Lucas V. Hartmann

Combining Model-Based and Heuristic Techniques for Fast Tracking the Maximum-Power Point of Photovoltaic Systems

This paper proposes a technique for accelerating the convergence to the maximum power point of photovoltaic (PV) systems based on the model obtained from manufacturers generator data. The influence of the temperature over the PV array performance is considered, and no measurement of solar radiation is required. Knowledge of the load model and expensive sensor circuitry are not necessary. The tracking speed is much faster than nonmodel-based techniques at the expense of an increase in the computational complexity. Simulation and experimental results are presented and demonstrate the feasibility of the proposed solution.

Using the model of the solar cell for determining the maximum power point of photovoltaic systems

This paper proposes a technique for accelerating the convergence to the maximum power point of photovoltaic (PV) systems based on the model obtained from manufacturers generator data. The influence of the temperature over the PV array performance is considered, and no measurement of solar radiation is required. No knowledge of the load model and no expensive sensor circuitry are necessary. The tracking speed is much faster than non model-based techniques at the expenses of an increase in the computational complexity. Simulation and experimental results are presented and demonstrate the feasibility of the proposed solution.

Single-phase current source converter with new modulation approach and power decoupling

In this work it is presented a Current Source Converter (CSC) topology that helps to mitigate double line frequency power ripple (low frequency) effect. Low frequency power ripple presented in single-phase systems propagates through DC-bus converter. This low frequency ripple reduction allows to increase the power converter density by reducing the volume of the DC inductor, without lack of stiffness at the DC-bus. The low frequency mitigation is achieved by using a different single-phase CSC topology that uses three series-connected switches per leg. Thus, it allows independent control for two merged CSCs which share the same DC-bus and the middle switches of the leg. This solution is adequate to connect photovoltaic panels to the electrical grid, among others applications. Evaluation of such a solution by assuming grid modeling is useful and may require powerful simulation tools such as real-time simulator. In order to comply with power processing restrictions, a low frequency model is derived. Performance of both models (high and low frequency) are compared to ensure usability of the low frequency model. Control strategies and modulation are presented. Simulation results are provided to validate the theoretical approach, and real-time simulation results, as well.

Double four-quadrants single-phase current source converter sharing the same DC-bus

In this work it is presented a novel topology of Current Source Converter (CSC) that allows to control two single-phase AC converters independently sharing the same DC-bus, with the advantage of having a reduced number of conducting switches, less switching and a lower DC-bus current. A conventional double single-phase CSC that uses the same DC-bus needs to have two two-legs (H-bridge) converters connected in series, which means that it will always have four conducting switches. The new topology proposed allows to generate any two AC output currents with the same number of switches, however having always only three conducting switches in a switching period, representing 25% less conducting losses comparing on the equivalent conventional double single-phase CSC. It is also presented a Scalar Pulse Width Modulation (SPWM) and Space Vector Modulation (SVM) to control the converters with switching optimization, which reduces the switching losses. Details of topology, control strategy and modulation are presented. Simulation results are provided to validate the theoretical approach.

Lead acid battery SoC estimation based on extended Kalman Filter method considering different temperature conditions

State of Charge (SoC) is the most important parameter to be estimated on a Battery Management System (BMS). Improper SoC management can cause faster battery degradation, reduce its operational lifetime and, on extreme cases of overcharge, it may lead to an explosion. In addition, batteries are complex electrochemical systems, and both the electrical components and chemical reactions vary significantly with changes in temperature. In this paper, it is presented the effect of the temperature on the Lead Acid battery SoC estimation. The data collection was performed varying the battery temperature, under a range of 10oC to 70oC. To determine the model parameters from the used battery, several data acquisition was performed. To obtain the SoC estimation it was implemented the Extended Kalman Filter that provide satisfactory results. The simulated results were obtained using the MATLAB environment. To verify the effectiveness and the performance of the implemented Kalman Filter it was applied the EKF for estimate the SoC of a Lead Acid battery described in the Introduction Section. It is important to realize that is a comparative study and the only evaluation comparison with the SoC estimation that we can do uses the Open Circuit Voltage (OCV).

