Search

This paper proposes a four-port AC/DC-DC/AC converter composed of a half-bridge converter and a full-bridge converter replacing their inductive filters by means of a transformer. The power balance between the ports is achieved through both duty-cycles and the phase angle between the voltages applied by these bridges. The analysis of the converter was accomplished by using the superposition principle allowing to define different modes of operation. Furthermore, a control strategy is proposed for an application of the converter and in order to corroborate the theoretical analysis, simulation and experimental results are introduced. Finally, the performance of the converter is assessed as a function of the delivered power.

In this paper, a novel single-phase five-level inverter is proposed. It is composed of eight switches and one flying-dc-source. Compared with the conventional active-neutral-point-clamped five-level inverter, the proposed structure has the same number of active devices and it does not require any sensor or balancing circuits to control the split dc-link capacitors. Thereby, the proposed converter reduces the cost and the complexity of the control system. Additionally, the proposed inverter has the capability of boosting the input voltage by a factor of two, which means it allows a reduction of 50 % in the DC-link voltage requirement and it does not require an intermediate DC-boosting stage for applications such as, photovoltaic panels and full-cells systems, characterized by a low and unregulated input voltage. Experimental results have been performed in order to validate the theoretical analysis of the proposed system.

A new five level inverter with six main inverter switches and two flying capacitors is proposed. A DC-DC boost-flyback converter (BFC) supplies the DC-link and also the two flying capacitors voltages. The principle used results in the smallest thermal stress and losses when compared with other investigated five-level topologies with reduced device count. Operating principle, switching states, and PWM strategy is presented. Simulated and experimental results validate the theoretical studies.

This paper presents the application of the Finite Control Set - Model Predictive Control (FCS-MPC), or simply MPC, for grid current control for three rectifier topologies based on dual converters. Two of the topologies have a reduced number of controlled switches, replacing some of the Insulated Gate Bipolar Transistors (IBGTs) by diodes. Despite these topologies have been discussed in the literature, they always employ Proportional-Integral (PI) controllers and pulsewidth modulation (PWM) strategies. This paper will show that the MPC method is able to provide sinusoidal currents with low harmonic content. Simulations are performed in order to compare MPC and PWM performances and an experimental result is provided for one of studied configurations. It is shown that for the same average switching frequency, MPC provides currents with harmonic content somewhat higher than PWM. On the other hand, transient response to reference changes is much faster and smoother when MPC is applied.

New questions related to the quality of the grid energy and reliability with the insertion of distributed energy resource (DER)s, and, new problems may arise as voltage variations by load variations and the determination of current limits. Thus, the control of the DER units should be cooperative and active to support the voltage regulation, as the frequency is still controlled from the main grid. Most of control strategies applied for distributed generation systems (DGS) have relied on power controls based on active (P) and reactive reactive (Q) power droop to achieve. This paper shows a comparative study between the classic PQ droop control and a accurate IV droop control.

Software startups play an important role to foster innovation, economic growth, and job creation in a region. Startups are likely to increase their odds of thriving if they are embedded in a startup ecosystem. Actors of an ecosystem cocreate value, share resources, and support the prosperous evolution of peers. In recent years, software startups have been the focus of intensive research by the software engineering community. In this paper, we conducted a tertiary study to synthesise literature in the field of requirements engineering in startups. We concluded that there are limited empirical studies reporting an in-depth contextual analysis on how software startups perform requirements engineering. In parallel, we conducted a case study of startups based at Digital Port ecosystem. Our empirical results confirm what has been presented by literature that startups adopt requirements practices in a flexible and informal manner. In fact, as novel empirical evidence, we observed that even as startups evolve by acquiring the first paying customers and growing the customer base, requirements practices remain very pragmatic. Our results also reveal how actors of the studied ecosystem interact to support the co-evolution of startups.

This paper reports a new five-level pulse-width modulation (PWM) that includes a flying capacitor supplied by a boost/flyback DC-DC converter that also provides the DC-bus voltage. There is a significant reduction in the number of power devices and capacitors required to implement a conventional five-level flying capacitor inverter. The topology is free from complex PWM control to regulate the capacitor voltage and is capable of operating under any power factor condition. Simulated and experimental results validate the converter principle.

