Víctor Guzmán

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

Analysis of Air Gap Flux to Detect Induction Motor Faults

This paper presents the application of motor flux signature analysis to the detection of stator winding failures, broken rotor bars and end ring faults in induction motors. Air gap flux analysis is a non-invasive, on line monitoring technique to diagnose faults in three-phase induction motor drives, detecting differences in the flux spectrum. In this work a programme developed in LabVIEW to perform data acquisition and analysis is presented. Data is read in real time form the working induction motor, and the program provides three fault indicators were found: rotor bar failure, rotor end ring failure and stator winding turn to turn short circuit. With these three indicators failure location, state and cause can be determined. The system has being validated in the laboratory with motors with known faults, and a portable version for industrial workshop tests is being developed

Advantages of the instantaneous reactive power definitions in three phase system measurement

The spatial vector concept of the instantaneous apparent power is defined. Some advantages obtained using these definitions in measuring power in a three-phase system and in vector control of electrical machines are discussed. Also, a physical interpretation of these definitions is given based on conventional electromagnetic theory.

Direct torque control of induction motors using fuzzy logic with current limitation

This work presents a DTC system controlled by a fuzzy logic system that also limits the stator current. The simulation and experimental results are presented for two different stator current limitation strategies. The proposed control scheme uses the fuzzy logic controller to modulate the voltage vector phase applied to the induction motor. This scheme keeps the control voltage vector magnitude almost constant, allowing variations only to limit the stator current. The proposed scheme performance was analyzed using simulation programs written in the C computer language, and the simulated predictions were validated with experimental measurements obtained using a 1 1/2 HP motor driven by a rectifier-inverter system called plataforma, developed by the SIEP Group at Simon Bolivar University.

Kernel selection for sensorless speed measurement of AC machines (Wigner vs Page representation)

This paper presents the analysis of the kernel effect on time-frequency representations used in measuring AC machine rotor speed, without the use of shaft mounted sensors. This speed measuring method is based on the analysis of speed related harmonics that arise from rotor slotting. In the present work, the use of the Wigner-Ville distribution and the Page distribution are analyzed.

A close loop DC motor speed control simulation system using SPICE

This paper presents a complete close loop DC motor speed control system model in SPICE. The results are validated comparing them with the data produced by a testing system.

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.