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This paper presents the stability analysis for a distribution static compensator (DSTATCOM) that operates in current control mode based on bifurcation theory. Bifurcations delimit the operating zones of nonlinear circuits and, hence, the capability to compute these bifurcations is of important interest for practical design. A control design for the DSTATCOM is proposed. Along with this control, a suitable mathematical representation of the DSTATCOM is proposed to carry out the bifurcation analysis efficiently. The stability regions in the Thevenin equivalent plane are computed for different power factors at the point of common coupling. In addition, the stability regions in the control gain space, as well as the contour lines for different Floquet multipliers are computed. It is demonstrated through bifurcation analysis that the loss of stability in the DSTATCOM is due to the emergence of a Neimark bifurcation. The observations are verified through simulation studies. Index Terms--Distribution static compensator (DSTATCOM), floquet multiplier, Neimark bifurcation, point of common coupling (PCC), stability regions.

This paper applies Kalman filtering techniques to the problem of detecting modal changes in large interconnected power systems. Short term alarming procedures are developed based on the statistics of the power spectral density of the Kalman filter innovation. The new technique is tested on both simulated data and real data obtained from power systems in normal operation. The particular advantage of the new method is its ability to detect changes very quickly. Index Terms--Interconnected power systems, Kalman filtering, power system stability, state space estimator.

This paper describes a new Fourier-based sliding window method for estimating the damping of exponentially decaying modes that occur in power networks as a result of electric disturbances. The key innovation in the new method is the use of multiple orthogonal sliding windows rather than just a single pair of sliding windows. The use of these multiple orthogonal windows allows least-squares averaging strategies to be used, enabling lower variance estimates to be obtained as a result. A statistical analysis is provided, and simulations are presented to illustrate the effectiveness of the new method. The technique is also applied to real power system data. Index Terms--Interconnected power systems, least-squares methods, parameter estimation, power system monitoring, power system transients, singular value decomposition.

Inclusion of voltage support distributed generation (VSDG) can reinforce the feeder voltage of distribution networks, especially in rural/remote areas where voltage dip and frequent blackouts are significant concerns for power utilities. However, installation of multiple distributed generators within a distribution grid system may introduce technical problems in network operation and control, including control interaction and/or voltage instability. This paper addresses the network issues that may occur during multiple VSDG inclusion in the network and presents analytical models and solutions to develop design criteria of VSDG installation in the networks. Voltage sensitivity of lines is investigated and the effect of DG real (P) and reactive (Q) power injections with Q priority is developed for optimal use of VSDG in correcting the network voltage. Interaction among VSDG controllers has been explored and a generalized model is presented to analyze this interaction between any number of VSDGs in the network. The model is tested on a sample VSDG system and test results are presented. The issue of which VSDG must be started recognizing the costs of starting is addressed using an inverse definite minimum time (IDMT) model. A prioritization and coordination scheme for start discrimination of multiple VSDGs is proposed which avoids hunting between multiple generators. Index Terms--Dynamics, eigenvalues and eigenfunctions, power distribution, power generation control, sensitivity, voltage control.

A computationally efficient method for estimating any or all parameters of polynomial-phase signals in white Gaussian noise is presented and a first-order statistical analysis of the technique is provided. Simulations are presented to support the theoretical analysis.

Key issues for distributed generation (DG) inclusion in a distribution system include operation, control, protection, harmonics, and transients. This paper analyzes two of the main issues: operation and control for DG installation. Inclusion of DG in distribution networks has the potential to adversely affect the control of voltage. Both DG and tap changers aim to improve voltage profile of the network, and hence they can interact causing unstable operation or increased losses. Simulations show that a fast responding DG with appropriate voltage references is capable of reduction of such problems in the network. A DG control model is developed based on voltage sensitivity of lines and evaluated on a single wire earth return (SWER) system. An investigation of voltage interaction between DG controllers is conducted and interaction-index is developed to predict the degree of interaction. From the simulation it is found that the best power factor for DG injection to achieve voltage correction becomes higher for high resistance lines. A drastic reduction in power losses can be achieved in SWER systems if DG is installed. Multiple DG can aid voltage profile of feeder and should provide higher reliability. Setting the voltage references of separate DGs can provide a graduated response to voltage correction. Index Terms--Dynamics, eigenvalues and eigenfunction, power distribution, power generation control, sensitivity, voltage control.

Interruptions to supply and sags of distribution system voltage are the main aspects causing customer complaints. There is a need for analysis of supply reliability and voltage sag to relate system performance with network structure and equipment design parameters. This analysis can also give prediction of voltage dips, as well as relating traditional reliability and momentary outage measures to the properties of protection systems and to network impedances. Existing reliability analysis software often requires substantial training, lacks automated facilities, and suffers from data availability. Thus it requires time-consuming manual intervention for the study of large networks. A user-friendly sag and reliability assessment tool (SRAT) has been developed based on existing impedance data, protection characteristics, and a model of failure probability. The new features included in SRAT are a) efficient reliability and sag assessments for a radial network with limited loops, b) reliability evaluation associated with realistic protection and restoration schemes, c) inclusion of momentary outages in the same model as permanent outage evaluation, d) evaluation of the sag transfer through meshed subtransmission network, and e) simplified probability distribution model determined from available faults records. Examples of the application of the tools to an Australian distribution network are used to illustrate the application of this model. Index Terms--Network reliability, object-oriented programming, power distribution, power quality.

