Non-Linear Control of a DC Microgrid for Electric Vehicle Charging Stations

Environmental concerns push governments to invest in renewable energy (RE). They are natural sources with a low carbon footprint and do not pollute locally. However, it is technically difficult to deploy high penetration of RE into the utility grid, due to the generation uncertainties and high installation costs, which are some of the most critical issues in RES use in this area. To address this issue, DC microgrids arise as a solution to integrate local distributed generation (DG) and storage, and to mitigate the issues related to AC/DC and DC/AC converters. Thanks to their main advantages for the power grid and energy consumers, microgrids have gained significant interest in recent years.  By another side, the electric vehicles (EVs) market is expected to grow in the coming years, which represent a new load that must be properly managed to avoid grid issues. Thus, this paper discusses the operation of DC microgrid considering the introduction of EVs. A nonlinear control is presented, including the modeling of charging of EVs. The simulated DC microgrid includes solar PV, a battery, and a supercapacitor. Significant variations from PV generation were included to highlight the performance of the methodology. The results show that the voltage fluctuations are small, which provides the DC microgrid with the required voltage stability. Moreover, it has been demonstrated that DC microgrids can be integrated in isolated locations that are not connected to the main grid in view of the RESs and EVs

Non-Linear Control of a DC Microgrid for Electric Vehicle Charging Stations

[EN] Environmental concerns push governments to invest in renewable energy (RE). They are natural sources with a low carbon footprint and do not pollute locally. However, it is technically difficult to deploy high penetration of RE into the utility grid, due to the generation uncertainties and high installation costs, which are some of the most critical issues in RES use in this area. To address this issue, DC microgrids arise as a solution to integrate local distributed generation (DG) and storage, and to mitigate the issues related to AC/DC and DC/AC converters. Thanks to their main advantages for the power grid and energy consumers, microgrids have gained significant interest in recent years. By another side, the electric vehicles (EVs) market is expected to grow in the coming years, which represent a new load that must be properly managed to avoid grid issues. Thus, this paper discusses the operation of DC microgrid considering the introduction of EVs. A nonlinear control is presented, including the modeling of charging of EVs. The simulated DC microgrid includes solar PV, a battery, and a supercapacitor. Significant variations from PV generation were included to highlight the performance of the methodology. The results show that the voltage fluctuations are small, which provides the DC microgrid with the required voltage stability. Moreover, it has been demonstrated that DC microgrids can be integrated in isolated locations that are not connected to the main grid in view of the RESs and EVs.This work belongs to the project SIS.JCG.19.03 from Universidad de las Américas - EcuadorBenamar, A.; Travaillé, P.; Clairand Gómez, J.; Escrivá-Escrivá, G. (2020). Non-Linear Control of a DC Microgrid for Electric Vehicle Charging Stations. International Journal on Advanced Science, Engineering and Information Technology. 10(2):593-598. https://doi.org/10.18517/ijaseit.10.2.10815S59359810

A common ground switched-quasi-Z-source bidirectional DC-DC converter with wide-voltage-gain range for EVs with hybrid energy sources

A common ground switched-quasi-Z-source bidirectional DC-DC converter is proposed for electric vehicles (EVs) with hybrid energy sources. The proposed converter is based on the traditional two-level quasi-Z-source bidirectional DC-DC converter, changing the position of the main power switch. It has the advantages of a wide voltage gain range, a lower voltage stress across the power switches, and an absolute common ground. The operating principle, the voltage and current stresses on the power switches, the comparisons with the other converters, the small signal analysis and the controller design are presented in this paper. Finally, a 300W prototype with Uhigh=240V and Ulow=40~120V is developed, and the experimental results validate the performance and the feasibility of the proposed converter

Differential Power Processing Converter Design for a Photovoltaic-Powered Charging Bag

