Search

The papers in this special section focus on control and power grid integration of MW-range wind and solar energy conversion systems. Globally, the energy provided by intermittent sources has been steadily increasing. For instance, the electrical energy now supplied worldwide by wind turbines has increased by a factor of more than three with respect to the 2008 figure. Solar-based energy generation has increased by more than ten times over the same period. In total, worldwide electrical energy consumption increased by approximately 6340 TWh from 2003 to 2013. Of that increase, about 11% was covered by a combination of wind power (564.8 TWh) and solar power (122.8 TWh). To meet the challenges created by intermittent energy generation sources, grid operators have increasingly demanded more stringent technical requirements for the connection and operation of grid-connected intermittent energy systems, for instance concerning fault ride through capability, voltage and frequency support, inertia emulation, etc. These considerations, combined with an ever-increasing push for lower cost, higher efficiency and higher reliability, are leading to a steady technological evolution in the areas related to intermittent energy conversion systems. Ongoing developments include new or improved high-voltage converters, power converters with higher power density, control systems to provide ride-through capability, implementation of redundancy schemes to provide more reliable generation systems, and the use of high-voltage direct current (HVdc) links for the connection of large off-shore intermittent energy systems. In all of these technological advances, industrial electronics is undeniably a key core contributor.

The behavior of a photovoltaic (PV) module may be captured via its current–voltage ( $I$ – $V$ ) characteristic. The single-diode model is able to adequately fit this characteristic while featuring limited parameterization difficulty, and is thus widely adopted to represent the performance of a PV module. However, the identification of the model's parameters is a complex task due to the nonconvex nature of the underlying optimization problem. In this paper, an efficient method for the parameter extraction of the single-diode PV model from experimental $I$ – $V$ curves is developed. This method features two advantages with respect to the existing procedures. On the one hand, it is able to find high-quality solutions at a reduced computational complexity. On the other hand, it does not rely on any preliminary data selection and it can thus be fully automated without user intervention. Numerical results obtained for case studies common in the literature and a large-scale repository show its performance. A computer program implementing the proposed methodology is available upon request via an e-mail to all interested researchers.

