Felipe Bovolini Grigoletto

Flexible Arrangement of Static Converters for Grid-Connected Wind Energy Conversion Systems

This paper presents a new flexible arrangement of static converters for grid-connected wind energy conversion systems (WECS). The proposed arrangement uses three-phase voltage-fed back-to-back mass-produced power converter modules with reconfiguration switches. The main features of the proposed flexible arrangement are as follows: 1) expanded reactive power capability limits; 2) high efficiency, mainly under low wind conditions where the active power is reduced; and 3) low current harmonic content. In addition, a detailed description of the operating modes, as well as of the grid, generator, and circulating current controller design, are given. Finally, experimental results support the theoretical development, and demonstrate the good performance and flexibility of the proposed arrangement.

A space vector PWM modulation scheme for back-to-back three-level diode-clamped converters

This paper proposes a modulation strategy for back-to-back NPC converters. This technique ensures that the low-frequency voltage oscillation in the dc-link capacitors is kept within established limits while minimizing the distortion of the ac side output voltages. Generally, space vector pulse width modulation schemes (SVPWM) to implement a given output voltage vector it is selected the nearest three vectors (N3V) to reduce the output distortion voltages. However this approach can lead to imbalances and oscillations in the dc-link capacitors voltages. To reduce this voltage oscillations the NS3V diagram can be used, although this technique penalize the THD of the converter output voltages. This work proposes the utilization of limits to the voltage imbalances as criterion to combine the N3V and the NS3V for the back-to-back NPC converter configuration. Thereby, it is established a compromise between the capacitor voltage oscillations and the output voltage distortion. This provide a degree of freedom to operate with a reduced THD in the voltages at the grid side while minimizing the imbalance in the dc-link voltages. Simulation results are given to demonstrate the good performance of the proposed technique.

A hybrid modulation strategy for voltage fed converters with multiple parallel legs

This paper presents a hybrid modulation strategy for voltage fed converters with multiple parallel magnetically coupled legs. The proposed hybrid modulation strategy combines the benefits of space vector, such as switching sequences flexibility and the simplicity of the modulation based on the geometric approach. As a result, it is possible to obtain multilevel equivalent voltages, as well as the equal sharing among the converter leg currents. In addition, the virtual vector concept is used which leads to the determination of the voltage limits required to impose the equal sharing among the leg currents and to avoid the saturation of the coupled inductor. Finally, simulation and experimental results show the good performance and flexibility of the proposed hybrid modulation technique.

Modulation and circulating current control of parallel connected back-to-back converters for WECS

This paper presents a modulation and control strategy for parallel connected back-to-back converters. The proposed modulation strategy has the following features: (i) to minimize the harmonic content of grid currents; (ii) to eliminate the circulating currents among the modules; (iii) to minimize the common mode voltage at the generator terminals. Furthermore, in the proposed strategy each power module has its own modulator and controller which make the overall system expandable to any number of modules in parallel. Finally, simulation results are presented to demonstrate the good performance of the proposed modulation and control strategies.

PD modulation strategy for modular multilevel converters

This paper proposes a Phase Disposition (PD) modulation strategy for the Modular Multilevel Converter (MMC). The proposed modulation strategy produces output line-to-line voltages with 4N+1 levels. Furthermore, a sorting algorithm guarantees the individual submodule capacitor voltage balancing and a hysteresis controller keeps the inner currents into a desired band. Simulation results are presented to demonstrate the good performance of the proposed modulation strategy.

Space vector pulse width modulation for Modular Multilevel Converters

This paper proposes a space vector vector pulse width modulation (SVPWM) stratey for Modular Multilevel Converters (MMCs). The proposed modulation generates multilevel output line-to-line voltages with 4N+1 levels. Furthermore, the virtual vectors are developed for the MMC and it allowed to establish the converter voltage limits and implement a proper inner currents control. Moreover, the voltages across the submodule dc capacitors can be well balanced with closed-loop controllers and a sorting algorithm. Finally, simulation results are presented to support the theoretical analysis demonstrating the good performance of the proposed modulation technique.

Nova modulação vetorial para o controle da tensão do ponto central do divisor capacitivo do conversor com ponto neutro grampeado

This paper presents a new space vector modulation strategy for the dc capacitor voltages control of neutral point clamped converters. By defining the neutral point current it is possible not only to ensure the balance of the dc voltages as well as to guarantee the elimination of low frequencies harmonic in neutral-point voltage under all load conditions in the entire converter linear operation region. Two switching sequences are explored to show the flexibility of propose method. Experimental results are presented and they show the good perform of the proposed modulation technique.

Projeto e implementação de um controlador de corrente robusto para inversores com filtro LCL conectados à rede com incertezas paramétricas

This paper addresses the design and implementation of a discrete controller for grid connected voltage source inverters with LCL-filter usually found in wind power generation systems. First a theorem that relates the controllability of the discrete dynamic equation of the inverter with LCL-filter and the sampling frequency is derived. Then, a condition to obtain a robust partial state feedback controller based on linear matrix inequalities is proposed. This controller guarantees the stability and damping of the LCL-filter resonance for a large set of grid conditions without requiring self-tuning procedures. Finally, an internal model controller is added to ensure asymptotic reference tracking and disturbance rejection, therefore reducing significantly the impact of grid background voltage distortion on the output currents. Simulation and experimental results are presented to support the theoretical analysis and to demonstrate the system performance.

Flexible arrangement of static converters for grid connected wind energy conversion systems

This paper presents a new flexible arrangement of static converters for grid connected Wind Energy Conversion Systems (WECS). The proposed arrangement uses three phase voltage fed back-to-back mass produced power converter modules with reconfiguration switches. The main features of the proposed flexible arrangement are: (i) expanded reactive power capability limits, (ii) high efficiency mainly under low wind conditions where the active power is reduced, and (iii) low current harmonic content. In addition, a detailed description of the operating modes, as well as the grid, generator and circulating current controllers design are given. Finally, simulation results demonstrate the good performance and flexibility of the proposed arrangement.