Advanced wind energy convertors using electronic power conversion.

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A TWELVE-PULSE LOAD COMMUTATED CONVERTER DRIVE SYSTEM WITH VSI FOR STARTING UP AND ACTIVE POWER FILTERING IN AN LNG APPLICATION

Variable Frequency Drives (VFDs) are an integral component of the industry in today’s age. VFDs provide a great range of control for electrical machines, and can be integrated in a variety of applications to meet the desired objectives of operation with improved reliability and efficiency. This thesis presents the Load-Commutated Converter (LCC) drive, which belongs to the Current Source Converter (CSC) based drive system family. Such drives are widely used in high power applications, due to power handling capabilities and the maturity of the drive system. The application under study is that of a helper/starter motor for a turbine compressor in a Liquefied Natural Gas (LNG) plant. Primarily, the thesis presents real-life scenarios of drive system operation such as constant/variable speed operation at constant/varying torque. The respective controllers for the LCC drive are presented alongside their results. In addition to simulating the drive system in this LNG application, current harmonic mitigation measures are presented in this study. The typical converter topology presented in this thesis is the 12-pulse type, however comparisons with different topologies (6, 18, and 24-pulse) have also been presented. Finally, a dual-purpose external Voltage Source Inverter (VSI) is used both as a starter and an Active Power Filter (APF), therefore addressing the issues of drive/load induced harmonics and LCC starting. As a conclusion, a controlled LCC drive model is simulated in SIMULINK to emulate the drive operation in actual plant conditions. The controlled drive is further studied for the presence of harmonics and their subsequent mitigation, by using passive as well as active power filters. The results obtained present the adequacy of the control system as well as the efficacy of the filters used for harmonics mitigation. Future work revolves around improving the efficiency of the APF, and the drive control system to be more robust and reliable. The system can further be investigated for enhancements as per operational requirements

Active Power Filter With Automatic Control Circuit For Neutral Current Harmonic Minimization Technique [QC446.3.H37 I98 2007 f rb].

Disertasi ini bertujuan untuk membangun penuras kuasa aktif yang cekap dan boleh dipercayai bagi meminimumkan lebihan harmonik arus neutral dan juga masalah harmonik di dalam talian neutral untuk sistem tiga fasa empat dawai. The aim of this thesis is to develop an efficient and reliable active power filter in order to minimize the excessive neutral current as well as harmonic problem in the neutral line for three phase four wire system

Optimised design of isolated industrial power systems and system harmonics

This work has focused on understanding the nature and impact of non-linear loads on isolated industrial power systems. The work was carried out over a period of 8 years on various industrial power systems: off-shore oil and gas facilities including an FPSO, a wellhead platform, gas production platforms, a mineral processing plant and an LNG plant. The observations regarding non-linear loads and electrical engineering work carried out on these facilities were incorporated into the report.A significant literature describing non-linear loads and system harmonics on industrial power systems was collected and reviewed. The literature was classified into five categories: industrial plants and system harmonics, non-linear loads as the source of current harmonics, practical issues with system harmonics, harmonic mitigation strategies and harmonic measurements.Off-shore oil and gas production facilities consist of a small compact power system. The power system incorporates either its own power generation or is supplied via subsea cable from a remote node. Voltage selection analysis and voltage drop calculation using commercially available power system analysis software are appropriate tools to analyse these systems. Non-linear loads comprise DC rectifiers, variable speed drives, UPS systems and thyristor controlled process heaters. All nonlinear loads produce characteristic and non-characteristic harmonics, while thyristor controlled process heaters generate inter-harmonics. Due to remote location, harmonic survey is not a common design practice. Harmonic current measurements during factory acceptance tests do not provide reliable information for accurate power system analysis.A typical mineral processing plant, located in a remote area includes its own power station. The power generation capacity of those systems is an order of magnitude higher than the power generation of a typical off-shore production facility. Those systems comprise large non-linear loads generating current and voltage interharmonics. Harmonic measurements and harmonic survey will provide a full picture of system harmonics on mineral processing plants which is the only practical way to determine system harmonics. Harmonic measurements on gearless mill drive at the factory are not possible as the GMD is assembled for the first time on site.LNG plants comprise large non-linear loads driving gas compressor, however those loads produce integer harmonics. Design by analysis process is an alternative to the current design process based on load lists. Harmonic measurements and harmonic survey provide a reliable method for determining power system harmonics in an industrial power system

