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One-stage and two-stage grid connected PV systems are compared in terms of compactness for both, 1000-V and 1500-V PV string voltage levels. Design space of the inverter’s output filter is investigated for case when dc bus voltage is very well controlled to its minimum value and when it varies in the full operating range. Full multivariable optimization is conducted for the analyzed design spaces in order to investigate possible compensation of the increase of the total system volume caused by the addition of a dc/dc stage by achieving more compact inverter stage for better controlled dc bus voltage. It is concluded that for the same efficiency, filter designs with lower dc bus voltage can occupy $\approx$ 50% less volume compared to the case when dc bus varies in the full operating range. Hybrid, multilevel, partial power processing topologies that employ new classes of 650-V and 900-V WBG devices, that are already reported in the literature and that occupy $\approx$ 0.8 -0.9dm 3 for the design rated for 1500-V PV system and 20kW of the output power are very good candidates for a dc/dc stage that can control dc bus voltage at the input of the inverter stage and that can improve significantly compactness of the inverter stage and of the whole system. All the analysis and estimations are justified by comprehensive simulations of the 1500-V grid-connected PV inverter in PSIM package.

Different architectures of 1000VDC and 1500VDC grid-connected PV systems for different AC grid voltage levels are compared in this paper with respect to energy harvesting during one year period. One stage architecture is compared with two two-stage concepts already presented in literature and industry - "mini-boost" and "string-optimizer". An idea of mini-boost considers a booster rated for a portion of the nominal power that operates only in the cases when MPP voltage is lower than minimum allowed DC bus. Otherwise it is by-passed and the inverter operates as in one-stage architecture. Another concept, "string-optimizer" can be considered as a buck-boost topology that controls DC bus voltage at the minimum value. In this way range of energy harvesting operation is increased and performances of the inverter are improved. However, buck-boost topology is less efficient than a boost and, additionally in this case, it needs to be rated for the full system power. All the analysis and comparison is based on comprehensive PV panel and converter loss models, real enviromental conditions measurements and real and commercially available circuit components. Experimental verification of the employed models is provided by the measurements conducted on 22kW grid-tied solar inverter.

Purpose:To compare rotational stability, centration and visual outcomes provided by three trifocal lens models that have the same optical zone design but different material, composition, and/or toricity.Methods:The study included 78 patients with symmetric bilateral intraocular lens implantation. The lenses under evaluation were trifocal intraocular lenses made of hydrophilic acrylic material: a spherical lens 26% hydrophilic acrylic (POD FineVision), a similar lens but having a toric design (POD Toric FineVision), and a trifocal lens 25% hydrophilic acrylic material (FineVision/MicroF). Moreover, the lenses share the same optical zone design. The lenses’ rotational stability and centration were measured by means of the PIOLET software, which relies on recording and image processing techniques to determine lens rotation and centration based on slit-lamp images. We also assessed patients’ visual quality by means of 25, 40, and 80 cm VA tests.Results:The best centration results were achieved with the POD Toric FineVision model, although the differences were not statistically significant. As for lens rotation, it was below 5° in all cases under study. Regarding VA, all subjects attained at least 0.3 logMAR for far distance uncorrected VA, at 80 cm VA was about 0.2 logMAR, at 40 cm it was above 0.15 logMAR, and at 25 cm it was about 0.3 logMAR for both lens types.Conclusion:All three intraocular lens models yield excellent visual results at far, near as well as intermediate distances. The POD FineVision and POD Toric FineVision models, with double C-loop design, yielded the best results centration-wise and rotation-wise. Differences had no clinical relevance.

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other work This paper presents a current controller that shapes, in the frequency domain, the input admittance of voltage-source converters connected to the grid. The controller is obtained by means of a H8 synthesis procedure, which minimizes the difference between the application closed-loop input admittance and a model-reference defined by the designer. This formulation achieves good accuracy in both modulus and phase. The proposed methodology allows the fulfilment of other current control objectives, such as current tracking, by defining frequency regions where each objective is desired. Experimental results show the good response of the proposed controller, both in frequency and time domain _

© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting /republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works This paper presents a grid current control of a grid connected Voltage Source Converter (VSC) with an LCL filter. The control method enables to shape the input admittance of the converter in addition to track a given current reference. By specifying a low resistive admittance profile, a suitable controller is obtained by using an H8 synthesis, which will actively damp the filter resonance and the harmonics/inter-harmonics from the grid in a wide frequency range. Additionally, the proposed system presents good robustness with respect to grid uncertainty.

