María Isabel Giménez

A New Simplified Multilevel Inverter Topology for DC–AC Conversion

Multilevel converters offer high power capability, associated with lower output harmonics and lower commutation losses. Their main disadvantage is their complexity, requiring a great number of power devices and passive components, and a rather complex control circuitry. This work reports a new multilevel inverter topology using an H-bridge output stage with a bidirectional auxiliary switch. The new topology produces a significant reduction in the number of power devices and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter; only five controlled switches, eight diodes, and two capacitors are required to implement the five-level inverter using the proposed topology. The new topology achieves a 37.5% reduction in the number of main power switches required (five in the new against eight in any of the other three configurations) and uses no more diodes or capacitors that the second best topology in the literature, the Asymmetric Cascade configuration. Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity. Theoretical predictions are validated using simulation in SPICE, and satisfactory circuit operation is proved with experimental tests performed on a laboratory prototype

A new multilevel inverter topology

Multilevel converters are being considered for an increasing number of applications due to their high power capability, associated with lower output harmonics and lower commutation losses. Their main disadvantage is their complexity which requires both a great number of power devices and a rather complex control circuitry. In this work a new inverter topology using an auxiliary switch is presented, reducing the number of power devices required to implement a multilevel output. The topology is tested in the design of a 5 levels H bridge simplified inverter; circuit operation is presented, simulated in SPICE and validated with experimental tests performed on a laboratory prototype. Additionally, the dedicated modulator circuit required for multilevel inverter operation is implemented using a FPGA circuit, reducing overall system cost and complexity.

A Flexible Hardware Platform for Applications in Power Electronics Research and Education

This work presents the design and development of a three-phase multilevel hardware platform for applications in power electronics. The emphasis of the proposed converter is in its flexibility to allow rapid set-ups of different experiments typically required in power electronics teaching and research. The proposed converter uses a cascaded H-bridge topology whereby multilevel operation with up to 9 voltage levels can be obtained. The selected power stage topology as well as the control, drivers and sensors boards designs, enable the platform to operate in multiple configurations, namely as inverter, controlled rectifier or active power filter, for one, two or three-phase systems.

Direct Torque Control of Induction Motors Using a Fuzzy Inference System for Reduced Ripple Torque and Current Limitation

In this work a fuzzy inference system is employed for the control of a PWM based direct torque control (DTC), driving an induction machine, to reduce ripple torque while limiting the current during start-up or when the stator flux magnitude changes. The proposed control scheme uses a fuzzy inference system to modulate the stator voltage vector applied to the induction motor, in magnitude and phase. This scheme allows for amplitude regulation according to the requirements of ripple reduction or stator current limitation. The proposed scheme performance was analyzed using simulation programs written in the C computer language and executed on a prototype system called PLATAFORMA III, developed by the SIEP Group at Universidad Simon Bolivar

Squirrel cage induction machine model for the analysis of sensorless speed measurement methods

In this work a squirrel cage induction machine model been developed to include the stator current effects on the MMF space harmonics, dynamic and static eccentricity harmonics, and slot harmonics. The proposed model is intended to be used on testing the behavior of different sensorless speed measurement techniques. This dynamic model has been developed using the superposition principle and a matrix description of the machine inductance. The model has been validated using experimental data, and tested using a time-frequency-distribution method for sensorless speed measurement.

PLATAFORMA: A useful tool for high level education, research and development

This work presents the PLATAFORMA system impact over the teaching and research activities of the lecturers and the post graduate students at Master and Doctorate levels working in the Power Electronics Industrial Systems group (Grupo de Sistemas Industriales de Electronica de Potencia, SIEP) of the Universidad Simon Bolivar. PLATAFORMA is an integrated test system intended for experiments requiring validation of different types of new strategies and control schemes, based on vector control theories, parametric estimation, neural networks and fuzzy logic control systems, applied to machine drives, and it can be also used for analyzing the effect of these control strategies over the mains quality. The equipment includes driver power stages, an instrumentation stage and a signal processing and control stage. PLATAFORMA has eliminated most of the tedious work that every single researcher or post graduate student in the GSIEP group had to do in order to obtain experimental results, enhancing the quality of the thesis and papers produced by the group members.

An experimental and training platform for uninterrupted power in isolated locations: wind turbine - electric generator - battery bank (TP-WT-UPS)

A new modular platform that can be used to combine different energy sources and power electronics conversion blocks in a training environment is presented. The proposed equipment, called training platform for wind turbine uninterruptible power supply (TP-WT-UPS) models a wind driven uninterruptible power supply feeding a critical load in an isolated location. Two energy sources are emulated (a wind turbine and a combustion engine driven AC generator), the three basic power electronic blocks (DC/DC, DC/AC AC/DC) and control electronics (microprocessor and data gathering subsystems) are provided in a modular architecture that can be modified to suit a particular configuration. Wherever possible, standard off-the-shelf car parts such as alternators and AVR are used. TP-WT-UPS can be used both in the training of engineers, giving them hands-on experience on these topics, and also as a design tool to expedite the development of new projects

Generalized Algorithm for Pulse Width Modulation using a Two-Vectors Based Technique

Abstract This paper presents a generalized and compact space vector modulation algorithm valid for both (a, b, c) and (x, y) coordinates, suitable for triangle comparison modulators. The proposed algorithm uses a two base-vectors duty cycle computation by mapping the solution space into only three parallelogram shaped zones (Fig. A). This generalized algorithm is especially suited for vector control applications requiring high dynamic response and for applications where changes in demand may happen at a frequency comparable with the modulator’s carrier frequency. Several carrier base modulation methods extensively described in the literature are obtained from the proposed generalized space vector modulation algorithm with the introduction of the null vector ratio δ. The proposed method has been experimentally tested, and a practical implementation of the generalized algorithm with low computational requirements is presented.

Direct torque control of PMSM using fuzzy logic with PWM

Since its development, permanent magnet synchronous machines (PMSM) has been used in a number of specific applications. However, in recent years PMSMs have become more attractive due to developments in new materials for permanent magnets and in semiconductor technology for converter design. Recent investigations have proposed some implementations applying the direct torque control (DTC) technique to PMSM motor drives, offering a fast and accurate control. This paper presents a modified DTC scheme, using fuzzy logic with pulse wide modulation (PWM) to improve stator flux and the electric torque by significantly reducing their ripple. The proposed method effectiveness has been verified by computer simulations and experimental tests on a laboratory prototype. These results are compared with the ones obtained with a modified DTC using a PI controlled PWM with current limit.

Sensorless speed control of the induction machine combining field oriented method and DTC

A direct torque control (DTC) scheme for an induction machine is presented. The rotor speed estimation is performed using the oriented field model. Time-frequency spectral methods are used for accurate speed estimation, using the stator current information. Combining these estimation techniques, a precise T/sub r/ adaptation is achieved in real time. The proposed method reduces the parameter dependence of the induction machine model in the controller, and removes the need for a speed sensor in the mechanical shaft. The dynamic control performance achieved with this technique is comparable to that obtained using optical encoders.