DIgSILENT PowerFactory Research Articles

Optimal Allocation of Battery Energy Storage Systems to Enhance System Performance and Reliability in Unbalanced Distribution Networks

The continuously increasing renewable distributed generation (DG) penetration rate significantly reduces environmental pollution and power generation cost and satisfies society’s rapid growth in electricity demand. Nevertheless, high penetration of renewable DGs, such as wind power and photovoltaics (PV), might deteriorate the system’s efficiency and reliability due to its intermittent and stochastic natures. Introducing battery energy storage systems (BESSs) to the distribution system provides a practical method to compensate for the above deficiency since it can deliver and absorb power when needed. Hence, it is important to determine the optimal allocation of BESS to achieve maximum assistance in the grid. This study proposes an optimal BESS allocation methodology to improve reliability and economics in unbalanced distribution systems. The optimal BESS allocation problem is solved by simultaneously minimizing the cost of energy interruption, expected energy not supplied, power loss, line loading, voltage deviation, and BESS cost. The proposed technique is implemented and analyzed on a high renewable DG penetrated unbalanced IEEE-33 bus network using DIgSILENT PowerFactory software (version 2020 SP2A). An enhanced grey wolf optimization (EGWO) algorithm is developed to optimize BESS location and size according to the selected objective function. The simulation results show that the proposed optimal BESS optimization technique significantly improves the economics and reliability in unbalanced distribution systems and the EGWO outperforms the gray wolf optimization (GWO) and particle swarm optimization (PSO) algorithms.

A Deep GMDH Neural-Network-Based Robust Fault Detection Method for Active Distribution Networks

The increasing penetration of distributed generation (DG) to power distribution networks mainly induces weaknesses in the sensitivity and selectivity of protection systems. In this manner, conventional protection systems often fail to protect active distribution networks (ADN) in the case of short-circuit faults. To overcome these challenges, the accurate detection of faults in a reasonable fraction of time appears as a critical issue in distribution networks. Machine learning techniques are capable of generating efficient analytical expressions that can be strong candidates in terms of reliable and robust fault detection for several operating scenarios of ADNs. This paper proposes a deep group method of data handling (GMDH) neural network based on a non-pilot protection method for the protection of an ADN. The developed method is independent of the DG capacity and achieves accurate fault detection under load variations, disturbances, and different high-impedance faults (HIFs). To verify the improvements, a test system based on a real distribution network that includes three generators with a capacity of 6 MW is utilized. The extensive simulations of the power network are performed using DIgSILENT Power Factory and MATLAB software. The obtained results reveal that a mean absolute percentage error (MAPE) of 3.51% for the GMDH-network-based protection system is accomplished thanks to formulation via optimized algorithms, without requiring the utilization of any feature selection techniques. The proposed method has a high-speed operation of around 20 ms for the detection of faults, while the conventional OC relay performance is in the blinding mode in the worst situations for faults with HIFs.

Medium voltage outdoor compact substations’ earthing system evaluation based on quantified risk analysis

This paper investigates the ISO 31000 Risk Assessment process in evaluating the performance of existing Earthing Systems in Power Distribution Grids and designing new ones, while considering techno-economic criteria. The primary goal of this paper is to investigate Medium Voltage (MV) earthing systems under various scenarios in terms of soil structure, fault clearing time and earthing mat design, using appropriate software tools such as SES CDEGS and DIgSILENT PowerFactory. Furthermore, purpose of this paper is to emphasize the importance of Risk Assessment as a complementary method to the conventional one suggested in IEEE Std. 80 in assessing the likelihood of a fatal accident occurring in the vicinity of an MV electrical equipment in the event of a Short Circuit (SC) such as Single Line to Ground Fault (SL). Since there is no international standard for designing an effective earthing system in MV power networks, this paper serves as a valuable guide, identifying worst-case scenarios and highlighting critical safety parameters for earthing system design.

