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Specialized power-electronic apparatus for harnessing electrical power from kinetic hydropower plantsMosallat, Farid 20 September 2012 (has links)
This thesis introduces a power electronic interface for a kinetic hydropower generation platform that enables extraction of electric power from a free-flowing water source such as a river or a stream. The implemented system transfers power from a high-frequency permanent magnet synchronous generator (PMSG) to a 60-Hz load. Special configurations and control techniques were developed to cater for the long distance between the generator and the power interface; and also to address the wide range of the PMSG frequency and voltage variations. The proposed power-electronic interface was constructed and tested in the laboratory as well as in the field.
The thesis also introduces two feasible methods for controlling a hydrokinetic plant to supply islanded loads or to deliver the maximum power available from the turbine-generator to the utility network. Application of multiple turbines in a kinetic farm was also investigated, and different approaches to controlling hydrokinetic turbines were developed.
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Specialized power-electronic apparatus for harnessing electrical power from kinetic hydropower plantsMosallat, Farid 20 September 2012 (has links)
This thesis introduces a power electronic interface for a kinetic hydropower generation platform that enables extraction of electric power from a free-flowing water source such as a river or a stream. The implemented system transfers power from a high-frequency permanent magnet synchronous generator (PMSG) to a 60-Hz load. Special configurations and control techniques were developed to cater for the long distance between the generator and the power interface; and also to address the wide range of the PMSG frequency and voltage variations. The proposed power-electronic interface was constructed and tested in the laboratory as well as in the field.
The thesis also introduces two feasible methods for controlling a hydrokinetic plant to supply islanded loads or to deliver the maximum power available from the turbine-generator to the utility network. Application of multiple turbines in a kinetic farm was also investigated, and different approaches to controlling hydrokinetic turbines were developed.
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Damping Subsynchronous Resonance Using Static Synchronous Series Compensators and Static Synchronous CompensatorsRai, Dipendra 04 September 2008
Electricity systems are very complex systems and are composed of numerous transmission lines, generators and loads. The generating stations are generally far away from load centres and that may cause transmission line congestion and overloading. Series capacitive compensation is the most economical way to increase transmission capacity and improve transient stability of transmission grids. However, one of the impeding factors for the widespread use of series capacitive compensation is the potential risk of Subsynchronous Resonance (SSR). Subsynchronous Resonance is a phenomenon in which electrical power is exchanged with the generator shaft system in an increasing manner which may result in damage to the turbine generator shaft system. Therefore, mitigating SSR continues to be a subject of research and development aiming at developing effective SSR countermeasures.<p>This research work presents new methods of alleviating the SSR problem using a Static Synchronous Series Compensator (SSSC) and a Static Synchronous Compensator (STATCOM). These methods are based on using the SSSC and STATCOM to inject unbalanced series quadrature voltages and unbalanced shunt reactive currents in transmission line just after clearing faults. When the subsynchronous oscillations drive unsymmetrical phase currents, the developed electromagnetic torque will be lower than the condition when the three-phase currents are symmetrical. The unsymmetrical currents result in a lower coupling strength between the mechanical and the electrical system at asynchronous oscillations. Therefore, the energy exchange between the electrical and the mechanical systems at subsynchronous oscillations will be suppressed, thus, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance condition. The validity of proposed methods are demonstrated by time simulation results using the electromagnetic transient program EMTP-RV.
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Advanced modulation techniques for power convertersMehrizi-Sani, Ali 14 September 2007 (has links)
Pulse-width modulation methods are widely used for the synthesis of ac voltages at
the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth
modulation (SPWM) has been used. A powerful alternative for this purpose is
space-vector modulation (SVM), in which the converter is placed in a finite number
of states in order to best approximate the reference voltage. This method offers
better utilization of the dc bus voltage and provides several degrees of freedom for
enhancement of the harmonic spectrum as well as switching losses.