The use of coupled inductor inverters (CII) is attracting due of its several advantages as: 3-level output voltage, reduced number of controlled switches and no dead-time requirement. However, while using the conventional phase-shifted pulse width modulation (PS-PWM) shows low performance, space vector techniques presented in the literature requires a complex algorithm implementation. This paper applies an enhanced phase-shifted PWM (EPS-PWM) in order to improve quality of CII phase and line-to-line voltages, also the phase currents. The CII operation principles are discussed, and its performance using the PS- and EPS-PWM are compared in therms of voltage and current harmonic distortions. Simulations and experimental results are presented in order to validate the presented modulation performance.

This paper presents a Finite Control Set Model Predictive Control (FCS-MPC) method applied to a Half-Controlled Boost Rectifier (HCBR) that can be used in variable-speed permanent magnet generator. Performance comparison of the system using conventional controls and predictive control methods, in order to regulate the input currents, is accomplished. Results show that the predictive control presents better performance than hysteresis and linear control with pulse width modulation.

This paper presents a dual converter-based system in order to connect a three-phase doubly-fed induction generator (DFIG) to a dc-microgrid. The dual converter consists in connecting a three-leg rectifier at each side of the stator windings, in an open-end winding (OEW) configuration, adding up to two rectifiers and therefore six converter legs. Usually, these legs are composed of Insulated Gate Bipolar Transistors (IGBTs). In order to reduce the number of controlled semiconductor switches and the cost of the system, one of the rectifiers has its IGBT switches replaced by diodes. Pulsewidth modulation (PWM), power control and a zero-sequence current minimization strategies are discussed. Simulation and experimental results were also obtained, showing steady state results for a 0.56 kW DFIG operating at unity power factor.

In this paper, a Four-Port AC/DC-DC/AC conversion system is proposed using two full-bridge converters and a high-frequency transformer following the principle of Dual Active Bridge Converter. Two full-bridge AC/DC single-phase converters are connected by coupling their boost inductance to create a high-frequency transformer of the resulting proposed converter. The isolated power transfer between converters is controlled by the duty cycles and the phase-shift applied to the primary and secondary of the split transformer. The boundaries of the switching modes and the power transferred through the high-frequency transformer were obtained analytically. The system feasibility was validated by simulations and by a 300 W prototype with 94.9% maximum efficiency.

This paper deals with a system composed by a photovoltaic array feeding a Neutral-Point-Clamped inverter by a dc-dc multilevel boost converter. The system is able to adequately operate under partial shading condition. A current control allows for the boost converter to operate at high frequency while the Maximum Power Point Tracking (MPPT) with the help of Fibonacci search. System operation is explained as well as its model, control and PWM strategy. Simulation and experimental results validate the theoretical studies.

Land surface emissivity (LSE) is a parameter that must be known to retrieve land surface temperature (LST). Thus, this work presents the application of NDVI Threshold Method (NDV/THM) in a field of coastal dunes with partial vegetation cover in Southern Brazil. We used a spectral library of quartz samples measured at different temperatures to minimize the error of the initial emissivity value in the method. Finally, we calculated LST through the improved single-channel (ISC) algorithm by using the band 10 (10,6-11,19μm) of a Landsat-8 image. The quartz emissivity was tested at two temperatures: (1) the emissivity value corresponding to the higher brightness temperature obtained from the image; (2) the emissivity value based on the saturation point of the spectral library. We verified that this approach is indispensable to acquire more reliable data. The ISC algorithm may produce an error up to 10K in the LST retrieval if the quartz emissivity is not correctly calibrated.

This paper proposes a discrete repetitive controller to be applied to control the output current of a full-bridge single-phase grid-connected inverter. The current is synchronized with the voltage grid by a phase-locked loop algorithm. The control design procedure assures system stability, robustness to voltage harmonic distortions and a fast error convergence. It is based on a notch filter which compensates the resonant peak from a plant formed by a LC filter at the inverter output in parallel with a local resistive load. To increase the margin stability of the system, a low-pass filter is employed in the positive feedback of the repetitive controller. To verify the control technique, simulations employing the PSIM software are performed. Moreover, a DSP-based kit board from Texas Instruments (TMDSHV1PHINVKIT) containing a full-bridge inverter and a LC filter is used to experimentally test the controller. Results demonstrate the method robustness against harmonic distortions and also show the control efficacy to promptly track abrupt changes in the reference amplitude for the current.

