Showing papers by "Neville R. Watson published in 2007"

Flexible power transmission--the HVDC options

Abstract: Chapter 1 INTRODUCTION. Chapter 2 SEMICONDUCTOR POWER DEVICES. Chapter 3 LINE COMMUTATED HVDC CONVERSION (LCC). Chapter 4 SELF-COMMUTATING CONVERSION. Chapter 5 PULSE WIDTH MODULATION (PWM). Chapter 6 MULTI-LEVEL CONVERSION. Chapter 7 MULTI-LEVEL DC REINJECTION. Chapter 8 LINE-COMMUTATED CSC TRANSMISSION. Chapter 9 DEVELOPMENTS IN LINE COMMUTATED HVDC SCHEMES. Chapter 10 VSC TRANSMISSION. Chapter 11 MULTI-LEVEL VSC AND CSC TRANSMISSION. REFERENCES.

Interharmonics: Theory and Modeling

Abstract: Some of the most remarkable issues related to interharmonic theory and modeling are presented. Starting from the basic definitions and concepts, attention is first devoted to interharmonic sources. Then, the interharmonic assessment is considered with particular attention to the problem of the frequency resolution and of the computational burden associated with the analysis of periodic steady-state waveforms. Finally, modeling of different kinds of interharmonic sources and the extension of the classical models developed for power system harmonic analysis to include interharmonics are discussed. Numerical results for the issues presented are given with references to case studies constituted by popular schemes of adjustable speed drives.

An Optimal PMU Placement Method Against Measurement Loss and Branch Outage

Abstract: This paper presents a new method for an optimal measurement placement of phasor measurement units (PMUs) for power system state estimation. The proposed method considers two types of contingency conditions (i.e., single measurement loss and single-branch outage) in order to obtain a reliable measurement system. First, the minimum condition number of the normalized measurement matrix is used as the criteria in conjunction with the sequential elimination approach to obtain a completely determined condition. Next, a sequential addition approach is used to search for necessary candidates for single measurement loss and single-branch outage conditions. These redundant measurements are optimized by binary integer programming. Finally, in order to minimize the number of PMU placement sites, a heuristic technique to rearrange measurement positions is also proposed. Numerical results on the IEEE test systems are demonstrated

An Optimal PMU Placement Method Against Measurement Loss and Branch Outage

Abstract: Summary form only given. This paper presents a new method for an optimal measurement placement of phasor measurement units (PMUs) for power system state estimation. The proposed method considers two types of contingency conditions, i.e. single measurement loss and single branch outage, in order to obtain a reliable measurement system. Firstly, the minimum condition number of the normalized measurement matrix is used as the criteria in conjunction with the sequential elimination approach to obtain a completely determined condition. Next, a sequential addition approach is used to search for necessary candidates for single measurement loss and single branch outage conditions. These redundant measurements are optimized by the binary integer programming. Finally, in order to minimize the number of PMU placement sites, a heuristic technique to re-arrange measurement positions is also proposed. Numerical results on the IEEE test systems are demonstrated.

LED replacement for fluorescent tube lighting

Abstract: Fluorescent tubes have long been the mainstay of lighting for many premises, due to relatively high efficiency and long life. LED efficiencies are set to exceed those of fluorescent tubes, with dimming and controllable colour rendering readily achievable. Two multichip LED lamps are presented, mounted in a four foot fluorescent fitting, with ballast replaced by driver electronics. The first lamp employs white LEDs with optional cyan and red/orange spectral improvement; the second lamp is based on primary colours. Spatial distribution, intensity and spectrum of light output are compared to those produced by a fluorescent tube with the same power input. Lighting systems are sensitive to power system voltage disturbances resulting in visible light flicker; the sensitivity of the white LED lamp is compared with that of fluorescent tubes under voltage modulation and transient dips and swells.

Light flicker sensitivity of high efficiency compact fluorescent lamps

Abstract: This paper presents a comparison between compact fluorescent lamps and incandescent lamps for flicker production under common power quality disturbances. The widespread adoption of these high efficiency lamps has highlighted the discrepancies between the measured flicker levels by the AS/NZS 61000-4-15 standard and the actual levels experienced by humans. Using a unique method of flicker detection, the actual instantaneous light levels produced by a lamp are analysed. This overcomes the limitations of the flickermeter standard and is used to demonstrate the sensitivity of the light CFLs produce in the presence of power system disturbances such as; interharmonics, phase jumps, dips and swells which are not normally associated with flicker.

An Approximate Method for Transient State Estimation

Abstract: Voltage dip is a frequently occurring power-quality problem that electricity consumers face. Knowledge of the source and magnitude of the voltage dip is desirable; however, complete monitoring of the power system is prohibitive. State estimation for both fundamental and harmonic frequencies was presented previously. Its ability to utilize limited measurements for system-wide estimation has proven to be very effective. In this paper, the technique is extended further to estimate power system transients. Transient state estimation (TSE) provides an effective and systematic approach in locating and identifying remote fault sources, thus allowing the problem to be addressed more efficiently. The proposed approach formulates the system using state-space theory and results in a system of first-order differential equations which are used to form the measurement system. The estimation is the simultaneous solution of the measurement system equations based on a time sequence of snapshots of the system measurements. Additional measurement information utilizes the voltage and current history measurements where they are approximated using backward Euler integration formula, are also supplied to the TSE algorithm. To evaluate the performance of the proposed TSE, transients caused by a sudden lost of a system load have been simulated on the test system. This paper provides a new methodology to estimate a complete transient profile of a power system.