The paper discusses load compensation using a distribution static compensator (DSTATCOM). It is assumed that the DSTATCOM is associated with a load that is remote from the supply. It is shown that the operation of a DSTATCOM assuming that it is connected to a stiff source in such situations will result in distortions in source current and voltage at the point of common coupling. To avoid this, the DSTATCOM is connected in parallel with a filter capacitor that allows the high frequency component of the current to pass. This however generates control issues in tracking, as standard controls such as a hysteresis control are not suitable in these circumstances. This paper proposes a new switching control scheme and demonstrates its suitability for this problem. It also proposes a scheme in which the fundamental sequence components of a three-phase signal can be computed from its samples. The overall performance of the proposed scheme is verified using digital computer simulation studies. Index Terms--DSTATCOM, load compensation, switching control, weak ac system.

A dynamic voltage restorer (DVR) is a power-electronic controller that can protect sensitive loads from disturbances in the supply system. In this paper, it is demonstrated that this device can tightly regulate the voltage at the load terminal against imbalance or harmonic in the source side. The behavior of the device is studied through steady-state analysis, and limits to achievable performance are found. This analysis is extended to the study of transient operation where the generation of the reference voltage of the DVR is discussed. Once the reference signals are generated, they are tracked using a switching band scheme. A suitable structure in which the DVR is realized by voltage-source inverters (VSIs) is also discussed. Particular emphasis to the rating of this device is provided. Extensive simulation results are included to illustrate the operating principles of a DVR. Index Terms--Power distribution, control, DVR, converter, power electronics.

In most high-performance applications of voltage source pulse-width modulation inverters, current control is an essential part of the overall control system. In this paper, a hysteresis current control technique for a single-phase five-level inverter with flying-capacitor topology is proposed. Logic controls and a programmable logic device are suitable for handling a large number of switches and implementation of state transitions. This method also considers how to improve unbalanced voltages of capacitors using voltage vectors in order to minimize switching losses. The simulation and experimental results describe and verify the current control technique for the inverter. Index Terms--Current control, multilevel inverter, PLD, pulse-width modulation.

Planar busbars are used widely in modern high power inverters and have been shown to provide a good way for minimizing stray inductance and overshoot voltage. Planar busbars, which consist of multilayer copper sheets and dielectric insulators, offer significant advantages such as low impedance, improved thermal characteristic and reduced system cost compared with other interconnection approaches. A common problem of hard switched inverters is stray inductance, which needs to be minimized to reduce the effect of over voltages. This paper presents a new physical structure for a voltage source inverter with symmetrical planar busbar structure, which minimizes the variation in stray inductance for different switching states. Three-dimensional (3-D) finite element simulations and experimental tests verify the theory. Index Terms--Inductance, planar busbar, voltage source inverter.

Multilevel converters can achieve an overall effective switch frequency multiplication and consequent ripple reduction through the cancellation of the lowest order switch frequency terms. This paper investigates the harmonic content and the frequency response of these multimodulator converters. It is shown that the transfer function of uniformly sampled modulators is a bessel function associated with the inherent sampling process. Naturally sampled modulators have a fiat transfer function, but multiple switchings per switch cycle will occur unless the input is slew-rate limited. Lower sideband harmonics of the effective carrier frequency and, in uniform converters, harmonics of the input signal also limit the useful bandwidth. Observations about the effect of the number of converters, their type (naturally or uniformly sampled), and the ratio of modulating frequency and switch frequency are made. Index Terms - Natural PWM, modulation, multilevel converters, uniform PWM.

The increasing penetration level of photovoltaic (PV) systems in low-voltage networks causes voltage regulation issues. This brief proposes a new voltage regulation strategy utilizing distributed battery energy storage systems (BESSs) while incorporating the inevitable communication delays. The proposed strategy ensures that the voltage regulation burden is appropriately shared among all involved BESSs in the network. The effects of communication delays on the performance of the proposed strategy are analyzed and an admissible delay bound is established. Case studies are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

This paper presents an algorithm which determines the best locations for placement of GPS (Global Positioning System) based voltage angle transducers. The sites are chosen so as to maximise their sensitivity to the lightly damped inter-area modes while minimising their sensitivity to the more heavily damped local modes. Furthermore the algorithm used ensures that transducers are placed so as to give the greatest coverage of the various inter-area modes as possible giving modal estimates with a high degree of precision. A study made on a longitudinal 21 bus, 6 machine system shows that the algorithm gives good results which are reasonable insensitive to system operating point. Caution is to be exercised in the application of this algorithm to meshed systems where mode shapes may depend on system operating point.

In this article, an augmented complex Kalman filter (ACKF) is proposed for distribution networks as a noniterative forecasting-aided state estimator. Although most of the distribution state estimator (DSE) algorithms deal with real and imaginary parts of distribution networks’ states independently, the proposed algorithm in this article considers the states as complex values. In the case of real-time DSE and the presence of a large number of customer loads in the system, employing DSEs in one single estimation layer is not computationally efficient. Consequently, our proposed method performs in several estimation layers hierarchically as a multilayer DSE based on an ACKF (DSE-MACKF). In the proposed method, a distribution network can be divided into one main area and several subareas. The aggregated loads in each subarea act like a big customer load in the main area. Customer load aggregation results in lower variability and higher spatial-temporal correlation. This increases the accuracy of the estimated states in the main estimation layer. Additionally, the proposed method is formulated to include unbalanced loads in low-voltage radial distribution networks. This approach is applied to two real distribution networks for comparison and evaluation. The effectiveness of the proposed method is discussed using several criteria such as computational time, standard deviation, and maximum and average voltage error. The performance of the proposed method has been assessed against the weighted least square estimation method, while the computational time and the average voltage error have been decreased from 14 to 2 s and 1.13% to 0.23%, respectively. [ABSTRACT FROM AUTHOR]