Sistemas híbridos de almacenamiento no convencionales orientados a aplicaciones móviles

La industria automotriz se ha convertido en una de las industrias más importantes a nivel mundial, no solo económicamente, sino también por su impacto en el sector de investigación y desarrollo. Además, hay una cantidad cada vez mayor de vehículos en las calles, lo que nos permite movernos de forma rápida y cómoda. Sin embargo, esto ha generado un aumento dramático de los niveles de contaminación en el aire en zonas urbanas (por ejemplo, de partículas finas, óxidos de nitrógeno, monóxido de carbono, dióxido de azufre, etc.). Por lo tanto, las autoridades de las naciones más desarrolladas están alentando el uso de vehículos eléctricos (EVs, del inglés Electric Vehicles) para disminuir la concentración de contaminantes en el aire, CO2, así como otros gases de efecto invernadero. Estos vehículos eléctricos deben poseer un sistema de almacenamiento de energía con alta densidad de energía másica para permitir una distancia de manejo larga, y alta densidad de potencia másica para la aceleración, frenado y manejo en ascenso. Sin embargo, las baterías actuales no pueden satisfacer ambos requerimientos al mismo tiempo. Por lo tanto, es necesario crear un sistema que reúna dos o más dispositivos cuyas características cumplan al menos una necesidad de los EVs. Combinar componentes en sistemas híbridos para aprovechar los beneficios de cada parte siempre fue una perspectiva atractiva. En los últimos años, varios proyectos han sido exitosos en construir estos sistemas híbridos de almacenamiento de energía para energía solar y eólica. Aunque la idea no es nueva, la tecnología aún se encuentra en una fase temprana. Los sistemas híbridos de almacenamiento de energía (siglas HESS, del inglés hybrid energy storage systems) pueden referirse a distintos tipos de arreglos, con lo único en común siendo que dos o más tipos de almacenamiento de energía son combinados para formar un único sistema. En este contexto, este trabajo tiene por objetivo realizar un estudio de un tipo de sistema híbrido particular, en el cual se combinan baterías de litio y supercapacitores para aplicaciones móviles. En los primeros tres capítulos se brinda una introducción a los elementos fundamentales en los que se basa este trabajo: los sistemas de almacenamiento, los convertidores electrónicos CC-CC utilizados para poder crear el sistema híbrido, y finalmente la arquitectura digital utilizada para implementar el sistema de control. Luego, a partir de los requerimientos dados para el sistema, se diseña e implementa un sistema de control propuesto. Por último, se realizan una serie de ensayos para corroborar el correcto funcionamiento del sistema a lazo cerrado de control.Facultad de Ingenierí

Designing a Smart Inverter for Voltage Sag Compensation Due to Motor Start-up

Starting a large induction motor will always follow up with an inrush current as the nature of an induction motor. On a less stiff power system, that inrush current will be causing a Voltage Sag (VS). A big VS can lead to significant disruptions in power quality and reliability. To address this, a Smart Inverter with an Artificial Intelligence (AI) -driven controller installed in a Photovoltaic (PV) farm is proposed for voltage sag recovery. During normal conditions, the PV farm acts as a power source supporting the main grid, but when large induction motors are started, the smart inverter connected to the PV is responsible for power conversion to recover sags caused by the Induction motor inrush current. The controller inside the Inverter ensures optimal operation. The use of AI also compares the effectiveness of using the Fuzzy Logic Controller (FLC) with the Proportional Integral (PI) Controller to assess their performance in reducing current spikes. Based on simulations, the FLC outperformed PI Controller in mitigating the voltage sag and avoiding the Low Voltage Ride-Through (LVRT). Simulation results show that voltage sag can be recovered for up to 97% of the nominal voltage, a significant improvement over the 80% sag recovery without the smart Inverter. At a nominal grid voltage of 6,600 volts, the VS Magnitude was successfully increased from 5,210 volts to 6,368 volts and the VS Duration also decreased from 6.96 s to 4.97 s. The results achieved validate the effectiveness of the approach in improving the power quality

CONTROL STRATEGIES OF DC MICROGRID TO ENABLE A MORE WIDE-SCALE ADOPTION

Microgrids are gaining popularity in part for their ability to support increased penetration of distributed renewable energy sources, aiming to meet energy demand and overcome global warming concerns. DC microgrid, though appears promising, introduces many challenges in the design of control systems in order to ensure a reliable, secure and economical operation. To enable a wider adoption of DC microgrid, this dissertation examines to combine the characteristics and advantages of model predictive control (MPC) and distributed droop control into a hierarchy and fully autonomous control of the DC microgrid. In addition, new maximum power point tracking technique (MPPT) for solar power and active power decoupling technique for the inverter are presented to improve the efficiency and reliability of the DC microgrid. With the purpose of eliminating the oscillation around the maximum power point (MPP), an improved MPPT technique was proposed by adding a steady state MPP determination algorithm after the adaptive perturb and observe method. This control method is proved independent with the environmental conditions and has much smaller oscillations around the MPP compared to existing ones. Therefore, it helps increase the energy harvest efficiency of the DC microgrid with less continuous DC power ripple. A novel hierarchy strategy consisting of two control loops is proposed to the DC microgrid in study, which is composed of two PV boost converters, two battery bi-directional converters and one multi-level packed-u-cell inverter with grid connected. The primary loop task is the control of each energy unit in the DC microgrid based on model predictive current control. Compared with traditional PI controllers, MPC speeds up the control loop since it predicts error before the switching signal is applied to the converter. It is also free of tuning through the minimization of a flexible user-defined cost function. Thus, the proposed primary loop enables the system to be expandable by adding additional energy generation units without affecting the existing ones. Moreover, the maximum power point tracking and battery energy management of each energy unit are included in this loop. The proposed MPC also achieves unity power factor, low grid current total harmonics distortion. The secondary loop based on the proposed autonomous droop control identifies the operation modes for each converter: current source converter (CSC) or voltage source converter (VSC). To reduce the dependence on the high bandwidth communication line, the DC bus voltage is utilized as the trigger signal to the change of operation modes. With the sacrifice of small variations of bus voltage, a fully autonomous control can be realized. The proposed distributed droop control of different unit converters also eliminates the potential conflicts when more than two converters compete for the VSC mode. Single-phase inverter systems in the DC microgrid have low frequency power ripple, which adversely affects the system reliability and performance. A power decoupling circuit based on the proposed dual buck converters are proposed to address the challenges. The topology is free of shoot-through and deadtime concern and the control is independent with that of the main power stage circuit, which makes the design simpler and more reliable. Moreover, the design of both PI and MPC controllers are discussed and compared. While, both methods present satisfied decoupling performances on the system, the proposed MPC is simpler to be implemented. In conclusion, the DC microgrid may be more widely adopted in the future with the proposed control strategies to address the current challenges that hinder its further development