Amauri Oliveira

Speed Estimation of an Induction Motor Operating in the Nonstationary Mode by Using Rotor Slot Harmonics

In this paper, an analysis of techniques of digital signal processing used for estimating the motor slip and rotational speed of an induction motor operating in stationary or nonstationary condition by using rotor slot harmonics observed in the stator current waveform is presented. The novelty of this paper is related with three topics. First, zoom short time Chirp-Z transform was used to find the fundamental supply frequency intending to improve accuracy without increasing computational complexity. Second, it presents a tool that can be used to identify whether a motor is capable or not of producing principal slot harmonics. Finally, an algorithm was developed to find an optimal window length using rotational speed maximum relative deviation. The use of this approach was analyzed when the motor was powered by a frequency converter driving a variable load and operating in strongly nonstationary conditions. The correctness of the method has been confirmed by experimental test results. Finally, the proposed method was implemented in a conventional sucker-rod pumping unit (25D-67-36-American Petroleum Institute), to estimate the rotational speed and slip when the motor is powered by a frequency converter.

A feedback I/sup 2/-controlled constant temperature solar radiation meter

The conventional thermoresistive sensor-based feedback constant temperature circuit have shown some performance limitations due to the input offset voltage of the amplifier. The d.c. analysis of this circuit has been presented to graphically demonstrate these limitations. Alternative feedback measurement scheme without employing the Wheatstone bridge is proposed. PI and predictive controller designs are described. Simulation results for these controllers and a practical configuration are presented.

A Method for Measuring Torque of Squirrel-Cage Induction Motors Without Any Mechanical Sensor

This paper presents a method for estimating the torque of three-phase squirrel-cage induction motors. The method is not invasive, since it does not rely on mechanical sensors and only the measurement of the stator current is required. The slip and the rotational speed of the motor are estimated from the spectrogram of the stator current signal either in stationary or in nonstationary operating conditions. The torque is estimated from the ratio of the estimated slip and the rated one. A test platform equipped with a rotational speed sensor and a dc motor for measuring the torque of a three-phase induction motor fed by a pulsewidth-modulated voltage source inverter operating under scalar and vector control was implemented to verify the correctness of the proposed method. The validity of the proposed approach is demonstrated by the close agreement between the estimated values of the speed and torque obtained with the proposed method and the ones that are obtained from direct measurement.

A digital differential thermal analysis instrument

Differential thermal analysis is usually employed to characterize new materials. The structure of a prototype of a differential thermal analysis instrument, based on a microcontroller is described. The design of the controllers for a constant rate reference temperature variation is discussed. Experimental and simulation results are presented.

An inherently linear transducer using thermistor practical approach

In this article we describe a feedback circuit, with thermoresistive sensor, based on thermal sigma-delta modulator. This circuit uses a one-bit first order sigma-delta modulator in which considerable part of conversion functions is performed by the sensor. This transducer circuit is able to perform digital measurement of physical quantities that interacts with the sensor: temperature, thermal radiation and fluid velocity. In this paper, this circuit was used to measure environment temperature. In this circuit, digital output voltage is linearly dependent on the environment temperature. We show the equations that support circuit behaviour, simulation results and experimental results. In addition, we present the thermal radiation architecture version in which digital output is intrinsically linear to the thermal radiation measure.

Analysis of spectral signatures of stator currents on a three-phase induction motor operating in non stationary mode for rotational speed and slip detection using rotor slot harmonics

This paper investigates some techniques of digital signal processing, using the rotor slot harmonics present in the stator currents waveforms, to estimate the motor slip and the rotational speed when operating in stationary or in nonstationary mode. This research also highlights the importance of identifying whether a motor is capable or not of producing rotor slots harmonics, and shows how it is possible to do this using simple tables. An algorithm to estimate the slip and speed variation was developed. Finally, it has been done some analysis about issues such as: sample rate, window length and the use of the chirp z-Transform with the short time Fourier transform to improve the tests results. It has also been analysed the use of this methodology when the motor is operating powered by a frequency converter and variable load. Furthermore, the efficiency of the method has been confirmed by experimental results.

A Constant Temperature Thermoresistive Sigma-Delta Anemometer

In this paper we propose a feedback measurement system, with thermoresistive sensor, based on sigma-delta modulation. The system uses a one-bit sigma-delta modulator for which a considerable part of the conversion functions is performed by a thermoresistive sensor. The sensor is modelled using the power balance principle and the constant temperature measurement method is employed. This transducer architecture is able to realize digital measurement of physical quantities that interacts with the sensor: temperature, thermal radiation and fluid velocity. This paper presents simulations and validates the structure of the sigma-delta converter as an anemometer. The advantage to directly convert physical quantities to digital, with the sensor as part of the A to D converter, makes possible the implementation of this measurement system in an integrated circuit. Another advantage of the IC implementation of this structure is the possibility to reduce noise interference due to discrete component connections in a printed circuit board.

A constant temperature operation thermo-resistive /spl Sigma/-/spl Delta/ transducer

In this paper, we propose a feedback architecture, with thermo-resistive sensor, based on the so called thermal sigma-delta principle. The architecture uses a 1-bit sigma-delta modulator in which a considerable part of the conversion function is performed by a thermo-resistive sensor. The sensor is modeled using the electrical equivalence principle and the applied measurement method is at constant temperature. This transducer architecture is able to realize digital measurement of physical quantities that interact with the sensor, such as temperature, thermal radiation, or fluid velocity.

Integrated circuit for real-time poly-phase power quality monitoring

Abstract Low power quality may cause serious problems in electricity networks, among them there are: reduction of equipment lifetime; false activation of protection devices; and increase in electrical and thermal losses. Considering this, it is very important to monitor electrical power quality of an industrial facility. This paper describes the architecture of an application-specific integrated circuit IP-core for power quality measurements. The main focus are the digital signal processing modules, which are designed based on IEC standards. The proposed Integrated Circuit, which uses TowerJazz 180 nm CMOS technology, comprises seven measurement channels for poly-phase systems and generates high precision estimation for power quality parameters. Experimental and simulated results are used to validate the proposed system.

Sigma-Delta Modulator with Thermoresistive Sensor Frequency Response

In our previous paper we proposed feedback architecture with thermo-resistive sensor, based on thermal sigma-delta principle to realize digital measurement of physical quantities that interacts with the sensor: temperature, thermal radiation, fluid velocity. This architecture uses 1-bit sigma-delta modulator in which considerable part of conversion functions is performed by a thermoresistive sensor. The sensor is modelled using electrical equivalence principle and the applied measure method is constant temperature. Now we present frequency response analysis and signal to noise ratio dependence on oversampling ratio for this architecture applied to thermal radiation measurement