B.J. Cardoso Filho

Wide bandwidth single and three-phase PLL structures for grid-tied PV systems

This paper presents a detailed description of a three-phase PLL (phase-locked loop) structure that fits the requirements of utility connected PV systems. The tuning of the PLL structure is discussed as well as its under utility distorted conditions. A new single-phase PLL topology is introduced. Its dynamic behavior is evaluated and its quasi-instantaneous ability to detect phase, frequency and amplitude of the utility voltage is highlighted. The analysis of the performance of the introduced single-phase PLL topology under islanding condition is also presented. Simulation and experimental results are included to support the theoretical study.

Design and implementation of a passively clamped quasi resonant DC link inverter

The passively clamped quasi resonant DC link (PCQRL) inverter is a novel soft switched inverter topology proposed to solve two major problems associated with the conventional passively clamped resonant DC link inverter: the high clamp factor problem and the lack of PWM capability. This paper deals with design and control of a three phase PCQRL inverter. Major design issues are discussed. Successful operation of this novel PCQRL inverter based on a prototype design is demonstrated. The results show that this novel converter can reduce the clamp factor from the value of 2.0 p.u. obtained in previous circuits to around 1.25 and add the PWM capabilities to the conventional passive clamp resonant DC link. Several results are presented to illustrate the performance of the proposed inverter topology.

Analysis of passive filters for high power three-level rectifiers

This paper studies passive filters for harmonic reduction in high power rectifiers. The paper presents some of the most important configurations of high power filter employed in medium voltage applications. The paper as well includes the ideal mathematic equations and models for those filters, and then compares the filter performances. In a very broad sense, the addition of some resonant harmonic traps to a conventional third order filter results in good filter adaptation to PWM strategies. The filter evaluation highlights this fact. Simulation of a high power three-level neutral point clamped-NPC rectifier also confirms those ideas. Results comprise a high quality waveform under low switching frequency with reasonable converter operation performance. Experimental results for selective harmonic elimination are included.

Detection of Rotor Faults in Squirrel-Cage Induction Motors using Adjustable Speed Drives

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. Addressing diagnostic techniques based on current signatures analysis (MCSA), the characteristic components introduced by specific faults in the current spectrum are investigated and a diagnosis procedure correlate the amplitudes of such components to the fault extent. In this paper, the impact of feedback control on asymmetric rotor cage induction machine behavior is analyzed. It is shown that the variables usually employed in diagnosis procedures assuming open-loop operation are no longer effective under closed-loop operation. Simulation results show that signals already present at the drive are suitable to effective diagnostic procedure. The utilization of the current regulator error signals and the influence of the regulators gains on their utilization in rotor failure detection are the aim of the present work. The use of a band-pass filter bank to detect the presence of sidebands is also proposed in the paper.

Current stiff converter topologies with resonant snubbers

In this paper, a study of resonant snubbers with auxiliary switches is presented as applied to three-phase current stiff power converter (CSC) topologies targeted for electric drives applications. Several realizations of CSCs with resonant snubbers are identified and characterized from a generalized three-phase commutation cell. The modulation characteristics associated with the operation of the CSCs with resonant snubbers are analyzed using the space vector approach. Simulation results are presented to illustrate the key aspects in this discussion. Experimental results are included for selected cases.

Sinusoidal voltages and currents in high power converters

This paper discusses the problem of producing sinusoidal voltage and current with high power converters. It shows that there is a strong compromise among three parts of process, which are the multilevel converter topology, the modulation strategy and some required harmonic reduction method. A careful selection of them leads to a high quality waveform with reasonable converter operation performance under low switching frequency and with reduced level structures. Simulation and experimental results support those ideas.

Blower drive system based on synchronous motor with solid salient-pole rotor: performance under starting and voltage sag conditions

This paper presents a study developed on a three-phase 11-MW synchronous motor with a solid salient-pole rotor of a blower drive system of a blast furnace at the Companhia Siderurgica Belgo-Mineira, Joao Monlevade, Brazil. A mechanical model including motor, gears, couplings, and blower is used in a simulation study to evaluate the torsional dynamics and stresses during motor startup and voltage sag conditions. In addition, the operation of the synchronous motor under voltage sag is analyzed with a comparative study between complete and approximated models of the motor. The utilization of a dynamic voltage restorer to protect the drive system under this abnormal situation is also evaluated.

Modelling and analysis of a nine-phase induction motor with third harmonic current injection

Using electric motors with a number of phases greater than three may present some advantages over conventional three phase machines in the following applications: high power levels, electric vehicles and applications that require high levels of reliability. Multiphase machines, meaning designs comprising more than three phases, also allows an increase in torque density from the injection of harmonic currents. It is shown in this paper a comprehensive approach for the derivation of equivalent circuits for steady state operation for both fundamental and third harmonic frequencies for a nine-phase motor with concentrated windings and full pitch. Besides that, simulation of the dynamic model of the machine is done to obtain the expected torque improvement.

Avoiding undesirable high-frequency phenomena in long cable drives: Rectifier-to-inverter connection through long DC cable — part I: Evaluation of the losses reduction and copper economy

Problems involving long cable PWM motor drive systems are well documented in the literature. Solutions based on passive filters are conventionally used to suppress the undesired high-frequency phenomena that take place in such systems, but, in turn, bring up new considerations concerning filter size, weight, cost and electrical losses. In this context, an alternative concept of a motor drive system that overcome all these problems is outlined in this paper, where the long cable is used to connect the rectifier to the inverter, thus establishing a DC power transmission link. This paper briefly discusses the benefits and important issues concerning the proposed system and presents a comprehensive analysis regarding one of its advantages, which is the copper (and cost) economy in relation to the traditional systems.

A simple and efficient method to simulate induction machines with rotor asymmetries

The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such effort is the modelling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. In this paper, it is introduced a new and simpler approach for the modelling and computer simulation of induction machines with rotor asymmetries. This approach is based on the well-known dq transient model of the symmetrical machine, with rotor asymmetries introduced through a linear transformation of the extended rotor current vector. Simulation results previously presented in the literature are reproduced to support the proposed approach.The need for detection of rotor faults at an earlier stage, so that maintenance can be planned ahead, has pushed the development of monitoring methods with increasing sensitivity and noise immunity. An important issue in such effort is the modelling of the induction machine including rotor bar and end-ring faults, with a minimum of computational complexity. In this paper, it is introduced a new and simpler approach for the modelling and computer simulation of induction machines with rotor asymmetries. This approach is based on the well-known dq transient model of the symmetrical machine, with rotor asymmetries introduced through a linear transformation of the extended rotor current vector. Simulation results previously presented in the literature are reproduced to support the proposed approach.