Voltage unbalance and inertia based frequency control framework considering intelligent load management for stand-alone operation of microgrid

The less inertial microgrid with high penetration of Renewable Energy Sources (RES) faces several issues including voltage and frequency unbalance. The intermittent nature of RES-based Distributed Generations (DGs) makes the system unstable in the absence of a control mechanism in a stand-alone microgrid. The integration of single-phase loads and sudden load switching on the distribution side make the system prone to several malicious events. The unbalance in voltage among the phases and the high Rate of Change of Frequency (RoCoF) are the major concern for degrading the system’s performance during peak and off-peak hours. The paper addresses a hierarchical dual loop voltage and frequency control mechanism where the primary control is equipped with droop strategy and Positive-Negative Sequence Control (PNSC) to maintain Voltage Unbalance Factor (VUF) and adhere to IEC-61000-3-13. Further, the inertial loop is also implemented to mitigate frequency deviation and reduce transient overshoot. The secondary control mechanism enables intelligent load management by scheduling Thermostatic Control Loads (TCLs) during peak hours. The utmost care is taken for the Customer’s Thermal Comfort (CTC) while scheduling the loads. The rigorous simulation is done in MATLAB Simulink and Digsilent Power Factory with a modified IEEE 13 bus system considering system dynamics. Further, the real-time simulation is also performed with OPAL-RT to validate the efficacy of the above methodology.

Multi-objective battery energy storage optimization for virtual power plant applications

The increasing share of renewable energy sources (RESs) in electricity generation leads to increased uncertainty of generation, frequency and voltage regulation as well as difficulties in energy management. A virtual power plant (VPP), as a combination of dispersed generator units, controllable load and energy storage system (ESS), provides an efficient solution for energy management and scheduling, so as to reduce the cost and network impact caused by the load spikes. This paper proposes a multi-objective optimization (MOO) of battery energy storage system (BESS) for VPP applications. A low-voltage (LV) network in Alice Springs (Northern Territory, Australia) is considered as the test network for this study. The BESS for each customer is used to store and release the energy when required to maintain the voltage regulation performance of the LV network and reduce the cost. To optimize the charge/discharge schedule in each battery, a multi-objective optimization tool (MOOT) is developed, where MOO can directly communicate with DIgSILENT PowerFactory platform to perform multi-time scale simulation. MOO mainly focuses on generating a set of trade-off schedule solutions for each customer over 24 h by considering the customer’s cost and network impact. Then according to the stakeholder’s prior preference, one of the solutions is selected and verified in DIgSILENT PowerFactory with a realistic LV network. We also design several scenarios with different penetrations of photovoltaics (PVs) and batteries to verify how they influence customer’s cost and LV network. With the increasing penetrations of PVs and batteries, the experimental results over the selected solution according to the customer preference show that the customers’ cost can be largely reduced by maintaining the network voltage regulation performance.

Overcurrent and ground fault relay protection settings at tranformator-1 150kV/20kV Braga substation

The occurrence of a malfunction at the substation results in power outages and losses in the electrical energy distribution system to consumers. Many tests are carried out to see the performance of the protection system, including the parameters of the over current relay (OCR) and ground fault relay (GFR) in the electrical energy distribution system. This research aims to analyze OCR and GFR values, analyze OCR setting, drop-off, and pick-up values, and analyze OCR time characteristics using DigSilent Power Factory 15.1 software based on existing equipment specification data at the Braga substation. The results show an OCR accuracy level of around 94% on the 20 kV and 150 kV sides. Meanwhile, 92.39% on the 20 kV GFR side and 94.87% on the 150 kV side. The setting value for the pick-up current is 0.92 A on the 20 kV side of the GFR and the drop-off current is 0.85 A on the 150 kV side with a pick-up current of 0.39 A and a drop-up current of 0.37 A. Setting a value on the 20kV side is greater than on the 150 kV side due to the difference in current transformer ratio values. The simulation results show that the OCR and GFR characteristic curves on both sides meet the criteria for a protection system with good performance.