This paper presents a single-phase to three-phase ac-dc-ac converter for a wind energy conversion system based on Doubly-Fed Induction Generator (DFIG). The ac-dc-ac converter has six-leg and is composed of three converters. The grid-side converter (GSC), which is responsible for power factor and dc-link voltage controls, the stator-side converter (SSC), which guarantees the control of the stator voltage, and the rotor-side converter (RSC), which is responsible for vector control of the generator. The GSC and SSC use an ac-dc-ac three-leg converter with a shared leg. The model system, pulse-width modulation (PWM) and control strategies are presented. Finally, simulation and experimental results are presented.

In this paper a Wind Energy Conversion System based on Doubly Fed Induction Generator (DFIG) with an additional Series Grid Side Converter (SGSC) without transformer is proposed. Unbalanced stator voltages may be compensated by SGSC, thus eliminating unbalanced stator and rotor currents, active and reactive power oscillations, and shaft torque oscillations. Moreover, the control strategy of the proposed system keeps sinusoidal grid currents with a high power factor even during voltage sags. Simulation and experimental results are presented to evaluate the proposed system.

This paper proposes a 5-level single-phase multilevel inverter topology with reduced number of components. In order to validate the proposed structure, simulation and experimental results are presented. In addition, the proposed topology is compared with an existing counterpart structure in terms of number of levels and number of devices and value of power supply.

Among the available renewable energy sources, the photovoltaic (PV) one is a fast growing market all over the world. Such renewable energy generation system is normally composed of dc-dc and dc-ac converters and correlated control circuits. Also, for medium and high power PV systems optimal operation, it is interesting to employ a decentralized maximum power point tracking (MPPT) control instead of a centralized one. This paper presents a two-input single switch dc-dc converter controlled by a single switch. The proposed converter performs independent energy flux control for each dc input while minimizing the number of switches and drivers. Maximum power point tracking technique is employed in order to confirm the performance of the proposed converter when applied to photovoltaic systems. Simulation and experimental results verify the proposed scheme feasibility.

This paper investigates three AC-DC-AC multilevel topologies for three-phase four-wire (3P4W) applications obtained from an interconnection of three-leg voltage source converters (VSCs). The topologies provide bidirectional power flow and can be applied in line voltage regulators, universal active power filters and uninterrupted power supplies (UPS). Operating principles, a pulse-width modulation (PWM) technique and an overall control strategy are developed. The PWM and control strategies are suitable to regulate the DC-link voltage and to optimize the harmonic distortion, reducing switching stress and power losses. Simulation results are used to compare the proposed configuration with a conventional solution in terms of harmonic distortion and semiconductor losses. Experimental results are presented to validate the theoretical considerations and were obtained by using IGBTs with dedicated drives and a digital signal processor (DSP) with appropriated plug-in boards and sensors.

Normally, a photovoltaic energy generation system is composed of dc-dc converter, dc-ac converter, and their corresponding control circuits. This paper presents a two-input two-output single switch dc-dc converter with a reduced number of switches, drivers and controllers. The proposed converter performs independent energy flux control for each dc input while producing two symmetrical, automatically balanced, output voltages. A very simple MPPT technique, based on fractional voltage control technique, is employed to confirm the performance of proposal. Simulation and experimental results verify the proposed scheme feasibility.

In this paper a control strategy of a wind turbine based on Doubly-Fed Induction Generator (DFIG) supply with unbalanced grid voltage is presented. In the proposed control strategy, the rotor side converter (RSC) is able to keep sinusoidal stator and rotor currents and also remove the pulsations in either stator active power or stator reactive power (this case eliminates the oscillation in electromagnetic torque). Unlike the other reported techniques, rotor currents scheme has been implemented in the stationary stator reference frame. These currents are regulated by a synchronous controller (similar to resonant type) without any positive or negative component decomposition. Simulation results are presented.

The power quality in grid is being deteriorated by the proliferation of nonlinear loads such as static power converters and electronics loads and reactive loads. On the other hand, the demand for energy has been increasing rapidly due to the growth of world population and technologies. In this scenario, cogeneration based on renewable energy sources as solar and wind, and alternative energy sources as fuel cells is a reality. In this sense, single-stage multifunctional converters which integrate functions as active power filter, power factor corrected rectifier and alternative source grid connected inverter. Thus, such converters are suitable for distributed generation systems besides reduced number of signal/power devices. This paper proposes a control strategy derived from One Cycle Control (OCC) technique for an integrated power quality converter. Important features of OCC technique are simplicity, fast response, large stability range, robustness and low cost. Essays of simulations are carried to confirm the operation of the proposal.

