576 research outputs found

    Applications of Power Electronics:Volume 1

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    Power Converters in Power Electronics

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    In recent years, power converters have played an important role in power electronics technology for different applications, such as renewable energy systems, electric vehicles, pulsed power generation, and biomedical sciences. Power converters, in the realm of power electronics, are becoming essential for generating electrical power energy in various ways. This Special Issue focuses on the development of novel power converter topologies in power electronics. The topics of interest include, but are not limited to: Z-source converters; multilevel power converter topologies; switched-capacitor-based power converters; power converters for battery management systems; power converters in wireless power transfer techniques; the reliability of power conversion systems; and modulation techniques for advanced power converters

    Lithium-Ion Ultracapacitor Energy Storage Integrated with a Variable Speed Wind Turbine for Improved Power Conversion Control

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    The energy of wind has been increasingly used for electric power generation worldwide due to its availability and ecologically sustainability. Utilization of wind energy in modern power systems creates many technical and economical challenges that need to be addressed for successful large scale wind energy integration. Variations in wind velocity result in variations of output power produced by wind turbines. Variable power output becomes a challenge as the amount of output power of the wind turbines integrated into power systems increases. Large power variations cause voltage and frequency deviations from nominal values that may lead to activation of relay protective equipment, which may result in disconnection of the wind turbines from the grid. Particularly community wind power systems, where only one or a few wind turbines supply loads through a weak grid such as distribution network, are sensitive to supply disturbances. While a majority of power produced in modern power systems comes from synchronous generators that have large inertias and whose control systems can compensate for slow power variations in the system, faster power variations at the scale of fraction of a second to the tens of seconds can seriously reduce reliability of power system operation. Energy storage integrated with wind turbines can address this challenge. In this dissertation, lithium-ion ultracapacitors are investigated as a potential solution for filtering power variations at the scale of tens of seconds. Another class of issues related to utilization of wind energy is related to economical operation of wind energy conversion systems. Wind speed variations create large mechanical loads on wind turbine components, which lead to their early failures. One of the most critical components of a wind turbine is a gearbox that mechanically couples turbine rotor and generator. Gearboxes are exposed to large mechanical load variations which lead to their early failures and increased cost of wind turbine operation and maintenance. This dissertation proposes a new critical load reduction strategy that removes mechanical load components that are the most dangerous in terms of harmful effect they have on a gearbox, resulting in more reliable operation of a wind turbine

    POWER QUALITY CONTROL AND COMMON-MODE NOISE MITIGATION FOR INVERTERS IN ELECTRIC VEHICLES

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    Inverters are widely utilized in electric vehicle (EV) applications as a major voltage/current source for onboard battery chargers (OBC) and motor drive systems. The inverter performance is critical to the efficiency of EV system energy conversion and electronics system electro-magnetic interference (EMI) design. However, for AC systems, the bandwidth requirement is usually low compared with DC systems, and the control impact on the inverter differential-mode (DM) and common-mode (CM) performance are not well investigated. With the wide-band gap (WBG) device era, the switching capability of power electronics devices drastically improved. The DM/CM impact that was brought by the WBG device-based inverter becomes more serious and has not been completely understood. This thesis provides an in-depth analysis of on-board inverter control strategies and the corresponding DM/CM impact on the EV system. The OBC inverter control under vehicle-to-load (V2L) mode will be documented first. A virtual resistance damping method minimizes the nonlinear load harmonics, and a neutral balancing method regulates the unbalanced load impact through the fourth leg. In the motor drive system, a generalized CM voltage analytical model and a current ripple prediction model are built for understanding the system CM and DM stress with respect to different modulation methods, covering both 2-level and 3-level topologies. A novel CM EMI damping modulation scheme is proposed for 6-phase inverter applications. The performance comparison between the proposed methods and the conventional solution is carried out. Each topic is supported by the corresponding hardware platform and experimental validation

    Special Power Electronics Converters and Machine Drives with Wide Band-Gap Devices

