Showing papers presented at "International Symposium on Industrial Electronics in 2012"

Power electronics and reliability in renewable energy systems

Abstract: Power Electronics are needed in almost all kind of renewable energy systems. It is used both for controlling the renewable source and also for interfacing to the load, which can be grid-connected or working in stand-alone mode. More and more efforts are put into making renewable energy systems better in terms of reliability in order to ensure a high availability of the power sources, in this case the knowledge of mission profile of a certain application is crucial for the reliability evaluation/design of power electronics. In this paper an overview on the power electronic circuits behind the most common converter configurations for wind turbine and photovoltaic is done. Next different aspects of improving the system reliability are mapped. Further on examples of how to control the chip temperature in different power electronic configurations as well as operation modes for wind power generation systems are given in order to reduce the temperature cycling.

A new grid-connected PV system based on cascaded H-bridge quasi-Z source inverter

Abstract: A new scheme for grid-connected photovoltaic (PV) interface by combination of a quasi-Z source inverter (qZSI) into cascaded H-bridge (CHB) is proposed in this paper. The proposed scheme enables PV string voltage boost to a higher level, and solves the imbalance problem of DC-link voltage in traditional CHB inverters. A multilevel voltage waveform of inverter output is generated by an improved phase shifted sinusoidal pulse width modulation (PS-SPWM) algorithm, which introduces shoot-through states into the conventional zero states to control qZS-CHB module. The effective control schemes are proposed to regulate the maximum power point tracking (MPPT) of each string, and control the DC-link voltage of each H-bridge, respectively. Grid injected power is controlled corresponding to the proportionality factors of each PV string output power. A 1.5 kW system is built in MATLAB/SIMULINK, and the simulation results verify the proposed novel multilevel PV interface inverter and its control principles.

SoC-based droop method for distributed energy storage in DC microgrid applications

Abstract: With the progress of distributed generation nowadays, microgrid is employed to integrate different renewable energy sources into a certain area. For several kinds of renewable sources have DC outputs, DC microgrid has drawn more attention recently. Meanwhile, to deal with the uncertainty in the output of microgrid system, distributed energy storage is usually adopted. Considering that the state-of-charge (SoC) of each battery may not be the same, decentralized droop control method based on SoC is shown in this paper to reach proportional load power sharing. With this method, the battery with higher SoC supplies more load power, while the one with lower SoC supplies less load power. Different kinds of relationship between SoC and droop coefficient are selected and their performance of power sharing speed is evaluated. Small signal model of SoC-based droop method is reached to test the system stability. Theoretical analysis is validated by both simulation and experimental results.

Comparison of soft-switching voltage-fed and current-fed bi-directional isolated Dc/Dc converters for fuel cell vehicles

Abstract: This paper presents a comparison of two potential soft-switching bi-directional high-frequency transformer isolated voltage-fed and current-fed dc/dc converters for fuel cell vehicle application. The given comparison and discussion is suitable for a front-end dc/dc converter for a fuel cell inverter. The circulating and peak currents, components' ratings, size, losses, and efficiency are compared. Current-fed converter has been justified due to its merits over voltage-fed converter for the given applications. Experimental results of the current-fed converter have been illustrated. Switching losses are reduced a lot due to soft-switching of primary and secondary devices and higher efficiency. It allows high switching frequency operation, which results in compact and low cost system.

Modeling and online parameter identification of Li-Polymer battery cells for SOC estimation

Abstract: Finding an accurate and easily to implement model of batteries is an essential step in properly estimating the state of charge (SOC) of the battery in real-time. In this paper, an equivalent circuit based battery model with nonlinear relationship between the open circuit voltage (V OC ) and the SOC is projected into several piece-wise linear functions. Moving window Least Squares (LS) parameter identification technique is then utilized to estimate and update the parameters of the battery model in each sampling time. The continuously updated parameters are fed to a linear observer to estimate the SOC of the battery. The effectiveness of the proposed modeling and estimation approach are verified experimentally on Lithium Polymer batteries.

