Frequency-domain nonlinear modeling approaches for power systems components - A comparison

Harmonic simulations play a key role in studying and predicting the impact of nonlinear devices on the power quality level of distribution grids. A frequency-domain approach allows higher computational efficiency, which has key importance as long as complex networks have to be studied. However, this requires proper frequency-domain behavioral models able to represent the nonlinear voltage-current relationship characterizing these devices. The Frequency Transfer Matrix (FTM) method is one of the most widespread frequency domain modeling approaches for power system applications. However, others suitable techniques have been developed in the last years, in particular the X-parameters approach, which comes from radiofrequency and microwave applications, and the simplified Volterra models under quasi-sinusoidal conditions, that have been specifically tailored for power system devices. In this paper FTM, X-parameters and simplified Volterra approaches are compared in representing the nonlinear voltage-current relationship of a bridge rectifier feeding an ohmic-capacitive dc load. Results show that the X-parameters model reaches good accuracy, which is slightly better than that achieved by the FTM and simplified Volterra models, but with a considerably larger set of coefficients. Simplified Volterra models under quasi-sinusoidal conditions allows an effective trade-off between accuracy and complexity

Impedance estimation of single-phase diode bridge rectifier using kalman filter

Today, the majority of electronic loads are non-linear. Electronic ballasts for discharge lamps, audio equipment, and personal computers are examples of non-linear loads. DC voltage is used to power these electronic loads. It is important to convert AC voltage to DC voltage since the power distribution system operates on AC voltage. In low-power applications, single phase rectifiers convert AC electricity to DC voltage. The aspects that influence nonlinear loads and allow a power quality study include power factor, displacement factor, and harmonic distortion. The study of these phenomena has grown in popularity as this type of load has become more prevalent in residential and commercial environments. Nonlinear load modeling is a critical tool for resolving this issue. Then specialized research into the modeling of these loads is required. As a result, this study create a Kalman filter model by using MATLAB Simulink for estimating the RLC parameters of a single-phase diode bridge rectifier. The system design was carried out using the MATLAB Simulink platform, with the appropriate RLC parameters taken from relevant literature studies. This study discovered that the amount of process noise in a system indicates the system's performance. The simulation is finished when all of the required conditions are met, which means the accuracy attained is at least 90%. When compared to the Analytical technique, simulation results show that the proposed method is more accurate. It specifies that with a modest value of process noise, the precision of equivalent capacitance, resistance, and inductance becomes more precise. For Section 1, the percentage of accuracy improved by 0.26%, 0.6%, and 9.84%, respectively, for resistance, inductance, and capacitance. Besides, for Section 2, the percentage of accuracy increased by 0.16%, 0.1%, and 1.3% for resistance, inductance, and capacitance respectively. Finally, the Kalman Filter can be used to calculate the R, L, and C parameter values for a single-phase diode bridge rectifier

Design and Advanced Model Predictive Control of Wide Bandgap Based Power Converters

