driving factor for this is the increased dependency on renewable energy sources and high voltage direct current transmission (HVDC). Various stability challenges due to the dynamics of reactive power - voltage (Q-V) balancing and active power - frequency (P-f) balancing seep into the system with such rise of non-synchronous generation (NSG). This paper investigates the projected impact of NSGs on the P-f dynamic performance of Nordic power system in 2030. As NSGs are systems with low inertia, power discrepancies lead to larger oscillations, higher Rate of Change of Frequency (RoCoF) and bigger maximum frequency deviation (MFD) values. To address these issues, Emulated Inertia (EI) control for wind turbines and Synthetic Inertia (SI) control for VSC-HVDC links are proposed in this paper. The simulation is carried out using DIgSILENT PowerFactory 2022 SP1 simulation software. The results obtained confirm the Effectiveness of the proposed EI and SI methods to enhance frequency response and mitigate deviations.

PROTECTION COORDINATION OF PHOTOVOLTAIC POWER PLANT IN THE TIME DOMAIN

The safety of workers and equipment in the power grid requires the shutdown of power plants in case of maintenance or malfunction. The shutdown relies on protective devices that must be properly coordinated to isolate only the part of the grid affected by the malfunction. Using the DIgSILENT PowerFactory software, an analysis was conducted on a model of an accurate real grid integrating a photovoltaic power plant with a capacity of 390 kW. Protection coordination testing was carried out for three-phase, two-phase, and single-phase short circuit currents at arbitrarily selected locations at medium and low voltage levels. Protection in the time domain is coordinated on lines and busbars to determine the speed and selectivity of protective devices. The analysis results indicate that adequately adjusting the three-phase short circuit at the main transformer output 110/10 kV with an impedance of 0 Ω and an allowed protection operation time of up to two seconds can be correctly addressed within 36.7 ms.

Simultaneous Assessment of Multiple Aspects of Stability of Power Systems With Renewable Generation

Modern power systems are operating much closer to stability limits due to the integration of uncertain Renewable Energy Sources (RES)-based generations and the decommissioning of traditional synchronous generations. Hence, different aspects of power system stability assessment have come into research focus again. Conventional system stability assessment typically uses dedicated stability indices describing a single aspect of system stability (e.g., voltage, frequency, angularity) or composite indices developed for one aspect of system stability. Such assessments can be ambiguous as the impacts of new devices and technologies on different aspects of system stability can be both, positive and negative to different extents. This paper introduces a probabilistic framework and two composite stability indices for the simultaneous assessment of multiple aspects of power system stability. The application of the indices is demonstrated on a range of case studies with modified IEEE 9-bus and modified IEEE 68-bus test systems without/with RES in a mixed Matlab and DigSilent PowerFactory simulation environment.

Quality analysis of electrical energy

This study exposes the measurements of electrical parameters carried out with a power quality analyzer in a transformer. The first measurement taking into account a capacitor bank that was already installed and then taking it out of operation. It presents the results graphed in "Power Log" and analyzed with respect to the standards CFE-L00045, IEEE 519- 1992 and the Regulatory Manual of Technical Requirements for the Connection of Load Centers. By disconnecting the capacitor bank, with the data records obtained from the measurement, it is possible to consider adding a harmonic filter that is presented as the proposal for improving the quality of electrical power, since it achieves an increase from 0.73 to 0.98 in the power factor without compromising the permissible values of harmonics in the system. The filter is calculated and simulated in "DigSILENT Power Factory" to demonstrate the feasibility of the proposal.

Techno-economic Analysis of New Wind Power Plant Development in Southern Sulawesi Electrical Power System

Global warming due to carbon emissions has resulted in climate change, which negatively impacts the lives of living things. On the other hand, electricity demand is increasing every year due to the increasing human population, economic growth and equipment electrification. At the moment, most of the electricity generation in Indonesia uses fossil energy power plants which produce carbon emissions. PT. PLN (Persero) is a State-Owned Enterprise tasked with managing the electricity system in Indonesia. PT. PLN (Persero) through the General Plan for Electricity Supply (RUPTL) for 2021-2030 is targeting the construction of New and Renewable Energy Power Plants. One of possible plan is the Wind Power Plant (WPP) construction in the Southern Sulawesi electrical power system. The use of WPP is expected to reduce carbon emissions. However, the integration of WPP causes other problems in the existing system such as dropped voltage, increased equipment loading, increased short circuit current and decreased stability. So, it is necessary to conduct a study on the effects of integrating WPP into the existing system. Using DIgSILENT Power Factory software, Load Flow, Short Circuit and Transient Stability simulations were carried out. Then an economic analysis was carried out including calculating net present value (NPV), internal rate of return (IRR), profitability index (PI), payback period (PBP) and levelized cost of energy (LCOE. The use of WPP at a certain capacity will not disrupt the stability of the system's power because it is still supported by the fast response generators in the system during variable WPP output. Also voltage drop, equipment loading and short circuit current will not exceed the design value of the system. From financial aspect, with certain assumptions, WPP development can be proven to be economically feasible.

