Tap Ratio Research Articles

Power efficiency improvement in reactive power dispatch under load uncertainty

Nowadays, there is a significant rise in electricity demand, posing challenges for power grid operators due to inaccurate forecasting, leading to excessive power losses and voltage instability. This paper addresses these issues by focusing on solving optimal reactive power dispatch (ORPD) while considering load demand uncertainty. The main objective of solving ORPD is to reduce power losses by adjusting generator voltage ratings, transformer tap ratio, and shunt capacitors' reactive power. Monte Carlo simulation (MCS) is employed to generate load scenarios using the normal probability density function, while a reduction-based technique is implemented to decrease the number of those scenarios. The improved gray wolf optimization (I-GWO) algorithm is introduced for the first time to address the stochastic ORPD problem. Experimentation is conducted on an IEEE-30 bus system when results are contrasted with conventional gray wolf optimization (GWO) and five other algorithms as stated in the literature. The I-GWO algorithm's performance is assessed with and without considering load demand uncertainty. Through Friedman's statistical tests, a significant decrease of 20.96% in active power losses and 63.06% in the summation of expected power losses is observed. The I-GWO algorithm's results on the ORPD problem demonstrate its effectiveness and robustness.

Discrete optimal power flow with prohibited zones, multiple-fuel options, and practical operational rules for control devices

Although the optimal power flow (OPF) problem has been extensively studied, solving realistic OPF models that accurately represent the operating behavior of power system components remains challenging. This paper proposes a novel model for the AC OPF problem, aiming to minimize the fuel costs of thermal units while taking into account valve-point loading effects (VPLE), prohibited operation zones (POZ), multiple fuel options (MFO), and operational rules associated with the discrete tap ratios of on-load tap changer (OLTC) transformers and with the discrete shunt susceptances of capacitor/reactor banks. These rules are represented using complementarity constraints. We propose a solution approach that integrates several strategies to address the non-smooth features of the objective function related to VPLE, the disjoint constraints and functions tied to POZ and MFO, the discrete characteristics of the reactive control variables, and the complementarity constraints governing operational rules linked to voltage control devices such as OLTC transformers and capacitor/reactor banks. The resulting optimization problem is designed to be compatible with commercial solver packages. Numerical tests on the IEEE 30, 118, and 300-bus systems aim to examine the cumulative impact of these operational factors on the optimal solution. The solution strategy proposed has demonstrated its effectiveness in solving the proposed OPF problem within reasonable computation times.

A data-driven Stackelberg game approach applied to analysis of strategic bidding for distributed energy resource aggregator in electricity markets

In the context of the participation of distributed energy resource (DER) aggregators in day-ahead energy and reserve markets, most of the existing analysis models of strategic bidding behavior of DER aggregators ignore the consideration of the safe operation of distribution systems. To this end, this paper builds a one-leader multi-follower Stackelberg game model considering the safety checking of distribution systems with the discrete features of capacitor banks and tap ratio of the substation transformer in the lower level. Mathematically, this model constitutes a bi-level mixed-integer nonlinear programming (BMINLP) problem. We convert the BMINLP model to a bi-level mixed-integer linear programming (BMILP) model based on KKT conditions, strong duality theorem, and big-M approach, which is still difficult to be solved directly. As a result, we propose a customized data-driven algorithm based on sampling without tuning hyper-parameters and an improved linear surrogate function method, to accurately fit the corresponding constraints of the lower-level model of BMILP problem, and then transform the BMILP problem into a single-level mixed-integer linear programming (MILP) problem to solve. The simulation of data-driven algorithm and comparison with the particle swarm optimization algorithm shows the high practicability of the bi-level Stackelberg game model and the effectiveness of the data-driven algorithm.

