New Topologies and Advanced Control of Power Electronic Converters for Renewable Energy based Microgrids

Solar energy-based microgrids are increasingly promising due to their many features, such as being environmentally friendly and having low operating costs. Power electronic converters, filters, and transformers are the key components to integrate the solar photovoltaic (PV) systems with the microgrids. The power electronic converters play an important role to reduce the size of the filter circuit and eliminate the use of the bulky and heavy traditional power frequency step-up transformer. These power converters also play a vital role to integrate the energy storage systems such as batteries and the superconducting magnetic energy storage (SMES) unit in a solar PV power-based microgrid. However, the performance of these power converters depends upon the switching technique and the power converter configuration. The switching techniques can improve the power quality, i.e. lower total harmonic distortion at the converter output waveform, reduce the converter power loss, and can effectively utilize the dc bus voltage, which helps to improve the power conversion efficiency of the power electronic converter. The power converter configuration can reduce the size of the power converter and make the power conversion system more efficient. In addition to the advanced switching technique, a supervisory control can also be integrated with these power converters to ensure the optimal power flow within the microgrid. First, this thesis reviews different existing power converter topologies with their switching techniques and control strategies for the grid integration of solar PV systems. To eliminate the use of the bulky and heavy line frequency step-up transformer to integrate solar PV systems to medium voltage grids, the high frequency magnetic linkbased medium voltage power converter topologies are discussed and compared based on their performance parameters. Moreover, switching and conduction losses are calculated to compare the performance of the switching techniques for the magnetic-linked power converter topologies. In this thesis, a new pulse width modulation technique has been proposed to integrate the SMES system with the solar PV system-based microgrid. The pulse width modulation technique is designed to provide reactive power into the network in an effective way. The modulation technique ensures lower total harmonic distortion (THD), lower switching loss, and better utilization of dc-bus voltage. The simulation and experimental results show the effectiveness of the proposed pulse width modulation technique. In this thesis, an improved version of the previously proposed switching technique has been designed for a transformer-less PV inverter. The improved switching technique can ensure effective active power flow into the network. A new switching scheme has been proposed for reactive power control to avoid unnecessary switching faced by the traditional switching technique in a transformer-less PV inverter. The proposed switching technique is based on the peak point value of the grid current and ensures lower switching loss compared to other switching techniques. In this thesis, a new magnetic-linked multilevel inverter has been designed to overcome the issues faced by the two-level inverters and traditional multilevel inverters. The proposed multilevel inverter utilizes the same number of electronic switches but fewer capacitors compared to the traditional multilevel inverters. The proposed multilevel inverter solves the capacitor voltage balancing and utilizes 25% more of the dc bus voltage compared to the traditional multilevel inverter, which reduces the power rating of the dc power source components and also extends the input voltage operating range of the inverter. An improved version magnetic-linked multilevel inverter is proposed in this thesis with a model predictive control technique. This multilevel inverter reduces both the number of switches and capacitors compared to the traditional multilevel inverter. This multilevel inverter also solves the capacitor voltage balancing issue and utilizes 50% more of the dc bus voltage compared to the traditional multilevel inverter. Finally, an energy management system has been designed for the developed power converter and control to achieve energy resiliency and minimum operating cost of the microgrid. The model predictive control-based energy management system utilizes the predicted load data, PV insolation data from web service, electricity price data, and battery state of charge data to select the battery charging and discharging pattern over the day. This model predictive control-based supervisory control with the advanced power electronic converter and control makes the PV energy-based microgrid more efficient and reliable

Developing A Medium-Voltage Three-Phase Current Compensator Using Modular Switching Positions

The objective of this thesis is to present the context, application, theory, design, construction, and testing of a proposed solution to unbalanced current loading on three-phase four-wire systems. This solution, known as the Medium-Voltage Unbalanced Current Static Compensator or MV-UCSC, is designed to recirculate currents between the three phases of adistribution system. Through this redistribution of the currents negative- and zero-sequence current components are eliminated and a balanced load is seen upstream from the point of installation. The MV-UCSC as it operates in the distribution system is presented followed by its effect on traditional compensation equipment. The construction of the MV-UCSC as well as 13.8 kV simulations are then shown. Development of the switching positions required by the MVUCSC is then given followed by a variation on this switching position with the intent to reduce part count. Finally, the testing the 13.8 kV three-phase four-wire, neutral-point-clamped, elevenlevel, flying-capacitor-based MV-UCSC connected directly to the grid is presented

Addressing control and capacitor voltage regulation challenges in multilevel power electronic converters

Multilevel power electronic converters are the current industry solutions for applications that demand medium voltage, reasonable efficiency, and high power quality. The proper operation of these types of power converters requires special control, modulation methods, and capacitor voltage regulation techniques. Both developing capacitor voltage regulation methods and addressing their associated issues with such fall within the primary focus of this dissertation. In this dissertation an investigation was conducted on the capacitor voltage regulation constraints in cascaded H-bridge multilevel converters with a staircase output voltage waveform. In the proposed method, the harmonic elimination technique is used to determine the switching angles. A constraint was then derived to identify modulation those indices that lead to voltage regulation of the capacitor. This constraint can be used in optimization problems for harmonic minimization to guarantee capacitor voltage regulation in these types of converters. Furthermore, a capacitor voltage regulation method was developed using redundant state selection for a flying capacitor active rectifier. This method reduces the number of switching instances by using both online and offline state selection procedure. Additionally, a start-up procedure is proposed that pre-charges the all of capacitors in the rectifier to both avoid overstressing the switches and obtain a smoother start-up. Finally, a flexible capacitor voltage regulation method is proposed that provides the ability to control the voltage of the capacitors in both cascaded H-bridge and hybrid multilevel converters. In this method, the capacitor voltage in each individual H-bridge cell is independently regulated by controlling the active power of each cell

