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Recently, the layout optimization of the secondary coils for wireless power transfer systems has been developed using the fixed grid (FG) representation. Although this method can effectively and efficiently determine the optimized coil design under the given conditions, a distinct discrepancy exists between the evaluated coil mass (i.e., simulation data) and the physical coil mass (i.e., experiment data). In this paper, the FG-based coil layout optimization is revisited based on the smooth boundary (SB) representation in order to resolve the inherent drawbacks of the FG representation. Induced voltage, electromagnetic field strength, and coil mass, which have been previously derived in the FG representation, are reformulated in terms of design variables (i.e., a reference turn and relative turns in this paper) in the SB representation. Through the layout optimization, the optimized layouts of the secondary coil are determined in order to minimize the coil mass while satisfying the constraints for induced voltage and magnetic field strength; then, they are postprocessed in order to obtain a smooth, elaborate boundary. The experimental validation demonstrates that the proposed SB-based approach outperforms the previous FG-based method in terms of coil mass and boundary representation. [ABSTRACT FROM AUTHOR]

This paper describes a systematic method for determining an area of vulnerability (AOV) to fault induced voltage sags. The concept of an AOV is very useful for evaluating vulnerability and the relationship between sensitive loads and system voltage sag performance. In general, a system performance assessment pertaining to voltage sags requires a determination of AOVs for system buses. Because voltage sags can be caused by remote faults in a transmission system, to completely identify an AOV, a large part of the power system including adjacent circuits and remote supply systems should be considered. Therefore, accurately calculating critical points and identifying AOVs are challenging tasks. In this paper, we present an effective numerical method to determine an accurate AOV in a large scale power system and to overcome limitations of other well-known methods. [ABSTRACT FROM PUBLISHER]

In high-voltage applications, the magnitude of total semiconductor losses (on-state and switching) determines the viability of modular-type multilevel converters. Therefore, this paper presents a new cell arrangement that aims to lower total semiconductor loss of the modular multilevel converter (MMC) to less than that of the half-bridge modular multilevel converter (HB-MMC). Additional attributes of the proposed cell are: it eliminates the protective thyristors used in conventional half-bridge cells that deviate part of the dc-fault current away from the antiparallel diode of the main switch when the converter is blocked during a dc short-circuit fault, and it can facilitate continued operation of the MMC during cell failures without the need for a mechanical bypass switch. Thus, the MMC that uses the proposed cell retains all advantages of the HB-MMC such as full modularity of the power circuit and internal fault management. The claimed attributes of the proposed cell are verified using illustrative simulations and reduced scale experimentations. Additionally, this paper provides brief and critical discussions that highlight the attributes and limitations of popular MMC control methods and different MMC cells structures proposed in the literature, considering the power electronic system perspective. [ABSTRACT FROM AUTHOR]

Electric power systems are going through a major upgrade with the integration of advanced technologies to enable the smarter electric grid (SEG). The SEG will use information and communications technology to have enhanced controllability and will become more interactive. This ongoing change also necessitates educating professionals and future generation of engineers to manage evolving complexity of the electric grid. This paper presents experiences in the design and teaching of a unique multidisciplinary team-taught course on smart grid cyber infrastructure to provide a new generation of engineers with a solid foundation of smart grid concepts and their associated challenges. This paper identifies the course topics covered, learning objectives, and assessment activities for the class as well as lessons learned based on course evaluations obtained from multiple offerings. All of the course material is available in public domain and can be easily adopted at another educational institution. [ABSTRACT FROM AUTHOR]

The matrix converter (MC) is a direct ac–ac power converter without an intermediate dc link. It has several attractive features, such as high power density, four-quadrant operation, and bidirectional power flow. However, the application of MCs in high-voltage and high-power systems is still limited by the device voltage levels. It is well known that the multilevel power converter technology can be a solution to enhance the voltage rating and improve harmonic performance in many applications. Therefore, an application of a multilevel topology based on a direct ac–ac power converter is proposed in this paper. This paper first introduce the topology structure, the switching pattern grouping method, and the proposed output voltage modulation method for a five-level capacitor clamped multilevel matrix converter (5LMC). Amplitude coefficient adjustment is also introduced as a part of modulation procedure to simplify the duty cycles calculation. Simulation from MATLAB/Simulink is given to demonstrate the theoretical work. Experimental results from a five-level matrix converter prototype are presented to validate the theoretical findings. [ABSTRACT FROM AUTHOR]

Due to the increasing penetration level of microgrids (MGs), it becomes a critical issue for MGs to help sustaining power system stability. Therefore, ancillary services, such as the low-voltage ride-through (LVRT) capability should be incorporated in MGs in order to guarantee stable operation of the utility grid during grid faults. In this paper, a LVRT control strategy based on positive/negative sequence droop control is proposed for grid-interactive MGs to ride-through voltage sags with not only inductive/resistive, but also complex line impedance. By using the proposed control strategy, MGs can support the grid voltage, make profits, and also ride-through the voltage dip during the whole fault period. A two-layer hierarchical control strategy is proposed in this paper. The primary controller consists of voltage and current inner loops, a conventional droop control and a virtual impedance loop, while the secondary controller is based on a positive/negative sequence droop scheme which is able to coordinate the power injection during voltage sags. Experimental results are obtained to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