${z}$ -Transform-Based Methods for Electromagnetic Transient Simulations

Abstract: This is an introductory paper on z-transform-based methods for electromagnetic transient simulations of power systems. Since the theory of the z-transform was originally developed for the analysis of time series data defined at equidistant time steps, simulation models developed using z-transforms can readily be used in electromagnetic transient simulations based on the same time step. First, this paper briefly introduces the basics of the z-transform, and then applications to electromagnetic transient simulations of power systems are reviewed.

Addition of four-quadrant power controllability to multi-level VSC HVDC transmission

Abstract: In self-commutating multi-level voltage source conversion (VSC) transmission, the reactive power contributions of the two converter terminals are interdependent. To overcome this problem, a new control scheme is proposed, applicable to high voltage direct current (HVDC) interconnections of large power ratings with more than one 12-pulse group per converter. The basis of the proposed strategy is the use of a controllable phase shift between the firings of the individual converter groups. The theory is verified by extensive EMTDC simulation.

A Back to Back HVdc Link With Multilevel Current Reinjection Converters

Abstract: Aback to back (BTB) HVdc interconnector consisting of multilevel current reinjection (MLCR) converters is described, based on the parallel converter configuration. Since the MLCR creates a zero current region during the commutations, the proposed BTB configuration permits the continued use of thyristor valves, without loosing the control flexibility of the self-commutating process. Extensive EMTDC simulation is used to demonstrate the satisfactory response of the proposed BTB HVdc interconnector control structure to varying active and reactive power operating conditions.

A Back to Back HVdc Link With Multilevel Current Reinjection Converters

Abstract: A back to back (BTB) HVdc interconnector consisting of multilevel current reinjection (MLCR) converters is described, based on the parallel converter configuration. Since the MLCR creates a zero current region during the commutations, the proposed BTB configuration permits the continued use of thyristor valves, without loosing the control flexibility of the self-commutating process. Extensive EMTDC simulation is used to demonstrate the satisfactory response of the proposed BTB HVdc interconnector control structure to varying active and reactive power operating conditions.

Application of the multi-level current reinjection concept to HVDC transmission

Abstract: The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reactive power control and harmonic elimination. This paper describes the structure and control of a current source HVDC transmission scheme using MLCR converters. Extensive EMTDC simulation is carried out to demonstrate the improved controllability of the proposed HVDC configuration.

Compact Fluorescent Lamps (CFL) - Implications for Distribution Networks

Abstract: The desire to reduce electrical loading by using energy efficient lighting has resulted in a high level of interest in replacing conventional incandescent lamps with Compact Fluorescent Lamps (CFL). CFLs are however, a nonlinear load hence inject harmonics into the electrical network. The CFL use electronic ballasts and the design of these have an enormous impact on the electrical performance of the CFL. In the past the harmonics injected into the network by CFLs has been ignored as each is very small as the typically CFL is only 20 Watts. However if widespread adoption of CFLs occurs the combined effect of all these small sources can be just as detrimental as one large source, and is even harder to mitigate due to their distributed nature. This paper presents the results of a study to quantify the effect widespread adoption of CFLs will have on a typical distribution network. The two aspects investigated were harmonic distortion and system losses.

Incorporation of VSC transmission in power-flow simulation

Abstract: The technical and economic advantages of HVDC transmission using self-commutated voltage source conversion, (VSC) otherwise known as HVDC Light, has seen a rapid uptake of this technology. This paper presents a method of incorporating self-commutated voltage source conversion into power-flow analysis by formulating the dc equations and Jacobian matrix to represent VSC. This new ac/dc power-flow algorithm is then demonstrated on a test system consisting of an HVDC link interconnecting two otherwise separate power systems.

Improved fitting of z-domain frequency dependent network equivalents for electromagnetic transient simulation

Abstract: The complexity of modern power systems often makes it impractical to model it in its entirety for electromagnetic transient studies Therefore, areas outside the immediate area of interest must be represented by some form of frequency dependent network equivalent (FDNE) The advantage of using z-domain fitting is that it can be directly implemented in a digital simulation program without any loss of accuracy Fitting in the s-domain always requires "discretizing" a continuous system and the inherent approximations This paper presents the formulation, investigates the effect of frequency range and accuracy of fitting at low frequencies The importance of accurate low frequency fitting is highlighted The frequency range and weighting issues are demonstrated by assessing the transient response of the Lower South Island of New Zealand test system

Application of the multi-level current reinjection concept to HVDC transmission

Abstract: The self-commutating multilevel current reinjection (MLCR) reduces the converter current waveform to zero during the valves commutations and, thus, removes the converter dependence on line commutation. This property provides the conventional thyristor converter with the same flexibility as the self-commutating multi-level schemes in terms of reactive power control and harmonic elimination. This paper describes the structure and control of a current source HVDC transmission scheme using MLCR converters. Extensive EMTDC simulation is carried out to demonstrate the improved controllability of the proposed HVDC configuration.

PMU-based two stages state estimation for power system with nonlinear devices

Abstract: This paper presents a two-stage state estimation method for power system containing multiple nonlinear devices. In this work two types of nonlinear devices are considered, phase-shifting transformers and unified power flow controllers. It is assumed that Phaser Measurement Units are available in order to obtain the required synchronized measurement values. The problem of state estimation is decomposed into linear and nonlinear sub-problems. First the bus voltages are estimated using measured data from the power network. Then these voltages and other measured data are used to estimate the nonlinear devices' states. The modified IEEE 14 bus test system is employed to demonstrate the effective of the proposed approach.