The presentation of sustainable power source assets in the field of intensity age assumes an imperative job

DC to DC converters to interface lesser-voltage higher-control supply to the essential stock shows the most raised proficiency was practiced in the full-connect converter. Non-separated converters bury unified inductor help converters with essential voltage gain and furthermore converters hold lesser profitability, yet they huge in structure, even the quantity of latent parts is diminished. In like manner gives proficient utilization of semiconductor switches, have higher voltage yield and are prepared to work in lesser estimation of D interestingly with every single disconnected converter. High addition topologies are regularly outfitted with high voltage security structures. Few non-disengaged topologies gives voltage hang security circuits are pointless since capacitive fragments and circuit plan are progressed to work under higher information voltage and low power. That requires lesser qualities for convincing RAC obstruction and entomb partnered inductance dispersal to achieve more prominent adequacy of intensity change. Larger supply current needs extensive region of core area inter allied inductors

Modular Multilevel Converters for Medium Voltage Applications: Low Switching Frequency Modulation Strategies and Circulating Current Control Techniques.

233 p.El objetivo de la presente tesis ha sido el aumento de la eficiencia y la mejora del funcionamiento de convertidores multinivel modulares (MMCs) en aplicaciones de media tensión (drives, STATCOMs, redes de media tensión en DC o colectores de energía en parques eólicos). Para ello se ha propuesto la utilización de una modulación de baja frecuencia de conmutación como la Eliminación Selectiva de Armónicos (SHE-PWM). De esta forma se reducen las pérdidas de conmutación significativamente. Las contribuciones de la tesis son:- Nueva formulación para implementar SHE-PWM: Esta nueva formulación, a diferencia de las existentes, proporciona un sistema único de ecuaciones que es válido para cualquier forma de onda. De esta forma, es posible buscar los ángulos de disparo y los patrones de conmutación, que resuelven el problema de SHE-PWM, sin necesidad de predefinir ninguna forma de onda. Por lo tanto, la búsqueda de ángulos de disparo se simplifica significativamente y se puede encontrar un alto número de soluciones diferentes, pudiendo optimizar el diseño de la forma de onda. Además, esta formulación es válida con simetrías de cuarto de onda y de media onda.- Controles de la corriente circulante en MMCs cuando se utiliza SHE-PWM: estos controles, a diferencia de los existentes, no distorsionan la tensión de fase de salida cuando se utiliza SHE-PWM y permiten mantener equilibradas las tensiones de los condensadores de los sub-módulos del MMC, además de reducir rizado de la corriente circulante. En concreto, se han propuesto dos controles, uno con (N+1) SHE-PWM y otro con (2N+1) SHE-PWM

Direct control of D-STATCOM based on 23-level cascaded multilevel inverter using harmonics elimination pulse width modulation

The distribution static synchronous compensator (D-STATCOM) is primarily used for solving power quality problems. Normally, the phase-shifted pulse width modulation (PS-PWM) switching is employed in conjunction with the direct control of the D-STATCOM. However, the PS-PWM exhibits high switching losses. To alleviate this problem, a direct control scheme for D-STATCOM based on the harmonic elimination PWM (HEPWM) switching is developed. Due to the difficulty in solving the equations for the HEPWM angles, no work is reported on the direct control for a multilevel voltage source inverter (MVSI) D-STATCOM with more than 15-levels. Thus, the main contribution of the work is the application of HEPWM for 23-level cascaded MVSI using a wide modulation index (MI) range (i.e. 5.40 – 8.15 p.u). The main motivation to utilize the high number of level is to allow for the output voltage of the D-STATCOM to be sufficiently high, thus avoiding the use of step-up transformer. Furthermore, the achieved MI keeps the total harmonic distortion of the MVSI output voltage below the IEEE 519 Standard (5%) over the entire operating range. The eleven HEPWM switching angles were computed using an optimization technique, known as the differential evolution. Since the angles were computed offline, they were retrieved from a look-up table whenever the output voltage of the MVSI was to be constructed. The HEPWM-based direct control was benchmarked against the popular PS-PWM using ± 6.5MVAr/11kV D-STATCOM modelled in MATLAB-Simulink and PLECS software. For the same switching frequency, the proposed HEPWM switching exhibited superior harmonic spectra, hence had lower losses. Furthermore, the size of the series coupling inductor can be reduced to at least half. Dynamically, the steady state value of the reactive current was reached in less than one mains cycle when a transition from the full inductive to full capacitive modes was imposed. In addition, the proposed D-STATCOM controller mitigated the swell and sag problems in less than one cycle