Optimal battery energy storage planning and control strategy for grid modernization using improved genetic algorithm

The flexible operation of battery energy storage systems (BESS) to support electricity grid modernization requires optimal planning and an efficient control strategy. This paper proposes the optimal allocation of BESS with photovoltaic systems for microgrids to enhance grid reliability and flexibility. An adaptive BESS control strategy is developed to allow the BESS to operate in both redundant and peak shaving modes. An evolutionary programming-based genetic algorithm implemented with an optimal power flow control is proposed to determine the BESS’s optimal location, sizing, and charge/discharge operation. The objective function is to maximize the benefits of energy loss reduction and peak shaving enhancement while minimizing the installation cost. The proposed approach is conducted with MATLAB and DIgSILENT PowerFactory software, which uses an intelligent automatic data exchange process to solve the optimal solution. A practical 22 kV grid-connected microgrid of Thailand is used as a test system to demonstrate the effectiveness of the planning and control strategy for the BESS installation. The simulation test results show that the proposed optimal BESS allocation and control strategy can significantly reduce the microgrid’s energy loss and peak demand and increase energy shaving leading to enhanced grid resiliency and reliability.

An enhanced sensitive power differential protection for series compensated transmission lines in renewable generation intensive power systems

Series compensation is widely used to improve the electrical characteristics of long transmission lines and increase the power transfer capability. However, the insertion of a series capacitor introduces various phenomena that affect the performance of traditional distance relays. Moreover, the fault characteristics of renewable generation systems coupled with generation outputs that vary with weather patterns produce additional complications to the protection of transmission lines. This paper proposes the application of an enhanced sensitive power differential protection (SPDP) algorithm to the protection of series compensated transmission lines. The algorithm incorporates a criterion that improves the security of the protection by inhibiting the SPDP algorithm from operating for faults external to the protected line. Performance of the enhanced SPDP algorithm has been evaluated on a test system built in Digsilent Powerfactory software. Various in-zone and out-of-zone fault cases were simulated at different compensation levels and fault resistances. The results showed that the enhanced SPDP protection technique can detect in-zone faults along practically the entire transmission line (99.99 %) for compensation levels up to 90 %. The method operated reliably for faults with resistances up to 330 Ω.

Design of Energy Storage for Frequency Stability in Low-Inertia Power Grid

Short-term frequency instability is one of the major concerns in power systems with high percentage of converter-interfaced renewable energy sources. Energy storage system (ESS) has proven to be a viable solution for the problem of short-term frequency instability by fast frequency response (FFR). However, the appropriate location, size, and operating strategy of ESS are the main challenges for FFR. Power injection at some buses in large grids may lead to angular separation and instability. In addition, oversizing ESS could lead to huge investments without appropriate returns and under sizing may jeopardizes grid stability. Capacity estimation of ESS for FFR considering the suitable location and overall deployment strategies are missing in the current literature for large power grids. Hence, this research proposes a technique to place and size ESS for better FFR in power grids. The proposed technique consists of two steps. In the first step, a methodology based on frequency dynamic signature (FDS) is developed to identify the most suitable location. In the second step, the required capacity of the ESS is estimated based on a step reduction iterative algorithm (SRIA). SRIA and FDS consider the complete dynamics of power system components that affect the frequency dynamics of the system. The proposed methodology is thoroughly verified for various operating conditions in IEEE 39-bus using DIgSILENT PowerFactory.

Transient stability enhancement in renewable energy integrated multi-microgrids: A comprehensive and critical analysis

Multi-microgrids offer various benefits including the decreased overloading of a single microgrid, more options during faulty conditions, and more utilization of renewable energy resources. However, the implementation of a multi-microgrid brings the challenges such as power system complexity, interconnection issues, bidirectional power flow management, and power flow balancing. In the presence of these challenges, the power flow stability of the multi-microgrids is a challenging problem. In this context, this study evaluates a transient stability analysis model in multi-microgrids using solar photovoltaics, wind power, and a unified power flow controller (UPFC). UPFC offers a more robust power flow control strategy compared with other flexible alternating current transmission systems (FACTS) devices. First, a multi-microgrid structure consisting of the two microgrids was designed in DIgSILENT PowerFactory software. Second, the load flow calculation was performed in the absence and presence of UPFC, short circuit fault, and grid connection. Third, the electromagnetic transients (EMT) simulation was performed for all these situations. The results exhibited that the UPFC would offer significant power flow stability in the multi-microgrids. It was observed that the UPFC resulted in more transient stability in the microgrid where it was located. However, it improved the power flow quality at all the locations in the multi-microgrids. In addition, UPFC offered significant transient stability during the fault occurrence. The results offer various insights into power flow management in multi-microgrids.

