Balanced Operating Conditions Research Articles

Optimal Selection among Various Three-Phase Four-Wire Back-to-Back (BTB) Converters with Comparative Analysis for Wave Energy Converters

Wave energy converters are attracting attention as an energy source that can respond to climate change. In order to increase the energy efficiency of the wave energy converters, efficient power converters are also required. The efficient converters require operation at a low switching frequency, which increases the weight and volume of the passive components. Therefore, in this paper, the performance of various types of topologies is compared to select the optimal power converter for wave energy converters. In order to cope with the unbalanced operation and unbalanced load of renewable energy, in this paper, the topology of the four-leg type is analyzed centrally. In addition, the analysis was performed by applying the model predictive control that can quickly respond to the rapid energy change of wave energy. In addition, model predictive control was applied to the four-leg converter analyzed in this paper because it is suitable for application to atypical topologies. For performance analysis of various types of topology, the loss and efficiency of each converter were analyzed by applying a loss analysis model, and output current harmonics and leakage current characteristics, capacitor voltage fluctuation rate, etc., were additionally analyzed at various switching frequencies. In conclusion, the three-level four-leg converter showed up to 2.28% and 2.7% higher efficiency under balanced and unbalanced operating conditions.

Balancing performance of active magnetic regenerators: a comprehensive experimental study of aspect ratio, particle size, and operating conditions

Effective and, at the same time, efficient active magnetic regenerator (AMR) performance requires balanced geometry and operating conditions. Here the influence of regenerator shape, magnetocaloric material size, operating frequency, and utilization on the performance of gadolinium packed-particle bed AMRs is demonstrated experimentally. Various metrics are applied to assess effectiveness and efficiency. Observed temperature spans and cooling powers across a wide range of operating conditions are used to evaluate system performance and estimate exergetic cooling power and exergetic power quotient. A new metric combining exergetic cooling power and pump power provides an estimate of the maximum achievable second law efficiency. Five regenerator geometries with equal volumes and the aspect ratio from 1.0 to 3.8, and four different ranges of Gd spherical particles between 182 and 354 µm, are investigated. Improvements in system performance are demonstrated by a boost in specific cooling power of gadolinium from 0.85 to 1.16 W g−1 and maximum temperature span from 8.9 to 15.1 K. The optimum exergetic cooling power is observed for 1.37 utilization and 3 Hz operating frequency, exergetic power quotient exhibits a maximum at the same utilization but at 2 Hz frequency, while the highest efficiency is recorded at 1 Hz and utilization of 0.5, demonstrating that multiple performance metrics must be balanced to achieve regenerator design meeting all performance targets.

Experimental Research of Flow Distribution at Reactor Core Inlet of ACP100

A 1/3 scaled-down mock-up reactor of ACP100 was used to simulate the flow field in the prototype reactor and to carry out the experiment of core inlet flow distribution. In the mock-up reactor, the major flow path of the reactor is linearly scaled except for the core region which is replaced by 57 dummy fuel assemblies. In addition, the experiment measures core inlet flow rates by a specially designed turbine installed in each dummy fuel assembly. In the experiment, both four-loop balanced and unbalanced operating conditions are tested. The experimental results show that the flow in the major flow path of the mock-up reactor has entered the self-modeling zone and the flow field characteristics are the same as the prototype. The core inlet flow rates of different tests show similar distributions, which all meet the hydraulic performance requirements. Moreover, the effect of impeller rotation on the flow field of the core inlet has also been studied. The study indicates that the flow distribution is almost unaffected by the swirl flow.

Harmonic Performance Analysis of Static Var Compensator Connected to the Power Transmission Network

The static var compensator (SVC) is a device which is designed to compensate reactive power, increase voltage stability and to reduce voltage fluctuations. Thyristor controlled reactors (TCRs) are composed of reactors in series with bidirectional pair of thyristors. Current through reactors can be continuously controlled by changing the firing angle of thyristor valves, thus
 the inductive power can be easily controlled. Typical applications of TCRs in AC systems are voltage stabilization and temporary overvoltage reduction, stability improvement, damping of power oscillations and load balancing. In this paper, harmonic performance analysis of SVC equipped with TCRs is presented. SVCs utilizing TCRs generate harmonic currents and therefore it is necessary to determine the effect of harmonics generated by the SVC on the power system and its elements. This includes interaction of the SVC with the system, the SVC performance under balanced and unbalanced operating conditions and finally, evaluation of countermeasures such as installation of harmonic filters. In order to carry out these analysis, it is necessary to determine harmonic characteristics of the network at the point of SVC connection, existing levels of harmonics, and to know appropriate standards regarding acceptable harmonic levels in the power system. Since harmonic distortions in the system are caused by the interaction between SVC and the system, all system contingencies which may affect system’s frequency response should be evaluated. Detailed power system model should be considered to make sure that parallel resonance points of system do not directly coincide with characteristic harmonics from the SVC. Harmonics generated by SVCs are largely dependent on the operating point within the SVC characteristic. A conservative approach is to use the maximum values of harmonics generated within the spectrum irrespective of the operating point. The results of harmonic performance analysis are important for appropriate design of SVC. Harmonic performance analysis related to SVC application which are presented in this paper include the determination of: frequency response of the transmission network impedance required for the specification and design of filters; the effects of SVC generated harmonics on the power system; the overall filter requirements and countermeasures to reduce harmonics to acceptable levels.

