Sergio Vidal Garcia Oliveira

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.

Comparison of digital LQR techniques for DC-DC boost converters with large load range

This work presents a comparison of three state feedback controllers suitable for application to DC-DC boost converters with large load range. These converters are an important stage in several renewable source systems. The first controller is a conventional LQR designed for a single operating point. The second controller uses the switching between LQR controllers designed for a set of load conditions (local controllers). The third controller is a fuzzy logic based controller which is based on the convex combination of the local controllers. The second and the third controllers use the load current as a decision variable. The implementation of all controllers is carried out in a TMS320F2812 fixed-point DSP, considering the transport delay and the limitation of data format from this digital control platform. Simulation and experimental results obtained for the three control strategies submitted to load disturbances allow to observe the quality of the transient and steady state responses, leading to the conclusion of the superiority of the fuzzy logic based controller in terms of a better tradeoff between performance and spent of control energy.

Parameters design for modular multilevel converter (MMC)

The modular multilevel converter is one of the most interesting transformerless multilevel converter topology intended for medium and high-voltage power conversion. Thus, as a new topology, a fewer design guidelines are presented in the literature, on the other hand there are many restrictions. This paper presents aims to be a design guide lines to project a MMC system. The minimum submodule capacitor requirement is presented as the capacitance related to the load displacement angle, operating frequency and output power. The arm inductor design include three parameters: current ripple, fault condition and circulating current. Semiconductor current stress are calculated using average quasi-instantaneous values and rms quasi-instantaneous values will be used. From the performed analysis some normalized abacus are derived and can be used as start point for a new MMC design. The results were validated using MATLAB simulation. Furthermore, experimental results based on 2.2 kW, 5 kHz switching frequency prototype are also include and analyzed.

Inner current control method for modular multilevel converter applied in motor drive

This paper presents the modular multilevel converter as medium voltage motor driver. An investigation of the capacitor requirements is performed and a novel control method, based in the inner current control, is proposed. This method can ensure the capacitor balancing as well minimizes the harmonic current in the converter phases. The control method is evaluated by computational simulations of a three-phase driver of a 350 kW, 2.3 kV induction motor. The simulated results have proven the effectiveness of the control structure in the startup procedure and steady state operation.

Design and comparative analysis of multiple controllers applied to DC-DC converters with large load range

This paper presents a new controller design methodology for DC-DC converters operating with load varying in a large range. The proposed methodology employs a genetic algorithm to find LQR controllers with optimum performance by means of ITSE criterium and control action. A fuzzy logic based strategy is then employed to combine these local controllers, resulting in a strategy which guarantees good performance for a large range of load values. From Tellegen theorem, a load resistance estimator is obtained. The estimated resistance is used as the decision variable for the fuzzy supervisor controller. The proposed methodology is compared with the conventional LQR technique, based in a single controller, and with a controller switching strategy. Simulation results illustrate the superior performance of the converter with the application of the proposed methodology.

A new high gain non-isolated DC-DC boost converter for photovoltaic application

This paper introduces a new topology of the high gain non-isolated DC-DC boost converter with central point on its output. The proposed converter is derived from the quadratic single switch boost converter and the three level boost converter. The static gain of this converter is bigger than the one from the conventional boost converter and the maximum voltage on both switches is half of the output voltage. Qualitative and quantitative analysis of the operation stages, the main waveforms and the experimental results of a 520 W prototype are presented. The converter is aimed for modular photovoltaic application.

Multiple controllers for boost converters under large load range: A GA and fuzzy logic based approach

This paper presents a new methodology to design controllers for boost converters operating in a wide range of load variation. The proposed technique uses genetic algorithm to find local LQR controllers providing optimal performance in terms of overshoot and ITSE criteria. Fuzzy logic strategy is then used to combine these local controllers, yielding a strategy that guarantees good performance for a large set of load conditions. The proposed approach is compared with a conventional technique based on a single controller and with a strategy of switching controllers. Simulation results illustrate the superior performance of the converter with the proposed controller.

Fuzzy control of a three-phase step-up DC-DC converter with a three-phase high frequency transformer

This paper presents a closed loop fuzzy logic control technique applied to three-phase step-up DC-DC converter with a three-phase high frequency isolation transformer. This converter was developed for industrial applications where the dc input voltage is lower than the output voltage, for instance, in installations fed by battery units, photovoltaic arrays or fuel cell systems. The converters main characteristics are: reduced input ripple current, step-up voltage, high frequency isolating transformer, reduced output voltage ripple due to three pulsed output current and the presence of only three actives switches connected at the same reference, this being a main advantage of this converter. By means of a specific switch modulation, the converter allows two operational regions. A Fuzzy logic control strategy is applied to input-current and output- voltage regulation. The chosen controller algorithm is a PI-like fuzzy control based on the error and change of error of the reference signal. The Takagi-Sugeno inference process was choosen due to lower processing required to obtain the results. Theoretical expressions and simulations results are presented for a 6.8 kW prototype, operating in region R2 in continuous conduction mode.

Analysis of PV arrays for residential applications using a Three-Phase step-up isolated DC-DC converter with High-Frequency Transformer

This paper has the objective of performing analyses with the series, parallel, and multi-string array with a few photovoltaic (PV) modules under partial shading conditions, with these analysis it is chosen an array of PV modules with total power installed of 6kW for powering a residence using a single DC-DC converter. With the chosen array configuration, it is performed the design of the three phase step-up isolated DC-DC converter with high frequency transformer, in charge of tracking the maximum power point and to provide energy to a grid-connected inverter. Simulation results are presented to demonstrate the advantages of the parallel array using the DC-DC converter.

Analysis and design of an isolated step-up DC-DC converter based on Three-Phase High-Frequency Transformer for PV applications

The objective of the proposed system is powering a residence with an array of PV modules with total power installed of 6kW. The choice among the series, parallel, and multi string arrangements is based on the analysis of photovoltaic (PV) under partial shading. Analyses are performed with different arrays of PV modules to obtain the better choice. From these analyses is designed a three-phase step-up isolated DC-DC converter with high frequency transformer to track the maximum power point and provide energy to a grid-connected inverter. Simulation results are presented for validation and demonstrate the advantages of using the DC-DC converter with the parallel array.