The field of power electronics (PE) is experiencing a revolution by harnessing the superior technical characteristics of wide-band gap (WBG) materials, namely Silicone Carbide (SiC) and Gallium Nitride (GaN). Semiconductor devices devised using WBG materials enable high temperature operation at reduced footprint, offer higher blocking voltages, and operate at much higher switching frequencies compared to conventional Silicon (Si) based counterpart. These characteristics are highly desirable as they allow converter designs for challenging applications such as more-electric-aircraft (MEA), electric vehicle (EV) power train, and the like. This dissertation presents designs of a WBG based power converters for a 1 MW, 1 MHz ultra-fast offboard EV charger, and 250 kW integrated modular motor drive (IMMD) for a MEA application. The goal of these designs is to demonstrate the superior power density and efficiency that are achievable by leveraging the power of SiC and GaN semiconductors. Ultra-fast EV charging is expected to alleviate the challenge of range anxiety , which is currently hindering the mass adoption of EVs in automotive market. The power converter design presented in the dissertation utilizes SiC MOSFETs embedded in a topology that is a modification of the conventional three-level (3L) active neutral-point clamped (ANPC) converter. A novel phase-shifted modulation scheme presented alongside the design allows converter operation at switching frequency of 1 MHz, thereby miniaturizing the grid-side filter to enhance the power density. IMMDs combine the power electronic drive and the electric machine into a single unit, and thus is an efficient solution to realize the electrification of aircraft. The IMMD design presented in the dissertation uses GaN devices embedded in a stacked modular full-bridge converter topology to individually drive each of the motor coils. Various issues and solutions, pertaining to paralleling of GaN devices to meet the high current requirements are also addressed in the thesis. Experimental prototypes of the SiC ultra-fast EV charger and GaN IMMD were built, and the results confirm the efficacy of the proposed designs. Model predictive control (MPC) is a nonlinear control technique that has been widely investigated for various power electronic applications in the past decade. MPC exploits the discrete nature of power converters to make control decisions using a cost function. The controller offers various advantages over, e.g., linear PI controllers in terms of fast dynamic response, identical performance at a reduced switching frequency, and ease of applicability to MIMO applications. This dissertation also investigates MPC for key power electronic applications, such as, grid-tied VSC with an LCL filter and multilevel VSI with an LC filter. By implementing high performance MPC controllers on WBG based power converters, it is possible to formulate designs capable of fast dynamic tracking, high power operation at reduced THD, and increased power density

Accurate modeling techniques for power delivery

“Power delivery is essential in electronic systems to provide reliable power from voltage sources to load devices. Driven by the ambitious user demands and technology evolutions, the power delivery design is posed serious challenges. In this work, we focus on modeling two types of power delivery paths: the power distribution network (PDN) and the wireless power transfer (WPT) system. For the modeling of PDN, a novel pattern-based analytical method is proposed for PCB-level PDN impedance calculations, which constructs an equivalent circuit with one-to-one correspondences to the PCB’s physical structure. A practical modeling methodology is also introduced to optimize the PDN design. In addition, a topology-based behavior model is developed for the current-mode voltage regulator module (VRM). This model includes all the critical components in the power stage, the voltage control loop, and the current control loop of a VRM device. A novel method is also proposed to unify the modeling of the continuous and discontinuous conduction modes for transient load responses. Cascading the proposed VRM model with the PCB-level PDN model enables a combined PDN analysis, which is much needed for modern PDN designs. For the modeling of WPT system, a system-level model is developed for both efficiency and power loss of all the blocks in WPT systems. A rectifier characterization method is also proposed to obtain the accurate load impedance. This model is capable of deriving the power capabilities for both the fundamental and higher order harmonics. Based on the system model, a practical design methodology is introduced to simultaneously optimize multiple system parameters, which greatly accelerates the design process”--Abstract, page iv

Fault Diagnostic System for Cascaded H-bridge Multilevel Inverter Drives Based on Artificial Intelligent Approaches Incorporating a Reconfiguration Technique

A fault diagnostic and reconfiguration system in a multilevel inverter drive (MLID) using artificial intelligent based techniques is developed in this dissertation. Output phase voltages of a MLID can be used as valuable information to diagnose faults and their locations. It is difficult to diagnose a MLID system using a mathematical model because MLID systems consist of many switching devices and their system complexity has a nonlinear factor. Therefore, a neural network (NN) classification is applied to the fault diagnosis of a MLID system. Multilayer perceptron (MLP) networks are used to identify the type and location of occurring faults. The principal component analysis (PCA) is utilized in the feature extraction process to reduce the NN input size. A lower dimensional input space will also usually reduce the time necessary to train a NN, and the reduced noise may improve the mapping performance. The genetic algorithm is also applied to select the valuable principal components. The comparison among MLP neural network (NN), principal component neural network (PC-NN), and genetic algorithm based selective principal component neural network (PC-GA-NN) are performed. Proposed neural networks are evaluated with simulation test set and experimental test set. The PC-NN has improved overall classification performance from NN by about 5% points, whereas PC-GA-NN has better overall classification performance from NN by about 7.5% points. Therefore, the application of a genetic algorithm improves the classification from PC-NN by about 2.5% point. The overall classification performance of the proposed networks is more than 90%. A reconfiguration technique is also developed. The effects of using the developed reconfiguration technique at high modulation index are addressed. The developed fault diagnostic system is validated with experimental results. The developed fault diagnostic system requires about 6 cycles at 60 Hz to clear an open circuit and about 9 cycles at 60 Hz to clear a short circuit fault. The experimental results show that the developed system performs satisfactorily to detect the fault type, fault location, and reconfiguration