Stochastic Multi-Objective Optimal Reactive Power Dispatch with the Integration of Wind and Solar Generation

The exponential growth of unpredictable renewable power production sources in the power grid results in difficult-to-regulate reactive power. The ultimate goal of optimal reactive power dispatch (ORPD) is to find the optimal voltage level of all the generators, the transformer tap ratio, and the MVAR injection of shunt VAR compensators (SVC). More realistically, the ORPD problem is a nonlinear multi-objective optimization problem. Therefore, in this paper, the multi-objective ORPD problem is formulated and solved considering the simultaneous minimization of the active power loss, voltage deviation, emission, and the operating cost of renewable and thermal generators. Usually, renewable power generators such as wind and solar are uncertain; therefore, Weibull and lognormal probability distribution functions are considered to model wind and solar power, respectively. Due to the unavailability and uncertainty of wind and solar power, appropriate PDFs have been used to generate 1000 scenarios with the help of Monte Carlo simulation techniques. Practically, it is not possible to solve the problem considering all the scenarios. Therefore, the scenario reduction technique based on the distance metric is applied to select the 24 representative scenarios to reduce the size of the problem. Moreover, the efficient non-dominated sorting genetic algorithm II-based bidirectional co-evolutionary algorithm (BiCo), along with the constraint domination principle, is adopted to solve the multi-objective ORPD problem. Furthermore, a modified IEEE standard 30-bus system is employed to show the performance and superiority of the proposed algorithm. Simulation results indicate that the proposed algorithm finds uniformly distributed and near-global final non-dominated solutions compared to the recently available state-of-the-art multi-objective algorithms in the literature.

A Simple 18-Pulse Star Rectifier Using Two Passive Auxiliary Circuits at DC Link

In this article, a simple 18-pulse star rectifier using two new passive auxiliary circuits at dc link is proposed for reducing the harmonics content in ac line current. The proposed rectifier combines a double-star rectifier and four-tapped interphase reactor (FTIPR) with four diodes. Passive auxiliary circuits increase the state of the output voltage and current of the double-star rectifier, thereby increasing the pulse number of the load voltage and step number of the input line current. When FTIPR is optimally designed, passive auxiliary circuits convert double-star rectifier to 18-pulse star rectifier. Tap ratios of the FTIPR are determined based on minimum total harmonic distortion (THD) of the input line current and minimum ripple of the output voltage. The proposed rectifier simultaneously reduces ripple of the output voltage and THD of the input line current. A prototype is developed to verify the theoretical analysis through experimental results. Theoretical THD of the input line current is about 10.1%, whereas experimental THD is about 5.44%.

Invertibility Conditions for the Admittance Matrices of Balanced Power Systems

The admittance matrix encodes the network topology and electrical parameters of a power system in order to relate the current injection and voltage phasors. Since admittance matrices are central to many power engineering analyses, their characteristics are important subjects of theoretical studies. This paper focuses on the key characteristic of \emph{invertibility}. Previous literature has presented an invertibility condition for admittance matrices. This paper first identifies and fixes a technical issue in the proof of this previously presented invertibility condition. This paper then extends this previous work by deriving new conditions that are applicable to a broader class of systems with lossless branches and transformers with off-nominal tap ratios.

Optimal Corrective Rescheduling of Real and Reactive Powers for Power System Security Enhancement.(Dept.E)

This paper presents an optimal technique for solving the corrective rescheduling problem in p ower system. A successive dual linear programming approach is used with linearized p ower flow model. The system real and reactive power generations and transformer tap ratios are optimized within their operating limits so that no limit voilations of the line flow and bus voltage magnitudes in either the base case and contengency cases. The rest results on IEEE-30 bus test system show that the proposed technique can be successfully employed in conjunction with any fast security assessment scheme for a fast on-line security assessment and control.

Temperature dependent optimal power flow using chaotic whale optimization algorithm

AbstractThis work presents a novel, nature inspired evolutionary based approach, the chaotic whale optimization algorithm, to solve a temperature dependent optimal power flow problem of a power system. Whale optimization is inspired by the bubble‐net hunting strategy of the humpback whales; logistic chaotic maps are used to improve its performance. Whale optimization and our proposal are evaluated on three test systems namely, the IEEE 30‐bus test power system, the 2383‐bus Winter Peak Polish system and the 2736‐bus Summer Peak Polish system to give a solution to the temperature dependant optimal power flow of the power systems where control of generator bus voltages, transformer tap ratios and reactive power sources are involved. Minimization of total fuel cost is considered here as the objective function for this problem. The superiority and the effectiveness of the proposed algorithm technique have been exhibited in comparison to the other evolutionary optimization techniques identified in the recent literature.

