In this study, a transformer-less STATic synchronous COMpensator (STATCOM) based on cascaded H-bridge (CHB) multilevel converter with floating DC links is presented. This study introduces a control strategy based on state feedback control algorithm in order to supply reactive power to the grid and to compensate the total losses in the internal H-bridge cells. Using this strategy, the converter stability and the fast dynamic response are guaranteed. Moreover, a voltage balancing strategy is proposed, which not only regulates the DC-link voltage of H-bridge cells to the reference value, but also evenly distributes total reactive power among the converter cells, even when there is difference between the losses of H-bridge cells. A 21-level CHB-based STATCOM is simulated in PSCAD/EMTDC environment to evaluate the performance and effectiveness of the new control strategy. Furthermore, the validity of new method is verified on a down-scaled 7-level CHB prototype.

https://ietresearch.onlinelibrary.wiley.com/doi/epdf/10.1049/iet-pel.2013.0941

State feedback control strategy and voltage balancing scheme for a transformer-less STATic synchronous COMpensator based on cascaded H-bridge converter

In this paper, a Selective Harmonic Elimination Pulse Width Modulation (SHE-PWM) method, which utilizes adjustable dc links, is presented for a Static Synchronous Compensator (STATCOM) based on Cascaded H-Bridge (CHB) multilevel converter. The proposed switching algorithm is able to fix the capacitors voltages at optimum and unequal values, while injecting the desired reactive power, in order to eliminate more low order harmonics. An indirect current control method is combined with a loss estimation block to control the dc link voltages that might have different losses. Moreover, by using unequal dc link voltages more levels at the output is achievable compared to the symmetrical multilevel converters that could be used in enhancing the power quality, while keeping the switching frequency near the fundamental (the maximum switching frequency can be kept below 150 Hz). The validity of the proposed method is verified by simulations in Matlab/Simulink environment.

Using variable DC sources in order to improve the voltage quality of a multilevel STATCOM with low frequency modulation

Arc furnaces are used in industries for induction heating and welding. Due to the rapid growth of non- linear loads, such as power electronic control equipments and Electric arc furnace (EAF) power quality problems such as harmonics and voltage flicker are introduced in the power system. It occurs because of the time-varying and non-linear behaviour of the electric arc furnace operation. Hence an Electric arc furnace model is needed to analyze the power quality. In this paper, a time domain model called hyperbolic model for electric arc furnace is analyzed using MATLAB. The model is used to study its behaviour on the power system using MATLAB. To improve the power quality D-STATCOM is proposed, in which the control strategies used are Direct, Indirect control and Hysteresis controller. Direct control technique uses P-Q theory in which transformation is based on orthogonal reference frame. Indirect control technique uses d-q theory in which transformation is based on synchronous reference frame. Hysteresis controller uses Hysteresis Bandwidth to produce the switching signals. Control strategies used in D-statcom are simulated using MATLAB/SIMULINK.

/pdf/harmonic-reduction-of-arc-furnaces-using-d-statcom-1qjgfpf93m.pdf

Harmonic Reduction of Arc Furnaces Using D-Statcom

This work proposes an improved modulation method at the fundamental frequency modulation for STATCOM modular multilevel static compensators. One of the reasons for the voltage unbalance across the capacitors in the DC link of the individual cells at the multi-level compensator is the non-sinusoidality of the currents. A distinctive feature of the proposed modulation method compared to traditional FFM technologies is the monitoring of the voltage across the capacitors every quarter of the period and the elimination of voltage unbalance through the use of switching patterns with different peak-to-peak voltage ripple of the dc capacitor. At the same time, the advantages of traditional FFMs are preserved - low switching frequency and high efficiency. In addition, this method is applicable for CMC with a sufficiently large number of cells in phase. The effectiveness of the proposed modulation method is confirmed by the simulation results of 35 MVA 12-chain STATCOM for an electric arc furnace (EAF), the real currents of which are accepted as test signals.

A Novel Fundamental Frequency Modulation Strategy for Cascaded Multilevel STATCOM with Non-sinusoidal Load Currents

This paper presents simulation study of an Electric Arc Furnace (EAF) model in the MATLAB/SIMULINK environment. EAF was modeled as a time domain controlled voltage source (CVS) model. Voltage flicker, a phenomenon of annoying light intensity fluctuation, caused by EAF, has been a major power quality concern for both power companies and customers. A model was developed for the EAF and it was applied in the simulation studies of cascaded H-bridge converter based Distribution STATic synchronous COMpensator (DSTATCOM) for voltage flicker mitigation. The controller for DSTATCOM was designed based on d-q model for the reactive power management, which helps in the mitigation of the flicker. With the validated EAF and STATCOM model, simulations are conducted to study the response of the compensator in the distribution system.

Voltage flicker mitigation by DSTATCOM for voltage source Arc furnace model

En el mundo se producen 7,5 millones de toneladas de chocolate, y el 64 % se consume como chocolate relleno. En el año 2012, la Unión Europea indico los niveles de cadmio no debían superar los 0,8 mg kg-1 en productos con una base de   pasta de cacao del 70 %. El propósito de esta investigación fue evaluar la efectividad de Rhizobium japonicum en la disminución de cadmio presente en semillas de cacao. Por lo cual, se aplicó tres concentraciones de Rhizobium japonicum 0 ml, 300 ml y 600 ml por cada dos kilos de masa fresca de cacao variedad Trinitario, para la fermentación se aplicó dos métodos por Rohan y hieleras en dos fincas (Los Ríos y Guayas). Se utilizó un diseño completamente al Azar Trifactorial (12 tratamientos y 2 repeticiones), evaluándose 24 semillas en total, las variables de calidad en la semilla evaluadas fueron: pH, temperatura, porcentaje de fermentación, índice de semilla, prueba de testa y cotiledón. El análisis sensorial se determinó mediante un panel de catadores semientrenados, para el análisis de cadmio se realizó con digestión ácido nitro perclórica por espectrometría de ICP OES. Durante la fermentación existió un aumento creciente del pH (3,6 - 4,2), temperatura (27 - 40,2 °C), el índice de semilla presentó el mayor promedio en el T5 (1,65 g), el contenido de cadmio disminuyó en un 79 %, por el método de fermentación en hieleras en la provincia de Los Ríos y un 78 %, por el método de fermentación en cajas Rohan en la provincia del Guayas.

https://revistas.sena.edu.co/index.php/recia/article/download/efectos-de-dos-metodos-fermentativos-en-cacao-theobroma-cacao-l-/efectos-de-dos-metodos-fermentativos-en-cacao-theobroma-cacao-l-

M. Naga Raju

Papers

Voltage flicker mitigation by DSTATCOM for voltage source Arc furnace model

Efectos de dos métodos fermentativos en cacao (Theobroma cacao L.) trinitario, inducido con Rhizobium japonicum para disminuir cadmio