Grid integration of renewable power generation

This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation.This thesis considers the use of three-phase voltage and current source inverters as interfacing units for renewable power, specifically photovoltaic (PV) into the ac grid. This thesis presented two modulation strategies that offer the possibility of operating PV inverters in grid and islanding modes, with reduced switching losses. The first modulation strategy is for the voltage source inverter (VSI), and exploits 3rd harmonic injection with selective harmonic elimination (SHE) to improve performance at low and high modulation indices, where the traditional SHE implementation experiences difficulties due to pulse dropping. The simulations and experimentation presented show that the proposed SHE allows grid PV inverters to be operated with less than a 1kHz effective switching frequency per device. This is vital in power generation, especially in medium and high power applications. Pulse dropping is avoided as the proposed modified SHE spreads the switching angles over 90°, in addition increasing the modulation index. The second proposed modulation strategy, called direct regular sampled pulse width modulation (DRSPWM), is for the current source inverter (CSI). It exploits a combination of forced and natural commutation imposed by the co-existence of an insulated gate bipolar transistor in series with a diode in a three phase current source inverter, to determine device dwell times and switching sequence selection. The DRSPWM strategy reduces switching frequency per device in a CSI by suspending each phase for 60°, similar to VSI dead-band, thus low switching losses are expected. Other benefits include simple digital platform implementation and more flexible switching sequence selection and pulse placement than with space vector modulation. The validity of the DRSPWM is confirmed using simulations and experimentation. This thesis also presents a new dc current offset compensation technique used to facilitate islanding or grid operation of inverter based distributed generation, with a reduced number of interfacing transformers. The proposed technique will enable transformerless operation of all inverters within the solar farm, and uses only one power transformer at the point of common coupling. The validity of the presented modulation strategies and dc current offset compensation technique are substantiated using simulations and experimentation

Active Power Filter With Automatic Control Circuit For Neutral Current Harmonic Minimization Technique

Disertasi ini bertujuan untuk membangun penuras kuasa aktif yang cekap dan boleh dipercayai bagi meminimumkan lebihan harmonik arus neutral dan juga masalah harmonik di dalam talian neutral untuk sistem tiga fasa empat dawai. The aim of this thesis is to develop an efficient and reliable active power filter in order to minimize the excessive neutral current as well as harmonic problem in the neutral line for three phase four wire system

Effective Design of STATCOM Considering Fundamental Frequency Current, Active Harmonic Filtering and Zero Sequence Current

The main objective of this thesis was to investigate the effect of parallel reactive power compensation (RPC) and active harmonic filtering (AHF) operation on a STATCOM design, in terms of needed number of submodules (SMs), DC link voltage capacity, MV busbar voltage, zero sequence current demand, transformer and coupling inductor reactance. To achieve this objective, two design scenarios were carried out. In the first scenario, fundamental reactive current of studied STATCOM was prioritized over its current for active harmonic voltage filtering. In the second scenario, studied STATCOM was required to produce the nominal fundamental reactive power and perform active harmonic voltage filtering simultaneously. The problem was studied in PSCAD based simulation environment. In all simulations, q-component current was supplied manually to enable the RPC operation of studied STATCOM. To enable AHF operation, harmonic current control mode was used, and the reference value of the desired harmonic filtering current was supplied accordingly. However, before proceeding with any simulation, first, the system limitations based on the studied STATCOM technology were studied and adequate majors were placed inside the simulation mode accordingly. Thereafter, simulations providing information on the basic STATCOM design operating in RPC mode only (and without AHF functionality) were carried out so that it can be compared later with the aforementioned scenarios of parallel RPC and AHF operations. In the first design scenario, it was found out that additional AHF operation affects the STAT-COM design in three ways. First was the magnitude of AHF current where an increment in the needed number of SMs w.r.t basic design was noticed with increasing magnitude of AHF current. The second was the phase angle references of AHF current where if phase angle references of AHF current are chosen such that peaks of produced voltage source converter’s (VSC’s) fundamental and harmonic voltages are aligned then the amount of needed SMs to produce the same VSC voltage was increased. But, if phase angle references of AHF current are such that the peaks of VSC voltages are opposite to each other, then fewer SMs are required to produce the same VSC voltage. The third effect on STATCOM design was based on the harmonic order of AHF current produced. It was noticed that when harmonic order of AHF current was high, then the amount of needed SMs to produce the same magnitude of AHF current was increased. In the second design scenario, it was found that maximum fundamental reactive current and maximum filtering current cannot be achieved at the same time with a geometrical summation principle of these currents, but possible with an arithmetical summation principle with a trade-off between optimum utilisation of current capacity and extra hardware cost. Hence, an optimum design to achieve the maximum of RPC and AHF current simultaneously exists between economical (based on the geometrical summation principle) and conservative (based on the arithmetical summation principle) design, but rather close to the economical one. In last, it was also noticed that the maximum demand of zero sequence current occurred when STATCOM was producing fundamental reactive current and negative sequence AHF current simultaneously in the maximum capacitive operation point, with an unbalanced network. And, peaks of positive and negative sequence network voltage and peaks of produced VSC voltages (fundamental and harmonic) were aligned

Industrial and Technological Applications of Power Electronics Systems

The Special Issue "Industrial and Technological Applications of Power Electronics Systems" focuses on: - new strategies of control for electric machines, including sensorless control and fault diagnosis; - existing and emerging industrial applications of GaN and SiC-based converters; - modern methods for electromagnetic compatibility. The book covers topics such as control systems, fault diagnosis, converters, inverters, and electromagnetic interference in power electronics systems. The Special Issue includes 19 scientific papers by industry experts and worldwide professors in the area of electrical engineering