System operators are required to serve the load in the most cost-effective way while maintaining the integrity of the system and heeding reliability requirements. In the day-ahead market, operators acquire reserves in an attempt to guarantee N-1 reliability; yet, reserve deliverability is not guaranteed. Prior research has shown that the use of transmission switching, or topology control, may help improve reserve deliverability. In this paper, transmission switching is used as a corrective mechanism to help the system achieve N-1-1 reliability, where not only has the system lost a single element, but also it experiences the loss of a second major element after an adjustment period. In an attempt to preserve N-1-1 reliability, for this paper, a day-ahead unit commitment model that acquires supplementary reserves is solved. The day-ahead market solution is then tested for N-1-1 reliability using contingency analysis models with and without transmission switching. The methodology can be employed at the day-ahead time stage to ensure the system has acquired sufficient supplemental reserves. The results demonstrate that not only can corrective transmission switching be beneficial post-contingency without inhibiting the ability to return to N-1 reliability, but it can also help obtain an N-1-1 reliable solution. [ABSTRACT FROM AUTHOR]

The introduction of the microprocessor-based numerical relay in the 1980s resulted in multifunctional, multidimensional, communications-enabled complex protection systems for zone and system protection. The increasing capabilities of this technology created new unintended challenges: 1) complexity has increased and selecting coordinated settings is a challenge leading to occasional miscoordination; 2) protection functions still rely on a small number of measurements (typically three voltages and three currents) limiting the ability of protection functions to dependably identify the type of fault conditions; and 3) present approaches are incapable of dealing with hidden failures in the protection system. Statistically, 10% of protection operations are misoperations. This paper presents a new approach to protection that promises to eliminate the majority of the problems that lead to misoperations. The approach is described, demonstrated in the laboratory, compared to traditional protection functions and its application to a substation coordinated protection system capable of detecting and dealing with hidden failures is described. This paper also discusses the planned field testing of the approach. [ABSTRACT FROM AUTHOR]

Due to the increase of generation sources in distribution networks, it is becoming very complex to develop and maintain models of these networks. Network operators need to determine reduced models of distribution networks to be used in grid management functions. This paper presents a novel method that synthesizes steady-state models of unbalanced active distribution networks with the use of dynamic measurements (time series) from phasor measurement units (PMUs). Since phasor measurement unit (PMU) measurements may contain errors and bad data, this paper presents the application of a Kalman filter technique for real-time data processing. In addition, PMU data capture the power system's response at different time-scales, which are generated by different types of power system events; the presented Kalman filter has been improved to extract the steady-state component of the PMU measurements to be fed to the steady-state model synthesis application. Performance of the proposed methods has been assessed by real-time hardware-in-the-loop simulations on a sample distribution network. [ABSTRACT FROM AUTHOR]

This paper presents analytical and simulation studies of wind farms (WFs) connected to power system through a unified interphase power controller (UIPC), which should control power flow and the short-circuit contribution of WF. The UIPC is based on an interphase power controller (IPC) in which the phase-shifting transforms are replaced by two series converters (SECs). In this paper, the UIPC model is developed based on phase angles of injected SEC voltage and a control scheme is proposed to control power flow and limit the short-circuit contribution of WF. The WF model is based on an equivalent aggregated variable-speed double-fed induction generator. The PSCAD/EMTDC simulation results show that the UIPC is an effective and novel solution for power-flow control and limitation of short-circuit contribution of WF in power systems. [ABSTRACT FROM AUTHOR]

Special protection schemes (SPSs) are an efficient alternative to increase the flexibility in the operation of power systems. The implementation of SPSs is often motivated by technical rather than economic reasons. The aim of this paper is to propose a novel framework for the analysis and development of SPSs in a context from the Chilean experience that comprises both technical and economic incentives to enable high penetration of solar energy. With this purpose, this paper explores the new capabilities of SPSs based on maximizing the cost-effective integration of solar power into a power system, given a set of technical challenges (congestion and dynamic response in case of contingencies) that must be considered in their design. In this framework, three main drivers were identified and discussed. The discussion includes the mechanisms associated with each driver that promote the massive integration of solar power. Moreover, within the proposed technical-economic framework, a methodology for driver selection and SPS design is proposed. The methodology and the drivers identified are evaluated in the Chilean power system. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for power system transient stability simulation, which is based on a semi-analytical solution (SAS) of power system differential-algebraic equations. In this paper, an SAS is derived using the Adomian decomposition method as a closed-form explicit function of symbolic variables such as time, the initial state, and other variables on system conditions and; hence, it can directly give a power system's dynamic trajectory being accurate for a certain time window. Unlike a traditional numerical integration based simulation approach, the proposed new approach offline derives an SAS and online evaluates the SAS by plugging in values of symbolic variables for a series of time windows making up the desired simulation period. This paper further studies the maximum length of the time window for an SAS being accurate and proposes a divergence indicator for simulation using adaptive time windows. Implementation of this new approach on parallel computers is also studied. The new approach is validated through contingency simulation of the IEEE 10-generator 39-bus system with detailed generator models. [ABSTRACT FROM AUTHOR]

