Heverton A. Pereira

A grid-connected photovoltaic system with a maximum power point tracker using passivity-based control applied in a boost converter

The power generated by a solar photovoltaic panel is strongly dependent on climate conditions. For this reason, a grid-connected system needs a good response for variations in the solar irradiance and temperature. A non-linear control technique which has a good rejection of disturbances is the passivity-based control. This work presents the application of the passivity-based control in a maximum power tracker boost converter for a grid-connected photovoltaic system. The fast response of the control allows a better use of the photovoltaic array energy, increasing the efficiency of the system, and ensuring stability for all operation range.

Performance comparison of phase shifted PWM and sorting method for modular multilevel converters

Modular Multilevel Converters (MMC) are the solution of preference in HVDC applications due to modularity, scalability, low losses and low filtering requirement. Carrier-based (PWM) and carrier-less (nearest level control) modulation can be applied. By using advanced sorting methods focusing on keeping the capacitor voltage ripple under some limit, unnecessary switching events are eliminated leading to reduced switching losses. This paper presents a comparison between the steady-state performances in terms of output voltage THD and equivalent switching frequency of the Phase Shifted Carrier PWM and NLC plus sorting methods.

Adaptive saturation scheme for a multifunctional single-phase photovoltaic inverter

Power inverters are essential components of photovoltaic systems and are designed to process the rated power generated by solar plant. Due to variations in solar irradiance, inverters have a current margin, which can be used in reactive power and harmonics compensation. This possibility, known as multifunctional operation, can be interesting in terms of power factor improvement and voltage control at point of common couple (PCC). Many works propose control strategies for multifunctional inverters. However, during multifunctional operation current limit of the inverter cannot be exceeded. Therefore, inverter needs to compensate partially reactive power and harmonics of the load. This fact is few related in literature. This work proposes a scheme of current dynamic saturation in order to compensate partially reactive power and harmonics of the load. This scheme is based on peak detection algorithm and prioritizes reactive power compensation. Conservative Power Theory (CPT) is used to separate the load current components. Simulation results show performance of the proposed dynamic saturation technique, providing adequate operation of the inverter and partial compensation.

Comparison of solar panel models for grid integrations studies

Photovoltaic systems are highly dependent on climatic conditions in which they are submitted. The incident solar irradiance and temperature are the main factors impacting on the power generated by a solar panel. This paper presents three different models of a solar panel and compare, through simulations, their accuracies and efficiencies, and also shows the advantages and applications of each model. Simulations for each model connected to the grid were also made through a controlled inverter. This inverter keeps the voltage at the terminals of the panel in a constant value equal to its maximum power point, provided by the manufacturer. In the end, it is possible to see that two of the presented models have almost the same behavior while the third one has some discrepancy.

Losses and cost comparison of DS-HB and SD-FB MMC based large utility grade STATCOM

Among the various multilevel converter topologies used in medium and high voltage grid applications, the Modular Multilevel Converter (MMC) has been the most promising since it combines good harmonic performance with low switching frequency and high reliability. A major concern however for inverter designers has been the associated cost due to the need for a large number of power devices and capacitors. This paper focuses on the application of MMC in transformer-less STATic synchronous COMpensators (STATCOMs). Initially, the double-star half bridge (DS-HB) and the single-delta full bridge (SD-FB) configurations are presented. Their specific components are designed in an analytical way followed by loss estimation. Finally, a comparison of the necessary components gives an insight of the total cost associated with each configuration.

Current control strategy for reactive and harmonic compensation with dynamic saturation

The main objective of a photovoltaic (PV) inverter is inject the PV power into the grid. However, due to variations in solar irradiance, inverters have a current margin, which can be used in reactive power and harmonics compensation. This possibility, known as multifunctional operation, can be interesting in terms of power factor improvement and reduction of nonlinear loads impact at point of common couple (PCC). This work applies the instantaneous power theory in order to obtain the harmonic and reactive components of the load current. These components are used as references in the inverter control strategy. Simulation results show reduction in the grid distortion, with improvements in the power quality indexes. However, during multifunctional operation, inverters present a current limit that cannot be exceeded. Thus, this work introduces a dynamic saturation scheme for a multifunctional three-phase inverter. This strategy possibilities partial or total reactive and harmonic compensation without injection of low order harmonics.

Implementation of fault tolerant control for modular multilevel converter using EtherCAT communication

Modular Multilevel Converter (MMC) is very promising technology this days. It offers fault tolerant capabilities and ensures high efficiency with low output voltage harmonic content which results in need for smaller filter size. A disadvantage of the system is that the control becomes more cumbersome due to the high number of the employed submodules. A very efficient way to control the MMC is by using a real time communication platform between the sub-modules and a central unit. Thus, the central unit can deal with the overall control and some of the tasks can be distributed to the submodules. This communication platform has to ensure a perfect synchronization between the modules, and it should be also fault tolerant. The analysis of a MMC based on EtherCAT is presented in this paper from implementation and module fault point of view. The experimental tests show that the MMC operates after communication or module hardware fault occurred.

A novel adaptive current harmonic control strategy applied in multifunctional single-phase solar inverters

The inverter multifunctional operation is based on the harmonic current compensation, generated by nonlinear loads. The traditional harmonic detection methods tracks all harmonic contents of the load current and the control tuning tends to be complex with low flexibility. In many works, the proportional resonant (PR) controllers are used to control the inverter current reference. However, one PR controller needs to be designed for each harmonic frequency and this fact increases the control algorithm complexity. Therefore, this work proposes a novel adaptive current harmonic control strategy applied in multifunctional single-phase solar inverters. The strategy is based on a novel detection method of the harmonic load current. The harmonic current detection method is frequency adaptive and able to detect the load harmonic current with higher amplitude. This method consists in a cascade association of two phase-locked loop based on second order generalized integrator (SOGI-PLL). The detected frequency is used as feedback by the proportional resonant controller. Therefore, only two PR controller are required: one to track the fundamental component and another to track the harmonic component with higher magnitude. Simulation and experimental results show the performance of the proposed control strategy, improving significantly the grid current quality.

Characterization of solar panel using capacitive load

This work aims to design and assembly a characterization of solar panel using capacitive load. This device provides information that allows the user to increase the efficiency of power generation in photovoltaic systems. Detection of operation issues or abnormal conditions such as partial shading caused by dirt or objects can affect adversely the maximum power point. Simulation results were used to validate the model and allowed the development of the device. Tests were realized with the prototype in a panel of 48 W. Measured results present accuracy when compared with the simulated results validating the prototype.

Capacitor voltage balance performance comparison of MMC-STATCOM using NLC and PS-PWM strategies during negative sequence current injection

This paper addresses the modular multilevel converter applied as a static synchronous compensator. The main objective of this work is to compare the converter performance considering two different submodule capacitor voltage balancing strategies: nearest level control and phase-shifted pulse width modulation, during positive and negative sequence current injection. Results of a 15 MVA MMC STATCOM show that the nearest level control strategy has lower average switching frequency compared to the phase-shifted pulse width modulation strategy, considering comparable submodule capacitance voltage ripple.