This thesis studies the SVM method for two- and three-level VSCs. A model
for implementation of SVM in the electromagnetic transients simulation program
PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear
as well as overmodulation range and is used to study the performance of different
SVM strategies in terms of their harmonic spectra and associated converter and harmonic
losses. The model is also used to demonstrate the suitability of the method
for network applications. The thesis also employs genetic algorithms to find an optimized
SVM sequence for improved harmonic performance. An objective function
is defined that seeks to minimize the most significant harmonic components of the
generated waveform, while keeping the other harmonic components within the acceptable
range outlined in the available standards. The obtained sequence shows
great improvement over the conventionally-used SVM sequence. / October 2007
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Damping Subsynchronous Resonance Using Static Synchronous Series Compensators and Static Synchronous CompensatorsRai, Dipendra 04 September 2008 (has links)
Electricity systems are very complex systems and are composed of numerous transmission lines, generators and loads. The generating stations are generally far away from load centres and that may cause transmission line congestion and overloading. Series capacitive compensation is the most economical way to increase transmission capacity and improve transient stability of transmission grids. However, one of the impeding factors for the widespread use of series capacitive compensation is the potential risk of Subsynchronous Resonance (SSR). Subsynchronous Resonance is a phenomenon in which electrical power is exchanged with the generator shaft system in an increasing manner which may result in damage to the turbine generator shaft system. Therefore, mitigating SSR continues to be a subject of research and development aiming at developing effective SSR countermeasures.<p>This research work presents new methods of alleviating the SSR problem using a Static Synchronous Series Compensator (SSSC) and a Static Synchronous Compensator (STATCOM). These methods are based on using the SSSC and STATCOM to inject unbalanced series quadrature voltages and unbalanced shunt reactive currents in transmission line just after clearing faults. When the subsynchronous oscillations drive unsymmetrical phase currents, the developed electromagnetic torque will be lower than the condition when the three-phase currents are symmetrical. The unsymmetrical currents result in a lower coupling strength between the mechanical and the electrical system at asynchronous oscillations. Therefore, the energy exchange between the electrical and the mechanical systems at subsynchronous oscillations will be suppressed, thus, avoiding the build-up of torsional stresses on the generator shaft systems under subsynchronous resonance condition. The validity of proposed methods are demonstrated by time simulation results using the electromagnetic transient program EMTP-RV.
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Advanced modulation techniques for power convertersMehrizi-Sani, Ali 14 September 2007 (has links)
Pulse-width modulation methods are widely used for the synthesis of ac voltages at
the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth
modulation (SPWM) has been used. A powerful alternative for this purpose is
space-vector modulation (SVM), in which the converter is placed in a finite number
of states in order to best approximate the reference voltage. This method offers
better utilization of the dc bus voltage and provides several degrees of freedom for
enhancement of the harmonic spectrum as well as switching losses.
This thesis studies the SVM method for two- and three-level VSCs. A model
for implementation of SVM in the electromagnetic transients simulation program
PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear
as well as overmodulation range and is used to study the performance of different
SVM strategies in terms of their harmonic spectra and associated converter and harmonic
losses. The model is also used to demonstrate the suitability of the method
for network applications. The thesis also employs genetic algorithms to find an optimized
SVM sequence for improved harmonic performance. An objective function
is defined that seeks to minimize the most significant harmonic components of the
generated waveform, while keeping the other harmonic components within the acceptable
range outlined in the available standards. The obtained sequence shows
great improvement over the conventionally-used SVM sequence.
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Efficient Modeling of Modular Multilevel HVDC Converters (MMC) on Electromagnetic Transient Simulation ProgramsGnanarathna, Udana 04 September 2014 (has links)
The recent introduction of a new converter topology, the modular multilevel converter (MMC) is a major step forward in voltage sourced converter (VSC) technology for high voltage, high power applications. To obtain a multilevel ac output waveform, a large number of semiconductor switches has to be used in the converter. The number of switches in the MMC for HVDC transmission is typically two orders of magnitudes larger than that in a two or three level VSC used in earlier generation. This large device count creates a computational challenge for electromagnetic transients (EMT) simulation programs, as it significantly increases the simulation time. The purpose of this research is to investigate whether the simulation can be speeded up.
This research develops an efficient, time-varying Thévenin's equivalent model for the MMC converter based on partitioning the system’s admittance matrix. EMT simulation results show that the proposed equivalent model can drastically reduce the computational time without loss of accuracy. The use of the proposed equivalent method is demonstrated by simulating a point to point MMC based HVDC transmission system successfully with more than 100 levels. This approach enables what was hitherto not practical; the modeling of large MMC based HVDC systems on personal computers.
With the assumption of ideal switch operation and using an equivalent average capacitor value based approach, an average valued model of MMC is also proposed in this thesis. The average model can be accurately used in most of the system level studies. The control algorithms and other modeling aspects of MMC applications are also presented in this thesis.
One of the advantages of multilevel converters is the low operating losses as the smaller switching frequency of each individual power electronics switch and the low voltage step change during each switching. Using a recently developed, time domain simulation approach, the operating losses of the MMC converter are estimated in this thesis. When comparing the MMC operating losses against the losses of two-level VSC, the power loss for the two-level VSC is found to be significantly higher than the power loss of the MMC.
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Advanced modulation techniques for power convertersMehrizi-Sani, Ali 14 September 2007 (has links)
Pulse-width modulation methods are widely used for the synthesis of ac voltages at
the terminals of a voltage-sourced converter (VSC). Traditionally sinusoidal pulsewidth
modulation (SPWM) has been used. A powerful alternative for this purpose is
space-vector modulation (SVM), in which the converter is placed in a finite number
of states in order to best approximate the reference voltage. This method offers
better utilization of the dc bus voltage and provides several degrees of freedom for
enhancement of the harmonic spectrum as well as switching losses.