Measurement of Simplified Single- and Three-Phase Parameters for Harmonic Emission Assessment Based on IEEE 1459-2010

This article investigates the feasibility of using a simplified approach, based on the measurement of power ratio parameters, for harmonic emissions assessment at the point of common coupling (PCC). The proposed approach comes from the common concept of power factor correction and the definitions of the IEEE Std. 1459-2010, where line utilization and harmonic pollution levels are evaluated by means of ratios between the power quantities of the apparent power decomposition. In addition to the IEEE Std. 1459-2010 indicators, in this article, the behavior is studied of additional parameters that are conceptually similar to those defined by the IEEE Std. 1459-2010. The suitability of such parameters is discussed, for both single- and three-phase balanced/unbalanced cases, taking into account both their behavior in different scenarios and their effectiveness when the measurement uncertainty is taken into account. The study is supported by some simulation results that have been obtained on an IEEE benchmark power system, which allows reproducing linear and nonlinear load conditions, balanced and unbalanced operating conditions, and the presence of capacitors for power factor correction.

On control and balancing of rigid bipolar MMC-HVdc links enabling subsystem-independent power transfer

High voltage direct current transmission schemes equipped with modular multilevel converter technology are considered in several realized and planned bulk power transmission projects. Especially in the case of dc cable links with high system lengths, the rigid bipolar configuration presents a suitable compromise between power rating, cost-efficiency and converter redundancy. Caused by the absence of a metallic return path, system degrees of freedom are reduced in contrast to the bipolar configuration with dedicated metallic return. Therefore, the dc currents in positive and negative bipolar subsystem are not independent. This leads to new challenges and motivates the development of advanced control and balancing concepts for rigid bipolar schemes. This paper focuses on balanced and unbalanced ac grid operating conditions with subsystem-independent active power set points in an ac split-busbar scenario, which has not yet been covered in literature. In order to validate the presented methodology, case studies are performed in electromagnetic transient software.

Mitigation of Unbalanced Voltage Sags and Swells of Power System in Utility Side by using Sen Transformer

Majority of the industrial electrical loads requires balanced three phase supply but in reality there is unbalanced supply due to single phase loads like railway tracks etc.increasing use of non linear loads in modern power distribution network there are some power quality issues like voltage sags and voltage swells, this distortion of the power supply effect the loads which are connected to power distribution network. In order to improve quality of the power, in this paper a Sen Transformer (ST) technique as been proposed to minimize unbalanced voltage sags and swells. The proposed technique mitigates both voltage sag and swell during balanced and unbalanced operating conditions. The proposed ST consists of a programmable tap controller to compensate ride through faults in power system network. The proposed work as been implemented using MATLAB/SIMULINK software. To validate the proposed work, simulation results are presented.

Frequency‐domain harmonic matrix model for three‐phase diode‐bridge rectifier

Three-phase diode-bridge rectifier is a common front end for variable frequency drives/dc-to-dc converters, and is a well-known harmonic source. The rectifier may operate in a dc current continuous or discontinuous mode, which creates a challenge in modelling the harmonic-generation characteristics of such device. This study proposes a method to determine the operational modes of the rectifier under balanced operating conditions and then develops appropriate frequency-domain harmonic models for each mode. The result is an integrated analytical harmonic matrix model for the three-phase diode-bridge rectifier. The matrix model can explicitly show the harmonic coupling effects between the rectifier ac supply voltages and its generated harmonic currents. Simulation and experiments have been done to verify the proposed model. The harmonic model has been applied to analyse the rectifier harmonic generating characteristics and the harmonic interactions between the rectifier and the grid.

Research on the Steady-State Performances of a Novel Energy-Efficient Single-Phase Induction Motor

In this paper, a novel energy-efficient single-phase induction motor with three parallel-connected stator windings and two external capacitors has been proposed. By selecting the appropriate capacitors, the currents in the three windings will be approximately symmetric at rated load, thus high rated efficiency can be obtained. Based on the symmetrical component method, the condition for balanced operation is analyzed and the method for determining the requested capacitances is also obtained. The approach for calculating the steady-state performance is proposed.