This paper proposes two seven level asymmetric inverter with coupled inductors that enable a reduction in the number of controlled switching devices. However, the lack of redundant states and difference in the maximum pole voltages reduce the performance of the inverters due to higher winding currents and saturation of magnetic core. For mitigating those issues, a coupled inductor with elevated magnetizing inductance is used. The operation principle, conducting states and modulation strategy are described. Simulation and experimental results demonstrate the feasibility of proposed topology.

This paper proposes a system composed of a three-level Neutral Point Connected inverter fed by photovoltaic panels. The system is able to operate adequately even under partial shading operation by controlling the DC-link neutral point injected current. System model, PWM strategy, maximum power point tracking, and control logic for balancing the DC-link capacitors voltages are presented. Experimental results corroborate the theoretical studies.

This paper proposes a 5-level three-phase hybrid multilevel inverter topology with improved capacitor voltage balance and reduced capacitor rating. In order to validate the proposed structure, simulation and experimental results are presented. In addition, the proposed topology is compared with an existing counterpart structure in terms of capacitor voltage oscillation, capacitance size, losses, number of devices and value of power supply.

This work proposes the usage of a repetitive-based control to dynamically restore the voltage applied to grid sensitive loads. The control is able to wipe off harmonic distortion and relies on simple transfer function. As a consequence, there is no need to apply harmonic selective filters. Moreover, the filter is able to work on sinusoid references and avoids employment of the dq transform. The design of the control parameters along with the system stability are discussed. A Simulink-based simulation has been built to verify the designed control performance. The experimental results are extracted from a setup of three-phase compensator which copes correctly with different scenarios of sagged and harmonic distorted voltages.

This paper investigates the fault-tolerant capacity of a modified three-level Active Neutral Point Clamped (ANPC) inverter when its switches are submitted to open and short-circuit failures. The main change consists on adding a thyristor in parallel with each inverter switch. This improves the behavior of the converter when a switch fails. Fault detection and identification methods are presented together with configured schemes for ten types of failures. Simulation and experimental results validate the theoretical studies.

In this work it is proposed a DSP based, OCC control strategy for APF, which is able to work in case of unbalanced grid voltage, i.e. when it is affected by a common mode voltage. Proposed strategy is based on an OCC rectifier control which utilizes an input resistance control to set up dc-link voltage and achieve a unity power factor as well, and a lead-lag compensator to average phase current. In this sense, APF proposed strategy uses input resistance control while lead-lag compensator is used to filter harmonics in grid current. Simulation and experimental results confirm present proposal.

In this work it is proposed a control strategy for a shunt Active Power Filter (APF) based on an One Cycle Control (OCC) Rectifier, implemented by DSR An input resistance controller to set up dc-link voltage and a lead-lag compensator to average grid current is part of this work. In addition, as DSP implementation can increase the possibilities of control of complex systems. An example of this feature is further investigated, as the ability of proposed OCC based APF to control unbalanced non-linear load. Simulation and experimental results validate the proposed work.

This paper proposes a modification in both topology and operation algorithm for the existent 2/3 level converter. Such strategy reduces the effort of the algorithm calculation. Also a reduction in the number of components is introduced while maintaining the previous characteristics. The THD and losses of the two-level converter, the NPC three-level converter and the 2/3-level converter are compared, since the last topology has characteristics inherent to the other two. Simulated and experimental results demonstrate the validity of the proposed method and its advantages.

This paper proposes a 5-level half-bridge hybrid converter topology with improved capacitor voltage balance and reduced kVA rating. In order to validate the proposed structure, experimental results are presented. In addition, it is compared with an existing counterpart structure in terms of capacitor voltage oscillation and capacitance size.

This paper presents two conversion systems based on six-phase machine (SPM) and three-phase and single-phase series-connected converters without isolation transformers. Configuration 1 can be used with induction (IM) or permanent magnet synchronous (PMSM) machines, while configuration 2 is partially reversible and is more indicated for permanent magnet synchronous machines. Compared with the conventional back-to-back nine-leg conversion system, the proposed converter permits to reduce the power processed by the converter switches, the dc-link voltage and the harmonic distortion or the switching frequency. Furthermore, the proposed configurations guarantee the feasibility of the system when highpower applications are considered. The complete analysis of the systems, including the PWM techniques, is presented and compared with the conventional one. The simulation and experimental results are presented.