Impact Study of the Hetauda-Dhalkewar-Inaruwa Transmission Line on the Operation of Integrated Nepal Power System

Despite Nepal’s abundant hydroelectric resources, a substantial disparity exists between its electricity supply and demand. This discrepancy is exacerbated by the absence of high-voltage transmission lines, hindering efficient power evacuation from a handful of generating plants. This not only incurs financial losses for the utility but also compromises the reliability of the power supply. A prime example is the protracted delay in the construction of the 576 KM long Hetauda-Dhalkebar-Inaruwa 400kV double-circuit Transmission Line, primarily due to challenges posed by local residents unwilling to relinquish their land.The Integrated Nepal Power System (INPS) heavily relies on power generation concentrated in the central mid-hills region. The construction of the Hetauda-Dhalkebar-Inaruwa (HDITL) 400kV double-circuit Transmission Line is crucial for routing power to industrialize these areas, potentially bolstering the national GDP and generating employment opportunities. Furthermore, it is essential to connect the current hydropower output of around 2300 MW to the INPS system via a high-voltage transmission line to maximize its utilization. The HDITL project not only reduces line losses but also enhances grid stability. It facilitates energy export and direct transmission of high-generation power, such as the 456 MW from Upper Tamakoshi, thus saving approximately 400 MW of power and preventing losses for both the Government of Nepal (GoN) and the Nepal Electricity Authority. This research not only calculates the reduction in power and energy losses with the commissioning of HDITL but also assesses its monetary benefits. Utilizing INPS data and Digsilent Power Factory 15.1 for power flow analysis, the study estimates that HDITL can prevent a power loss of about 26.276 MW. Furthermore, it demonstrates that HDITL significantly improves the total generation power factor in INPS, from 0.88 to 0.99, and enhances the voltage profile, underscoring its critical role in Nepal’s energy infrastructure development.

Overcurrent and Directional Overcurrent Protection for Microgrid

Microgrids will become common in future electrical distribution networks. Numerous operating modes that occur in microgrids make the development of protection schemes and settings challenging. This paper aims to develop a simple protection scheme for the Microgrid IEC Benchmark without any expensive equipment such as communication apparatus. The scheme consists of directional and non-directional overcurrent relays with standard inverse characteristics. For the simulation tool, Digsilent powerfactory is employed. Four operating modes of the microgrid are applied to verify the relays’ coordination. The results show that the proposed scheme successfully protects the microgrid during short circuit faults with acceptable time margins.

Optimizing Real and Reactive Power Dispatch Using a Multi-Objective Approach Combining the ϵ-Constraint Method and Fuzzy Satisfaction

Optimal power dispatch is essential to improve the power system’s safety, stability, and optimal operation. The present research proposes a multi-objective optimization methodology to solve the real and reactive power dispatch problem by minimizing the active power losses and generation costs based on mixed-integer nonlinear programming (MINLP) using the epsilon constraint method and fuzzy satisficing approach. The proposed methodology was tested on the IEEE 30-bus system, in which each objective function was modeled and simulated independently to verify the results with what is obtained via Digsilent Power Factory and then combined, which no longer allows for the simulation of Digsilent Power Factory. One of the main contributions was demonstrating that the proposed methodology is superior to the one available in Digsilent Power Factory, since this program only allows for the analysis of single-objective problems.

Development of Simulation Model of Single-Phase Circuit Lock in the Digsilent Powerfactory Program

Abstract The most common types of damage in distribution networks with a voltage of 6-35 kV have been analyzed. It is shown that the majority of them are single-phase circuits, which can cause overvoltages at the point of damage and negatively affect electrical equipment, which can lead to a decrease in economic indicators. The methods of increasing the reliability of distribution networks with a voltage of 6-35 kV have been analyzed. The main attention is focused on the method of increasing reliability due to grounding of the neutral through an arc reactor, the main advantage of which in operation is the continuation of single-phase ground fault operation without disconnection of consumers. A simulation model of the distribution network in single-phase ground fault mode was developed and its main parameters were calculated. The DiGSILENT PowerFactory software complex is used as a simulation environment. A concrete example of parameter calculation when using the proposed simulation model in the DiGSILENT PowerFactory program, which contains 5 overhead and 5 cable power transmission lines with a voltage of 35 kV with a length of 10 to 100 kilometers. The use of this model will make it possible to study transient processes in the mode of single-phase grounding, to prevent emergency situations in distribution networks. The goal of the work ist development of the simulation model of the distribution network in the mode of single-phase circuit to land and the calculation of its basic parameters.