Secondary control for reactive power sharing in droop-controlled islanded microgrids

Abstract: This paper focuses on the islanded operation of microgrids. In this mode of operation, the microsources are required to cooperate autonomously to regulate the local grid voltage and frequency. Droop control is typically used to achieve this autonomous voltage and frequency regulation. However, droop control has real and reactive power sharing limitations when there are mismatches between the microsources. This paper analyses the effect due to mismatches in the power line impedances connecting the source inverters to the microgrid. From the simulations results obtained, it was shown that the reactive power demand is unequally shared between the microsource inverters when there are mismatches between the power line impedances. To achieve equal reactive power sharing between the inverters, an external loop requiring low bandwidth communications was implemented in a central controller. Simulation results are presented showing the feasibility of the proposed solution in achieving reactive power sharing between the inverters connected to the microgrid.

Characterization and modeling of silicon carbide power devices and paralleling operation

Abstract: This paper presents recent research on several silicon carbide (SiC) power devices. The devices have been tested for both static and dynamic characteristics, which show the advantages over their Si counterparts. The temperature dependency of these characteristics has also been presented in this paper. Then, simulation work of paralleling operation of SiC power MOSFETs based on a verified device model in Pspice is presented to show the impact of parasitics in the circuit on the switching performance.

No-Load Performance of Axial Flux Permanent Magnet Machines Mounting Magnetic Wedges

Abstract: Axial flux permanent magnet (AFPM) machines are being increasingly used in a variety of industrial, direct drive applications which benefit from their extreme axial compactness. In particular, slotted AFPM machines are of great interest, since they allow to achieve high torque densities together with an adequate constant power speed range. This paper analyzes a particular aspect related to the design of such machines, i.e. the use of soft magnetic composite (SMC) wedges to close stator slots. Magnetic circuit-based analyses and 2-D and 3-D finite-element analyses are performed on a 10 kW AFPM machine; various magnetic wedge configurations are adopted; the no-load performance is compared with that of the same machine using nonmagnetic wedges in terms of flux linkage, cogging torque, and no-load losses. Finally, experimental tests and results on a full-scale prototype machine mounting magnetic wedges are reported.

Control method of the transient compensation process of a hybrid energy storage system based on battery and Ultra-capacitor in Micro-grid

Abstract: This paper mainly presents the research on the hybrid energy storage system in a Micro-grid with a DC Bus and an AC bus. The storage system is based on battery and Ultra-capacitor. When a sudden load was switched into the Micro-grid, the voltage of the DC Bus should be maintained to avoid stability problems. To fulfill the requirement, a parallel structure of two bi-directional DC/DC converters has been chosen for and also a control method has been proposed. Simulation results have proved that the energy storage system designed and the control method proposed are applicable and effective for the Micro-grid.

Decoupled current control of modular multilevel converter for HVDC applications

Abstract: The continuous growing of energy market prompt for energy sources every time more distant to energy consumption centres. In this scenario, high voltage DC systems have proved to be the best alternative to transmit power over long distances. Among the different converter topologies used in HVDC systems, the modular multilevel converter provides the highest modularity, reliability, availability and power quality. These converters usually have a complex control scheme, due to the coupled currents and the DC voltage balance. This paper is focused on the control of currents and average voltage proposing a decoupled control of output, input and circulating current components which simplifies drastically the control scheme. Simulation results using a MMC with 200 cells per arm show the performance of the proposed scheme.

Real-time grid impedance estimation technique for grid-connected power converters

Abstract: Grid impedance is one of the most important parameters for operating and controlling of grid-connected converters, especially with the high penetration of renewable energy sources into microgrid and smart grid. One of the technical challenges is how to fast and accurately estimate the grid impedance, even under the distorted and unbalanced conditions. Many impedance estimation methods have been presented in the past decades. Most of them intentionally inject one or more disturbance signals, low frequency or high frequency, to excite the grid response. And then the grid impedance can be estimated by the voltage/current information of two steady-state operating points before and after the disturbance. However, these injected disturbances will deteriorate the power quality. In order to mitigate the problem, a new impedance estimation method is presented in this paper. Its basic idea lies in the inherent switching feature of the grid-connected power converter. Therefore, the grid impedance can be easily estimated with no need of the intentionally injected disturbance signals anymore. The theoretical analysis and performance evaluation results verify the effectiveness of the proposed method.

MoBots: A new generation of botnets on mobile devices and networks

Abstract: Mobile devices are now well integrated with advanced capabilities and technologies such as the Internet. Today, mobile security has become a globally critical issue due to the high usage of mobile devices, their convenience and mobility. However, they are not properly protected compared to computer and computer networks, and the users pay less attention to the security updates. Recently, mobile devices and networks have been targeted by one of the most dangerous cyber threats, known as botnets. Mobile botnets have not yet been fully explored as they have only recently migrated to mobile infrastructures. Therefore, in this paper, we present an overview of mobile botnets including studies on the new command and control mechanisms, actual examples and malicious activities. We also review the current challenges and limitations of botnet detection in mobile environments, as well as existing solutions.