In a recent paper, we proposed a system identification method for constructing reduced-order models for the electro-mechanical dynamics of large power systems, divided into multiple coherent clusters, using Synchrophasors. Every cluster in the actual model was represented as an aggregate generator in the reduced-order model. An aggregate network graph connected one aggregate generator to another. In this paper, we extend this identification approach to differential-algebraic (DAE) models. First, every cluster is associated with a unique terminal bus, referred to as the pilot bus, that couples its internal network to the rest of the system. The proposed algorithm uses Synchrophasor measurements from the pilot buses to identify the dynamic model of the aggregate generator for each cluster using nonlinear least squares while retaining the identity of all the pilot buses. The resulting reduced-order model is in the form of a nonlinear electric circuit described by aggregate differential and algebraic equations. We illustrate our results using two case studies, one for the IEEE 9-bus power system and another for the IEEE 39-bus power system. We also discuss how these reduced-order DAE models may be useful for designing shunt controllers at the pilot buses by using Synchrophasor feedback. [ABSTRACT FROM AUTHOR]

This two-part paper presents a framework for the characterization and minimal representation of the feasibility regions of power systems in the demand space. These feasibility regions are called loadability sets, and they represent the projection of generation-demand-network space onto the demand space only. Loadability sets have been characterized previously for power systems with either no or a single active line flow constraint. In Part I of this two-part paper, we generalize this characterization to power systems with any number of active line flow constraints. The proposed characterization approach makes use of the Fourier–Motzkin elimination method which leads to the generation of a large number of constraints. We set course to address this shortcoming in the second part of this paper. The notion of umbrella set is revisited in Part II to identify and remove the redundant constraints produced in the loadability set characterization process. The outcome of the proposed framework is the minimal representation of the power system feasibility region in the demand space. We envision multiple applications for the proposed framework in power system planning, operations planning, and real-time operation. [ABSTRACT FROM AUTHOR]

This paper applies a phasor-only state estimator (PSE) to a large power system consisting of two control regions, using synchrophasor data from 56 765/345/230 kV substations. Although the technique has been previously developed, this paper describes a topology processor to determine the redundant clusters of connected buses such that the PSE can be used in real time. This PSE allows corrections for phase biases, transformer taps, and current magnitude scaling. The ability to simultaneously solve the PSE for the two control regions is due to a PMU monitoring a tie-line between these two regions. The results show that with this method, the total vector errors of the measured voltage phasor data in these two control regions average to less than 0.5% under ambient conditions. The PSE also computes virtual phasor measurements on 70 buses that do not have PMUs, including large steam generator and wind-turbine generator substations. [ABSTRACT FROM AUTHOR]

Atmospheric corona discharge plasmas are the most common diversely occurrence in the electric power system. In this paper, four elementary processes occurred in corona discharge are taken into account, including elastic collision, excitation, attachment, and ionization. As one of the most important parameters in corona characteristics analysis, the effective Townsend ionization coefficient is completely calculated by the Boltzmann equation under the consideration of humidity. This paper also derives the electron energy distribution function (EEDF) in water vapor and dry air, respectively. With reference to previous researches and the existing literature, comparisons and validations on ionization and attachment coefficient are conducted. Besides, the effects of humidity, pressure, and temperature on the effective ionization coefficient are also discussed in this paper. It is concluded that humidity can enhance both ionization and attachment. The results show that the ionization coefficient in this paper is well consistent with traditional ones, while there are variations for attachment coefficient. In normal condition, the effective ionization coefficient varies slightly with humidity, but it increases significantly with a decreased pressure or an increased temperature, which cause the change in critical electric field correspondingly. [ABSTRACT FROM PUBLISHER]

Power electronic devices are inherently discontinuous systems. Square waves, produced by interconnected transistors, are commonly used to control inverters. This paper proposes a novel phasor transform, based on the theory of moments, which allows to analyze the steady-state behavior of discontinuous power electronic devices in closed-form, i.e., without approximations. In the first part of this paper, it is shown that the phasors of an electric circuit are the moments on the imaginary axis of the linear system describing the circuit. Exploiting this observation, in the second part of this paper, we focus on the analysis of circuits powered by discontinuous sources. The new “discontinuous phasor transform” is defined and the $ v$–$ i$ characteristics for inductors, capacitors, and resistors are described in terms of this new phasor transform. Since the new quantities maintain their physical meaning, the instantaneous power and average power can be computed in the phasor domain. The analytic potential of the new tool is illustrated studying the steady-state response of power inverters and of wireless power transfer systems with non-ideal switches. [ABSTRACT FROM AUTHOR]