Distributed Widely Linear Kalman Filtering for Frequency Estimation in Power Networks

Motivated by the growing need for robust and accurate frequency estimators at the low- and medium-voltage distribution levels and the emergence of ubiquitous sensors networks for the smart grid, we introduce a distributed Kalman filtering scheme for frequency estimation. This is achieved by using widely linear state space models, which are capable of estimating the frequency under both balanced and unbalanced operating conditions. The proposed distributed augmented extended Kalman filter (D-ACEKF) exploits multiple measurements without imposing any constraints on the operating conditions at different parts of the network, while also accounting for the correlated and noncircular natures of real-world nodal disturbances. Case studies over a range of power system conditions illustrate the theoretical and practical advantages of the proposed methodology.

The Output Filter Identification of Three-Phase PWM Converter Using Weighted Least Square Method

This paper proposed the Weighted Least Square method (WLS method) to identify the output filter of three-phase PWM converter, which incorporates the signal processing as well as mathematical techniques into conventional Least Square method. It sets different weights to different measurements according to the phase where it locates, based on the discovery of the correlation between accuracy and phase of current. The algorithm is tested in both simulation and experimental environment, and the results validate that proposed method gives accurate estimation in steady state, and can response within 10ms in when grid voltage drops. This method can work under both balanced and unbalanced operating conditions, therefore provides a powerful tool for various control strategies to better understand the operating conditions. Compared with the invasive method, which intentionally inject a series of white noise in the system, proposed WLS method does not bring any turbulence, while compared with conventional Least Square method, it possesses better stability as well as higher accuracy.

Research on the Condition for Balanced Operation of the Single-Phase Induction Motor with Three Parallel-Connected Windings

Research on the Condition for Balanced Operation of the Single-Phase Induction Motor with Three Parallel-Connected Windings

Going Private and Going Dark Strategies: Literature Review and Directions for Future Research

Corporate delistings can be related to a wide variety of circumstances and operations (going private transactions, going dark strategies, mergers, buy-outs, involuntary delistings, etc.), representing a very complex and highly differentiated phenomenon, whose relevance has recently increased as one of the many effects of the ongoing global financial crisis.In this paper, on the basis of a systematic review of the existing international literature, we give reasons for the need for a wider and deeper theoretical framework for corporate delistings, which we consider to be an essential premise for the conduction of further studies on corporate governance changes and the dynamics of corporate value associated with going-private and going-dark strategies. We provide a possible classification of corporate delistings that deepens the fundamental distinction between voluntary and involuntary delistings. A particular focus is on voluntary delistings, which we differentiate in the light of three main characterising aspects: the subjects who pursue delisting, the strategic context and the operating conditions of the delisted company. We define some uniform areas of observation, which may represent a useful framework for future deeper studies concerning corporate delistings (pre-sale delistings, hidden potential delistings, control strengthening delistings and takeover delistings, either in balanced operating conditions or in presence of crisis/operating distress).

Performance Simulation and Analysis of a Novel Single-Phase Permanent Magnetic Synchronous Motor

This paper presents a novel energy-efficient single-phase permanent magnet synchronous motor with three-phase stator windings which are connected to two external capacitors in series connection, supplied by the single-phase AC power. The positive sequence impedance and negative sequence impedance of the novel single-phase permanent magnet synchronous motor are presented based on the symmetrical component method, the condition for balanced operation is analyzed and the method for determining the requested capacitances is also obtained. The simulation model of the motor is constructed in d-q stationary reference frame. The transient performance of the proposed motor is simulated and the simulation results proved the validity of the proposed motor.

Simulation Research on the Single-Phase Operation of a Line Start Permanent Magnet Synchronous Motor

In this paper, the single-phase operation of a line start permanent magnet synchronous motor (LSPMSM) has been analyzed in detail. At first, based on symmetrical component method, the condition for balanced operation is derived. Secondly, steady state performances are analyzed by computer programming. Thirdly, the transient performances are studied on the basis of MTLAB/Simulink. The results demonstrated that the LSPMSM running on a single-phase supply has lower efficiency but higher power factor than three-phase balanced operation, besides good starting and operating performances can be achieved.