Background: Acute myeloid leukemia (AML) is a heterologous hematological malignancy in which the p53-mutated subset is associated with the most guarded prognosis. Induction therapy for AML with cytarabine (cytosine arabinoside, ARA-C) is routinely used in combinations with anthracyclines. Annamycin (ANN) is an antitumoral anthracycline whose anti-leukemia activity, in contrast to doxorubicin (DOX) and daunorubicin, is unaffected by P-glycoprotein (ABCB1)-related multidrug resistance (MDR1). Unlike conventional anthracyclines, ANN accumulates in multidrug resistant cell lines, inducing DNA damage and apoptosis. Additionally, in preclinical toxicology studies, ANN displayed a greatly reduced cardiotoxicity profile compared to DOX. A liposomal formulation of ANN, termed L-Annamycin (L-ANN), is being evaluated in patients with acute myeloid leukemia (AML) in two phase Ib/IIa clinical trials in both the US and Europe. The patients are stringently followed for cardiotoxicity (Shephard et al., ASH 2020, submitted). There was no decrease in ejection fractions observed in any of the 20 patients treated to date and all cardiotoxicity biomarkers including troponin remained normal. In addition, echocardiogram analyses by the Duke cardio-oncology lab, and independently by a cardio-oncologist at Cleveland Clinic, were all normal. Considering that cardiotoxicity and MDR1-limited anthracyclines like daunorubicin are routinely used in a combination with ARA-C as induction therapy in AML, we here evaluated the combination of Ara-C with L-ANN pre-clinically. Objective: The objective of the study was to assess in vivo efficacy of the combination of L-ANN with ARA-C in a pre-clinical model of AML. Methods: The efficacy of L-ANN alone or in combination with ARA-C was investigated in a highly aggressive AML mouse model characterized by the p53-/-, MLL, ENL-FLT3, ITD mutations and genetically tagged with the cyan fluorescent protein mTurquoise2 for flow cytometry and microscopic visualization. L-ANN was intravenously administered at different dosing regimens (days 1, 2, 3 or 1, 3, 5 weekly, or 1 dose of 4 mg/kg once a week). ARA-C was administered by 5 daily intraperitoneal injections at 50 mg/kg, which was repeated every other week up to 3 times. The level of leukemia cells in peripheral circulation was analyzed by flow cytometry and AML cell presence in organ tissues was imaged by thick-mount fresh tissue confocal microscopy, in various disease stages. Results: In all tested L-ANN administration regimens (days 1, 2, 3 or 1, 3, 5 weekly, or 1 dose of 4 mg/kg once a week), we observed a significant increase in the survival of ANNARAC cohorts (combination of L-ANN with ARA-C), when compared with the respective single agents. Specifically, upon intravenous infusion of 1x105 AML1-mTurq2 cells into syngeneic immunocompetent C57BL6 mice, lethal AML disease developed with median survival of 14 days. Administration of L-ANN on a weekly basis significantly delayed leukemia progression, as evaluated by flow cytometry and fluorescence microscopy, resulting in survival increase to 34 to 40 days, in multiple experiments. The mice treated with 50 mg/kg of ARA-C daily for 5 days a week every other week using intraperitoneal injections showed moderate to limited response to the therapy with median survival ranging from 17 to 30 days. In contrast, the median survival of animals treated with the L-ANN/ARA-C combination using different schedules ranged from 44 to 76 days, with a fraction of animals living more than 180 days after implantation of AML cells. Remarkably, imaged on day 36, the bone marrow, spleen and lungs of mice receiving combination of L-ANN (4 mg/kg once a week) with ARA-C (50 mg/kg five times per week) showed no residual disease. These results are consistent with the increased survival observed for this combination. Conclusion: This study demonstrated vastly higher efficacy of the L-ANN/ARA-C combination (ANNARAC) over that of the single agents in an immune-competent setting of an aggressive, p53-null AML model. Overall, these experiments indicate that L-ANN has the capacity to sensitize AML cells to the ARA-C induction regimen and support initiation of clinical development of L-ANN in combination with ARA-C in AML patients. Disclosures Zal: Daiichi-Sankyo: Research Funding; Moleculin Biotech, Inc.: Research Funding. Zielinski:CNS Pharmaceuticals: Current equity holder in private company, Patents & Royalties; Moleculin Biotech, Inc.: Consultancy, Current equity holder in publicly-traded company, Patents & Royalties, Research Funding. Grela:Moleculin Biotech, Inc.: Current Employment, Current equity holder in private company, Patents & Royalties. Skora:Moleculin Biotech, Inc.: Current equity holder in private company, Patents & Royalties; CNS Pharmaceuticals: Current equity holder in private company, Patents & Royalties. Fokt:CNS Pharmaceuticals: Current equity holder in private company, Patents & Royalties; Moleculin Biotech, Inc.: Consultancy, Current equity holder in private company, Patents & Royalties, Research Funding. Andreeff:Centre for Drug Research & Development; Cancer UK; NCI-CTEP; German Research Council; Leukemia Lymphoma Foundation (LLS); NCI-RDCRN (Rare Disease Clin Network); CLL Founcdation; BioLineRx; SentiBio; Aptose Biosciences, Inc: Membership on an entity's Board of Directors or advisory committees; Daiichi-Sankyo; Jazz Pharmaceuticals; Celgene; Amgen; AstraZeneca; 6 Dimensions Capital: Consultancy; Amgen: Research Funding; Daiichi-Sankyo; Breast Cancer Research Foundation; CPRIT; NIH/NCI; Amgen; AstraZeneca: Research Funding. Shephard:Moleculin Biotech, Inc.: Current Employment, Current equity holder in private company, Patents & Royalties. Priebe:Animal Life Sciences: Current equity holder in private company, Other: Scientific Advisor; WPD Pharmaceuticals: Current equity holder in publicly-traded company, Other: Chairman of Scientific Advisory Board, Patents & Royalties, Research Funding; CNS Pharmaceuticals: Current equity holder in private company, Other: Chairman of Scientific Advisory Board, Patents & Royalties, Research Funding; Moleculin Biotech: Current equity holder in publicly-traded company, Other: Membership of Scientific Advisory Board, Patents & Royalties, Research Funding; Reata Pharmaceuticals: Current equity holder in publicly-traded company; Houston Pharmaceuticals: Current equity holder in private company.

Uninterruptible power supply units are system formed by power electronics converters to supply sinusoidal voltages to feed critical loads. In this paper, a fixed switching frequency model predictive control strategy is presented for the control of the output voltage in an LC filter connected to a three-level NPC converter. The control objectives of the system are the tracking of the voltage reference and balance of the voltages of the dc-link capacitors. The mathematical model of the converter and the LC filter is developed and the control strategy is explained. Simulation results obtained in the Matlab/Simulink enviroment are presented to validate the control strategy

Phase-Locked Loops (PLLs) are a recognised alternative to detect grid frequency and phase angle, which allows grid synchronisation of distributed generation units. Nevertheless, frequency and phase angle estimation becomes complex in microgrid applications where unbalanced and distorted voltages are frequent. Therefore, a novel PLL structure for unbalanced and distorted grids is introduced in this paper. The proposed PLL is based on a parallel Fast Delayed Signal Cancellation (FDSC) structure. Several FDSC is connected in parallel to identify and eliminate different harmonics, allowing a fast and efficient fundamental frequency and phase angle estimation. Simulations results are presented to test the performance of the proposed PLL under severe imbalances and harmonics.

Future distribution grids will require to integrate renewable energies in higher penetration levels than we are used to today in conventional power systems. To make this possible, key aspects of their operation such as reliability and robustness must been in safe levels. To accomplish the latter, two different technologies have been proposed: (a) Virtual Synchronous Machines and (b) Smart Transformers. Despite all the benefits that each one of these technologies provide, solid-state transformers have not been very successful in operating as smart transformers. Then, hybrid transformers were proposed as a more feasible solution and with the capability of providing ancillary services to the distribution grid. In this paper, a new type of hybrid transformer that incorporate features of a virtual synchronous machine is proposed. The proposed transformer is capable of emulating virtual inertia as an ancillary service, and, at the same time, providing other basic services such as reactive power injection and voltage compensation. Simulation results provide evidence of the advantages of using this type of hybrid transformers in distribution grids.