Analysis of Voltage Profiles, Unbalance Voltages and Phase Balance Optimization of Single-Phase Customer and Photovoltaic Connection at Real Low Voltage Feeder

Abstract Voltage unbalance is common issue encountered in low voltage distribution networks, caused by uneven allocation of single-phase customers among phases. This paper analyses part of real low voltage distribution network in Bosnia and Herzegovina. The impact of single-phase customers and single-phase connected micro photovoltaic power plants (MPPP-s) were analysed. To reduce unbalance and improve voltage profiles, Phase Balance Optimization toolbox in DIgSILENT PowerFactory software was performed in six scenarios with different distribution of customers and different percentage of penetration of MPPS-s. The aim was to find method with least number of changes in customer and photovoltaic phase connection that fits within defined limits of voltage variations and voltage unbalance of European standard for power quality (EN 50160). Conclusion is that MPPP-s cause voltage increases in the network, as well as an increase in voltage unbalance, but these effects can be mitigated by proper distribution of customer loads and MPPS-s among phases.

Profile Optimisation in Real Distribution Networks (Case Study Long MV Feeder)

Abstract In the dynamic field of power systems, integrating distributed generation (DG) sources like solar photovoltaic (PV) plants is crucial for enhancing reliability and fostering sustainability. However, this integration poses voltage profile management challenges in electrical grids. This study investigates voltage profile optimization in Bosnia and Herzegovina’s Gračanica network, focusing on a medium voltage feeder with 68 buses. Using DIgSILENT PowerFactory software, six scenarios with different configurations of solar plants are analyzed for their impact on voltage profiles and power losses. Results show that while DG integration offers benefits, incorrect sizing or placement can increase power losses. Optimal DG benefits are linked to specific sizes and locations. This research emphasizes the need for balancing PV generation with load demands and provides insights for optimal PV plant size and output to minimize negative impacts. These findings aid energy planners and policymakers in implementing distributed solar PV in medium voltage networks.

Deep Neural Network-Based Autonomous Voltage Control for Power Distribution Networks with DGs and EVs

This paper makes use of machine learning as a tool for voltage regulation in distribution networks that contain electric vehicles and a large production from distributed generation. The methods of voltage regulation considered in this study are electronic on-load tap changers and line voltage regulators. The analyzed study-case represents a real-life feeder which operates at 10 kV. It has 9 photovoltaic systems with various peak installed powers, 2 electric vehicle charging stations, and 41 secondary substations, each with an equivalent load. Measurement data of loads and irradiation data of photovoltaic systems were collected hourly for two years. Those data are used as inputs in the feeder’s model in DigSilent PowerFactory where Quasi-Dynamic simulations are run. That will provide the correct tap positions as outputs. These inputs and outputs will then serve to train a Deep Neural Network which later will be used to predict the correct tap positions on input data it has not seen before. Results show that ML in general and DNN specifically show usefulness and robustness in predicting correct tap positions with very small computational requirements.

Developing a collector system aggregation technique of a large-scale grid-connected wind farm

The increasing complexity of power systems necessitates the development of aggregation techniques to address specific issues. Model reduction is crucial to expand simulation capacity, ensuring the stability and reliability of power system design. This paper presents a collector system full aggregation technique based on the per unit system model and power loss-based aggregation technique applied to the impedance model of a large-scale grid-connected Wind Farm (WF). The purpose of the proposed technique is to obtain a fully aggregated equivalent representation of the WF collector system, which includes High Voltage (HV) three-winding transformer(s) or more than one HV two-winding transformer, to reduce the simulation time and the system complexity while maintaining similar performance compared to the Detailed Model (DM) and high-accuracy results in both steady-state and dynamic conditions. To be validated, the presented Per Unit Full Aggregation (PUFA) technique is used to obtain a Full Aggregated Equivalent Model (FAEM) of the existing Gabel El-Zeit WF, Egypt, Detailed Model (DM) that contains two HV three-winding transformers. The PUFA model is tested using the DIgSILENT PowerFactory software package, leading to a significant reduction in model order and simulation time with respect to the DM. The PUFA technique is compared to the DM and other aggregated models in terms of power flow using Quasi-Dynamic Simulation (QDS), dynamic response using Low Voltage Right Through (LVRT) simulation, Modal Analysis (MA), and small signal simulation. The comparison between the different models and the proposed one has confirmed that it realizes very competitive results with high accuracy in both steady-state and dynamic conditions with the least simulation time.