Department of Electrical EngineeringTraditional photovoltaic (PV) systems are stationary PV systems mounted in one location and, generally, receive consistent and even illumination across the PV panels. However, solar photovoltaic (PV) power is also getting widely used in lower-power emerging applications, like wearables or internet of things (IoT) devices. One fundamental challenge of using PV power in wearable applications is that individual PV cells may be pointing in different angles, receiving different light intensities. Under these uneven illumination, resulting system efficiency depends on the configurations of the PV cells and converters. Through this thesis, the system efficiencies of five configurations are compared with nine realistic test cases. The five configurations are: PV in series with central converter, PV in parallel with central converter, PV with cascaded converters, PV in series with differential power processing (DPP) converters, and PV in parallel with DPP converters. The nine test cases are composed of an ideal case (all PV cells at 1,000 W/m2) and eight realistic illumination cases based on the weather (sunny or cloudy) and realistic usage scenarios. Based on these cases the system efficiency is calculated for each configuration considering a range of converter efficiencies (70% to 100%). Results show that the parallel DPP configuration shows the highest system efficiency in all cases. Parallel DPP converters can achieve individual PV control and maximizing output power by processing small fraction of the PV power. There are two types of parallel DPP architectures which are with and without a front-end converter. Two parallel DPP architectures are analyzed and compared for a target 5-W wearable application. Between the two architectures, the DPP system without a front-end converter shows consistently high performance and operates properly over a wider range of lighting conditions. Therefore, the proper operation, such as maximum power point tracking (MPPT) of PV cells, using parallel DPP converters without the front-end converter is validated through simulation and hardware experiments. The PV-powered wearable prototype is able to charge a portable battery under low-light and partial shading conditions.ope

Multi-objective day-ahead scheduling of microgrids using modified grey wolf optimizer algorithm

YesInvestigation of the environmental/economic optimal operation management of a microgrid (MG) as a case study for applying a novel modified multi-objective grey wolf optimizer (MMOGWO) algorithm is presented in this paper. MGs can be considered as a fundamental solution in order for distributed generators’ (DGs) management in future smart grids. In the multi-objective problems, since the objective functions are conflict, the best compromised solution should be extracted through an efficient approach. Accordingly, a proper method is applied for exploring the best compromised solution. Additionally, a novel distance-based method is proposed to control the size of the repository within an aimed limit which leads to a fast and precise convergence along with a well-distributed Pareto optimal front. The proposed method is implemented in a typical grid-connected MG with non-dispatchable units including renewable energy sources (RESs), along with a hybrid power source (micro-turbine, fuel-cell and battery) as dispatchable units, to accumulate excess energy or to equalize power mismatch, by optimal scheduling of DGs and the power exchange between the utility grid and storage system. The efficiency of the suggested algorithm in satisfying the load and optimizing the objective functions is validated through comparison with different methods, including PSO and the original GWO.Supported in part by Royal Academy of Engineering Distinguished Visiting Fellowship under Grant DVF1617\6\4

Advanced Power Loss Modeling and Model-Based Control of Three-Phase Induction Motor Drive Systems

Three-phase induction motor (IM) drive systems are the most important workhorses of many industries worldwide. This dissertation addresses improved modeling of three-phase IM drives and model-based control algorithms for the purpose of designing better IM drive systems. Enhancements of efficiency, availability, as well as performance of IMs, such as maximum torque-per-ampere capability, power density, and torque rating, are of major interest. An advanced power loss model of three-phase IM drives is proposed and comprehensively validated at different speed, load torque, flux and input voltage conditions. This model includes a core-loss model of three-phase IMs, a model of machine mechanical and stray losses, and a model of power electronic losses in inverters. The drive loss model shows more than 90% accuracy and is used to design system-level loss minimization control of a motor drive system, which is integrated with the conventional volts-per-hertz control and indirect field-oriented control as case studies. The designed loss minimization control leads to more than 13% loss reduction than using rated flux for the testing motor drive under certain conditions. The proposed core-loss model is also used to design an improved model-based maximum torque-per-ampere control of IMs by considering core losses. Significant increase of torque-per-ampere capability could be possible for high-speed IMs. A simple model-based time-domain fault diagnosis method of four major IM faults is provided; it is nonintrusive, fast, and has excellent fault sensitivity and robustness to noise and harmonics. A fault-tolerant control scheme for sensor failures in closed-loop IM drives is also studied, where a multi-controller drive is proposed and uses different controllers with minimum hand-off transients when switching between controllers. A finite element analysis model of medium-voltage IMs is explored, where electromagnetic and thermal analyses are co-simulated. The torque rating and power density of the simulated machine could be increased by 14% with proper change of stator winding insulation material. The outcome of this dissertation is an advanced three-phase IM drive that is enhanced using model-based loss minimization control, fault detection and diagnosis of machine faults, fault-tolerant control under sensor failures, and performance-enhancement suggestions

Diseño e implementación de un sistema de almacenamiento de energía bidireccional para una nanored DC