When generators of a power system are subject to a large disturbance, their electromechanical oscillations (EOs) are essentially nonlinear as observed from their rotor angle waveforms due to the nonlinear power network. However, traditional modal analysis has not given enough considerations to nonlinearities in EOs. This paper analytically formulates the accurate oscillation frequency (OF) of an EO mode addressing nonlinearities. It is revealed that when the system model and condition are fixed, the OF of any EO mode is energy-dependent as a function of the oscillation amplitude (OA). That is characterized by a new tool named Frequency-Amplitude (F-A) curve regarding each mode, from which the frequency decreases from the natural frequency toward zero when the amplitude grows to a critical threshold. The paper proves that an F-A curve is actually a projection of the system trajectory between the stable equilibrium and the stability boundary onto the OF-OA plane regarding one mode. Based on the concept of F-A curve, a stability index is defined and estimated from measurements for online angle stability analysis. The proposed methodology is presented in detail using an SMIB system and then demonstrated on the IEEE 9-bus system and WECC 179-bus system having multiple EO modes. [ABSTRACT FROM PUBLISHER]

This paper presents a new method for studying electromechanical transients in power systems using three phase, combined transmission and distribution models (hybrid models). The methodology models individual phases of an electric network and associated unbalance in load and generation. Therefore, the impacts of load unbalance, single phase distributed generation and line impedance unbalance on electromechanical transients can be studied without using electromagnetic transient simulation (EMTP) programs. The implementation of this methodology in software is called the Three Phase Dynamics Analyzer (TPDA). Case studies included in the paper demonstrate the accuracy of TPDA and its ability to simulate electromechanical transients in hybrid models. TPDA has the potential for providing electric utilities and power system planners with more accurate assessment of system stability than traditional dynamic simulation software that assume balanced network topology. [ABSTRACT FROM PUBLISHER]

The dc–dc modular multilevel converter (MMC), which originated from the ac–dc MMC, is an attractive converter topology for the interconnection of medium-/high-voltage dc grids. This paper presents design considerations for the dc–dc MMC to achieve high efficiency with reduced component sizes. A steady-state mathematical model of the dc–dc MMC in the phasor domain is developed. Based on the developed model, a design approach is proposed to size the components and to select the operating frequency of the converter to satisfy a set of design constraints while achieving high efficiency. The design approach includes sizing the arm inductor, submodule capacitor, and phase filtering inductor along with selection of the ac operating frequency of the converter. The accuracy of the developed model and the effectiveness of the design approach are validated based on the simulation studies in the PSCAD/EMTDC software environment. The analysis and developments of this paper can be used as a guideline for designing the dc–dc MMC. [ABSTRACT FROM PUBLISHER]

This paper proposes an improved voltage regulation method in a multisource-based dc electrical power system in the more electric aircraft. The proposed approach, which can be used in terrestrial dc microgrids as well, effectively improves the load sharing accuracy under high droop gain circumstance with consideration of cable impedance. Since no extra communication line and controllers are required, it is easily implemented and also increases the system modularity and reliability. By using the proposed approach, the dc transmission losses can be reduced and the system stability is not deteriorated for normal and fault scenarios. In this paper, optimal droop gain settings are investigated and the selection of individual droop gains as well as the proportional power sharing ratio has been described. Simulation and experimental results validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

This paper proposes a new topological configuration for a unified power quality conditioner (UPQC). Generally, the power structure of the three-phase three-wire UPQC consists of two back-to-back connected six-switch inverters. For this configuration, out of 12 switches, six of the series inverter switches will be underutilized most of the time. To improve the semiconductor utilization and consequently to reduce the total switch count, this paper proposes a new reduced switch topology for the UPQC. The proposed topology is realized using only ten switches and retains all the performance merits of the 12-switch UPQC while minimizing its underutilization without increasing the switch VA rating. The paper provides a detailed analytical study and evaluation by comparing the proposed topology with the twelve- and nine-switch-based UPQC system configurations. The feasibility of the proposed topology is validated through experimental investigation. [ABSTRACT FROM AUTHOR]

This paper addresses the problem of predictive diagnostic in high-power transformers. Particularly, this paper is focused on their use in uninterruptible power supply systems for safety critical applications, such as railway interlocking signaling installations. With respect to the state of the art, where typically only thermal and electrical faults are monitored, this work proposes a distributed network of measuring nodes where also vibration-based mechanical stress diagnosis is implemented. Mechanical degradation is tracked through vibration measures, using multichannel accelerometers, with sensitivity down to 0.5 mg and local signal processing in the transformed frequency domain, up to 1 kHz. A compact hardware-software implementation of the nodes is also presented. The performances of the diagnostic system are assessed through experimental measurements on real three-phase high-power transformers used in railway applications. [ABSTRACT FROM AUTHOR]

