Hybrid Population Based MVMO for Solving CEC 2018 Test Bed of Single-Objective Problems

The MVMO algorithm (Mean-Variance Mapping Optimization) has two main features: I) normalized search range for each dimension (associated to each optimization variable); ii) use of a mapping function to generate a new value of a selected optimization variable based on the mean and variance derived from the best solutions achieved so far. The current version of MVMO offers several alternatives. The single parent-offspring version is designed for use in case the evaluation budget is small and the optimization task is not too challenging. The population based MVMO requires more function evaluations, but the results are usually better. Both variants of MVMO can be improved considerably if additionally separate local search algorithms are incorporated. In this case, MVMO is basically responsible for the initial global search. This paper presents the results of a study on the use of the hybrid version of MVMO, called MVMO-PH (population based, hybrid), to solve the IEEE-CEC 2018 test suite for single objective optimization with continuous (real-number) decision variables. Additionally, two new mapping functions representing the unique feature of MVMO are presented.Intelligent Electrical Power Grid

Evaluation of Phase Imbalance Compensation for Mitigating DFIG-Series Capacitor Interaction

This paper assesses the suitability of the phase imbalance concept as an alternative approach for series compensating a transmission line, with the goal to eliminate adverse subsynchronous interactions between a DFIG and the transmission system. The performance of this concept, under a predefined degree of asymmetry, is compared with the classical series compensation scheme. First, it is concluded that the phase imbalance concept can reduce subsynchronous oscillations, as this concept results in lower resonance frequencies, which in turn lead to increased damping. Second, as these resonance frequencies remain in the DFIG's negative resistance region, the subsynchronous oscillations cannot be fully mitigated.Virtual/online event due to COVID-19 Accepted author manuscriptIntelligent Electrical Power Grid

Hybrid Single Parent-Offspring MVMO for Solving CEC2018 Computationally Expensive Problems

Mean-Variance Mapping Optimization (MVMO) belongs to the family of evolutionary algorithms, and has proven to be competitive in solving computationally expensive problems proposed in the Icompetitions CEC2014, CEC2015, and CEC2016. MVMO can tackle such problems by evolving a set of solutions (population based approach) or a single solution (single parent-offspring approach). The evolutionary mechanism of MVMO performs within a normalized search space in the range [0, 1]. The power of MVMO stems from its ability - based on statistical analysis of the evolving solution based on a mapping function - to adaptively shift the search priority from exploration to exploitation. This paper introduces a newly defined mapping function as well as a new rule for using an embedded local search strategy, and presents several tests conducted by using the test bed of the CEC2018 competition. Numerical results indicate significant improvements on the results obtained in CEC2016 competition.Intelligent Electrical Power Grid

Beyond SCR in Weak Grids: Analytical Evaluation of Voltage Stability and Excess System Strength

Due to the continuous increase (decrease) in the number of inverter-based (synchronous) generators in modern electrical power systems, the theoretical foundations behind widely used system strength and voltage stability assessment methods require thorough revision. The existing evaluation methods such as the Short-Circuit Ratio (SCR) are often based on simplifications which may produce inaccuracies, particularly when studying weak systems. As a result, a misleading estimation of voltage stability can occur, exposing systems to unnecessary renewables curtailment or other inappropriate remedial actions that may cause partial disruptions or potential instability. This paper provides a rigorous analytical revision of voltage stability assessment to confidently evaluate the maximum power transfer under various operating conditions. Subsequently, the proposed approach is applied as an enhanced method of system strength evaluation. The method is extensively tested on a single-machine-infinite-bus test system. Numerical results show a notably more accurate assessment relative to the common alternative methods.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid

Impact of Modelling Assumptions on the Voltage Stability Assessment of Active Distribution Grids

Renewable energy sources (RES) penetrate power grids at all voltage levels. A large number of RES units are connected to medium-voltage (MV) and low-voltage (LV) levels resulting in a significant share of overall generation. Therefore, the dynamic behavior of such distribution grids should be thoroughly examined. The goal of this paper is to show how various changes in the composition of the dynamic power flows interact with Low-Voltage Ride Through (LVRT) requirements, and how they affect the very important aspect of the RES-penetrated grids – voltage stability. The analysis is performed on a selected network, which is modeled with real grid data. The concluding concepts, however, are applicable for any distribution grid topology with a large number of distributed energy resources (DER). The results show essential grid details that should be modeled more precisely. This paper also addresses the level of complexity needed to obtain accurate results. Models are generally always imperfect and therefore, having more detailed data for a specific study is of the uttermost importance.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid

