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- Solid-state bipolar Marx modulators and generation of complementary pulses recovering the energy of the magnetizing inductancesPublication . Canacsinh, Hiren; Redondo, Luis; Silva, José FernandoA new methodology to reset an inductive load during the operation of solid-state bipolar Marx modulators is analyzed. In fact, after applying a positive (or negative) pulse to an inductive load, the reset of the magnetizing energy is evaluated considering the application of a voltage amplitude ranging from one to all capacitors voltage after each pulse: i) immediately after the pulse; ii) with a delay after the pulse. These reset alternatives make it possible to produce several current waveforms that can be used to produce magnetic fields used today in magnetic therapy. Four-stage laboratory prototypes of two bipolar Marx modulators have been assembled using 1200 V insulated gate bipolar transistors (IGBTs) and matching diodes, to operate at 1 kV dc input voltage. Outputs are 4-kV bipolar pulses, 0.5% duty ratio, into inductive load and 1 kHz frequency.
- A multilevel converter topology for a STATCOM system based on four-leg two-level inverters and cascaded Scott TransformersPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, José FernandoThis paper presents a new power electronic topology for a STATCOM allowing the generation of multilevel AC voltages. This topology is characterized by a modular configuration since it uses two well known four-leg two-level voltage source inverters. A Scott transformer with multiple secondary windings connects the two four-leg inverters to the grid. One of the important features of the proposed power topology is the capability to generate AC voltages with high number of levels, in spite of using only two four-leg two-level voltage source inverters. To maximize the number of voltage levels a geometric progression ratio of 3 between the windings of the transformers connected in cascade is proposed. However, to reduce the turns-ratio span, alternatively a fractional geometric ratio of 1.5 is also proposed and analyzed. A control strategy adapted to the proposed power converter topology is also presented. Besides the control of the reactive power the regulation of the four-leg inverter DC voltage will also be considered. To support the theoretical studies and assumptions, simulations and experiments are presented. Experimental results were obtained using a low power laboratory prototype. The results shown give evidence to the characteristics and features of the proposed power converter topology and control system.
- Dual 3-phase bridge multilevel inverters for AC drives with voltage sag ride-through capabilityPublication . Fernao Pires, Vitor; Monteiro, Joaquim; Silva, José FernandoOne of the main power quality issues that can affect variable speed drives (VSDs) is the occurrence of voltage sags on their AC power supply. Voltage sags can affect the inverter nominal operation, leading to a malfunction of the AC motor. This paper presents an inverter with resilient capability to voltage sags. The topology consists of two conventional three-phase bridge inverters arranged to require just a single DC source. This inverter is also characterized by a voltage multilevel operation, providing the full advantages of multilevel converters without the need for level balancing. Associated with this AC motor driver, a control system based on a field-oriented controller with a vector voltage modulator that will enable voltage sag ride-through capability is proposed. The proposed control system does not require any changes in the occurrence of voltage sags. To verify the characteristics of the proposed drive and control system, simulation tests are provided. Simulation results confirm the voltage sag resilient capability of the proposed multilevel converter.
- Integrated battery charger for electric vehicles based on a dual-inverter drive and a three-phase current rectifierPublication . Fernao Pires, Vitor; Monteiro, Joaquim; Cordeiro, Armando; Silva, José FernandoThis paper presents a new three-phase battery charger integrated with the propulsion system of an electric vehicle. The propulsion system consists of a dual-inverter topology connected to an induction motor via open windings. The electrical vehicles (EV) batteries are divided by two inverters. This will result in a drive with multilevel characteristics reducing the total harmonic distortion (THD) of the voltage applied to the motor. The modularity of the multilevel inverter will be maintained since two classical three-phase inverters are used. The charger will be fed by a three-phase high power factor current source rectifier. The motor windings will take the role of the DC-inductor required by the rectifier. In this way, an intermediate storage element between the grid and the batteries of the vehicle exist. For the control system of the battery charger, we propose the use of the instantaneous power theory and a sliding mode controller for the three-phase charger input currents. Finally, to verify the behavior and characteristics of the proposed integrated battery charger and control system, several tests are be presented.
- Control of single-phase electrolytic capacitor-less isolated converter for DC low voltage residential networksPublication . Santos, Nelson; Silva, José Fernando; Soares, VascoIn recent years, there has been a desire to improve electricity generation and consumption, to reach sustainability. Technological solutions today allow a rational use of electricity with good overall performance. Traditionally, from production to distribution, electrical energy is AC-supported for compatibility reasons and easy voltage level transformation. However, nowadays most electric loads need DC power to work properly. A single high-efficiency central AC-DC power converter may be advantageous in eliminating several less efficient AC-DC embedded converters, distributed all over a residential area. This paper presents a new single-phase AC-DC converter using one active bridge (most isolated topologies are based on the dual active bridge concept) and a high-frequency isolation transformer with low-value non-electrolytic capacitors, together with its control system design. The converter can be introduced into future low-voltage DC microgrids for residential buildings, as an alternative to several embedded AC-DC converters. Non-linear control techniques (sliding mode control and the Lyapunov direct method) are employed to guarantee stability in the output DC low voltage with near unity power factor compensation in the AC grid. The designed converter and controllers were simulated using Matlab/Simulink and tested in a lab experimental prototype using digital signal processing (DSP) to evaluate system performance.