Modern aircrafts are evolving toward more electric aircraft (MEA), resulting in greater reliance on the electrical system for safe flight. On-board power system of MEA integrates a large number of power electronic converters, and it is reported that semiconductor devices and electrolytic capacitors in power converters are the most vulnerable links impacted by loading conditions; thus, reliability becomes a critical concern in an MEA power system. This paper proposes a hierarchical approach for systematic reliability modeling and evaluation for the on-board power system of MEAs. It consists of three hierarchical levels (HLs): component level (HL1), subsystem level (HL2), and system level (HL3). In HL1, failure rates of power electronic components are modeled considering relevant inner structure and loading conditions; in HL2, the reliability of individual subsystems such as converters are constructed; in HL3, the system reliability is quantified based on the network architecture and reliability of the subsystems. The impacts of different parts (components/subsystems) on the overall system are assessed effectively with the identification of the vulnerable parts. This also provides a guideline for reliability enhancement by using thermal control techniques, adding redundancies or performing maintenance on the vulnerable parts to ensure the satisfactory of system reliability requirements. The proposed method is demonstrated on the future MEA power system architectures (hybrid ac–dc architecture and HVdc architecture). [ABSTRACT FROM AUTHOR]

The electric power system is witnessing a shift in the technology of generation. Conventional thermal generation based on synchronous machines is gradually being replaced by power electronics interfaced renewable generation. This new mode of generation, however, lacks the natural inertia and governor damping, which are quintessential features of synchronous machines. The loss of these features results in increasing frequency excursions and, ultimately, system instability. Among the numerous studies on mitigating these undesirable effects, the main approach involves virtual inertia (VI) emulation to mimic the behavior of synchronous machines. In this paper, explicit models of grid-following and grid-forming VI devices are developed for inertia emulation and fast frequency response in low-inertia systems. An optimization problem is formulated to optimize the parameters and location of these devices in a power system to increase its resilience. Finally, a case study based on a high-fidelity model of the South-East Australian system is used to illustrate the effectiveness of such devices. [ABSTRACT FROM AUTHOR]

The more electric aircraft concept aims to improve the fuel consumption, the weight, and both the maintenance and operating costs of the aircraft, by promoting the use of electric power in actuation systems. According to this scenario, electromechanical actuators for flight control systems represent an important technology in next generation aircraft. This paper presents a linear-geared electromechanical actuator for secondary flight control systems, where the safety and availability requirements are fulfilled by replicating the electric drive acting on the drivetrain. Indeed, the architecture considered consists of two power converters feeding as many electrical machines coupled to the same mechanical system. The design of both the permanent magnet synchronous machine and the power converter are addressed. Preliminary results on the electric drive prototype are also provided and compared to the design requirements. Finally, the electromechanical actuator performance at system-level is evaluated in Dymola environment, analyzing different operating modes. [ABSTRACT FROM AUTHOR]

With the goal to decrease weight and increase overall efficiency, power electronics is proliferating in the aircraft applications. The conventional mechanical, pneumatic, and hydraulic systems are substituted with on-board electrical distribution systems. The new power electronics based distribution architectures should comply with the airworthiness standards by providing adequate redundancy to operate even under multiple failures. However, each redundant system adds to more weight and cost, and hence optimizing redundancy without compromising safety still remains a challenge. In this scenario, modular power converters offer a promising solution for obtaining reliable operation. Apart from ensuring availability and operation of the system, the modular converters enable controlling the stress for the individual converter cell and therefore their wear-out. This paper considers the failure mechanisms of the most sensitive devices in the system, the power semiconductors, and predicts their remaining useful lifetime (RUL). Based on this RUL, an optimization of the system loading is performed in order to delay the wear-out based failures in the system without reducing the mean lifetime of the building blocks. A study case is shown in order to demonstrate the lifetime extension of the system with the proposed algorithm. [ABSTRACT FROM AUTHOR]

DC power distribution systems typically consist of several source converters supplying load converters through single or multiple dc buses. Such complex systems are prone to stability issues caused by the interactions among feedback-controlled converters. Additionally, dc interconnected systems typically undergo considerable changes in their operating points. This can cause a system that is well-stabilized at a certain operating point to go unstable for another operating condition. Therefore, a stabilization method that is capable of adapting to variations in system operating conditions is highly desirable. This paper presents an adaptive stabilization method implemented on the source-side. The system stability is periodically analyzed by real-time measurement of the system bus impedance, which is dominated by the source impedance. Accordingly, the source converter control is modified by the proposed method to guarantee stability and high performance of the entire system after system changes. The approach has several advantages, including ease of design and implementation, minimal deviation from the nominal controller, and robustness due to the real-time adaptive implementation. Simulation and experimental results are presented that confirm the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