Modeling toolkit for comparing AC vs. DC electrical distribution efficiency in buildings, A

2021 Summer.Includes bibliographical references.An increasing proportion of electrical devices in residential and commercial buildings operate from direct current (DC) power sources. In addition, distributed power generation systems such as solar photovoltaic (PV) and energy storage natively produce DC power. However, traditional power distribution is based on an alternating current (AC) model. Performing the necessary conversions between AC and DC power to make DC devices compatible with AC distribution results in energy losses. For these reasons, DC distribution may offer energy efficiency advantages in comparison to AC distribution. However, reasonably fast computation and comparison of electrical efficiencies of AC-only, DC-only, and hybrid AC/DC distributions systems is challenging because DC devices are typically (nonlinear) power-electronic converters that produce harmonic content. While detailed time-domain modeling can be used to simulate these harmonics, it is not computationally efficient or practical for many building designers. To address this need, this research describes a toolkit for computation of harmonic spectra and energy efficiency in mixed AC and DC electrical distribution systems, using a Harmonic Power Flow (HPF) methodology. The toolkit includes a library of two-port linear and nonlinear device models which can be used to construct and simulate an electrical distribution system. This dissertation includes a description of the mathematical theory and framework underlying the toolkit, development and fitting of linear and nonlinear device models, software implementation in Modelica, verification of the toolkit with laboratory measurements, and discussion of ongoing and future work to employ the toolkit to a variety of building designs

