Soft-Switched Step-Up Medium Voltage Power Converters

With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight. This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes

Soft-Switched Step-Up Medium Voltage Power Converters

With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight. This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes

Soft-Switched Step-Up Medium Voltage Power Converters

With a ten-year average annual growth rate of 19 percent, wind energy has been the largest source of new electricity generation for the past decade. Typically, an offshore wind farm has a medium voltage ac (MVac) grid that collects power from individual wind turbines. Since the output voltage of a wind turbine is too low (i.e., typically 400 690 V) to be connected to the MVac grid (i.e., 20 40 kV), a heavy line-frequency transformer is used to step up the individual turbines output voltage to the MV level. To eliminate the need for bulky MVac transformers, researchers are gravitating towards the idea of replacing the MVac grid with a medium voltage dc (MVdc) grid, so that MV step-up transformers are replaced by MV step-up power electronic converters that operate at the medium frequency range with much lower size and weight. This dissertation proposes a class of modular step-up transformerless MV SiC-based power converters with soft-switching capability for wind energy conversion systems with MVdc grid. This dissertation consists of two parts: the first part focuses on the development of two novel groups of step-up isolated dc-dc MV converters that utilize various step-up resonant circuits and soft-switched high voltage gain rectifier modules. An integrated magnetic design approach is also presented to combine several magnetic components together in the modular high voltage gain rectifiers. The second part of this dissertation focuses on the development of several three-phase ac-dc step-up converters with integrated active power factor correction. In particular, a bridgeless input ac-dc rectifier is also proposed to combine with the devised step-up transformerless dc-dc converters (presented in the first part) to form the three-phase soft-switched ac-dc step-up voltage conversion unit. In each of the presented modular step-up converter configurations, variable frequency control is used to regulate the output dc voltage of each converter module. The operating principles and characteristics of each presented converter are provided in detail. The feasibility and performance of all the power converter concepts presented in this dissertation are verified through simulation results on megawatts (MW) design examples, as well as experimental results on SiC-based laboratory-scale proof-of-concept prototypes

Design and construction of a laboratory system for neuromuscular stimulation of the lower extremities during cycling

Functional Neuromuscular Stimulation (FNS) is a method by which paralyzed muscles are stimulated electrically in order to produce a useful movement. The design and testing of a laboratory system for the modulated control of the lower extremities during FNS-induced cycling on an exercising device (Paracycle) is described. The system hardware, which is designed around a standard IBM compatible Personal Computer, features six independent stimulation channels. Waveform characteristics such as pulse frequency, width and amplitude are defined as a function of the crank position of the Paracycle for each channel. An extensive software package allows programmability of the waveform parameters and supports the user in the definition of stimulation sequences. The effective performance of the complete FNS-controller/ Paracycle system has been demonstrated during a controlled case study with two paraplegic subjects

Towards Active Transducers

One of the trends within consumer audio systems is the requirement for surround sound systems, based on 5-7 or even more audio channels, resulting in the same number of power amplifier channels and loudspeakers for each system. Most systems on the market today are based on linear amplifiers techniques developed in the middle of last century, which is surprising when the last few decades’ development within the audio source material, that is CD, DVD and SACD to mention the most popular, are taken into account. Audio performance of linear amplifiers has reached a level suitable for high quality audio reproduction many product generations ago, but the biggest disadvantages are still left untouched; power efficiency, size and cost. With today’s technology, high efficient switch mode, or class D audio amplifiers based on pulse width modulation, PWM, are realizable. With the class D technology, consumer audio systems can benefit significantly from the highly increased power efficiency of class D amplifiers as well as their reduced size without need for bulky heat sinks, and also very important, low cost. The topic of this project is a total integration of switch mode audio amplifiers and loudspeakers into one single unit using the voice coil of the loudspeaker as output filter for the amplifier, with a perspective of highly reduced system power losses, system size and cost. Standard switch mode audio amplifiers and loudspeakers on the market are designed for use in traditional audio systems, and cannot without severe modifications be used for the integrated system without sacrifice of power efficiency. For this reason techniques for dedication of amplifier and loudspeaker for the specific purpose of the integration has been of major importance in this project. This thesis is a fundamental study of the loss mechanisms in loudspeakers and amplifiers and suggestions for optimizations are made to reduce the system power losses and cost without compromising the audio performance. Some of the results obtained in the project are redesign of and optimization of the parts in a loudspeaker, so the function of output filter for the amplifier can be obtained without significant power losses. Guidelines for dedication of speaker and amplifier to the integration process with significantly lower system power losses are also given. Furthermore, the work done in the project has resulted in new switch mode amplifier topologies, with very high audio performance realizable at a very low cost

Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

Power converters and electric machines represent essential components in all fields of electrical engineering. In fact, we are heading towards a future where energy will be more and more electrical: electrical vehicles, electrical motors, renewables, storage systems are now widespread. The ongoing energy transition poses new challenges for interfacing and integrating different power systems. The constraints of space, weight, reliability, performance, and autonomy for the electric system have increased the attention of scientific research in order to find more and more appropriate technological solutions. In this context, power converters and electric machines assume a key role in enabling higher performance of electrical power conversion. Consequently, the design and control of power converters and electric machines shall be developed accordingly to the requirements of the specific application, thus leading to more specialized solutions, with the aim of enhancing the reliability, fault tolerance, and flexibility of the next generation power systems

Modeling and Analysis of Power Processing Systems (MAPPS), initial phase 2

The overall objective of the program is to provide the engineering tools to reduce the analysis, design, and development effort, and thus the cost, in achieving the required performances for switching regulators and dc-dc converter systems. The program was both tutorial and application oriented. Various analytical methods were described in detail and supplemented with examples, and those with standardization appeals were reduced into computer-based subprograms. Major program efforts included those concerning small and large signal control-dependent performance analysis and simulation, control circuit design, power circuit design and optimization, system configuration study, and system performance simulation. Techniques including discrete time domain, conventional frequency domain, Lagrange multiplier, nonlinear programming, and control design synthesis were employed in these efforts. To enhance interactive conversation between the modeling and analysis subprograms and the user, a working prototype of the Data Management Program was also developed to facilitate expansion as future subprogram capabilities increase

Harmonic domain modelling and analysis of the electrical power systems of onshore and offshore oil and gas field /platform