More electric aircrafts (MEAs) comprise a vast amount of power electronic loads, which usually behave as constant power loads (CPLs). The incremental negative impedance of CPLs threatens system stability. To ensure an effective control of power flow in MEAs, eliminating the undesired behavior of CPLs is a necessity. This aim requires spontaneous power estimation of the time-varying uncertain loads. In this paper, an adaptive backstepping controller, which is interconnected to a third-degree cubature Kalman filter, is developed for a dc microgrid (MG) feeding nonideal CPLs. At first, the load power is considered as an artificial state and augmented into the system states, which enables estimation of not only the dc MG states but also the unknown value of the load power. The estimated load power is then forwarded to a backstepping controller. The systematic approach of this controller allows obtaining the control signal, which is the duty ratio of the switch, to not only system stabilizing but also tracking a desired voltage of the dc bus under the load power variations. The proposed adaptive controller is tested on a dc MG that has one CPL. The conducted experimental results verify the proposed nonlinear control in tracking the desired voltage of the dc bus under slow and fast variations of the load power. [ABSTRACT FROM AUTHOR]

AC cascaded system is one of the basic components of the power conversion system in the modern more-electric aircraft (MEA). However, the ac cascaded system suffers from an instability problem, i.e., even if each subsystem is stable individually, the formed cascaded system may become unstable. Most of the existing stabilization methods are a linear control method, which is based on a small signal model and can only ensure small signal stability near the operation point in theory. Therefore, these existing linear stabilization methods may be ineffective to fix large-signal stability issues. In this paper, a large signal stability constraining dichotomy solution (SCDS)-based model predictive control (MPC) is proposed to improve the stability of the ac cascaded system in the MEA by the Lyapunov criteria. This approach first theoretically presents how to add the system stability item to the MPC cost function in an analytic way instead of using the traditional “experience-based” weight method. Besides, the SCDS-MPC itself is also an improvement to the existing finite control set MPC. It can realize a constant switching frequency and achieve better steady-state/dynamic current control performance. Finally, a 1.5 kW ac cascaded system is fabricated in the laboratory to verify the proposed SCDS-MPC method. [ABSTRACT FROM AUTHOR]

This paper introduces a sliding mode control (SMC) strategy for three-phase dynamic voltage restorers (DVRs) with a 12-switch voltage source inverter. The compensating voltage references needed in the SMC strategy are generated by an adaptive notch filter (ANF), which exhibits excellent performance under grid voltage anomalies such as voltage sags, swells, and unbalanced and distorted grid voltage conditions. The consequence of using the ANF eliminates the use of phase-lock loop or frequency-lock loop and low-pass filter, which makes it distinguishable from the existing reference signal generation solutions. In addition, the use of the SMC strategy with its attractive properties makes the control implementation simple. Theoretical results are supported by simulation results as well as real-time laboratory results over a range of grid voltage anomalies. These results show that the proposed control strategy not only offers an excellent dynamic response independent from the parameter variations and disturbances but also compensates the voltage sags, swells, and harmonics on the load terminals under the defined limits of the IEEE-519 standard. [ABSTRACT FROM AUTHOR]

In this paper, a method to determine load conditions under which the armature current of a salient pole synchronous machine is on the q-axis is described. The proposed method allows the determination of a locus in the $P-Q$ space in which the armature current is completely on the q-axis. The derivation of these conditions simplifies the determination of the machine q-axis parameters during load rejection tests, since it eliminates the necessity for trial and error procedures or power angle estimation. The method was tested in a 100 MVA, 13.8 kV, 60 Hz, 40 poles salient pole synchronous machine installed in a hydro power plant. Tests results show that loads calculated with the proposed method are in fact points where the armature current is on the q-axis. [ABSTRACT FROM AUTHOR]

Coordination of directional relays in large-scale power systems that are multi-loop structured is a complicated and time consuming problem. Therefore, determination of the directional loops and the minimum break point set (MBPS) or a set close to it, which is essential to start relay coordination, is challenging. So far, several heuristics and exact methods have been proposed for the determination of the MBPS. In this paper, a new heuristic method based on a new implementation of depth-first search algorithm is proposed, which considerably facilitates the detection of directional loops (if any) in the network. The proposed method is tested on a 5-bus, four IEEE and four Polish test systems. The results show the efficiency of the proposed method in finding optimal or near-optimal solutions in a rational amount of time. [ABSTRACT FROM AUTHOR]

In this paper, a new synchronous machine model is developed for electromagnetic transients program type simulations. The stator circuit is expressed in the abc phase domain. The machine model is represented as a Norton equivalent with a current source in parallel with a constant Norton admittance. The machine equations are reformulated so that the computational effort required for the modeling of the machine is reduced. Test studies demonstrate the accuracy of the proposed synchronous machine model and show that the proposed model is computationally more efficient than the existing constant conductance phase domain model and voltage-behind-reactance model. [ABSTRACT FROM AUTHOR]

The paper proposes a centralized protection scheme with a localized backup for a MVDC microgrid. The centralized scheme is implemented using the percentage differential current approach backed up with a localized scheme employing running autoregressive smoothing average. An adaptive mathematical analysis of the parameters employed is performed for a justified assent. The proposed scheme is ratified to be accurate and immune to the system configuration, voltage fluctuations, and high-resistance faults with its security, dependability, and selectivity validated for different transients and fault contingencies employing minimum solid state circuit breakers in the microgrid. [ABSTRACT FROM AUTHOR]