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

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

A novel dynamic inertial control of wind turbines based on event size estimation

High penetration of variable renewable energy sources causes volatile grid frequency movements in low inertia systems. Large-scale wind turbines (WTs) are stipulated to participate in frequency control upon occurring a disturbance event. This paper proposes a novel inertial control scheme aimed at improving the frequency nadir based on frequency event size (FES) estimation. Upon occurring a frequency event, the WTs immediately inject a stepwise active power into the grid, and its corresponding frequency deviation is measured to estimate the FES using mean absolute error solution of a sinusoidal exponential function regression. Subsequently, an inertial control is developed to mitigate the frequency movements taking into account the available kinetic energy in rotating masses of WTs and estimated FES. To ensure a safe rotor speed recovery to its maximum power point tracking mode within this scheme, the rotor speed recovery time, and the second frequency drop can be flexibly adjusted. The WTs overproduction and recovery stages are dynamically adapted to wind speed fluctuations based on the defined modifications and rules. Additionally, the scheme considers the latency of communication delay during FES estimation. The proposed method is validated using a large-scale wind farm integrated into IEEE 9-bus and 39-bus test systems in Digsilent PowerFactory. Comparison results with existing methods in the literature demonstrate that the proposed scheme achieves better frequency nadir improvement across various types and sizes of events and wind speeds. Furthermore, it exhibits robust performance against communication latencies. Finally, the experimental results support the findings in terms of FES estimation.

Enhanced DC-link voltage control of PMSG-based wind turbine generators by machine-side converter during asymmetrical grid faults

Under asymmetrical grid fault conditions, oscillating active power can occur on the grid-side converter (GSC) of permanent magnet synchronous generator (PMSG)-based wind turbine generators. The oscillating active power flows into the DC-link, causing voltage oscillations that can lead to a shortened lifetime of DC-link capacitors and additional harmonics injected into the grid. While conventional methods can mitigate the oscillating active power through negative sequence current injection by the GSC, this hinders the grid support of the GSC regarding negative sequence reactive current during grid fault. To address this issue, a novel control scheme is proposed that uses the machine-side converter (MSC) to transfer the oscillating power to the motor. Firstly, the active power capacity of the MSC is analyzed and compared with that of GSC, and the results show that MSC has enough capacity to accommodate the oscillating active power. On this basis, a novel MSC control scheme is proposed to transfer the oscillating active power on the DC-link to the motor, which has a much larger inertia to buffer the power oscillation. Compared with conventional methods, the proposed control scheme relieves the GSC from mitigating the power oscillation to support the grid. Simulation studies using DIgSILENT PowerFactory are presented to verify the effectiveness of the proposed control scheme for PMSG-based wind turbine generators.

Flexibility enhancement of multi-district DISCOs considering a trade-off between congestion and extractable reserve capacity from virtual energy storage systems

One of the fundamental concerns of distribution companies (DISCOs) is how to satisfy security requirements under uncertain conditions and real-time contingencies. To address this concern, it is vital to employ operational flexibility levers aimed at mitigating congestion and retaining optimal reserve capacity, particularly in critical feeders. Increased interaction between DISCOs and virtual energy storage systems (VESSs) offers an unparalleled opportunity to unlock the energy flexibility of distribution grids at the local level without increasing operational complexity. According to the state-of-the-art, models that tap the economic performance of VESSs while respecting the flexibility and security setpoints adopted by DISCOs in a distributed manner have remained scarce. This study goes beyond by developing a flexibility-oriented decision-making strategy as a single-leader multi-followers stochastic model; in which a multi-district DISCO involves the flexibility setpoints and congestion management strategy in the market participation plan of each VESS locally to enhance the energy flexibility of each district. In the upper level, DISCO aims to deal with stressful situations in real-time sessions by (i) determining the minimum reserve capacity requirements in each district to be provided by VESSs with respect to the existing uncertainty sources and the importance of each district, and (ii) alleviating the congestion in critical feeders to release the feeder capacity for deployment of the available reserve power promptly. In the lower level, each VESS makes optimal decisions on power and reserve bidding in day-ahead, reserve, and real-time markets that are affected by the flexibility services required by the DISCO. Inspired by the activity schedule of different users, it also examines how demand response programs can affect DISCO’s ability to unlock consumer-side flexibility in realizing congestion management strategies. The developed bi-level scheduling model is first reformulated as single-level mathematical program with equilibrium constraints (MPEC) by employing Karush–Kuhn–Tucker (KKT) optimality conditions and then linearized into a mixed-integer linear program (MILP). The proposed strategy is validated through extensive simulations conducted on the modified IEEE 33-bus test system consisting of three districts with different users. Furthermore, DIgSILENT PowerFactory is used to verify the feasibility of the proposed model under contingency cases and to provide insights for DISCOs to control multiple VESSs and capacity-correlated uncertainties.