This thesis studies the SVM method for two- and three-level VSCs. A model
for implementation of SVM in the electromagnetic transients simulation program
PSCAD/EMTDC is developed. The model is able to generate firing pulses in linear
as well as overmodulation range and is used to study the performance of different
SVM strategies in terms of their harmonic spectra and associated converter and harmonic
losses. The model is also used to demonstrate the suitability of the method
for network applications. The thesis also employs genetic algorithms to find an optimized
SVM sequence for improved harmonic performance. An objective function
is defined that seeks to minimize the most significant harmonic components of the
generated waveform, while keeping the other harmonic components within the acceptable
range outlined in the available standards. The obtained sequence shows
great improvement over the conventionally-used SVM sequence.
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Component Modeling and Three-phase Power-flow Analysis for Active Distribution SystemsKamh, Mohamed 19 January 2012 (has links)
This thesis presents a novel, fast, and accurate 3 steady-state power-flow analysis (PFA) tool for the real-time operation of the active distribution systems, also known as the active distribution networks (ADN), in the grid-tied and islanded operating modes. Three-phase power-flow models of loads, transformers, and multi-phase power lines and laterals are provided. This thesis also presents novel steady-state, fundamental-frequency, power-flow models of voltage-sourced converter (VSC)-based distributed energy resource (DER) units. The proposed models address a wide array of DER units, i.e., (i) variable-speed wind-driven doubly-fed asynchronous generator-based and (ii) single/three-phase VSC-coupled DER units. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host DER unit within the context of the developed PFA tool. Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed DER models represent (i) the salient VSC control strategies and objectives under balanced and unbalanced power-flow scenarios and (ii) all the operating limits and constraints of the VSC and its host DER unit.
Also, the slack bus concept is revisited, associated with the PFA, where a 3 distributed slack bus (DSB) model is proposed for the PFA and operation of islanded ADNs. Distributing the real and reactive slack power among several DER units is essential to provide a realistic power-flow approach for ADNs in the absence of the utility bus. The proposed DSB model is integrated with the developed 3 PFA tool to form a complete ADN PFA package.
The new PFA tool, including the proposed DER and DSB models, is tested using several benchmark networks of different sizes, topologies, and parameters. Many case studies, encompassing a wide spectrum of DER control specifications and operating modes, are conducted to demonstrate (i) the numerical accuracy of the proposed models of the DER units and their operating constraints, (ii) the effectiveness of the proposed DSB model for the islanded ADN PFA, and (iii) the computational efficiency of the integrated PFA software tool irrespective of the network topology and parameters.
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Component Modeling and Three-phase Power-flow Analysis for Active Distribution SystemsKamh, Mohamed 19 January 2012 (has links)
This thesis presents a novel, fast, and accurate 3 steady-state power-flow analysis (PFA) tool for the real-time operation of the active distribution systems, also known as the active distribution networks (ADN), in the grid-tied and islanded operating modes. Three-phase power-flow models of loads, transformers, and multi-phase power lines and laterals are provided. This thesis also presents novel steady-state, fundamental-frequency, power-flow models of voltage-sourced converter (VSC)-based distributed energy resource (DER) units. The proposed models address a wide array of DER units, i.e., (i) variable-speed wind-driven doubly-fed asynchronous generator-based and (ii) single/three-phase VSC-coupled DER units. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host DER unit within the context of the developed PFA tool. Novel closed forms for updating the corresponding VSC power and voltage reference set-points are proposed to guarantee that the power-flow solution fully complies with the VSC constraints. All the proposed DER models represent (i) the salient VSC control strategies and objectives under balanced and unbalanced power-flow scenarios and (ii) all the operating limits and constraints of the VSC and its host DER unit.
Also, the slack bus concept is revisited, associated with the PFA, where a 3 distributed slack bus (DSB) model is proposed for the PFA and operation of islanded ADNs. Distributing the real and reactive slack power among several DER units is essential to provide a realistic power-flow approach for ADNs in the absence of the utility bus. The proposed DSB model is integrated with the developed 3 PFA tool to form a complete ADN PFA package.
The new PFA tool, including the proposed DER and DSB models, is tested using several benchmark networks of different sizes, topologies, and parameters. Many case studies, encompassing a wide spectrum of DER control specifications and operating modes, are conducted to demonstrate (i) the numerical accuracy of the proposed models of the DER units and their operating constraints, (ii) the effectiveness of the proposed DSB model for the islanded ADN PFA, and (iii) the computational efficiency of the integrated PFA software tool irrespective of the network topology and parameters.
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