Fundamental study on the influence of dynamic load and distributed energy resources on power system short-term voltage stability

The number of Distributed Energy Resources (DER) and dynamic loads is increasing rapidly in modern power systems. Their aggregated effects on power grid dynamics are, however, still insufficiently explored. It is expected that distribution-transmission interactions will be more pronounced in the future, resulting in a stronger need to analyse such effects. One of the emerging issues in modern systems’ distribution-transmission interactions is short-term voltage stability (STVS), which at present receives relatively low attention among the researchers. This paper utilizes advanced load and DER models in a large-system study, intending to determine the relationship between various distribution system specifics and the bulk power system STVS. Based on a developed heuristic method that generates a big data set by performing an extensive number of simulations, it is shown how the dynamic load and DER interact with each other in terms of STVS, and what load and DER amounts and types are beneficial or detrimental to modern systems. The study improves the understanding of modern distribution-transmission interactions related to STVS and emphasizes the importance of more accurate future modelling and analyses.Intelligent Electrical Power Grid

Comprehensive review of short-term voltage stability evaluation methods in modern power systems

The possibility to monitor and evaluate power system stability in real-time is in growing demand. Whilst most stability-related studies focus on long-term voltage stability and frequency stability, very little attention is given to the issue of short-term (voltage) instability. In this paper, the most common evaluation methods present in the literature are summarized, with a focus on their applicability to modern power systems with a large amount of renewable energy integration. The paper presents a first-of-a-kind structured review of this topic. We find that all existing methods have noteworthy limitations that necessitate further improvements. Additionally, the need of having an inclusive short-term instability prediction method is demonstrated, due to strong interactions between various short-term instability mechanisms. These findings provide a good foundation for further research and advancement in the field of real-time stability monitoring.Intelligent Electrical Power Grid

System Strength: Classification, Evaluation Methods, and Emerging Challenges in IBR-dominated Grids

To facilitate the increasing penetration of inverter-based resources, understanding and evaluating system strength becomes one of the central questions for the resilient operation of power systems. However, this is a very challenging and nuanced task, currently without a clear consensus in the industry and academia. This paper provides a comprehensive review of the proposed notion for system strength, followed by a consequent introduction of a novel classification. Furthermore, an exhaustive examination of present system strength evaluation methods is performed. Finally, a critical outlook on remaining and emerging challenges of system strength evaluation is presented, with several key recommendations for future research directions.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Intelligent Electrical Power Grid

Security Assessment of System Frequency Response

Low inertia power systems experience more extreme frequency dynamics immediately after a disturbance. A higher rate of change of frequency (ROCOF) contributes to a lower frequency nadir which could trigger load shedding schemes. Active power injections in a time frame of two seconds or less are necessary to maintain frequency stability. This paper develops an analysis of the closed-loop transfer function of a single-area power system model for frequency response (FR). This model is useful to study the frequency dynamics following a sudden load imbalance in a highly meshed system in which all the generating units are combined into a single equivalent unit with an aggregated inertia constant. The dynamics of the turbine and speed governor are included as first-order lag functions in the Laplace domain. A numeric example of the impact of system inertia and frequency controllers in the UK power system is then developed in MATLAB, and minimum values for Primary and Fast Frequency Response (FFR) power injections are calculated.Intelligent Electrical Power Grid

Simulation based Analysis of Transformerless Photovoltaic Inverter Topologies for Reactive Power handling Capability

This study investigates the reactive power generation capability of the existing transformerless Photovoltaic Inverter Topologies (PVIT) with their conventional switching strategies. The topologies such as H5, families of H6 (H6, H6-I, H6-II, H6-III and H6-IV), HERIC, and clamped topologies (optimized H5, passive clamped H6 and HBZVR) have been selected for analysis. Matlab/Simulink simulation platform is employed for the analysis of PVIT. It has been observed that transformer-less PVIT with their conventional switching strategies are not suitable for reactive power injection. These topologies are generating highly distorted current at zero crossings during the reactive power flow. The improved switching strategies are needed to make these topologies suitable for the reactive power applications without any modification in the structure of the inverter.Accepted author manuscriptPhotovoltaic Materials and DevicesIntelligent Electrical Power Grid