Fast Atom Search Algorithm for Reactive Power Optimization of Power Grid with High-Penetration Wind and Solar Energies

This paper constructs a reliable reactive power optimization (RPO) model of power grid with the controlled participation of high-penetration wind and solar energies and provides a novel fast atom search optimization (FASO) algorithm to reach a set of solutions to the RPO problem. The developed FASO algorithm owns prominent merits of high searching efficiency and premature convergence avoidance compared with the original atom search optimization (ASO) algorithm, which is applied to determine the optimal dispatch scheme including terminal voltage of generators, the capacity of static VAR compensator (SVC), reactive power output of wind and solar energies, and the tap ratio of transformers. There are two objective functions to be minimized for maintaining the safe and reliable operation of power grid, i.e., total power loss of transmission lines and total voltage deviation of nodes. Meanwhile, the regulation capacities of wind farms and photovoltaic (PV) stations are evaluated based on different weather conditions, i.e., wind speed and solar irradiation. Particularly, the reactive power outputs of wind and solar energies can be globally controlled to coordinate with other controllable units instead of a local self-control. Eventually, the extended IEEE 9-bus and IEEE 39-bus systems are introduced to test the performance of the FASO algorithm for RPO problem. It has been verified that FASO can not only meet the optimal regulation requirements of RPO but also obtain high-quality regulation schemes with the fastest convergence speed and highest convergence stability in contrast with else algorithms.

Retrospective evaluation of lumbar puncture and intrathecal chemotherapy in thrombocytopenic patients

IntroductionLumbar puncture (LP) and intrathecal chemotherapy (IT CT) are common procedures and treatment options for hematologic patients. Although they can also be used in thrombocytopenic patients, there is no consensus on the safe cutoff value of platelet counts for LP and IT CT practices. AimThis research aimed to determine the safety of LP and IT CT administration in thrombocytopenic patients using different cutoff platelet values. MethodsOne hundred and fifty-two adult patients who had LP indications were evaluated. Among them, 42 patients received IT CT. The cerebrospinal fluid results from 100 procedures were available. ResultsThe preprocedural platelet count was <100.000/mm3 and <50.000/mm3 in 41 (41 %) and 18 (18 %) patients, respectively. Ten of these patients received platelet transfusion prior to LP. In the untransfused group, the platelet count was <50.000/mm3 in 12 (12 %) patients, among whom seven patients had a platelet count of <30.000/mm3. The traumatic tap was comparable among the transfused and untransfused groups (p = 0.632). No correlation was observed between the thrombocyte value and the traumatic tap (p = 0.891). The ratio of the traumatic tap was not significant between the patient groups with a platelet count of ≥50.000/mm3 or <50.000/mm3 (p = 0.418). After adding the transfused patients, the traumatic tap ratio remained nonsignificant between the two groups (p = 0.851). ConclusionHemorrhagic complications were rare in the thrombocytopenic patients who received IT CT after the LP procedure applied by experienced specialists. However, further prospective large studies evaluating the safety of procedures in thrombocytopenic patients are needed to make clear conclusion.

Reactive Power Control using Sine Cosine Algorithm for Active Power Loss Minimization with Voltage Profile Enhancement

The major purpose of optimal reactive power dispatch (ORPD) is to detect control variables like the voltage ratings of the generator, switchable shunt condenser banks, and the tap ratio of the tap setting transformer to reduce the active power loss for fixed economic power planning when taking on a set of constraints. This paper introduces the application of the sine cosine algorithm (SCA) to find the novel solution for the reactive power dispatch of power systems with different test systems (Standard IEEE 14-bus, IEEE 57-bus and IEEE 118-bus) with specific cases like reducing active power losses and increasing bus voltages in test systems. Obtained results validate the high tone of the proposed algorithm, with better, fast and consistent results comparing with existing literatures.