A novel non-iterative based framework for quick dynamic assessment of wind energy dominated multi-machine power system

Renewable Energy Sources have considerably expanded in recent years to address the widening energy deficit in modern power systems. Integrating these sources raises significant concerns for power system management, with transient stability constraints of networks being one of the growing issues for engineers and researchers. In this paper, the impact of Doubly Fed Induction Generators integration is analyzed to examine the transient stability on two test models. A Coupling Strength Index formulated from Network Structural Characteristics Theory is explored to detect the weakest transmission line. This method identifies line 7 to 8 and 5 to 6 as the weakest line with coupling strength index of 0.02739 and 0.105158 for IEEE 9 and 39 bus system, respectively. The system’s transient stability is then investigated with and without the Doubly Fed Induction Generators, considering a three-phase short-circuit fault applied at the middle of the identified line. Several characteristics associated with the system such as generator speed, rotor angle, and electric power were investigated. The simulation was carried out using DIgSILENT Power Factory and the results indicate that the systems are negatively impacted by the integration of Doubly Fed Induction Generators.

Participation of battery energy storage system for frequency control in wind dominated power systems: An analytical approach

The frequency performance of a power grid is effectively maintained through the utilization of inertia and power reserve provided by synchronous generators. The growing concerns surrounding global warming and the greenhouse effect have led to a significant increase in the integration of wind energy into the grid. But the system may face frequency instability following a contingency due to lack of sufficient inertia and headroom of wind generators. Therefore, the grid operator may require shedding some loads to prevent the system from severe frequency excursion. In this paper, we have estimated proper amount of load shedding through the formulation of analytical expression that will keep a highly wind penetrated & Battery Energy Storage System (BESS) integrated system stable. For this purpose, the maximum amount of wind power penetration level (WPPL) is first calculated using a fast analytical approach which utilizes two frequency response performance metrics, frequency nadir and Rate of Change of Frequency (ROCOF). In scenarios where the wind penetration level exceeds the calculated allowable threshold, it becomes necessary to implement load shedding measures following a contingency event. After installation of BESS, grid frequency response is much enhanced, hence, the required load shedding amount is also different. Therefore, we have derived an analytical expression for a quick measurement of frequency response enhancement attained by BESS. Finally, a frequency nadir-based load shedding scheme, being the goal of this paper, is proposed for a heavily wind penetrated grid with BESS, using the previously derived expression, to retain the grid at its nominal operating condition following a severe contingency. Our proposed scheme incorporates an analytical method to prevent over load shed. We have used DIgSILENT PowerFactory to validate our proposed analytical approaches through dynamic simulation. Results obtained from the proposed approaches nearly resemble the simulated one. Hence, this paper can help generating simplified yet effective models to conduct analysis on a wind integrated grid. This paper can also be regarded as a guide to ensure a wind penetrated resilient grid in view of frequency stability.

Low-Voltage Network Modeling and Analysis with Rooftop PV Forecasts: A Realistic Perspective from Queensland, Australia

Recent years have seen a rapid uptake in distributed energy resources (DER). Such technologies pose a number of challenges to network operators, which ultimately can limit the amount of rooftop solar photovoltaic (PV) systems that can be connected to a network. The objective of this industry-based research was to determine the potential network effects of forecast levels of customer-owned rooftop solar PV on Energy Queensland’s distribution network and formulate functions that can be used to determine such effects without the requirement for detailed network modeling and analysis. In this research, many of Energy Queensland’s distribution feeders were modeled using DIgSILENT PowerFactory and analyzed with forecast levels of solar PV and customer load. Python scripts were used to automate this process, and quasi-dynamic simulation (QDSL) models were used to represent the dynamic volt–watt and volt–var response of inverters, as mandated by the Australian Standard AS/NZS 4777. In analyzing the results, linear relationships were revealed between the number of PV systems on a feeder and various network characteristics. Regression was used to form trend equations that represent the linear relationships for each scenario analyzed. The trend equations provide a way of approximating network characteristics for other feeders under various levels of customer-owned rooftop solar PV without the need for detailed modeling.