A lightweight and secure TFTP protocol for smart environment

Abstract: “Internet of Things” (IOT) has become the everyday buzz words in recent years. As part and parcel of the Smart environment where human beings and things interact intelligently, trust and mobility becomes the basic prerequisites. However, to unify trust and mobility, a security protocol must be used for information exchanges among human and things; as well as between things and things (such as between Wi-Fi Client and Wi-Fi AP). In this paper, we present an enhancement of a security protocol for bulk data transfer amongst embedded devices (similar to the practices in IOT). We also proposed a security framework for enhancing security, trust and privacy (STP) for embedded system infrastructure. We suggested the use of lightweight symmetric encryption (for data) and asymmetric encryption (for key exchange) protocols in Trivial File Transfer Protocol (TFTP). The target implementation of TFTP is for embedded devices such as Wi-Fi Access Points (AP) and remote Base Stations (BS). We have chosen Das U-Boot (Universal Boot loader) as the horizontal security platform for this new security implementation which is suitable for Smart Environment.

Control of the active and reactive power using dq0 transformation in a three-phase grid-connected PV system

Abstract: This paper presents a three-phase grid-connected photovoltaic generation system with unity power factor for any situation of solar radiation. The modelling of the PWM inverter and a control strategy using dq0 transformation are proposed. The system operates as an active filter capable of compensate harmonic components and reactive power, generated by the loads connected to the system. An input voltage clamping technique is proposed to control the power between the grid and photovoltaic system, where it is intended to achieve the maximum power point operation. Simulation and experimental results are presented to validate the proposed methodology for grid connected photovoltaic generation system.

Adaptive voltage estimation for EV Li-ion cell based on artificial neural networks state-of-charge meter

Abstract: This paper reports some results relating to adaptive cell modeling from neural network state-of-charge (SOC) estimation in a full-electric-vehicle (EV) application. The cells in question are commercialized ones, Lithium-ion Polymer based, with a nominal capacity of about 100 Ah and dedicated to energy applications. Using a recurrent neural network, we developed a SOC predictor that takes into account operational conditions. More importantly, the predictor allows very precise SOC estimation, therefore allowing the vehicle controller to confidently use the battery pack's full operating range without problem of over- or under-charging cells. In this work, the estimated SOC values helped to estimate the parameters of an adaptive-dynamic battery model using RLS algorithm with time-dependent forgetting factor. Simulation results confirmed the accuracy of the terminal voltage estimation of the battery.

Rough design of a Double-Stator Axial Flux Permanent Magnet generator for a rim-driven Marine Current Turbine

Abstract: This paper deals with the rough design of a Double-Stator Axial Flux Permanent Magnet Machine (DSAFPM) for a rim-driven Marine Current Turbine (MCT). The DSAFPM machine will be compared to a previously developed and realized Radial Flux Permanent Magnet Machine (RFPM); given the same rim-driven MCT specifications. For that purpose, a first-order electromagnetic design model and a thermal one are developed and used to compare active part mass, cost, and thermal behavior of the two machines. The obtained results show that such a structure of poly-air gap axial flux machine can be more interesting in terms of compactness and thermal behavior for rim-driven marine current turbines.

Texture feature extraction using 2-D Gabor Filters

Abstract: Texture feature extraction is a procedure of computing and describing the features and characteristics of image which numerically describes that texture image properties. This paper investigated texture feature extraction using 2-D Gabor Filter to extract the texture features of Inverse Fast Fourier Transform (IFFT), texture energy and transformed IFFT. The Gabor filter bank experimented on seventy two collected samples of skull-stripped T1-weighted, T2-weighted and FLAIR MRI brain images utilizing four frequencies and four orientations. Results showed that texture feature extractions of two highest frequencies with all four orientations produced the highest acceptance rate.

