Janeth Alcalá

High-quality output PWM AC voltage regulator based on Cuk converter

This paper describes the design of an AC–AC converter capable of generating a high-quality output. It is based on the Cuk configuration, with the transistors replaced by bidirectional switches. Since there are no transformers in the configuration, the converter lends itself to a compact and lightweight implementation. The design process is aimed at using, as much as possible, the tools and devices already developed for DC–DC applications. This approach greatly simplifies the design and implementation of the converter. An integrated circuit, developed for DC–DC applications, is used to control the converter. Both the set-point and the feedback signal are rectified in order to fit the input range of the controller. Tests performed show that the output exhibits a maximum total harmonic distortion of 3% (resistive load). The efficiency is slightly higher than 89%, and the average output regulation is 0.3%. The converter is capable of correcting voltage sags down to 60% and voltage swells up to 30%, with the output returning to its nominal value within one mains cycle. The results show that the converter is suitable for energizing information-processing equipment.

Improving power flow in transformers using a BTB converter to balance low voltage feeders

This paper proposes a method to balance the power of transformers in low voltage distribution by using the Back-to-Back (BTB) converter. Through the exchange of active power and the compensation of reactive power between feeders, the overloading of transformers is avoided. In the proposed method, the load is considered as a variable that is constantly changing. The control structure is designed in the dq frame of reference and classical theory is employed. A test system composed by two 50kVA transformers supplying several loads is used to validate the efficacy of the method. For simulations a 30kVA BTB converter is used, and for experimental results a 10:1 BTB converter is implemented.

Evaluating the performance of the BTB converter under unbalanced voltage sags

In this work, a control structure to maintain the power flow transference in renewable energy systems based on wind turbines operating under unbalanced voltage conditions is presented. In the proposed scheme, the Back-to-Back (BTB) converter preserves the electrical cogeneration under the occurrence of voltage sags type B, C and D in three-phase systems. The control modeling is developed in the dq reference frame and two control schemes are proposed to control the BTB converter. A per-phase analysis at the interconnected grid side is considered; on the other hand, for the load side, a three-phase analysis is established. The effectiveness of the BTB converter to compensate voltage sags is shown through simulation and experimental results.

Power control of a multi-cell solid-state transformer with extended functions

Electric energy is usually generated through power stations (hydroelectric, gas, coil, nuclear) interconnected to ensure the power supply; but in the last years a massive number of renewable energy resources have been integrated in the electric grid helping to fulfill the power demand. Nevertheless, the interconnection of multiple generation along the distribution system affects the power quality in medium and low voltage grids (MVAC, LVAC respectively). A solution for this is the incorporation of power quality compensators to the MVAC-LVAC coupling transformers; known as Solid-State Transformer (SST) substituting the conventional transformer and adding power quality compensation features. This paper presents a modular multilevel converter based on SST for the coupling of a low voltage grid (127 Vrms) to a medium voltage distribution system at 3.6 kV, with harmonic filtering capabilities.

A reduced-order generalized average model for a grid-connected HF-link micro-inverter

This paper presents a reduced-order generalized average model for a grid-connected High-Frequency-link micro-inverter for renewable energy sources applications; the grid-connected topology is based on the DC/DC Dual-Active-Bridge (DAB) converter without the intermediate DC-link. The switched model for the system is presented and from it the reduced-order generalized average model is obtained. Harmonic spectra are presented from the simulation results for the specialized software PSIM and compared with the switched and reduced-order generalized average models computed in MATLAB-Simulink for the open-loop system, the simulation results are validated through experimental results.

Modular multilevel BTB converter with parallel cells

This article presents the analysis of a single-phase Back-to-Back converter with a generalized parallel structure, in order to manage bidirectional active power flow between two AC systems. The considered topology is formed by single-phase cells coupled magnetically through a power transformer. The main strategy to operate the converter is to distribute the active power flow symmetrically between the n cells in the parallel arrangement. Also, the parallel structure is used to compensate the reactive power independently at each AC system. The proposed converter is validated through simulation, considering a power structure of 30 kVA, with three parallel cells.

Modelado y Diseño del Controlador para un Sistema de Tracción de un Vehículo Eléctrico

In this paper the basic structure and design of a torque controller for an electric vehicle driven by induction motor is presented. The basic structure of the electric vehicle in question and its mathematical model is presented first. After that, the operation principle of the conventional direct torque control is analyzed and from this a new controller with fixed constant switching frequency is designed. To generate the switching pulses sine PWM is used instead of the hysteresis comparator and switching table commonly used in direct torque control. Finally, simulation comparison was performed. This shows that better performance was achieved with the proposed controller with lower torque and flux errors, and lower torque and stator current ripple.

Análisis del Convertidor CA/CD/CA (Back to Back) para la Gestión del Flujo de Potencia

Este articulo presenta una solucion basada en el convertidor CA/CD/CA (Back to Back, BTB) para la gestion del flujo de potencia entre dos sistemas interconectados de corriente alterna. El objetivo es mostrar las ventajas que presenta el convertidor BTB para la transferencia de potencia activa y de potencia reactiva entre dos sistemas de corriente alterna interconectados. Mediante una estrategia de control lineal es posible desacoplar los terminos activos y reactivos de corriente y controlar de forma independiente la potencia activa y reactiva. El control se desarrolla en el marco de referencia sincrono de cuadratura directa (DQ) asumiendo un sistema trifasico balanceado. Los resultados de simulacion se evaluan en un sistema de 3kVA y para las pruebas experimentales se utiliza un prototipo de laboratorio de la misma capacidad.

Characterization of tracking performance for a three-phase reference signal generator for utility connected applications

Grid connected applications require the use of sinusoidal reference signals having low distortion and good frequency tracking performance. This paper presents a reference signal generator for use in three phase power electronics application where grid tracking must be provided. The proposed generator drift from the traditional DQ generator and is a hardware solution. The implementation is intended to be able of release digital control systems from the task of calculating the reference signals. Many control stages of three phase power electronics systems rely on DQ transformation operations to generate the low distorted reference signals. The major drawback of these transformations becomes clear when the grid is unbalanced or there is a frequency drift. A comparison between a DQ generator and the proposed scheme is presented; the testing conditions are severe sag ranging form 50% to 100% of nominal utility value, and frequency variations of around the nominal frequency value. The proposed scheme shows THD levels below 2% in every case simulated, a much lower value than the ones obtained with the classical approach. Experimental values are above 2%, but still below the maximum values of the DQ generator.