This paper presents the design of the current control loop of a three-phase voltage source converter (VSC) connected to the grid by applying the Quantitative Feedback Theory (QFT). This technique allows a robust controller design able to maximize performance for a certain previously known uncertainty and it creates faster and lower order controller than other robust techniques. In this work, the QFT technique has been adapted to achieve sine-wave reference tracking. The obtained experimental results verify the theoretical development.

This paper presents a current control scheme for a voltage-source converter connected to the grid through an LCL filter. The proposed current control is based on the linear quadratic (LQ) Gaussian (LQG) servo controller technique, which combines the LQ regulator and the Kalman filter (KF). The use of the KF instead of a Luenberger estimator improves the quality of the estimation of state variables in noisy environments, increasing the noise immunity of the control loop. This paper focuses on giving some criteria and practical hints to choose both the KF and LQ design parameters to achieve null steady-state tracking error, channel decoupling, and noise immunity. Furthermore, this paper analyzes the steady-state KF approximation that allows a significant decrement in the computational complexity of the algorithm at nearly no cost in accuracy. Simulation and experimental results prove the correct operation of the proposed LQG current control and the possible advantages of using KF to estimate the state vector.

This paper proposes improvements to the control method based on the complete dynamical model published by Komurcugil and Kukrer, which is very simple by operation in the stationary reference frame and lacks ac-line-current sensors. Nevertheless, the basic control method is very sensitive to variations of the line inductances, which provide difficulties in many industry applications. The modifications proposed in this paper overcome this disadvantage using a fuzzy logic controller to tune parameters and do more robust the basic control in view of line inductance parameters variations. Unfortunately, the new tuning method needs information about the reactive line current; therefore, ac-line-current reconstruction algorithm based on the dc-link current measurement has been included to keep the same number of sensors as the basic solution. Simulation and experimental results have proved the correct system operation at wide variations of the line inductance.

This paper presents a sensor system for robot localization based on the information obtained from a single camera attached in a fixed place external to the robot. Our approach firstly obtains the 3D geometrical model of the robot based on the projection of its natural appearance in the camera while the robot performs an initialization trajectory. This paper proposes a structure-from-motion solution that uses the odometry sensors inside the robot as a metric reference. Secondly, an online localization method based on a sequential Bayesian inference is proposed, which uses the geometrical model of the robot as a link between image measurements and pose estimation. The online approach is resistant to hard occlusions and the experimental setup proposed in this paper shows its effectiveness in real situations. The proposed approach has many applications in both the industrial and service robot fields.

This paper proposes a grid impedance monitoring system for distributed power generation electronic interfaces. The system estimates the grid equivalent impedance and voltage source from the voltage measurements performed at the point of common coupling. The estimation algorithm is based on a recursive least-squares algorithm implemented in the complex field. Simultaneously, the system evaluates the quality of the estimation, minimizing its influence on the grid and detecting islanding situations. The proposed system performance has been evaluated under experimental testing.

This paper describes the hardware and software modules of a remote Internet-based laboratory for experimentation with a 120 KVA multilevel power converter. The key feature of this laboratory is the utilization of a multilevel converter that can be controlled and supervised remotely in a secured way. A wide variety of laboratory experiments are supported, from grid connection to ac motor control. The users can choice the control structure, the control parameters and the kind of load and get the graphical results of the measurements, all in real time.

New energy concepts such as distributed power generation systems (DPGSs) are changing the face of electric distribution and transmission. Power electronics researchers try to apply new electronic controller solutions with the capacity of implementing new and more complex control algorithms combined with internal high-speed communication interfaces. Thus, it is possible to monitor, store, and transfer a large number of internal variables that can be sent online to local or remote hosts in order to take new set points of different generation units. With this objective, this paper presents the design, implementation, and test of an industrial multiprocessor controller based on a floating-point digital signal processor (DSP) and a field-programmable gate array, which operate cooperatively. The communication architecture, which has been added to the proposed electronic solution, consists of a universal serial bus (USB), implemented with a minimum use of the DSP core, and a controller area network (CAN) bus that permits distributed control. Although the proposed system can be readily applied to any DPGS, in this paper, it is focused on a 150-kVA back-to-back three-level neutral-point-clamped voltage source converter for wind turbine applications.