The Modular Multilevel Converter (MMC) is a topology suitable for high-power medium-voltage variable-speed drives. However, the behaviour of this converter is highly affected by the power fluctuations of its modules. This paper analyses the influence of the dc-port voltage on these power fluctuations. It is demonstrated that the manipulation of this voltage offers several advantages for the operation of the drive. For example, it is possible to reduce: the voltage fluctuations in the capacitors, the capacitance of each cell or the application of mitigating variables during low machine speeds. Additionally, a reduction in the required common-mode voltage during low-speed operation is also feasible. The effectiveness of the proposed control schemes is demonstrated through simulation studies.

In this paper, a distributed secondary control strategy for hybrid ac/dc-microgrids is proposed. The control strategy restores the variables modified by the primary control loop, i.e. voltage on the DC-side and voltage amplitude and frequency of the AC-side, to their nominal values while maintaining a good power-sharing capability between AC- and DC-units, A distributed communication network among the generation units is needed for the proper performance of the control strategy, however, a high bandwidth communication network is not needed to ensure a good behaviour of the proposed control scheme. The effectiveness of the control scheme is validated through simulation of a 9.0kW hybrid ac/dc-microgrid.

This article presents a novel circulating current control scheme for the Modular Multilevel Matrix Converter (M3C). The proposed method is based on a Model Predictive Control strategy (MPC), where an optimization problem is defined for minimizing the tracking error of the circulating currents. The output of the control scheme are circulating voltage references that are defined by a suitable linear transform. The effectiveness of this strategy is compared with a traditional scheme by simulation results of a M3C prototype composed of 27 modules. The reported results exhibit an important enhancement in the regulation of arm currents, specially during transient performance.

Recently, the extraction of energy from the incoming waves has taken more importance in the energy generation based on renewable resources. However, most of the attention has been directed towards the Power-Take-Off systems more than in the interaction between several generating units. Consequently, in this work, there are presented and carefully analysed a novel topology of Interconnected Wave-Energy Converters (IWECs) and its associated control system. A representative set of data of a real wave frequency and height variation from the South Uist island, in Scotland, and a proof-of-concept simulation show that the energy requirements of the proposed IWEC are lower than those required for individual WECs.

In this paper, two predictive modulation schemes are derived for a hybrid modular multilevel converter. The modulation scheme considers the electric model of both full and half bridge cells to predict the capacitor voltages in the next sampling period. The performance of both modulators is assessed through simulations and experimental results for different modulation indices.

During the last years, the Modular Multilevel Matrix Converter (M3C) has been investigated due to its capacity tooperate in high voltage and power levels. This converter is appropriate for Wind Energy Conversion Systems (WECSs), due to its advantages such as redundancy, high power quality, expandability and control flexibility. For Double-Fed Induction Generator (DFIG) WECSs, the M3C has advantages additional benefits, for instance, high power density in the rotor, with a more compact modular converter, and control of bidirectional reactive power flow. Therefore, this paper presents a WECS composed of a DFIG and an M3C. The modelling and control of this WECS topology are described and analyzed in this paper. Additionally, simulation results are presented to validate the effectiveness of this proposal.

The modular multilevel matrix converter (M^3C) is a power converter topology for ac to ac conversion that is suitable for high-power applications. The control of this converter is complex, particularly if ac system frequencies are similar. In these cases, the floating capacitors can present large voltage oscillations. Therefore, this study presents a new vector control system to enable the operation of the M^3C when the frequencies at the input and output are virtually the same. The effectiveness of the proposed method has been validated using simulations and experimental results from a prototype M^3C power converter with 27 cells.

Modulated model predictive control (M 2 PC) allows fixed switching frequency operation of power converters, producing lower ripple and lower total harmonic distortion (THD) in the output signals than those obtained using regular model predictive control (MPC) algorithms. However, the design of the M 2 PC algorithm and its performance depend on, among other factors, the tuning of weighting factors, which are required by the cost functions typically used in predictive control algorithms. In this paper, a novel Pareto-based multi-objective M 2 PC (MO-M 2 PC) strategy is proposed. In this case, the use of weighting factors is not required, and the optimization problem is solved using a multi-objective approach. The aim of the proposed MO-M 2 PC strategy is to consider practical rules, such as satisfaction of soft constraints, to calculate the control actions. The proposed Pareto-based MO-M 2 PC strategy can be applied to any power converter topology. In this paper, experimental validation of the proposed methodology is pursued using a 3-phase 3 kW power converter operating as a shunt active power filter (SAPF). The proposed control is implemented in a control platform based on the dSPACE ds1103 system. The simulation and experimental results demonstrate the advantages and flexibility achieved by the proposed Pareto-based MO-M 2 PC.

