Showing papers by "Neville R. Watson published in 2009"

Implications for Distribution Networks of High Penetration of Compact Fluorescent Lamps

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). This has resulted in the New Zealand Government, through the Electricity Commission of New Zealand, running campaigns to install five CFLs in every home by, subsidizing the cost of suitable CFLs. 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. To enable 28 800 homes to be represented a methodology for modelling a large number of distributed loads using Norton equivalents was developed and applied. In order to assess losses, a fundamental frequency power-flow was also incorporated.

Self-Commutating Converters for High Power Applications

Abstract: Preface. 1 Introduction. 1.1 Early developments. 1.2 State of the large power semiconductor technology. 1.3 Voltage and current source conversion. 1.4 The pulse and level number concepts. 1.5 Line-commutated conversion (LCC). 1.6 Self-commutating conversion (SCC). 1.7 Concluding statement. References. 2 Principles of Self-Commutating Conversion. 2.1 Introduction. 2.2 Basic VSC operation. 2.3 Main converter components. 2.4 Three-phase voltage source conversion. 2.5 Gate driving signal generation. 2.6 Space-vector PWM pattern. 2.7 Basic current source conversion operation. 2.8 Summary. References. 3 Multilevel Voltage Source Conversion. 3.1 Introduction. 3.2 PWM-assisted multibridge conversion. 3.3 The diode clamping concept. 3.4 The flying capacitor concept. 3.5 Cascaded H-bridge configuration. 3.6 Modular multilevel conversion (MMC). 3.7 Summary. References. 4 Multilevel Reinjection. 4.1 Introduction. 4.2 The reinjection concept in line-commutated current source conversion. 4.3 Application of the reinjection concept to self-commutating conversion. 4.4 Multilevel reinjection (MLR) - the waveforms. 4.5 MLR implementation - the combination concept. 4.6 MLR implementation - the distribution concept. 4.7 Summary. References. 5 Modelling and Control of Converter Dynamics. 5.1 Introduction. 5.2 Control system levels. 5.3 Non-linearity of the power converter system. 5.4 Modelling the voltage source converter system. 5.5 Modelling grouped voltage source converters operating with fundamental frequency switching. 5.6 Modelling the current source converter system. 5.7 Modelling grouped current source converters with fundamental frequency switching. 5.8 Non-linear control of VSC and CSC systems. 5.9 Summary. References. 6 PWM-HVDC Transmission. 6.1 Introduction. 6.2 State of the DC cable technology. 6.3 Basic self-commutating DC link structure. 6.4 Three-level PWM structure. 6.5 PWM-VSC control strategies. 6.6 DC link support during AC system disturbances. 6.7 Summary. References. 7 Ultra High-Voltage VSC Transmission. 7.1 Introduction. 7.2 Modular multilevel conversion. 7.3 Multilevel H-bridge voltage reinjection. 7.4 Summary. References. 8 Ultra High-Voltage Self-Commutating CSC Transmission. 8.1 Introduction. 8.2 MLCR-HVDC transmission. 8.3 Simulated performance under normal operation. 8.4 Simulated performance following disturbances. 8.5 Provision of independent reactive power control. 8.6 Summary. References. 9 Back-to-Back Asynchronous Interconnection. 9.1 Introduction. 9.2 Provision of independent reactive power control. 9.3 MLCR back-to-back link. 9.4 Control system design. 9.5 Dynamic performance. 9.6 Waveform quality. 9.7 Summary. References. 10 Low Voltage High DC Current AC-DC Conversion. 10.1 Introduction. 10.2 Present high current rectification technology. 10.3 Hybrid double-group configuration. 10.4 Centre-tapped rectifier option. 10.5 Two-quadrant MLCR rectification. 10.6 Parallel thyristor/MLCR rectification. 10.7 Multicell rectification with PWM control. 10.8 Summary. References. 11 Power Conversion for High Energy Storage. 11.1 Introduction. 11.2 SMES technology. 11.3 Power conditioning. 11.4 The SMES coil. 11.5 MLCR current source converter based SMES power conditioning system. 11.6 Simulation verification. 11.7 Discussion - the future of SMES. References. Index.

Four quadrant multilevel current source power conditioning for superconductive magnetic energy Storage

Abstract: The main purpose of this paper is to describe advances in high current source converter (CSC) and control for use in superconductive magnetic energy storage (SMES) schemes instead of the conventional PWM-chopper based VSC configurations. The Multi-level Current Reinjection (MLCR) CSC provides the simplest structure, as well as switching at zero current, a property that permits retaining the use of basic thyristors in the main converter bridges. Extensive PSCAD/EMTDC simulation is carried out to verify the theoretical predictions.

An Investigation of Excessive Rural Network Harmonic Levels Caused by Particular Irrigation Pumps

Abstract: High and increasing voltage Total Harmonic Distortion (THD) and 5th harmonic voltage levels have been measured in recent years on Orion NZ Ltd's rural 11 kV distribution network in Canterbury, New Zealand. On occasion, at Points of Common Coupling (PCC), the THD has exceeded the 5% limit and the 5th harmonic has exceeded the 4% limit. It has been suspected that these summer season high harmonic levels are due to the large existing and increasing density of farm irrigation deep well pump loads. It is likely that adverse effects on the network and neighbouring loads would become apparent if the increasing harmonic levels are left unchecked. A practical and theoretical investigation was conducted by the Electric Power Engineering Centre (EPECentre), University of Canterbury, on behalf of Orion to determine what are the primary causes of the high harmonic levels and provide mitigation options. Several farms with installed irrigation pumps were visited and the harmonic current and voltage levels were measured when the pumps were operating. Substation measurements were also simultaneously taken. A computer harmonic model of the local 11 kV network and loads was created that provided an accurate description of actual network conditions. An examination of Orion's system from the view of harmonic management was performed. The investigation revealed that the most significant cause of high harmonics levels is the comparatively large harmonic current injections by local irrigation pumps using Variable Speed Drives. A secondary cause is resonances in the network, often dynamically created by Power Factor (PF) capacitors switching online at various farms. To keep the rural network infrastructure in an effective and sustainable operating condition, mitigation measures are needed. Options researched included simulations of harmonic filters placed at various network points, and the use of alternate vector group transformers. Suggestions are made regarding objectives for harmonic limits at different network voltage levels, so as to determine harmonic limits for load installations.

Derivation of a Four-Quadrant Control System for MLCR-HVDC Conversion

Abstract: Although the multilevel current reinjection concept has been presented as a possible self-commutating alternative to line-commutated conversion for large power HVDC transmission, in its present form, the lack of independent reactive power control at the two converter terminals constitutes a severe limitation to its eventual acceptability. For very large power ratings, the use of double-group converter terminals has been shown theoretically to overcome the reactive power interdependence; however, the high nonlinearities involved make it difficult to design a practical control system, which is the main purpose of this paper. Comprehensive PSCAD/EMTDC simulation is used to verify that the dynamic and steady-state response of the proposed control system design are perfectly satisfactory.