Three-Phase Asymmetric Transformer Aging Considering Voltage-Current Harmonic Interactions, Unbalanced Nonlinear Loading, Magnetic Couplings, and Hysteresis

A new aging calculation method for three-phase three-leg power transformers under (un)balanced and (non)sinusoidal operating conditions is proposed where the impacts of magnetic saturation, couplings, and hysteresis are accurately included. The aging estimation is carried out through a recently developed and validated time-domain model of a nonlinear three-phase three-leg transformer. The model outputs are used to compute aging based on Arrhenius' thermal reaction theory. The combined aging effects from transformer core asymmetry and load nonlinearity, as well as current and voltage harmonic interactions from nonsinusoidal input excitations and nonlinear loading are considered in the calculation. The model improves upon the conventional weighted harmonic factor (WHF) approach of aging estimation by direct evaluation of additional fundamental and harmonic losses generated by the iron-core, nonlinear loads, and terminal voltage distortions. The main contribution is a new transformer aging estimation method with wider applicability to three-phase transformers considering harmonic current-voltage interactions from unbalanced nonlinear loads, terminal voltage distortions and imbalances, as well as magnetic hysteresis and flux-coupling effects in asymmetric iron-core structures. Several case studies are presented for comparing the proposed model based aging method with the conventional WHF approach.

Improved phase-locked loop for robust and fast tracking of three phases under unbalanced electric grid conditions

Modern electric power transmission and distribution systems need accurate phase information on three-phase grid voltages and/or currents. Conventional three-phase synchronous reference frame-based phase-locked loop (SRF-PLL) is generally sufficient for phase tracking during balanced operating conditions. However, SRF-PLL becomes inadequate when unbalance exists in the three-phase input signal. Because, unbalance in input signal set causes a double-frequency ripple and as a result, an ideal output signal cannot be obtained. Previous studies have focused on improving the SRF-PLL performance by removing this ripple with using delayed signals methods such as delayed signal cancellation (DSC)-PLL methods. Although these methods give ideal output signals, a certain time delay is occurred. In this study, an effective method DIF-PLL based on adding another signal, which has reverse polarity ripple is proposed for obtaining ideal output signal and fast tracking of phase angle. Performance of the DIF-PLL is compared with the performances of SRF-PLL and DSC-PLL methods. The performances of these methods are also examined for the presence of the harmonics. The results show that the proposed method has a better three-phase tracking performance than the others under balanced and unbalanced electric grid conditions.

Study of a Novel Energy Efficient Single-Phase Induction Motor With Three Series-Connected Windings and Two Capacitors

This paper presents a novel energy efficient single-phase induction motor with three series-connected windings and two capacitors. By suitable selection of capacitors, the currents in three windings are approximately symmetrical, and thus, the motor can operate approximately symmetrically from single-phase supply. Based on the symmetrical components method, the condition for balanced operation is studied, and the method for determining capacitances is proposed. The performance analysis method is put forward to calculate the steady performances. Performance tests are performed on the proposed motor and three-phase induction motor. It is proved that their rated efficiency is approximately the same, while the power factor of the former is higher than that of the latter. In comparison with the ordinary single-phase induction motor, it has the advantages of higher efficiency and smaller volume, thus can take the place of the latter in some applications.

A Scalar Resonant-Filter-Bank-Based Output-Voltage Control Method and a Scalar Minimum-Switching-Loss Discontinuous PWM Method for the Four-Leg-Inverter-Based Three-Phase Four-Wire Power Supply

An all-scalar-control and pulsewidth-modulation (PWM) approach for the four-leg-inverter (FLI)-based three-phase transformerless four-wire power supply (PS) is proposed. The output voltage of each phase is controlled independently, and its controller is formed by a stationary-frame resonant-filter bank accompanied with proportional-control and output-capacitor current-based active-damping loops. The simple and easy to implement scalar-control method exhibits superior overall steady-state and dynamic performance in the PS applications involving loads with high crest factor and/or significant load imbalance. Utilizing the inverter zero-state partitioning, a generalized form of scalar PWM for the FLI is developed. A novel minimum loss discontinuous PWM method, which provides minimum switching losses under all loading conditions (including load imbalance), is derived. This simple scalar method provides superior performance, and unlike the vector methods, it is easy to implement. The controller and modulator design and implementation details for the system are given. Linear and nonlinear loads for balanced and imbalanced load operating conditions are considered. The scalar-control and PWM methods are proven by means of theory, simulations, and thorough laboratory experiments of a 5-kVA PS.

An Output-Power-Control Strategy for a Three-Phase PWM Rectifier Under Unbalanced Supply Conditions

Instantaneous power regulation is an effective way to improve the performance of a pulsewidth-modulation rectifier operating under unbalanced supply-voltage conditions. By properly setting current commands, this approach aims to achieve performance features that are normally achievable only under ideal balanced operating conditions. This paper proposes an instantaneous power-regulation strategy called output-power-control method, in which the current commands are determined so as to appropriately distribute the input power to maintain a constant dc output voltage and sinusoidal line currents. Although the power factor is not directly controlled, it is shown that the proposed scheme results in near unity vector power factor. The current commands are given by a set of simple linear equations in which the proposed control scheme can be easily implemented. Experimental results obtained with a 1-kW laboratory prototype demonstrate that the proposed scheme fulfils all the main objectives of a high-performance rectifier.