Battery Energy Storage Systems (BESS) are important for applications related to both microgrids and electric vehicles. If BESS are used as the main energy source, then it is required to include adequate procedures for the estimation of critical variables such as the State of Charge (SoC) and the State of Health (SoH) in the design of Battery Management Systems (BMS). Furthermore, in applications where batteries are exposed to high charge and discharge rates it is also desirable to estimate the State of Maximum Power Available (SoMPA). In this regard, this paper presents a novel approach to the estimation of SoMPA in Lithium-Ion batteries. This method formulates an optimisation problem for the battery power based on a non-linear dynamic model, where the resulting solutions are functions of the SoC. In the battery model, the polarisation resistance is modelled using fuzzy rules that are function of both SoC and the discharge (charge) current. Particle filtering algorithms are used as an online estimation technique, mainly because these algorithms allow approximating the probability density functions of the SoC and SoMPA even in the case of non-Gaussian sources of uncertainty. The proposed method for SoMPA estimation is validated using the experimental data obtained from an experimental setup designed for charging and discharging the Lithium-Ion batteries.

The modular multilevel matrix converter has been proposed as a suitable option for high power applications such as flexible AC transmission systems. Among flexible AC transmission systems, the unified power flow controller stands out as the most versatile device. However, the application of the modular multilevel matrix converter has not been thoroughly analyzed for unified power flow controller applications due to the sophisticated control systems that are needed when its ports operate at equal frequencies. In this context, this paper presents a cascaded control structure for a modular multilevel matrix converter based unified power flow controller. The control is implemented in a decoupled reference frame, and it features proportional-integral external controllers and internal proportional multi-resonant controllers. Additionally, the input port of the modular multilevel matrix converter is regulated in grid-feeding mode, and the output port is regulated in grid-forming mode to provide power flow compensation. The effectiveness of the proposed vector control system is demonstrated through simulation studies and experimental validation tests conducted with a 27-cell 5 kW prototype.

In this work, a methodology for the design and implementation of a microgrid for supplying electricity to indigenous Mapuche communities in Chile is proposed. The challenge in designing this microgrid lies in making it compatible with a community’s socio-cultural situation, thereby allowing active community participation in all stages of project development. To achieve this, we propose a participatory model of technological innovation that fits in with the local culture. The proposal is based on taking advantage of the communication and energy infrastructure of the microgrid to build a smart farm system to improve the quality of life of Mapuche rural communities. The smart farm consists of a set of technological devices and software applications related to communitarian farm activities that attempt to reduce the gap of information technologies. To demonstrate the potential of the smart farm system, we propose solutions for livestock monitoring and rational water use at the local level since these two applications represent needs expressed by the communities themselves. To develop a harmonious project consistent with the socio-cultural situation of the Mapuche people and to obtain effective community participation in the different stages of the project, we suggest performing a participatory socio-environmental diagnosis to identify the project’s potential and existing initial barriers to its implementation in these communities. Subsequently, we will evaluate its potential impact on the social welfare and development of the communities. This design will result in a participatory project with community management for ensuring its sustainability under a concept of development shared by the community.

Frequency identification is one of the most critical issues for grid-connected power converters, especially when the grid is unbalanced or distorted. Therefore, this paper proposes a novel frequency estimator with fast convergence for balance and unbalanced grid-voltage faults. The proposed algorithm is based on a Phase Locked Loop (PLL), enhanced with a fast positive and negative sequence detector. Delayed Signal Cancellation methodology with fast convergence is investigated under single-phase and two-phase voltage dip. The effectiveness of the proposed PLL is validated using simulations and experimental results.

© 2018 IEEE. This paper proposes a sequential Phase-Shifted Model Predictive Control (PS-MPC) strategy for three-level Active Neutral Point Clamped (3L-ANPC) converter. The proposed predictive control strategy is formulated to fully exploit a phase-shifted pulse width modulation (PS-PWM) stage. By means of an appropriate choice of synchronized average models for each carrier, the proposed predictive controller obtains independent optimal duty cycles for each carrier in a sequential manner. This allows one to formulate the optimal control problem not only to govern the output current but also to balance the dc-link capacitor voltages, similarly to the finite-control-set MPC (FCS-MPC) case. As evidenced by the simulation results, the 3L-ANPC converter governed by the proposed sequential PS-MPC can attain a faster dc-link voltage balancing dynamic when compared to a standard PS-PWM implementation. Moreover, it generates an output voltage with fix-spectrum in the steady state with a constant commutation rate and evenly distributed power losses, which outperforms a standard FCS-MPC strategy.

The trend of multimegawatt (Multi-MW) wind turbines, especially for offshore installations, has positioned Modular Multilevel Cascade Converters (MMCCs) as a promising solution for Wind Energy Conversion Systems (WECSs). Additionally, High Voltage Direct Current (HVDC) Transmission is likely to be the preferred option for future offshore wind farms. In both applications, Modular Multilevel Converters are an appropriate solution due to its characteristics such as high-voltage operation, controllability, redundancy, power quality and reliability. This paper presents the application of the Modular Multilevel Matrix Converter to locally interface a single wind turbine to a medium-voltage ac point of connection. Moreover, the Modular Multilevel Converter is proposed to link the wind farm to the grid onshore through an HVDC transmission line. Both converters are regulated using decoupled Vector Control Strategies. Experimental results obtained with a 27 Modular Multilevel Matrix Converter connected to a 30 power cell Back-to-Back Modular Multilevel Converter are presented to validate the effectiveness of the Proposed Control Strategies.