Optimal deloading of PV power plants for frequency control: A techno-economic assessment

Due to the lack of inertial support from photovoltaic (PV) systems, large-scale PV integration into the existing grid poses a major threat to frequency stability. To address this, numerous techniques for incorporating energy storage systems have been proposed in the existing literature, but they incur significant operational costs. PV systems with deloading mechanisms have been researched as an alternative efficient strategy in many studies as a key frequency response support after a disturbance. However, deloaded PV systems incur a cost burden due to idle reserve capacity during regular operation. Consequently, an optimum deloading of PV systems is required to enhance the grid's frequency stability while minimizing its total operating cost. To that aim, this paper proposes a gradient descent-based optimization method to determine the optimum deloading of PV systems. The optimization considers both frequency response constraints (frequency nadir and rate of change of frequency – ROCOF) and operating cost constraints (generation, up-regulation, and value of lost load cost). The proposed technique is employed in a modified IEEE 39 bus New England System for varying levels of PV integration under two distinct cases. The optimization and relevant simulations are performed in Python and DIgSILENT PowerFactory platforms. In the case of a major generator outage with PV penetrations of 30%, 40%, and 50%, the optimal deloading percentages are 6.96%, 5.931%, and 4.968%, respectively, with no load shedding. Moreover, in the interconnection outage case, the optimal deloading percentages increase to 14.92%, 13.3%, and 12.42%, respectively, with load shedding. Nevertheless, in each case, deloaded PV systems consistently preserve frequency stability in the grid while incurring minimized operating costs. Furthermore, the performance and cost of the proposed solution are compared to two other primary frequency response support systems, viz. Battery Energy Storage System (BESS) and Synchronous Condenser (SC). The optimally deloaded PV system outperforms both these devices considering both technical and economic aspects.

A novel inertia emulator to reduce the rate of change of frequency for power systems with solar PV and battery energy storage

Abstract Energy access, climate change and public health issues are some major drivers for the need for renewable sources. However, most renewable sources, excluding large hydro, have zero or negligible rotational inertia, which is critical to stabilizing the power system after contingency. Therefore, this paper proposes a droop-based inertia emulator to reduce the rate of change of frequency and frequency deviations. The robustness of the controller is analysed by applying various uncertainties and disturbances of power system components that were carried out using DIgSILENT PowerFactory simulations. The obtained results are compared with existing literature and the desired performance shows an improvement in the rate of change of frequency of 34.78% for an IEEE 6-bus system, 24.32% for a 12-bus system and 18% for a 39-bus system.

Sistem Koordinasi Rele Jarak Untuk Pengaman Utama Dengan Rele Arus Lebih Pada Saluran Udara Tegangan Tinggi Di Wilayah Buduran

The transmission system plays an important role in maintaining the continuity of the distribution of electrical energy from one region to another. Disturbances in transmission lines are caused by short circuits, overloads, lightning surges, natural disturbances and others. For this reason, a protection system is needed that is reliable and can identify disturbances quickly while protecting the disturbed part of the system from other parts that can still operate normally. However, the protection system can experience operational failure due to various factors, therefore, apart from the main protection, backup protection is needed which can work when the main protection fails to work. Distance relays can be used as primary protection as well as remote backup protection on high voltage overhead lines. Meanwhile, the overcurrent relay is used as local backup protection if the distance relay fails to work. In this paper, a protection system is designed for the Buduran Main Substation channel using a combination of distance relays as main protection and overcurrent relays as backup protection using simulation method the Digsilent Power Factory. The overcurrent relay will trip at 0.5 and 0.15 seconds. From the Load Flow results, the value is obtained = 3,615 kA, = 4,67 kA and The range impedance according to the conductor cable data at the Buduran region 0,9676, Zone1 1 0,79Ω; 80%, Zone2 1,19Ω; 120% dan Zone3 as 1,48Ω is 150%. Thus the research can be declared successful in carrying out overcurrent protection