El presente documento muestra el proceso de construcción de un sistema de almacenamiento energético para una nano-red DC cuyo DC link se encuentra en 48 V. El documento inicia dando algunas definiciones básicas y necesarias, tales como nano-red, para desarrollar así el contexto que permita entender el papel que desempeña el sistema de almacenamiento de energía dentro de este tipo de redes y porqué la necesidad de enforcar esfuerzos en mejorar sus características de funcionamiento. Luego de esto se realiza una búsqueda bibliográfica de las topologías DC-DC bidireccionales en la que resumen sus principales propiedades eléctricas y se contrastan con las necesidades del proyecto, surgidas a partir los objetivos propuestos. Con esta comparación se evalúa cuál de las topologías estudiadas es la que mejor se adapta a los requerimientos del proyecto. Posteriormente, se desarrolla el modelo matemático del convertidor elegido, que incluye la batería a usar y su sistema de estimación de estado de carga. Una vez hecho esto, se desarrollan los controladores, se implementa el sistema y se realizan diferentes pruebas de laboratorio en las que se somete al sistema a diferentes situaciones para evaluar su rendimiento. De estas pruebas se encuentra niveles satisfactorios de regulación y robustez que le permiten operar al dispositivo en todo el rango planteado en los objetivos, reportando los respectivos tiempos de restablecimiento para cada uno de los casos y los sobrepicos generados en la transición de cambios tipo escalón. Finalmente se muestran las conclusiones surgidas a partir del análisis de los resultados obtenidos y donde se plantean posibles mejoras a tener en cuenta para trabajos futuros.Abstract: The present document shows the building process of an energy storing system for a DC nano-grid, whose DC-link is 48 V. This document starts off by giving some basic and necessary definitions, such as nano-grid, which is used to develop the necessary context that allow us to understand the roll of the energy storing system in the nano-grid. Then, it is explained why making efforts to improve the electrical features of this device. Later, in order to choose the most adequate topology, a literature search is carried out, where several DC-DC bidirectional converter topologies are analyzed and their features are compared to the project requirements. Next, the converter mathematical model is developed, including the battery model and its state of charge estimation system. Once this is done, the controllers are developed and the system and its subsystems are implemented. With the purpose of evaluate the device performance, this was tested to different operating condition. From this test, it can be said that the regulation and robustness system are adequate and allow it to operate in all operation range proposed in the objectives. Among the results of this test, the settling times and overshoots of each controller were reported. Finally, the conclusions of this work are shown and some suggestions for future works are presentedMaestrí

Bidirectional Electric Vehicles Service Integration in Smart Power Grid with Renewable Energy Resources

As electric vehicles (EVs) become more popular, the utility companies are forced to increase power generations in the grid. However, these EVs are capable of providing power to the grid to deliver different grid ancillary services in a concept known as vehicle-to-grid (V2G) and grid-to-vehicle (G2V), in which the EV can serve as a load or source at the same time. These services can provide more benefits when they are integrated with Photovoltaic (PV) generation. The proper modeling, design and control for the power conversion systems that provide the optimum integration among the EVs, PV generations and grid are investigated in this thesis. The coupling between the PV generation and integration bus is accomplished through a unidirectional converter. Precise dynamic and small-signal models for the grid-connected PV power system are developed and utilized to predict the system’s performance during the different operating conditions. An advanced intelligent maximum power point tracker based on fuzzy logic control is developed and designed using a mix between the analytical model and genetic algorithm optimization. The EV is connected to the integration bus through a bidirectional inductive wireless power transfer system (BIWPTS), which allows the EV to be charged and discharged wirelessly during the long-term parking, transient stops and movement. Accurate analytical and physics-based models for the BIWPTS are developed and utilized to forecast its performance, and novel practical limitations for the active and reactive power-flow during G2V and V2G operations are stated. A comparative and assessment analysis for the different compensation topologies in the symmetrical BIWPTS was performed based on analytical, simulation and experimental data. Also, a magnetic design optimization for the double-D power pad based on finite-element analysis is achieved. The nonlinearities in the BIWPTS due to the magnetic material and the high-frequency components are investigated rely on a physics-based co-simulation platform. Also, a novel two-layer predictive power-flow controller that manages the bidirectional power-flow between the EV and grid is developed, implemented and tested. In addition, the feasibility of deploying the quasi-dynamic wireless power transfer technology on the road to charge the EV during the transient stops at the traffic signals is proven