The Modular Multilevel Converter (MMC) is a promising topology for high power drive applications. However, large voltage fluctuations are produced in the floating capacitors when the machine is operating with high stator currents at low rotational speed. To compensate these oscillations, relatively large mitigation currents are required to keep the capacitor voltages within an acceptable range. In this paper, a new integrated control scheme is discussed to regulate the voltage fluctuations. The strategy is based on closed-loop vector-control of the voltage fluctuations, maintaining them inside a pre-defined threshold. The proposed control system is also augmented using flux weakening operation of the machine at low rotational speeds. An experimental prototype composed of eighteen power cells, feeding a vector-controlled induction machine in the whole speed range, is used to validate the effectiveness and feasibility of the proposed control strategies.

In this paper, finite-set model-predictive control (FS-MPC) methodologies for a grid-connected three-level neutral-point-clamped converter are investigated. The proposed control strategies produce fixed switching frequency, maintaining all the advantages of predictive control such as fast dynamic response, inclusion of nonlinearities and restrictions, and multivariable control using a single control loop. The first of the proposed FS-MPC strategies is based on a multiobjective cost function, designed to regulate both the inverter currents and the balancing of the dc-link capacitor voltages. The second FS-MPC strategy is derived from the first one, and it is based on a cost function that regulates only the grid current, with the balancing of the capacitor voltages being realized by controlling the duty cycles of the redundant vectors. The proposed control systems are experimentally validated using a 5-kW prototype. The experimental results show a good performance for both strategies, in steady-state and transient response, with a total harmonic distortion lower than $\text{2}\%$ for the currents supplied to the grid.

This paper presents a topology for a three-phase generation system for an isolated unbalanced load fed by a doubly fed induction generator with a neutral wire to include single-phase loads. The challenges of unbalanced loads connected to the system are presented along with a proposal for mitigating current imbalance by employing a four-leg rectifier. The proposed compensation method is based on the sequence decomposition analysis, and thus, it is based on previous works that use current control in double synchronous reference frames. Nevertheless, a conceptual analysis is presented that vindicates the use of resonant controllers in the stationary $abc$ frame.

This paper considers the control of a seven-leg back-to-back voltage source inverter arrangement, feeding a four-wire load from a three-phase permanent-magnet synchronous generator (PMSG) operating at variable speed. The PMSG is controlled using a sensorless model reference adaptive system to obtain the rotor position angle. The seven-leg converter is regulated using resonant controllers at the load side and self-tuning resonant controllers at the generator side. The control system is augmented by a feedforward compensation algorithm that improves the dynamic performance during transients. Experimental results, which are obtained from a prototype, are presented and discussed.

This paper introduces a novel fuzzy model based structure for the characterisation of discharge processes in lead-acid batteries. This structure is based on a fuzzy model that characterises the relationship between the battery open-circuit voltage (Voc), the state of charge (SoC), and the discharge current. The model is identified and validated using experimental data that is obtained from an experimental system designed to test battery banks with several charge/discharge profiles. For model identification purposes, two standard experimental tests are implemented; one of these tests is used to identify the Voc–SoC curve, while the other helps to identify additional parameters of the model. The estimation of SoC is performed using an Extended Kalman Filter (EKF) with a state transition equation that is based on the proposed fuzzy model. Performance of the proposed estimation framework is compared with other parametric approaches that are inspired on electrical equivalents; e.g., Thevenin, Plett, and Copetti.

Most low voltage microgrids have four wires and operate mainly unbalanced. This paper considers a new droop control per phase of a four-wire microgrid to solve the problems associated to unbalanced operation (e.g. high neutral current). Unlike the conventional approaches, in this work, the active power per phase of each converter is shared varying the output voltage angle of each inverter phase. The proposed control system is based on a hierarchical control structure. The inner control loop of the inverter output voltage is implemented using resonant controllers, applying an active damping strategy to improve the system response. On the primary control loop, the angle droop control strategy is applied to share the active power per phase, according to the nominal ratings of the generation units. Then, a secondary control loop is utilised to restore the unbalance of the voltages to the nominal values. Experimental results obtained with a 3 kW four-wire microgrid prototype are presented and discussed to validate the proposed control system.

The Modular Multilevel Converter has emerged as a suitable topology for high power drive applications. However, high voltage fluctuations could appear in the converter capacitors depending on the operating drive point. Then, mitigating signals, which lead to oversized dimensioning, are required to keep the capacitor voltages within an acceptable range. In this paper, a new control scheme is proposed to regulate the capacitor voltages within a desired margin reducing the mitigating signals as the machine frequency increases. The effectiveness of the proposed control strategy is validated with a laboratory-based prototype composed of eighteen power cells, feeding a vector-controlled induction machine.

This paper presents a simple and innovative Capacitor Voltage Balancing (CVB) strategy for Modular Multilevel Converters (MMC) based on full H-bridge cell topologies. The method computes specific modulation indexes for each cell using the explicit solution of an underlying optimal control problem. Based on the structure of its analytical solution, the proposed CVB scheme is integrated to a Phase-Shifted PWM scheme with an easy implementation. Experimental results obtained from a nine-cell single-phase converter demonstrate an improved performance of the proposed method, especially under transient operating conditions.