Novel cost-efficient contactless distributed monitoring concept for smart battery cells

Abstract: The market breakthrough of electric vehicles is mainly delayed by the still too high costs of the battery system. The novel distributed battery cell monitoring and management concept presented in this paper allows a significant reduction of the final battery pack costs. Further, due to economies of scale, it provides reduced development costs and much lower time-to-market. The proposed concept provides a contactless cost-efficient data transmission interface with capacitive coupling, thus making the development of a battery monitoring circuit for each battery module type needless. The costs are mainly reduced thanks to the high volume manufacturing approach of novel smart battery cells integrating all the sensors of the monitoring electronics together with passive cell balancing and cell heating function. This paper describes the possibilities offered by the proposed concept and shows implementation examples of such a contactless distributed battery cell monitoring.

State of the art of fuel cells for ship applications

Abstract: Fuel cells promise to be far more efficient, produce lower or zero emissions, and operate cleaner than conventional internal-combustion engine and gas turbine. They are already used for transportation application (buses, cars and tramways). Fuel cells can also be an interesting solution for ships power. However the developments of fuel cell systems for ship are in infancy. The only exception is the PEMFC in the submarines. This solution allows obtaining an air-independent propulsion (AIP) system, which has been adopted in several countries. This paper presents a comprehensive review of different fuel cells and their application on ships. The pro and the cons of the use of fuel cell in ship application are discussed particularly in terms of lifetime and cost.

A survey on ellipse detection methods

Abstract: Ellipses and elliptical features are evident in abundance, in a wide variety of digital images. Much of these features carry within itself useful statistical and geometrical information that can be exploited for a broad range of real-world applications. Algorithms developed of late for ellipse detection are application specific and are mainly based on traditional least-square fitting and Hough transform methods. This, in essence, is a step away from building a fully autonomous system with ellipse detection capabilities. This review attempts to redirect the research focus back towards a common goal of generating new ideas through the introduction of a modular framework.

Short circuit current analysis of DFIG-type WG with crowbar protection under grid faults

Abstract: For doubly fed induction generator (DFIG) based wind power systems, rotor crowbar is a commonly used protection method against rotor surge current during low voltage ride-through (LVRT) periods. One of the basic problems is the rotor surge current characteristic analysis of DFIG, the other is the investigation of effective crowbar circuit and appropriate control methods. Based on the detailed analysis of the complete stator and rotor flux response of DFIG after crowbar fired, a time domain analytical expression of the short circuit current of DFIG applied to (a) symmetrical grid faults is proposed. In order to improve the stator terminal power characteristic of DFIG during crowbar fired, a novel crowbar consisting of resistance in series with capacitor is proposed, and the capacitor value selection method is also given. A typical 1.5 MW DFIG wind energy conversion system is used for case study. The analysis and simulation results validate the accuracy of the analytical expression of the short circuit current and the effectiveness of the proposed novel crowbar.

Modelling and fuzzy logic control of DFIG based Wind Energy Conversion Systems

Abstract: This paper proposes the modelling and control of Wind Energy Conversion Systems (WECS) based on Doubly Fed Induction Generator (DFIG). The fuzzy logic control is used to improve the extracted wind power. At given wind velocity, the mechanical power available from a wind turbine is a function of its shafts speed. Then, the rotor side converter (RSC) is controlled in the aim to follow the optimal torque for given maximal wind power. A new maximum power point tracking (MPPT) strategy based on the fuzzy logic controller was developed. Moreover, a new approach to estimate the speed from the measurement of the power is presented. The effectiveness of the proposed control strategies is validated by theoretical analysis and simulation carried out in Matlab/Simulink environment.

A genetic algorithm for the Dubins Traveling Salesman Problem

Abstract: In this paper the authors study the Traveling Salesman Problem for the Dubins vehicle (DTSP). A genetic algorithm is designed to find the shortest path for DTSP and the performance is evaluated in numerical study. The proposed algorithm can perform better than the well-known Alternating Algorithm and Random Headings Algorithm, in both low waypoint density and high waypoint density situations.

Dynamic Programming Algorithm for minimizing operating cost of a PEM fuel cell vehicle

Abstract: A PEM (Proton Exchange Membrane) fuel cell city bus utilizes a PEM fuel cell engine as the primary source, and a li-ion battery system as the auxiliary power source. By optimizing the power split strategy and recycling braking energy, this kind of power-train has advantages of zero emission and high energy efficiency. However, the cost of hydrogen gas is far more expensive than that of the electric energy. How to split the power between the two power sources so as to minimize the operating cost, as well as guarantee the vehicle dynamic performance, becomes an important topic. This paper proposes a Dynamic Programming Algorithm (DPA) to solve the minimizing problem. Some details of the DPA are discussed, e.g. the principles of selecting parameters for the algorithm. The effectiveness of the algorithm is verified by comparing simulating results of different algorithms. Results show that, 1) by using the DPA algorithm, we can find the optimal control strategy in an objective way. 2) The constraints of vehicle dynamic performance on the optimal problem have great influences on the optimal results. 3) To predict the power requirement in the near future is very important to achieve an optimal real-time strategy.