This paper applies a proposed digital One-Cycle Control technique to the three-phase Active Neutral Point Clamped (ANPC) rectifier and three derived topologies as well. Its principal advantages are simplicity, robustness and low cost besides the fact that it does not need any voltage detector, template or multiplier for the utility power factor control. Experimental results confirm the feasibility of both the proposed controller and topologies.

This paper investigates the digital implementation of a modulation strategy that can completely remove the low-frequency voltage oscillation, which appears in the neutral point, for all the operating points and for any kind of loads. The implementation is based on a hybrid modulation technique that produces low switching losses and is simple to implement. Losses, average switching frequency, and performance in terms of voltage balance and low frequency neutral point oscillation, THD, and WTHD are investigated. Simulation and experimental results confirm the feasibility of the approach.

This paper investigates multilevel topologies based on the concept of nested arrangement. Such topologies are called nested multilevel converters since the central point of the legs are connected at the same point, with the external leg involving the internal one. The main contribution of this paper is to furnish a formal presentation of the nested multi-level configuration, including its generalization. This configuration presents advantages when compared to the equivalent NPC topology in terms of reduced number of diodes and consequently higher efficiency. The studied configurations can be considered as an interesting option for applications that demand a number of levels higher than or equal to four. Simulated and experimental results are presented to validate the theoretical expectations.

Main goal of this paper is to investigate four three-phase proposed AC-to-AC converters. Coupling of input inductors of a basic topology, allows improve the input power factor and input current waveform and the introduction of a three-level leg allows for DC-bus voltage control. This happens without any complicated switching modulation or current feedback control. The topologies can operate with either variable or fixed output frequency. The main characteristics of the proposed configurations are presented and experimental results verify the theoretical studies.

The three-phase three-level neutral-point-clamped (NPC) topology is widely employed in rectifiers, active power filters, and electric machine drives. This paper proposes an alternative control strategy for the NPC topology based on the one-cycle control technique and the hybrid pulsewidth modulation strategy. Optimal unbalanced load compensation is achieved with the proposed scheme, of which the principal advantages are simplicity, robustness, and low cost. Experimental results confirm the feasibility of the proposed controller.

Wavelets are attractive for applications that require analysis of electrical signals. In contrast to classical methodologies used to determine the spectrum of a signal in steady-state or not, and thanks to the STFT (Short Time Fourier Transform), wavelets are an interesting approach which is efficient to localize temporal peculiarities. This work presents a methodology to identify and diagnose a furtive or intermittent fault in three-phase inverter converter using a function wavelet mother type Mexican Hat. Such monitoring is based on the stator current analysis of an induction motor. Simulation and experimental results validate this study considering only the fault in the converter supplying the machine in open loop.

The main goal of this paper is to propose three single-phase AC-to-AC converters based on an improved version of the AC-DC Nabae converter. The proposed topologies improve input power factor and input current waveform without any complicated switching modulation, such as pulse width modulation, or feedback control. These topologies can operate with either variable output frequency or fixed output frequency. The main characteristics of the proposed configurations are presented and experimental results verify the theoretical studies.

This paper aims to apply a universal filter configuration to supply a three-phase motor from the single-phase grid, in this case the motor must be supplied with the same frequency of grid. The initial hypothesis consider that is possible to minimize the converter's losses through the variation of motor voltage phase and through selection of an appropriate transformer. To reduce the IGBT dual module losses means to reduce the operational cost of the system. The initial investment of this configuration is very attractive for treating of a converter that works in shunt, in other words, only a part of the load power flows through the converter. Analysis in steady state has been realized, as well. Experimental results are showed to demonstrate the theoretical studied.

The large conversion rate boost converter is widely applied in uninterruptible power supply (UPS), and in fuel, embedded, and photovoltaic systems. Its most important feature is the conversion efficiency, followed by the converter size and cost. However, disadvantages that come out when large conversion ratio is required are: near unity duty cycles lead to difficulties in the operation at higher switching frequencies; also the boost switch suffer from both high voltage and current stresses, which leads to high power losses, independently of its operation in either continuous conduction mode or borderline conduction mode. The dc-dc converter investigated, based on the inductor split, reduces switching power losses and reduces the conduction power losses. Also, the borderline conduction mode is investigated and a control strategy is conceived from one-cycle control technique. Finally, a ZVS/ZCS softswitching circuit with regenerative clamping action is implemented. Simulation and experimental results validate the theory.