Made available in DSpace on 2018-12-11T17:32:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-06-01 Four-wire microgrids (MGs) and distribution systems are inherently unbalanced with the presence of negative and zero sequence components in voltages and currents. In small autonomous systems, the imbalance, in addition to the harmonic distortion produced by nonlinear loads, can significantly affect the power quality, loadability, and stability of the system. Furthermore, in isolated networks with significant generation from intermittent renewable energy sources, the stiffness of the system is reduced and this could amplify the effects of imbalance on the stability and power quality. To mitigate some of these problems, a novel methodology based on the application of a four-leg active power filter is proposed in this paper. The control of the compensator is based on the conservative power theory augmented by resonant controllers. The behavior of the proposed system is demonstrated using an experimental prototype deployed in a laboratory scale MG. Department of Electrical Engineering Facultad de Ciencias Físicas y Matemáticas University of Chile PEMC Group University of Nottingham São Paulo State University (Unesp) Institute of Science and Technology São Paulo State University (Unesp) Institute of Science and Technology

The following work introduces the use of a modified four-level medium voltage converter in a back-to-back configuration for its application on wind energy conversion systems (WECS). The proposed converter topology is based on a three-level neutral-point clamped converter (3L-NPC) without clamping diods or power switches, so that dc-link capacitors are in a floating condition respect to the neutral point. The implementation of the back-to-back configuration enables the topology for its application in variable speed SM - Permanent Magnet Synchronous Generator WECS.

For power conversion systems interfaced to four-wire supplies, four-leg converters have become a standard solution. A four-leg converter allows good compensation of zero-sequence harmonics and full utilisation of the dc-link voltage. These are very important features when unbalanced and/or nonlinear loads are connected to the system. This paper proposes a three-dimensional space vector modulation (SVM) algorithm and provides a comprehensive analysis of the algorithm implemented on a three-level, four-leg neutral-point-clamped converter. The algorithm allows a simple definition of the different switching patterns and enables balancing of the dc-link capacitor voltages using the redundancies of the converter states. A resonant controller is selected as the control strategy to validate the proposed SVM algorithm in a 6 kW experimental rig.

To interface generation sources and loads to four-wire distribution networks it is important to use power converters and modulation methods, which provide high performance, flexibility, and reliability. To achieve these goals, this paper proposes a simple and efficient space vector modulation (SVM) algorithm in $\alpha \beta \gamma$ coordinates for neutral point clamped (NPC) converters. The proposed SVM method reduces a 3-D ( $\alpha \beta \gamma$ ) search amongst modulating vectors into a simple 2-D ( $\alpha \beta$ ) problem. Moreover, the algorithm provides full utilization of the dc-link voltage and full utilization of the redundant vectors, and it can be applied to any other four-leg converter topology. The proposed SVM has been successfully validated using a 6-kW three-level four-leg NPC converter, achieving control over the voltages of the dc-link capacitors and a simple definition of the switching patterns for shaping the frequency spectrum.

Modular multilevel converters (M $^{\text{2}}$ C) are considered an attractive solution for high power drive applications. However, energy balancing within the converter is complex to achieve, particularly when the machine is operating at low rotational speeds. In this paper, a new control system, based on cascaded control loops and a vector-power-voltage ( $vPV$ ) model of the M $^{\text{2}}$ C, is proposed. The control system is implemented in a $dq$ -synchronous frame rotating at $\omega _e$ rad/s with the external loop regulating the capacitor voltages using proportional-integral (PI) controllers. The internal loop controls the converter currents using PI and resonant controllers. In addition, the control systems required to operate the machine at other points, i.e., at medium and high rotational speeds, are also discussed in this paper. Experimental results obtained with an M $^{\text{2}}$ C-based drive laboratory prototype with 18 power cells are presented in this paper.

The papers in this special section brings together papers focused on the recent advancements and breakthroughs in the technology of modeling and enhanced active/reactive power control of wind power conversion systems, ranging from components of wind turbines to wind farms.

The nominal power of single Wind Energy Conversion Systems (WECS) has been steadily growing, reaching power ratings close to 10MW. In the power conversion stage, medium-voltage power converters are replacing the conventional low-voltage back-to-back topology. Modular Multilevel Converters have appeared as a promising solution for Multi-MW WECSs, due to their modularity, and the capability to reach high nominal voltages. This paper discusses the application of the Modular Multilevel Matrix Converter (M3C) to drive MultiMW WECSs. The modelling and control systems required for this application are extensively analysed and discussed in this paper. The proposed control strategies enable decoupled operation of the converter, providing maximum power point tracking (MPPT) capability at the generator-side, grid code compliance at the grid-side [including Low Voltage Ride Through Control (LVRT)], and good steady state and dynamic performance for balancing the capacitor voltages in all the clusters. Finally, the effectiveness of the proposed control strategy is validated through simulations and experimental results conducted with a 27 power-cell prototype.