License plate detection using Haar-like features and histogram of oriented gradients

Abstract: The Haar-like cascaded classifier has been used in license plate detection and yields a high detection rate, but it often has high false positives. We introduced a classifier which was trained through histogram of oriented gradients (HOG) features to judge the likelihood of candidate plates detected by Haar classifier, and selected the candidate with highest likelihood as the final plate, in order to reduce the false positives. This method was tested on 3000 images to obtain a recall rate of 95.2%, and accuracy of 94.0% as opposed to 66.4% without using HOG features. It was shown that the proposed method is able to eliminate most of the false candidate plates, such as barriers and incomplete plates.

Energy harvesting for Wireless Sensors from electromagnetic fields around overhead power lines

Abstract: In this paper, capacitive and inductive energy harvesting devices are proposed to extract energy from the electric and magnetic fields surrounding 132kV overhead transmission lines. Research has been done to determine what parameters affect these energy harvesters. In-lab testing has been done on both the inductive and capacitive energy harvesters and results look promising. A single IC solution for 3.3V voltage regulation and energy storage was also tested.

DC voltage balance control in a modular multilevel cascaded converter

Abstract: Modular multilevel cascaded converter provides high modularity, availability, and high power quality, being specially suited for high voltage DC transmission systems. However, DC voltage balance and circulating currents require a high performance controller which take into account both, the internal dynamics and also the external dynamics like input and output currents. This paper is focused on the DC voltage balancing strategy where a two stage approach is presented. The first stage performs the control of DC voltages inside each arm, achieving a high dynamics which makes the model of each arm as simply as only one cell. The second stage controls the balance between arms adding a common mode term from the arm voltages, modifying the arm current and power, but without producing a change in the output voltage. Simulation results shown the performance of the proposed strategy when it is included into a complete modular multilevel converter control scheme.

A novel zero-current-detector for DCM operation in synchronous converter

Abstract: Discontinuous-conduction mode (DCM) operation is usually employed in DC-DC converters for small inductor on printed circuit board (PCB) and high efficiency at light load. However, it is normally difficult for synchronous converter to realize the DCM operation, especially in high frequency applications, which requires a high speed and high precision comparator to detect the zero crossing point at cost of extra power losses. In this paper, a novel zero current detector (ZCD) circuit with an adaptive delay control loop for high frequency synchronous buck converter is presented. Compared to the conventional ZCD, proposed technique is proven to offer 8.5% efficiency enhancement when performed in a buck converter at the switching frequency of 4MHz and showed less sensitivity to the transistor mismatch of the sensor circuit.

Improvement of operating performance for the wind farm with a novel CSC type wind turbine-SMES hybrid system

Abstract: The purpose of this paper is to propose and analyze the high-performance control strategies for a novel current source converter (CSC) based wind turbine-superconducting magnetic energy storage system (SMES) hybrid system, which in turn improves the operating performance for the whole wind farm, not only in the grid-connected operation, but also in the islanding operation. The key is to design the effective active power controller and the AC bus voltage controller for the grid-connected CSC based hybrid system, in such a way that the better power smoothing performance and robust operation under faulty grid voltage can be achieved. Furthermore, the capacitor voltage control scheme is proposed for the CSC hybrid system to offer the effective operation for the wind farm in the islanding operation. Based on simulation, the CSC based wind turbine-SMES hybrid system has been verified to provide improved operating performance for the wind farm with the proposed control schemes.

A surveillance task for a UAV in a natural disaster scenario

Abstract: This paper presents a design for an unmanned aerial vehicle (UAV) with a modular embedded architecture. This research is structured in three stages: (a) embedded systems, (b) communications link and (c) inertial navigation system. Systems integration was satisfactorily implemented and several remotely controlled flight tests were conducted. Finally, real time experiments were conducted during an environmental disaster in mountainous region, making aerial reconnaissance of areas devastated by mudslides. In this test the system has shown to be adequate and robust.