Lazhar Ben-Brahim

Speed control of induction motor without rotational transducers

This paper describes a newly developed speed sensorless induction motor drive control scheme based on neural network techniques. The backpropagation neural network technique is used to provide a real-time adaptive identification of the motor speed. The estimation objective is defined in terms of a desired or target trajectory that the neural networks model output should match or trade as closely as possible. The backpropagation algorithm is used to adjust the motor speed so that the neural model output follows the target trajectory. This backpropagation mechanism forces the estimated speed to follow precisely the actual motor speed. The zero speed crossing phenomena is also described and experimental results are presented and analysed.

A fully digitized field-oriented controlled induction motor drive using only current sensors

A field-oriented control method based on a predictive observer with digital current regulation of an induction motor, without speed and voltage sensors, is proposed. Measuring only stator currents and estimating motor speed and rotor fluxes by a predictive state observer with variable pole selection the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. The resulting speed and rotor fluxes are estimated with low sensitivity to parameter variation, and the torque ripples are reduced. The proposed method consists of four parts: identification of the rotor speed, derivation of a digital control law, construction of a state observer that predicts the rotor flux and the stator currents, and derivation of field-oriented control. A theoretical analysis of the method, computer simulations, and experimental results are described. >

On the compensation of dead time and zero-current crossing for a PWM-inverter-controlled AC servo drive

Conventional dead-time compensation methods, for pulsewidth-modulated (PWM) inverters, improve the current output waveforms; however, the zero-current crossing effect is still apparent. This letter proposes a new method, based on angle domain repetitive control, to reduce the distortions in the PWM inverters output waveforms caused by the dead time and the zero-crossing problem.

Digital current regulation of field oriented controlled induction motor based on predictive flux observer

The switching frequency of an inverter for a high-power induction motor drive cannot become higher than a few kilohertz, and such a switching frequency produces a large current ripple, which in turn produces torque ripple. To minimize the current ripple, a new method based on deadbeat current regulation under field oriented control is proposed, in which the pulse-width modulation (PWM) pattern is determined at every sampling instant. Measuring stator currents and motor speed and computing the rotor flux vector by a predictive state observer with variable pole selection, the stator currents are controlled to be exactly equal to the reference currents at every sampling instant. A theoretical analysis, computer simulations, and experimental results are described.<<ETX>>

A high precision resolver-to-DC converter

A newly developed resolver converter, providing a pseudolinear voltage proportional to the shaft angle, is presented. This converter is based on a new concept involving the absolute values of the demodulated sine and cosine resolver signals together with a dedicated linearization technique. The converter enables instantaneous determination of the mechanical angle with a theoretical error of nonlinearity below 0.011/spl deg/ over the 360/spl deg/ range. The practical performance of this converter is compared to that of a 10/sup 5/ pulses per revolution optical encoder arrangement. The theory of operation, computer simulation, full circuit details, and experimental results are given.

A novel resolver-to-360/spl deg/ linearized converter

A novel and simple resolver-to-dc converter is presented. It is shown that by appropriate processing of the sine and cosine resolver signals, the proposed converter may produce an output voltage proportional to the shaft angle. A dedicated compensation method is applied to produce an almost perfectly linear output. This enables determination of the angle with reasonable accuracy without a processor and/or a look-up table. The tests carried out under various operating conditions are satisfactory and in good agreement with theory. This paper gives the theoretical analysis, the computer simulation, the full circuit details, and experimental results of the proposed scheme.

A Resolver Angle Estimator Based on Its Excitation Signal

A resolver generates a pair of signals proportional to the sine and cosine of the angular position of its shaft. A new low-cost method for converting the amplitudes of these sine/cosine transducer signals into a measure of the input angle without using lookup tables is proposed. The new method takes advantage of the components used to operate the resolver, the excitation (carrier) signal in particular. This is a feedforward method based on comparing the amplitudes of the resolver signals to those of the excitation signal together with another shifted by pi/2. A simple method is then used to estimate the shaft angle through this comparison technique. The poor precision of comparison of the signals around their highly nonlinear peak regions is avoided by using a simple technique that relies only on the alternating pseudolinear segments of the signals. This results in a better overall accuracy of the converter. Beside simplicity of implementation, the proposed scheme offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal.

The analysis and compensation of dead-time effects in three phase PWM inverters

The switching lag-time, which prevents the phase shortage of inverter arms, causes serious distortions of the output voltage of the inverter. This effect is well known as the dead-time effect. Several compensation methods have been proposed to improve the output waveforms. These proposed approaches did improve the inverters output voltage waveforms. The improved waveforms however still suffer from the zero-crossing phenomenon. A new approach to overcome the zero current clamping in voltage-fed PWM inverters is proposed. This paper describes the analysis of dead-time effect in three-phase PWM inverters and the proposed scheme. The conventional compensation methods, as well as the zero crossing problem, are highlighted. Theoretical analysis and digital simulation were carried out to verify the analysis and the proposed scheme for dead time compensation.

A New Low Cost Linear Resolver Converter

A new low cost converter topology is proposed for sinusoidal position encoders. The converter enables determination of the angle from the sine and cosine signals of the encoder. When used with resolvers, the implementation of the present scheme takes advantage of the available excitation signal used to operate the device. This trigonometric reference signal is optimally used to generate an analogue signal equivalent to a digital look-up table (LUT). This enables determination of the mechanical angle without using LUT, A/D, and D/A converters. The scheme is optimized in order to achieve highest possible precision. Beside simplicity of its implementation, the proposed converter offers the advantage of robustness to amplitude fluctuation of the transducer excitation signal. The converter was implemented using ordinary low-cost analog components. The theory of operation, computer simulation, and experimental results are given.

A Discontinuous PWM Method for Balancing the Neutral Point Voltage in Three-Level Inverter-Fed Variable Frequency Drives

The paper describes a new discontinuous carrier-based pulsewidth modulation (PWM) method for use in variable frequency drives (VFD) driven by three-level inverters. The method introduces three different switching patterns for the full range of operating speeds. Depending on the actual operating speed, the proposed algorithm is developed to select the most suitable PWM switching pattern that improves the VFD performance. This results in low imbalance in the DC-link capacitor voltage, and low current distortions without increasing switching losses. Theory, simulation, and experimental results are presented.