Purpose – The purpose of this paper is to investigate a control strategy to fulfill low-voltage ride through (LVRT) requirements in wind energy conversion system (WECS). Design/methodology/approach – This paper considers an active front-end converter of a grid connected WECS working under grid fault conditions. Two strategies based on symmetrical components are studied and proposed: the first one considers control only for positive sequence control (PSC); the second one considered a dual controller for positive and negative sequence controller (PNSC). The performance of each strategy is studied on LVRT requirements fulfillment. Findings – This paper shows presents a control strategy based on symmetrical component to keep the operation of grid-connected WECS under unsymmetrical grid fault conditions. Research limitations/implications – This work is being applied to a 2 kVA laboratory prototype. The lab prototype emulates a grid connected WECS. Originality/value – This paper validate the PNSC strategy to LVRT requirements fulfillment by experimental results obtained for a 2 kVA laboratory prototype. PNSC strategy allows constant active power delivery through grid-voltage dips. In addition, the proposed strategy is able to grid-voltage support by injection of reactive power. Additional features are incorporated to PNSC: sequence separation method using delay signal cancellation and grid frequency identification using phase locked loop.

Ovarian cancer (OC) is the most lethal cancer in all of the gynecological cancers.Despite the recent advancements in the treatment of OC, it remains the seventh most common cancer in women worldwide. Cancer stem cells (CSCs) are a unique cell population described by their ability to indefinitely self-renew, proliferate, initiate, and propagate. Evidence suggest that the interaction between cancer stem cells with their microenvironment play a critical role for cancer progression. Exosomes which are the key players of microenviroment are nano-sized (50-180nm) endosomal pathway-derived vesicles that present in almost all biological fluids.Transporting information via exosomes and exosomal miRNAs is deemed to be the crucial way of intercellular communication that is as essential as the cell-to-cell contact-dependent signaling. As a key regulator of cellular signaling, both normal, and cancer stem cells secrete exosomes to orchestrate diverse autocrine and paracrine functions which alter tumor micro-environment, growth, progression and putative immunological function. There is still not much known about how ovarian cancer stem cells (OCSCs) interact with their tumor microenvironment to promote oncogenic phenotype. Thus, in this study we investigate whether the OCSCs-derived exosomal miRNAs mirror and orchestrate that of the tumor microenvironment and thus could be used diagnostically in ovarian cancer patients.To this end,we evaluated significantly differentially expressed miRNAs between OCSCs exosomes and their cells of origin using the Affymetrix Gene Chip miRNA 4.0 microarrays. Several miRNAs were found to be significantly upregulated in both OCSCs and their exosomes. In addition we found many common up/down regulated miRNAs (miR-103a-3p, miR-20a-5p, miR-125b-5p, miR-17-5p, miR-27a-3p, miR-8075, miR-4487) with the microarray data in which tumor-associated macrophage (TAM) exosomes and their cells of origin were compared. We also found that OCSCs secrete exosomes enriched in miR-103a-3p, which has been shown to increases cancer migration, invasion and angiogenesis and induces polarization of M0 type macrophages toward immunosuppressive M2-type macrophages. In addition TAMs promote cancer stem cell-like properties by enhancing their epithelial–mesenchymal transition capacity. We are currently validating the identified miRs and investigating the role of these miRs in OC cells and CSCs proliferation, migration, invasion and tumor growth. Our findings also indicate that the interaction between TAMs and OCSCs are bidirectional. Overall, our data suggest that OCSCs and OCSCs secreted exosomes may contribute tumor microenvironment especially by regulating TAMs by transferring oncogenic miRs and using them as a progression and invasion tools within tumor microenvironment. Citation Format: Fahriye Duzagac, Gabriel Lopez-Berestein, Pinar Kanlikilicer, Cristian Rodriguez-Aguoya, Roberto Cardenas-Zuniga, Ummu Guven, Gulperi Oktem, Bulent Ozpolat. Regulatory role cancer stem cells (CSCs)-derived exosomal miRNAs in ovarian cancer growth and progression [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3686.

This paper proposes a low-complexity small signal model for a 3-leg converter connected to a balanced three-phase, three-wire weak grid and synchronised to this grid using a PLL implemented in a synchronous rotating d-q axis. A thorough analysis of the system stability as a function of the PLL bandwidth and the short circuit ratio (SCR) of the grid is performed based on a linearised model. By using the proposed model, an improved design process is proposed for the commonly used dq-PLL that accounts for the potential stability issues which may occur in weak grids. Using the proposed approach, it is possible to optimise the PLL design to find the fastest PLL that can operate stably considering the SCR of the grid. In addition, the proposed model is very simple, resulting in a straightforward design tool that could also be used for online stability monitoring. The method is validated through simulations and experimental results from a 5kW laboratory system.

Generators working with variable speed, rather than fixed speed, have many advantages, which are well documented in the literature. Higher efficiency, better power to size ratio and less mechanical stress in the system are some of the characteristics of variable speed generators. In particular, variable speed diesel generators can be used to provide small highly portable generation systems for emergency vehicles and military/aerospace applications. Such systems can be used to feed stand-alone linear/non-linear loads if an adequate power converter interface is provided. Four-leg matrix converters can be used as the power electronic interface between variable speed generators and stand-alone loads. The fourth leg provides a neutral point for single phase loads and a path for the circulation of zero sequence currents. When non-linear loads are connected to the matrix converter output, relatively high harmonic distortion can be produced in the load voltage unless an appropriate control system is provided. In this paper the application of a repetitive control system to improve the quality of the load voltage is presented. Experimental results obtained from a prototype are shown and fully analysed.

