arXiv subjects

Aleksandar Dimitrovski

Publications and source records attributed to Aleksandar Dimitrovski.

11 recordsLinked to original sources

arXiv2023

Comprehensive G-C Modeling of a Gapless Continuously Variable Series Reactor

The paper presents a comprehensive model of Continuously Variable Series Reactor (CVSR) in the Gyrator-Capacitor (G-C) framework. CVSR is a device capable of controlling the reactance in an ac circuit using the nonlinear characteristic of ferromagnetic core. Bias magnetic flux produced by a dc winding can be used to regulate the equivalent ac reactance for various applications, such as power flow control, oscillation damping, or fault current limiting. A novel variant of CVSR that features gapless ferromagnetic core and a split two-coil ac winding is considered. Its nominal reactance is entirely determined by leakage fluxes. The Gyrator-Capacitor (G-C) approach is used to model the interface between the magnetic, electronic, and electric circuits, to maintain consistency of active and reactive powers in these circuits and allow additional flexibility. For accurate representation of the gapless CVSR, in addition to a realistic nonlinear and lossy core, elaborate models of different flux leakages are given. Results from analyses for a range of distances between the coils of the ac winding at different bias currents are presented.

physics.ins-det↗

arXiv2022

A Bayesian Approach to Probabilistic Solar Irradiance Forecasting

The output of solar power generation is significantly dependent on the available solar radiation. Thus, with the proliferation of PV generation in the modern power grid, forecasting of solar irradiance is vital for proper operation of the grid. To achieve an improved accuracy in prediction performance, this paper discusses a Bayesian treatment of probabilistic forecasting. The approach is demonstrated using publicly available data obtained from the Florida Automated Weather Network (FAWN). The algorithm is developed in Python and the results are compared with point forecasts, other probabilistic methods and actual field results obtained for the period.

stat.AP↗

arXiv2022

An Incremental Negative Sequence Admittance Method for Fault Detection in Inverter-Based Microgrids

Superimposed sequence quantities have been relied on for years to provide pure fault components for various applications in protection schemes. In more recent times, they have been employed in various solutions to the challenges introduced by integration of distributed generation in distribution systems. To improve the overall reliability of protection schemes deployed in such active distribution networks, this paper evaluates a new approach for detecting unbalanced faults using negative sequence quantities. A proposed superimposed negative sequence admittance element is validated using simulation tests on a modelled community microgrid. The performance of the method is tested for various fault scenarios in MATLAB/Simulink.

eess.SY↗

arXiv2021

Modeling of A Realistic DC Source in A CVSR

Continuously Variable Series Reactor (CVSR) can adjust the total reactance in an ac circuit using the saturation characteristic of the ferromagnetic core, shared by an ac and a dc winding. The bias magnetic flux produced by the dc winding can regulate the equivalent ac inductance in order to control power flow, damp oscillations, or limit fault currents. Gyrator-Capacitor approach is used to model the interface between the magnetic and the electric circuits. Two different dc control source models are considered: the usual ideal dc source and a realistic dc source composed of a power electronics-based converter and an ac voltage source. This paper investigates CVSR's behaviour in terms of induced voltage across ac winding, flux densities (B) throughout the CVSR core, and power interchange with the dc control circuit during normal conditions in both cases.

eess.SY↗

arXiv2021

Gyrator-Capacitor Modeling of a Continuously Variable Series Reactor in Different Operating Modes

Continuously Variable Series Reactor (CVSR) can regulate its reactance on the ac side using the nonlinear ferromagnetic core, shared by an ac and a dc winding for applications like power flow control, oscillation damping, load balancing and others. In order to use a CVSR in the power grid, it is essential to know its operating characteristics. The Gyrator-Capacitor approach has been applied to model the magnetic circuit coupled with the electrical circuit. In the paper, we investigate the CVSR behavior in terms of induced voltages across the dc winding, flux densities (B) through the core legs, and power exchange between the ac controlled and the dc control circuit.

eess.SY↗

arXiv2021

A Practical Assessment of the Power Grid Inertia Constant Using PMUs

Installation of phasor measurement units (PMUs) in a number of substations in the power grid can help assess a set of its values and parameters, in particular those related to the dynamics when disturbances occur in the system. Inertia constant of the power grid is one of the system stability related parameters that is essential for planning of the system spinning reserve. Estimates of the grid inertia constant require precise information of the system frequency at the time of disturbance. In this paper, an improved method for such estimate is presented, which is based on the derived data of frequency variations obtained from PMUs. In addition, a way to obtain the appropriate interval for the lowest error estimate is discussed. The method has been applied to assess the inertia constant of the Iranian power grid, by obtaining the rate of change of frequency after a disturbance in the defined interval, and the rate of specified power imbalance between electrical power input and output.