ANALYSIS OF THE IMPACT OF DIFFERENT DISTRIBUTED GENERATOR TECHNOLOGIES ON HARMONIC VOLTAGES

While distributed generators (DGs) can reduce carbon dioxide emissions, they can also cause disturbances and lead to power quality (PQ) issues, with harmonic voltages being an important parameter to consider. In this paper, the impact of 14 connected photovoltaics (PVs) and a small hydropower plant (sHPP) on harmonic voltage distortions in a real medium voltage (MV) and low voltage (LV) distribution network in Bosnia and Herzegovina was analyzed. Simulation tools carried out by DigSILENT PowerFactory offer a wide range of advantages that give system operators the ability to have insight into PQ behavior in the presence of intermittent renewable energy sources (RES). Due to the inverter-based electricity generation, PV power plants inject harmonics into the LV network. The impact is relatively small and does not violate the limits from the European PQ standard EN 50160 due to the relatively small power of the modelled existing PVs. However, integrating additional PVs could lead to a violation of limits. Therefore, where a large power of PV power plants is installed, if it is possible to integrate sHPP, they will contribute to the reduction of generated harmonics without the need to reduce the power of PV. The contribution of this paper is that it compares the impact of different power generation technologies on harmonic voltages using data from a real network rather than a test network.

Multi-Stage Proactive Scheduling of Strategic DISCOs in Mutual Interaction With Cloud Energy Storage and Deferrable Loads

Unexpected events have underscored the need for proactive preparedness in local energy systems, especially strategic distribution companies (DISCOs). The state-of-the-art methods to take proactive approaches in DISCOs are to use battery energy storage systems (BESS). However, there is a lack of established approaches that include the inter-dependencies of techno-socio economic features. To overcome this limitation, this paper constitutes a multi-stage resilience-promoting proactive strategy with linear decisions to enhance the strategic DISCOs preparedness level to deal with unscheduled islanding operation under uncertainties. In particular, this strategy provides operational solutions to survive DISCOs under stressful conditions by incorporating the economic operation of cloud energy storage (CES), which manages many BESS, and correlated demand response (DR) programs in resiliency issues. To this end, the lexicography algorithm is employed to prioritize different objectives based on the pre-avoidance, avoidance, survival, and post-disaster stages, which captures the BESS' energy level as well as socio-economic features of DISCO and CES. The effectiveness of the proposed strategy is demonstrated both analytically and empirically. At first, the features of the proposed strategy are examined in responding to islanding state using a set of numerical studies conducted on the IEEE 69-bus test system in GAMS software. After that, insightful analyses are performed via DIgSILENT PowerFactory to verify the feasibility of the proposed strategy.

Simulation of the influence of STATCOM on power system losses

The supply of growing electricity demand is possible through continuous technological advances and the expansion of national and international electrical systems. This scenario could introduce voltage drops and consequent changes in the reactive power flow throughout the electrical network. In order to control these problems, various strategies have been developed as a solution to improve the transport and distribution of electrical energy. One of them is the Flexible Alternating Current Transmission System (FACTS), and more specifically the STATic synchronous COMpensator (STATCOM). This paper investigates the influence and effectiveness of STATCOM to mitigate the losses in the transmission lines and its impacts on bus voltage drops. The simulations are performed using the software DIgSILENT PowerFactory and the results showed that STATCOM reduces the power system losses in an interval of 23.86% until 32.86%, and in addition, the STATCOM decreases the annual energy cost by 7.82% in the implemented test case.

The Frequency Spectrum Analysis of Wideband Oscillations of Grid-Connected Voltage Source Converter

With the widespread application of voltage source converters (VSCs) in power systems with high renewable resource penetration, the problem of wideband oscillations caused by interactions between power converters and the power grid has drawn great attention. This paper presents a new methodology for simplifying the mathematical derivations of the impedance model of a VSC. Using the new simplified model, the stability and spectrum characteristics of the performance of the VSC can be clearly analyzed. The proposed second-order d-q impedance model of a grid-connected VSC in the presence of a PLL not only mathematically demonstrates that wideband oscillatory modes always occur in conjugate pairs, but also delivers a clear vision of the physical essence of these wideband oscillations. A classic modal analysis is executed in this paper to demonstrate the stability and frequency spectral characteristics of wideband oscillations in a VSC integrated system. The impact of the control parameters of the VSC on wideband oscillatory stability is thoroughly analyzed by modal analysis using ‘DIgSILENT PowerFactory’ as well as hardware-in-the-loop experiments. This methodology can be considered a powerful tool for the control design of VSCs in the modern power system.