This thesis first focuses on harmonic studies of high voltage cable and power line, more specifically the harmonic resonance. The cable model is undergrounded system, making it ideal for the harmonics studies. A flexible approach to the modelling of the frequency dependent part provides information about possible harmonic excitations and the voltage waveform during a transient. The power line is modelled by means of lumped-parameters model and also describes the long line effect. The modelling depth and detail of the cable model influences the simulation results. It compares two models, first where an approximate model which make use of complex penetration is used and the second where an Bessel function model with internal impedance is used. The both models incorporate DC resistance, skin effect and their harmonic performances are investigated for steady-state operating condition. The methods illustrate the impotance of including detailed representation of the skin effect in the power line and cable models, even when ground mode exists. The cable model exhibit lower harmonics comparable to overhead transmission lines due to strong influence of the ground mode. Due to the application of voltage source converter (VSC) technology and pulse width modulation (PWM) the VSC-HVDC has a number of potential advantages as compared with CSC-HVDC, such as short circuit current reduction, independent control of active power and reactive power, etc. With these advantages VSC-HVDC will likely be widely used in future oil and gas transmission and distribution systems. Modular multilevel PWM converter applies modular approach and phase-shifted concepts achieving a number of advantages to be use in HVDC power transmission. This thesis describes the VSC three-phase full-bridge design of sub-module in modular multilevel converter (MMC). The main research efforts focus on harmonic reduction using IGBTs switches, which has ON and OFF capability. The output voltage waveforms multilevel are obtained using pulse width modulation (PWM) control. The cascaded H-bridge (CHB) MMC is used to investigate for two-level, five-level, seven-level, nine-level converter staircase waveforms. The results show that the harmonics are further reduced as the sub-module converter increases. The steady-state simulation model of the oil platform for harmonic studies has been developed using MATLAB. In order to save computational time aggregated models are used. The load on the platforms consists of passive loads, induction motors, and a constant power load representing variable speed drives on the platforms. The wind farm consists of a wind turbine and an induction machine operating at fixed speed using a back-to-back VSC. Simulations are performed on system harmonics that are thought to be critical for the operation of the system. The simulation cases represent large and partly exaggerated disturbances in order to test the limitations of the system. The results show low loss, low harmonics, and stable voltage and current. With the developments of multilevel VSC technology in this thesis, multi-terminal direct current (MTDC) systems integrating modular multilevel converters at all nodes may be more easily designed. It is shown that self-commutated Voltage Source Converters (VSC) is more flexible than the more conventional Current Source Converter (CSC) since active and reactive powers are controlled independently. The space required by the equipment of this technology is smaller when compared to the space used by the CSCs. In addition, the installation and maintenance costs are reduced. With these advantages, it will be possible for several oil and gas production fields connected together by multi-terminal DC grid. With this development the platforms will not only share energy from the wind farms, but also provide cheaper harmonic mitigation solutions. The model of a multi-terminal hypothetical power system consisting of three oil and gas platforms and two offshore wind farm stations without a common connection to the onshore power grid is studied. The connection to the onshore grid is realized through a High Voltage Direct Current (HVDC) transmissions system based on Voltage Source Converter (VSC) technology. The proposed models address a wide array of harmonic mitigation solutions, i.e., (i) Local harmonic mitigation (ii) semi-global harmonic mitigation and (iii) global harmonic mitigation. In addition, a computationally-efficient technique is proposed and implemented to impose the operating constraints of the VSC and the host IGBT-PWM switches within the context of the developed harmonic power flow (HPF). 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 platform models represent (i) the high voltage AC/DC and DC/AC power conversion applications under balanced harmonic power-flow scenario and (ii) all the operating limits and constraints of the nodes and its host modular converter (iii) three-phase VSC coupled IGBT-PWM switches

Control and Modulation Techniques for the Three-to-Five Phase Indirect Matrix Converter

This thesis focuses on the development and practical assessment of novel modulation techniques for the three-to-five phase indirect matrix converter. The increasing popularity of five-phase systems necessitates power converter systems capable of interfacing with the three-phase grid and the use of the proposed indirect matrix converter facilitates this interface whilst eliminating the energy storage component in the dc-link. An indirect space vector PWM-based technique that performs zero-current switching at the rectifier stage is proposed and developed for the three-to-five phase indirect matrix converter. The technique controls the three-phase input power factor and ensures that a zero voltage vector is applied in the alpha2-beta2 vector space while generating the reference output voltage vector in the alpha1-beta1 vector space. A modified symmetrical switching sequence is proposed with single leg commutation. The modulation technique is then extended to simultaneously generate alpha1-beta1 and alpha2-beta2 voltage vectors. These techniques are experimentally validated for the three-to-five phase indirect matrix converter. Three novel overmodulation techniques to extend the voltage transfer ratio (VTR) are proposed and practically assessed. They enable the three-to-five phase indirect matrix converter to generate a higher output phase voltage, at the cost of generating a non-zero voltage vector in the alpha2-beta2 vector space. The superior of the three techniques adapts the ratio between the large and medium vectors based on the value of VTR and utilizes the dc-link ripple to reduce the voltage vector production in the alpha2-beta2 vector space. A control and modulation technique is proposed for reverse power flow allowing power from a five-phase source, in this thesis a permanent magnet machine, to inject power into the three-phase grid. The control technique operates the indirect matrix converter in a voltage boost mode thereby injecting power into the grid from a generator phase voltage that is lower than the grid phase voltage. A prototype three-to-five phase indirect matrix converter with a DSP and FPGA controller was designed and developed. Experimental results from this system verify the techniques and their benefits