Large-scale integration of wind generation changes the power swing characteristics of a power system and may result in the misoperation of legacy power swing protection schemes. This paper presents a qualitative study on the impact of wind generation on power swing protection. The objective is to provide an understanding of the problem through case studies and present possible solutions and adjustments in protection schemes to ensure the efficiency of protection under large-scale integration of wind generation. The misoperation of power swing protection functions, namely power swing blocking and out-of-step tripping (OST), as a result of increased wind generation levels, are shown through case studies. It is also shown that the electrical center of a power system may move due to wind generation. In this case, it would be necessary to revise the optimal location of the OST protection. Finally, the impact of various factors, such as wind generator type, control scheme and fault-ride-through function, and wind generation level and capacity are investigated to determine the key features that need to be accounted for in practical protection studies. [ABSTRACT FROM AUTHOR]

Severe generation outages may affect the power system frequency stability and cause abnormal frequency declines especially under the high penetration of low inertia generation technologies. Under frequency load shedding (UFLS), as a special protection scheme, is utilized to restore the power balance and maintain system frequency in an acceptable range. This paper develops a semi-adaptive UFLS plan in which the multistage load shedding is triggered based on the rate of change of frequency value. The proposed semi-adaptive UFLS plan activates predetermined later stage as early stage under the severe generation deficiencies. Most credible power imbalance scenarios including conventional generation outages and islanding scenarios are considered in semi-adaptive setting of the proposed UFLS plan. In order to achieve the optimal settings, the proposed UFLS plan is formulated as a mixed integer linear programming model. The dynamic of governors and load damping are considered in the discretized system frequency response. A scoring method is developed to select the UFLS settings with the most desired system frequency response. The performance of the proposed UFLS plan is verified over the IEEE 39-bus test system under credible and most likely scenarios of generation outages. [ABSTRACT FROM AUTHOR]

This paper introduces a condition monitoring (CM) algorithm based on the circuit breaker (CB) arcing power and its related energy to estimate the electrical wear of arcing contacts. There is an electric arc occurring between the CB arcing contacts mainly during opening operations. Instantaneous voltage across the terminals of the CB and instantaneous current going through the CB are measured to calculate the arcing power and its related energy, which only exist under arcing events. Therefore, the power-based algorithm does not require the time synchronization to the power system frequency for measuring the CB arcing powers. The cumulative arcing energy of the CB is a good indication of the degradation level of arcing contacts and it is used to estimate the CB contact wear. Unlike the current-based CM method, the proposed power-based algorithm detects arc restrikes that produce more arcing energies and cause a greater contact wear. Thus, it allocates a higher amount of contact wear for interruptions with arc restrikes that makes it a more reliable and accurate technique. The outcomes of computer simulation and real-time test studies demonstrate that the power-based method can estimate the electrical wear of arcing contacts accurately, and thus, provides accurate inspection or maintenance times of CB's arcing contacts. [ABSTRACT FROM AUTHOR]

With substantially increasing penetration levels of wind power, electric power system flexibility is needed to address the variability and uncertainty of wind power output. Thus, it has become an urgent issue to obtain an optimal tradeoff between economics and reliability, and to price system uncertainties. This paper proposes a new electricity market-clearing mechanism based on locational marginal prices (LMPs) for pricing uncertain generation and load. The uncertainty contained locational marginal price (U-LMP) is derived from a distributionally robust chance-constrained optimal power flow model in which only the first-order and second-order moments of the uncertain sources’ probability distribution are needed. Compared with traditional LMPs, the proposed U-LMP formulation includes two new uncertainty components: transmission line overload uncertainty price and generation violation uncertainty price. These LMP uncertainty components are the price signals reflecting the system costs as a result of wind generation and demand uncertainty at different locations. Finally, using parametric case studies, the relationship among uncertainty levels, system generation cost, and LMP uncertainty components are established. Case studies performed on the PJM 5-bus and IEEE 118-bus systems verify the proposed U-LMP method. [ABSTRACT FROM AUTHOR]

Increasing interdependency between electric power systems and natural gas systems creates additional dimensions of flexibility of system operation; but it may also escalate risk levels if the two systems are managed without proper coordination. This paper presents a robust security region (RSR) for electricity-gas integrated energy systems (IESs). It is a collection of uncertain parameters, especially wind power generations, under which system power flow has at least one feasible solution. First, a nonlinear optimization model is employed to obtain a set of uniformly distributed points on power flow solvability boundaries, from which the IES security region is constructed using a convex hull. Then, the proposed RSR is constructed to provide secure operation for the base-case scenario, where uncertain wind power generation values are replaced with expected values, and provide a feasible redispatch plan for each wind power generation scenario. Other implications of the RSR on IES security assessment are also envisioned. Results for two test systems indicate that the convex hull approach provides a more accurate approximation of the IES security region than a hyperplane approach. Meanwhile, the benefits of RSR are demonstrated by comparing test results with those obtained for a deterministic security region. [ABSTRACT FROM AUTHOR]