Modeling and identification of power electronic converters

Nowadays, many industries are moving towards more electrical systems and components. This is done with the purpose of enhancing the efficiency of their systems while being environmentally friendlier and sustainable. Therefore, the development of power electronic systems is one of the most important points of this transition. Many manufacturers have improved their equipment and processes in order to satisfy the new necessities of the industries (aircraft, automotive, aerospace, telecommunication, etc.). For the particular case of the More Electric Aircraft (MEA), there are several power converters, inverters and filters that are usually acquired from different manufacturers. These are switched mode power converters that feed multiple loads, being a critical element in the transmission systems. In some cases, these manufacturers do not provide the sufficient information regarding the functionality of the devices such as DC/DC power converters, rectifiers, inverters or filters. Consequently, there is the need to model and identify the performance of these components to allow the aforementioned industries to develop models for the design stage, for predictive maintenance, for detecting possible failures modes, and to have a better control over the electrical system. Thus, the main objective of this thesis is to develop models that are able to describe the behavior of power electronic converters, whose parameters and/or topology are unknown. The algorithms must be replicable and they should work in other types of converters that are used in the power electronics field. The thesis is divided in two main cores, which are the parameter identification for white-box models and the black-box modeling of power electronics devices. The proposed approaches are based on optimization algorithms and deep learning techniques that use non-intrusive measurements to obtain a set of parameters or generate a model, respectively. In both cases, the algorithms are trained and tested using real data gathered from converters used in aircrafts and electric vehicles. This thesis also presents how the proposed methodologies can be applied to more complex power systems and for prognostics tasks. Concluding, this thesis aims to provide algorithms that allow industries to obtain realistic and accurate models of the components that they are using in their electrical systems.En la actualidad, el uso de sistemas y componentes eléctricos complejos se extiende a múltiples sectores industriales. Esto se hace con el propósito de mejorar su eficiencia y, en consecuencia, ser más sostenibles y amigables con el medio ambiente. Por tanto, el desarrollo de sistemas electrónicos de potencia es uno de los puntos más importantes de esta transición. Muchos fabricantes han mejorado sus equipos y procesos para satisfacer las nuevas necesidades de las industrias (aeronáutica, automotriz, aeroespacial, telecomunicaciones, etc.). Para el caso particular de los aviones más eléctricos (MEA, por sus siglas en inglés), existen varios convertidores de potencia, inversores y filtros que suelen adquirirse a diferentes fabricantes. Se trata de convertidores de potencia de modo conmutado que alimentan múltiples cargas, siendo un elemento crítico en los sistemas de transmisión. En algunos casos, estos fabricantes no proporcionan la información suficiente sobre la funcionalidad de los dispositivos como convertidores de potencia DC-DC, rectificadores, inversores o filtros. En consecuencia, existe la necesidad de modelar e identificar el desempeño de estos componentes para permitir que las industrias mencionadas desarrollan modelos para la etapa de diseño, para el mantenimiento predictivo, para la detección de posibles modos de fallas y para tener un mejor control del sistema eléctrico. Así, el principal objetivo de esta tesis es desarrollar modelos que sean capaces de describir el comportamiento de un convertidor de potencia, cuyos parámetros y/o topología se desconocen. Los algoritmos deben ser replicables y deben funcionar en otro tipo de convertidores que se utilizan en el campo de la electrónica de potencia. La tesis se divide en dos núcleos principales, que son la identificación de parámetros de los convertidores y el modelado de caja negra (black-box) de dispositivos electrónicos de potencia. Los enfoques propuestos se basan en algoritmos de optimización y técnicas de aprendizaje profundo que utilizan mediciones no intrusivas de las tensiones y corrientes de los convertidores para obtener un conjunto de parámetros o generar un modelo, respectivamente. En ambos casos, los algoritmos se entrenan y prueban utilizando datos reales recopilados de convertidores utilizados en aviones y vehículos eléctricos. Esta tesis también presenta cómo las metodologías propuestas se pueden aplicar a sistemas eléctricos más complejos y para tareas de diagnóstico. En conclusión, esta tesis tiene como objetivo proporcionar algoritmos que permitan a las industrias obtener modelos realistas y precisos de los componentes que están utilizando en sus sistemas eléctricos.Postprint (published version

Design and analysis of field-powered transponders integrated in metallic objects

[no abstract

High Voltage Pulsed Power Converters for the ESS Linear Accelerator.

Material science has become an important research area in order to fulfill today’s requirements on lighter, cheaper and more sustainable materials. The European spallation source is a research center based on the world’s most powerful neutron source, which will enable new possibilities to evaluate material properties down to an atomic level. The linear accelerator (Linac), accelerates with help of electromagnetic fields, protons to a speed of 96.2 % of the light. Due to high power and the pulsing nature of the accelerator an extremely advanced electrical supply is required. This master´s thesis comprises a concept topology for solving the impact of such pulsed power supplies on the AC grid power quality. The electrical supply consists of two series connected stages, which will be stacked in modulators. The first stage is a low voltage grid connected capacitor bank charger, the second stage converts the power to a high voltage pulsing pattern. This project comprises the first stage (the capacitor charger) which consists of an Active Front End in series with a DC/DC-converter. The main objectives are to fulfil the international standards regarding power quality, where main focus will be on flicker, low frequency harmonics emission and unitary power factor. In order to fulfill these goals with pulsating loads connected, a completely new developed power control introduced. Mathematical models have been derived in order to verify the functionality and to tune all the developed controls. A complete final implementation is done with the help of Matlab Simulink to more in-depth verify the different control parameters. This implementation is also used to check that the international standards are met. Complete calculations of power losses are also presented with evaluation of results and possible improvements. Together with the limitations, goals of the degree project and basic equations are derived in this report. The topology is shown to be extremely effective with very good results in terms of output voltage quality (capacitor charging voltage) and on flicker and low frequency harmonics impact on the grid. Almost every effects due to the pulsing output nature are totally erased seen from the grid side