In the last past years, some countries are enforcing stringent grid codes to regulate the connection of Wind Energy Conversion Systems (WECSs) to the electrical network, mainly because of the high penetration of electric power from this renewable source. Additionally, the trend of wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters appear then as a promising solution for large WECSs, due to its high reliability, controllability and the capability to reach high power ratings. In this scenario, this paper presents a control strategy for the application of the Modular Multilevel Matrix Converter in Multimegawatts Wind Turbines. Extensive computer simulations and a downscaled laboratory prototype, with twenty-seven power cells, are presented to validate the effectiveness of the proposed control system.

Drives based on modular multilevel topologies are the next generation of high-power/voltage converters. In this paper, the Modular Multilevel Converter model is extended to the Back to Back scheme, allowing its control as an unique system, instead two separated converters. Additionally, the proposed control strategy is able to regulate the ac ports and to perform the voltage balancing in both converters by using circulating currents and common mode voltage, providing independence between the converters and the ac ports. Extensive computer simulation and a laboratory prototype of a Modular Multilevel Converter with eighteen power cells feeding an induction machine validate the effectiveness of the presented control algorithm.

In this paper a new methodology to compensate double-frequency power oscillations in unbalanced 4-leg distribution networks is presented. The zero sequence components in the voltages and currents are used to provide an extra degree of freedom to compensate reactive and active power pulsations. A novel closed-loop algorithm for the compensation of fluctuations in the converter side, instead of the grid side is presented in this work. Simulation results are discussed, validating the proposed control system.

Modular Multilevel Converters (M2C) are considered an attractive solution for high power drives. However, its operation at low rotational speeds can produce undesired voltage fluctuations in the M2C capacitors. In this paper, two methodologies to improve the converter performance in this speed range are analysed and tested. The first strategy proposes the control of the inner converter currents combining a synchronous dq rotating frame and resonant controllers to improve the current tracking and to reduce the voltage fluctuations. The second strategy achieves the reduction of the voltage fluctuations by adjusting the DC Port voltage as a function of the machine frequency. Both methods are validated by simulation and experimental work, where a 18 cell M2C prototype is applied to drive an induction machine.

The trend in wind turbines has shown an ongoing power rating growth, reaching sizes up to 10 MW. Multilevel converters have therefore become a favourable solution for Multi-MW Wind Energy Conversion Systems (WECSs), due to high efficiency, reliability, controllability and the ability to reach high power/voltage ratings. Moreover, stringent grid codes to regulate the connection of WECSs to the electrical networks have been developed in countries with a high penetration of wind energy. In this context, this paper introduces the novel application of the Modular Multilevel Matrix Converter for interfacing Multi-MW Wind Turbines to provide decoupled input-output regulation, variable speed operation and fulfilment of modern grid codes.

Owing to the high penetration of electrical energy from wind energy conversion systems (WECSs), some countries are enforcing stringent grid codes to regulate low-voltage-ride-through (LVRT) operation of WECSs. This study presents a self-tuning resonant control (RC) system which can be used for LVRT control of the grid interface in the presence of symmetrical or asymmetrical faults. Only two RCs are required to fully control the four degrees of freedom of the converter output current. Sequence component separation is achieved using a new fast-convergence delayed signal cancellation method which is also discussed in this work. The mathematical analysis and design procedure of the control system are presented. Simulation and experimental results obtained from a 3 kW prototype are discussed in this study.

[EN] The open-ended winding induction machine fed from a standard two-level Voltage Source Inverter (VSI) arrangement is an attractive solution for AC drives. An alternative power converter approach is to use an Indirect Matrix Converter (IMC) consisting of a matrix converter AC-DC input stage and two VSI output stages. This latter topology provides fully bidirectional power flow operation and requires only a small input filter. In this paper, a vector control strategy for an open-ended winding cage induction machine fed by a two-output IMC is presented. The modulation scheme for the input power converter stage aims to modify the virtual DC link voltage depending on the load voltage requirement. Additionally, the modulation strategy for the dual-inverter output aims to eliminate the zero sequence voltage applied to the load. A vector control scheme is used and the full system is modelled using a PSIM and MATLAB/Simulink platform. Experimental results from a 7.5 kW prototype are presented, demonstrating the feasibility of the topology and control strategy., This work was supported by The Chilean Research Fondecyt [grant number 1151325]; CONICYT/FONDAP/15110019.

One of the well-known methods to share active and reactive power in microgrids (MGs) is droop control. A disadvantage of this method is that in steady state the frequency of the MG deviates from the nominal value and has to be restored using a secondary control system (SCS). The signal obtained at the output of the SCS is transmitted using a communication channel to the generation sources in the MG, correcting the frequency. However, communication channels are prone to time delays, which should be considered in the design of the SCS; otherwise, the operation of the MG could be compromised. In this paper, two new SCSs control schemes are discussed to deal with this issue: 1) a model predictive controller (MPC); and 2) a Smith predictor-based controller. The performance of both control methodologies are compared with that obtained using a conventional proportional integral-based SCS using simulation work. Stability analysis based on small signal models and participation factors is also realized. It is concluded that in terms of robustness, the MPC has better performance.