eess.SY↗

arXiv2021

Comprehensive Analysis of Continuously Variable Series Reactor Using G-C Framework

Continuously Variable Series Reactor (CVSR) has the ability to regulate the reactance of an ac circuit using the magnetizing characteristics of its ferromagnetic core, shared by an ac and a dc winding to control power flow, damp oscillations and limit fault currents. In order to understand and utilize a CVSR in the power grid, it is essential to know all of its operational characteristics. The gyrator-capacitor approach has been applied to model electromagnetic coupling between the two circuits, controlled ac circuit and control dc circuit of the device. In this paper, we investigate some of the CVSR side behavior in terms of the induced voltage across the dc winding, flux density within the core's branches, and the power exchange between the two circuits during normal operation and fault conditions.

eess.SY↗

arXiv2018

Optimal Allocation of Series FACTS Devices in Large Scale Systems

Series FACTS devices, such as the variable series reactor (VSR), have the ability to continuously regulate the transmission line reactance so as to control power flow. This paper presents a new approach to optimally locating such devices in the transmission network considering multiple operating states and contingencies. To investigate optimal investment, a single target year planning with three different load patterns is considered. The transmission contingencies may occur under any of the three load conditions and the coupling constraints between base case and contingencies are included. A reformulation technique transforms the original mixed integer nonlinear programming (MINLP) model into mixed integer linear programing (MILP) model. To further relieve the computational burden and enable the planning model to be directly applied to practical large scale systems, a two phase decomposition algorithm is introduced. Detailed numerical simulation results on IEEE 118-bus system and the Polish 2383-bus system illustrate the efficient performance of the proposed algorithm.

math.OC↗

arXiv2017

The Allocation of a Variable Series Reactor Considering AC Constraints and Contingencies

The Variable Series Reactors (VSRs) can efficiently control the power flow through the adjustment of the line reactance. When they are appropriately allocated in the power network, the transmission congestion and generation cost can be reduced. This paper proposes a planning model to optimally allocate VSRs considering AC constraints and multi-scenarios including base case and contingencies. The planning model is originally a non-convex large scale mixed integer nonlinear program (MINLP), which is generally intractable. The proposed Benders approach decomposes the MINLP model into a mixed integer linear program (MILP) master problem and a number of nonlinear subproblems. Numerical case studies based on IEEE 118-bus demonstrate the high performance of the proposed approach.

math.OC↗

arXiv2017

Optimal Investment on Series FACTS Devices Considering Contingencies

Series FACTS devices are capable of relieving congestion and reducing generation costs in the power system. This paper proposes a planning model to optimally allocate TCSCs in the transmission network considering the base case and $N-1$ contingencies. We consider a single target year and select three distinct load patterns to accommodate the yearly load profile. A reformulation technique is utilized to linearize the nonlinear power flow constraint introduced by a TCSC. Numerical case studies based on the IEEE 118-bus system demonstrate the high performance of the proposed planning model.

math.OC↗

arXiv2017

Security Constrained Multi-Stage Transmission Expansion Planning Considering a Continuously Variable Series Reactor

This paper introduces a Continuously Variable Series Reactor (CVSR) to the transmission expansion planning (TEP) problem. The CVSR is a FACTS-like device which has the capability of controlling the overall impedance of the transmission line. However, the cost of the CVSR is about one tenth of a similar rated FACTS device which potentially allows large numbers of devices to be installed. The multi-stage TEP with the CVSR considering the $N-1$ security constraints is formulated as a mixed integer linear programming model. The nonlinear part of the power flow introduced by the variable reactance is linearized by a reformulation technique. To reduce the computational burden for a practical large scale system, a decomposition approach is proposed. The detailed simulation results on the IEEE 24-bus and a more practical Polish 2383-bus system demonstrate the effectiveness of the approach. Moreover, the appropriately allocated CVSRs add flexibility to the TEP problem and allow reduced planning costs. Although the proposed decomposition approach cannot guarantee global optimality, a high level picture of how the network can be planned reliably and economically considering CVSR is achieved.

math.OC↗