DC/DC converter for offshore DC collection network

Large wind farms, especially large offshore wind farms, present a challenge for the electrical networks that will provide interconnection of turbines and onward transmission to the onshore power network. High wind farm capacity combined with a move to larger wind turbines will result in a large geographical footprint requiring a substantial sub-sea power network to provide internal interconnection. While advanced HVDC transmission has addressed the issue of long-distance transmission, internal wind farm power networks have seen relatively little innovation. Recent studies have highlighted the potential benefits of DC collection networks. First with appropriate selection of DC voltage, reduced losses can be expected. In addition, the size and weight of the electrical plant may also be reduced through the use of medium- or high-frequency transformers to step up the generator output voltage for connection to a medium-voltage network suitable for wide-area interconnection. However, achieving DC/DC conversion at the required voltage and power levels presents a significant challenge for wind-turbine power electronics.This thesis first proposes a modular DC/DC converter with input-parallel output-series connection, consisting of full-bridge DC/DC modules. A new master-slave control scheme is developed to ensure power sharing under all operating conditions, including during failure of a master module by allowing the status of master module to be reallocated to another healthy module. Secondly, a novel modular DC/DC converter with input-series-input-parallel output-series connection is presented. In addition, a robust control scheme is developed to ensure power sharing between practical modules even where modules have mismatched parameters or when there is a faulted module. Further, the control strategy is able to isolate faulted modules to ensure fault ride-through during internal module faults, whilst maintaining good transient performance. The ISIPOS connection is then applied to a converter with bidirectional power flow capability, realised using dual-active bridge modules.The small- and large-signal analyses of the proposed converters are performed in order to deduce the control structure for the converter input and output stages. Simulation and experimental results demonstrate and validate the proposed converters and associated control schemes.Large wind farms, especially large offshore wind farms, present a challenge for the electrical networks that will provide interconnection of turbines and onward transmission to the onshore power network. High wind farm capacity combined with a move to larger wind turbines will result in a large geographical footprint requiring a substantial sub-sea power network to provide internal interconnection. While advanced HVDC transmission has addressed the issue of long-distance transmission, internal wind farm power networks have seen relatively little innovation. Recent studies have highlighted the potential benefits of DC collection networks. First with appropriate selection of DC voltage, reduced losses can be expected. In addition, the size and weight of the electrical plant may also be reduced through the use of medium- or high-frequency transformers to step up the generator output voltage for connection to a medium-voltage network suitable for wide-area interconnection. However, achieving DC/DC conversion at the required voltage and power levels presents a significant challenge for wind-turbine power electronics.This thesis first proposes a modular DC/DC converter with input-parallel output-series connection, consisting of full-bridge DC/DC modules. A new master-slave control scheme is developed to ensure power sharing under all operating conditions, including during failure of a master module by allowing the status of master module to be reallocated to another healthy module. Secondly, a novel modular DC/DC converter with input-series-input-parallel output-series connection is presented. In addition, a robust control scheme is developed to ensure power sharing between practical modules even where modules have mismatched parameters or when there is a faulted module. Further, the control strategy is able to isolate faulted modules to ensure fault ride-through during internal module faults, whilst maintaining good transient performance. The ISIPOS connection is then applied to a converter with bidirectional power flow capability, realised using dual-active bridge modules.The small- and large-signal analyses of the proposed converters are performed in order to deduce the control structure for the converter input and output stages. Simulation and experimental results demonstrate and validate the proposed converters and associated control schemes