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    Power electronic converters play a key role in power generation, storage, and consumption. The major portion of power losses in the converters is dissipated in the semiconductor switching devices. In recent years, new power semiconductors based on wide band-gap (WBG) devices have been increasingly developed and employed in terms of promising merits including the lower on-state resistance, lower turn-on/off energy, higher capable switching frequency, higher temperature tolerance than conventional Si devices. However, WBG devices also brought new challenges including lower fault tolerance, higher system cost, gate driver challenges, and high dv/dt and resulting increased bearing current in electric machines. This work first proposed a hybrid Si IGBTs + SiC MOSFETs five-level transistor clamped H-bridge (TCHB) inverter which required significantly fewer number of semiconductor switches and fewer isolated DC sources than the conventional cascaded H-bridge inverter. As a result, system cost was largely reduced considering the high price of WBG devices in the present market. The semiconductor switches operated at carrier frequency were configured as Silicon Carbide (SiC) devices to improve the inverter efficiency, while the switches operated at fundamental output frequency (i.e., grid frequency) were constituted by Silicon (Si) IGBT devices. Different modulation strategies and control methods were developed and compared. In other words, this proposed SiC+Si hybrid TCHB inverter provided a solution to ride through a load short-circuit fault. Another special power electronic, multiport converter, was designed for EV charging station integrated with PV power generation and battery energy storage system. The control scheme for different charging modes was carefully developed to improve stabilization including power gap balancing, peak shaving, and valley filling, and voltage sag compensation. As a result, the influence on the power grid was reduced due to the matching between daily charging demand and adequate daytime PV generation. For special machine drives, such as slotless and coreless machines with low inductance, low core losses, typical drive implementations using conventional silicon-based devices are performance limited and also produce large current and torque ripples. In this research, WBG devices were employed to increase inverter switching frequency, reduce current ripple, reduce filter size, and as a result reduce drive system cost. Two inverter drive configurations were proposed and implemented with WBG devices in order to mitigate such issues for 2-phase very low inductance machines. Two inverter topologies, i.e., a dual H-bridge inverter with maximum redundancy and survivability and a 3-leg inverter for reduced cost, were considered. Simulation and experimental results validated the drive configurations in this dissertation. An integrated AC/AC converter was developed for 2-phase motor drives. Additionally, the proposed integrated AC/AC converter was systematically compared with commonly used topologies including AC/DC/AC converter and matrix converters, in terms of the output voltage/current capability, total harmonics distortion (THD), and system cost. Furthermore, closed-loop speed controllers were developed for the three topologies, and the maximum operating range and output phase currents were investigated. The proposed integrated AC/AC converter with a single-phase input and a 2-phase output reduced the switch count to six and resulting in minimized system cost and size for low power applications. In contrast, AC/DC/AC pulse width modulation (PWM) converters contained twelve active power semiconductor switches and a common DC link. Furthermore, a modulation scheme and filters for the proposed converter were developed and modeled in detail. For the significantly increased bearing current caused by the transition from Si devices to WBG devices, advanced modeling and analysis approach was proposed by using coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which took into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. Possible bearing current issues in axial-flux machines, and possibilities of computation time reduction, were also discussed. Two experimental validation approaches were proposed: the time-domain analysis approach to accurately capture the time transient, the stationary testing approach to measure bearing capacitance without complex control development or loading condition limitations. In addition, two types of motors were employed for experimental validation: an inside-out N-type PMSM was used for rotating testing and stationary testing, and an N-type BLDC was used for stationary testing. Possible solutions for the increased CMV and bearing currents caused by the implementation of WGB devices were discussed and developed in simulation validation, including multi-carrier SPWM modulation and H-8 converter topology

    Sliding Mode Control of Photovoltaic Energy Conversion Systems

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    Increasing interest and investment in renewable energy give rise to rapid development of high penetration solar energy. The focus has been on the power electronic converters which are typically used as interface between the dc output of the photo voltaic (PV) panels and the terminals of the ac utility network. In the dual-stage grid-connected PV (GPV) system, the dc dc stage plays a significant role in converting dc power from PV panel at low voltage to high dc bus voltage. However, the output of solar arrays varies due to change in solar irradiation and weather conditions. More importantly, high initial cost and limited lifespan of PV panels make it more critical to extract as much power from them as possible. It is, therefore, necessary one to employ the maximum power point tracking (MPPT) techniques in order to operate PV array at its maximum power point (MPP). A fast-and-robust analog-MPP tracker is thus proposed by using the concepts of Utkin’s equivalent control theory and fast-scale stability analysis. Analytical demonstration has also been presented to show the effectiveness of the proposed MPPT control technique. After the dc stage, the dc-ac inverter stage is employed to convert dc power into ac power and feed the power into the utility grid. The dc-ac stage is realized through the conventional full-bridge voltage source inverter (VSI) topologies. A fixed frequency hysteresis current (FFHC) controller, as well as an ellipsoidal switching surface based sliding mode control (SMC) technique are developed to improve the steady state and dynamic response under sudden load fluctuation. Such a control strategy is used not only maintains good voltage regulation, but also exhibits fast dynamic response under sudden load variation .Moreover, VSI can be synchronized with the ac utility grid. The current injected into the ac grid obeys the regulations standards (IEEE Std 519 and IEEE Std 1547)and ful fills the maximum allowable amount of injected current harmonics. Apart from that, controlling issues of stand-alone and grid-connected operation PV have also been discussed. A typical stand-alone PV system comprises a solar array and battery which is used as a backup source for power management between the source and the load .A control approach is developed for a 1-_ dual-stage transformer less inverter system to achieve voltage regulation with low steady state error and low total harmonic distortion (THD) and fast transient response under various load disturbances. The SMC technique is employed to address the power quality issues. A control technique for battery charging and discharging is also presented to keep the dc-link voltage constant during change in load demand or source power. This battery controller is employed for bidirectional power flow between battery and dc-link through a buck-boost converter in order to keep the input dc voltage constant. The robust stability of the closed-loop system is also analyzed. Finally, modeling and control of a 1-_ dual-stage GPV system has been analyzed. A small-signal average model has been developed for a 1-_ bridge inverter. The proposed controller has three cascaded control loops. The simulation results and theoretical analysis indicate that the proposed controller improves the efficiency of the system by reducing the THD of the injected current to the grid and increases the robustness of the system against uncertainties