- A buck-boost converter with extended duty-cycle range in the buck voltage region for renewable energy sourcesPublication . Monteiro, Joaquim; Fernao Pires, Vitor; Foito, Daniel; Cordeiro, Armando; J. F. Silva, Fernando Silva, Fernando A Silva, J. Fernando Silva, J F A Silva, Fernando Silva José; Pinto, SoniaBuck-boost DC-DC converters are useful as DC grid interfaces for renewable energy resources. In the classical buck-boost converter, output voltages smaller than the input voltage (the buck region) are observed for duty cycles between 0 and 0.5. Several recent buck-boost converters have been designed to present higher voltage gains. Nevertheless, those topologies show a reduced duty-cycle range, leading to output voltages in the buck region, and thus require the use of very low duty cycles to achieve the lower range of buck output voltages. In this work, we propose a new buck-boost DC-DC converter that privileges the buck region through the extension of the duty-cycle range, enabling buck operation. In fact, the converter proposed here allows output voltages below the input voltage even with duty cycles higher than 0.6. We present the analysis, design, and testing of the extended buck-boost DC-DC converter. Several tests were conducted to illustrate the characteristics of the extended buck-boost DC-DC converter. Test results were obtained using both simulation software and a laboratory prototype.
- Novel design of the converter for an active UPS application based on Marx modulator concept with supercapacitorsPublication . Pestana, Celso; Canacsinh, Hiren; Chaves, Miguel; Gamboa, Paulo; Cordeiro, Armando; Luís, Ricardo; Martins, Ana Alexandra; Encarnação, Luís; Pereira, Fernando; Silva, José Fernando; Santos, NunoA new Marx modulator 4-leg multilevel converter is proposed to replace the well-known 4-leg inverter fed from batteries in Uninterruptible Power Supply (UPS) applications. The novel design concept for the Marx modulator based multilevel converter is presented and described. Each leg uses 2 Marx modulator modules, each one using an Electrochemical Double-Layer Capacitor (EDLC) (also known as supercapacitor (SC)) energy storage bank. The new topology concept enables multilevel operation with five voltage level per phase, allowing high quality voltage and current waveforms, distributed supercapacitor storage and reduction of supercapacitor bank voltage. The proposed converter can operate as UPS or as Active Power Filter (APF), powering non-linear or/and unbalanced loads, while balancing each leg supercapacitor voltage. A control strategy to choose the redundant vector configuration to balance the supercapacitor voltages is explained. Simulation results are presented for a Marx modulator based interactive 40 kVA UPS.
- High step-up DC-DC converter for fuel cell vehicles based on merged quadratic boost-cukPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, Daniel; Silva, José FernandoMost fuel cell electric vehicles require wide voltage-gain DC-DC converters to increase and equalize the relatively low voltage of fuel cell stacks with DC link bus or energy-storage devices, such as supercapacitors or batteries. This paper proposes two new non-isolated DC-DC converters suitable for such applications, which can be extended to other electric vehicles as well. The proposed converters combine the main characteristics of both quadratic Boost and Cuk converters, offering high step-up voltage and control simplicity using only one ground referenced active power switch. Additionally, the proposed topologies present reduced voltage stress across the active power switch when compared to other boost converters. Considerations about the design of the proposed converters will also be presented. Experimental results obtained using a laboratory prototype validate the effectiveness and feasibility of the proposed topologies and its suitability for fuel cell electric vehicles.
- Dual resonant voltage droop compensation for bipolar solid-state Marx generator topologiesPublication . Canacsinh, Hiren; Silva, J. Fernando A.; Redondo, Luís Manuel dos SantosThis paper discusses a novel methodology to increase the voltage droop compensation range in generalized solid-state bipolar high-voltage Marx modulators with one resonant stage. To maintain the modularity characteristic of bipolar Marx modulators, the imbedding of additional resonant stages is not straightforward. Nevertheless, this paper proposes to add a second resonant stage to the already existing resonant-type voltage droop compensation stage. This second stage increases the voltage droop compensation percentage of a generalized solid-state bipolar Marx generator. The compensation of the bipolar pulse voltage droop is now achieved by adding two auxiliary synchronous compensation resonant voltages, to the output capacitive decaying voltage. Simulation and experimental results are presented for six Marx plus two resonant stages, 16% voltage droop, with 3-kV pulse amplitude, 100-μs pulsewidth, 40-ms relaxation time, and 10-Hz pulse repetition rate.
- Output voltage quality evaluation of stand-alone four-leg inverters using linear and non-linear controllersPublication . Luís, Ricardo; Silva, José Fernando; Quadrado, José CarlosThis paper presents the design and experimental voltage quality evaluation of controllers for the output voltages of 3-phase four-leg voltage source inverters. These inverters are needed in stand-alone power systems to supply linear and non-linear, balanced or unbalanced loads with constant RMS value voltages at fixed frequency. Comparisons include closed loop outer voltage controllers based on predictive, sliding mode and decoupled proportional-integral controllers in dqo synchronous space, fitted with an inner hysteretic current loop vector controller in alpha beta gamma space. The 3-phase four-leg VSI output voltages waveform quality is analysed under unbalanced and non-linear loads.