Increasing use of natural gas for electricity production places added strains on pipeline systems that are used for transporting fuel. Pipeline constraints require power system operators to account for natural gas-supply restrictions in their operational processes. This paper proposes separate optimization models for clearing day-ahead wholesale markets for scheduling power and natural gas systems. We then develop a market-based mechanism that allows for efficient co-ordination of the two systems. Importantly, the co-ordination mechanism only requires the exchange of fuel-price, -supply, and -demand information between the two markets. This can be contrasted with other co-ordination mechanisms that require operations of the two systems by a single entity. Thus, we provide a computationally tractable co-ordination mechanism that does not require the exchange of proprietary information between natural gas and electricity system operators. We demonstrate the effectiveness and scalability of the technique using a numerical example. [ABSTRACT FROM AUTHOR]

In this paper, feedback linearization (FBL) technique together with disturbance observer (DO) approach is proposed to mitigate the effect of the resonant frequency of grid-tied LCL filter systems. The state-feedback control law is employed to achieve stabilization of the LCL filter system under a wide range of resonant frequency variation. The DO is designed to counteract the effect of model uncertainty and unknown disturbance aiming to achieve asymptotic stability under FBL control. Specifically, the observer is designed to estimate an additional input, representing uncertainty and unknown disturbance, from measurable variables. Then, the FBL control utilizes the disturbance estimate to compensate for its effect. An interesting feature of the composite controller is its ability to meet the transient response specifications even in the presence of model uncertainty and external disturbance. The composite controller was implemented for simulation and experimental evaluation, and performance testing. High performance with respect to disturbance rejection and parameter variation has been demonstrated. [ABSTRACT FROM AUTHOR]

Taylor–Fourier (TF) filters represent a powerful tool to design phasor measurement unit (PMU) algorithms able to estimate synchrophasor, frequency, and rate of change of frequency (ROCOF). The resulting techniques are based on dynamic representations of the synchrophasor, and hence, they are particularly suitable to track the evolution of its parameters during time-varying conditions. Electrical quantities in power systems are typically three-phase and weakly unbalanced, but most PMU measurement techniques are developed by considering them as a set of three single-phase signals; on the contrary, this peculiarity can be favorably exploited to improve accuracy and reduce the computational cost. In this respect, this paper proposes to directly perform the TF expansion of the space vector (SV) samples obtained from three-phase measurements. A new paradigm allows to independently estimate positive and negative sequence synchrophasors along with system frequency and ROCOF, leveraging the three-phase characteristics. The performance of the proposed technique is assessed by using test signals inspired by the standard IEEE C37.118.1-2011, including noise as well as magnitude and phase unbalance. Achieved results highlight the flexibility of the enhanced SV-based approach, which is capable to combine excellent dynamic performance together with an accurate estimation of both positive and negative sequence components. [ABSTRACT FROM AUTHOR]

Effective monitoring and management applications on modern distribution networks (DNs) require a sound network model and the knowledge of line parameters. Network line impedances are used, among other things, for state estimation and protection relay setting. Phasor measurement units (PMUs) give synchronized voltage and current phasor measurements, referred to a common time reference (coordinated universal time). All synchrophasor measurements can thus be temporally aligned and coordinated across the network. This feature, along with high accuracy and reporting rates, could make PMUs useful for the evaluation of network parameters. However, instrument transformer behavior strongly affects the parameter estimation accuracy. In this paper, a new PMU-based iterative line parameter estimation algorithm for DNs, which includes in the estimation model systematic measurement errors, is presented. This method exploits the simultaneous measurements given by PMUs on different nodes and branches of the network. A complete analysis of uncertainty sources is also performed, allowing the evaluation of estimation uncertainty. Issues related to operating conditions, topology, and measurement uncertainty are thoroughly discussed and referenced to a realistic model of a DN to show how a full network estimator is possible. [ABSTRACT FROM AUTHOR]

Voltage sags and swells are power quality events commonly observed in power systems; however, none of the existing methods allows determining their point-on-wave inception and recovery instants (and consequently, their duration) accurately in all cases. The primary goal of this paper is to determine these instants with little or no delay, by calculating the absolute rms voltage difference between two adjacent sliding windows. The proposed method is based on the assumption that this difference is maximum when the sample under analysis corresponds to either the inception or the recovery instant. This method is valid for both sag and swell events, with or without transients. Evaluation of the proposed method performance for different types of events shows that it is robust and highly accurate in determining the inception and recovery instants. The estimation error for the majority of the events analyzed is either zero or one sample (each sample corresponds to a phase angle difference of 2.81 $^\circ$), while the worst performance is three samples. [ABSTRACT FROM AUTHOR]