Modern energy concepts as Distributed Power Generation are changing the appearance of electric distribution and transmission and challenging power electronics researchers, which try to develop new solutions of electronic controllers. The aim is to enable the implementation of new and more complex control algorithms to verify the last standards related to the grid energy quality for new power converters, and, also, for equipments which nowadays are operating. This paper presents the design, implementation and test of a novel real-time controller for a Neutral Point Clamped (NPC) (three-level) multilevel converter based on a floating-point Digital Signal Processor (DSP) and on a Field-Programmable Gate Array (FPGA), by operating in a cooperative way. Although the proposed system can be readily applied to any power electronic application, in this work, it is focused on the next system: a 150 kVA back-to-back three-level NPC Voltage Source Converter (VSC) for wind power applications.

As the number of wind power applications with power electronic interfaces in the grid increases, it is becoming unacceptable to disconnect the generating units every time disturbances occur, especially under voltage dips, as was a common practice in the past. Keeping the converter online during unbalanced voltage, and guaranteeing the actual standards of the converter connected to the grid, is becoming a very critical issue. From these goals, the design of a robust back-to-back neutral point clamped (three levels) voltage source converter of 150 kVA is developed in this paper. The converter is divided into two main parts: the power electronic system and the control electronic system. Concerning the first part, on the one hand, the paper presents the designs of active and passive components as insulated gate bipolar transistor, free-wheeling diodes, clamping diodes, grid filter, DC-bus capacitors, etc.; and on the other hand, the converter requirements are analyzed to ride through real grid conditions, i.e., unbalanced voltage dips. Concerning the control electronic system, the chosen electronic structure and the task distribution between the two processors used are shown.

This paper proposes an H ∞ current controller that allows power converter input admittance shaping, both in modulus and in phase, in a three phase voltage source converter to grid connection through an L filter. In addition to this new feature, controller allows grid current tracking. Proposed controller tries to solve then trade-off problem between stand-alone converter performance (current tracking) and its influence on global stability (admittance control) by an intuitive controller design. Time and frequency domain simulated results demonstrate the good performance of the proposed method.

This paper introduces an H ∞ current controller that allows the shaping of power converters' input admittance in frequency domain, allowing to define not only its magnitude but also its phase. In addition to admittance shaping, some current tracking specification are also introduced to the algorithm demonstrating that both admittance shaping and tracking performance are possible, but not at the same frequencies. The correct performance (both in time and frequency domain) of the proposed method is demonstrated in an L-filter grid-connected single-phase VSC.

This paper presents an optimal LQR control for a static-series compensator (SSC) and propounds a design criterion for the choice of the LQR weights in order to mitigate grid-voltage dips. The authors present a SSC state-space model that considers the modelling of grid, transformer and R-L load. The proposed control works in the Stationary-Reference Frames (SRF) and implements AFC resonant controllers, allowing the direct control of unbalanced dips in a three wire grid-load connection.

This paper proposes the use of a robust loop-shaping H ∞ procedure for the current control loop of VSCs connected to the grid through LCL filters. The proposed method yields robust controllers for systems connected to grids whose equivalent impedance is only known in a predefined range. The design procedure is based on simplified classical loop-shaping principles. The result is a discrete-time controller, suitable for being executed on a Digital Signal Processor and executable in real-time that is robust for the considered conditions. The procedure has been verified by simulation and experimental testing.

This article presents the results of a study that looks at how participation in a robot competition conducted by university students in engineering contributed the development of basic professional skills in the creators of the robots. The study was performed by circulating one survey to the participants of robot competitions in two different contexts: The first, using open questions was done using participants of the prestigious international competition EUROBOT during the 2007 final held in France; The second, more extensive survey, was done using a wide selection of participants from the competition held at the University of Alcala.

This work proposes a novel method based on a prediction error minimization (PEM) algorithm to identify the discrete state-space model of a LCL filter which is used as interface between a Voltage Source Converter and the utility grid. This model is used to design directly a discrete state-space current control based on a servo controller. The so-obtained model makes easier the use of advanced control techniques as Linear Quadratic Regulators, state estimators, Robust Control, etc. The main advantage of using an identification process against to design the controller starting from the manufacturer data is that the control is not sensitive to modeled errors. The method can be applied to closed-loop systems, being suitable for adaptive control designs.

This paper proposes a method based on a prediction error minimization (PEM) algorithm to identify the discrete state-space model of a LCL filter used as interface between a Voltage Source Converter and the electrical grid. This model can be used to design directly a discrete current controller in the state space using techniques as Linear Quadratic Regulator, state estimators, etc. The method can be applied to a closed-loop system, being suitable for adaptive control designs.

