Showing papers by "Telles Brunelli Lazzarin published in 2017"

A Family of Single-Phase Voltage-Doubler High-Power-Factor SEPIC Rectifiers Operating in DCM

Abstract: This paper extends the voltage-doubler concept to the single-phase SEPIC rectifier in discontinuous conduction mode and, as a consequence, novel rectifiers are proposed. A comparison with the classic SEPIC rectifier shows that the proposed converters can either provide reduced voltage stress on the semiconductors for the same output voltage level or supply double the gain of the output voltage with the same voltage stress. The proposed voltage-doubler SEPIC rectifiers provide a high power factor with no current control and they can be applied in order to improve the static gain of the structure, which can make the SEPIC rectifier suitable for applications that require a high voltage level. In this paper, the generic structure based on a three-state switch, four different implementations of the proposed concept (including bridgeless structures), steady-state analysis, a dynamic model, system control, and experimental results are presented. The proposed rectifiers were verified by experimental results obtained with a prototype built with the following specifications: 1000 W output power, 220 V input voltage, 400 V output voltage, and 50 kHz switching frequency. Peak efficiency of 95.84%, THD of 2%, and power factor of 0.9997 were obtained and, most importantly, double the gain of the output voltage was verified.

Modular ISOP Flyback converter: Analysis of auto-balancing mechanism in steady state

Abstract: DC-DC Modular converters have been proposed as a solution to reduce electrical stresses on semiconductors due to the capacity of sharing current or voltage among modules. This characteristic allows the increasing of the switching frequency, the use of low voltage/current semiconductors and the standardization and expansion of converters. This paper presents a steady-state analysis of an input-series-output-parallel (ISOP) modular Flyback converter operating in the discontinuous conduction mode (DCM). The analysis of the average input voltage and output current balance is presented, whose results depend on the magnetizing inductance and on the duty cycle of any number of modules. Once the equations are obtained, all the results are underpinned by a set of simulations undertaken for three modules. In order to evaluate the theoretical analysis, a prototype consisting of three Flyback modules in DCM operation, with a rated power of 600 W and conversion ratio from 600 V to 200 V, was built. The obtained waveforms show the independence of each module to the connection, leading to an equal division of the current and voltage stresses over the semiconductors. This characteristic, added to the modularity, high efficiency and high current gain, makes the converter an alternative to DC/DC systems where the output voltage must be lower than the input voltage.

DCM forward-flyback converter integrated with a 5-order cockcroft-walton voltage multiplier: A steady-state and resonant current analysis

Abstract: This paper presents the steady state and resonant current analysis of a Forward-Flyback Voltage Multiplier operating in discontinuous conduction mode. The operation stages are approached, taking into account the resonant current. The static gain and the conditions for the operations modes are obtained. A sinusoidal approximation is proposed to represent the resonant current with respect to the number of stages, voltage multiplier capacitors and leakage inductance. The characteristics of voltage sharing among capacitors, that allows the use of small voltage components, and the high-gain with reduced turns of the transformer are verified. Bench tests were made for a 200 V/2000 V prototype, from one to five stages, highlighting the overall circuit effects for a 200 W output power. Obtained waveforms for different number of voltage multiplier stages validate the theoretical and simulated results, making this converter an alternative to isolated DC/DC systems where the output voltage must be higher than the input voltage.

Load voltage compensation of two modes single-phase VSI

Abstract: A typical distributed generation application (DG) only operates in grid-connected mode, for safety reasons. Recently, changes in Brazilian legal framework authorized islanded operation in some cases. This paper presents a dual mode LCL VSI for DG applications. The proposed system can operate in both, grid-connected or islanded, commutating between modes seamlessly. It was designed to operate with non-linear loads for both of its modes, acting as an active filter in grid-connected mode or compensating, through a virtual capacitor strategy, the non-linear voltage drop of the grid-side inductor in islanded mode. A computer simulation was developed and 500 W prototype was build in order to verify the theoretical analysis.

A Single-phase Hybrid Switched-capacitor Inverter For High Step-down Applications

Abstract: In this paper, a novel single-phase inverter topology is proposed, which was derived from the integration of the conventional voltage source inverter with switched-capacitor dc-dc converters. The inverter circuit can provide a low ac output voltage from a high dc input voltage, using low-voltage devices (switches and capacitors). The modulation scheme is the same employed in conventional inverters and the capacitor voltages are self-balanced. The proposed topology is suitable for applications with high conversion ratios. A 2.5 kW prototype (800 V/220 V), which achieved a peak efficiency of 97.8%, was built to show the feasibility of the novel inverter.

Six-phase active PWM rectifier with stationary frame reference control

Abstract: Poly-phase systems have been used for many years in machines and recently in wind power generations. They usually are built by a dual three-phase system, shifted by 30 electrical degrees from each other and with no neutral connection. Typically, this system employs a twelve-pulse diode rectifier to converter ac to dc voltages. However, it may be improved if an active rectifier is used, because it can provide lower distortion in generator currents and regulated output voltage. Taking that into account, this paper proposes a six-phase active rectifier topology for a dual three-phase system. A stationary frame reference for six-phase system is applied to obtain the converter dynamic model in the αβ coordinates and thus a control strategy is proposed in this frame reference. The proposed topology, dynamic model and control strategy were verified by simulation for following specification: 12 kW, 220 V at input voltage and 800 V at the output voltage. The results were appropriated, providing a regulated output voltage, an input current with reduced harmonic distortion and thus high power factor.