Leandro Michels

Autonomous street lighting system based on solar energy and LEDs

This work presents an autonomous street lighting system based on solar energy as primary source, batteries as secondary source, and lighting emitting diodes (LEDs) as lighting source. This system is being presented as an alternative for remote localities, like roads and crossroads. Besides, it presents high efficiency, because all power stages are implemented in DC current. The design of LEDs fixture, in order to replace a 70W high pressure sodium (HPS) lamp, is performed. This design takes into account the human eye response in scotopic conditions. LEDs driver and battery charger experimental results are presented. The battery charger presents three control modes: maximum power point tracker (MPPT) mode; constant current mode; and constant voltage mode. The control mode depends on the battery state (charged/discharged), and solar irradiance level. The battery charger input impedance is analyzed in order to ensure that the MPPT is obtained for any solar irradiance and panel temperature.

Modeling and Digital Control of a Single-Stage Step-Up/Down Isolated PFC Rectifier

This paper presents the dynamic modeling and digital control of a single-stage isolated current rectifier with power factor correction based on the integration of full-bridge and flyback converters. This converter is designed to operate with adjustable output voltage so that it can operate in two distinct operation modes, depending on the input and output voltages. Therefore, small-signal state-space average models are obtained for the converter operating in step-down and step-up operation modes, and analysis and design of the digital control system are included for different operating points. Experimental results based on a 3-kW prototype are presented to validate the proposed control system under distinct conditions.

Comparative analysis of series and parallel photovoltaic arrays under partial shading conditions

This paper presents a comparative analysis among different arrays of photovoltaic (PV) modules under partial shading conditions. This scenario is typical of a residential area where partial shading can occur due to trees or neighbor buildings. The main objective is to evaluate the power extraction under partial shading in parallel and series PV modules arrays, and compare the results. Simulation and experimental results are presented to validate the proposed analysis.

Regenerative Undeland Snubber Using a ZVS PWM DC–DC Auxiliary Converter Applied to Three-Phase Voltage-Fed Inverters

This paper proposes an energy regeneration circuit for three-phase voltage-fed inverters using a modified Undeland snubber. The proposed system uses a quasi-square-wave zero voltage switching dc-dc auxiliary converter to regenerate the energy from snubber capacitor to the dc bus. The regenerative circuit uses a single active switch, and it operates independently of the three-phase inverter. Operation stages, theoretical waveforms, and a design methodology are presented. Experimental results based on a 4.5-kVA three-phase inverter prototype are included to validate the proposed topology.

Analysis and Design of an Electronic On-Load Tap Changer Distribution Transformer for Automatic Voltage Regulation

Current solutions for voltage regulation close to the consumers usually require technicians for manually changing the taps of the transformer, which may entail high maintenance costs and uncontrolled voltage levels. In this context, electronic on-load tap changers (OLTCs) are a prospective solution for present-day and future power grids, since they provide automatic voltage regulation. This paper presents the analysis and design guidelines for an electronic OLTC applied to a distribution transformer, encompassing the physical layout design for external access to the transformer tap terminals, the evaluation of current and voltage transients during the commutation process, and the dimensioning of the electronic switches and protection system. The dielectric withstand of the proposed physical layout is also analyzed through the finite-element approach, guaranteeing adequate insulation for the electronic circuits located outside the transformer tank, which facilitates circuitry maintenance and provides high modularity. The electronic switches and the protection circuit of the electronic OLTC are experimentally tested under normal and faulty operational conditions in a 5 kVA, 7.69 kV/220 V, single-phase earth return distribution transformer.

Design of a LCL filter for leakage current reduction in transformerless PV grid-connected three-level inverter

This paper presents a new methodology to design a passive damped LCL filter for a transformerless three-level photovoltaic grid-connected inverter. In addition to the conventional specifications, this paper also includes the leakage current limits in the filter design. An analysis of the passive damping scheme is presented aiming to define the LCL filter resonance damping which in turn affects directly the behavior of leakage current. It is shown also that grid inductance can modify the passive damping design parameters, once that leakage current and stability are affected. Experimental results are given to demonstrate the good performance of 10 kW PV inverter and to validate the proposed filter design methodology.

Modeling and analysis of single phase full-bridge PFC boost rectifier using the LTP approach

Most design techniques for power factor correction converters considers the cascade control technique assumes that output voltage ripple is removed from the feedback path using a compensator with low-pass characteristic. This strategy allows power factor correction and output voltage regulation but result in voltage loop with a poor dynamic performance. In order to mitigate this problem many designers have used notch filters in the control loop to increase the bandwidth of the controller without compromise the power factor characteristic. However, conventional linear time invariant approach is no longer valid to analyze the stability of these systems. This paper presents the linear time periodic systems approach to analyze the stability of these systems using harmonic transfer functions formulation. The paper details the analysis of a full-bridge power factor correction boost rectifier, including harmonic transfer function converter modeling, frequency response description, time-domain simulation and a stability analysis. Simulation results for two different controllers are carried out to compare linear time invariant and linear time periodic approaches.

Integrated control of a stand-alone photovoltaic system based on decentralized DC-DC converters

This paper presents a scheme for supervisory control of decentralized stand-alone PV systems. The control is designed to maintain the DC bus regulated independently of solar irradiation, battery charge and load demands. In order to achieve this objective we propose an overall power management strategy to control power flows among PV arrays, battery bank, and inverter. Experimental results for a 480VA converter are provided to validate the proposed supervisory system.

A new digital control system for a single-phase half-bridge rectifier with fast dynamic response

This paper proposes a digital control system for a half-bridge boost rectifier, which composes the input stage of a single-phase transformerless double-conversion UPS. The proposed control system has an inner current loop and two outer voltage loops to maintain near unity input power factor and to regulate the dc bus voltages. The control loops operate with distinct sampling frequencies, so that current loop operates with high sampling frequency, and voltage loops operate with reduced sampling frequency and moving average filters to improve the dynamic response, without affecting the input power factor. Experimental results are included to demonstrate the performance of the closed-loop system.

Active Damping Scheme for Leakage Current Reduction in Transformerless Three-Phase Grid-Connected PV Inverters

This paper analyzes the benefits of the active damping applied to transformerless three-phase grid-connected photovoltaic (PV) inverters using modified LCL (MLCL) filter for leakage current reduction. In comparison with passive damping techniques, the active damping can reduce the MLCL filter resonance peaks, improving the dynamic performance of the control system without addition of power losses. Besides these classical advantages, this paper demonstrates that the active damping also contributes for PV leakage current reduction, preserving the high-frequency attenuation of the MLCL filter. Additionally, an active damping for the inverter common-mode circuit is also proposed, reducing the low-frequency leakage current caused by the common-mode signal used to extend the inverter modulation index. Experimental results are given to demonstrate the leakage current reduction and the grid current control for a 10 kW PV inverter.