Multi-objective voltage control and reactive power optimization based on multi-objective particle swarm algorithm

This paper presents multi-objective particle swarm optimization (MOPSO) for voltage control and reactive power optimization. The optimization objective is to minimize active power loss and improve power system voltage profiles can be achieved by controlling a number of control variables such as generator voltages, transformer tap ratios and shunt capacitors, etc. A Fuzzy membership function is used to obtain the best compromise solution out of the available Pareto-optimal solutions. The results MOPSO are compared to the multi-objective genetic algorithm (MOGA), genetic algorithm (GA) and Particle Swarm Optimization (PSO). The IEEE 14 bus and IEEE 30 bus standards systems were used as test systems to demonstrate the applicability and efficiency of the proposed method.

Incorporation of Controlled Islanding Scenarios and Complex Substations in Optimal WAMS Design

An efficient wide-area measurement system (WAMS) should be able to preserve system observability in foreseen abnormal situations, such as intentional controlled islanding (ICI). In this paper, an optimal WAMS design model is proposed while ensuring power system observability in the base case and all plausible scenarios of ICI. Thus, quasi-observable states that are undesirable in state estimation are avoided. The model minimizes the cost of substation disruptions imposed by PMU installation and the cost of WAMS components subject to diverse economic and technical constraints. In order to optimally retain system observability in different operational configurations of substations, complex buses of switchgears with bus sectionalizers and couplers are modeled. Also, the indeterminacy of transformer tap ratios is considered to have realistic solutions. The proposed method is examined on IEEE standard test systems as well as Polish 2383-bus and 2746-bus large-scale systems to demonstrate its applicability to real systems.

Sparse Equalization in Aeronautical Telemetry Using Two Transmit Antennas

This correspondence explores the application of sparse equalizers in generalized time-reversed space-time block codes (GTR-STBCs) for a two-transmit/one-receive antenna aeronautical telemetry link. It is shown that the jointly optimum design of the sparse equalizer coefficients and the power sharing parameter $\rho$ in GTR-STBCs is computationally challenging because the active tap ratio of the sparse equalizers is a non-convex function of $\rho$ . A search algorithm based on a grid search followed by an interpolation is shown to yield impressive results. Our numerical results demonstrate that depending on signal-to-noise ratio and channel conditions, the number of non-zero taps of sparse equalizers for GTR-STBCs can be reduced by 53% to $86\%$ at the cost of 0.25 dB relaxation in the mean-squared error.

Femtosecond-laser-assisted implementation of an inline power tap in a multimode fiber

An inline power tap has been demonstrated and realized by inscribing an optical track in a standard 62.5/125 μm multimode fiber. The fiber-optic tap may resort to a single track or a pair of tracks, which can be created by incorporating a single instance or double instances of femtosecond laser scanning, respectively. For the single-track configuration, the built-in tap is formed to traverse the center of the core, while a pair of parallel taps is designed to vertically flank the core for the double-track configuration. The tap ratio can be practically tuned from 1.0% to 3.4% by tailoring the laser-writing power in accordance with the configuration of the tap. The hybrid double-track structure helped reduce the polarization sensitivity to as low as 0.8 dB. The excess loss was consistently kept below 0.2 dB.

Coordinated Optimal Network Reconfiguration and Voltage Regulator/DER Control for Unbalanced Distribution Systems

Network reconfiguration has long been used by distribution system operators to achieve certain operation objectives such as reducing system losses or regulating bus voltages. In emerging distribution systems with a proliferation of distributed energy resources (DERs), co-optimizing network topology and DERs’ dispatches could further enhance such operational benefits. This paper focuses on the optimal network reconfiguration problem of distribution systems via an unbalanced ac optimal power flow framework, which rigorously addresses operation characters of unbalanced network, DERs, and voltage regulators (VRs). Two VR models with continuous and discrete tap ratios are studied and compared. The proposed co-optimization problem is formulated as a mixed-integer chordal relaxation-based semidefinite programming model with binary variables indicating line-switching statuses and tap positions. Several acceleration strategies by studying the structure of distribution networks are explored for reducing the number of binary variables and enhancing the computational performance. Case studies on modified IEEE 34-bus and 392-bus systems illustrate the effectiveness of the proposed approach.