Grid-converters in applications such as active rectifiers, active filters, uninterruptible power supplies, and distributed generation systems need an optimal control of the active and reactive powers interchanged with the grid. It reduces considerably the total harmonic distortion of grid currents. Anyway, though grid converters have optimal controllers, with a perfect tuning of all constants, the final response can be seriously compromised if the acquired analog signals are very noisy. This situation is very frequently, especially in medium and high power grid converters. This work proposes different algorithms, as digital filters and Kalman filters, which have as objective reduce the noise to the input of converter controllers. In this way, the quality of the current grids improves considerably.

New energy concepts such as Distributed Power Generation are changing the face of electric distribution and transmission. Power electronics researchers try to apply new electronic controller solutions enabling the implementation of new and more complex control algorithms. This paper presents the design, implementation and test of the Field-Programmable Gate Array (FPGA) tasks of a novel real-time controller for a NPC (Neutral Point Clamped) (three-level) multilevel converter. The controller is based on a floating-point Digital Signal Processor (DSP) and a FPGA, by operating in a cooperative way. The proposed system is instantiated to the next system: a 150 kVA back-to-back three-level NPC VSC (Voltage Source Converter) for wind turbine applications.

The objective of this paper is to analyse the influence of a non-ideal grid over hysteresis controllers of converters connected to the grid through both L and LCL filters. The paper will describe the different possible configurations in both cases, analysing the effect of a general R-L grid. Limit values for both grid inductance and resistance are given for the L structure. In the case of LCL connection, the analysis will overview important issues such as active damping, and switching behaviour giving limits to stability as a function of grid impedance value.

The rapid increase in current harmonics in the AC systems due to large introduction of solid state power switching devices is deteriorating the power quality. Consequently the interest in active filters is growing. However for their correct operation it is imperative to know the harmonic parameters such as magnitude and phase. Hence many algorithms have been developed to detect the harmonics. The frequency-domain-based algorithms (generally adopting the Fourier Transform) request high computation resources. The time-domain techniques work on the instantaneous values of signals, therefore they request fewer calculations. By these reasons, the time-domain algorithms are frequently used in active filter control. In this work, a review of principal time-domain methods is carried out. Also, their principal problems are indicated and the possible solutions and improvements are proposed. The analysis is validated by experimental results obtained with digital signal processor TMS320C6713.

Nowadays the most used multilevel topology for variable-speed wind turbines (WTs) is the a back-to back three-level NPC (Neutral Point Clamped) VSCs (voltage source converter). One of the most critical elements in the design of this type of converters is the DC-bus capacitors. The calculus of these depends on the same factors that the same two-levels topology, and, moreover it is function of a low frequency ripple due to the current by NP point. In this work, the value of these capacitors is obtained from the analytical equations of the DC-bus voltage ripple due to the i DC (DC-bus current) and the i NP (NP current). These expressions are verified through simulation and practical results.

The intensive use of power converters and other non-linear loads in industry and by consumers in general, has produced an increasing deterioration of the power systems voltage waveforms. The presence of harmonic distortion in power lines results in greater power losses in the distribution systems, interference problem in communication systems and, sometimes, in operation failures of electronics equipments. Owing to these problems and to preserve the power quality, the active filters are used for harmonic elimination. In this filters, a perfect harmonic identification is fundamental, therefore, nowadays many identification algorithms are available, such as, DFT, Fourier Series, ect. However, in this work a more robust algorithm based on Kalman filtering is presented. Also, several grid voltage models in state variable are shown, since the Kalman Filter needs a model of the evaluated system (in this case, of the grid). Moreover, the advantages of this method with respect to the most used technique, FFT, are commented.

This paper proposes a new control scheme for the neutral-point balance in single-phase three level neutral-point clamped converters. The control is addressed, considering the plant under study a Non-Linear Time-Variant system and applying a quasi-exact linearization to it. This way it is possible to apply classic control techniques. The method depicted is simple, general and suitable to back and boost topologies as well as to inverter or rectifier operating modes. Correct operation is verified under both simulation environment and experimental operation. Experimental operation has been verified with linear and non-linear load.

Due to the intensive use of power converters and other non-linear loads in industry and by consumers in general, it can be observed an increasing deterioration of the power quality. The presence of harmonics in power lines results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, operation failures of elecronic equipments. Owing to these problems, active filters are used for harmonic elimination and they need a reliable identification method to operate efficiently. Many algorithms have been developed to estimate the harmonic parameters such as magnitude and phase. In this work, it is reported a comparison of identification techniques for single-phase systems, moreover, improvements on these methods and a new algorithm based on correlators are proposed. This comparison can guide in choosing a suitable technique in each application. Simulation and experimental results (obtained with digital signal processor TMS320C6713) validate the proposed comparison.