Design of an intelligent electronic device based on TivaC platform for smart grid applications

Smart Grid (SG) can be defined as a modern electric power grid infrastructure for improved efficiency, reliability and safety, with smooth integration of renewable and alternative energy sources, through automated control and modern communications technologies. The increased need for more effective control on electrical power systems has led to the development and the increased research interest on SG. The construction of SG involves the positive transformation of traditional electricity networks, with one-way power flow, to a system with a new technology, by adding intelligent sensors, distributed generation and storage system, back-end information systems, smart meters and communications networks, to permit two-way power flow with communication and control. All this information should be obtained from the network. So, the development and implementation of Intelligent Electronic Device (IED) improves the efficiency, reliability and security of the electric power system. This paper presents the development of an IED, based on TivaC platform for Smart Grid applications, with high capacity processing, communication features, portability/versatility, low cost, easy integration (interoperability) and maintenance. For the communication the proposed IED uses the Hybrid Network Architecture (HNA) concept and open source programming.

Design and implementation of a flexible intelligent electronic device for smart grid applications

According to the International Energy Agency/USA (lEA): “a smart grid (SG) is an electricity grid that uses digital technology to monitor and manage the transportation of electricity from all sources of generation, finding a variety of demands and users. These networks will be able to coordinate the needs and capabilities of all generators, operators, end-users and stake holders of the electricity market in order, to optimize the use and operation of the assets in the process, minimizing environmental costs and impacts while maintaining reliability, resilience and stability of the system”. The increasing need for more effective power electrical systems (generation, transmission and distribution) control has made the development of SG the main object of study for many researchers. In this context and looking for the integration and convergence of different systems to incorporate an infrastructure of a SG, this work designs and implements an flexible intelligent electronic device (lED). The proposed lED differs from the existing lEDs presenting a flexible capacity, as it can perform the acquisition of different variables (voltage, current, temperature, pressure, etc.) with different conditioning values, furthermore, the conditioning is carried out by software. The IED can operate as a smart meter, as a dynamic controller (local) and/or as a supervisory controller, thus improving the efficiency, reliabihty and security of the system. Other advantages of the proposed lED are: low cost, versatility (changes can be made by software), high processing capacity (ARM processor), communication features (hybrid network architecture (HNA)), easy integration (interoperability), easy maintenance (modularity) and scalability.

Estimation of lithium-ion battery model parameters using experimental data

Lithium battery cells are commonly modeled using an equivalent circuit with large lookup tables for each circuit element, allowing flexibility for the model to match measured data as close as possible. Pulse discharge curves and charge curves are collected experimentally to characterize the battery performance at various operating points. It can be extremely difficult to fit the simulation model to the experimental data using optimization algorithms, due to the number of values in the lookup tables. This paper describes a detailed procedure of how estimate the battery model parameters using experimental data. the experiment is realized with a computer that realize the control of charge and discharge process sending SCPI commands via serial communication to the Four Quadrant Power Supply from Kepco Inc. with 100V and 10A as limits. The estimation of each battery model parameter is made to lithium-ion battery with a capacity of 20 Ah, and the presented methodology can be easily adapted to any type of battery. The mean objective of the results is estimate the battery parameters to posteriorly use the battery model to estimate the SoC by adaptive method. As results, after the estimation of each parameter, it is possible to observe the resistances exponential behavior, where they decrease as SoC decrease. As conclusions, this paper can contribute to the field of measurement of magnetic and non electric quantities, where it helps to determine the Battery Equivalent Circuit Model and its parameters.

A simple circuit for characterization of photovoltaic module under uniform radiation and shading conditions

This paper proposes a practical method for characterization of photovoltaic (PV) systems under uniform radiation and under shading conditions, based on voltage and current graphics. A simple circuit to detect these shading conditions is projected to enhance the visualization of disturb caused by blocking one or more cells of the PV module. Therefore, this circuit is very interactive, because the curve changes instantly when the shading condition occurs. Thanks to it, this project is quite useful for educational purposes, in study of characterization of photovoltaic systems curves. The characteristic curves of the PV system under uniform radiation are necessary to compare with experimental results. Using an oscilloscope, the curves of a PV module under uniform radiation and partial shading are analyzed.

Network-capable smart batteries for smart grid and battery management systems

This paper presents a low cost Battery Information System, based on intelligent modules to be embedded inside single battery cells. The module design is cost-optimized, including only minimal functionality to uniquely identify each cell, and measure voltage and temperature. Current measurement is accomplished be an addition module added to each series-connected battery stack, avoiding unnecessary cost of redundant current sensors. Data from several modules is aggregated via a time-triggered proprietary wireless network, and then relayed to a remote, centralized server over standard TCP/IP WiFi connection. The remote battery database is supposed to be installed at the battery manufacturers server, and can potentially aggregate data from all manufactured batteries. Such an extensive database is expected to enable advanced analysis and modeling of batteries, as well as provide online monitoring and reporting services as an added value for customers.