    LLCL-Filter Based Single-Phase Grid-Tied Aalborg Inverter

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    THERMAL STRESS MITIGATION OF SINGLE-PHASE SINEWAVE INVERTER BY USING DOUBLE SWITCH H BRIDGE CONFIGURATION

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    The increasing demand for renewable energies and the ongoing advancement in the industry require continuously evolving power converters in terms of efficiency, power density, and reliability. Furthermore, power converters’ applications in harsh and remote environments such as offshore wind turbines demand robust and reliable designs to help reduce operational costs. Power switch failure is a critical reliability issue that leads to the converter going out of service, causing an unscheduled maintenance event. The main reason behind power switch failure is thermal cycling. Therefore, the first part of this thesis attempts to develop an effective double switch H bridge inverter topology aiming to lessen thermal cycling subjected to power switches, increasing the expected lifetime of power switches, improving the system\u27s overall reliability, and reducing operational costs. Meanwhile, the second focus of the thesis is to develop a visual interpretation of an empirical lifetime estimation model that enables the evaluation of the proposed inverter topology compared to the conventional topology. This is done by producing a novel lifetime improvement evaluation curve based on a common empirical lifetime estimation model using MATLAB®. Moreover, the interpretation of the empirical lifetime estimation models as a lifetime improvement evaluation curve helps to bridge the gap between any thermal condition change and its impact on the expected lifetime. The percentage reduction in the junction’s median temperature %_ and the percentage reduction in the temperature swing %Δ_ are taken as the main contributors to the change in the switch’s estimated cycles to failure . The effectiveness of the proposed topology was verified via simulation of the thermal parameters for the two topologies via PLECS® software. Several test scenarios were performed to illustrate the impact of shifting from the conventional topology to the proposed topology. Following that, numerous loading conditions were considered to perform an extensive comparative analysis between the proposed and the conventional topologies. Three power factor values were adopted at high, medium, and low values; to compare the two topologies while covering an adequate loading range for each power factor value. The assessment indices, namely, Life Prolonging Factor (LPF), and the average LPF (in a temperature range) obtained promising results, especially for high loading levels conditions. The LPF reached values more than ‘2’ under some conditions, indicating a more than double lifetime increase. Furthermore, the average LPF in a specific temperature range indicated promising results in general for common loading conditions with an advantage for higher loading conditions over lower loading conditions

    Grid Converters for Stationary Battery Energy Storage Systems

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    Control Strategies for Power Electronic Interfaces in Unbalanced Diesel Hybrid Mini-Grids with Renewable Sources and Storage

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    Traditionally, remote communities worldwide consist of autonomous power systems (mini-grids) supplied almost exclusively by diesel-engine generator sets (gensets) at relatively high costs. Integration of renewable energy sources (RESs), such as, photovoltaic (PV) and wind, can substantially reduce the cost of electricity generation and emissions in these remote communities. However, the highly variable load profile typical of mini-grids and the fluctuating characteristics of the RESs, cause frequent operation of the diesel genset at low loading condition, at low efficiency points and subject to carbon build up, which can significantly affect the maintenance costs and even the life time of the genset. Another important issue that is frequently overlooked in small (< 100 kVA) mini-grids, which usually present a low number of loads thus reducing the averaging effect, is load unbalance. Diesel gensets supplying unbalanced loads experience overheating in the synchronous generator and vibration in the shaft. For efficient operation, the genset should be operated near its full capacity and also in balanced mode. In order to address the above mentioned issues, a fast and reliable multi-mode battery energy storage system (BESS) employing voltage source inverter (VSI), is proposed in this thesis. In the genset support mode, as a basic feature, it can provide minimum loading for the genset and supplement it under peak load conditions. In addition, it can also provide load balancing and reactive power compensation for the mini-grid system. Therefore, the genset operates in balanced condition and within its ideal power range. In cases when the power demand from the genset is low, due to high supply of RESs and/or low load consumption, the genset can be shut-down and the BESS forms the grid, regulating voltage and frequency of the mini-grid system in the grid forming mode. Besides, the logic for defining the operating mode of the BESS and for achieving smooth transitions between modes are also presented in this thesis. The conventional approach for the control of three-phase VSI with unbalanced loads uses three-phase vector (dq) control and symmetrical components calculator which usually results in slow dynamic responses. Besides, the common power (P) vs. frequency (f) droop characteristic of the genset results in the mini-grid operating with variable frequency what further complicates the design of the controller for the VSI. Therefore, a new frequency adaptive per-phase dq-control scheme for three-wire and four-wire three-phase VSI based on the concept of fictive axis emulation is presented. It enables the control of current/voltage of each phase separately to achieve better dynamic performance in the variable frequency diesel hybrid mini-grid system. The effectiveness of the proposed techniques is demonstrated by means of simulation and experimental results
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