A very interesting feature of VSC based back-to-back converters connected to the grid is their capacity to work in the four quadrants, and consequently their capability to change the converter power flow direction eventually. Variable speed wind turbines represent one of the main applications of these devices. The objective of this article is the study of the influence of R/sub L/ and C/sub DC/ value over a back-to-back converter from a classic linear control point of view. The analysis that is presented in this article begins with the extraction of two different models for the DC bus which permits the deduction of ranges of nominal values for the DC bus capacitor (C/sub DC/) and for the load resistance (R/sub L/) which ensures system stability. A stability analysis of these models as a function of the operating mode of the VSC (rectifier, inverter), of the DC-bus capacity and of the value and sign of the current across the DC-bus is the objective of the second part of this article. Finally, a control scheme for both models is proposed. Special interest is dedicated to the effects of DC-bus parameters (R/sub L/ and C/sub DC/) over the controller operation and to a correct chose for that values: an analytic method for constant design is presented. Control system correct operation is verified under a non-linear back-to-back simulation environment.

Accurate phase information is crucial for most of modern power electronic systems such as VSC connected to the grid. In this paper, it is proposed an algorithm software phase-locked loop (SPLL) to obtain phase and frequency information of the grid voltage. This is based in an algorithm of on-line separation of the grid voltage sequences (DSC), and a discrete traditional PLL. A criterion to tune the SPLL constants from a PLL discrete linearized model is discussed. The SPLL response is evaluated for different grid disturbances and different SPLL parameters. Besides, a VSC connected to the grid through and L filter with the SPLL obtained in this paper has been tested for different configurations of SPLL and different grid perturbations. Conclusions about where to apply the SPLL different configurations are obtained from these last tests.

The drawback of using a VSC as an interface with the grid is its sensitivity in presence of system disturbances as grid voltage harmonics. In this paper, a new current controller structure to harmonics compensation is proposed. It consists of using two control loops. The first is based in synchronous PI working in rotating coordinates with DC components; and the second uses synchronous-frame generalized integrators (Gl) tuned to the harmonics frequency. The proposed algorithm temporal responses under grid voltage harmonics are presented, and also, the proposed digital control electronics system, where the algorithms run, is shown.

As the number of wind power with power electronics interfaces in the grid increases, it becomes unacceptable to disconnect the generating units every time a disturbance occurs, as was a common practice in the past. Keeping the converter online during unbalanced voltage and guaranteeing the actual standards of the converter connected to the grid becomes a very critical issue. From these goals, the design of a robust back-to-back NPC (three levels) converter of 100 KVA is researched in this work. The converter is divided into two main parts: the power electronics system and the control electronics system. In both designs, some important contributions are shown. Concerning the first part, the paper presents primarily the converter limitations to compensate unbalanced dips, the grid filter design and the DC-bus capacitor design. Concerning the control electronics system, the chosen electronic structure and the tasks distribution between the chosen processors are shown.

The aim of this paper is to propose a current control of VSCs connected to the grid through an LCL-filter. The proposed algorithm controls the grid current using only two sensors. Other variables are obtained with a state estimator, and the possible disturbances of the system are attenuated with active damping. The control algorithm has been proved for different disturbances, such as temporal variations in the components of the model and perturbations in the grid, and also with the linear and nonlinear models.

This letter proposes a new control scheme for the neutral-point (NP) balance in single-phase three-level NP-clamped converters. The control is addressed considering the plant under study, a nonlinear time-variant system. A quasi-exact linearization is applied allowing the application of classic control techniques. The described method is simple, general, and suitable for buck and boost topologies, as well as for inverter or rectifier operating modes under either linear or nonlinear loading. Correct operation is verified under simulated and experimental operation.

© 2016 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works This paper presents a novel active damping technique of current-controlled grid-connected power converters through LCL filters. Based on H8 synthesis algorithms, a grid current controller is obtained so that the grid-connected power converted-based application admittance resembles a given frequency reference. By defining a low resistive admittance as the reference, considered application resonance is effectively damped, reducing grid current oscillations under grid voltage variations and avoiding their associated stability problems. Presented grid current controller senses only the PCC grid voltage and current, and is experimentally tested in both time and frequency domains. Additionally, the effectiveness of presented damping method is proved under different grid impedance scenarios. _