Carlos Marcelo de Oliveira Stein

Dynamic behavior of the PV Grid-connected inverter based on L and LCL filter with active damping control

PV Grid-connected inverters must fulfill the standards specifications of current harmonics injected to the grid. In order to satisfy these grid requirements, passive filters are connected between the inverter and the grid. This paper compares the response characteristic of the traditional inductive (L) filter with the inductive-capacitive-inductive (LCL) filter. It is shown that the increasing the inductance L leads to a good ripple current suppression around the inverter switch frequency. The LCL filter provides better harmonic attenuation and reduces the filter size. The main drawback is the LCL filter impedance, which is characterized by a typical resonance peak, which has to be damped to avoid instability. Passive or active techniques can be used to damp the LCL resonance. To address this issue, this paper presents a comparison of passive and active damping strategies. Experimental results are given to support the theoretical analysis and to illustrate the performance of grid connected PV inverter system.

A power electronics and digital control experiment applied to teaching interdisciplinary in electrical engineering

This paper presents a interdisciplinary teaching experience applied to power electronics and digital control. The boost converter with a discrete-time PI controller implemented in a microcontroller is used in this experiment. It is presented a boost converter model and the controller design, beyond the description of instrumentation circuit used. Finally are presented experimental and simulated results. This experiment is applied to UTFPR electrical engineering students.

Input command strategies and analysis for energy optimization of induction motor drives

This paper proposes an analysis of energy consumption in three-phase induction motors (TIM) drives. The main control is based on the indirect field-oriented (IFOC) approach. A performance analysis is carried out for different types of input commands to the speed motor drive, such as the usual step and ramp inputs. Moreover, sigmoid and model reference step based inputs are proposed to smooth the transient behavior as well as to improve the overall drive energy efficiency. In this way, Matlab simulations are carried out to analyze reference inputs for several operation conditions. In order to verify the approach in real situations, a three-phase 4hp motor drive platform is implemented using a PWM inverter and a F28069 DSP. The energy consumption performance is demonstrated through simulations and experimental results.

Emulation of Wind Turbines

This chapter presents the modeling, simulation, and emulation for small wind turbine (WT) systems. The main objective of the emulation system is to reproduce the WT torque dynamic behavior in the generator shaft, which must be similar to one of real horizontal WTs used for distributed generation. The aerodynamic, mechanical, and electrical models for horizontal axis wind turbines (HAWTs) are presented in detail. The models are used for simulation analysis and emulation synthesis. The emulator consists a (i) computational platform, which is based on LabVIEW® environment and runs the model of the WT and (ii) an induction motor (IM) with AC power drive with torque control. The IM shaft is directly coupled with the real small wind generator and corresponding load. Experimental waveforms are also presented to demonstrate the functionality of the system.

Comparison of diode full-bridge rectifier and voltage-doubling diode rectifier in the output stage of active-clamping current-fed half-bridge isolated DC-DC converter

This paper proposes the use of voltage-doubling diode rectifier in the output stage of the zero-voltage-switching active-clamping current-fed half-bridge isolated DC-DC converter and presents a comparison with the classic diode full-bridge rectifier. The design methodology was revised to include the voltage-doubling rectifier and lower side clamp capacitor connection. Two converters (diode bridge rectifier and voltage-doubling rectifier) were designed and experimented to show the expected results and waveforms.

Evaluation of control strategies for LCL grid-tied distributed generation systems

The LCL filter is one of the most used filters in grid connected distributed generation. It is mainly due to its efficiency and reduced physical size when compared to a typical L filter. However, the LCL filter has an inherent resonance frequency that can lead the system to instability or power quality degradation. The converter or the grid current can be used as controlled variable in the current controller. Based in this context, this paper analyzes the stability and studies the control issues brought by the dynamics of the LCL filter. A comparative analysis of the results provided by the use of different controlled variable in the current controller is presented. An evaluation of PI and PD control is done to verify which one is the better option to be used in the current control. A theoretical analysis is carried out based in the pole-zero map of the system, Bode diagrams and numerical simulation.

Design and analysis of a bidirectional battery charger

This work proposes the design and analysis of a bidirectional and isolated battery charger for applications that involve energy storage like UPS or hybrid generation systems. Bidirectional characteristic is fundamental to allow the charge and discharge of batteries in a single equipment, reducing the number of systems and volume in applications that involve energy storage. In addition, the proposed converter provides low voltage and current ripple that are important to reduce electromagnetic interference and to improve the battery life cycle, as well as reducing semiconductors requirements.

Improvement of an emulator-based platform for design of photovoltaic converters and controllers

Platforms based on emulators have become extremely useful in designing the development of static converters and controllers. The Solar Explorer Kit is one of the most used commercial platforms with a photovoltaic panel emulator. This paper presents relevant improvements made in the setup of the mentioned platform. First, the curves for the photovoltaic emulator were modified, since the curves originally used by the platform do not represent the voltage x current relationship of a real photovoltaic panel. Also, a maximum power point tracking (MPPT) technique based on Fuzzy logic was included in the platform for a comparison to the original ones: “perturb and observe” and “incremental conductance”. The three techniques are compared using computer simulations and experimental implementation in the platform mentioned above. The simulation of the system was made using the software PSIM®, and practical implementation was made using the Solar Explorer Kit. Results demonstrate the improvement of the proposed modifications.

Single-phase grid-tied inverters: Guidelines for smoother connection and suitable control structure

This paper presents an analysis of grid connection synchronization characteristics to provide guidelines with a suitable control structure for single-phase grid-tied inverters. Thus, it is analyzed the grid voltage phase for a smooth connection. Moreover, different active power references and the arising of a DC grid current that may occur in the grid synchronization are also considered. Furthermore, it is discussed the effect of the grid voltage phase on the DC current magnitude, as well as the effect of the grid resistance, the grid inductance and their relation to weak grids. Therefore from the grid connection analysis a adequate control structure is suggested. To attain the grid synchronization this paper applies a resonant phase locked loop (PLL). Moreover, a current reference generation in the stationary frame is detailed. A proportional resonant controller is used for the current loop which can additionally provide selective harmonic compensation achieving the pursued control structure. Simulations results present the inverter and grid waveforms for the aforementioned analysis and control structure.

Stability analysis of three-phase stand-alone inverters with LCL filter

The LCL filter is widely used in distributed generation systems. This filter provides a good harmonic attenuation and has smaller physical size when compared with the L filter. One drawback of this filter is its inherent resonance that may lead the system to instability or degrade the performance of the system. The stability of the system is analyzed in the literature just for the grid-tied inverter, but the resonance also damage the power quality when the inverter is in the stand-alone mode of operation. This paper aims to analyze the stability of the inverter operation in stand-alone mode with LCL output filter. The control is done using PI controller in the voltage loop and P controller in the damping loop. The analysis is carried out based in root contour and Bode diagrams. Simulation results ensure the theoretical analysis.