A 36-Pulse Diode Rectifier with an Unconventional Interphase Reactor

This paper proposes a simple 36-pulse diode rectifier with an unconventional interphase reactor (IPR) and single-phase full-wave rectifier (SFR). The primary winding of the unconventional IPR is double tapped and the secondary winding is connected with SFR. The operation mode of the unconventional IPR is analyzed, and the optimal tap ratio and turn ratio of the unconventional IPR are designed from both viewpoints of input line current and load voltage. With the optimal parameters of the unconventional IPR, the proposed rectifier extends the conventional 24-pulse rectifier operation to 36-pulse operation and draws near sinusoidal input line currents, the total harmonic distortion (THD) of which is about 5.035%. The kVA rating of the unconventional IPR is about 2.6% of the output power. Compared with the conventional 36-pulse rectifier with triple-tapped IPR, the proposed 36-pulse rectifier is easy and simple to implement instead of using control circuits. Experiment results are provided to verify the theoretical analysis.

Optimum Design of 48-Pulse Rectifier Using Unconventional Interphase Reactor

In order to simultaneously reduce the harmonics of input line current and ripple of load voltage in multipulse rectifier, this paper proposes a 48-pulse rectifier using the unconventional interphase reactor (IPR) with an auxiliary single-phase diode-bridge rectifier at the dc link. The primary winding of the unconventional IPR is triple-tapped, and the secondary winding is connected with a single-phase diode-bridge rectifier. The operation mode of the unconventional IPR is analyzed, and the optimal tap ratio and turn ratio are designed. With the optimal parameters of the IPR and the optimal conduction time sequence of power devices, the proposed rectifier extends the conventional 36-pulse rectifier operation to a 48-pulse operation and draws near sinusoidal input line currents, the total harmonic distortion (THD) of which is about 3.81%. The proposed 48-pulse rectifier is easy and simple to implement, and it is more suitable for high-voltage and large-current application. Some simulation and experiments are provided to validate the theoretical analysis.

A Fast Adjustment Method of Magnetically Controlled Reactor with Multi-taps

Magnetically controlled reactor (MCR) can compensate the capacitive reactive power generated by transmission line and enhance the stability of power supply, which is widely used in ultrahigh-voltage (UHV) power systems. In this paper, a novel structure for MCR with multi-taps is proposed. The MCR with multi-taps can switch its taps based on operation condition. The higher tap ratio is used to adjust the reactive power, and the lower tap ratio is fit for the stable grid. A switching algorithm is designed to make it work harmoniously and flexibly. For the adjustment of reactive power, this novel structure can perform better in regulated time without using higher tap ratios in practical operation, compared with the traditional structures.

Interior/exterior-point methods with inertia correction strategy for solving optimal reactive power flow problems with discrete variables

Interior/exterior-point methods have been widely used for solving Optimal Reactive Power Flow problems (ORPF). However, the utilization of such methods becomes difficult when transformer taps and/or capacitor/reactor banks are more rigorously represented in the problem formulation by means of discrete control variables. This work investigates the solution of the ORPF problem when transformer tap ratios are modeled as discrete variables. The solution method proposed handles discrete variables by means of sinusoidal penalty function, while the penalized problems are solved by an exterior-point method. An inertia correction strategy is proposed in order to assure that only local minima are obtained for the penalized problems. New search directions are also investigated that combine predictor and corrector directions. Numerical simulations are performed involving the IEEE 14, 30 and 57 bus systems. The results show the efficiency of the proposed inertia correction strategy and also reveals that the proposed exterior-point method outperforms traditional interior-point methods in terms of the number of iterations and computation times.